JP7787663B2 - Vehicle control device, vehicle control method, and vehicle control system - Google Patents

Description

The present invention relates to a vehicle control device, a vehicle control method, and a vehicle control system.

Patent Document 1 discloses a braking control device that includes: means for determining the control amount of a friction braking device based on a target friction braking amount calculated from the required braking force and the amount of regeneration performed; and means for correcting the control amount of the friction braking device so that the target friction braking amount matches the actual friction braking amount based on the braking energy absorbed by friction braking from the start of friction braking operation.

Japanese Patent Application Laid-Open No. 2008-120220

However, in Patent Document 1, the correction coefficient is determined by referring to a map of correction coefficients corresponding to changes in pad temperature that is set in advance, so there is a risk that the correction coefficient may not be determined with high accuracy when the situation changes.
One method of vehicle control is to generate a driving force in the opposite direction to the target braking force when the vehicle is coming to a stop, which can make the vehicle come to a smooth stop. However, if the target braking force cannot be determined accurately due to changes in the brake characteristics caused by temperature changes, the difference between the target braking force and the actual braking force may become large, making it difficult to stop the vehicle smoothly.
One object of the present invention is to provide a vehicle control device, a vehicle control method, and a vehicle control system that can improve the smoothness of a vehicle stopping in vehicle control that generates a driving force in the opposite direction to a target braking force when the vehicle is stopping.

A vehicle control method in one embodiment of the present invention acquires the wheel angular velocity of the vehicle, acquires a target braking force required to decelerate the vehicle, and calculates a first correction gain that corrects the target braking force to cancel out an error between the reference friction coefficient and the estimated friction coefficient based on a reference friction coefficient of the brake pad that has been acquired in advance and an estimated friction coefficient of the brake pad that has been calculated based on the target braking force, the specific heat of the brake pad, the mass of the brake pad, the wheel angular velocity of the vehicle, and the outside air temperature; when decelerating the vehicle based on the target braking force, acquires the acceleration and jerk of the vehicle, and calculates a second correction gain that corrects the target braking force to cancel out an error between the target braking force and the actual braking force based on the acceleration and jerk acquired during the previous stop; and when decelerating the vehicle based on the target braking force, corrects a control command to be output to generate a driving force by a drive device while a frictional braking force is being generated, based on the magnitudes of the first correction gain and the second correction gain.

Therefore, this invention can improve the smoothness of a vehicle stopping.

1 is a configuration diagram of a control system for an electric vehicle according to a first embodiment. FIG. 2 is a control block diagram of a vehicle control device 17 for performing anti-jerk control. FIG. 3 is a control block diagram of a target braking torque correction unit 31. FIG. 2 is a temperature-friction coefficient characteristic diagram of a brake pad. 10 is a time chart showing the operation of the anti-jerk control when the target braking force is smaller than the actual braking force. 10 is a time chart showing the operation of the anti-jerk control when the target braking force is larger than the actual braking force. FIG. 3 is a control block diagram of a temperature-based correction gain calculation unit 34. FIG. 3 is a control block diagram of a friction coefficient correction gain calculation unit 35. 4 is a time chart showing the operation of the anti-jerk control.

[Embodiment 1]
FIG. 1 is a configuration diagram of a control system for an electric vehicle according to the first embodiment.
The electric vehicle 1 has front wheels 2FL, 2FR and rear wheels 2RL, 2RR, and friction brakes (friction braking devices) 3FL, 3FR, 3RL, 3RR (hereinafter, the friction brakes of each wheel will be collectively referred to as friction brake 3) that are provided on each wheel and generate friction braking force on the wheel.
The electric vehicle 1 has a rear motor (drive unit) 7 that outputs torque to rear wheels 2RL, 2RR. The rear wheels 2RL, 2RR are also collectively referred to as drive wheels 2. Power is transmitted between the rear motor 7 and the rear wheels 2RL, 2RR via a reduction gear 8, a differential 10, and rear axles 6RL, 6RR.

Each wheel 2FL, 2FR, 2RL, 2RR has a wheel speed sensor 11FR, 11FL, 11RL, 11RR that detects the wheel speed. The rear motor 7 has a rear wheel resolver 13 that detects the motor rotation speed. The electric vehicle 1 also has a G sensor 5 that detects the longitudinal acceleration of the vehicle.
The friction brake 3 generates a braking force by frictional force by pressing brake pads against brake rotors that rotate integrally with each wheel in the direction of the rotation axis of the wheel. The friction brake 3 in the first embodiment is described as being configured to press the brake pads by wheel cylinders that are actuated by brake fluid pressure, but is not particularly limited and may be configured to press the brake pads via a ball screw mechanism or the like driven by an electric motor.

The electric vehicle 1 has a low-voltage battery 14 and a high-voltage battery 15. The low-voltage battery 14 is, for example, a lead-acid battery. The high-voltage battery 15 is, for example, a lithium-ion battery or a nickel-metal hydride battery. The high-voltage battery 15 is charged with power boosted by a DC-DC converter 16.
The electric vehicle 1 has a vehicle control device (control unit) 17, a brake control device 18, a rear motor control device 20, and a battery control device 19. The control devices 17, 18, and 20 share information with each other via a CAN bus 21.

The vehicle control device 17 performs integrated control of the vehicle by acquiring information from various sensors such as the rear wheel resolver 13, an accelerator pedal sensor 22 that detects the amount of accelerator operation, a brake sensor 23 that detects the amount of brake operation, and a gear position sensor 24. The vehicle control device 17 outputs a driver-requested torque that should be output by the rear motor 7 in accordance with the requested distribution torque in response to the requested torque according to the driver's accelerator operation, brake operation, etc.
The brake control device 18 acquires information from various sensors such as the brake sensor 23, sets a target braking torque which is a torque equivalent value of the vehicle's target braking force, generates the necessary brake fluid pressure for each wheel according to the target braking torque, and outputs it to the friction brake 3 through hydraulic piping 18a.

The battery control device 19 monitors the charge/discharge state of the high-voltage battery 15 and the single battery cells that make up the high-voltage battery 15. The battery control device 19 calculates a battery required torque limit value based on the charge/discharge state of the high-voltage battery 15. The battery required torque limit value is the maximum torque permitted in the rear motor 7. For example, when the charge level of the high-voltage battery 15 is low, the battery required torque limit value is set to a value smaller than normal.
The rear motor control device 20 controls the power supplied to the rear motor 7 based on the rear required torque.

In the electric vehicle 1 of embodiment 1, anti-jerk control is implemented to suppress unpleasant vehicle shaking when the vehicle is stopped and reduce occupant fatigue, by outputting a drive torque equivalent to the actual braking torque from the rear motor 7 when the vehicle is stopped. This reduces the longitudinal jerk (jerk) that occurs when the vehicle is stopped with a constant amount of brake operation by approximately 68% compared to when anti-jerk control is not used. In other words, smooth stopping can be achieved even without skillful brake operation. In anti-jerk control, under the assumption that the target braking torque and the actual braking torque are similar, an anti-jerk control torque equivalent to the target braking torque is output from the rear motor 7.

FIG. 2 is a control block diagram of the vehicle control device 17 for carrying out anti-jerk control.
The target braking torque correction unit 31 receives the target braking torque and a friction coefficient correction gain (described later) and outputs an estimated actual braking torque. FIG. 3 is a control block diagram of the target braking torque correction unit 31. The target braking torque correction unit 31 calculates the estimated actual braking torque by multiplying the target braking torque by the friction coefficient correction gain multiplied by the set nominal friction coefficient value (reference friction coefficient). The nominal friction coefficient value is a value that is set at the start of driving and, once set, does not change while driving. The temperature-friction coefficient characteristics of the brake pads, as shown in FIG. 4, are acquired in advance as a map and set by referring to the map. The temperature may be the outside air temperature at the start of driving, or a predetermined temperature (e.g., 20°C).
The vibration suppression control unit 32 receives the estimated actual braking torque, the G sensor value, and the vehicle speed, and outputs the anti-jerk control torque and the gradient estimation results (estimated gradient value, estimated gradient resistance value). The G sensor value is the output value of the G sensor 5. The vehicle speed can be calculated from the output values of the wheel speed sensor 11 and the rear wheel resolver 13.

The vibration suppression control unit 32 calculates an estimated grade resistance value, which is the resistance acting on the vehicle due to the road gradient, from the vehicle speed and the G sensor value. Specifically, the vibration suppression control unit 32 obtains an estimated grade resistance value from the deviation between the estimated acceleration calculated from the vehicle speed and the G sensor value (actual acceleration), and calculates an estimated grade resistance value from the estimated grade value. This is to prevent an excessive decrease in vehicle deceleration when adding anti-jerk control torque due to the gradient of a downhill slope.
The vibration suppression control unit 32 subtracts the torque corresponding to the gradient resistance from the estimated actual braking torque to calculate an anti-jerk control torque capable of suppressing vibration in the pitching direction. The torque corresponding to the gradient resistance is subtracted in order to avoid application of an anti-jerk control torque that generates a driving force exceeding the braking force.

The vehicle behavior-based correction gain calculation unit 33 inputs the gradient estimation result, target braking torque, G sensor value, vehicle speed, and brake operation amount, and outputs a correction gain based on vehicle behavior. When the pad temperature characteristics (temperature-friction coefficient characteristics) change due to factors such as brake pad aging, even if the temperature-based correction gain calculation unit 34 (described later) corrects the target braking torque for the change in friction coefficient due to pad temperature, a discrepancy still occurs between the anti-jerk control torque based on the target braking torque and the actual braking torque. As shown in Figure 5, when the target braking torque is smaller than the actual braking torque, the anti-jerk control torque is insufficient compared to the actual braking torque, resulting in a strong shock when stopping. Note that in Figure 5, the maximum value (peak value) of the jerk occurring when stopping is referred to as the maximum jerk. On the other hand, as shown in Figure 6, when the target braking torque is greater than the actual braking torque, the anti-jerk control torque is excessive compared to the actual braking torque, resulting in a longer braking distance. Note that in Figure 6, the maximum amplitude of acceleration occurring when stopping is referred to as the acceleration fluctuation range. Therefore, in the first embodiment, the percentage error between the target braking torque and the actual braking torque is learned based on the vehicle behavior (jerk, acceleration) that occurs while the vehicle is stopped, and a gain (a correction gain based on vehicle behavior) is calculated to correct the target braking torque to cancel out the error the next time the vehicle is stopped.

For example, when the vehicle speed drops below a specified speed and the maximum jerk is equal to or greater than the maximum jerk threshold, the vehicle behavior-based correction gain is set to a positive value, and the larger the maximum jerk, the larger the correction gain. This reduces the anti-jerk control torque's insufficiency relative to the actual braking torque. Also, when the vehicle speed drops below a specified speed and the maximum jerk is equal to or less than the specified speed and the maximum jerk is equal to or greater than the acceleration fluctuation threshold, the vehicle behavior-based correction gain is set to a negative value, and the larger the acceleration fluctuation, the smaller the correction gain (the larger the absolute value). This reduces the anti-jerk control torque's excess relative to the actual braking torque. The maximum jerk threshold may be determined by comparing the target braking torque plus the torque equivalent of the estimated gradient resistance value with the specified braking torque. If the former is equal to or greater than the specified braking torque, the maximum jerk threshold is set to the first threshold X1. If the former is less than the specified braking torque, the maximum jerk threshold is set to the second threshold X2 (|X1| > |X2|).

The temperature-based correction gain calculation unit 34 inputs the target braking torque, the correction gain based on vehicle behavior, the wheel angular velocity (output value of the wheel speed sensor 11), the outside air temperature, and the coolant temperature, and outputs a temperature-based correction gain. When the pad friction coefficient changes due to temperature changes, a deviation occurs in the anti-jerk control torque based on the target braking torque compared to the actual braking torque. Therefore, the pad temperature and pad friction coefficient are estimated, and a gain (temperature-based correction gain) is calculated to correct the target braking torque to offset the error in the estimated pad friction coefficient from the nominal friction coefficient value.

Figure 7 is a control block diagram of the temperature-based correction gain calculation unit 34. The pad temperature estimation and friction coefficient estimation unit 341 estimates the pad temperature from a correction gain based on the target braking torque, wheel angular velocity, outside air temperature, coolant temperature, and vehicle behavior, and calculates an estimated pad friction coefficient from the estimated pad temperature by referring to the brake pad temperature-friction coefficient characteristic diagram shown in Figure 4. Pad temperature T1 is calculated using the following equation (1), but at the start of driving, it is calculated using equation (2).

T1(t)＝T1(t－1)－{(T1(t－1)－T2(t))×K(t)＋α×Tb(t)×ω(t)}/(C×m) …(1)
T1(0)＝T2(0) …(2)
Here, T2 is the outside air temperature, K(t) is a correction coefficient (calculated from a defined map) for natural convection, forced convection, etc., α is the proportion of braking heat flowing into the brake pad, Tb(t) is the actual braking torque, ω(t) is the wheel angular velocity, C is the specific heat of the brake pad, and m is the mass of the brake pad. The actual braking torque Tb(t) is calculated by multiplying the target braking torque by the pad friction coefficient μ(t). The pad friction coefficient μ(t) is calculated using the following equation (3).
μ(t) = nominal friction coefficient × temperature-based correction gain × (1 + vehicle behavior-based correction gain) ... (3)

The temperature-based correction gain calculation unit 342 outputs the value obtained by dividing the estimated pad friction coefficient by the nominal friction coefficient value (estimated pad friction coefficient/nominal friction coefficient value) as the temperature-based correction gain.
The friction coefficient correction gain calculation unit 35 receives the vehicle behavior-based correction gain and the temperature-based correction gain, and outputs the friction coefficient correction gain. Fig. 8 is a control block diagram of the friction coefficient correction gain calculation unit 35. The friction coefficient correction gain calculation unit 35 outputs the value {(1 + vehicle behavior-based correction gain) × temperature-based correction gain} obtained by multiplying the temperature-based correction gain by the vehicle behavior-based correction gain added to 1.

Next, the effects of the first embodiment will be described.
FIG. 9 is a time chart showing the operation of the anti-jerk control.
In Section 1, the difference between the nominal friction coefficient value and the actual friction coefficient is estimated based on the outside air temperature at the start of driving, and the temperature-based correction gain is corrected accordingly. Furthermore, by changing the temperature-based correction gain in accordance with changes in pad temperature during deceleration, the aim is to have an effect on temperature changes from the start of driving. However, in Figure 9, the current temperature-friction coefficient characteristics of the brake pads differ from the originally acquired characteristics, so temperature-based correction alone is not sufficient, and the actual braking torque exceeds the target braking torque, resulting in a large jerk just before the vehicle comes to a stop.

In Section 2, the temperature-based gain is corrected in the same way as in Section 1. Furthermore, when the maximum jerk exceeds the maximum jerk threshold during vehicle stoppage in Section 1, the vehicle behavior-based correction gain calculation unit 33 detects that good stopping was not achieved, and updates the vehicle behavior-based correction gain. The target braking torque is corrected using the friction coefficient correction gain calculated from these two gains, thereby calculating an anti-jerk control torque equivalent to the actual braking torque. In cases like Section 1, where an anti-jerk control torque equivalent to the actual braking torque cannot be calculated using only the temperature-based correction gain, it is assumed that the temperature-friction coefficient characteristics of the brake pads have changed due to aging or other reasons. Therefore, by correcting the friction coefficient correction gain using the vehicle behavior-based correction gain, it is possible to address changes in the temperature-friction coefficient characteristics of the brake pads and achieve an anti-jerk control torque equivalent to the actual braking torque.

In Section 3, the brakes are not used for a long period of time after the vehicle has stopped in Section 2, and the pad temperature has dropped to a level equivalent to the outside air temperature at the start of driving. In Section 3, the pad temperature is lower than in Section 2, but the temperature-based correction gain calculation unit 34 updates the estimated pad temperature over time and sets a temperature-based correction gain that is deemed more appropriate based on the temperature-friction coefficient characteristics of the brake pads, based on the estimated temperature at that time. Furthermore, since the correction gain calculation unit 33 based on the vehicle behavior when stopped also takes into account changes in the temperature-friction coefficient characteristics due to aging of the brake pads in Section 2, an anti-jerk control torque equivalent to the actual braking torque can be achieved.

As described above, when decelerating the vehicle in accordance with the target braking torque, the vehicle control device 17 of embodiment 1 corrects the control command (target braking torque) output to generate anti-jerk control torque, which is the driving force from the rear motor 7, using a friction coefficient correction gain corresponding to the temperature of the brake pads of the friction brakes 3 while friction braking force is being generated. This makes it possible to achieve an anti-jerk control torque equivalent to the actual braking torque, even if the friction coefficient of the brake pads changes due to changes in pad temperature during deceleration, thereby improving the smoothness of the vehicle when stopping.

When the vehicle is decelerated according to the target braking torque, the vehicle control device 17 acquires the vehicle's acceleration and jerk, and learns from the acquired acceleration and jerk what percentage error there is in the target braking torque compared to the actual braking torque. The next time the vehicle stops, it calculates a correction gain based on the vehicle behavior to cancel out the error and corrects the friction coefficient correction gain. This makes it possible to achieve an anti-jerk control torque equivalent to the actual braking torque, even if the temperature-friction coefficient characteristics have changed due to aging of the brake pads, etc., thereby improving the smoothness of the vehicle's stopping.

The vehicle control device 17 calculates a temperature-based correction gain from the outside air temperature T2, wheel angular velocity ω, brake pad mass m, brake pad specific heat C, target braking torque, nominal friction coefficient, and pre-stored temperature-friction coefficient characteristics of the brake pad, and increases the friction coefficient correction gain the larger the temperature-based correction gain. This makes it possible to calculate the deviation of the pad friction coefficient from the nominal friction coefficient without actually measuring the brake pad temperature. Then, by correcting the target braking torque using a friction coefficient correction gain proportional to this deviation, it is possible to achieve an anti-jerk control torque equivalent to the actual braking torque.

Other Embodiments
The above describes an embodiment for carrying out the present invention, but the specific configuration of the present invention is not limited to the configuration of the embodiment, and design changes and the like that do not deviate from the gist of the invention are also included in the present invention.
For example, although the present embodiment is applied to a rear-wheel drive electric vehicle, the present invention may also be applied to a front-wheel drive electric vehicle or a four-wheel drive electric vehicle.Furthermore, the present invention is not limited to electric vehicles, and may also be applied to vehicles equipped with an internal combustion engine or hybrid vehicles that can run using both an engine and a motor.
The target braking force includes not only the brake operation by the driver but also automatic braking and the like.

1. Electric vehicle, 3. Friction brake (friction braking device), 7. Rear motor (drive unit), 17. Vehicle control device (control unit)

Claims (3)

A vehicle control device is provided on a vehicle having a friction braking device with brake pads that generate a friction braking force on the vehicle and a drive device that generates a drive force on the vehicle, the vehicle control device comprising a control unit that outputs a result of calculation based on input information,
The control unit
obtaining a wheel angular velocity of the vehicle;
obtaining a target braking force required to decelerate the vehicle;
calculate a first correction gain for correcting the target braking force to cancel out an error between the reference friction coefficient and the estimated friction coefficient, based on a reference friction coefficient of the brake pad obtained in advance and an estimated friction coefficient of the brake pad obtained based on the target braking force, the specific heat of the brake pad, the mass of the brake pad, the wheel angular velocity of the vehicle, and an outside air temperature;
acquiring an acceleration and a jerk of the vehicle when decelerating the vehicle based on the target braking force;
calculating a second correction gain for correcting the target braking force to cancel an error between the target braking force and the actual braking force based on the acceleration and the jerk obtained when the vehicle was last stopped;
when the vehicle is decelerated based on the target braking force, in a state in which the frictional braking force is generated, a control command to be output for generating a driving force by the driving device is corrected based on the magnitudes of the first correction gain and the second correction gain.
Vehicle control device. A vehicle control method comprising: a friction braking device having brake pads that generate a friction braking force in a vehicle; and a drive device that generates a drive force in the vehicle; and the vehicle control method is executed by a control unit mounted on the vehicle,
obtaining a wheel angular velocity of the vehicle;
obtaining a target braking force required to decelerate the vehicle;
calculate a first correction gain for correcting the target braking force to cancel out an error between the reference friction coefficient and the estimated friction coefficient, based on a reference friction coefficient of the brake pad obtained in advance and an estimated friction coefficient of the brake pad obtained based on the target braking force, the specific heat of the brake pad, the mass of the brake pad, the wheel angular velocity of the vehicle, and an outside air temperature;
acquiring an acceleration and a jerk of the vehicle when decelerating the vehicle based on the target braking force;
calculating a second correction gain for correcting the target braking force to cancel an error between the target braking force and the actual braking force based on the acceleration and the jerk obtained when the vehicle was last stopped;
when the vehicle is decelerated based on the target braking force, in a state in which the frictional braking force is generated, a control command to be output for generating a driving force by the driving device is corrected based on the magnitudes of the first correction gain and the second correction gain.
Vehicle control method. a friction braking device including brake pads that generate a friction braking force on a vehicle;
a drive device that generates a drive force for the vehicle;
A control device that outputs a result of calculation based on input information,
obtaining a wheel angular velocity of the vehicle;
obtaining a target braking force required to decelerate the vehicle;
calculate a first correction gain for correcting the target braking force to cancel out an error between the reference friction coefficient and the estimated friction coefficient, based on a reference friction coefficient of the brake pad obtained in advance and an estimated friction coefficient of the brake pad obtained based on the target braking force, the specific heat of the brake pad, the mass of the brake pad, the wheel angular velocity of the vehicle, and an outside air temperature;
acquiring an acceleration and a jerk of the vehicle when decelerating the vehicle based on the target braking force;
calculating a second correction gain for correcting the target braking force to cancel an error between the target braking force and the actual braking force based on the acceleration and the jerk obtained when the vehicle was last stopped;
when the vehicle is decelerated based on the target braking force, in a state in which the frictional braking force is generated, a control command to be output for generating a driving force by the driving device is corrected based on the magnitudes of the first correction gain and the second correction gain.
the control device;
A vehicle control system comprising: