JP7632082B2 - Vehicle brake control device - Google Patents

Description

This disclosure relates to a vehicle braking control device.

Patent Document 1 describes that the device aims to "provide a brake control device capable of preventing the motor from unintentionally stopping or being unable to restart rotation," and that the device "includes a pump (6) capable of drawing in hydraulic fluid and discharging it to a fluid passage (31) connected to the wheel cylinder (21), an electric motor (60) for driving the pump (6), and an electronic control unit (9) capable of controlling the rotation speed of the motor (60) by PWM control, and configured to continuously drive the motor (60) with a duty ratio of 100% when the fluid pressure on the discharge side of the pump (6) is higher than a predetermined first fluid pressure."

The applicant has developed a braking control device as described in Patent Documents 2 and 3. Specifically, in the braking control device, the hydraulic pressure (braking hydraulic pressure) of the wheel cylinder is adjusted by throttling the braking fluid discharged by a fluid pump driven by an electric motor with an electromagnetic valve (pressure regulating valve). Here, the maximum output of the electric motor is designed to achieve the maximum value of the braking hydraulic pressure (i.e., the maximum hydraulic pressure that can be adjusted by the pressure regulating valve). However, a situation may occur in which the electric motor stalls due to a decrease in output of the electric motor or the occurrence of an excessive load. In particular, in a brake-by-wire type braking control device, since the electric motor is used as the power source, it becomes difficult to appropriately adjust the braking hydraulic pressure due to stalling of the electric motor. For this reason, a braking control device that can avoid stalling of the electric motor is desired.

JP 2020-019335 A JP 2019-059458 A JP 2019-137202 A

The object of the present invention is to provide a braking control device for a vehicle powered by an electric motor that can avoid stalling of the electric motor.

The vehicle brake control device according to the present invention includes a pressure adjusting unit (KU) that adjusts the pressure (Pa, Pb) of the brake fluid (BF) discharged by a fluid pump (QA) driven by an electric motor (MA) using pressure adjusting valves (UA, UB), and a controller (ECU) that adjusts the brake fluid pressure (Pw) in the wheel cylinder (CW) by controlling the pressure adjusting unit (KU).

In the vehicle braking control device according to the present invention, the controller (ECU) limits the current value (Ia, Ib) to the pressure regulating valve (UA, UB) based on a load state quantity (Jm) that indicates the degree of load on the electric motor (MA). For example, the controller (ECU) does not execute the limit when the load state quantity (Jm) is less than a predetermined quantity (jm), and executes the limit when the load state quantity (Jm) is equal to or greater than the predetermined quantity (jm).

In the vehicle braking control device according to the present invention, the controller (ECU) limits the current value (Ia, Ib) to the pressure regulating valve (UA, UB) based on the power supply voltage (Vm) of the electric motor (MA). For example, the controller (ECU) does not execute the limit when the power supply voltage (Vm) is equal to or higher than a predetermined voltage (vm), and executes the limit when the power supply voltage (Vm) is less than the predetermined voltage (vm).

Electric motor stalls are likely to occur when the load state of the electric motor is excessively large or when the power supply voltage of the electric motor is low. With the above configuration, in a braking control device that uses an electric motor as a power source, in a situation where the probability of motor stall occurring is high, the current value of the pressure regulating valve is limited, so that the stall can be prevented in advance.

1 is a schematic diagram for explaining an entire vehicle equipped with a vehicle brake control device SC according to the present invention. FIG. 2 is a schematic diagram for explaining a first configuration example of a fluid unit HU. FIG. 4 is a flow chart for explaining a first processing example of pressure regulation control. FIG. 11 is a characteristic diagram for explaining current flow restriction of the pressure regulating valve UA. FIG. 11 is a flow chart for explaining a second processing example of pressure regulation control. FIG. 13 is a schematic diagram for explaining a second configuration example of the fluid unit HU.

The following describes an embodiment of a vehicle braking control device SC according to the present invention with reference to the drawings.

<Symbols of components>
In the following description, components, signals, values, etc. that are given the same symbol, such as "CW", have the same function. The subscripts "f" and "r" added to the end of various symbols related to wheels are generic symbols that indicate whether the element is related to the front wheels or the rear wheels. Specifically, "f" indicates an element related to the front wheels, and "r" indicates an element related to the rear wheels. For example, a wheel cylinder CW is written as "front wheel cylinder CWf, rear wheel cylinder CWr". Furthermore, the subscripts "f" and "r" may be omitted. When these are omitted, each symbol represents its generic name.

<Vehicle JV equipped with brake control device SC>
The overall configuration of a vehicle JV equipped with a braking control device SC will be described with reference to the schematic diagram of Fig. 1. Here, the vehicle equipped with the braking control device SC is also referred to as the "host vehicle JV" in order to distinguish it from other vehicles (e.g., the preceding vehicle SV).

The vehicle JV is a hybrid vehicle or an electric vehicle equipped with an electric motor GN for driving. The electric motor GN for driving also functions as a generator (electric generator) for energy regeneration. For example, the generator GN is provided on the front wheels WHf. The generator GN is controlled (driven) by a generator controller EG. Here, the device including the generator GN and its controller EG is referred to as the "regenerative braking device KC." The vehicle JV is equipped with a storage battery BT (also called a "driving storage battery") for the regenerative braking device KC. In other words, the regenerative braking device KC also includes the driving storage battery BT.

When the electric motor/generator GN operates as an electric motor for driving (for example, when the vehicle JV is accelerating), power is supplied to the electric motor/generator GN from the storage battery BT via a controller EG for the regenerative braking device (also simply referred to as a "regenerative controller"). On the other hand, when the electric motor/generator GN operates as a generator (when the vehicle JV is decelerating), power from the generator GN is stored in the storage battery BT via the regenerative controller EG (so-called regenerative braking is performed). In regenerative braking, a regenerative braking force Fg is generated by the front wheel generator GN.

The vehicle JV is equipped with a brake device SX. The brake device SX generates front and rear wheel frictional braking forces Fmf and Fmr on the front and rear wheels WHf and WHr. The brake device SX includes a rotating member (e.g., a brake disc) KT and a brake caliper CP. The rotating member KT is fixed to the wheel WH, and the brake caliper CP is provided to sandwich the rotating member KT. The brake caliper CP is provided with a wheel cylinder CW. Brake fluid BF adjusted to a brake fluid pressure Pw is supplied to the wheel cylinder CW from the brake control device SC. The brake fluid pressure Pw presses a friction member (e.g., a brake pad) MS against the rotating member KT. The rotating member KT and the wheel WH are fixed to rotate together, and the frictional force generated at this time generates a frictional braking force Fm on the wheel WH.

The vehicle JV is provided with a brake operating member BP and various sensors (BA, etc.). The brake operating member (e.g., brake pedal) BP is a member that the driver operates to decelerate the vehicle. The vehicle JV is provided with a brake operating amount sensor BA that detects the operation amount (braking operation amount) Ba of the brake operating member BP. As the brake operating amount sensor BA, at least one of an input hydraulic pressure sensor PN that detects the hydraulic pressure Pn (referred to as "input hydraulic pressure") in the input chamber Rn (described later), an operation displacement sensor SP that detects the operation displacement Sp of the brake operating member BP, and an operation force sensor FP that detects the operation force Fp of the brake operating member BP is adopted. In other words, the operation amount sensor BA detects at least one of the input hydraulic pressure Pn, the brake operating displacement Sp, and the brake operating force Fp as the brake operating amount Ba. The brake operating amount Ba is input to a controller ECU (also simply referred to as "brake controller") for the brake control device SC. The vehicle JV is equipped with various sensors, including a wheel speed sensor VW that detects the rotation speed (wheel speed) Vw of the wheels WH. The detection signals (Ba, Vw, etc.) of these sensors are input to the brake controller ECU. The brake controller ECU calculates the vehicle speed Vx based on the wheel speed Vw.

The vehicle JV is equipped with a brake control device SC so that so-called regenerative cooperative control (control in which the regenerative braking force Fg and the friction braking force Fm are operated in cooperation with each other) can be performed. For example, a brake-by-wire type brake control device is used as the brake control device SC. The brake control device SC adjusts the actual brake fluid pressure Pw according to the operation amount Ba of the brake operating member BP. The brake control device SC then supplies the brake fluid pressure Pw to the brake device SX (particularly the wheel cylinder CW) via the front and rear wheel connection paths HSf and HSr.

The brake control device SC is composed of a fluid unit HU (also called an "actuator") that includes a master cylinder CM, and a controller ECU (brake controller) for the brake control device SC. The fluid unit HU (described below) is controlled by the brake controller ECU. The controller ECU for the brake control device SC is composed of a microprocessor MP that performs signal processing, and a drive circuit DD that drives the solenoid valves and the electric motor.

The vehicle JV is provided with a driving assistance device UC that performs automatic braking in place of or to assist the driver. The driving assistance device UC is composed of an object detection sensor OB that detects the distance Ds (relative distance) to an object OJ (including a preceding vehicle SV traveling in front of the vehicle JV) in front of the vehicle JV, and a controller ECA for the driving assistance device. For example, a radar sensor, a millimeter wave sensor, an image sensor, etc. are used as the object detection sensor OB. The driving assistance controller ECA calculates the target deceleration Gd (target value of the vehicle body acceleration in the longitudinal direction of the vehicle JV) of the vehicle JV based on the detection result Ds (relative distance) of the object detection sensor OB. The target deceleration (target vehicle body longitudinal acceleration) Gd is transmitted from the driving assistance controller ECA to the brake controller ECU via the communication bus BS. Then, the brake control device SC generates braking forces Fg and Fm according to the target deceleration Gd.

The brake controller ECU, the regenerative braking controller EG, and the driving assistance controller ECA are each connected to a communication bus BS. Therefore, information (detected values, calculated values) is shared between these controllers via the communication bus BS. For example, the vehicle speed Vx is calculated by the brake controller ECU and transmitted to the driving assistance controller ECA (also simply referred to as the "driving assistance controller") via the communication bus BS. The target deceleration Gd is calculated by the driving assistance controller ECA and transmitted to the brake controller ECU via the communication bus BS. The brake controller ECU receives inputs of the braking operation amount Ba, the wheel speed Vw, the target deceleration Gd, and the like. Based on these signals, the brake controller ECU controls the fluid unit HU. Here, the braking operation amount Ba and the target deceleration Gd are collectively referred to as the "deceleration request value Bs" because they are required values for decelerating the vehicle JV. The braking controller ECU and the driving assistance controller ECA are supplied with power from a storage battery BU (called the "auxiliary storage battery") that is separate from the driving storage battery BT.

<First Configuration Example of Fluid Unit HU>
A first configuration example of the fluid unit HU will be described with reference to the schematic diagram of FIG. 2. The fluid unit HU is a pressure source for increasing and adjusting the hydraulic pressure (braking hydraulic pressure) Pw of the four wheel cylinders CW. In this example, the fluid unit HU is integrated with a single-type master cylinder CM. A front-rear type (also called "II type") braking system is adopted. The fluid unit HU is composed of an apply unit AU (including the master cylinder CM) and a pressurizing unit KU. The fluid unit HU and the wheel cylinders CW are connected by a communication path HS, an input path HN, a reservoir path HR, a return path HK, and a servo path HV. These are fluid paths through which the brake fluid BF is moved, and correspond to the fluid piping, the paths in the fluid unit HU, hoses, etc. The apply unit AU and the pressurizing unit KU are controlled by a brake controller ECU.

<<Apply Unit AU>>
The apply unit AU is composed of a master reservoir RV, a master cylinder CM, a master piston NM, a master spring DM, an input cylinder CN, an input piston NN, an input spring DN, an input valve VN, a release valve VR, a stroke simulator SS, and an input hydraulic pressure sensor PN. The apply unit AU is provided with various hydraulic chambers, including an input chamber Rn, a servo chamber Ru, a rear chamber Ro, and a master chamber Rm. Here, the "hydraulic chambers" are chambers filled with braking fluid BF and sealed by a seal member SL. The volumes of the respective hydraulic chambers are changed by the movement of the input piston NN and the master piston NM.

The master reservoir (also called the "atmospheric pressure reservoir") RV is a tank for hydraulic fluid, and brake fluid BF is stored inside it. The master reservoir RV is connected to the master cylinder CM (particularly, the master chamber Rm).

The master cylinder CM is a cylinder member having a bottom. A master piston NM is inserted inside the master cylinder CM, and the inside is sealed with a seal member SL to form a master chamber Rm. The master cylinder CM is a so-called single type. The master chamber Rm is ultimately connected to the front wheel cylinder CWf via the front wheel connection passage HSf and the hydraulic pressure modulator MJ. When the master piston NM is moved in the forward direction Ha (the direction in which the volume of the master chamber Rm decreases), brake fluid BF at hydraulic pressure Pm (referred to as "supply hydraulic pressure") is supplied from the fluid unit HU (particularly the master cylinder CM) to the hydraulic pressure modulator MJ (ultimately, the front wheel cylinder CWf).

The master piston NM is provided with a flange Tp. This flange Tp further divides the interior of the master cylinder CM into a servo chamber Ru and a rear chamber Ro. The servo chamber Ru is disposed opposite the master chamber Rm across the master piston NM. The rear chamber Ro is sandwiched between the master chamber Rm and the servo chamber Ru and is disposed between them. The servo chamber Ru and the rear chamber Ro are also sealed by the seal member SL as described above.

For example, the pressure-receiving area of the flange portion Tp (i.e., the pressure-receiving area of the servo chamber Ru) ru is set to be equal to the pressure-receiving area of the master piston NM (i.e., the pressure-receiving area of the master chamber Rm) rm. In this case, the hydraulic pressure Pa (described below) introduced into the servo chamber Ru and the supply hydraulic pressure Pm are the same in the steady state (i.e., since "ru = rm", "Pa = Pm").

The input cylinder CN is fixed to the master cylinder CM. An input piston NN is inserted inside the input cylinder CN and sealed with a seal member SL to form an input chamber Rn. The input piston NN is mechanically connected to the brake operating member BP via a clevis (U-shaped link). A flange portion (flange) Tn is provided on the input piston NN. An input spring DN is provided between the mounting surface of the input cylinder CN to the master cylinder CM and the flange portion Tn of the input piston NN. The input spring DN presses the flange portion Tn against the bottom of the input cylinder CN along the central axis of the master cylinder CM.

When braking is not being applied, the master piston NM (particularly the end surface Mp) and the input piston NN (particularly the end surface Mn) have a gap Ks (also called the "separation distance") inside the input cylinder CN. When braking is not being applied, the pistons NM and NN are at their most rearward position Hb (called the "initial position" of each piston). The gap Ks in this state is called the "predetermined distance ks (also called the "initial gap"). In the input chamber Rn, the master piston NM and the input piston NN are separated by the separation distance Ks, creating a state in which no brake fluid pressure Pw is generated even though the brake operating member BP is being operated. In other words, the separation distance Ks makes it possible to execute regenerative cooperative control. The separation distance Ks is controlled (adjusted) by the servo fluid pressure Pa (described later).

The input chamber Rn and the rear chamber Ro are connected via an input path HN. An input valve VN is provided in the input path HN. The input path HN is connected to the master reservoir RV via an open valve VR and a reservoir path between the rear chamber Ro and the input valve VN. The input valve VN and the open valve VR are two-position solenoid valves (also called "on-off valves") that have an open position (connected state) and a closed position (blocked state). A normally closed solenoid valve is used as the input valve VN. A normally open solenoid valve is used as the open valve VR.

A stroke simulator (also simply referred to as "simulator") SS is connected to the rear chamber Ro. The simulator SS generates an operating force Fp for the brake operating member BP. A piston and an elastic body (e.g., a compression spring) are provided inside the simulator SS. When brake fluid BF flows into the simulator SS, the piston is pushed by the brake fluid BF. A force is applied to the piston by the elastic body in a direction that prevents the inflow of brake fluid BF, so that an operating force Fp for the brake operating member BP is generated. In other words, the operating characteristic of the brake operating member BP (the relationship between the operating displacement Sp and the operating force Fp) is formed by the simulator SS.

An input hydraulic pressure sensor PN is provided to detect the hydraulic pressure Pn in the input chamber Rn (referred to as the "input hydraulic pressure"). The input hydraulic pressure Pn is also the hydraulic pressure in the simulator SS and the rear chamber Ro. The input hydraulic pressure sensor PN is one of the braking operation amount sensors BA described above, and the input hydraulic pressure Pn is input to the braking controller ECU as the braking operation amount Ba.

In addition to the input hydraulic pressure sensor PN, the fluid unit HU is provided with a braking operation amount sensor BA, which includes an operation displacement sensor SP that detects the operation displacement Sp of the brake operating member BP, and/or an operation force sensor FP that detects the operation force Fp of the brake operating member BP. In other words, at least one of the input hydraulic pressure sensor PN, the operation displacement sensor SP (stroke sensor), and the operation force sensor FP is used as the braking operation amount sensor BA. Therefore, the braking operation amount Ba is at least one of the input hydraulic pressure Pn, the operation displacement Sp, and the operation force Fp.

<Pressure unit KU>
The pressurizing unit KU is composed of an electric motor MA, a fluid pump QA, a pressure regulating valve UA, a supply fluid pressure sensor PM, and a servo fluid pressure sensor PA. In the pressurizing unit KU, the pressure of the brake fluid BF discharged by the fluid pump QA driven by the electric motor MA is adjusted by the pressure regulating valve UA. Here, the fluid pressure adjusted by the pressure regulating valve UA is referred to as the "servo fluid pressure Pa." The servo fluid pressure Pa is supplied to the apply unit AU (particularly the servo chamber Ru) and the rear wheel cylinder CWr, and ultimately generates front and rear wheel brake fluid pressures Pwf, Pwr (=Pw).

An electric pump is formed by the combination of "one electric motor MA" and "one fluid pump QA driven by the electric motor MA." The electric motor MA is a power source for generating and adjusting the hydraulic pressure (braking hydraulic pressure) Pw in the wheel cylinder CW during braking. The electric motor MA is provided with a motor rotation speed sensor NS to detect the rotation speed Ns of the electric motor MA. A rotation angle sensor (not shown) may also be provided to detect the rotation angle Ka of the electric motor MA. In this case, the motor rotation speed Ns is calculated by differentiating the motor rotation angle Ka with respect to time.

In the fluid pump QA, the suction section Qs and discharge section Qt are connected via a return path HK. The suction section Qs of the fluid pump QA is also connected to the master reservoir RV via a reservoir path HR. When the electric motor MA is driven and the fluid pump QA rotates, the brake fluid BF circulates through the return path HK. When the amount of brake fluid BF is insufficient in the return path HK, the apply unit AU, the wheel cylinder CW, etc., the brake fluid BF is sucked from the master reservoir RV via the reservoir path HR. A check valve is provided in the return path HK to prevent the fluid pump QA from rotating in reverse.

A pressure regulating valve UA is provided in the return path HK to adjust the pressure Pa (servo fluid pressure) of the brake fluid BF discharged by the fluid pump QA. The pressure regulating valve UA is a linear solenoid valve (also called a "proportional valve" or "differential pressure valve") whose valve opening amount (lift amount) is continuously controlled according to its energized state (e.g., supply current). A normally open solenoid valve is used as the pressure regulating valve UA.

When the electric motor MA is operating, a circulating flow KN of brake fluid BF (the flow of fluid returning to its original flow, also simply called "backflow") is generated in the return flow path HK, as indicated by the dashed arrow. The pressure regulating valve UA throttles the return flow KN (the so-called orifice effect), thereby adjusting the servo fluid pressure Pa (the pressure between the discharge section Qt of the fluid pump QA and the pressure regulating valve UA). Note that since the pressure regulating valve UA is normally open, it is fully open when not energized, and the servo fluid pressure Pa is "0".

The return path HK is connected to the servo chamber Ru via the servo path HV between the discharge section Qt and the pressure regulating valve UA. Therefore, the servo hydraulic pressure Pa is supplied to the servo chamber Ru. In a configuration in which the pressure receiving area ru of the servo chamber Ru is equal to the pressure receiving area rm of the master chamber Rm, when the servo hydraulic pressure Pa is supplied to the servo chamber Ru, a supply hydraulic pressure Pm that is the same pressure as the servo hydraulic pressure Pa is output from the master chamber Rm (i.e., "Pm = Pa"). Furthermore, even in a configuration in which the pressure receiving areas ru and rm are different, the relationship between them (for example, the ratio of the pressure receiving areas) is known, so the supply hydraulic pressure Pm and the servo hydraulic pressure Pa can be converted into each other.

The master chamber Rm of the master cylinder CM is connected to the front wheel cylinder CWf via the front wheel connection passage HSf and the hydraulic pressure modulator MJ. The hydraulic pressure modulator MJ is used to independently and individually adjust the hydraulic pressure Pw of each wheel cylinder CW for antilock brake control, vehicle stability control, etc. The front wheel connection passage HSf is branched into two in the hydraulic pressure modulator MJ. The branched front wheel connection passages HSf are connected to each of the front wheel cylinders CWf. A supply hydraulic pressure sensor PM is provided in the front wheel connection passage HSf to detect the hydraulic pressure Pm of the brake fluid BF supplied from the master chamber Rm. For example, the supply hydraulic pressure sensor PM is included in the hydraulic pressure modulator MJ. Here, when the hydraulic pressure modulator MJ is not operated, the supply hydraulic pressure Pm is equal to the hydraulic pressure (front wheel brake hydraulic pressure) Pwf in the front wheel cylinder CWf.

When adjusting (e.g., pressurizing) the front wheel brake fluid pressure Pwf, the servo fluid pressure Pa is transmitted via the master cylinder CM in the order of "Ru → Rm → CWf". On the other hand, when adjusting (e.g., pressurizing) the rear wheel brake fluid pressure Pwr, the servo fluid pressure Pa is supplied directly to the rear wheel cylinder CWr. Specifically, the rear wheel connection passage HSr is connected to the return passage HK between the discharge section Qt and the pressure regulating valve UA. Furthermore, the rear wheel connection passage HSr is branched into two within the fluid pressure modulator MJ and connected to each of the rear wheel cylinders CWr. A servo fluid pressure sensor PA is provided in the rear wheel connection passage HSr to detect the servo fluid pressure Pa. In addition, when the apply unit AU is configured with "ru = rm", although there is a time lag between the servo hydraulic pressure Pa and the supply hydraulic pressure Pm, they are substantially (steadily) equal, so one of the servo hydraulic pressure sensor PA and the supply hydraulic pressure sensor PM may be omitted. Similarly, when the hydraulic pressure modulator MJ is not operated, the servo hydraulic pressure Pa is equal to the hydraulic pressure (rear wheel brake hydraulic pressure) Pwr in the rear wheel cylinder CWr.

<<Driving of the hydraulic unit HU by the brake controller ECU>>
A signal of a deceleration request value Bs (a collective term for a braking operation amount Ba and a target deceleration Gd) is input to the brake controller ECU. Here, the braking operation amount Ba is a signal indicating the degree of operation of the brake operating member BP, and is at least one of an input hydraulic pressure Pn, an operating displacement Sp, and an operating force Fp. Signals (Pa, etc.) from various sensors (PA, etc.) provided in the fluid unit HU are input to the controller ECU. Based on these signals and a control algorithm programmed in a microprocessor MP provided in the controller ECU, a drive signal Vn of the input valve VN, a drive signal Vr of the release valve VR, a drive signal Ua of the pressure regulating valve UA, and a drive signal Ma of the electric motor MA are calculated. The controller ECU is supplied with power from a storage battery BU. Based on this power supply, the solenoid valves "VN, VR, UA" constituting the fluid unit HU and the electric motor MA are controlled (driven) in accordance with the drive signals "Vn, Vr, Ua, Ma".

Specifically, the braking controller ECU is equipped with a drive circuit DD to drive the solenoid valves "VN, VR, UA" and the electric motor MA. The drive circuit DD is supplied with power from the auxiliary storage battery BU. In the drive circuit DD, a bridge circuit is formed by switching elements (power semiconductor devices such as MOS-FETs and IGBTs) to drive the electric motor MA. The energized state of each switching element is controlled based on the motor drive signal Ma, and the output of the electric motor MA is controlled. The drive circuit DD also controls the energized state (i.e., excited state) of the solenoid valves "VN, VR, UA" based on the drive signals "Vn, Vr, Ua" to drive the valves.

The drive circuit DD is provided with a voltage sensor VM to detect the supply voltage value Vm (also called "power supply voltage") from the auxiliary battery BU (power source). The drive circuit DD is also provided with a current sensor ID to detect the actual current value Id of the electric motor MA and the solenoid valves "VN, VR, UA". Note that the current sensor ID is a general term for multiple current sensors. Specifically, the current sensor ID includes a motor current sensor IM that detects the current value Im (motor current value) of the electric motor MA, and a pressure regulating valve current sensor IA that detects the current value Ia (pressure regulating valve current value) of the pressure regulating valve UA, etc.

The drive circuit DD is provided with a circuit temperature sensor TD to detect the temperature Td of the drive circuit DD (particularly the switching element). The electric motor MA is provided with a motor temperature sensor TM to detect the temperature Tm of the electric motor MA. The circuit temperature Td and the motor temperature Tm are used in the determination based on the load state quantity Jm (described below).

During braking, when the brake operating member BP is operated, the input valve VN is opened and the release valve VR is closed. Therefore, in conjunction with the movement of the brake operating member BP, the brake fluid BF discharged from the input chamber Rn is moved to the simulator SS. This generates the operating force Fp of the brake operating member BP. During braking, the electric motor MA and the pressure regulating valve UA are driven. The brake fluid BF discharged from the fluid pump QA is throttled by the pressure regulating valve UA to adjust the servo fluid pressure Pa. The servo fluid pressure Pa is transmitted from the servo chamber Ru to the master chamber Rm via the master piston NM, and is supplied to the front wheel cylinder CWf as the supply fluid pressure Pm. On the other hand, the servo fluid pressure Pa is directly supplied to the rear wheel cylinder CWr.

<First Processing Example of Pressure Regulation Control>
A first processing example of the pressure regulation control in the fluid unit HU (particularly, the pressurizing unit KU) will be described with reference to the flow diagram of FIG. 3. The "pressure regulation control" is a process in which the electric motor MA is driven to form a return flow KN of the brake fluid BF, and the return flow KN is throttled by the pressure regulation valve UA to regulate the servo hydraulic pressure Pa (ultimately, the brake hydraulic pressure Pw). Here, the fluid unit HU that regulates the servo hydraulic pressure Pa by utilizing the return flow KN generated by the electric motor MA as the power source is called a "return type". The pressure regulation control includes a specific control that takes into account the load state quantity Jm of the electric motor MA to avoid stalling of the electric motor MA (i.e., a phenomenon in which the electric motor stalls or stops due to an excessive load). The algorithm of the pressure regulation control is programmed in the microprocessor MP in the brake controller ECU.

The explanation is based on the following assumptions: The vehicle JV is an electric vehicle and is equipped with a regenerative braking device KC that can generate a regenerative braking force Fg on the front wheels WHf. The pressure regulation control includes regenerative cooperative control. "Regenerative cooperative control" is a braking control that decelerates the vehicle JV by coordinating the frictional braking force Fm by the fluid unit HU of the brake control device SC and the regenerative braking force Fg by the regenerative braking device KC.

In step S110, various signals including the deceleration request value Bs, the supply hydraulic pressure Pm, the servo hydraulic pressure Pa, the motor temperature Tm, the circuit temperature Td (e.g., element temperature), the motor current value Im, the pressure regulating valve current value Ia, the motor rotation speed Ns, the power supply voltage Vm, etc. are read. Here, the deceleration request value Bs is a request value for decelerating the vehicle JV, and is a collective term for the braking operation amount Ba and the target deceleration Gd. The supply hydraulic pressure Pm and the servo hydraulic pressure Pa are detected by the supply hydraulic pressure sensor PM and the servo hydraulic pressure sensor PA. The motor temperature Tm and the circuit temperature Td are detected by the motor temperature sensor TM and the circuit temperature sensor TD. The motor current value Im and the pressure regulating valve current value Ia are detected by the current sensor ID (collectively). The motor rotation speed Ns is detected by the motor rotation speed sensor NS. The power supply voltage Vm (the actual voltage of the power supply BU) is detected by the power supply voltage sensor VM.

In step S120, the target vehicle body posture force Fv is calculated based on the deceleration request value Bs (braking operation amount Ba or target deceleration Gd). The "target vehicle body posture force Fv" is a target value corresponding to the braking force Fb acting on the vehicle body (i.e., the braking force of the vehicle JV as a whole). The target vehicle body posture force Fv is calculated to be "0" based on the deceleration request value Bs and the calculation map Zfv when the deceleration request value Bs is less than a predetermined amount bo. When the deceleration request value Bs is equal to or greater than the predetermined amount bo, the target vehicle body posture force Fv is calculated to increase from "0" as the deceleration request value Bs increases. Here, the predetermined amount bo is a preset value (constant).

In step S130, the limit regenerative braking force Fx is acquired. The "limit regenerative braking force Fx" is the maximum value (limit value) of the regenerative braking force Fg that the regenerative braking device KC can generate. In other words, the limit regenerative braking force Fx is a state quantity (variable) that represents the limit of the regenerative braking force Fg. The limit regenerative braking force Fx is determined based on the operating state of the regenerative braking device KC. Specifically, the operating state of the regenerative braking device KC corresponds to at least one of the rotation speed Ng of the generator GN (i.e., the front wheel speed Vwf), the state (temperature, etc.) of the regenerative controller EG (particularly, power transistors such as IGBTs), and the state (charge acceptance amount, temperature, etc.) of the driving storage battery BT. The limit regenerative braking force Fx is determined (calculated) by the regenerative controller EG and input to the brake controller ECU via the communication bus BS.

In step S140, the target regenerative braking force Fh and the target frictional braking force Fn are calculated based on the target vehicle body tension force Fv and the limit regenerative braking force Fx. The "target regenerative braking force Fh" is a target value corresponding to the actual regenerative braking force Fg generated by the regenerative braking device KC. The "target frictional braking force Fn" is a target value corresponding to the actual frictional braking force Fm generated by the brake control device SC.

In step S140, it is determined whether the target vehicle body position force Fv is greater than the limit regenerative braking force Fx. If the target vehicle body position force Fv is equal to or less than the limit regenerative braking force Fx (i.e., if Fv≦Fx), the target regenerative braking force Fh is calculated to the target vehicle body position force Fv, and the target frictional braking force Fn is calculated to be 0 (i.e., Fh=Fv, Fn=0). On the other hand, if the target vehicle body position force Fv is greater than the limit regenerative braking force Fx (i.e., if Fqf>Fxf), the target regenerative braking force Fh is calculated to be the limit regenerative braking force Fx, and the target frictional braking force Fn is calculated to be the target vehicle body position force Fv minus the limit regenerative braking force Fx (i.e., Fh=Fx, Fn=Fv-Fx).

The target regenerative braking force Fh calculated in step S140 is sent from the brake controller ECU to the regenerative controller EG. The regenerative controller EG then controls the generator GN so that the actual regenerative braking force Fg approaches and coincides with the target regenerative braking force Fh.

In step S150, the target hydraulic pressure Pt is calculated based on the target frictional braking force Fn. The "target hydraulic pressure Pt" is a target value corresponding to the servo hydraulic pressure Pa (and thus the actual braking hydraulic pressure Pw). Specifically, the target frictional braking force Fn is converted to the target hydraulic pressure Pt based on the specifications of the braking device SX, etc. (pressure-receiving area of the wheel cylinder CW, effective braking radius of the rotating member KT, friction coefficient of the friction member MS, effective radius of the wheel (tire), etc.).

In step S160, the load state amount Jm is calculated. The load state amount Jm is a state amount (variable) that represents the load state (degree of load) of the electric motor MA. For example, the load state amount Jm is calculated (determined) by at least one of the methods listed below.
(1) The load state quantity Jm is calculated based on the temperature Tm of the electric motor MA. For example, the temperature Tm of the electric motor MA is determined as the load state quantity Jm (i.e., "Jm = Tm"). Here, the motor temperature Tm is detected by a motor temperature sensor TM provided in the electric motor MA.
(2) The load state quantity Jm is calculated based on the temperature Td of the drive circuit DD (particularly, the switching element) that drives the electric motor MA. For example, the temperature Td of the drive circuit DD is determined as the load state quantity Jm (i.e., "Jm = Td"). Here, the circuit temperature Td is detected by a circuit temperature sensor TD provided in the drive circuit DD.
(3) The load state quantity Jm is calculated based on a ratio Hm of the output of the electric motor MA to an actual current value Im (a value detected by the motor current sensor IM) supplied to the electric motor MA. For example, the ratio Hm is determined as the load state quantity Jm (i.e., "Jm = Hm"). Here, the rotation speed Ns of the electric motor MA (a value detected by the rotation speed sensor NS) is used as the output of the electric motor MA. In addition, the brake fluid pressure Pw (i.e., the servo fluid pressure Pa, the supply fluid pressure Pm) may be used as the output of the electric motor MA.
In other words, the load state quantity Jm (the magnitude of the load on the electric motor MA) is determined based on at least one of the motor temperature Tm, the drive circuit temperature Td, and the output (e.g., the actual servo hydraulic pressure Pa, the actual supply hydraulic pressure Pm, the actual motor rotation speed Ns) relative to the motor current Im (i.e., the input to the electric motor MA).

In step S170, it is determined whether the load on the electric motor MA is excessive (referred to as "overload determination"). The overload determination is to predict the probability of stalling of the electric motor MA. Specifically, the overload determination is based on the load state amount Jm and determines whether the load state amount Jm is equal to or greater than a predetermined amount jm. The predetermined amount jm is a determination threshold in the overload determination and is a preset value (constant). If "Jm < jm", the motor load is relatively small and the probability of motor stall is low, the overload determination is denied and the process proceeds to step S180. On the other hand, if "Jm ≥ jm", the motor load is large and the probability of motor stall is high, the overload determination is affirmative and the process proceeds to step S190.

In step S180, normal pressure regulation control (referred to as "normal control") is executed. In normal control, the electric motor MA is driven based on the target hydraulic pressure Pt. Specifically, the target rotation speed Nt (a target value corresponding to the actual motor rotation speed Ns) is calculated based on the target hydraulic pressure Pt, and the supply current Im to the electric motor MA is adjusted based on the target rotation speed Nt. For example, in the drive control of the electric motor MA, the target rotation speed Nt is calculated to increase with an increase in the time change amount dP of the target hydraulic pressure Pt (i.e., the time derivative value of the target hydraulic pressure Pt). Then, pulse width modulation control (so-called PWM control) is executed so that the actual motor rotation speed Ns approaches and matches the target rotation speed Nt. In other words, in the drive control of the electric motor MA, rotation speed feedback control is performed.

In the rotation speed feedback control, the deviation hN is calculated based on the target rotation speed Nt and the actual rotation speed Ns (the detection value of the motor rotation speed sensor NS, or the time differential value of the detection value of the rotation angle sensor) (i.e., "hN = Nt - Ns"). Then, the current value Im to the electric motor MA (for example, the duty ratio in PWM control) is adjusted so that the rotation speed deviation hN approaches and matches "0". In detail, when the rotation speed deviation hN is larger than the predetermined rotation speed hn, the current value Im of the electric motor MA is increased, and the electric motor MA is accelerated. On the other hand, when the rotation speed deviation hN is less than the predetermined rotation speed "-hn", the current value Im of the electric motor MA is decreased, and the electric motor MA is decelerated. Here, the predetermined rotation speed hn is the dead zone of the control and is a predetermined value (a constant with a positive sign) that is set in advance. Note that the target rotation speed Nt is not a function of the target hydraulic pressure Pt, but may be a predetermined value (constant) that is set in advance.

Furthermore, in the normal control of step S180, the pressure regulating valve UA is driven based on the target hydraulic pressure Pt. Specifically, the supply current Ia of the pressure regulating valve UA is adjusted so that the servo hydraulic pressure Pa approaches and matches the target hydraulic pressure Pt. For example, in the current control for driving the pressure regulating valve UA, the target current value It (the target value corresponding to the actual current value Ia) is calculated to increase as the target hydraulic pressure Pt increases based on the target hydraulic pressure Pt and the calculation map Zip (IP characteristics described below). Then, the actual current value Ia is controlled to approach and match the target current value It (so-called current feedback control).

Furthermore, in the drive control of the pressure regulating valve UA, the target current value It may be adjusted so that the servo hydraulic pressure Pa approaches and matches the target hydraulic pressure Pt. Specifically, the deviation hP is calculated based on the target hydraulic pressure Pt and the servo hydraulic pressure Pa (i.e., "hP = Pt - Pa"). Then, the current value Ia (for example, the duty ratio in PWM control) to the pressure regulating valve UA is adjusted so that the hydraulic pressure deviation hP approaches and matches "0". In detail, when the hydraulic pressure deviation hP is greater than the predetermined hydraulic pressure hp, the target current value It (resulting in the actual current value Ia) of the pressure regulating valve UA is increased, and the valve opening amount of the pressure regulating valve UA is reduced. On the other hand, when the hydraulic pressure deviation hP is less than the predetermined hydraulic pressure "-hp", the current values It and Ia of the pressure regulating valve UA are reduced, and the valve opening amount of the pressure regulating valve UA is increased. Here, the specified hydraulic pressure hp is the dead zone of the control and is a preset value (a constant with a positive sign).

In step S190, pressure regulation control (referred to as "first specific control" or simply "specific control") is executed when the load on the electric motor MA is excessive. In the first specific control, the current supply to the pressure regulating valve UA is limited so that the electric motor MA does not stall or stop. In step S190, the electric motor MA is driven in the same manner as in step S180. Meanwhile, the current Ia supplied to the pressure regulating valve UA is limited in the manner described below.

<Current Limitation of Pressure Regulating Valve UA>
The current limiting of the pressure regulating valve UA in the first specific control in step S190 will be described with reference to the characteristic diagram in Fig. 4. "Current limiting" is to limit the current Ia supplied to the pressure regulating valve UA to reduce the load on the electric motor MA so as to avoid stalling of the electric motor MA when the overload determination is affirmative. The characteristic diagram is a calculation map that expresses the relationship between the current value supplied to the pressure regulating valve UA and the hydraulic pressure output, and is called "IP characteristics." In the calculation map (IP characteristics) Zip, the horizontal axis indicates the target current value It (resulting in the current value Ia) and the vertical axis indicates the target hydraulic pressure Pt (resulting in the actual servo hydraulic pressure Pa).

Since the pressure regulating valve UA is normally open, as the supply current Ia increases, the valve opening amount decreases and the servo hydraulic pressure Pa (resulting in an increase in the supply hydraulic pressure Pm and the brake hydraulic pressure Pw) increases. In the calculation map Zip, point X is the maximum operating point required for the brake control device SC. Therefore, the rated value ix of the supply current (referred to as the "rated current") corresponds to the rated value px of the servo hydraulic pressure Pa (referred to as the "rated hydraulic pressure") required for the brake control device SC. In the normal control of step S180, the pressure regulating valve UA adjusts the current value Ia in the range from "0" to the rated current ix, thereby adjusting the servo hydraulic pressure Pa in the range from "0" to the rated hydraulic pressure px (the range indicated by the two-dot chain line in the figure). The "rated hydraulic pressure px" corresponds to the maximum value of the servo hydraulic pressure Pa (resulting in a increase in the brake hydraulic pressure Pw) that the brake control device SC can continuously generate.

When the load on the electric motor MA is excessive (i.e., when the overload determination in step S170 is positive), in the specific control in step S190, as shown by the operating point S, a limit is set so that the current value It (target value) and Ia (actual value) supplied to the pressure regulating valve UA do not exceed the limited current value Iz. By limiting the current values It and Ia to the limited current value Iz, the output (hydraulic pressure) Pt and Pa from the pressurizing unit KU is limited to the limited hydraulic pressure Pz. Here, the control result of the target hydraulic pressure Pt (target value) is the servo hydraulic pressure Pa (actual value). In the first specific control, the operating point of the brake control device SC is limited to the range from the origin (0,0) to point S (Iz,Pz) in the calculation map Zip (the range shown by the dashed line in the figure).

For example, the load state quantity Jm, which indicates the degree of load (degree of overload) of the electric motor MA, is determined (calculated) based on the temperature Tm of the electric motor MA and/or the temperature Td of the drive circuit DD of the electric motor MA. This is based on the fact that the higher the load, the higher the temperature Tm (temperature of the body of the electric motor MA) and Td (temperature of the drive circuit DD). The load state quantity Jm may also be calculated based on the relationship between the input (i.e., motor current value Im) and the output (i.e., servo hydraulic pressure Pa, supply hydraulic pressure Pm, motor rotation speed Ns) in the electric motor MA. Specifically, the ratio Hm of the output to the input is calculated, and the load state quantity Jm is determined according to the ratio Hm. Note that "the electric motor MA is in an overload state (positive condition for overload determination)" is determined based on "the load state quantity Jm (variable) being equal to or greater than a predetermined quantity jm (constant) set in advance".

If the overload determination is positive, the first specific control limits the target current value It (resulting in the actual current value Ia) to be equal to or less than the limited current value Iz. As a result of this limitation, a current greater than the limited current value Iz is not supplied to the pressure regulating valve UA, and as a result, the servo hydraulic pressure Pa is limited to be equal to or less than the limited hydraulic pressure Pz. The limited current value Iz (variable) is calculated based on the load state amount Jm and the calculation map Zjm, as shown in block X190. Specifically, the larger the load state amount Jm is, the smaller the limited current value Iz is determined according to the calculation map Zjm. Therefore, the larger the load state amount Jm is, the lower the limited hydraulic pressure Pz is set. In addition, the limited current value Iz (resulting in the limited hydraulic pressure Pz) may be set as a predetermined value (constant) that is set in advance. Since the load of the electric motor MA is limited by the first specific control, stalling of the electric motor MA can be avoided. The pressure regulating valve UA can then continue to regulate the brake fluid pressure Pw.

For example, pulse width modulation control (PWM control) is performed in the drive control of the pressure regulating valve UA. In PWM control, the duty ratio Du of the pulse width (the ratio of the pulse width in the on state to the period of a periodic pulse wave) is determined based on the target current value It and a preset calculation map. The final voltage supplied to the pressure regulating valve UA is determined by the input voltage (power supply voltage, the voltage of the storage battery BU) and the duty ratio Dt in the pressure regulating valve UA, and as a result, the current value Ia of the pressure regulating valve UA is determined. Therefore, when PWM control is adopted in the drive of the pressure regulating valve UA, the duty ratio Du may be limited in the limit based on the limit current value Iz. In other words, by limiting the duty ratio Du, the current value Ia is essentially limited.

Furthermore, the current limit based on the load state quantity Jm may be performed by limiting the target hydraulic pressure Pt. This is because the pressure regulating valve UA controls the actual current Ia based on the target current value It corresponding to the target hydraulic pressure Pt. In other words, the actual current value Ia can be limited by limiting the target hydraulic pressure Pt based on the load state quantity Jm.

<Second Processing Example of Pressure Regulation Control>
A second processing example of the voltage regulation control will be described with reference to the flow chart of FIG. 5. In the first processing example, the current value Ia was limited based on the load state quantity Jm, which indicates the overload state of the electric motor MA. Instead, in the second processing example, the current value Ia is limited based on the power supply voltage Vm of the electric motor MA (i.e., the voltage of the storage battery BU). In the second processing example, in the calculation steps with the same symbols as in the first processing example (i.e., steps S110 to S150 and step S180), the same calculation processing as in the first processing example is performed. Therefore, the description of the processing in these calculation steps will be omitted. Below, the differences from the first processing example will be described.

In step S200, it is determined whether the voltage Vm of the auxiliary battery BU (power source) has dropped (referred to as "voltage drop determination"). The power source voltage Vm is the voltage input (supplied) from the battery BU to the drive circuit DD to drive the electric motor MA. For example, the power source voltage Vm is detected by a power source voltage sensor VM provided in the drive circuit DD. Specifically, the voltage drop determination is based on whether the power source voltage Vm is less than a predetermined voltage vm. Here, the predetermined voltage vm is a preset value (constant). If "Vm ≧ vm", the voltage drop determination in step S200 is negative, the process proceeds to step S180, and normal control is executed. On the other hand, if "Vm < vm", the power source voltage Vm has dropped, so the voltage drop determination in step S200 is positive, and the process proceeds to step S210.

In step S210, pressure regulation control (referred to as "second specific control" or simply "specific control") is executed when the power supply voltage Vm of the electric motor MA is low. In the second specific control, as in the first specific control, the current supply to the pressure regulating valve UA is limited so that the electric motor MA does not stall or stop. In step S210, the electric motor MA is driven in the same manner as in step S180. Meanwhile, the supply current Ia to the pressure regulating valve UA is limited in the same manner as in step S190.

Referring again to the characteristic diagram of FIG. 4, the current restriction of the pressure regulating valve UA in the specific control of step S210 will be described. The current restriction by the second specific control is to limit the supply current Ia to the pressure regulating valve UA to avoid stalling of the electric motor MA when the determination of the drop in the power supply voltage Vm is affirmative, thereby reducing the load on the electric motor MA. When the power supply voltage Vm of the electric motor MA is dropping (i.e., when the determination of step S200 is affirmative), the current It (target value) and Ia (actual value) supplied to the pressure regulating valve UA are limited by the limit current value Iz in the specific control of step S210. As a result, the hydraulic pressure Pt (target value) and Pa (actual value) from the pressurizing unit KU are limited to be equal to or less than the limit hydraulic pressure Pz (see operating point S). That is, in the second specific control, as in the first specific control, the operating point of the brake control device SC is limited to the range from the origin (0,0) to point S (Iz,Pz) in the calculation map Zip (the range indicated by the dashed line in the figure). The power supply voltage Vm is detected by the power supply voltage sensor VM provided in the drive circuit DD.

If the voltage drop determination is positive, the second specific control limits the target current value It (resulting in the current value Ia) so as not to exceed the limit current value Iz. Due to this limitation, a current greater than the limit current value Iz is not supplied to the pressure regulating valve UA, so that the servo hydraulic pressure Pa (resulting in the supply hydraulic pressure Pm, the braking hydraulic pressure Pw) is limited to the range up to the limit hydraulic pressure Pz. The limit current value Iz (variable) is calculated based on the power supply voltage Vm and the calculation map Zvm, as shown in block X190. Specifically, the smaller the power supply voltage Vm is, the smaller the limit current value Iz is determined according to the calculation map Zvm. Therefore, the greater the degree of decrease in the power supply voltage Vm, the lower the limit hydraulic pressure Pz is set. In addition, the limit current value Iz (resulting in the limit hydraulic pressure Pz) may be set as a predetermined value (constant) set in advance. The second specific control limits the load on the electric motor MA, so that stalling of the electric motor MA is avoided and the pressure regulating valve UA can continue to regulate the brake fluid pressure Pw. As described above, when the pressure regulating valve UA is driven by PWM control, the duty ratio Du may be limited in the current limit. This is based on the fact that limiting the duty ratio Du essentially limits the current value Ia.

As above, current limitation may be performed by limiting the target hydraulic pressure Pt. Current control of the pressure regulating valve UA is performed according to a target current value It calculated based on the target hydraulic pressure Pt. Therefore, the actual current value Ia can be limited by limiting the target hydraulic pressure Pt based on the power supply voltage Vm.

<Second Configuration Example of Fluid Unit HU>
A second configuration example of the fluid unit HU will be described with reference to the schematic diagram of FIG. 6. The fluid unit HU according to the second configuration example is also applied to a vehicle JV equipped with a regenerative braking device KC on the front wheels WHf. In the second configuration example, members (MA, etc.) with the same symbols as those in the first configuration example have the same functions as those in the first configuration example. Therefore, differences from the first configuration example will be described. In the example, the fluid unit HU is configured so that the pressure receiving areas ru and rm are the same.

In the second configuration example, a second pressure regulating valve UB is provided in the return flow path HK between the fluid pump QA and the pressure regulating valve UA (also referred to as the "first pressure regulating valve"). The second pressure regulating valve UB is a normally open linear solenoid valve similar to the first pressure regulating valve UA. In the second configuration example, the brake fluid BF discharged by the fluid pump QA is adjusted by throttling in two stages. Here, the fluid pressure Pa between the first pressure regulating valve UA and the second pressure regulating valve UB is referred to as the "first servo fluid pressure". Also, the fluid pressure Pb between the second pressure regulating valve UB and the fluid pump QA is referred to as the "second servo fluid pressure". The second servo fluid pressure Pb is adjusted by the second pressure regulating valve UB so as to increase from the first servo fluid pressure Pa. Therefore, in the magnitude relationship between the first servo hydraulic pressure Pa and the second servo hydraulic pressure Pb, the second servo hydraulic pressure Pb is always equal to or greater than the first servo hydraulic pressure Pa (i.e., "Pb ≧ Pa"). The second pressure regulating valve UB is controlled by a drive signal Ub. The fluid unit HU is also provided with first and second servo hydraulic pressure sensors PA and PB to detect the first and second servo hydraulic pressures Pa and Pb.

The return flow path HK is connected to the servo chamber Ru via the servo path HV at the portion Xa between the first pressure regulating valve UA and the second pressure regulating valve UB. Therefore, the first servo hydraulic pressure Pa is supplied to the servo chamber Ru and is output from the master chamber Rm as the supply hydraulic pressure Pm (i.e., since "ru = rm", "Pm = Pa = Pwf"). The return flow path HK is also connected to the rear wheel cylinder CWr via the rear wheel connection path HSr at the portion Xb between the fluid pump QA and the second pressure regulating valve UB. Therefore, the second servo hydraulic pressure Pb is supplied to the rear wheel cylinder CWr (i.e., "Pb = Pwr"). In the second configuration example, the front wheel brake fluid pressure Pwf and the rear wheel brake fluid pressure Pwr are adjusted separately within the range of "Pwf≦Pwr", so that in a vehicle JV equipped with a regenerative braking device KC on the front wheels WHf, the ratio between the front wheel braking force Fxf and the rear wheel braking force Fxr (the so-called front/rear braking force distribution) is maintained constant, and regenerative cooperative control can be performed.

In the second configuration example, as in the first configuration example, if at least one of the overload determination (see step S170) and the voltage drop determination (see step S200) is positive, the current flow to the first and second pressure regulating valves UA and UB is limited as described with reference to Figures 3 to 5. This prevents the motor from stalling, and the pressure regulating control by the first and second pressure regulating valves UA and UB can be continued without being interrupted by the motor stall.

When the fluid unit HU according to the second configuration example is applied to a vehicle JV equipped with a regenerative braking device KC on the rear wheels WHr, the first servo hydraulic pressure Pa is supplied to the rear wheel cylinder CWr, and the second servo hydraulic pressure Pb is supplied to the servo chamber Ru. With this configuration, the above-mentioned current flow restriction is performed, thereby achieving the same effect as above.

<Other configuration examples of fluid unit HU>
As the fluid unit HU of the brake control device SC according to the present invention, a configuration example including a single type master cylinder CM and a CN (see FIG. 2) and a configuration example including a pressurizing unit KU capable of adjusting pressure in two stages (see FIG. 6) have been described. Instead of these, in the brake control device SC according to the present invention, a configuration including a tandem type master cylinder CM as the fluid unit HU (see, for example, Japanese Patent Application Laid-Open No. 2020-032833), a configuration in which the wheel cylinder CW and the pressurizing unit KU are connected via an electromagnetic valve (see, for example, Japanese Patent Application Laid-Open No. 2021-014157), etc. may be adopted. In any case, in the fluid unit HU included in the brake control device SC according to the present invention, the brake fluid BF discharged by the fluid pump QA driven by the electric motor MA is adjusted by a pressure regulating valve (UA, etc.).

Furthermore, the above configuration example is a brake-by-wire type in which the stroke simulator SS generates the operating force Fp of the brake operating member BP, and the return type pressurizing unit KU realizes the function of a service brake (also called a "service brake"). Alternatively, the pressurizing unit KU may not be used for the service brake, and may be operated only for the execution of vehicle stability control or regenerative cooperative control (particularly, the switching operation immediately before the vehicle stops) (see, for example, JP 2014-213854 A and JP 2015-095966 A).

It is more effective to apply the current restriction by the first and second specific controls to the brake control device SC that realizes the service brake. For example, if the electric motor MA stops while the service brake is operating, the adjustment of the brake hydraulic pressure Pw must be switched from the pressure unit KU to manual braking (braking by the driver's muscle strength alone). However, in the brake control device SC, although the rated hydraulic pressure px that the pressure unit KU can generate is limited, the electric motor MA continues to be driven, so the pressure regulation control by the pressure unit KU can continue. In other words, when an overload state of the electric motor MA occurs, manual braking cannot be immediately switched to. Therefore, when the brake control device SC malfunctions, no sudden performance degradation occurs and the continuity of the pressure regulation control is guaranteed, so the discomfort felt by the driver can be reduced.

<Summary of the embodiments of the brake control device SC>
The brake control device SC according to an embodiment of the present invention is composed of a pressurizing unit KU that adjusts the pressure Pa (servo fluid pressure) of the brake fluid BF discharged by a fluid pump QA driven by an electric motor MA using a pressure regulating valve UA, and a controller ECU that adjusts the brake fluid pressure Pw of the wheel cylinder CW by controlling the pressurizing unit KU.

In the brake control device SC, the controller ECU limits the current value (Ia, etc.) supplied to the pressure regulator valve (UA, etc.) based on the load state quantity Jm, which indicates the degree (magnitude) of the load on the electric motor MA. This current limit is not performed when the load state quantity Jm is less than a predetermined quantity jm, but is performed when the load state quantity Jm is equal to or greater than the predetermined quantity jm. Specifically, the load state quantity Jm is calculated based on the temperature Tm of the electric motor MA. The load state quantity Jm can also be calculated based on the temperature Td of the circuit DD (particularly the drive element of the electric motor MA) that drives the electric motor MA. Furthermore, the load state quantity Jm may be calculated based on the ratio Hm of the motor output to the supply current value Im in the electric motor MA. Here, at least one of the servo hydraulic pressures Pa, Pb, the supply hydraulic pressure Pm, and the motor rotation speed Ns is adopted as the state quantity related to the output of the electric motor MA.

In the return-type pressurizing unit KU, the servo hydraulic pressure Pa, etc. are adjusted by the orifice effect when the brake fluid BF discharged from the fluid pump QA is throttled by the pressure regulating valve UA, etc. In detail, the (first) pressure regulating valve UA (hereinafter, the same applies to the second pressure regulating valve UB) is a normally open linear solenoid valve, and is controlled by the brake controller ECU. The pressure regulating valve UA includes a valve body driven by a solenoid, and when the solenoid is energized, a thrust (called "attraction force") that tries to draw the plunger into the fixed coil is generated in the solenoid. This attraction force acts on the valve body fixed to the solenoid so as to prevent the brake fluid BF from the fluid pump QA from flowing into the pressure regulating valve UA. Here, the force acting on the valve body by the brake fluid BF is called "fluid force". The suction force of the valve disc of the pressure regulating valve UA and the fluid force due to the flow of brake fluid BF (i.e., the return flow KN) face each other and oppose each other. When the suction force and the fluid force are in balance, the valve opening amount of the pressure regulating valve UA (i.e., the gap between the valve disc and the valve seat) is determined, and the servo hydraulic pressure Pa is determined.

The electric motor MA is designed to generate a rated hydraulic pressure px (maximum hydraulic pressure that can be continuously achieved). In other words, the electric motor MA has a sufficient output to generate the rated hydraulic pressure px. However, if the load state quantity Jm of the electric motor MA becomes excessively large, a situation may arise in which the output of the electric motor MA decreases relatively. For example, the following situations are assumed.
- Increased torque losses due to increased friction in the bearings (eg, bearings) of the electric motor MA and/or fluid pump QA.
- Increased torque losses due to increased friction at the coupling between the electric motor MA and the fluid pump QA.
- Increased torque loss due to foreign matter entering the fluid pump QA.
- Reduction in power output due to overheating of the electric motor MA.

As described above, the fluid force of the brake fluid BF is generated by using the electric motor MA as a power source. When the output of the electric motor MA decreases relatively due to the influence of increased torque loss and the fluid force corresponding to the suction force of the pressure regulating valve UA cannot be generated, it becomes difficult to adjust the servo fluid pressure Pa (and thus the brake fluid pressure Pw). Furthermore, if the torque loss increases further, the likelihood of a motor stall (a phenomenon in which the electric motor MA stalls and comes to a stop) increases. In the unlikely event that a motor stall occurs, the power to generate the circulating flow KN is lost, and the servo fluid pressure Pa (and thus the brake fluid pressure Pw) cannot be generated. In this situation, braking by the brake control device SC is switched to manual braking (braking by the driver's muscle strength alone).

In the brake control device SC according to the present invention, when the load state quantity Jm becomes excessive (i.e., when "Jm ≧ jm"), the current value It (target value) and Ia (actual value) to the pressure regulating valve UA are limited to the limited current value Iz. This limits the suction force (i.e., the force acting as a resistance to the fluid force of the return flow KN) in the pressure regulating valve UA. This makes it possible to avoid stalling in the electric motor MA. As a result, the adjustment control of the brake fluid pressure Pw by the brake control device SC (particularly the pressurizing unit KU) can be maintained without interruption. In other words, even if the load on the electric motor MA becomes excessive, the pressure adjustment control with the rated fluid pressure limited is continued. Therefore, even if an overload state of the electric motor MA occurs, the brake control is not immediately switched to manual braking, so that the driver's discomfort is suppressed.

The degree of relative output reduction of the electric motor MA due to an increase in load depends on the load state quantity Jm. Therefore, it is desirable to set the limit current Iz to be smaller as the load state quantity Jm increases (see the calculation map Zjm in block X190). However, even if the limit current Iz is preset as a predetermined value (constant), motor stall prevention is achieved.

In the brake control device SC, the controller ECU limits the current value (Ia, etc.) supplied to the pressure regulating valve (UA, etc.) based on the power supply voltage Vm of the electric motor MA. Here, the power supply voltage Vm is the output voltage of the storage battery BU and is the input voltage to the drive circuit DD. Current limitation is not performed when the power supply voltage Vm is equal to or greater than a predetermined voltage vm, but is performed when the power supply voltage Vm is less than the predetermined voltage vm.

When the power supply voltage Vm drops, a phenomenon similar to the above-mentioned situation where the load state quantity Jm becomes excessive (i.e., the output of the electric motor MA drops relatively, increasing the probability of motor stall) may occur. In the brake control device SC, when the power supply voltage Vm drops (i.e., when "Vm<vm"), the current value It (target value) and Ia (actual value) to the pressure regulating valve UA are limited. Furthermore, the limit current Iz may be preset as a predetermined value (constant), but it is preferable to set the limit current Iz to be smaller as the power supply voltage Vm becomes smaller (see the calculation map Zvm in block X190). The current limit of the pressure regulating valve provides the same effect as above (i.e., prevention of motor stall).

SC...Brake control device, BP...Brake operation member, CM...Master cylinder, CW...Wheel cylinder, HU...Fluid unit, KU...Pressurization unit, QA...Fluid pump, MA...Electric motor (for driving fluid pump QA), UA...Pressure regulator valve (first pressure regulator valve), UB...Second pressure regulator valve, ECU...Controller (for braking), BA...Braking operation amount sensor, Ba...Braking operation amount, Pt...Target hydraulic pressure, It...Target current value, Ia...Actual current value, ID...Current sensor (generic name), IA...Pressure regulator current sensor, IM...Motor current sensor Sa, Pa...servo fluid pressure (first servo fluid pressure), Pb...second servo fluid pressure, Pm...supply fluid pressure, PA...servo fluid pressure sensor (first servo fluid pressure sensor), PB...second servo fluid pressure sensor, PM...supply fluid pressure sensor, Jm...load state quantity, Vm...power supply voltage, VM...power supply voltage sensor, BU...auxiliary equipment storage battery (power supply), DD...drive circuit, Pw...braking fluid pressure, Tm...motor temperature, TM...temperature sensor, Td...drive circuit temperature (e.g., element temperature), TD...temperature sensor, Ns...motor rotation speed, NS...motor rotation speed sensor.

Claims (3)

A vehicle brake control device including a pressurizing unit that adjusts the pressure of brake fluid discharged by a fluid pump driven by an electric motor using a pressure regulating valve, and a controller that adjusts the brake fluid pressure in a wheel cylinder by controlling the pressurizing unit,
The controller:
a current value to the pressure regulating valve is limited based on a load state quantity that indicates a degree of load on the electric motor ,
The controller:
A braking control device for a vehicle, which does not implement the restriction when the load state amount is less than a predetermined amount, and implements the restriction when the load state amount is equal to or greater than the predetermined amount . 2. The vehicle brake control device according to claim 1 ,
The controller:
A vehicle braking control device that performs the limitation based on a power supply voltage of the electric motor. 3. The vehicle brake control device according to claim 2 ,
The controller:
A braking control device for a vehicle, which does not enforce the restriction when the power supply voltage is equal to or higher than a predetermined voltage, and enforces the restriction when the power supply voltage is less than the predetermined voltage.