JPH07322411A - Brake for electric vehicle - Google Patents

Abstract

PURPOSE:To avoid unstable behavior and delay in braking a vehicle by braking on regeneration-priority mode during ordinary operation and repeating opening and closing the rear-wheel bypass valves rapidly, in order to boost hydraulic pressure on the rear wheels when the front wheels have a high slip ratio. CONSTITUTION:Front wheels (Fr) are driven with an electric motor 2 and rear wheels (Rr) idle. Each wheel is provided with a wheel cylinder 5 for hydraulic braking. The front wheels (Fr) are also subjected to regenerative braking. A hydraulic pressure generated in a brake master cylinder 4 according to a tread on a brake pedal 21 is fed to pipings 61, 62, and then to the (Fr) and Rr through relief valves 6, 56, and by-pass valves 7, 52, 53. The Rr is provided with a proportioning valve 23. A motor CEU2 controls the electric motor 2, and a brake CEU26 controls hydraulic braking and regenerative braking. While a slip ratio (S) is low, the (Fr) is subjected to only regenerative braking with the valves closed. With an increase in (S), the by-pass valve 53 opens to increase braking force, thereby applying braking force efficiently and stopping a car at the shortest distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking device that can be used in, for example, an electric vehicle.

[0002]

2. Description of the Related Art For example, in the case of a general electric vehicle, the energy that can be used for traveling is only the electric power charged in the battery, and the electric power that can be charged in the battery is limited. In order to increase the distance that the vehicle can travel, it is necessary to effectively use the energy of the vehicle.
Therefore, the use of regenerative braking is a very effective means in electric vehicles. That is, when braking, the electric motor connected to the wheels is driven by the kinetic energy of the vehicle, and the electric power generated by the electric motor is returned to the battery, thereby reducing wasteful consumption of energy. be able to.

However, since there is a limit to the regenerative braking, if the regenerative braking limit or more is exceeded, the hydraulic brake is used to compensate, and the hydraulic brake is used in combination with the regenerative braking.

In the braking system of a general automobile, the distribution of the front wheel braking force and the rear wheel braking force has conventionally been determined so as to be as close as possible to a characteristic curve called ideal braking force distribution. However, in the case of an electric vehicle, if the distribution of the hydraulic brakes of the driven wheels is large, the energy due to regenerative braking will increase.
The collection efficiency is reduced.

Therefore, in order to improve the efficiency of energy recovery by regenerative braking, a special regenerative priority mode is provided,
It has been proposed to set the distribution of the front wheel side braking force and the rear wheel side braking force to a characteristic different from the ideal braking force distribution.

For example, in the technique disclosed in Japanese Unexamined Patent Publication No. Hei 5-161210, a regeneration priority mode is provided to shut off all hydraulic brakes and perform only regenerative braking in a region where a required braking force is relatively small. There is. In addition, JP-A-5-16121
In the technique disclosed in Japanese Patent No. 2, a regeneration priority mode is usually implemented,
When the friction coefficient of the road surface is small and the lock of the wheels is detected, automatic control is performed to shift to the normal mode according to the ideal distribution of the braking force. Further, in the technique disclosed in Japanese Patent Laid-Open No. 5-161213, switching between the regeneration priority mode and the normal mode is performed based on the stepping force of the brake pedal or the rate of increase thereof.
It is carried out automatically.

[0007]

By the way, when shutting off the hydraulic brake force in the regenerative priority mode, a master cylinder for generating hydraulic pressure according to the stroke of the brake pedal and each The on / off valve inserted in the oil flow path between the wheel cylinder and the wheel cylinder located near the wheel closes. When the brake pedal is depressed to some extent with the on / off valve closed, the master cylinder oil pressure increases in response to the depression stroke, but the wheel cylinder oil pressure is maintained at a low level. A large differential pressure is generated at. In such a state, when the on / off valve is opened in order to switch from the regeneration priority mode to the normal mode, the on / off valve is operated through the on / off valve until the oil pressure of the wheel cylinder approaches the oil pressure of the master cylinder. Oil suddenly flows to the wheel cylinder. For this reason, sudden depression of the brake pedal, generation of heavy oil noise, and step-like rapid deceleration
Shock etc. occurs. Therefore, the braking feeling is bad and unstable behavior is likely to occur in the vehicle.

Therefore, when switching from the regeneration priority mode to the normal mode, it is necessary to use some means to moderate the increase in the hydraulic pressure of the wheel cylinder. However, if the hydraulic pressure rise speed of the front or rear wheel cylinders is too slow, the braking force applied to the entire vehicle will not increase quickly even if the brake pedal is strongly depressed when the rear wheels or the front wheels are locked. Delay, braking distance (distance traveled until the car stops) becomes long.

Therefore, the present invention is based on the master cylinder and wheel.
When the on / off valve inserted in the oil flow path between the cylinder and the cylinder is switched from the closed state to the open state, the brake pedal suddenly sinks, a heavy oil noise is generated, and a step-like rapid deceleration causes G It is an object to suppress the occurrence of a shock and the like, and to prevent the braking distance of the vehicle from being lengthened thereby.

[0010]

In order to solve the above problems, in the present invention, an on-vehicle battery (1) for storing electric energy; an electric drive for driving wheels by electric power from the on-vehicle battery Means (2); Regenerative braking means (D1 to D6) for returning the electric power generated by the electric driving means to the on-board battery in accordance with the rotation of the wheels; Hydraulic pressure corresponding to the operation amount of the brake pedal. Generated hydraulic pressure generating means (4); Hydraulic pressure braking means (5 (Fr), 5 (Rr)) for applying braking force to wheels according to the hydraulic pressure generated by the hydraulic pressure generating means; A braking device for an electric vehicle, comprising: valve means (6, 56) for limiting the transmission of hydraulic pressure from the means to the hydraulic braking means, the restriction of the valve means being released when a predetermined condition is satisfied. And supplying the hydraulic pressure of the hydraulic pressure generating means to the hydraulic braking means. The braking state detecting means (46) for detecting the braking state of the wheel; and the transition state of the switching detected by the braking state detecting means when the predetermined condition is satisfied and the valve means is switched from the restricted state to the open state. Switching control means (47, 48), which is determined according to the braking state of the wheels, is provided.

According to a second aspect of the present invention, the switching control means opens and closes the valve means of the driven wheel in accordance with the duty ratio determined according to the rotational deceleration of the drive wheel when the drive wheel is operated. Is repeated.

Further, in claim 3, the driving wheel connecting the electric driving means is a front wheel (FR) and the rear wheel (RR) is a driven wheel.

Further, in claim 4, the switching control means is
When the predetermined condition is satisfied and the valve means is switched from the restricted state to the open state, the transition state of switching is determined according to the degree of decrease in the regenerative braking force (3J, 3K,
3L, 3G).

The symbols shown in the above parentheses are the reference numerals of the corresponding elements in the examples described later, but each component of the present invention is a specific element in the examples. It is not limited to only.

[0015]

According to the present invention, when the braking mode is switched, that is, when the valve means is switched from the restricted state to the open state, the transition state of the switching is set to the braking state of the wheel detected by the braking state detecting means. Determine accordingly.

For example, when the valve means is an on / off valve means (53) such as a differential pressure valve, when the on / off valve means is switched from the closed state to the open state in order to switch the braking mode, The operation of alternately switching the on / off valve means between the open state and the closed state is repeated. Further, the opening / closing duty ratio of the on / off valve means at this time is automatically determined according to the wheel deceleration detected by the deceleration detecting means (46).

If the on / off valve means is opened and closed in a short time when there is a difference in the hydraulic pressure between the hydraulic pressure generating means and the hydraulic braking means, the hydraulic pressure of the hydraulic braking means gradually rises, and eventually the hydraulic pressure. It becomes the same as the hydraulic pressure of the pressure generating means. In this case, the changing speed of the hydraulic pressure of the hydraulic braking means changes according to the opening / closing duty ratio of the on / off valve means. That is, when the opening / closing duty ratio is small (the opening time ratio is small), the hydraulic pressure of the hydraulic braking means rises slowly, and when the opening / closing duty ratio is large (the opening time ratio is large). The hydraulic pressure of the hydraulic braking means rises in a short time.

When a linear valve is used as the valve means, when the linear valve is switched from the fully closed state to the fully opened state in order to switch the braking mode, the opening degree of the linear valve is gradually increased, for example, in a step shape. Increase to. Further, the inclination of the opening change at this time (opening change speed) is automatically determined according to the wheel deceleration detected by the deceleration detecting means (46).

That is, since the opening / closing duty ratio of the on / off valve means or the inclination of the opening change of the linear valve is automatically determined according to the detected deceleration of the wheel, it depends on the driving situation. A desirable braking can be realized.

For example, in a front-wheel drive vehicle, the front wheels are the drive wheels, and regenerative braking can be performed only on the front wheels. Therefore, during braking, there may be a case where the front wheels are regeneratively braked and the rear wheels are hydraulically braked, and a case where the front wheels are regeneratively braked and the rear wheels are not braked. Here, when the rear wheels are hydraulically braked, the regeneration efficiency is reduced. Therefore, in order to improve the regeneration efficiency, it is considered that the rear wheels are not braked. However, if the rear wheels are not braked, the front wheels are likely to be locked ahead on low μ roads. Therefore, for example, when the front lock of the front wheels occurs, it is necessary to hydraulically brake the rear wheels to increase the braking force of the rear wheels.

In the invention of claim 1, the "predetermined condition"
For example, when "the front wheels are locked", the valve means is opened when the front wheels are locked, and the hydraulic pressure generated by the hydraulic pressure generating means can be directly applied to the hydraulic braking means. Therefore, it is possible to improve the regeneration efficiency and prevent the front wheel leading lock.
Even when the front wheels, which are the driving wheels, suddenly become unable to perform regenerative braking, the valve means is opened and the hydraulic pressure generated by the hydraulic pressure generating means is directly applied to the hydraulic braking means to increase the braking force by hydraulic braking. You can

Thus, according to the invention of claim 1,
By providing valve means (for example, a differential pressure valve or a linear valve) that opens when the "predetermined condition" is satisfied, regenerative braking efficiency can be improved and hydraulic braking can be applied under the "predetermined condition". .

Here, when the valve means is opened from the closed state, the braking force due to the hydraulic braking suddenly increases, which may cause a shock to the vehicle. However, in the invention of claim 1, switching is performed according to the braking state. By changing the transition state of
This shock can be relieved. The braking state may be estimated, for example, from the rotational deceleration of the wheels, or from the locked state or the slipped state of the wheels. If the rotation deceleration of the wheels is high, it is easy to lock the front wheels ahead of time, or if you want to stop the vehicle quickly.Therefore, at this time or when the wheels are about to lock, the slip ratio When becomes high, the duty ratio of opening / closing the valve means may be increased to promptly increase the braking force.

In the present invention, the valve means is normally closed for the driving wheel and the driven wheel so that only the hydraulic braking force equivalent to the braking force required by the driver minus the regenerative braking force is applied. There is. Therefore, the regeneration efficiency is increased. Here, since the driven wheel has a weaker braking force with respect to the drive wheel, the drive wheel easily locks in advance. Here, for example, the slip ratio detection means obtains the slip ratio of the drive wheel from the wheel speed of the drive wheel and the vehicle body speed, but when the slip ratio exceeds a predetermined value, the lock of the drive wheel starts and the rotation speed of the drive wheel decreases. The speed increases rapidly. Since the duty ratio of the valve means is determined according to the rotational deceleration of the drive wheel, the correspondence of the driven wheel can be determined according to the locked state. For example, if the rotation deceleration of the drive wheel is high, the hydraulic braking force of the driven wheel is quickly increased to prevent the drive wheel from being locked.If the rotation deceleration of the drive wheel is low, the hydraulic braking force of the driven wheel is slowly increased. It is possible to increase the braking force of the driven wheels while reducing the shock generated in the vehicle by increasing the. Therefore, when the preceding lock of the drive wheels occurs, it is possible to balance the urgency of the recovery of the preceding lock with the occurrence of the shock of the vehicle, and to take a preferable response according to the state of the vehicle.

The ideal braking force distribution line showing the ideal distribution of the braking force on the front wheel (Fr) side and the braking force on the rear wheel (Rr) side is
Generally, it becomes as shown by a virtual line in FIG. More preferable braking is performed as the actual braking force distribution approaches the ideal braking force distribution line. However, in a region above the ideal braking force distribution line, a behavior such as a spin is likely to occur in the vehicle. Therefore, the actual braking force distribution is generally shown by a dotted line in FIG. 7 so as not to exceed the ideal braking force distribution line. Is set as follows. In the case of an electric vehicle, in order to improve the efficiency of energy recovery by regenerative braking, the hydraulic braking system is decompressed and the braking force distribution (regeneration priority mode) shown by the solid line in FIG. 7 is made. Is desirable. However, when the slip ratio of the front wheels is large, there is a high possibility that the front wheels will be locked, and when the front wheels are locked, the braking force of the front wheels will not increase any further. Therefore, when the slip ratio of the front wheels is large, the braking force of the rear wheels is increased to bring the braking force distribution close to the ideal braking force distribution line (distribution shown by the dotted line in FIG. 7).

In claim 3, the driving wheels connecting the electric drive means are the front wheels (FR) and the rear wheels (RR) are the driven wheels. Therefore, if the braking force distribution is set as shown by the solid line in FIG. 7, for example. As compared with the rear wheels that are the driven wheels, the kinetic energy of the vehicle is consumed more by the front wheels that are the driving wheels, and the energy can be recovered with high efficiency by the regenerative braking of the driving wheels.

Further, in claim 4, when the predetermined condition is satisfied and the valve means is switched from the restricted state to the open state, the transition state of the switching is determined according to the degree of decrease of the regenerative braking force.

For example, when an abnormality appears in the voltage, current, temperature, etc. of the motor that is the drive source of the electric vehicle and the inverter that supplies power to the motor during regenerative braking, regenerative braking is performed. Although there is no choice but to stop braking and switch to hydraulic braking, even in such a case, there are cases where immediate switching is required (when regenerative braking is not possible) and cases where slow switching does not cause any problems. There is. In the latter case,
By slowly increasing the hydraulic braking force, the shock generated in the vehicle can be softened. But,
If the decreasing curve of the regenerative braking force and the increasing curve of the hydraulic braking force are different at the time of this switching, even if the brake pedal is constantly depressed, the braking force (fluid The pressure braking force + regenerative braking force) will fluctuate temporarily. According to the fourth aspect, the increasing curve of the hydraulic braking force is determined according to the degree of decrease of the regenerative braking force. Therefore, at the time of switching, the hydraulic braking force is adjusted so as to compensate for the decrease amount of the regenerative braking force. It is possible to increase and suppress the fluctuation of the braking force.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of main parts of a drive system and a braking system of an electric vehicle according to an embodiment. Referring to FIG. 1, in this embodiment, the front wheels Fr are driving wheels and the rear wheels Rr are driven wheels. The drive shaft of the electric motor 2, which is the drive source, is connected to the axle of the front wheel Fr via a transmission (T / M) 25. In FIG. 1, one front wheel Fr and one rear wheel Rr are omitted, but the vehicle of the embodiment is a four-wheel vehicle. Wheel cylinders (W / C) 5 for hydraulic braking are mounted near the respective wheels. Since the front wheels Fr are drive wheels, regenerative braking by the electric motor 2 is also possible.

First, the hydraulic system of FIG. 1 will be described. Hydraulic pressure corresponding to the stroke of the brake pedal 21 is generated at the output of the brake master cylinder (M / C) 4 and supplied to the front wheel side pipe 61 and the rear wheel side pipe 62. A relief valve 6, a check valve 29, a bypass valve 7, and an initial pressure cut valve 51 are inserted in parallel in a flow path connecting the pipe 61 and the pipe 63 of the wheel cylinder 5 (Fr) on the front wheel side. ing. Further, the pressure sensor 11 is installed in the pipe 61, and the pressure sensor 12 is installed in the pipe 63.

The pipe 62 and the wheel cylinder 5 on the rear wheel side
The relief valve 5 is provided in the flow path connecting to the (Rr) side pipe 64.
6, a check valve 54, a bypass valve 53, an initial pressure cut valve 55, and a bypass valve 52 are inserted in parallel. The bypass valve 52 has a role of releasing the decompression of Rr when Fr fails. Further, the pipe 64 and the wheel cylinder 5 (R
Proportioning valve 23 is inserted between r).

In the relief valve 6, the oil pressure in the pipe 61 is
When the hydraulic pressure of 3 is higher than a predetermined level, it opens and mechanically pipes 6
The differential pressure between 1 and the pipe 63 is controlled to be constant. Check valve 29
Is normally closed, but pipe 61
When the hydraulic pressure of the pipe 63 becomes higher than the hydraulic pressure of
The hydraulic pressure of 3 is released to the pipe 61. The bypass valve 7 is a solenoid valve, which is normally in a closed state. However, when a failure occurs in the electrical system, the bypass valve 7 is controlled to be opened so that the hydraulic pressure of the pipe 61 and the hydraulic pressure of the pipe 63 become the same. The initial pressure cut valve 51 opens when the hydraulic pressure in the pipe 61 is very low, and closes when the hydraulic pressure exceeds a predetermined level (when the initial pressure application to the wheel cylinder 5 (Fr) is completed).

Similarly, the relief valve 56 opens when the hydraulic pressure in the pipe 62 is higher than the hydraulic pressure in the pipe 64 by a predetermined amount or more, and mechanically controls the differential pressure between the pipe 62 and the pipe 64 to be constant. Although the check valve 54 is normally closed, when the hydraulic pressure in the pipe 64 becomes higher than the hydraulic pressure in the pipe 62 for some reason, the check valve 54 opens and allows the hydraulic pressure in the pipe 64 to escape to the pipe 62. Bypass valve 5
Reference numeral 3 denotes a solenoid valve, which is normally in a closed state, but is controlled to open mainly when a failure occurs in the electric system, and the pipe 62 is provided.
And the oil pressure of the pipe 64 are made the same. The initial pressure cut valve 55 opens when the hydraulic pressure in the pipe 61 is very low, and closes when the hydraulic pressure reaches or exceeds a predetermined level (when the initial pressure application to the wheel cylinder 5 (Rr) is completed). The bypass valve 52 is
Normally closed, but opened when the hydraulic pressure in the pipe 62 becomes higher than the pipe 61 by a predetermined level or more. Normally, the hydraulic pressure of the pipe 61 and the hydraulic pressure of the pipe 62 are the same.

The proportioning valve 23 operates when the inlet hydraulic pressure on the master cylinder 4 side is below a predetermined pressure.
The outlet side hydraulic pressure on the side of the cylinder 5 (Rr) is the same as the inlet side hydraulic pressure, and when the inlet side hydraulic pressure exceeds the predetermined pressure, the inlet side and the outlet side are separated, and the outlet side hydraulic pressure with respect to the change of the inlet side hydraulic pressure. It works to reduce the rate of change of. By providing the proportioning valve 23, the braking force distribution of the front and rear wheels by the hydraulic braking can be made to have a broken line characteristic as shown by, for example, a dotted line and a solid line in FIG. 7, and can be brought close to the ideal distribution line.

A brake switch 22 for detecting whether or not the brake pedal 21 is depressed is installed near the brake pedal 21. The potentiometer 28 is connected to an accelerator pedal (not shown) and detects a depression stroke of the accelerator pedal. In the vicinity of each wheel, a wheel speed sensor 57, 5 for detecting the speed of each wheel is provided.
8 are installed.

Next, the electric system will be described. The electric motor 2 used in this embodiment is an induction motor, and the rotor has magnetic poles formed by permanent magnets.
Three-phase windings are installed on the stator. By applying AC power to the three-phase windings of the stator, a rotating magnetic field can be generated and the rotor can be driven to rotate. Further, when the rotor of the electric motor 2 is rotating due to the rotation of the wheels, braking can be applied by generating a magnetic field in the direction of stopping the rotation in the winding of the stator. The electromotive force generated in the child winding can be recovered (regenerative braking) in the power supply. A detector 2a for detecting the position of the magnetic pole of the rotor is installed inside the electric motor 2.

A motor ECU 27 and a brake ECU 26 are provided as an electric circuit for controlling the electric motor 2. The motor ECU 27 and the brake ECU 26 each have a microcomputer inside, and the former mainly controls the driving of the electric motor 2 and the latter mainly controls the hydraulic braking and the regenerative braking. carry out. Further, the two microcomputers are connected to each other, and can exchange information with each other.

The structure of the main part of the motor ECU 27 is shown in FIG. Referring to FIG. 2, the motor ECU 27 is provided with an inverter INV, and three output lines L1, L2 and L3 of the inverter INV are connected to respective windings of the electric motor 2. . Inverter INV power line LP
And LM are respectively connected to the plus and minus terminals of the on-vehicle battery-1. For example, a lead-acid battery may be used as the vehicle battery-1, but a large-capacity capacitor, a sub-battery or the like may be connected in parallel with the lead-acid battery.

This inverter INV has six switching output transistors Q1, Q2, Q3, Q4, Q.
5 and Q6, the upper transistor Q1,
By turning on at least one of Q3 and Q5 and at least one of the lower transistors Q2, Q4 and Q6, a current can be passed from the battery-1 to each winding of the electric motor 2. However, transistors Q1, Q2, and Q
3 and Q4, and Q5 and Q6 do not turn on at the same time.

Transistors Q1, Q2, Q3, Q4, Q
The drivers DV1 and DV1 are connected to the control terminals of 5 and Q6, respectively.
The outputs of DV2, DV3, DV4, DV5 and DV6 are connected, and the input terminals of these drivers DV1 to DV6 are connected to the output ports of the microcomputer CPU. That is, a micro computer CPU
Are transistors Q1, Q2, Q3, Q4, Q5 and Q6
By controlling the on / off of each of the coils, the energization of each winding of the electric motor 2 is controlled.

In order to rotate the electric motor 2 continuously, the positions of the magnetic poles formed by the stator windings are sequentially arranged in the direction of driving the magnetic poles of the rotor of the electric motor 2. It is necessary to move to Microcomputer C
The PU determines the timing of the control signal applied to the drivers DV1 to DV6 based on the signal from the detector 2a built in the electric motor 2.

Further, by adjusting the timing of the control signal applied to the drivers DV1 to DV6, the electric mode is adjusted.
It is also possible to brake the rotation of the motor 2. During this braking, the electric motor 2 functions as a generator, so that electric power is induced in the stator winding, but this electric power is recovered by the battery-1.

That is, when the voltage of the output line L1 becomes higher than that of the power supply line LP due to the counter electromotive force generated by the stator winding, a current flows from the output line L1 to the power supply line LP through the diode D1. When the voltage of the output line L1 becomes lower than that of the power supply line LM, the output line L1
Current flows through the power source line LM from the diode D2 to charge the battery-1. Similarly, the output line L
2 becomes higher than the power supply line LP, a current flows from the output line L2 to the power supply line LP via the diode D3, and the voltage of the output line L2 changes to the power supply line LM.
Lower than that, the output line L2 to the diode D4
A current flows through the power supply line LM via and the battery-1 is charged. Further, when the voltage of the output line L3 becomes higher than that of the power supply line LP, a current flows from the output line L3 to the power supply line LP through the diode D5, and when the voltage of the output line L3 becomes lower than that of the power supply line LM, Power line L from output line L3 via diode D6
A current flows through M, and battery-1 is charged.

The description will be continued with reference to FIG. 1 again. The motor ECU 27 detects the depression amount of the accelerator pedal based on the signal output from the potentiometer 28, and controls the driving amount (rotation speed) of the electric motor 2 according to the depression amount. In addition, the brake ECU 26 executes the regenerative braking.
, The braking amount of the electric motor 2 is controlled according to the instruction. The drive torque and the braking amount of the electric motor 2 are adjusted by adjusting the pulse width of the signal applied to the control terminals of the transistors Q1, Q2, Q3, Q4, Q5 and Q6 of the inverter INV. .

The brake ECU 26 includes a pressure sensor 11
From the pressure sensor 12, the signal from the brake switch 22, the signal from the transmission 25, and the signal from the electric motor 2. Break ECU 26
Performs braking control based on these input signals, outputs information for regenerative braking to the motor ECU, and, for hydraulic braking, bypass valves 7 and 53 as necessary. ON / OFF control.

The main parts of the operation of the microcomputer provided in the brake ECU 26 are shown in FIGS. First, a description will be given with reference to FIG. When the power is turned on, initialization is first performed in step 31, and the process proceeds to step 32.

At step 32, the state of the ignition switch (IG_SW) is referred to, and while it is off, it waits, and when it is on, it proceeds to the next step 33. In step 33, the flag FA is referenced, and in step 34, the flag FB is referenced. When both the flags FA and FB are 0, the process proceeds to step 35, when FA is 0 and FB is not 0, the process proceeds to step 36, and when FA is not 0, the process proceeds to step 37.
Proceed to.

In step 35, the bypass valve 53 is closed (energization is turned on), and in the next step 36, the bypass valve 7 is closed (energization is turned on). By closing the bypass valve 53, the hydraulic pressure of the output of the master cylinder 4 becomes a predetermined value or more (ΔPr:
Until the release valve 56 determines), no hydraulic pressure other than the initial pressure is applied to the wheel cylinder 5 (Rr). Further, by closing the bypass valve 7, the hydraulic pressure of the output of the master cylinder 4 is equal to or higher than a predetermined value (ΔPr: relief valve 6
Wheel cylinder 5 (F
No hydraulic pressure other than the initial pressure is applied to r).

In step 37, the state of the electric motor 2 is detected. Specifically, the presence or absence of a failure of the electric motor 2, the current rotation speed (rpm) of the electric motor 2, the temperature of the electric motor 2, the voltage of the motor, the current, the inverter Enter the information. In the next step 38, the state of the battery-1 is detected. Specifically, information on the presence / absence of a failure of the battery-1, the depth of discharge of the battery-1, and the temperature of the battery-1 is input. In the next step 39, the state of the transmission 25 (shift position) is detected.

In step 3A, the above steps 37, 3
Based on the information input in 8, 39, etc., it is identified whether or not the condition for executing regenerative braking is satisfied. In this embodiment, if all of the following conditions are satisfied,
"Regenerative braking is possible".

A. Both the motor and the inverter have not failed, b. Within a predetermined range in which the voltages of the motor and the inverter operate normally, c. Within a predetermined range in which the currents of the motor and the inverter operate normally, d. Within a predetermined range in which both the motor and inverter temperatures operate normally, e. The rotation speed of the motor is within a range that the shaft, bearing, and gear can withstand. F. The voltage of the battery is within a predetermined range (a voltage that allows the motor and the inverter to operate normally, and a voltage that does not cause electrolysis), g. The current of the battery is within its allowable current range, h. The depth of discharge of the battery is within a chargeable range, i. The temperature of the battery is within its normal operating range, and j. The gear position of the transmission is other than back or neutral.

In the next step 3D, first the pressure sensor 1
The information of the master cylinder pressure Pm detected by 1 is input, then the information of the wheel cylinder pressure Pw detected by the pressure sensor 12 is input, and Pm and Pw are compared. If Pm = Pw, the process returns to step 32 through step 3B, and if not, the process proceeds to step 3E.

In step 3B, the discrimination result in step 3A is referred to identify whether the regeneration is prohibited or not. If the regeneration is prohibited, the process proceeds to step 3C. In step 3C, the flag FB is cleared, the bypass valve 53 is opened (energization off), the bypass valve 7 is opened (energization off), the flag FA is set to 1, and the process returns to step 32. By opening the bypass valves 53 and 7, the hydraulic pressure output from the master cylinder 4 is directly applied to the wheel cylinder 5 (Fr) and the pipe 64.

In step 3E, the identification result of step 3A is referred to. If the result of step 3A is not "regenerative braking is possible", that is, if the condition for prohibiting the regenerative operation due to a failure or the like during the regenerative braking operation is satisfied, it is determined that "regeneration must be stopped" and the process proceeds to step 3F. When the result of step 3A is "regenerative braking is possible", the process proceeds to step 41 of FIG.

In step 3F, an instruction to stop regenerative braking is output to the motor ECU, and the process proceeds to the next step 3G. At this time, a differential pressure (ΔPr) is generated between the pipe 61 and the pipe 63 by the relief valve 6, and the relief valve 56
Due to this, a pressure difference (ΔPr) is generated between the pipe 62 and the pipe 64.

In step 3G, the bypass valves 53 and 7
Open and close the valve, wait until the pressure difference disappears, then proceed to the next step 3H.
Proceed to. Here, since the regenerative braking force is lost, in order to quickly increase the hydraulic braking force, 8 mse of the map in FIG.
The hydraulic pressure is raised at a constant control time duty ratio with the steepest gradient of c open and 30 msec closed. That is, as shown in FIG. 9, the bypass valve 53 is opened and closed within a short time period, and the operation is repeated. On the other hand, in step 48 of FIG. 4, which will be described later, the hydraulic pressure increase in the pipes 63 and 64 is controlled in accordance with the rotation deceleration.

In step 41 of FIG. 4, first, the flag F
A and FB are cleared to 0, the information of the master cylinder pressure Pm detected by the pressure sensor 11 is input, and the information of the wheel cylinder pressure Pw detected by the pressure sensor 12 is input. Further, the differential pressure ΔP between Pm and Pw is calculated, and a predetermined function f
The differential pressure ΔP is substituted into () as a parameter to carry out the calculation, and the calculation result is taken as the regenerative braking amount M. Then, the regenerative braking amount M and the regenerative braking command are given to the motor ECU 27,
Perform regenerative braking.

In the next step 42, first, the traveling speed Vo of the vehicle body is detected based on the current rotation speed of the electric motor 2, and then the wheel speed of the front wheels is referred to by referring to the output of the wheel speed sensor 57. Vw is detected, and further, based on Vo and Vw,
Calculate the slip ratio S of the front wheels. S = (Vo-Vw) /
Vo.

In step 43, the slip ratio S obtained in step 42 is compared with the threshold value Sref. Sref> S
If so, the process returns to step 32 in FIG. Otherwise, proceed to step 45.

In step 45, the flag FB is set to 1. In the next step 46, the wheel deceleration G is obtained by differentiating the wheel speed of the front wheels with reference to the signal output from the wheel speed sensor 57. In the following step 47, the bypass valve 53
The pressure increasing characteristic when increasing the oil pressure of the rear wheel cylinder is determined by the control of. Specifically, using the control time map (see FIG. 9) held in advance in the memory, the open time and the close time are selected based on the rotation deceleration G obtained in step 46. For example, when the deceleration G is smaller than the threshold value α, the opening time is 3 msec and the closing time is 80 ms.
ec (opening / closing cycle is 83 msec). When the deceleration G is smaller than the threshold value β, the opening time is set to 8 msec,
The closing time is set to 30 msec (opening / closing cycle is 38 msec) (α
<Β). That is, the duty ratio of the opening time to the opening / closing cycle becomes larger when the rotation deceleration G (absolute value) is larger than when it is small.

In step 48, the bypass valve 53 is opened for the opening time obtained in step 47, and then the bypass valve 53 is closed for the closing time obtained in step 47. This opening / closing operation is repeated. In the next step 49, the master cylinder pressure Pm detected by the pressure sensor 11 is input, and in the following step 4A, the wheel cylinder pressure Pwr on the rear wheel side is obtained by estimation. In step 4B, the master cylinder pressure Pm
And the wheel cylinder pressure Pwr of the rear wheel are compared. If they do not match, the process returns to step 48 to repeat the above process, and if they match, the process returns to step 32 in FIG.

The process for estimating the wheel cylinder pressure Pwr on the rear wheel side will be described. Step 4 of FIG.
A more detailed view of the processing of parts 8, 49, 4A and 4B is shown in FIG. Further, there is generally a correlation between the wheel cylinder pressure Pw and the flow rate C as shown in FIG. Although C is calculated from Pw or Pw is calculated from C based on this characteristic, the characteristic is different for each device. Therefore, here, the result measured in advance is registered as a table in the memory of the computer. Yes, use the contents of this table.

In order to estimate the wheel cylinder pressure Pwr at an arbitrary time while the bypass valve 53 is opened and closed, the initial value Pwo of the wheel cylinder pressure is first obtained. Lily
Assuming that the differential pressure across the valve when the valve is opened is Pth (20 kg / cm ^{2 in} this example), when the master cylinder pressure Pm is larger than Pth when the bypass valve 53 is opened and closed, the relief valve is In the open state, the wheel cylinder pressure becomes Pm-Pth. If Pm is less than or equal to Pth, the relief valve is closed and the wheel cylinder pressure is zero.

Therefore, when N = 0, step 105
To 106, Pm and Pth are compared, and Pm> P
If th, in step 107 Pm-Pth is set to the initial value Pwo
If Pm ≦ Pth, the initial value Pw is obtained in step 108.
Set o to 0.

At step 109, the flow rate C0 at that time is obtained from the initial value Pwo of the wheel cylinder pressure by referring to the contents of the table storing the relationship of FIG. This flow rate C0 is Cx. The flow rate change of oil flowing through the wheel cylinder is expressed by the following equation.

[0066]

[Equation 1]

Therefore, the flow rate Cx at an arbitrary time point is obtained by sequentially calculating this equation, and from this flow rate Cx,
The wheel cylinder pressure Pwr is obtained based on the table showing the relationship shown in FIG. Actually, C in step 10C
After obtaining Pwr from x, next time Cx in step 10A
Is stored in Cp, Pwr is stored in Pp, and in step 10B, Cp is taken as the previous flow rate value, Pp is regarded as the latest wheel cylinder pressure, and the square root of (Pm-Pp) is multiplied by the coefficient β. The integrated value is added to Cp to obtain the current flow rate Cx. From this flow rate Cx, Pwr is obtained based on the table in the next step 10C.

The relationship between the master cylinder (M / C) pressure and the rear wheel wheel cylinder (W / C) pressure during braking in this embodiment is shown in FIG. 5, and the relationship between the vehicle body speed and the wheel speed is shown. 6, the distribution of the braking force on the front wheel (Fr) side and the braking force on the rear wheel (Rr) side is shown in FIG. 7, and the relationship between the master cylinder pressure and the braking force is shown in FIG.

First, description will be made with reference to FIG. In this embodiment, when the slip ratio S is small, the braking force distribution line is
The characteristic B2 is shifted considerably downward compared to the ideal braking force distribution line B1. That is, in the region where the braking force of the front wheels is smaller than Ba, the bypass valve 7 for the front wheels and the bypass valve 53 for the rear wheels are closed, so that the hydraulic brake force is 0 for both the front and rear wheels, and the front wheels are regenerated by the regenerative braking. Only braking force is generated.

In the region where the braking force of the front wheels is larger than Ba, the wheel cylinder 5 of the front wheels is passed through the relief valve 6.
Since hydraulic pressure is applied to (Fr) and hydraulic pressure is applied to the wheel cylinder 5 (Rr) of the rear wheel via the relief valve 56, the front wheel is affected by both the regenerative brake and the hydraulic brake. Further, braking force is generated on the rear wheels by the hydraulic brake.
The broken line of the braking force distribution line B2 is an effect of the proportioning valve 23.

When the slip ratio S is large, the braking force distribution line has a characteristic B3 closer to the ideal braking force distribution line B1. That is, since the bypass valve 53 of the rear wheel is opened, the pipe 6
Since the hydraulic pressure of 2 and the hydraulic pressure of the pipe 64 are the same, and the hydraulic pressure of the wheel cylinder 5 (Rr) of the rear wheels is increased as compared with the normal pressure, the braking force increases and the braking force distribution line moves upward. Shift to. By bringing the braking force distribution line closer to the ideal braking force distribution line B1, more effective braking is performed and the vehicle can be stopped at the shortest distance.

When the braking force is distributed according to the braking force distribution line B2, the ratio of using the regenerative braking is larger than that of the hydraulic braking, so that the energy can be efficiently recovered by the regenerative braking. However, in that case, the front wheels are more likely to lock than the rear wheels during braking. When the front wheels are locked, the braking force on the front wheels does not increase any more. Therefore, it is necessary to increase the braking force on the rear wheels in order to increase the braking force on the entire vehicle. Therefore, in this embodiment, when the front wheels are locked, the distribution of the braking force is switched from the braking force distribution line B2 to the braking force distribution line B3. For example, in FIG. 7, A on the braking force distribution line B2
When it is at the point, by opening the bypass valve 53, the braking force on the rear wheel side increases, and B on the braking force distribution line B3 is increased.
Move to the point. As a result, braking force acts on both the front and rear wheels,
The total braking force is increased.

However, if the braking force distribution line B2 is switched to the braking force distribution line B3 all at once, the brake pedal suddenly sinks, oily noise is generated, G shock is generated, and the vehicle is unstable. Occurs. In order to eliminate such a problem, in this embodiment, when the braking mode is switched from the braking force distribution line B2 to the braking force distribution line B3, the bypass valve 53 is used as in the case of a failure of regenerative braking. By repeating the opening and closing operation of the above in a short time, the change of the hydraulic pressure is moderated (step 48). In this case, the bypass valve 5
The opening time and closing time of No. 3 are determined based on the detected deceleration G of the wheel speed of the front wheels and the map shown in FIG. 9 (step 47).

As shown in FIG. 6, when the deceleration of the wheel speed is small, the wheels are locked (the wheel speed becomes 0).
However, when the deceleration of the wheel speed is large, the time until the wheel locks is short. In the former case, even if the hydraulic pressure is changed over a relatively long period of time, it takes time for the wheels to lock. Therefore, it is better to change the hydraulic pressure over a longer period of time because the brake pedal suddenly changes. It is effective in avoiding inconveniences such as sinking, oily noise, G shock, and unstable vehicle behavior. However, in the latter case, if the change in hydraulic pressure is too slow, the braking force when the wheels are locked may be insufficient, and braking may be delayed.

Depending on the detected deceleration G (absolute value) of the wheel speed of the front wheels, the hydraulic pressure is changed over a long time when G is small, and the hydraulic pressure is changed in a relatively short time when G is large. There is no braking delay, and
It is possible to minimize inconveniences such as sudden depression of the pedal, generation of oily noise, generation of G shock, and unstable behavior of the vehicle.

In the above embodiment, the wheel deceleration is determined and the duty ratio for opening / closing the bypass valve is changed according to the magnitude of the wheel deceleration. However, instead of the wheel deceleration, To detect the locked state of the wheels,
The opening / closing duty ratio of the bypass valve may be changed according to the locked state of the wheels. For example, the hydraulic pressure may be promptly changed when the wheels are locked or at the time when the wheels are likely to be locked. Further, the slip state of the wheel may be detected instead of the rotational deceleration of the wheel, and the duty ratio of opening / closing the bypass valve may be changed according to the slip state of the wheel. For example, the hydraulic pressure may be promptly changed when the slip amount of the wheel is large.
Further, the brake pedal force may be detected instead of the rotational deceleration of the wheel, and the hydraulic pressure may be promptly changed when the brake pedal force is large or the rate of change of the brake pedal force is high. .

FIG. 12 shows the configuration of one modified embodiment.
In this embodiment, linear valves 81 and 82 are used in place of the relief valve of the above embodiment. The opening of each of the linear valves 81 and 82 changes in proportion to the amount of electricity supplied. In this example, when the current is 0, it is fully opened, and when the current is large, the opening is small. In this embodiment, FIG.
The energization amount of the linear valve is controlled as shown in. That is, when the regenerative braking is performed, the differential pressure (Pm-Pw) at both ends of the linear valve is controlled to be constant and Pw ≧ 0. Is gradually decreased to increase the opening with time. As a result, the same effect as in the above embodiment can be obtained.

A modification of the control shown in FIG. 3 is shown in FIG.
In FIG. 15, the same steps as those in FIG. 3 are designated by the same step numbers. Referring to FIG. 15, the process corresponding to step 3F in FIG. 3 is performed in steps 3J, 3K, 3L.
Has been changed to. The changed processing will be described below.

At step 3J, the regenerative operation stop mode is determined. In this embodiment, four modes A, B, C and D are provided as the regenerative operation stop modes. The conditions for determining the mode are as follows.

A. When the motor or the inverter is out of order, the mode D, b1. When the voltages of the motor and the inverter are in the first abnormal range, mode A, b2. When the voltages of the motor and the inverter are in the second abnormal range, mode B, b3. When the voltages of the motor and the inverter are in the third abnormal range, mode C, c1. When the currents of the motor and the inverter are in the first abnormal range, mode A, c2. When the currents of the motor and the inverter are in the second abnormal range, mode B, c3. When the motor and inverter currents are in the third abnormal range, mode C, d1. When the temperatures of the motor and the inverter are in the first abnormal range, mode A, d2. When the temperatures of the motor and the inverter are in the second abnormal range, mode B, d3. When the temperatures of the motor and the inverter are in the third abnormal range, mode C, e1. When the rotation speed of the motor is within the first abnormal range, mode A, e2. When the rotation speed of the motor is in the second abnormal range, mode B, e3. When the rotation speed of the motor is in the third abnormal range, mode C, f1. When the voltage of the battery is in the first abnormal range, mode A, f2. When the voltage of the battery is in the second abnormal range, mode B, f3. When the voltage of the battery is in the third abnormal range, mode C, g1. When the current of the battery is in the first abnormal range, mode A, g2. When the current of the battery is in the second abnormal range, mode B, g3. When the current of the battery is in the third abnormal range, mode C, h1. When the depth of discharge of the battery is in the first abnormal range, mode A, h2. When the depth of discharge of the battery is in the second abnormal range, mode B, h3. When the depth of discharge of the battery is in the third abnormal range, mode C, i1. When the temperature of the battery is in the first abnormal range, mode A, i2. When the temperature of the battery is in the second abnormal range, mode B, i3. Mode C when the temperature of the battery is in the third abnormal range, and j. Mode D when the transmission is in the reverse or neutral position.

In step 3K, the motor ECU 27 is instructed to stop the regenerative braking operation. Actually, the code of the mode (one of A to D) at that time, which indicates the regenerative operation stop mode, is sent from the brake ECU 26 to the motor ECU 27. In that case, the motor EC
U27 gradually reduces the regenerative braking force at a predetermined reduction rate according to the received code (see FIG. 16).
Actually, as shown in the map of FIG. 14, each mode is associated with the decreasing speed (dM / dt) of the regenerative braking force, and dM / dt is the most when mode A is selected. Small, mo
Immediately at the time of de D, the regenerative braking force becomes 0 (the reduction speed is the fastest).

In step 3L, the bypass valve opening / closing time (opening time, closing time, opening / closing cycle) corresponding to the regenerative operation stop mode (any one of A to D) determined in step 3J.
Is read and determined from a map (see FIG. 14) held in advance on the brake ECU 26. Then, in the next step 3G, the opening / closing of the bypass valve 53 and the opening / closing of the bypass valve 7 are repeated according to the bypass valve opening / closing time determined in step 3L until Pm = Pw.

The increasing speed of the hydraulic braking force changes according to the opening / closing time of the bypass valves 53 and 7. Also, FIG.
As is clear from the map shown in FIG. 4, in this example, the decreasing speed (dM / dt) of the regenerative braking force and the bypass valves 53 and 7
Since there is a correlation with the opening / closing time of, there is also a correlation between the decreasing speed (dM / dt) of the regenerative braking force and the increasing speed of the hydraulic braking force. In reality, as shown in FIG. 16, the amount of decrease in the regenerative braking force and the amount of increase in the hydraulic braking force always match, and even when the regenerative operation is stopped, the total braking force (regenerative braking force + The dM / dt is related to the increasing speed of the hydraulic braking force so that the hydraulic braking force does not change.

In the above embodiment, the actual regenerative braking force decrease rate (dM / dt) matches the regenerative braking force decrease rate previously associated with the regenerative operation stop mode selected at that time. Since it is assumed that the motor EC
If U27 cannot precisely control the regenerative braking force, the error between the decrease in the regenerative braking force and the increase in the hydraulic braking force may increase. In such a case, use a sensor to measure, for example, the regenerative current value and voltage value, calculate the actual regenerative braking force, and increase the hydraulic braking force to compensate for the change in the calculated regenerative braking force. The speed (opening / closing time of the bypass valves 53 and 7) may be determined.

[0085]

As described above, according to the present invention, the transition state of the switching of the valve means from the restricted state to the open state is automatically performed according to the detected braking state, for example, the rotational deceleration of the wheel. Since it is changed, it is possible to realize preferable braking according to the driving situation. For example, when the braking force of the front wheels is distributed more than that of the rear wheels, the front wheels are easier to lock than the rear wheels, but when the front wheels are locked, the braking force does not increase any further. It is necessary to lift the restriction of the valve means and increase the braking force of the rear wheels. When the rotational deceleration of the wheels is large, the front wheels lock quickly, so by increasing the braking force of the rear wheels in a short time,
It is possible to quickly compensate for the lack of braking force and avoid delay in braking. Also, when the wheel rotation deceleration is small,
There is enough time to lock the front wheels,
In order to avoid the inconvenience caused by the sudden increase in pressure of the hydraulic braking means, the opening / closing duty ratio of the on / off valve means or the inclination of the opening degree change of the linear valve is made small, and the rear wheel It is desirable to increase the braking force. That is, braking delay does not occur, and no heavy oil noise or unstable vehicle behavior occurs.

Further, according to the second aspect, when the slip of the driving wheel is detected, the opening / closing operation of the valve means of the driven wheel is repeated according to the duty ratio determined according to the rotation deceleration of the driving wheel. Since the braking force of the hydraulic braking system of the driving wheels can be increased to bring the braking force distribution closer to the ideal braking force distribution line, it is possible to minimize the braking distance.

In the third aspect, since the drive wheels connecting the electric drive means are the front wheels (FR) and the rear wheels (RR) are the driven wheels, if the braking force distribution is set as shown by the solid line in FIG. 7, for example. As compared with the rear wheels that are the driven wheels, the kinetic energy of the vehicle is consumed more by the front wheels that are the driving wheels, and the energy can be recovered with high efficiency by the regenerative braking of the driving wheels.

According to the fourth aspect, when the valve means is switched from the restricted state to the open state, the transition state of the switching is determined according to the degree of decrease of the regenerative braking force, so that the hydraulic braking force is increased. The curve is determined according to the degree of decrease in the regenerative braking force, and the hydraulic braking force can be increased so as to compensate for the decrease in the regenerative braking force, and fluctuations in the braking force can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing main parts of a drive system and a braking system of an electric vehicle of an embodiment.

FIG. 2 is a block diagram showing a main part configuration of the motor ECU shown in FIG.

FIG. 3 is a flowchart showing the operation of the brake ECU of FIG.

FIG. 4 is a flowchart showing the operation of the brake ECU of FIG.

FIG. 5 is a time chart showing an example of a change in hydraulic pressure of the device shown in FIG.

FIG. 6 is a time chart showing a change in speed of a vehicle wheel and a vehicle body during braking.

FIG. 7 is a graph showing distribution of braking force between front wheels and rear wheels.

FIG. 8 is a graph showing the relationship between master cylinder hydraulic pressure and braking force.

9 is a map showing a part of the memory contents on the brake ECU of FIG. 1. FIG.

FIG. 10 is a graph showing the relationship between W / C pressure and flow rate.

FIG. 11 is a flowchart showing details of a part of FIG. 4.

FIG. 12 is a block diagram showing a configuration of a modified example.

13 is a time chart showing the operation of the apparatus of FIG.

FIG. 14 is a diagram showing the data on the memory used in the embodiment of FIG.
It is a map showing a part of the data.

FIG. 15 is a flowchart showing the operation of the brake ECU of one modified embodiment.

FIG. 16 is a time chart showing changes in braking force.

[Explanation of symbols]

1: Battery-2: Electric motor 4: Master cylinder (M / C) 5 (Fr), 5 (Rr): Wheel cylinder (W / C) 6,56: Relief valve 7,52,53 : Bypass valve 11, 12: Pressure sensor 21: Brake pedal 22: Brake switch 23: Proportioning valve 25: Transmission 26: Brake EC
U 27: Motor ECU 28: Potentiometer 29, 54: Check valve 51, 55: Initial pressure cut valve 57, 58: Wheel speed sensor 61, 62, 63,
64: Piping 81, 82: Linear valve Fr: Front wheel Rr: Rear wheel D1 to D6: Diode

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Osamu Ohori 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Toshiyuki Sakai 2-1-1, Asahi Town, Kariya City, Aichi Prefecture Within Seiki Co., Ltd.

Claims (4)

[Claims] 1. An on-board battery for storing electric energy; an electric drive means for driving a wheel by electric power from the on-board battery; an electric power generated by the electric drive means as the wheel rotates; Regenerative braking means for returning to the on-board battery; hydraulic pressure generating means for generating hydraulic pressure according to the operation amount of the brake pedal; hydraulic pressure for applying braking force to wheels according to hydraulic pressure generated by the hydraulic pressure generating means A braking device for an electric vehicle, comprising: braking means; and valve means for limiting transmission of hydraulic pressure from the hydraulic pressure generating means to the hydraulic braking means. In the case where the restriction is released and the hydraulic pressure of the hydraulic pressure generating means is supplied to the hydraulic braking means: a braking state detecting means for detecting a braking state of a wheel; Switch to open state And a switching control means for determining the transition state of the switching according to the braking state of the wheel detected by the braking state detecting means.
Braking device for electric vehicles. 2. The switching control means determines a duty that is determined according to a rotational deceleration of the drive wheel when the drive wheel slips.
The braking device for an electric vehicle according to claim 1, wherein the opening / closing operation of the valve means of the driven wheels is repeated according to the tee ratio. 3. The braking device for an electric vehicle according to claim 2, wherein the drive wheels connecting the electric drive means are front wheels and the rear wheels are driven wheels. 4. The switching control means determines a transition state of switching in accordance with a degree of decrease in regenerative braking force when the valve means is switched from a restricted state to an open state when the predetermined condition is satisfied. The braking device for an electric vehicle according to claim 1.