JPH08237807A - Braking control apparatus for electric vehicle - Google Patents

Abstract

PURPOSE: To provide a braking control apparatus by which the loss, of regenerative electric power, generated when the number of revolutions of a motor used to start a delay control operation is made constant is prevented or reduced and which prevents the overcharge of a battery more surely. CONSTITUTION: When a brake pedal is stepped on, a required braking force is changed from a point F to a point H and further to a point I. Then, a point B out of points A, B, C, D, E for a maximum regenerative torque characteristic which is given as a map is changed. At this time, the point B is rewritten in such a way that the SOC of a battery is higher, the number of revolutions ω0 becomes higher. At a point of time when the number of revolutions ω of a motor becomes equal to the number of revolutions ω0 , the rewriting operation of a maximum regenerative torque map is stopped, and a braking operation is executed by the same map after that. Since the number of revolutions ω0 is changed according to the SOC, the loss of regenerative electric power can be reduced even when a delay control operation is executed, and the overcharge of the battery can be prevented surely.

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 the regenerative braking force and the fluid pressure braking force of the electric vehicle.

[0002]

2. Description of the Related Art An electric vehicle is a type of electric vehicle that can use both hydraulic braking (generally, fluid pressure 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, and therefore power efficiency is good. Therefore, by preferentially using the regenerative braking over the hydraulic braking, it is possible to improve the electric power efficiency of the vehicle and extend the travelable distance per battery charge. As a technique for preferentially applying the regenerative braking force over the hydraulic braking force, for example, Japanese Patent Laid-Open No. 6-
Some are disclosed in Japanese Patent No. 153313. In this publication, the shortage of the regenerative braking force with respect to the required braking force (stepping amount of the brake pedal) is supplemented 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 together and the shortage of the regenerative braking force with respect to the required braking force is compensated for 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 the hydraulic braking force is introduced due to the shortage of the 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 alleviate such deterioration of pedal feeling, it is sufficient 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 originally introduced. On the other hand, the total regenerative and hydraulic pressure braking force must match the required braking force, so at the same time, the regenerative braking force is reduced earlier than it should be. By executing such control, that is, the delay control of the regenerative braking force and the hydraulic braking force, while realizing the required braking force by the total of the regenerative pressure and the hydraulic pressure and using the regenerative power in preference to the hydraulic pressure, It is possible to mitigate or prevent the deterioration of the pedal feeling.

However, a new problem arises only by executing such delay control. That is, when executing the delay control as described above, 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. In this way, if the regenerative braking force is reduced earlier than it should be, then the braking energy for that amount cannot be recovered to the battery as regenerative power. 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, the regenerative power is lost.

The present invention has been made to solve the above problems, and by improving the procedure related to the delay control, it is possible to prevent or reduce the loss of regenerative power. It is an object of the present invention to solve the problems associated with the upper limit of the battery voltage, which has been executed to prevent the battery from being overcharged.

[0006]

In order to achieve such an object, the present invention provides a motor for traveling a vehicle, a battery for supplying driving power to the motor, and a battery charged by regenerative power from the motor, and In a braking control device that is mounted on an electric vehicle having at least a fluid pressure braking system that applies fluid pressure braking force to driving wheels, and that controls the motor to control the regenerative braking force, the regenerative power acceptability of the battery and the rotation speed of the motor To detect the maximum regenerative braking force based on the number of revolutions of the motor and the control characteristic that the regenerative braking force is reduced and the fluid pressure braking force is introduced as the number of revolutions decreases. A means for controlling the regenerative braking force with the target and the maximum regenerative braking force as a limit, and means for controlling the fluid pressure braking force with the target of the shortage of the regenerative braking force with respect to the required braking force. A means for changing the control characteristic according to the regenerative power acceptability of the battery, such that the rotation speed of the motor in which the fluid pressure braking force is introduced with the decrease in the rotation speed becomes higher as the regenerative power acceptability becomes lower, It is characterized by having.

[0007]

In the present invention, first, the regenerative power acceptability of the battery and the rotation speed of the motor are detected. When the rotation speed of the motor is detected, the maximum regenerative braking force is determined based on the rotation speed of the motor. This maximum regenerative braking force is given according to a control characteristic that the regenerative braking force is reduced and the fluid pressure braking force is introduced as the rotation speed decreases. Furthermore, the regenerative braking force is
It is controlled with the target braking force given in the form of the amount of depression of the brake pedal by the vehicle operator. At that time, the upper limit of the regenerative braking force is limited by the maximum regenerative braking force obtained as described above. The resulting shortage, that is, the shortage of the regenerative braking force with respect to the required braking force is compensated by the introduction of the fluid pressure braking force.

Here, in the present invention, the rotational 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 is, the higher the rotational speed is. That is, when the rotation speed of the motor decreases as the braking progresses, the regenerative braking force is reduced and the fluid pressure braking force is introduced with the decrease in the rotation speed. In stead of the amount, the fluid pressure braking force starts to be introduced (delay control starts). In the present invention, the rotation speed of the motor at which the delay control is started is changed and set so that the lower the regenerative power acceptability is, the higher the revolving power acceptability is. The battery is less likely to be continuously charged in a state where it is likely to occur, and the reliability of the system is improved. Also,
When regenerative power acceptability is high, the delay control is started because the number of rotations of the motor is lower. Therefore, the loss of regenerative power due to the delay control, more strictly, the number of rotations 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 EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the system configuration of an electric vehicle according to an embodiment of the present invention. The electric vehicle shown in this figure is a front-wheel drive vehicle, and the motor 10 is provided on the axle of the front wheels. The drive power of the motor 10 is supplied from the battery 14 via the inverter 12. Under the control of the EVECU 16, the inverter 12 converts the DC power supplied from the battery 14 into AC power and supplies the AC power to the motor 10. When powering the motor 10, the EVECU 16 determines a torque command based on information such as an accelerator pedal depression amount 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 this torque command. As a result, the output torque of the motor 10 becomes a value corresponding to the amount of depression of the accelerator pedal.

The electric vehicle shown in this figure has both hydraulic braking and regenerative braking as braking means. First, as a hydraulic braking system, a master cylinder 20 that internally generates hydraulic pressure according to the amount of depression of the brake pedal 18, wheel cylinders 22 and 24 that apply hydraulic braking force to the front wheels or rear wheels, and the master cylinder 20 are used.
From the hydraulic cylinders 22 and 24 to hydraulic pressure control valves 26 and 28. The hydraulic control valves 26 and 28 are valves controlled by the regenerative ECU 30. The regenerative ECU 30 uses the master cylinder 20 detected by the hydraulic pressure sensors 32 and 34.
The hydraulic control valves 26 and 28 are controlled based on the hydraulic pressures on the side of the wheel cylinder 22 and the wheel cylinder 22 and according to a predetermined control characteristic. This control is performed so that the braking force distribution between the front and rear wheels becomes the target distribution, and the braking force related to the front wheels, which are the driving wheels, becomes the regenerative braking force priority distribution. Therefore, reincarnation E
The CU 30 exchanges information with the EVECU 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 the front wheels and a drum brake is used for the rear wheels, but the present invention does not depend on the type of the front and rear wheels. It is not limited to front-wheel drive vehicles.

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

As shown in this figure, the regenerative ECU 30
First, based on the hydraulic pressure in the master cylinder 20 (master cylinder pressure) 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 rises according to the amount of depression of the brake pedal 18, the required braking force Tttl can be determined by detecting the master cylinder pressure. Furthermore, regeneration EC
U30 is the SOC of the battery 14 from the battery ECU 36, and the motor 10 from the rotation sensor 17 via the EVECU 16.
The respective rotation speeds ω are input (102).

The rotation speed ω of the quantity input in step 102 can be used to use the maximum regenerative torque Tmax (104). That is, the control characteristic of the motor 10 is given, for example, by the maximum regenerative torque map 200 given by ABCDE in FIG. 3, and by referring to this map 200 at the rotational speed ω, the maximum outputtable at the rotational speed ω can be obtained. Regenerative torque T
You can know max. 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 EVECU 16. As a result, the regenerative torque of the motor 10 is controlled with the regenerative torque command value Tbrk as the target (108). Further, the regenerative ECU 30 controls the hydraulic control valve 26 in accordance with the hydraulic braking force command value Thyd determined in step 106 to cause the wheel cylinder 22 to make up for the shortage of the regenerative torque command value Tbrk with respect to the required braking force Tttl. It is realized as a hydraulic braking force (110). Regenerative ECU
At that time, 30 also supplies a control signal to the hydraulic pressure control valve 28 so that the wheel cylinder 24 applies the braking force to the rear wheels so that the required front-rear wheel braking force distribution is realized.

The first feature of this embodiment is that the delay control as shown in FIG. 3 is executed. First, when delay control is not performed,
As the maximum regenerative torque Tmax is determined according to the maximum regenerative torque map indicated by ABCDE in FIG. 3, as the rotational speed ω decreases with the progress of braking, the straight line AB has a steep slope, and therefore, after the point G. The hydraulic braking force is rapidly introduced.
As a result, the brake pedal 18 is inserted and the pedal feeling is deteriorated. In order to prevent this, in the present embodiment, the point G is moved to the point G ′ by moving the rewriting point B of the map 200 to, for example, the point B ′ when executing the regenerative braking. By rewriting the map 200 as described above, rapid introduction of hydraulic pressure is avoided, and as a result, the brake pedal 18 is less likely to enter.

However, if only such control is performed,
Regenerative 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 in the battery 14. Therefore, in this embodiment, point B
The maximum regenerative torque map 200 is rewritten so that ′ becomes different depending on the rotation speed ω.

Therefore, in FIG.
After 2 executions, the ω ₀ map 300 is referenced by the SOC (112). Here, the ω ₀ map is a map that associates the motor rotational speed ω ₀ related to the point B ′ in FIG. 3 with the SOC of the battery 14, and has the content as shown in FIG. 4 (A), for example. ing. In this figure, in the region where the SOC of the battery 14 is 80% or less, that is, in the region where the regenerative power acceptability of the battery 14 is good, the rotation speed ω ₀ is set to a constant low value. On the other hand, in the region where the SOC exceeds 80%, that is, in the region where the regenerative power acceptability of the battery 14 is low, the rotation speed ω ₀ linearly increases as the SOC increases. However, the present invention uses such a ω ₀ map 300.
The map is not limited to this, and a map in which the rotational speed ω ₀ rises in a curve in a region where the SOC is 80% or more may be used as shown in FIG. A map that rises stepwise as shown in FIG. 4 (C) may be used. In addition, the SOC value, which is the boundary of whether or not the rotation speed ω ₀ becomes constant, does not have to be fixed at 80%, and may be fixed at another value. The value may be changed.
Further, when a battery whose receptive power acceptability 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 2 is compared with the rotation speed ω ₀ obtained in step 112 (114). As a result, when ω <ω ₀ is not established, the regenerative ECU 3
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 is established, the process proceeds to step 104 without passing through step 116.

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

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

After that, when the rotation speed ω decreases as the braking progresses, steps 112 and 116 are repeatedly executed, and as a result, the point B gradually starts to move to the high rotation side. For example, as shown in FIG. 5B, the point B is the first point B.
It moves to the point Bi located on the high rotation side when viewed from s.
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 some point, ω <ω ₀ is established at step 114.
Accordingly, as shown in FIG. 5C, the rotation speed ω ₀
Is fixed at ω _0e and point B is fixed at point Be. The maximum regenerative torque map 200 is not rewritten from the point I where the rotational speed ω ₀ is fixed at ω _0e until the braking further progresses and the braking ends (until the point O) (FIG. 5).
(D)).

Therefore, in the example shown in FIGS. 5A to 5D, rewriting of the ω ₀ map 300 causes a delay corresponding to the hatching in the figure. That is, the regenerative torque is reduced to moderate the introduction of the hydraulic braking force. This delay amount is determined by the regenerative power acceptability (given by SOC here) of the battery 14 in the state of FIG. 5 (C).

Here, the higher the regenerative power acceptability of the battery 14, the more the point G'in FIG. 5 (D) is located on the low rotation side, so that the loss of the regenerative power is suppressed to the minimum. be able to. Also in that case, by appropriately setting the point Bs and the like, it is possible to prevent deterioration of the brake feeling due to the depression of the brake pedal 18.

On the contrary, when the regenerative power acceptability of the battery 14 is low, the delay indicated by the hatching in FIG. 5D becomes large. Thereby, overcharge of the battery 14 can be prevented without using a voltage sensor or the like. That is, instead of limiting 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), it is not necessary to increase the voltage. Therefore, the battery 14
It is possible to reliably prevent overcharging.

In the above description, when ω ≧ ω ₀ is satisfied, the maximum regenerative torque map 200 is rewritten regardless of SOC or the like.
As shown in (A) to (C), when the ω ₀ map 300 in which the rotation speed ω ₀ is constant is used in the low SOC region, the step 116 is omitted when the SOC is low. can do. As a result, the frequency of rewriting the maximum regenerative torque map 200 can be suppressed.
Further, when the voltage of the battery 14 is low, the battery 14 can be charged with regenerative power without considering overcharging. Therefore, again, the step 116 should be executed only when the voltage of the battery 14 is high. May be. In addition, in the present embodiment, the battery 14 is charged with regenerative power as the braking progresses, and as a result, the point B gradually moves from Bs to Bi to Be toward the high rotation side. Since this movement is relatively slow, steps 112 to 116 do not have to be executed every time, and may be executed at predetermined time intervals.

[0028]

As described above, according to the present invention,
Since the rotation speed of the motor that starts the delay control is changed so that the lower the regenerative power acceptability is, the higher the rotation speed is, it is possible to prevent overcharging of the battery while preventing loss of regenerative power. It is possible to realize an efficient electric vehicle.

[Brief description of 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 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.

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

FIG. 5 is a diagram showing an example of a change in a maximum regenerative torque map with the 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 regeneration ECU, 32, 34 hydraulic sensor, 36 battery ECU.

Claims (1)

[Claims] 1. An electric vehicle including a motor for driving a vehicle, a battery that is supplied with driving power to the motor and is charged by regenerative power from the motor, and a fluid pressure braking system that exerts fluid pressure braking force on at least driving wheels. In a braking control device that is mounted on a vehicle and controls the regenerative braking force by controlling the motor, a means for detecting the regenerative power acceptability of the battery and the number of revolutions of the motor, and the regenerative braking force is reduced as the number of revolutions decreases. A means for obtaining the maximum regenerative braking force based on the control characteristics in which the fluid pressure braking force is introduced and based on the number of revolutions of the motor, and a method for controlling the regenerative braking force with the required braking force as a target and the maximum regenerative braking force as a limit. A means for controlling the fluid pressure braking force targeting the shortage of the regenerative braking force with respect to the required braking force, and a motor in which the fluid pressure 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.