JPH08149606A - Electric vehicle braking system - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent the drive wheels from being locked by an inexpensive device and a simple control procedure without lowering the braking energy recovery efficiency during regenerative braking and without deteriorating the brake feeling. [Structure] The vehicle speed V and the wheel speed Vω of the driving wheels are detected (110), the differential value V ^· ω of the wheel speed Vω is calculated ^, and the regenerative torque command value Tb is calculated based on V−Vω and V ^· ω.
The reduction amount ΔTbrk of rk is calculated (114). When outputting the command value Tbrk, the decrease amount ΔTbrk is decreased (116).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking system for an electric vehicle that brakes a drive wheel and a driven wheel by fluid pressure such as hydraulic pressure and brakes the drive wheel by regenerating braking energy.

[0002]

2. Description of the Related Art A fluid pressure braking device using an incompressible fluid, such as a hydraulic braking device, is widely used as a means for braking a vehicle. When the vehicle to be braked is an electric vehicle, it is also possible to use a regenerative braking device that collects braking energy by a traveling motor.

One of the differences between hydraulic braking and regenerative braking is that the braking energy recovered by regenerative braking can be stored in a main battery which is a power source of a traveling motor. Therefore, in an electric vehicle, both the hydraulic braking device and the regenerative braking device are mounted, but the regenerative braking is preferentially used over the hydraulic braking in terms of suppressing the charging frequency of the main battery and extending the travelable distance. preferable.

The example shown in FIG. 4 is an example of rear wheel (Rr) drive. In this example, the sum of the regenerative braking force and the hydraulic braking force matches the required braking force (here, the required braking force (here, the required braking force). In the region where the master cylinder pressure: M / C pressure) is smaller than the predetermined value P _0, only the regenerative braking force is applied, and in the region where it is large, the hydraulic braking force is applied while maintaining the regenerative braking force at the maximum regenerative braking force. By performing such control, the required braking force can be realized while collecting the braking energy as much as possible.

Further, the control of the regenerative braking force can be realized by controlling the power conversion operation when supplying electric power to the traveling motor in accordance with the required braking force. The hydraulic braking force is controlled by opening the valve on the oil passage from the M / C to the wheel cylinder (W / C: caliper) of the driving wheel when the difference between the master cylinder pressure and the wheel cylinder pressure reaches P ₀ , and The master cylinder pressure can be realized by providing a differential pressure valve that holds the differential pressure P ₀ .

In such a regeneration priority mode, as shown in FIG. 5, the braking force distribution between the driving wheel (rear wheel in the case of rear wheel drive) and the driven wheel (the front wheel: Fr) is equal to the road surface. It is located on the drive wheel lock side when viewed from the ideal distribution that makes the most effective use of friction. If the lock limit of the road surface having a certain friction coefficient μ is indicated by the broken line in the figure, the drive wheels lock at point A in the figure as the brake pedal is depressed. In order to avoid this, in Japanese Patent Laid-Open No. 5-161212, the regenerative braking force is reduced along the 45 ° line (a line where the sum of the braking forces of the front and rear wheels is constant) indicated by the alternate long and short dash line in the figure. Hydraulic pressure is introduced to the driving wheel side. By such control, the drive wheels can be prevented from being locked.

[0007]

However, the procedure of such lock avoidance control is complicated and difficult to carry out. In addition, since a hydraulic pressure is introduced to the driven wheel side, it is necessary to use a linear valve or the like, which causes an increase in cost. In order to avoid such a problem, as disclosed in Japanese Patent Application Laid-Open No. 2-141354 regarding an air brake and an electric brake of an electric vehicle, only a certain amount of regenerative braking force is reduced when a wheel slip is detected. You can use this method.
By adopting this method, the control procedure is simplified and the device cost is reduced, but on the other hand, the braking energy recovery efficiency is not always good when the regenerative braking force is reduced, and the brake feeling is deteriorated. Will also occur.

The present invention has been made to solve the above problems, and an inexpensive device and a simple control can be achieved by determining the reduction amount of the regenerative braking force using an appropriate index. The purpose is to maintain good braking energy recovery efficiency and good brake feeling in the procedure.

[0009]

In order to achieve such an object, a first structure of the present invention comprises means for hydraulically braking a driving wheel and a driven wheel, and means for regeneratively braking a driving wheel.
The regenerative braking force command value is determined according to the required braking force from the operator, etc., and the regenerative braking is limited while limiting the fluid pressure braking force so that the braking energy recovery by the regenerative braking takes precedence over the braking energy consumption by the fluid pressure braking. A control unit that controls the regenerative braking force based on the braking force command value, and the braking force distribution to the drive wheels and the driven wheels is biased to the drive wheel lock tendency side, and the control is performed in the braking device mounted on the electric vehicle. Means for detecting the rotational speed of the drive wheel to obtain the deceleration of the drive wheel, means for determining the regenerative braking force reduction amount according to the deceleration of the drive wheel, and reduction of the regenerative braking force from the regenerative braking force command value. And means for reducing the amount.

According to a second aspect of the present invention, the control means compares the rotational speed of the drive wheel and the vehicle body speed with the means for detecting the rotational speed of the drive wheel and the vehicle body speed, and regenerative control is performed according to the result. It is characterized by having a means for determining the power reduction amount and a means for subtracting the regenerative braking force reduction amount from the regenerative braking force command value.

[0011]

In the first structure of the present invention, the rotational speed of the drive wheels is detected and the deceleration of the drive wheels is obtained based on the result. Further, the regenerative braking force reduction amount is determined according to the calculated deceleration, and the regenerative braking force is controlled based on the regenerative braking force command value obtained by subtracting the regenerative braking force reduction amount. At this time, since the fluid pressure braking force is limited so that the braking energy recovery by the regenerative braking takes precedence over the braking energy consumption by the fluid pressure braking, the total braking force acting on the drive wheels is reduced by the regenerative braking force. The amount is reduced according to the amount, and the locking of the drive wheels is promptly released by an inexpensive device and a simple control procedure. Further, in this configuration, the regenerative braking force reduction amount that should be subtracted from the regenerative braking force command value is determined according to the deceleration of the drive wheels, so the regenerative braking force is not reduced unnecessarily. Since it is possible to keep the minimum reduction amount necessary for avoiding lock, the braking energy recovery efficiency by regenerative braking remains within a relatively good range,
Brake feeling is also improved.

In the second configuration of the present invention, the rotational speed of the drive wheels and the speed of the vehicle body are detected, and the regenerative braking force reduction amount is determined according to the result of comparison between the two detected values. As a result, an action similar to that of the first configuration occurs, and the braking force distribution finally converges near the ideal distribution.
The drive wheel lock can be suppressed more reliably.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. The same components as those of the conventional example shown in FIGS. 4 and 5 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 shows a system configuration of an electric vehicle according to an embodiment of the present invention, particularly a configuration of a braking system. The system shown in this figure is an example in which the present invention is applied to a rear-wheel drive vehicle, but the present invention can also be applied to a front-wheel drive vehicle.

The system shown in this figure comprises a main battery 10, an inverter 12, a motor 14 and an ECU 16 as means for driving the vehicle. The discharge output of the main battery 10 is converted into three-phase AC power by the inverter 12 under the control of the ECU 16. In the case of this embodiment, the traveling motor 14 is a three-phase AC motor, and the inverter 12
It is rotationally driven by three-phase AC power supplied from. As a result, the driving force of the vehicle is generated. In addition, the ECU 16
Controls the switching operation of the switching element forming the inverter 12 according to the operation of the accelerator pedal or the like. Therefore, the output torque of the traveling motor 14 becomes a torque according to the depression of the accelerator pedal by the vehicle operator.

Further, this system has both a regenerative braking system and a hydraulic braking system as a braking system. The regenerative braking system is realized by controlling the inverter 12 by the ECU 16. That is, when the depression of the brake pedal 18 is detected by the brake switch 20 attached to the brake pedal 18, the ECU 16 detects the hydraulic pressure sensors 22 and 24 provided on the oil passages for the drive wheels.
The hydraulic pressure in the master cylinder 26 (master cylinder pressure) and the wheel cylinder (caliper) 2 on the drive wheel side.
The hydraulic pressure (wheel cylinder pressure) at 8r is detected, and the necessary regenerative torque is calculated based on these. ECU16
Controls the inverter 12 so that the calculated regenerative torque is realized. This realizes regenerative braking.

The hydraulic braking system includes wheel cylinders 28r and 28f provided corresponding to the brake wheels 30r and 30f of the driving wheels (rear wheels in this embodiment) and driven wheels (front wheels in this embodiment), Master cylinder 2
6 from each hydraulic chamber to each wheel cylinder 28r and 28f
It is composed of various valves provided on the oil passage leading to. Of these valves, solenoid valves 32r and 32f are ECUs.
A valve that shuts off the oil passage in response to the command of 16 and is in the shut-off state except when the regenerative braking force fails (when the desired regenerative braking force cannot be obtained) or when the brake pedal 18 is pressed very shallowly. Maintained at. In addition, the differential pressure valves 34r and 34f correspond to the corresponding wheel cylinders 28r or 28f.
When the master cylinder pressure becomes higher than a predetermined valve opening value P ₀ as compared with the wheel cylinder pressure in the above, the corresponding wheel cylinders 28r and 2r are opened while maintaining this differential pressure.
Supply braking oil to 8f. Hydraulic cutoff valves 36r and 36f
Shuts off the oil passage when the master cylinder pressure is higher than the wheel cylinder pressure. Relief valves 38r and 38f
Opens the brake fluid when the wheel cylinder pressure exceeds the master cylinder pressure.

Also in this embodiment, the drive wheels are controlled by the regeneration priority mode shown in FIG. 4 as in the above-mentioned conventional example. That is, while the difference between the master cylinder pressure detected by the hydraulic pressure sensor 22 and the wheel cylinder pressure detected by the hydraulic pressure sensor 24 is lower than the valve opening value P ₀ of the differential pressure valve 34r, the brake wheel 3 on the drive wheel side.
The hydraulic pressure does not act on 0r, and the regenerative braking control by the ECU 16 is performed during that period. By such control, as shown in FIG.
The regeneration priority mode shown in is realized.

Therefore, also in this embodiment, the braking force distribution between the front and rear wheels tends to lock the rear wheels (driving wheels) as compared with the ideal distribution, as in the conventional example. The feature of the present embodiment is that when the friction coefficient μ of the road surface is low and the drive wheels are about to be locked, this can be avoided with an inexpensive device and a simple procedure, and It is to realize a process of reducing the regenerative braking force associated with the operation so as not to cause a remarkable deterioration of the braking energy recovery efficiency due to the regenerative braking. Next, this point will be described with reference to FIGS.

FIG. 2 shows the regenerative braking control executed by the ECU 16, and FIG. 3 shows the braking force distribution and lock avoiding operation in this embodiment.
As shown in FIG. 2, the ECU 16 executes a predetermined initialization process and then determines whether the vehicle is stopped (10
2) and whether or not the brake switch 20 is turned on (104). Whether or not the vehicle is stopped
The determination can be made by using any output of the rotation sensor 40 attached to the motor 14, the wheel speed sensor 42 for detecting the rotation speed of the driving wheels, and the vehicle body speed sensor 44 for detecting the vehicle body speed. When the vehicle is stopped, it is not necessary to perform regenerative braking, so the command value Tbrk of the regenerative torque and its reduction amount ΔTbrk are set to 0, and the solenoid valve 3
2r and 32f are opened and reset to a state where the braking oil can flow (106). Even if the vehicle is not stopped, if the brake switch 20 is on, the same step 106 is executed.

When the vehicle is not stopped and the brake switch 20 is on, it is necessary to control the regenerative braking force, so the ECU 16 realizes the regenerative braking force shown in FIG. A command value Tbrk of the regenerative torque is calculated based on the master cylinder pressure and the wheel cylinder pressure (108). Command value Tbrk obtained by calculation
Is used for controlling the inverter 12 after undergoing reduction correction in steps 110 to 114 (regenerative torque output: 116).

When the command value Tbrk is corrected to be decreased, first, the vehicle speed V is detected by the vehicle speed sensor 44 and the wheel speed Vω of the driving wheels is detected by the wheel speed sensor 42 and read into the ECU 16 (110). The ECU 16
At that time, the difference between the two

[Equation 1] Is calculated. The ECU 16 subsequently calculates the differential value V ^· ω of the wheel speed Vω (112). That is, the deceleration of the driving wheels is obtained. The ECU 16 uses the value thus obtained to calculate the reduction amount ΔTbrk of the regenerative torque command value based on the following equation (114).

[0023]

[Equation 2] In step 116, the command value Tbrk reduced and corrected by the following equation

(Equation 3) Is output.

When such control is performed, as shown in FIG. 3, the locking of the drive wheels is preferably avoided. That is, when the driving wheels are about to be locked at the point A due to running on a low μ road while braking in the regeneration priority mode, a difference is generated between the vehicle body speed V and the wheel speed Vω. The regenerative torque command value Tbrk is reduced and corrected.
Then, as a result of the regenerative braking force being reduced, the distribution of the braking force to the driving wheel (rear wheel) side is reduced, and the operating point is changed from A to B. At this time, when the differential pressure valve 34r is closed, when the vehicle operator further depresses the brake pedal 18, the torque command value Tbrk increases as the master cylinder pressure increases, and the operating point shifts from B to C. At this point, the command value Tbrk of the regenerative torque is again reduced and corrected, and as a result, the operating point further shifts to D. After such an operation is repeated, when the operating point shifts to the point E near the ideal distribution, the control operation becomes stable at this point because the difference between the vehicle body speed V and the wheel speed Vω becomes almost zero.

Therefore, according to the present embodiment, Japanese Patent Laid-Open No.
It is possible to reliably prevent the drive wheels from locking without using a linear valve or using a complicated control procedure as in No. -1611212. Further, unlike Japanese Patent Application Laid-Open No. 2-141354, the regenerative torque command value Tbr
Since the decrease amount ΔTbrk of k is determined based on the above equation, neither the brake feeling is deteriorated nor the braking energy recovery efficiency during regenerative braking is deteriorated.
Therefore, according to the present embodiment, it is possible to obtain an electric vehicle that is cheaper and more energy efficient than the conventional one, and thus has a long travelable distance per charge of the main battery 10.

In the above description, the rear-wheel drive vehicle is taken as an example, but the present invention can also be applied to the front-wheel drive vehicle. Comparing the case where it is applied to the front-wheel drive vehicle and the case where it is applied to the rear-wheel drive vehicle, it can be seen that the application to the rear-wheel drive vehicle has less decrease in the braking force of the total regenerative and hydraulic pressure and the higher vehicle stability. There are merits.

[0027]

As described above, according to the first configuration of the present invention, the deceleration of the drive wheel is obtained based on the detection result of the rotational speed of the drive wheel, and the regenerative braking force is calculated according to the obtained deceleration. Since the reduction amount is determined, the drive wheels can be quickly unlocked with an inexpensive device and a simple control procedure, and the regenerative braking force is not reduced unnecessarily and the minimum required to avoid the drive wheel locks. Since the reduction amount can be limited to the limit, the braking energy recovery efficiency by regenerative braking can be kept in a relatively good range, and the brake feeling can be improved.

According to the second configuration of the present invention, the rotational speeds of the drive wheels and the vehicle body speed are detected and the regenerative braking force reduction amount is determined according to the comparison result of the two detection values.
In addition to the effect similar to that of the above configuration, the braking force distribution finally converges to the vicinity of the ideal distribution, so that the drive wheel lock can be more reliably suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of a system according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of operation of an ECU in this embodiment.

FIG. 3 is a diagram conceptually showing the contents of a drive wheel lock avoidance operation in this embodiment.

FIG. 4 is a diagram showing an example of regeneration priority control.

FIG. 5 is a diagram showing an example of a conventional lock avoidance operation.

[Explanation of symbols]

10 Main Battery 12 Inverter 14 Motor 16 ECU (Electronic Control Unit) 18 Brake Pedal 22, 24 Oil Pressure Sensor 26 Master Cylinder (M / C) 28f, 28r Wheel Cylinder (W / C) 30f, 30r Brake Wheel 34f, 34r Differential Pressure Valve 40 rotation sensor 42 wheel speed sensor 44 vehicle body speed sensor Tbrk regenerative torque command value ΔTbrk regenerative torque command value decrease amount V vehicle speed Vω driving wheel wheel speed V ^· ω wheel speed differential value (deceleration)

Claims (2)

[Claims] 1. A means for hydraulically braking a driving wheel and a driven wheel, a means for regeneratively braking a driving wheel, and a regenerative braking force command value which is determined according to a braking force required by a driver or the like. Control means for controlling the regenerative braking force based on the regenerative braking force command value while limiting the fluid pressure braking force so that the braking energy recovery takes precedence over the consumption of the braking energy by the fluid pressure braking. In the braking device mounted on the electric vehicle, the braking force distribution to the driving wheels is biased toward the driving wheel lock tendency side, and in the braking device mounted on the electric vehicle, the control means detects the rotation speed of the driving wheels and obtains the deceleration of the driving wheels, A braking device comprising: a unit that determines the regenerative braking force reduction amount according to the deceleration of 1. and a unit that subtracts the regenerative braking force reduction amount from the regenerative braking force command value. 2. A means for hydraulically braking the driving wheel and the driven wheel, a means for regeneratively braking the driving wheel, and a regenerative braking force command value determined according to a braking force required by a driver or the like, and regenerative braking is performed. Control means for controlling the regenerative braking force based on the regenerative braking force command value while limiting the fluid pressure braking force so that the braking energy recovery takes precedence over the consumption of the braking energy by the fluid pressure braking. In the braking device installed in an electric vehicle, the braking force distribution to the driving wheels is biased toward the driving wheel lock tendency side, and in the braking device mounted on the electric vehicle, the control means detects the driving wheel rotation speed and the vehicle body speed, and the driving wheel rotation speed. And a speed of the vehicle body, and means for determining the regenerative braking force reduction amount according to the result, and means for subtracting the regenerative braking force reduction amount from the regenerative braking force command value.