JP7822909B2 - Damping force control device and damping force control method - Google Patents

Description

The present invention relates to a damping force control device and a damping force control method.

Shock absorbers (hereafter referred to as dampers) generate heat when damping vibrations, causing the temperature of the hydraulic oil inside to rise. If the temperature of the hydraulic oil (hereafter referred to as oil temperature) exceeds a certain temperature, the damping force of the damper will decrease, so this is prevented by detecting the oil temperature. However, installing a sensor to directly detect oil temperature is difficult due to cost and manufacturing efficiency considerations, and for this reason, it is currently estimated based on other detected values.

Patent Document 1 introduces an oil temperature estimation device that estimates the oil temperature of a damper using variables such as the sprung weight, the vertical acceleration of the sprung mass, and the relative velocity calculated from the differential value of the relative displacement between the sprung and unsprung mass.

Japanese Patent Application Laid-Open No. 2002-274138

According to the oil temperature detection device introduced in Patent Document 1, due to the nature of the damper, which converts kinetic energy into heat, the oil temperature rises as the number of times it operates increases, even for the same sprung mass, relative velocity between the sprung and unsprung mass, and vertical acceleration of the sprung mass. Previously, the frequency of damper operation, which is affected by oil temperature, was not taken into consideration, and there was room for improvement in the method of estimating oil temperature, which is performed continuously while the vehicle is running.

One object of the present invention is to provide a damping force control device and a damping force control method that enable more accurate estimation of the oil temperature inside the damper. Other objects of the present invention will become apparent to those skilled in the art by referring to the following exemplary aspects and best modes, as well as the accompanying drawings.

Below, we will provide examples of embodiments according to the present invention to facilitate an understanding of the overview of the present invention.

In an aspect according to the present invention, a damping force control device that controls the damping force of a damper provided in a vehicle includes an operation value calculation unit that calculates the damper operation amount, damper operation time, damper operation speed, and input frequency to the unsprung mass of the vehicle; an operation frequency calculation unit that calculates the damper operation frequency from the input frequency; an oil temperature estimation unit that estimates the damper oil temperature using at least the operation amount, the operation time, the operation speed, and the operation frequency; and a control value calculation unit that adjusts the damping force in accordance with at least the oil temperature.

The first aspect provides a damping force control device that can more accurately estimate the oil temperature inside the damper.

Those skilled in the art will readily understand that the exemplified embodiments of the present invention can be further modified without departing from the spirit of the present invention.

1 is a diagram schematically illustrating an example of the configuration of a vehicle to which a damping force control device and a damping force control method according to a first embodiment of the present invention are applied; 1 is a side view showing a configuration of a suspension device according to a first embodiment of the present invention. 1 is a cross-sectional view showing a configuration of a hydraulic shock absorber according to a first embodiment of the present invention. 1 is a cross-sectional view showing a configuration of a solenoid valve according to a first embodiment of the present invention. 1 is a block diagram showing an example of a functional configuration of a damping force control device according to a first embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a map showing the correlation between oil temperature and a damping force adjustment coefficient. FIG. 10 is a diagram showing an example of a map for searching a target current from a damper speed and a target damping force. 4 is a flowchart showing the operation of the damping force control device according to the first embodiment of the present invention. FIG. 10 is a block diagram showing an example of the functional configuration of a damping force control device according to a second embodiment of the present invention. 10 is a flowchart showing the operation of a damping force control device according to a second embodiment of the present invention. 10 is a graph showing the relationship between the temperature of the electromagnetic coil and time for each value of current flowing through the electromagnetic coil.

The best mode described below is used to facilitate understanding of the present invention. Therefore, those skilled in the art should note that the present invention is not unduly limited by the embodiment described below.

[Embodiment 1]
Hereinafter, a first embodiment of the present invention (hereinafter referred to as the first embodiment) will be described in detail.

Figure 1 is a diagram showing a schematic example of the configuration of a vehicle 1 to which the damping force control device and damping force control method of this embodiment 1 are applied.

(Vehicle configuration)
1, a total of four wheels 3, 4, for example, left and right front wheels 3 and left and right rear wheels 4 (only one shown), are provided on the underside of a vehicle body that constitutes the body of a vehicle 1. Front-wheel suspension devices 5, 5 (hereinafter referred to as front wheel suspensions 5) are provided between the left and right front wheels 3 and the vehicle body, respectively. The front wheel suspensions 5 include suspension springs 6 (hereinafter referred to as springs 6) and adjustable damping shock absorbers (dampers 7) provided in parallel with the springs 6.

Rear-wheel suspension devices 8, 8 (hereinafter referred to as rear wheel suspensions 8) are installed between the left and right rear wheels 4 and the vehicle body. The rear wheel suspensions 8 include suspension springs 9 (hereinafter referred to as springs 9) and adjustable damping shock absorbers (dampers 10) installed in parallel with the springs 9. The dampers 7, 10 are configured, for example, as semi-active dampers, which are hydraulic cylinder devices (variable damping shock absorbers) that allow for adjustable damping force. In other words, the vehicle 1 is equipped with a semi-active suspension system that uses variable damping shock absorbers.

Here, dampers 7 and 10 are variable damping force generating devices (variable damping shock absorbers) installed between the body and wheels 3 and 4 of vehicle 1. The damping force characteristics (damping force characteristics) of dampers 7 and 10 are variably controlled by an ECU (typically, suspension ECU 21) serving as a damping force control device. To this end, dampers 7 and 10 are equipped with actuators (215 in Figure 5, described below) consisting of a damping force adjustment valve and a solenoid, etc., to continuously (or in multiple stages) adjust the damping force characteristics from hard to soft. The damping force characteristics of dampers 7 and 10 are variably adjusted in response to a control command value (current) supplied from the suspension ECU 21 to actuator 215 (Figure 5).

The damping force adjustment valve can employ conventional structures, such as a pressure control system that controls the pilot pressure of the damping force generating valve or a flow control system that controls the passage area. Furthermore, dampers 7 and 10 may be pneumatic dampers, electromagnetic dampers, electrorheological fluid dampers, or magnetic fluid dampers, as long as they can adjust the damping force continuously (or in multiple stages). Dampers 7 and 10 may also be air dampers (air suspension) using air springs, hydraulic dampers (height adjustment devices) that connect front, rear, left, and right hydraulic cylinders with piping, or stabilizers that apply force to the movement of the left and right wheels. Furthermore, dampers 7 and 10 may be fully active dampers composed of hydraulic actuators, electric actuators, or pneumatic actuators that can generate thrust. In other words, vehicle 1 may be equipped with a fully active suspension system using fully active dampers.

Next, various sensors _S11 , _S12 , _S13 , _S14 , _S15 , and _S16 that detect the state of the vehicle 1 will be described.

As shown in Fig. 1, the vehicle 1 is provided with a vehicle speed sensor _S11 , a wheel speed sensor _S12 , a longitudinal acceleration sensor _S13 , a lateral acceleration sensor _S14 , a steering angle sensor _S15 , and a displacement sensor _S16 . These sensors _S11 , _S12 , _S13 , _S14 , _S15 , and _S16 are sensors mounted on the vehicle 1 as examples of behavior sensors S shown in Fig. 5. More specifically, these sensors are mainly used to control braking, driving, and steering of the vehicle 1.

The vehicle speed sensor _S11 is provided, for example, on an output shaft (not shown) of a transmission mounted on the vehicle 1. The vehicle speed sensor _S11 detects the vehicle body speed, which is the speed of the vehicle 1 (vehicle body). The detection information of the vehicle speed sensor _S11 (a signal corresponding to the vehicle body speed) is output to a vehicle control ECU (vehicle control ECUs other than the suspension ECU 21 (such as an accelerator ECU, brake ECU, steering ECU, etc.)) mounted on the vehicle 1 (vehicle body) via, for example, a CAN (Control Area Network), which is an in-vehicle LAN communication. Note that the vehicle control ECU is not shown in the figure.

The wheel speed sensor _S12 is provided, for example, on a wheel support hub unit (not shown) that supports the wheels 3, 4. The wheel speed sensor _S12 is provided corresponding to each of the wheels 3, 4. The wheel speed sensor _S12 detects the rotational speed of the wheels 3, 4. Information (wheel speed) from the wheel speed sensor _S12 is output via the CAN to the vehicle control ECU (accelerator ECU, brake ECU, steering ECU) and the suspension ECU 21. Note that the vehicle speed sensor _S11 may be omitted, and the vehicle speed may be obtained from the wheel speed of the wheel speed sensor _S12 .

The longitudinal acceleration sensor _S13 and the lateral acceleration sensor _S14 are provided, for example, on the vehicle body on the sprung side of the vehicle 1. The longitudinal acceleration sensor _S13 detects the acceleration in the longitudinal direction of the vehicle 1 (vehicle body). The lateral acceleration sensor _S14 detects the acceleration in the lateral direction (lateral acceleration) of the vehicle 1 (vehicle body). The detection data of the longitudinal acceleration sensor _S13 (signal corresponding to the longitudinal acceleration) and the detection data of the lateral acceleration sensor _S14 (signal corresponding to the lateral acceleration) are output to the vehicle control ECUs (accelerator ECU, brake ECU, steering ECU) and the suspension ECU 21 via the CAN.

The steering angle sensor _S15 is provided, for example, on a steering wheel (not shown) of the vehicle 1. The steering angle sensor _S15 detects the steering angle (rotation angle) or the steering angle of the wheels (front wheels 3) generated by a steering operation by a driver who drives the vehicle 1. Detection data (a signal corresponding to the steering angle) of the steering angle sensor _S15 is output to a vehicle control ECU (steering ECU) via the CAN.

The displacement sensor _S16 is attached to the sprung side, for example, to detect the relative displacement (stroke) of the unsprung side relative to the sprung side, and the tip of an arm extending from the sensor is attached to the unsprung side or a portion that moves up and down together with the unsprung side. The detection data of the displacement sensor _S16 is output to the suspension ECU 21. The displacement sensor _S16 detects the relative displacement of the unsprung side relative to the sprung side by detecting the inclination of the arm relative to the body using a potentiometer or the like. The vehicle height can also be calculated from the detection results of the displacement sensor _S16 . The displacement sensor may be configured to directly measure the expansion and contraction of the shock absorber itself, instead of the above configuration.

These behavior sensors (S ₁₁ to S ₁₅ ) excluding the displacement sensor S ₁₆ are typically not sensors dedicated to the suspensions 5, 8. That is, they are sensors mounted on the vehicle for purposes other than controlling the dampers 7, 10, in other words, sensors mounted on the vehicle to mainly control on-board devices other than the dampers 7, 10. Specifically, they are mounted on the vehicle 1 as sensors mainly for controlling the engine that drives and/or brakes the vehicle 1, the driving motor, vehicle braking/driving devices (accelerator, brake) such as hydraulic brakes and electric brakes, and steering devices such as an electric power steering device that steers the vehicle 1.

(Configuration of suspensions 5 and 8)
FIG. 2 is a side view showing the configuration of the suspensions 5 and 8 in FIG. 1. The suspensions 5 and 8 have the same configuration, as an example. As shown in FIG. 2, the suspensions 5 and 8 include a hydraulic damper 101 (damper 7 and 10 in FIG. 1) and a coil spring 102 (spring 6 and 9 in FIG. 1) arranged outside the hydraulic damper 101. The coil spring 102 is held between spring seats 103 and 104. One end of the suspension 5 is fixed to the vehicle body by a bolt 105, and the other end is attached to the axle of the wheels 3 and 4 via an axle-side mounting portion 106.

The shock received by the vehicle 1 from the road surface is absorbed by the compression of the coil spring 102. The hydraulic damper 101 generates a force (damping force) that attenuates the kinetic energy of the coil spring 102.

3A and 3B are cross-sectional views showing the configuration of the hydraulic damper 101. As indicated by the arrows in the figures, Fig. 3A shows a compression-side stroke in which the piston rod 20 enters the first cylinder 11, and Fig. 3B shows an extension-side stroke in which the piston rod 20 retracts from the first cylinder.
3(a) and 3(b), the hydraulic damper 101 has a triple-tube structure in which a second cylinder 12 is disposed outside a first cylinder 11, and a damper case 13 is disposed outside the second cylinder 12. The first cylinder 11, the second cylinder 12, and the damper case 13 are arranged coaxially.

A piston rod 20 is inserted into the first cylinder 11, and a piston 30 located at the tip of the piston rod 20 slides against the inner wall surface of the first cylinder 11. Hydraulic oil is stored in the internal space of the first cylinder 11, and this internal space is divided by the piston 30 into a piston-side oil chamber A1 and a rod-side oil chamber A2.

A bottom unit 40 is provided at the axle-side ends of the first cylinder 11 and the second cylinder 12, and a rod guide 15 is provided at the vehicle-body-side ends of the first cylinder 11 and the second cylinder 12. The bottom unit 40 and rod guide 15 define both ends of the oil chamber formed inside the first cylinder 11 and the second cylinder 12.

The rod guide 15 has an opening 16 into which the piston rod 20 is inserted.

An annular oil chamber A3 is formed between the outer wall surface of the first cylinder 11 and the inner wall surface of the second cylinder 12. A shared flow path 17 is formed between the rod guide 15 and the vehicle body side end of the first cylinder 11, and the annular oil chamber A3 and the rod side oil chamber A2 are connected via the shared flow path 17.

A reservoir chamber A4 is formed between the outer wall surface of the second cylinder 12 and the inner wall surface of the damper case 13. The reservoir chamber A4 stores hydraulic oil to compensate for the volume of the piston rod 20 moving in and out of the first cylinder 11.

A solenoid valve 50, which is an electromagnetic valve that adjusts the damping force generated by the hydraulic damper 101, is provided on the side of the damper case 13. The solenoid valve 50 is fixed by a valve stopper 551 to a side flow path 57 that penetrates the wall of the second cylinder 12 and the wall of the damper case 13.

Hydraulic oil flows from the annular oil chamber A3 into the solenoid valve 50 through one opening of the side flow passage 57. A valve body 531 having a protrusion 531a is disposed in the other opening of the side flow passage 57. The valve body 531 adjusts the opening area of the damping flow passage 561 that penetrates the wall surface of the side flow passage 57 and the valve stopper 551. Specifically, the protrusion 531a engages with the inner wall surface of the side flow passage 57, and the relative position of the protrusion 531a with respect to the opening of the damping flow passage 561 changes, thereby adjusting the opening area of the damping flow passage 561. In the example shown in Figure 3, multiple damping flow passages 561 are formed, but it is sufficient that at least one damping flow passage 561 is formed.

The hydraulic oil that passes through the damping flow path 561 flows into the cylindrical oil chamber 50b defined by the housing of the solenoid valve 50, and then flows into the reservoir chamber A4 through the outlet 58.

The solenoid valve 50 comprises an electromagnetic coil 511 and a core 521 as a solenoid mechanism. When current is applied to the electromagnetic coil 511, an electromagnetic force is generated that moves the valve element 531 away from the core 521. The coil 511 and core 521 are housed in a control chamber 50a that is separated from the cylindrical oil chamber 50b in which the valve element 531 is located.

Note that a solenoid valve other than a solenoid valve may be used as the solenoid valve that adjusts the damping force of the hydraulic damper 101. For example, a solenoid valve that uses an electromagnetic fluid (magnetic fluid) may be used as the solenoid valve.

The spring 541 is provided between the valve stopper 551 and the valve body 531, and exerts a spring force in the direction of widening the gap between the valve stopper 551 and the valve body 531. By providing the spring 541, it is possible to prevent the valve body 531 from colliding with the valve stopper 551 when it moves toward the valve stopper 551.

A pressure-side flow passage 31 is formed in the piston 30, allowing hydraulic oil to flow from the piston-side oil chamber A1 to the rod-side oil chamber A2. A pressure-side check valve 32 is disposed at the vehicle-side opening of the pressure-side flow passage 31.

The bottom unit 40 is formed with an extension-side flow passage 41 that allows hydraulic oil to flow from the reservoir chamber A4 to the piston-side oil chamber, and an extension-side check valve 42 is located at the vehicle-side opening of the extension-side flow passage 41. The axle-side surface of the bottom unit 40 is formed with an annular protrusion 43 that protrudes toward and abuts against the bottom 14 of the damper case 13. A bottom flow passage 44 is formed in this annular protrusion 43, and hydraulic oil in the reservoir chamber A4 flows through the bottom flow passage 44 toward the extension-side flow passage 41.

(Flow of hydraulic oil during compression stroke)
When the vehicle 1 receives an impact force from the road surface, the piston rod 20 enters the first cylinder 11 ( FIG. 3( a): compression stroke). As a result of this movement, the piston 30 compresses the hydraulic oil in the piston-side oil chamber A1, and the compressed hydraulic oil passes through the compression-side flow path 31, opens the compression-side check valve 32, and flows into the rod-side oil chamber A2.

Meanwhile, as the piston rod 20 enters the first cylinder 11, the volume of the first cylinder 11 decreases, causing the hydraulic oil in the rod-side oil chamber A2 to flow through the shared flow path 17 into the annular oil chamber A3. The hydraulic oil that flows into the annular oil chamber A3 then flows through the side flow path 57 into the solenoid valve 50 and passes through the damping flow path 561. Because the opening area of the damping flow path 561 is narrowed by the protrusion 531a of the valve body 531, a damping force is generated as the hydraulic oil passes through the damping flow path 561.

The hydraulic oil that flows into the cylindrical oil chamber 50b through the damping flow path 561 flows into the reservoir chamber A4 through the outlet 58.

(Flow of hydraulic oil during extension stroke)
During the stroke in which the piston rod 20 retracts from the first cylinder 11 ( FIG. 3( b): extension stroke), the hydraulic oil in the rod-side oil chamber A2 is pushed out by the piston 30 and flows into the annular oil chamber A3 through the shared flow path 17. The hydraulic oil that has flowed into the annular oil chamber A3 passes through the side flow path 57 and the damping flow path 561, similar to the compression stroke, and generates a damping force.

The hydraulic oil that flows into the cylindrical oil chamber 50b through the damping flow path 561 flows into the reservoir chamber A4 through the outlet 58.

As the piston rod 20 moves out of the first cylinder 11, negative pressure is created in the piston-side oil chamber A1. As a result, hydraulic oil in the reservoir chamber A4 flows through the bottom flow path 44 and the extension-side flow path 41, opening the extension-side check valve 42 and flowing into the piston-side oil chamber A1.

Figure 4 is a cross-sectional view showing the configuration of the solenoid valve 50 according to the first embodiment. The solenoid valve 50 is provided on the side of the damper case 13. As shown in Figure 4, the solenoid valve 50 includes a solenoid cylinder 50S, a solenoid mechanism 51, an intake port 52, a valve stopper 53, a valve body 54, a spring 55, and a discharge ring 56.

The solenoid cylinder 50S is a cylindrical member with one axial opening facing the case opening 13H of the damper case 13. In this embodiment, the solenoid cylinder 50S is installed to the side of the damper case 13, facing in a direction intersecting the axial direction.

The solenoid mechanism 51 has a coil 511, a housing 511H, a plunger 512, a magnetic body 513, and a fixed core 514.

Electromagnetic coil 511 is arranged along the axial direction of plunger 512 and is held in housing 511H. A conductor (not shown) is connected to coil 511, and generates a magnetic field when electricity is applied via the conductor. The flow of electricity to coil 511 is controlled by solenoid control units A to D, which will be described later.

The plunger 512 is supported by the housing 511H via a bearing so that it can move axially. A magnetic body 513, such as a magnet, is fixedly attached to the plunger 512. One end of the plunger 512 contacts the valve body 54.

The fixed core 514 is positioned closer to the valve body 54 than the magnetic body 513 in the axial direction of the plunger 512. The fixed core 514 is configured to be excited by receiving the magnetic field generated when the coil 511 is energized.

The suction port 52 is a generally cylindrical member. In this embodiment, the suction port 52 has a one-end opening 5211 and a second-end opening 5212 that has a larger diameter than the first-end opening 5211. The first-end opening 5211 is fitted into the inside of the joint member 12G of the outer cylinder body 121 via a seal member. The second-end opening 5212 faces the solenoid mechanism 51 with the discharge ring 56 sandwiched between them.

The valve stopper 53 is a thick-walled cylindrical member with an annular oil flow path 53r formed inside. It is attached to the inside of the opening 5212 on the other end of the suction port 52.

The valve element 54 is a cylindrical member with a tip 54p that protrudes cylindrically in the axial direction from its center. The valve element 54 is configured so that the tip 54p faces the valve stopper 53 and fits into the annular flow path 53r. The valve element 54 receives force from the plunger 512 on the side opposite the valve stopper 53, causing it to move axially.

The spring 55 is provided between the valve stopper 53 and the valve body 54. It exerts a spring force in the direction of widening the gap between the valve stopper 53 and the valve body 54.

The discharge ring 56 is a cylindrical member with multiple circular openings circumferentially formed on its outer periphery. The discharge ring 56 is positioned around the valve stopper 53, valve body 54, and spring 55, and discharges oil that has passed through the throttle section V (described below) into the cylinder inner chamber 50R.

In this embodiment, the annular flow path 53r of the valve stopper 53 and the tip 54p of the valve body 54 form the oil throttle section V in the solenoid valve 50. That is, in the solenoid valve 50 of this embodiment, the throttle section V narrows the oil flow path cross-section, generating a damping force. Furthermore, the plunger 512 of the solenoid mechanism 51 changes the distance of the valve body 54 from the valve stopper 53, thereby changing the flow path cross-sectional area of the oil and adjusting the damping force.

In addition, electromagnetic fluid may be used as the oil in the suspension. Furthermore, a proportional solenoid may be used for the solenoid mechanism 51. A proportional solenoid is a solenoid in which the protruding position of the plunger 512 changes depending on the magnitude of the current supplied. By using a proportional solenoid, for example, the protruding position of the plunger 512 can be freely adjusted by appropriately changing the duty ratio.

(Configuration of the suspension ECU 21)
Next, the suspension ECU 21 that controls the hydraulic damper 101 will be described.

The suspension ECU 21 is a damping force control device that controls the damping force of the hydraulic damper 101, and as shown in the functional block diagram of Figure 5, includes an operation value calculation unit 211, an operation frequency calculation unit 212, an oil temperature estimation unit 213, and a control value calculation unit 214.

The operation value calculation unit 211 acquires vehicle information from the behavior sensor S and has the function of calculating the operation amount, operation time, operation speed, and input frequency to the unsprung mass of the vehicle 1 of the hydraulic damper 101.

The operation value calculation unit 211 acquires the wheel speed, which is the rotational speed of the wheels 3 and 4 of the vehicle 1, from the wheel speed sensor _S12 , and calculates the operation amount, operation time, operation speed, and input frequency using a function that uses at least this wheel speed as an input. That is, the operation value calculation unit 211 calculates the unsprung resonance frequency of the vehicle 1 from the vibration component contained in the wheel speed signal, which is the rotational speed signal of the wheels 3 and 4, and calculates the load fluctuation from this unsprung resonance frequency. Then, by analyzing this load fluctuation, the operation amount, operation time, operation speed, and input frequency of the hydraulic damper 101 are obtained.

Methods for extracting the resonant frequency, which is the peak frequency, from the vibration signal can be performed using digital signal processing such as the FFT (Fast Fourier Transform) method disclosed in Japanese Patent No. 2836652, the LPC (Linear Predictive Coding) method disclosed in Japanese Patent No. 3152151, or the zero-cross count method disclosed in Japanese Patent Laid-Open No. 2001-91390.

As described above, the wheel speed sensor _S12 is not provided exclusively for calculating the operation value of the hydraulic damper 101, but is a sensor used for controlling the running of the vehicle 1, and is therefore preferable because the operation amount, operation time, operation speed, and input frequency are calculated based on information obtained from this wheel speed sensor.

There are no particular limitations on how the actuation amount, actuation time, actuation speed, and input frequency of the hydraulic damper 101 are calculated, but for example, the actuation amount of the hydraulic damper 101 will be described as a relative displacement value (damper displacement) of the unsprung part with respect to the sprung part connected to the vehicle body, detected by a displacement sensor S16 provided in _{the unsprung part} , the actuation speed of the hydraulic damper 101 will be described as a value obtained by time-differentiating the damper displacement detected by the displacement sensor _S16 , and the actuation time of the hydraulic damper 101 will be described as a value obtained by dividing the damper displacement detected by the actuation speed. Furthermore, the input frequency to the unsprung part of the vehicle 1 is the frequency of a load change acting in the vertical direction on the vehicle 1 or the frequency of a load change acting in the front-rear and left-right directions of the vehicle 1, and may be calculated from a spring vertical acceleration signal detected by a front-rear acceleration sensor _S13 provided in the sprung part, or the amplitude of the wheel speed detected by a wheel speed sensor _S12 .

Methods for extracting the resonant frequency, which is the peak frequency, from the vibration signal can be performed using digital signal processing such as the FFT (Fast Fourier Transform) method disclosed in Japanese Patent No. 2836652, the LPC (Linear Predictive Coding) method disclosed in Japanese Patent No. 3152151, or the zero-cross count method disclosed in Japanese Patent Laid-Open No. 2001-91390.

The actuation amount of the hydraulic damper 101, the actuation time of the hydraulic damper 101, the actuation speed of the hydraulic damper 101, and the input frequency to the unsprung mass of the vehicle 1 calculated by the actuation value calculation unit 211 are supplied as state estimation values to the oil temperature estimation unit 213 and the control value calculation unit 214. In addition, the input frequency calculated by the actuation value calculation unit 211 is supplied to the actuation frequency calculation unit 212.

The operation frequency calculation unit 212 has the function of calculating the operation frequency of the hydraulic damper 101 from the input frequency output from the operation value calculation unit 211 and outputting the calculated frequency to the oil temperature estimation unit 213. The operation frequency calculation unit 212 can output the operation frequency, for example, by performing random vibration analysis on the input frequency. Details will be described later.

The oil temperature estimation unit 213 has the function of estimating the oil temperature of the hydraulic damper 101 using at least the estimated state values (actuation amount, actuation time, actuation speed) of the hydraulic damper 101 output from the actuation value calculation unit 211 and the actuation frequency output from the actuation frequency calculation unit 212. The oil temperature estimation unit 213 uses a "damper oil temperature model" to estimate the oil temperature.

Here, the "damper oil temperature model" is a temperature characteristic map that models the optimal oil temperature by, for example, examining in advance how much the actual oil temperature measurement value for each operation frequency output from the operation frequency calculation unit 212 deviates from the estimated state value (operation amount, operation time, operation speed, input frequency) of the hydraulic damper 101 output from the operation value calculation unit 211, and setting a coefficient for each actual measurement frequency that can eliminate or reduce this deviation. This temperature characteristic map is stored in advance in RAM built into the suspension ECU 21.

The oil temperature estimation unit 213 estimates the oil temperature by searching the temperature characteristics map, and supplies the estimated state values (actuation amount, actuation time, actuation speed) of the hydraulic damper 101 calculated by the actuation value calculation unit 211 to the control value calculation unit 214.

The control value calculation unit 214 has the function of calculating a control value that adjusts the damping force according to at least the oil temperature output from the oil temperature estimation unit 213. The correlation between ideal vehicle state values and current values in multiple situations obtained in advance through tests, etc. is mapped, and the control value calculation unit 214 calls up the corresponding value from the map as needed to perform control.

Figure 8 is a flowchart showing the operation of embodiment 1. Below, the operation of the suspension ECU 21 shown in Figure 5 will be explained in detail with reference to the flowchart in Figure 8.

(Acquisition of vehicle information)
The suspension ECU 21 first acquires vehicle information detected by the behavior sensor S (step S101). Here, the suspension ECU 21 acquires wheel speed, which is the rotational speed of the wheel, from the wheel speed sensor _S12 and supplies the wheel speed to the operation value calculation unit 211.

The suspension ECU 21 may also acquire a displacement signal from the damper displacement sensor _S16 , a longitudinal acceleration signal from the longitudinal acceleration sensor _S13 , a lateral acceleration signal from the lateral acceleration sensor _S14 , and a wheel speed signal from the wheel speed sensor _S12 . These signals can also be acquired by applying known mathematical processing to information acquired along a target route by an imaging device or a GPS (Global Positioning System) mounted on the vehicle 1 for navigation or automatic driving, instead of by using the behavior sensor S.

For example, the lateral acceleration signal used for rolling suppression is calculated by first calculating the target route change rate (X t, Y t) using the following equation (1) based on the vehicle's heading direction recognized from images captured in time series by the imaging unit and the driving route ( ^Xt , Yt), which is the current position information of the vehicle 1 updated every time t by a GPS ^or the like.

Here, ^X is the target path change speed in the longitudinal direction [m/s], ^Y is the target path change speed in the lateral direction [m/s], dt is the sampling time, X is the target path value in the longitudinal direction [m], Y is the target path value in the lateral direction [m], and dt is the sampling time.

Next, the route angle ψ is calculated by calculating the following equation (2), that is, by taking the inverse tangent (tan ⁻¹ ) of (target longitudinal change speed X ^· t [m/s]/target lateral route change speed Y ^· t [m/s]).

Then, the following equation (3) is calculated to convert the target route change speed Y ^· t [m/s] from the absolute coordinate system to the vehicle coordinate system. Here, the target route change speed is the lateral speed of the vehicle, which is a value obtained by first differentiating the lateral displacement component of the future route. Note that the absolute coordinate system is a coordinate system fixed to the ground, whereas the vehicle coordinate system is a Cartesian coordinate system fixed to the road surface.

Here, ut is the target path change speed [m/s] of vehicle 1 in the longitudinal direction, vt is the target path change speed [m/s] of vehicle 1 in the lateral direction, and ψ is the path angle [rad] of vehicle 1.

Next, the lateral acceleration _ayt (m/ ^s2 ) is calculated from the target route by calculating the following equation (4): where ψ ^· is the time derivative (rad/s) of the route angle ψ (rad). In other words, the lateral acceleration _ayt (m/ ^s2 ) is the lateral acceleration of the vehicle 1 obtained by twice differentiating the lateral displacement component of the target route.

In this way, lateral acceleration can be obtained through mathematical processing. In this case, the behavior of vehicle 1 can be obtained without using sensors, which solves problems such as noise superimposition on the sensor and time delays that occur when using a filter on the sensor output to increase accuracy.

(Generation of State Estimates)
The suspension ECU 21 acquires vehicle information from the behavior sensor S or through mathematical processing, and the operation value calculation unit 211 calculates the operation amount, operation time, operation speed, and input frequency to the unsprung mass of the vehicle 1 of the hydraulic damper 101 (step S102).

That is, the operation value calculation unit 211 calculates the operation amount of the hydraulic damper 101 from the relative displacement between the sprung and unsprung parts detected by a displacement sensor _S16 provided in the unsprung part of the vehicle 1, calculates the operation speed by time differentiating the operation amount of the hydraulic damper 201, and calculates the operation time by dividing the operation amount of the hydraulic damper 101 by the operation speed. The operation value calculation unit 211 also calculates an input frequency based on a spring vertical acceleration signal detected by a longitudinal acceleration sensor _S13 provided in the sprung part. Note that the operation amount, operation time, operation speed, and input frequency of the hydraulic damper 101 may be calculated by frequency analysis from the wheel speed, which is the rotational speed of the wheel, detected by the wheel speed sensor S12.

The actuation amount of the hydraulic damper 101, the actuation time of the hydraulic damper 101, the actuation speed of the hydraulic damper 101, and the input frequency to the unsprung mass of the vehicle 1 calculated by the actuation value calculation unit 211 are supplied as state estimation values to the oil temperature estimation unit 213 and the control value calculation unit 214. In addition, the input frequency calculated by the actuation value calculation unit 211 is supplied to the actuation frequency calculation unit 212.

(Calculation of operation frequency)
The operation frequency calculation unit 212 calculates the operation frequency of the hydraulic damper 101 from the input frequency output from the operation value calculation unit 211 and outputs the calculated frequency to the oil temperature estimation unit 213 (step S103). For example, the operation frequency calculation unit 212 converts the waveform of the input frequency into a power spectral density (PSD) indicating the occurrence frequency of each frequency using a statistical method, treats it as a spectrum value of the load (acceleration), and can output the occurrence probability (operation frequency) of the load using random vibration analysis.

(oil temperature estimation)
The oil temperature estimation unit 213 estimates the oil temperature of the hydraulic damper 101 using at least the state estimation values (operation amount, operation time, operation speed) of the hydraulic damper 101 output from the operation value calculation unit 211 and the operation frequency output from the operation frequency calculation unit 212 (step S104).

The oil temperature estimation unit 213 uses a damper oil temperature model to estimate the oil temperature. Here, the damper oil temperature model is a model that, for example, determines in advance how much the actual measured values for each operation frequency output from the operation frequency calculation unit 212 deviate from the estimated state values (operation amount, operation time, operation speed) of the hydraulic damper 101 output from the operation value calculation unit 211, and sets a coefficient for each actual measurement frequency that can eliminate or reduce this deviation, thereby modeling the optimal oil temperature. In other words, the damper oil temperature model reflects the operation frequency of the hydraulic damper 101 for oil temperature estimation.

The oil temperature estimation unit 213 supplies the oil temperature estimated according to the damper oil temperature model to the control value calculation unit 214, along with the estimated state values (actuation amount, actuation time, actuation speed) of the hydraulic damper 101 calculated by the actuation value calculation unit 211.

(Control value calculation)
There is a correlation between oil temperature and the control value (current), and as the oil temperature increases, the damping force decreases. However, if the damping force is increased to compensate for the decreased damping force, the oil temperature will rise further, and there is a concern that the damping force will decrease again. Therefore, in this embodiment, as shown in Figure 6, for example, as the oil temperature increases (T1 > T2), the damping force adjustment coefficient is set to a smaller value (C1 > C2) to control the damping force in a direction that decreases it, thereby suppressing the increase in oil temperature and allowing the oil temperature to decrease quickly. This relationship is stored in advance in the RAM built into the suspension ECU 21 as a temperature characteristic map.

The RAM also pre-stores, for example, an Ft-It map used to search for a target current from one of the estimated state values of the hydraulic damper 101, such as the operating speed (damper speed Vp [m/s]), and the target damping force Ft (N) reflecting the control value calculated by the control value calculation unit 214, as shown in FIG. 7. The target damping force in this Ft-It map reflects the damping force adjustment coefficient C of the temperature characteristics map shown in FIG. 6. Note that the estimated state value is not limited to the damper speed, and may instead be, for example, the operating amount (required load) of the hydraulic damper 101.

In Figure 7, the Ft-It map is a map that searches for the target current It from the target damping force Ft and the damper speed Vp. When the damper speed Vp is constant, the target current It increases as the target damping force Ft increases, and when the target damping force Ft is constant, the target current It decreases as the damper speed Vp increases. This is adjusted appropriately by multiplying the damper speed or required load by a gain in PID (Proportional Integral Differential) control. The gain in PID control can be determined by an appropriate method, such as testing.

The control value calculation unit 214 obtains the target current It as a control command value by searching the Ft-It map shown in FIG. 7, and supplies it to the actuator 217 (step S105). In the Ft-It map shown in FIG. 7, when the target damping force Ft is Ft1 and the damper speed Vp is Vpt, the target current is It5. However, when the damper speed Vp increases to Vpt1, the target current decreases to It4, and when the damper speed Vp decreases to Vpt2, the target current increases to It6.

The actuator 215 controls the damping force of the hydraulic damper 101 by passing current through the electromagnetic coil 511 (Figure 3) in accordance with the control command value supplied by the control value calculation unit 214 (step S106). In other words, the damping force can be controlled in accordance with the oil temperature estimated according to the operation frequency of the hydraulic damper 101, in addition to the operation amount, operation time, and operation speed of the hydraulic damper 101. The gain in PID control can be determined by an appropriate method, such as testing.

(Effects of the First Embodiment)
As explained above, according to the first embodiment, by using the operation frequency of the hydraulic damper 101 to estimate the oil temperature, it is possible to more accurately estimate the oil temperature inside the hydraulic damper 101, and as a result, optimal damping force control is possible. Note that while oil temperature is one cause of changes in the viscosity of the hydraulic oil, in the hydraulic damper 101, in the low-frequency range where changes in expansion and contraction are slow (particularly in the sprung resonance frequency of 1 to 2 Hz), a decrease in viscosity due to an increase in oil temperature leads to a longer stroke than necessary. Therefore, by performing the above-mentioned damping force control taking this timing into consideration, it is possible to reduce the calculation load and expect greater effects.

In addition, by estimating the state estimate value output by the actuation value calculation unit 211 through calculation rather than using a sensor, sensors that are subject to superimposed noise are no longer required, and the use of filters that are required to improve the accuracy of sensor output is no longer necessary, making it possible to achieve smooth anti-roll control without control delays.

Dampers, which generate damping force using the viscosity of oil, are temperature dependent, and the damper oil temperature is constantly changing depending on the environment and driving conditions, making it difficult to maintain ideal behavior. In other words, as the damper oil temperature increases, the damping force decreases, and as the oil temperature decreases, the damping force increases. If the damping force is low, the required amount of damping will be insufficient, causing significant spring height at times of high input and resulting in rebound shock noise. On the other hand, if the damping force is high, ride comfort will deteriorate on rough roads and damper slapping noise will be more likely to occur.

In contrast, in this first embodiment, information related to damper operation (damper operation amount, operation time, operation speed, input frequency) is obtained through calculation and used as a state estimate. In addition, the input frequency is added as a variable to use an oil temperature damper model to obtain the optimal oil temperature. Furthermore, a gain for achieving the optimal damping force is calculated from a temperature characteristics map that shows the correlation between oil temperature and damping force. This provides benefits such as preventing rebound shock noise and reducing the bouncy feeling on the sprung mass at high temperatures, and improving ride comfort on rough roads and reducing or preventing damper slapping noise at low temperatures.

Note that the term "gain" is used here to refer to the function of converting one value into another. This "conversion" may involve different units before and after the conversion, or may involve adding or removing units.

[Embodiment 2]
Next, a damping force control device will be described below as embodiment 2, which sets the control target to "viscous damping force at an oil temperature of 20°C" and reproduces the viscous damping force at the initial value (oil temperature of 20°C) at each temperature range of outside air temperature or coil temperature.

Fig. 9 is a block diagram showing the functional configuration of a suspension ECU 21 serving as a damping force control device of embodiment 2. The difference between embodiment 2 shown in Fig. 9 and embodiment 1 shown in Fig. 5 is that, in addition to the behavior sensor S, a temperature sensor _S20 is added that measures the outside air temperature or the temperature (coil temperature) of the electromagnetic coil 511 (Fig. 3) that controls the damping force in accordance with the current, or that an outside air temperature estimating unit (coil temperature estimating unit) 216 is added to the suspension ECU 21. In other words, in embodiment 2, if either the outside air temperature sensor (coil temperature sensor) _S20 or the outside air temperature (coil temperature) estimating unit 216 is present, the other is not necessary.

Another operational difference is that the control value calculation unit 214 has a built-in map containing the control amounts required to reproduce an oil temperature of 20°C for each temperature range of the outside air temperature (coil temperature) detected by the outside air temperature (coil temperature) sensor S20 or the outside air temperature (coil temperature) estimated by the outside air temperature (coil temperature) estimation unit 216, and calculates the control value by searching this map.

The outside air temperature (coil temperature) estimation unit 216 has a function of estimating the oil temperature using the outside air temperature or the coil temperature. For example, the outside air temperature (coil temperature) estimation unit 216 can extract the unsprung resonance frequency from the rotation speed of the wheels 3, 4 detected by the wheel speed sensor _S12 , and calculate the amount of change in the outside air temperature based on the amount of change in the unsprung resonance frequency.

Figure 10 shows a flowchart of the operation of embodiment 2. The flowchart in Figure 10 differs from embodiment 1 shown in Figure 8 in that step S200 of "outside air temperature (coil temperature) estimation processing" is added between step S104 of "oil temperature estimation processing" and step S105 of "target current search processing." The rest is the same as embodiment 1.

(Outside temperature estimation)
When the vehicle 1 travels on a road, the tires vibrate due to forces acting in the vertical and longitudinal directions caused by the unevenness of the road surface. It is known that this vibration appears near the resonant frequency of the vibration component of the wheel speed extracted from the wheel speed signal.

To estimate the outside air temperature (coil temperature), the power spectrum density (PSD), which is the result of frequency analysis of the wheel rotation speed signal, which is the wheel speed obtained from the wheel speed sensor _S12 , is used to obtain the resonance frequency from this PSD, and the amount of change in the outside air temperature is estimated from the temperature characteristic diagram of the resonance frequency (step S200).

A method for extracting the resonant frequency using the PSD described above and estimating the amount of change in outside air temperature from a temperature characteristic diagram of the resonant frequency is disclosed in Figures 3-5, paragraphs [0053] to [0057] of Patent 3,952,927.

(Electromagnetic coil temperature estimation)
The temperature of the electromagnetic coil 511 may be estimated from the value of the current flowing through the electromagnetic coil 511. For example, as shown in Fig. 11 , a graph is prepared in advance showing the relationship between the temperature of the electromagnetic coil 511 and time for each value of the current flowing through the electromagnetic coil 511. In the graph of Fig. 11 , the vertical axis represents the integrated temperature value (in other words, the temperature of the electromagnetic coil) calculated by integrating the heat generation amount of the electromagnetic coil 511, and the vertical axis represents time.

After time T has elapsed since current was passed through the electromagnetic coil 511, the temperature of the electromagnetic coil 511 changes depending on the value of the current flowing through the electromagnetic coil 511. The ambient temperature (coil temperature) estimation unit 216 estimates the coil temperature by linearly approximating the heat generation amount of the electromagnetic coil 511 relative to the value of the current flowing through the electromagnetic coil 511. Here, "linearly approximating" means that, within a certain current value range, where the current value is x and the heat generation amount is y, the heat generation amount is calculated using the relationship y = ax + b. Here, the temperature of the electromagnetic coil 511 can be estimated by approximating the heat generation amount corresponding to the current value detected by the current sensor using the slope a for each of multiple current ranges.

Note that the processes (steps S101 and S102) in which the operation value calculation unit 211 generates estimated state values (operation amount, operation time, operation speed, input frequency) of the hydraulic damper 101 based on the output of the behavior sensor S or an estimation of the behavior of the vehicle 1, the process (step S103) in which the operation frequency calculation unit 212 calculates the operation frequency of the hydraulic damper 101 by analyzing the input frequency from the estimated state values, and the process (step S104) in which the oil temperature estimation unit 213 estimates the oil temperature using a damper oil temperature model that reflects the operation frequency of the hydraulic damper 101 are the same as in the first embodiment, and therefore will not be described here to avoid duplication.

(Calculation of control value)
The outside air temperature (coil temperature) estimated by outside air temperature (coil temperature) estimation unit 216 is supplied to control value calculation unit 214. Control value calculation unit 214 searches a map having control variables necessary to reproduce an oil temperature of 20°C in each temperature range of the outside air temperature (coil temperature) detected by outside air temperature (coil temperature) sensor S20 or the outside air temperature (coil temperature) estimated by outside air temperature (coil temperature) estimation unit 216, thereby calculating a control command value (current) whose control target is the viscous damping force at an oil temperature of 20°C and supplying the control command value to actuator 215 (step S105).

The actuator 215 controls the damping force of the hydraulic damper 101 by passing current through the electromagnetic coil 511 (Figure 3) in accordance with the control command value supplied by the control value calculation unit 214 (step S106). That is, in addition to the operating amount, operating time, and operating speed of the hydraulic damper 101, the damping force can be controlled in accordance with the oil temperature estimated according to the operating frequency of the hydraulic damper 101 (step S106).

(Effects of the Second Embodiment)
According to the second embodiment, similar to the first embodiment, by using the operation frequency of the hydraulic damper 101 to estimate the oil temperature, it is possible to more accurately estimate the oil temperature inside the hydraulic damper 101, and as a result, it is possible to optimally control the damping force of the hydraulic damper 101. In particular, in order to achieve the control target of "viscous damping force at an oil temperature of ₂₀ °C", by reproducing the viscous damping force at an oil temperature of 20°C in each temperature range of the outside air temperature or electromagnetic coil temperature detected or estimated by the outside air temperature or coil temperature sensor S20, it is possible to achieve a high effect in correcting for disturbances.

Furthermore, by controlling the damper damping force as described above with the goal of always ensuring a damping force equivalent to 20°C, it is possible to achieve smooth anti-roll control without control delay, as in embodiment 1, and also to achieve other effects, such as preventing rebound shock noise and reducing the bouncy feeling on the sprung mass at high temperatures, improving ride comfort on rough roads at low temperatures, and reducing or preventing damper knock noise.

(Damping force control method)
The damping force control method of the present invention is, for example, a damping force control method for controlling the damping forces of the dampers 7, 10 provided in the vehicle 1 of Fig. 1. For example, as shown in the flowchart of Fig. 8, the method includes operation value calculation steps (S101, S102) for calculating the operation amount, operation time, operation speed, and input frequency of the dampers 7, 10 to the unsprung mass of the vehicle 1, an operation frequency calculation step (S103) for calculating the operation frequency of the dampers 7, 10 from the input frequency, an oil temperature estimation step (S104) for estimating the oil temperature of the damper from the operation amount, operation time, operation speed, and operation frequency, and a control value calculation step (S105) for calculating a control value for adjusting the damping force in accordance with at least the oil temperature.

According to the damping force control method of the present invention, by using the operation frequency of the hydraulic damper 101 to estimate the oil temperature, it is possible to more accurately estimate the oil temperature inside the hydraulic damper 101, resulting in optimal damping force control. Furthermore, by calculating the estimated state values of the hydraulic damper 101 (operation amount, operation time, operation speed, input frequency) through calculations rather than using sensors, the problem of noise superimposed on the sensor is resolved, and the filter required to improve the accuracy of the sensor output is no longer necessary, eliminating control delays and achieving smooth anti-roll control.

The present invention is not limited to the exemplary embodiments described above, and those skilled in the art could easily modify the exemplary embodiments described above to the extent that they fall within the scope of the claims.

1...vehicle, 6, 9...spring, 7, 10...damper, S...behavior sensor, _S12 ...wheel speed sensor, _S13 ...vertical acceleration sensor, _S14 ...lateral acceleration sensor, _S16 ...displacement sensor, _S20 ...outside air temperature (coil temperature) sensor, 21...damping force control device (suspension ECU), 101...hydraulic damper, 211...operation value calculation unit, 212...operation frequency calculation unit, 213...oil temperature estimation unit, 214...control value calculation unit, 215...actuator, 216...outside air temperature (coil temperature) estimation unit, 511...electromagnetic coil.

Claims (5)

A damping force control device that controls the damping force of a damper provided in a vehicle,
an operation value calculation unit that calculates an operation amount of the damper, an operation time of the damper, an operation speed of the damper, and an input frequency to an unsprung part of the vehicle;
an operation frequency calculation unit that calculates an operation frequency of the damper from the input frequency;
an oil temperature estimation unit that estimates an oil temperature of the damper using at least the actuation amount, the actuation time, the actuation speed, and the actuation frequency;
a control value calculation unit that calculates a control value for adjusting the damping force in accordance with at least the oil temperature;
A damping force control device comprising: The actuation value calculation unit
2. The damping force control device according to claim 1, wherein a wheel speed, which is the rotational speed of a wheel of the vehicle, is acquired, and the actuation amount, actuation time, actuation speed, and input frequency are calculated using a function that uses at least the wheel speed as an input. The vehicle further includes at least one of an outside air temperature sensor that acquires an outside air temperature of the vehicle and an outside air temperature estimation unit that estimates the outside air temperature of the vehicle,
The oil temperature estimation unit
3. The damping force control device according to claim 1, wherein the oil temperature is estimated using the outside air temperature. The damping force control device includes:
an electromagnetic coil that controls the damping force in response to a current;
The electromagnetic coil temperature sensor further includes at least one of a coil temperature sensor that acquires the coil temperature and a coil temperature estimation unit that estimates the coil temperature,
The oil temperature estimation unit
3. The damping force control device according to claim 1, wherein the oil temperature is estimated further using the coil temperature. A damping force control method for controlling a damping force of a damper provided in a vehicle, comprising:
an operation value calculation step of calculating an operation amount of the damper, an operation time of the damper, an operation speed of the damper, and an input frequency to an unsprung part of the vehicle;
an operation frequency calculation step of calculating an operation frequency of the damper from the input frequency;
an oil temperature estimating step of estimating an oil temperature of the damper from the actuation amount, the actuation time, the actuation speed, and the actuation frequency;
a control value calculation step of calculating a control value for adjusting the damping force in accordance with at least the oil temperature;
A damping force control method comprising: