JP7854464B2 - Vehicle control system - Google Patents

Description

This disclosure relates to a vehicle control system.

Patent Document 1 describes a technique for controlling the drive source based on a creep drive force set to prevent the vehicle from rolling backward when stopped on an incline, and for reducing the drive force when the braking force generated by the driver's brake operation is greater than the creep drive force.

Furthermore, Patent Document 2 describes a technique in which, when a brake operation is detected while the vehicle is stopped, the amount of torque while the vehicle is stopped is changed according to the amount of road surface inclination acquired by a road surface condition acquisition means (G sensor).

International Publication No. 2015/019766 Japanese Patent Publication No. 2014-166053

While Patent Document 1 describes reducing the driving force generated by the motor when sufficient braking force is applied to prevent the vehicle from rolling backward, it does not describe the control required when the brakes are released and the driving force generated by the motor is restored. Therefore, the technology described in Patent Document 1 carries the risk of significant rolling backward when the vehicle is stopped on a slope, especially if the brakes are released very quickly.

Furthermore, the technology described in Patent Document 2 retains creep torque corresponding to the incline (angle of incline) when a slope is detected, which may suppress vehicle rollback even when the brakes are released. However, it has the drawback of increasing the vehicle's energy consumption. Also, sensors that detect road surface gradient (e.g., G-sensors) have variations in their detection values, and if the road surface gradient detected by the sensor is smaller than the actual road surface gradient, there is a risk of vehicle rollback when the brakes are released.

This disclosure was made in consideration of the above facts, and aims to provide a vehicle control device that can suppress vehicle rollback when returning from creep-cut control.

The vehicle control device according to the first embodiment includes a control unit that performs creep-cut control to reduce the output torque of the motor, which is the drive source of the vehicle, when the vehicle is stopped and the brakes are applied, and when it is determined that the brakes have been turned off based on the rate of change of brake fluid pressure while the output torque is being reduced, it performs recovery control to output a torque from the motor that is equal to or greater than the guaranteed gradient equivalent torque set to prevent the vehicle from sliding down on an uphill road with a predetermined road surface gradient, and the control unit determines that the brakes have been turned off when the rate of change of brake fluid pressure is equal to or greater than a first predetermined value and the absolute value of the brake fluid pressure is less than a second predetermined value .

In the first embodiment, when the vehicle is stopped and the brakes are applied, creep-cut control is performed to reduce the output torque of the motor, which is the driving source of the vehicle. This improves the vehicle's energy efficiency. Furthermore, in the first embodiment, the brakes are deactivated based on the rate of change in brake fluid pressure while the motor's output torque is being reduced. By using the rate of change in brake fluid pressure in this way, it is possible to quickly determine that the brakes have been deactivated, even if the brakes are deactivated rapidly.

In the first embodiment, when it is determined that the brakes have been released, a recovery control is performed in which the motor outputs a torque equal to or greater than the guaranteed gradient equivalent torque set to prevent the vehicle from sliding backward on an uphill road with a predetermined road surface gradient. This makes it possible to suppress the vehicle from sliding backward when recovering from creep-cut control with simple control. In particular, when the road surface on which the vehicle is stopped is less than a predetermined road surface gradient, the vehicle can be reliably suppressed when recovering from creep-cut control without being affected by variations in the detected values of the gradient detection sensor.
Furthermore, in the first embodiment, it is determined that the brakes have been released when the rate of change of the brake fluid pressure is equal to or greater than a first predetermined value and the absolute value of the brake fluid pressure is less than a second predetermined value. This makes it possible to appropriately determine that the brakes have been released not only when they are released quickly, but also when they are released slowly.

In the second embodiment, in the first embodiment, if the control unit determines that the vehicle has started to slide backward after determining that the brake has been turned off, it increases the output torque at a higher rate than when it has not determined that the vehicle has started to slide backward.

In the second embodiment, if it is determined that the vehicle has started to slide backward after it has been determined that the brakes have been released, the motor's output torque is increased at a higher rate than when it is not determined that the vehicle has started to slide backward. This increases the rate at which the motor's output torque increases when the vehicle starts to slide backward, thereby reducing the amount of vehicle slide.

In the third embodiment, as in the second embodiment, the control unit determines the rise rate such that the rise rate increases as the road surface gradient detected by the gradient detection sensor increases.

In the third embodiment, the rate at which the output torque increases is increased as the road surface gradient detected by the gradient detection sensor increases. This reduces the amount of vehicle sliding down when the road surface gradient is relatively large.

A fourth aspect is that, in the first aspect, the control unit does not perform the creep-cut control when the vehicle's shift position is first shifted to the drive range after the vehicle's ignition is turned on.

According to the fourth embodiment, when the vehicle is stopped on a slope, there is no risk of the vehicle rolling backward when the drive range is first shifted during restart.

This disclosure has the effect of suppressing the occurrence of vehicle rollback when returning from creep-cut control.

This is a block diagram showing the schematic configuration of a vehicle control device according to an embodiment. This flowchart shows the creep-cut/recovery control process performed by the HEV ECU. This is a timing chart showing the rate of increase in the output torque of the MG (motor generator). This diagram shows an example of the relationship between the road surface gradient and the rate of increase in MG output torque when a vehicle slides backward.

The following describes in detail an example of an embodiment of this disclosure with reference to the drawings. The vehicle equipped with the vehicle control device 10 shown in Figure 1 is a Hybrid Electric Vehicle (HEV) equipped with an engine (not shown), a motor-generator (hereinafter referred to as "MG") 30 that operates as a motor to drive the vehicle or as a generator, and a high-voltage battery (not shown). The vehicle control device 10 includes a brake ECU 18, a power control unit (hereinafter referred to as "PCU") 26 equipped with an HEV ECU (Electronic Control Unit) 20 and an MG ECU 28, and the MG 30. Note that the MG 30 is an example of a motor in this disclosure.

The PCU26 is connected to the MG30 and the aforementioned high-voltage battery. The PCU26 includes an inverter capable of converting AC power to DC power and DC power to AC power. When the MG30 operates as a motor, power is supplied to the MG30 from the high-voltage battery via the PCU26. When the MG30 operates as a generator, the power generated by the MG30 is supplied to the high-voltage battery via the PCU26, thereby charging the high-voltage battery.

The MG ECU 28 includes a CPU (Central Processing Unit), memory such as ROM (Read Only Memory) and RAM (Random Access Memory), non-volatile storage such as an HDD (Hard Disk Drive) and SSD (Solid State Drive), and an I/F (Interface) unit. When the MG 30 operates as a motor, the MG ECU 28 receives a torque command value from the HEV ECU 20 and controls the operation of the MG 30 so that the output torque from the MG 30's rotation shaft matches the received torque command value. The MG ECU 28 also receives a detected value of the rotation speed (rotational velocity) of the MG 30's rotation shaft from the rotation detection sensor 32 built into the MG 30 and outputs the received rotation speed value to the HEV ECU 20.

On the other hand, the brake ECU 18 includes a CPU, memory such as ROM and RAM, a non-volatile storage unit such as an HDD and SSD, and an I/F unit. The brake ECU 18 is connected to a G-sensor 12 mounted on the vehicle and a brake system 14 including a hydraulic pressure sensor 16. The value detected by the G-sensor 12 is used to calculate the detected value of the road surface gradient θ. The G-sensor 12 is an example of a gradient detection sensor in this disclosure.

The hydraulic pressure sensor 16 detects the hydraulic pressure P of the brake fluid in the master cylinder of the brake system 14. The brake ECU 18 performs hill-hold control to maintain the brakes engaged when the brakes are released while the vehicle is stopped on an uphill road with a road gradient θ greater than or equal to a second threshold θth2. The second threshold θth2 is related to the first threshold θth1 (described later) in the relationship θth2 > θth1, and is, for example, a road gradient of approximately 7%. The brake ECU 18 is connected to the HEV ECU 20 and outputs the detected values of the G sensor 12 and the hydraulic pressure sensor 16 to the HEV ECU 20.

The HEV ECU 20 includes a CPU, memory such as ROM and RAM, a non-volatile storage unit such as an HDD or SSD, and an I/F unit. A shift position sensor 24 is connected to the HEV ECU 20 to detect the vehicle's shift position. The HEV ECU 20's memory unit stores a control program. The HEV ECU 20 functions as a control unit 22 when the control program is read from the memory unit and loaded into memory, and then executed by the CPU. The control unit 22 then performs creep-cut/recovery control processing (described later) while the vehicle's ignition is on.

The control unit 22 performs creep-cut control to reduce the output torque of the MG 30 when the vehicle is stopped and the brakes are applied. Furthermore, if the control unit 22 determines that the brakes have been released based on the rate of change of the brake fluid pressure P while the output torque of the MG 30 is being reduced, it performs recovery control to output a guaranteed gradient equivalent torque from the MG 30, which is set to prevent the vehicle from sliding backward on an uphill road with a predetermined road surface gradient θ. Note that the control unit 22 is an example of a control unit in this disclosure.

Next, the creep-cut/recovery control process performed by the control unit 22 while the vehicle ignition is on will be described with reference to Figure 2.

In step 100, the control unit 22 determines whether the vehicle's current shift position is in the D range based on the shift position signal input from the shift position sensor 24. Note that the D range is an example of a drive range in this disclosure. Furthermore, if the vehicle's current shift position is in the D range, the control unit 22 determines whether the shift from a range other than D to the D range is the first shift to the D range after the ignition is turned on.

If the determination in step 100 is affirmative, the process proceeds to step 122. A torque command value is output to the MG ECU 28 so that the output torque from the MG 30 matches the normal creep torque, and the creep cut/recovery control process is terminated. The normal creep torque is, for example, the torque at which the vehicle's creep speed reaches a predetermined value (approximately 5-10 km/h) when the vehicle is on a flat road. Thus, if the determination in step 100 is affirmative, the creep cut control described later is not performed, preventing the vehicle from sliding backward in a parking lot if the parking lot is on an uphill slope.

Furthermore, if the determination in step 100 is rejected, the process proceeds to step 102. In step 102, the control unit 22 determines whether the conditions for implementing creep-cut control have been met. Examples of conditions for implementing creep-cut control include, as shown by arrow A in Figure 3, the case where the rotation speed of the MG 30 detected by the rotation detection sensor 32 becomes 0, the brake is turned on and the brake flag switches to a value indicating brake on, and the detected value of the road surface gradient θ is less than the first threshold θth1. The first threshold θth1 is the road surface gradient amount corresponding to the maximum value of the detection variation of the road surface gradient amount θ by the G sensor 12, and is, for example, a road surface gradient amount of approximately 3.5%.

If the determination in step 102 is affirmative, the process proceeds to step 108. In step 108, the control unit 22 switches the creep cut control flag (see Figure 3) to a value indicating that creep cut control is in progress, and performs creep cut control to reduce the output torque of the MG30. In creep cut control, the output torque of the MG30 may be set to 0, or it may be set to a value smaller than the output torque before creep cut control was started and greater than 0, for example, a value corresponding to the detected road surface gradient θ. Performing this creep cut control can improve the vehicle's energy efficiency.

If creep-cut control is performed in step 108, the system proceeds to step 110. In step 110, the control unit 22 determines whether the rate of change of the brake fluid pressure P has become greater than or equal to a first predetermined value. If the determination in step 110 is negative, the system proceeds to step 112. In step 112, the control unit 22 determines whether the absolute value of the brake fluid pressure P has become less than a second predetermined value. If the determination in step 112 is also negative, the system returns to step 110 and repeats steps 110 and 112 until the determination in step 110 or step 112 is positive.

For example, if the brake is released quickly, the determination in step 110 is affirmed when the rate of change of the brake fluid pressure P exceeds the first predetermined value. In this case, it is possible to determine early that the brake has been released. Furthermore, if the brake is released slowly, the determination in step 112 is affirmed when the absolute value of the brake fluid pressure P falls below the second predetermined value. This allows for appropriate determination of brake release even when the brake is released slowly.

If the determination in step 110 or step 112 is affirmative, the brake flag is switched to a value indicating brake off, and the creep cut control flag is switched to a value indicating that creep cut control is not in operation (see also arrow B in Figure 3), before proceeding to step 114. Then, the recovery control is performed from step 114 onward.

In other words, in step 114, the control unit 22 outputs a torque command value to the MG ECU 28 so that the MG 30 outputs a guaranteed gradient equivalent torque, which is set to prevent the vehicle from sliding down on an uphill road with a road surface gradient of the first threshold θth1. The rate at which the output torque increases at this time is the reference torque rate (see Figure 3).

This allows for the suppression of vehicle rollback during recovery from creep-cut control with simple control. In particular, in this embodiment, the first threshold θth1 is set to the maximum value of the road surface gradient θ detected by the G sensor 12, and creep-cut control is performed when the detected value of the road surface gradient θ is less than the first threshold θth1. This reduces the influence of variations in the G sensor 12's detection value and suppresses the frequency of vehicle rollback during recovery from creep-cut control.

In step 116, the control unit 22 determines whether the rotation detection sensor 32 has detected reverse rotation of the MG30's rotation axis, i.e., whether the vehicle has slipped backward. If the determination in step 116 is negative, the process proceeds to step 120. In step 120, the control unit 22 determines whether to terminate the return control by determining whether the termination conditions for the return control have been met, such as the vehicle moving forward. If the determination in step 120 is negative, the process returns to step 116, and steps 116 and 120 are repeated.

Furthermore, if vehicle slippage occurs, the determination in step 116 is affirmed, and the slippage determination flag is switched to a value indicating that slippage is occurring (see also arrow C in Figure 3), before proceeding to step 118. In step 118, the control unit 22 outputs a torque command value to the MG ECU 28 such that the output torque from the MG 30 is greater than the reference torque rate and increases at an increase rate (slippage determination rate: see Figure 3) corresponding to the detected road surface gradient θ. In this way, by making the increase rate of the output torque from the MG 30 greater than the reference torque rate, the amount of vehicle slippage can be reduced.

Furthermore, the rate of increase in output torque corresponding to the detected road surface gradient θ should be determined such that the rate of increase in output torque is higher when the detected road surface gradient θ is above a predetermined value than when the detected road surface gradient θ is below a predetermined value.

Specifically, as shown in Figure 4(A), for example, the rate of increase in output torque may be determined so that the rate of increase in output torque increases in steps with increasing road gradient θ. Alternatively, as shown in Figure 4(B), for example, the rate of increase in output torque may be determined so that the rate of increase in output torque increases linearly with increasing road gradient θ. Furthermore, as shown in Figure 4(C), for example, the rate of increase in output torque may be determined so that the rate of increase in output torque increases quadratically with increasing road gradient θ. This can reduce the amount of vehicle sliding when the road gradient θ is relatively large.

After completing step 118, the process proceeds to step 120. If the determination in step 120 is positive, step 122 involves outputting normal creep torque from the MG30, followed by the termination of the creep cut/recovery control process.

Furthermore, in the determination in step 102, if the detected value of the road surface gradient amount θ is greater than or equal to the first threshold θth1, the creep cut/recovery control process is terminated via step 122.

As described above, in this embodiment, the control unit 22 performs creep-cut control to reduce the output torque of the MG 30 when the vehicle is stopped and the brakes are applied. Furthermore, when it is determined that the brakes have been released based on the rate of change in brake fluid pressure while the output torque of the MG 30 is being reduced, it performs recovery control to output a guaranteed gradient equivalent torque from the MG 30, which is set to prevent the vehicle from sliding backward on an uphill road with a predetermined road surface gradient (first threshold θth1). This makes it possible to suppress vehicle sliding backward when recovering from creep-cut control with simple control.

Furthermore, in this embodiment, if the control unit 22 determines that the vehicle has started to slide backward after determining that the brakes have been released, it increases the output torque of the MG 30 at a higher rate than when it has not determined that the vehicle has started to slide backward. This reduces the amount of vehicle sliding backward.

Furthermore, in this embodiment, the control unit 22 determines the upward rate such that the upward rate increases as the road surface gradient detected by the G sensor 12 increases. This reduces the amount of vehicle sliding down when the road surface gradient is relatively large.

Furthermore, in this embodiment, the control unit 22 does not perform creep-cut control when the vehicle's shift position is first shifted to the D range after the vehicle's ignition is turned on. This prevents the vehicle from rolling backward in a parking lot if the parking lot is on an uphill slope.

In the above embodiment, the vehicle equipped with the vehicle control device 10 was described as an HEV (Hybrid Electric Vehicle), but the vehicle equipped with the vehicle control device 10 may also be an EV (Electric Vehicle).

Furthermore, in the above embodiment, a method was described in which the MG30 outputs a torque equivalent to the guaranteed gradient in step 114 of Figure 2. However, this disclosure is not limited to this, and the MG30 may also output a torque exceeding the torque equivalent to the guaranteed gradient.

Furthermore, while the above embodiment describes a method of detecting vehicle slippage by the reverse rotation of the MG30's rotation axis, this disclosure is not limited to this, and vehicle slippage may also be detected by the reverse rotation of the vehicle's wheels. Alternatively, vehicle slippage may be detected using a GNSS (Global Navigation Satellite System) sensor or the like.

The following additional information is disclosed regarding the embodiments described above.

(Note 1)
A vehicle control device including a control unit that performs creep-cut control to reduce the output torque of the motor, which is the drive source of the vehicle, when the vehicle is stopped and the brakes are applied, and when it is determined that the brakes have been released based on the rate of change of brake fluid pressure while the output torque is being reduced, the control unit that performs recovery control to output a torque from the motor that is equal to or greater than the guaranteed gradient equivalent torque set to prevent the vehicle from sliding backward on an uphill road with a predetermined road surface gradient.

(Note 2)
The vehicle control device according to Appendix 1, wherein the control unit determines that the vehicle has started to slide down after it has determined that the brake has been turned off, and increases the output torque at a higher rate than when it has not determined that the vehicle has started to slide down.

(Note 3)
The control unit determines the rate of increase as the amount of road gradient detected by the gradient detection sensor for detecting the amount of road gradient increases, as described in Appendix 2 of the vehicle control device.

(Note 4)
The vehicle control device according to Appendix 1, wherein the control unit does not perform the creep cut control when the vehicle's shift position is first shifted to the drive range after the vehicle's ignition is turned on.

(Note 5)
The vehicle control device according to Appendix 1, wherein the predetermined road surface gradient amount is a road surface gradient amount corresponding to the maximum value of the detection variation in the gradient detection sensor that detects the road surface gradient amount.
According to the embodiment described in Appendix 5, even when the detection variability of the gradient detection sensor is relatively large, the motor can output sufficient torque to suppress the vehicle from sliding downwards.

(Note 6)
The vehicle control device according to Appendix 1, wherein the control unit does not perform the creep cut control when the vehicle is stopped and the brakes are applied, and the amount of road surface gradient detected by the gradient detection sensor that detects the amount of road surface gradient is equal to or greater than the predetermined amount of road surface gradient.
According to the embodiment described in Appendix 6, it is possible to reliably suppress the occurrence of vehicle sliding down in areas where the detected road surface gradient amount is equal to or greater than a predetermined road surface gradient amount.

(Note 7)
The vehicle control device according to Appendix 1, wherein the control unit determines that the brakes have been turned off when the rate of change of the brake fluid pressure is greater than or equal to a first predetermined value and the absolute value of the brake fluid pressure is less than a second predetermined value.
According to the embodiment described in Appendix 7, even when the brake is released slowly, it is possible to appropriately determine that the brake has been released.

10. Vehicle control device 12. G sensor (gradient detection sensor)
16. Hydraulic pressure sensor 20. HEV ECU
22 Control Unit 30 MG
32. Rotation detection sensor

Claims (4)

The control unit includes a creep-cut control that reduces the output torque of the motor, which is the drive source of the vehicle, when the vehicle is stopped and the brakes are applied, and a return control that, when it is determined that the brakes have been turned off based on the rate of change of brake fluid pressure while the output torque is being reduced, outputs a torque from the motor that is equal to or greater than the guaranteed gradient equivalent torque set to prevent the vehicle from sliding backward on an uphill road with a predetermined road surface gradient .
The control unit is a vehicle control device that determines that the brakes have been turned off when the rate of change of the brake fluid pressure is greater than or equal to a first predetermined value and the absolute value of the brake fluid pressure is less than a second predetermined value . The vehicle control device according to claim 1, wherein the control unit, after determining that the brake has been turned off, determines that the vehicle has started to slide backward, and increases the output torque at a higher rate than when it has not determined that the vehicle has started to slide backward. The vehicle control device according to claim 2, wherein the control unit determines the rate of increase as the amount of road gradient detected by the gradient detection sensor increases. The vehicle control device according to claim 1, wherein the control unit does not perform the creep cut control when the vehicle's shift position is first shifted to the drive range after the vehicle's ignition is turned on.