JPH09104333A - Braking device for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a high regenerating braking force without a valve to cut off an oil pressure according to regeneration and as drive wheel lock is prevented from occurring. SOLUTION: In a case of a rear wheel-drive automobile, a regenerative braking force is controlled in such a manner that a braking force line in a regeneration and oil pressure total does not run across a rear lock prohibition region on a braking force distribution diagram between front and rear wheels. In a case of a front wheel-drive automobile, a regenerative braking force is controlled in such a manner that a braking force line in a regeneration and oil pressure total is prevented from extending across a front lock prohibition region on a braking force distribution diagram between front and rear wheels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric vehicle that uses both fluid pressure braking (for example, hydraulic braking) and regenerative braking,
In particular, it relates to a braking device used in this electric vehicle.

[0002]

2. Description of the Related Art In an electric vehicle such as an electric vehicle propelled by a motor, fluid pressure braking utilizing an incompressible fluid such as hydraulic braking, and regenerative braking for recovering braking energy by a vehicle running motor are performed. It is possible. Regenerative braking is superior to fluid pressure braking in that braking energy can be collected in a battery for driving a motor, etc., and thus contributes to improvement of vehicle energy efficiency. In the prior art disclosed in Japanese Patent Application Laid-Open No. 5-161211, etc., regenerative braking is preferentially used over fluid pressure braking. Therefore, a valve is used to interrupt hydraulic pressure transmission and instead apply regenerative braking force. , Is used.

[0003]

The method using a valve has a problem that a valve and a member such as a sensor attached to the valve are required and a cost for the method is generated. In order to avoid this, for example, as shown in FIG. 6, a predetermined regenerative braking force is applied at the same time when the brake pedal is depressed, and the hydraulic pressure on the front wheel side (“front hydraulic pressure” in the figure) and the hydraulic pressure on the rear wheel side ( Regeneration control may be performed such that the "rear hydraulic pressure" in the figure is not shut off (see also Japanese Patent Laid-Open No. 5-161213). However, the method of FIG. 6 has a problem that the regenerative braking force cannot be increased so much and the energy efficiency of the vehicle cannot be improved so much in order to ensure vehicle stability.

For example, assume that the method of FIG. 6 is applied to a rear-wheel drive vehicle, for example. In this case, as shown in FIG. 7, the braking force line of the total regenerative / hydraulic pressure is biased to the rear side (more generally to the driving wheel side) in the front-rear wheel braking force distribution diagram. If this total braking force line is largely biased toward the rear side, rear lock is likely to occur and vehicle stability is impaired. Therefore, when the method of FIG. 6 is carried out, the hydraulic pressure in FIG. 6 should be adjusted so that the rear lock does not occur, specifically, the total braking force line does not cross the rear lock prohibited area defined by law. The regenerative braking force to be added to the braking force must be set. Even when the method of FIG. 6 is applied to a front-wheel drive vehicle, it is necessary to similarly set the front lock prohibited area. Under such a setting, the ratio of the regenerative braking force to the hydraulic braking force becomes low in the normal use region at the lower left of the broken line in FIG. 7, that is, in the region where a relatively low deceleration is sufficient, which is sufficient. Cannot recover energy.

The present invention has been made to solve the above problems, and a valve for shutting off fluid pressure such as hydraulic pressure according to regeneration is used by improving a control method of regenerative braking force. It is an object of the present invention to realize an electric vehicle that can perform sufficient energy recovery without doing so and without locking the drive wheels.

[0006]

In order to achieve such an object, the braking device for an electric vehicle according to the first aspect of the present invention applies a fluid pressure braking force corresponding to a required braking force to at least the driving wheels. And a means for applying a regenerative braking force to the drive wheels by the vehicle drive motor, and a total braking force line indicating the sum of the fluid pressure braking force and the regenerative braking force on the front and rear wheel braking force distribution diagram. Means for controlling the regenerative braking force so as to be located at or near the lock limit. In this way, in this configuration, the regenerative braking force is controlled so as to be maximized within the range where the drive wheels are not locked. Therefore, the braking energy can be sufficiently recovered.
Further, it is not necessary to cut off the fluid pressure braking force, and therefore, the valve for cutting off the fluid pressure according to regeneration and the member associated therewith can be eliminated.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an electric vehicle according to an embodiment of the present invention. In the figure, thick lines indicate electric power wiring, broken lines indicate electric signal wiring, and solid lines indicate hydraulic piping. The electric vehicle shown in this figure is a rear-wheel drive vehicle, and uses a three-phase AC motor as the vehicle driving motor 11. Driving power is supplied to the motor 11 from the battery 13 via the inverter 12. The inverter 12 converts the output of the battery 13 from DC to three-phase AC under the control of the motor ECU (electronic control unit) 14. The motor ECU 14 determines the power running torque command value based on the accelerator opening during power running, and regenerates E during braking.
The regenerative torque command value Treg is input from the CU 16. The motor ECU 14 refers to the state of charge (SOC) of the battery 13 detected by the battery ECU 15 and controls the power conversion operation by the inverter 12 based on these torque command values, so that the torque according to the torque command value is controlled. Is output from the motor 11. Motor ECU 14
Also supplies information such as SOC to the regenerative ECU 16.

When the vehicle operator depresses the brake pedal 1, hydraulic pressure Pmc starts to be generated in the master cylinder 2 in response to this. When the hydraulic pressure sensor 3 detects that the hydraulic pressure Pmc has begun to be generated, the regenerative ECU 16 thereafter determines the regenerative torque command value Treg by executing the procedure described below, and outputs this to the motor ECU 14. Further, the master cylinder 2 is connected to the front and rear wheel cylinders 6 and 4 without passing through a valve for shutting off hydraulic pressure according to regeneration. Therefore, ABS
Except when the (antilock brake system) is operating, when the hydraulic pressure Pmc is generated, the hydraulic pressure Pmc acts on the front and rear brake discs 7 and 5 as a hydraulic braking force without being interrupted. In the figure, reference numeral 8
P is provided between the rear hydraulic chamber of the master cylinder 1 and the rear wheel cylinder 4 in order to give ideal distribution to the hydraulic braking force or front and rear wheel distribution close thereto.
(Proportioning) Valve 8.

FIG. 2 shows an example of the operation flow of the regenerative ECU 16. As shown in this figure, regenerative E
The CU 16 executes a predetermined initialization process (100).
The operation after step 101 is started. At that time, reincarnation E
The CU 16 first determines whether or not the brake pedal 1 is depressed, by determining whether or not the hydraulic pressure Pmc exceeds a predetermined minute value, or based on the state of a brake switch (not shown) attached to the brake pedal 1, It is detected (101). When the brake pedal 1 is stepped on, the regenerative ECU 16 determines whether the front wheels or the rear wheels are slipping (102). This determination can be performed by detecting the speed of each wheel (wheel speed) and the speed of the vehicle (vehicle speed), and determining the difference between the two by a threshold value.

When it can be considered that none of the wheels has slipped, the regenerative ECU 16 determines the charging upper limit power, that is, the motor 11 to the battery 1 based on the SOC of the battery 13.
Calculate the maximum power Pbatt that can be regenerated to 3 (10
3). In general, the output of the motor 11 can be represented by the product of the number of rotations and the torque, so that the charging upper limit power Pbat
When t is determined, the curve “battery constraint upper limit” in FIG. 3 is determined.
The curve "motor rating" in FIG. 3 shows the characteristic of the maximum output torque (maximum regenerative torque) of the motor 11 during regeneration with respect to the motor rotational speed wm. This characteristic is the motor 1
Since the maximum regenerative torque is limited by the rated power Pmot of 1, the maximum regenerative torque includes a high rotation region in which the maximum regenerative torque is inversely proportional to the motor rotation speed wm, and a low rotation region in which the maximum regenerative torque is substantially constant.
Therefore, the regenerative ECU 16 limits the maximum regenerative torque by the rated power Pmot, and the charging upper limit power Pb of the battery 13.
In order to reflect both the limitation of the regenerative electric power by att in the determination of the regenerative torque command value Treg, the following equation

## EQU1 ## The power constraint value Pmax is obtained according to Pmax = Min (Pmot, Pbatt), and this is further calculated by the following equation.

## EQU2 ## Conversion to the regenerative torque upper limit value Tmax according to Tmax = Pmax / wm (10
4). However, in these expressions, Min (·) is a minimum value function. Although not shown, the rotation speed wm can be detected by a sensor attached to the motor 11 or can be estimated from the current flowing through the inverter 12.

Next, the regenerative ECU 16 refers to the map PmcMAP shown in FIG. 4 with the hydraulic pressure Pmc to determine the regenerative torque command value.

## EQU00003 ## Treg = PmcMAP (Pmc) is obtained and is calculated by the following equation.

## EQU4 ## The upper limit is set according to Treg = Min (Treg, Tmax) (105), and the motor ECU 14
(107). The map shown in FIG. 4 shows the hydraulic pressure P.
mc is a map that associates mc with the regenerative torque command value Treg, and the content thereof is the total braking force distribution line obtained by adding the regenerative braking force to the hydraulic braking force determined by the P valve 8 on the front and rear wheel braking force distribution diagram. It is set so that it is located at a position where it does not cross the rear lock prohibited area (see FIG. 5). The regenerative ECU 16 also executes step 105.
After execution, prior to step 107, regenerative torque command value Tre
g is low-pass filtered to smooth out its rise (106).

The above operation is repeated until the key switch (not shown) is turned off by the vehicle operator (10).
8). When it is determined in step 109 that one of the wheels is slipping or is about to slip, the regenerative ECU 16 causes the ABS ECU 9 and / or
Alternatively, the wheel cylinder 4 may be formed in a predetermined pattern using 10 or 10.
The hydraulic pressures of 6 and 6 are changed (109). When it is determined in step 101 that the brake pedal 1 is not depressed, the regenerative ECU 16 determines that the regenerative torque command value Tr
Eg is set to 0 (110). Step 109 or 110
After execution, step 106 is executed. Step 108
When it is detected that the key switch is off, the process of (111) in FIG. 2 ends after a predetermined end process.

As described above, in the present embodiment, since the valve for shutting off the fluid pressure such as the hydraulic pressure according to the regeneration is not used, the valve and the members such as the sensor attached thereto are not required, and the cost is lower. A system having a simple structure can be realized. The operation procedure of the regenerative ECU 16 may be simple. Further, since the regenerative torque command value Treg is determined using the map of FIG. 4, the maximum regenerative braking force can be obtained within the range where the rear lock is not performed, that is, without impairing the vehicle stability. The braking energy can be satisfactorily recovered even in a region where the braking force is low (normal use region located on the lower left side of the broken line in FIG. 5). In addition, the regenerative torque command value Tr
Since eg is low-pass filtered, regenerative torque does not suddenly occur at the initial stage of braking (when the brake pedal 1 is started to be depressed), and the linearity of the brake pedal depression force and the braking force is relatively good. This leads to improved brake feeling. Furthermore, since the upper limit of the regenerative torque command value Treg is limited by the regenerative torque upper limit value Tmax determined based on the motor rating Pmot and the charging upper limit power Pbatt, the rating of the motor 11 and the S of the battery 13 are limited.
It is possible to achieve both regeneration limitation by OC and maximum recovery of braking energy.

In the above description, an electric vehicle is taken as an example, but the present invention can be applied to various electric vehicles that use both fluid pressure braking and regenerative braking. Further, the invention is not limited to the rear-wheel drive vehicle, but can be applied to the front-wheel drive vehicle and the four-wheel drive vehicle.

Further, in the above-described embodiment, the boundary line of the rear lock prohibited area defined by law is treated as the rear lock limit. However, the braking force distribution for actually locking the rear wheels and the rear lock prohibited area are treated. Does not necessarily coincide with the boundary line of. Considering this point, in the above-described embodiment, ABS is used together to surely prevent slip. However, since it is determined in step 102 whether or not the wheels are slipping (or whether or not there is a tendency), this is used to significantly reduce the operating frequency of the ABS or abolish the ABS. It is possible. That is, the contents of the map of FIG. 4 are updated based on the braking force distribution when the wheel slip is detected in step 102, or a plurality of maps of FIG. 4 are prepared in advance for each friction coefficient of the road surface. It is only necessary to add to step 109 a procedure of selecting one of the maps based on the braking force distribution when the wheel slip is detected in step 102. In this way, by updating or selecting the map according to the friction coefficient of the road surface, regenerative braking force control adapted to the friction coefficient becomes possible, and more braking energy can be recovered. When ABS is abolished, the device configuration becomes simple.

[0017]

As described above, according to the first configuration of the present invention, the regenerative control is performed so that the total braking force line is located at or near the drive wheel lock limit on the front-rear wheel braking force distribution diagram. Since the power is controlled, it is possible to recover a large amount of braking energy while preventing the driving wheels from locking. Further, it is not necessary to cut off the fluid pressure braking force, and therefore the valve for cutting off the fluid pressure according to the regeneration and the member associated therewith can be eliminated, and the cost can be reduced.

[0018]

[Addendum] The present invention can be understood as the following inventions.

(1) In the braking control device according to the second aspect of the present invention, a means for causing at least the drive wheels to exert a fluid pressure braking force corresponding to the required braking force, and a vehicle running motor to regenerate the drive wheels. Means for applying power, and mounted on an electric vehicle comprising: a front and rear wheel braking force distribution diagram, so that the total braking force line is located at or near the drive wheel lock limit,
It is characterized by having a means for controlling the regenerative braking force.
According to this configuration, the same operational effect as the first configuration can be obtained.

(2) In the braking method according to the third aspect of the present invention, the step of applying a fluid pressure braking force corresponding to the required braking force to at least the driving wheels, and the above-mentioned total on the braking force distribution diagram between the front and rear wheels. A step of applying a regenerative braking force to the drive wheels by the vehicle traveling motor so that the braking force line is located at or near the drive wheel lock limit, and is executed by the electric vehicle. . According to this configuration, the same operational effect as the first configuration can be obtained.

(3) A fourth structure of the present invention is characterized in that, in the first to third structures, a drive wheel lock limit which changes according to a friction coefficient of a traveling road is detected. According to this configuration, the regenerative braking force control adapted to the friction coefficient of the traveling road can be further performed, and more braking energy can be recovered.

(4) In the fifth configuration of the present invention, in the first to fourth configurations, when the regenerative braking force is applied, it rises (for example, low-pass filtering is performed).
It is characterized by the following. According to this configuration, when the braking force request is generated, the regenerative braking force does not act immediately, but the regenerative braking force gradually acts, so that, for example, the brake feeling becomes good in a region where the deceleration is low.

(5) The sixth structure of the present invention is the first to fifth structures, wherein the maximum torque that can be output from the vehicle driving motor and / or the maximum regenerative power that can be received by the motor driving battery. Set the upper limit of the regenerative braking force in accordance with the above, and apply the regenerative braking force to the drive wheels with the vehicle drive motor so that the total braking force line approaches the drive wheel lock limit as much as possible within the range below the set upper limit. Is characterized by.
According to this configuration, even when the upper limit of the regenerative braking force is limited according to the rating of the vehicle traveling motor and the charging state of the motor driving battery, the braking energy can be maximized.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing a flow of operations of a regenerative ECU in this embodiment.

FIG. 3 is a rotational speed vs. regenerative torque characteristic diagram showing a method for determining a regenerative torque upper limit value in this embodiment.

FIG. 4 is a map diagram showing a method of determining a regenerative torque command value in this embodiment.

FIG. 5 is a diagram showing a braking force distribution between front and rear wheels in this embodiment.

FIG. 6 is a diagram showing a pedaling force-braking force characteristic at the time of constant regeneration.

FIG. 7 is a diagram showing a braking force distribution between front and rear wheels when regeneration is constant.

[Explanation of symbols]

1 brake pedal, 2 master cylinder, 3 oil pressure sensor, 4,6 wheel cylinder, 5,7 brake disc, 8 P (proportioning valve) valve,
9,10 ABS (anti-lock brake system) valve, 11 motor, 12 inverter, 13 battery,
14-16 ECU (electronic control unit), Pbatt
Charge upper limit power, Tmax regenerative torque upper limit value, Tr
egg Regenerative torque command value.

Claims (1)

[Claims] 1. A means for exerting a fluid pressure braking force on at least a driving wheel according to a required braking force, a means for exerting a regenerative braking force on a driving wheel by a vehicle traveling motor, and a braking force distribution diagram between front and rear wheels. And a means for controlling the regenerative braking force so that the total braking force line indicating the sum of the fluid pressure braking force and the regenerative braking force is located at or near the drive wheel lock limit, and the braking of the electric vehicle is characterized by: apparatus.