JP3344144B2 - Brake control device for electric vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking control device for an electric vehicle which is mounted on an electric vehicle such as an electric vehicle and controls a regenerative braking force and a fluid pressure braking force.

[0002]

2. Description of the Related Art An electric vehicle is a type of electric vehicle that can use both hydraulic braking (generally, hydraulic braking with an incompressible fluid) and regenerative braking as braking means. Among these braking means, the regenerative braking has an advantage that at least a part of the braking energy can be regenerated to a vehicle-mounted battery or the like, so that power efficiency is high. Therefore, by using the regenerative braking with priority to the hydraulic braking, the power efficiency of the vehicle can be improved, and the travelable distance per charge of the battery can be extended. As a technique for giving priority to the regenerative braking force as compared with the hydraulic braking force, for example, Japanese Unexamined Patent Publication No.
There is one disclosed in JP-A-153313. In this publication, the shortage of the regenerative braking force with respect to the required braking force (the amount of depression of the brake pedal) is compensated by the introduction of the hydraulic braking force.

[0003]

As described above, according to the system configuration in which the regenerative braking force and the hydraulic braking force are used in combination, the shortage of the regenerative braking force with respect to the required braking force is compensated by the hydraulic braking force. Since the regenerative braking force can be used with priority, the power efficiency of the vehicle can be improved. However, when hydraulic braking force is introduced due to lack of regenerative braking force in this type of system, if the hydraulic braking force is rapidly introduced, so-called pedal entry occurs, and the brake pedal feeling deteriorates. . In order to prevent or mitigate such deterioration of the pedal feeling, it is only necessary to avoid a rapid increase in the hydraulic braking force when introducing the hydraulic braking force. That is, the hydraulic braking force may be gradually introduced at a time earlier than the time when the hydraulic braking force should be introduced. On the other hand, since the total braking force of the regenerative and hydraulic pressures needs to match the required braking force, at the same time, the regenerative braking force is reduced earlier than it should be. By performing such control, that is, delay control of the regenerative braking force and the hydraulic braking force, while realizing the required braking force by the sum of the regenerative and hydraulic pressures, and using the regenerative brake prior to the hydraulic pressure as described above, This can alleviate or prevent the deterioration of the pedal feeling.

However, simply executing such delay control causes another problem. That is, when performing the above-described delay control, instead of gradually introducing the hydraulic braking force, the regenerative braking force is reduced earlier than it should be, so that the required braking force is accurately realized. I have to. If the regenerative braking force is reduced earlier than it should be, it becomes impossible to recover the corresponding braking energy as regenerative power in the battery. Therefore, even though the regenerative power acceptability of the battery is good, that is, even when the state of charge (SOC) of the battery is low, a loss occurs in the regenerative power.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is possible to prevent or reduce regenerative power loss by improving a procedure related to delay control. An object of the present invention is to make it possible to solve the problem associated with the upper limit of the battery voltage, which has been executed to prevent overcharging of the battery.

[0006]

In order to achieve the above object, the present invention provides a motor for driving a vehicle, a battery which supplies driving power to the motor while being charged by regenerative power from the motor, and In a braking control device mounted on an electric vehicle having a fluid pressure braking system that applies a fluid pressure braking force to at least drive wheels and controlling a regenerative braking force by controlling a motor, a regenerative power acceptability of a battery and a rotation speed of the motor are controlled. A means for detecting the maximum regenerative braking force, based on the control characteristic of the motor, in which the regenerative braking force is reduced and the fluid pressure braking force is introduced as the rotational speed decreases, and based on the rotational speed of the motor. Means for controlling the regenerative braking force as a target and the maximum regenerative braking force as a limit, while controlling the fluid pressure braking force as a target for the shortage of the regenerative braking force with respect to the required braking force; Means for changing the control characteristic according to the regenerative power acceptability of the battery, such that the rotational speed of the motor at which the fluid pressure braking force starts to be introduced with a decrease in the rotational speed is higher as the regenerative power acceptability is lower, It is characterized by having.

[0007]

In the present invention, first, the regenerative power acceptability of the battery and the number of revolutions of the motor are detected. When the rotational speed of the motor is detected, the maximum regenerative braking force is determined based on the rotational speed of the motor. The maximum regenerative braking force is given in accordance with a control characteristic in which the regenerative braking force is reduced as the rotational speed decreases and the fluid pressure braking force is introduced. Furthermore, the regenerative braking force is
Control is performed with a target braking force given in the form of the amount of depression of the brake pedal or the like by the vehicle operator as a target. At this time, the upper limit of the regenerative braking force is limited by the maximum regenerative braking force obtained as described above. The resulting shortage, ie, the shortage of the regenerative braking force with respect to the required braking force, is compensated by the introduction of the hydraulic braking force.

Here, in the present invention, the rotation speed at which the delay control is started is changed by the above-described control characteristic changing process so that the lower the regenerative power acceptability, the higher the rotation speed. That is, when the rotational speed of the motor decreases as the braking progresses, the regenerative braking force is reduced and the fluid pressure braking force is introduced as the rotational speed decreases. Fluid pressure braking force starts to be introduced instead of minutes (start of delay control). In the present invention, the rotational speed of the motor at which the delay control is started is changed and set so that the lower the regenerative power acceptability, the higher the rotational speed. A situation in which the battery continues to be charged in a state that is likely to occur is less likely to occur, and the reliability of the system is improved. Also,
If the regenerative power acceptability is high, the motor speed at which the delay control is started will be lower, so the regenerative power loss due to the delay control, more strictly the speed at which the delay control is started, is fixed As a result, the loss of regenerative power due to the operation is eliminated, and a more power-efficient system can be obtained.

[0009]

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

FIG. 1 shows a system configuration of an electric vehicle according to one embodiment of the present invention. The electric vehicle shown in this figure is a front-wheel drive vehicle, and a motor 10 is provided on the axle of the front wheels. The driving power of the motor 10 is supplied from a battery 14 via an inverter 12. The inverter 12 converts DC power supplied from the battery 14 into AC power and supplies the AC power to the motor 10 under the control of the EV ECU 16. When powering the motor 10, the EV ECU 16 determines a torque command based on information such as the amount of depression of an accelerator pedal provided from the outside and a motor rotation speed ω obtained by a rotation sensor 17 attached to the motor 10. The power conversion operation of the inverter 12 is controlled based on the torque command. As a result, the output torque of the motor 10 becomes a value corresponding to the depression amount of the accelerator pedal and the like.

The electric vehicle shown in FIG. 1 has both hydraulic braking and regenerative braking as braking means. First, as a hydraulic braking system, a master cylinder 20 that internally generates a hydraulic pressure corresponding to the amount of depression of a brake pedal 18, wheel cylinders 22 and 24 that apply a hydraulic braking force to front wheels or rear wheels, respectively, and a master cylinder 20.
And hydraulic pressure control valves 26 and 28 for controlling hydraulic pressure transmission from the hydraulic cylinders to the wheel cylinders 22 and 24. The hydraulic control valves 26 and 28 are valves controlled by the regenerative ECU 30. The regenerative ECU 30 detects the master cylinder 20 detected by the hydraulic sensors 32 and 34.
The hydraulic control valves 26 and 28 are controlled based on the hydraulic pressures on the side and the wheel cylinder 22 and according to predetermined control characteristics. This control is performed such that the braking force distribution between the front and rear wheels becomes the target distribution, and the braking force relating to the front wheels, which are the driving wheels, becomes the distribution giving priority to the regenerative braking force. Therefore, regeneration E
The CU 30 exchanges information with the EV ECU 16. Further, the regenerative ECU 30 inputs the SOC of the battery 14 detected by the battery ECU 36.

In this figure, a disc brake is used for a front wheel and a drum brake is used for a rear wheel. However, the present invention is not affected by the type of brake for the front and rear wheels. It is not limited to a front wheel drive vehicle.

FIG. 2 shows a regenerative ECU in this embodiment.
The procedure of the regenerative braking control executed by 30 is shown.

As shown in FIG.
First, based on the hydraulic pressure (master cylinder pressure) in the master cylinder 20 detected by the hydraulic pressure sensor 32, the braking force distribution between the front and rear wheels is determined, and the required braking force Tttl for the front wheels is determined (100). Since the master cylinder pressure increases in accordance with the amount of depression of the brake pedal 18, the required braking force Tttl can be determined by detecting the master cylinder pressure. Furthermore, regenerative EC
U30 is a signal from the battery ECU 36, the SOC of the battery 14, and the rotation sensor 17 from the motor ECU 10 via the EV ECU 16.
Are input (102).

The rotation speed ω of the amount input in step 102 can be used to use the maximum regenerative torque Tmax (104). That is, the control characteristics of the motor 10 are given by, for example, a maximum regenerative torque map 200 given by ABCDE in FIG. 3, and by referring to this map 200 at the rotation speed ω, the maximum output that can be output at the rotation speed ω Regenerative torque T
max can be known. The regenerative ECU 30 compares the maximum regenerative torque Tmax with the required braking force Tttl,
The smaller one is set as the regenerative torque command value Tbrk, while the value obtained by subtracting the regenerative torque command value Tbrk from the required braking force is set as the hydraulic braking force command value Thyd (10
6). The regenerative ECU 30 supplies the regenerative torque command value Tbrk thus determined to the EV ECU 16. Thus, the regenerative torque of the motor 10 is controlled with the regenerative torque command value Tbrk as a target (108). The regenerative ECU 30 controls the hydraulic control valve 26 in accordance with the hydraulic braking force command value Thyd determined in step 106, so that the wheel cylinder 22 determines the shortage of the regenerative torque command value Tbrk with respect to the required braking force Tttl. This is realized as a hydraulic braking force (110). Regenerative ECU
At this time, the control signal 30 is also supplied to the hydraulic control valve 28 to apply the braking force to the rear wheels by the wheel cylinder 24 so that the necessary braking force distribution between the front and rear wheels is realized.

The first feature of this embodiment is that delay control as shown in FIG. 3 is performed. First, when delay control is not performed,
When the rotational speed ω decreases with the progress of braking in which the maximum regenerative torque Tmax is determined according to the maximum regenerative torque map indicated by ABCDE in FIG. Hydraulic braking force is rapidly introduced.
As a result, the brake pedal 18 enters and the pedal feeling deteriorates. In order to prevent this, in the present embodiment, the point G is moved to the point G 'by rewriting the map 200 to move the point B to, for example, the point B' when performing regenerative braking. Such rewriting of the map 200 avoids the rapid introduction of hydraulic pressure, resulting in less entry of the brake pedal 18.

However, only by performing such control,
Regeneration power loss occurs. That is, as a result of changing the point B to the point B ', the braking energy for AGG' cannot be regenerated to the battery 14. Therefore, in this embodiment, the point B
The maximum regenerative torque map 200 is rewritten so that 'differs depending on the rotational speed ω.

For this reason, in FIG.
After 2 run, omega ₀ map 300 is referenced by the SOC (112). Here, the ω ₀ map is a map for associating the motor rotation speed ω ₀ at the point B ′ in FIG. 3 with the SOC of the battery 14, and has, for example, contents as shown in FIG. ing. In this figure, in a region where the SOC of the battery 14 is 80% or less, that is, in a region where the regenerative power acceptability of the battery 14 is good, the rotational speed ω ₀ is set to a constant low value. In contrast, the region where the SOC exceeds 80%, i.e. the regenerative power acceptance is low region of the battery 14, the rotation number omega ₀ according to the increase of the SOC is increasing linearly. However, the present invention is such ω ₀ map 300
However, for example, as shown in FIG. 4B, a map in which the rotational speed ω ₀ rises in a curve in the region where the SOC is 80% or more may be used. A map that rises stepwise as shown in FIG. 4 (C) may be used. In addition, the SOC value, which is a boundary of whether or not the rotation speed ω ₀ becomes constant, does not need to be fixed to 80%, and may be fixed to another value, and may be fixed to another value depending on the temperature or the like. The value may be changed.
Furthermore, when a battery whose regenerative power receiving ability depends on the internal pressure, such as a sealed alkaline battery, is used as the battery 14, the internal pressure may be used instead of the SOC.

The regenerative ECU 30 further executes step 10
The rotation speed ω input in step ₂ is compared with the rotation speed ω ₀ obtained in step 112 (114). As a result, in the case where ω <ω ₀ is not satisfied, the regenerative ECU3
0, a point on the maximum regenerative torque map 200 so that rotation speed omega ₀ of the point B moves to the value obtained in step 112 B
Is moved (116), and then the process proceeds to step 104. If ω <ω ₀ holds, the process proceeds to step 104 without passing through step 116.

FIG. 5 shows an outline of a change in the maximum regenerative torque map 200 in this embodiment.

First, at the start of the braking operation, the S
Assume that the OC has a low value of 80% or less. Since the regenerative priority braking force control is being performed, the SOC of the battery 14 increases due to charging as the braking progresses. However, as shown in FIG. 5A, the point B does not move (B = Bs) from the point F at which the braking is started to the point H at which the SOC of the battery 14 reaches 80%. That is, the rotational speed ω ₀ is maintained at the value ω _0s at the start of braking.

Thereafter, when the rotational speed ω decreases as the braking progresses, steps 112 and 116 are repeatedly executed, and as a result, the point B gradually starts moving toward the higher rotational speed side. For example, as shown in FIG. 5B, point B is the first point B
s, it moves to a point Bi located on the high rotation side.
That is, the rotation speed ω ₀ on the maximum regenerative torque map 200
Moves to ω _i .

When such an operation is repeated, at a certain point, ω <ω ₀ is satisfied in step 114.
Accordingly, as shown in FIG. 5 (C), rotation speed omega ₀
Is fixed at _ω0e , and point B is fixed at point Be. The maximum regenerative torque map 200 is not rewritten from the point I at which the rotational speed ω ₀ is fixed at ω _0e until the braking further proceeds and the braking is completed (until the point O) (FIG. 5).
(D)).

[0024] Thus, in the example shown in FIG. 5 (A) ~ (D) , the rewriting of omega ₀ maps 300, minute delay indicated by hatching in the drawing is generated. That is, the regenerative torque for reducing the introduction of the hydraulic braking force is reduced. The amount of the delay is determined by the regenerative power acceptability of the battery 14 (given by the SOC here) in the state of FIG. 5C.

Here, as the regenerative power acceptability of the battery 14 is higher, the point G 'in FIG. 5D is located on the lower rotation side, so that the loss of the regenerative power is suppressed to the minimum. be able to. At this time, by appropriately setting the point Bs and the like, it is possible to prevent the brake feeling from being deteriorated due to the entry of the brake pedal 18.

Conversely, when the regenerative power acceptance of the battery 14 is low, the delay indicated by the hatching in FIG. Thus, overcharging of the battery 14 can be prevented without using a voltage sensor or the like. That is, instead of restricting the regeneration after the voltage of the battery 14 exceeds a predetermined value, the rotational speed ω ₀ is sequentially changed while monitoring the SOC of the battery 14 and the regenerative power acceptability (for example, S
Since the delay control is started according to OC), there is no need to increase the voltage. Therefore, the battery 14
Overcharge can be reliably prevented.

In the above description, when ω ≧ ω ₀ holds, the maximum regenerative torque map 200 is rewritten regardless of the SOC or the like.
When the rotation speed omega ₀ SOC is low region as shown in (A) ~ (C) is using the omega ₀ map 300 which is a constant, so as to omit the step 116 when the SOC is low can do. Thereby, the frequency of rewriting the maximum regenerative torque map 200 can be suppressed.
When the voltage of the battery 14 is low, the battery 14 can be charged with regenerative power without considering overcharging. Therefore, the step 116 is executed only when the voltage of the battery 14 is high. You may. In addition, in the present embodiment, the battery 14 is charged with the regenerative electric power as the braking progresses, and as a result, the point B gradually moves from Bs to Bi via Be to the high rotation side. Since this movement is relatively slow, steps 112 to 116 do not need to be performed every time, and may be performed at predetermined time intervals.

[0028]

As described above, according to the present invention,
The motor speed at which the delay control is started is changed so that the lower the regenerative power acceptability is, the higher the rotational speed is. An efficient electric vehicle can be realized.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating a procedure of regenerative braking control executed by a regenerative ECU in this embodiment.

FIG. 3 is a conceptual diagram showing the contents of delay control.

4 is a diagram showing an example of omega ₀ map used in this embodiment.

FIG. 5 is a diagram showing an example of a change in a maximum regenerative torque map with progress of braking.

[Explanation of symbols]

10 motor, 12 inverter, 14 battery, 16
EV ECU, 18 brake pedal, 20 master cylinder, 22, 24 wheel cylinder, 26, 28 hydraulic control valve, 30 regenerative ECU, 32, 34 hydraulic sensor, 36 battery ECU.

Claims (1)

(57) [Claims] 1. An electric vehicle including a motor for driving a vehicle, a battery that supplies driving power to the motor and is charged by regenerative power from the motor, and a hydraulic braking system that applies a hydraulic braking force to at least driving wheels. A braking control device mounted on a vehicle to control regenerative braking force by controlling a motor; a means for detecting regenerative power of a battery and the number of rotations of a motor; a regenerative braking force is reduced with a decrease in the number of rotations. Means for obtaining the maximum regenerative braking force in accordance with the control characteristic in which the fluid pressure braking force is introduced and based on the number of rotations of the motor, while controlling the regenerative braking force while targeting the required braking force and limiting the maximum regenerative braking force Means for controlling the hydraulic braking force with a target of the regenerative braking force shortage with respect to the required braking force, and a motor in which the hydraulic braking force starts to be introduced as the rotational speed decreases. Speed, so that the lower the regenerative power acceptance high rotational speed, the brake control apparatus characterized by comprising means for changing the control characteristics corresponding to the regenerative power acceptance of the battery, the.