JPH1118207A - Braking controller for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller which can enable the driver of an electric vehicle provided with a speed change gear for predicting the degree of the braking force which is applied to the automobile, when the driver releases the accelerator pedal of the automobile and to smoothly drive the automobile by utilizing the regenerative braking force, which is applied to the automobile when the controller is incorporated in the automobile. SOLUTION: A motor control section sets the present change gear ratio (gear step) between a motor and wheels and running ranges (D and L) of an electric automobile and finds a brake pedal pressing force F. The axle speed reducing torque to be generated from a wheel corresponds to the reference values (TD and TL), corresponding to the running range and the brake pedal pressing force F. The motor control section finds the regenerative torque required for obtaining the axle speed reducing torque based on the change gear ratio so as to cause a motor to generate the regenerative torque. For both the first and second gears, the braking torque generated from an axle and the deceleration of the automobile becomes the same.

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, and more particularly to a device for reducing a vehicle speed by using regenerative braking of an electric motor.

[0002]

2. Description of the Related Art Various electric vehicles have been proposed and some of them have been put to practical use in order to meet the demands for low pollution and low noise of vehicles. Conventional electric vehicles have no transmission and have a fixed speed ratio between a motor and wheels. This is because the motor can generate a sufficient driving torque in a wide rotation speed range and is quiet even at a high rotation speed. This is in contrast to the need for a transmission in an engine-equipped vehicle to ensure torque at low vehicle speeds.

In an electric vehicle, it is well known that the vehicle is decelerated using regenerative braking of a motor when an accelerator is turned off or a brake is turned on. By the regenerative braking, a regenerative torque is generated in the motor in a direction opposite to the driving direction, and the same braking force as that of the engine brake in the vehicle equipped with the engine is obtained. By turning off the accelerator on a slope or the like, the driver can adjust the vehicle speed with the same feeling as using the engine brake. During regenerative braking, the motor operates as a generator. By charging the battery with the generated power,
Energy efficiency is improved.

Japanese Patent Laid-Open Publication No. Hei 6-70406 describes an electric vehicle that does not have a transmission and that performs regenerative braking when the accelerator is off. The electric vehicle of the publication includes D,
A shift lever for selecting a travel range such as 2, 1 is provided. Generally, in an engine vehicle, the running range generally indicates a range of gears set by the transmission. Although the publication does not have a transmission,
By adjusting the driving torque, a plurality of running ranges are realized in a pseudo manner. In particular, in this publication, the regenerative torque when the accelerator is off is set to different magnitudes, large, medium, and small, according to the travel range. The driver can adjust the magnitude of the braking force by selecting the traveling range as if driving an engine-equipped vehicle.

[0005]

As described above, most electric vehicles have no transmission. However, without a transmission, the frequency of using the motor at a high rotation frequency increases, and the burden on motor-related accessories also increases. Therefore, it has been proposed to provide a transmission between the motor and the wheels for efficient use of the motor. However, in an electric vehicle with a transmission, the gear ratio increases or decreases according to the gear position, and torque transmission is interrupted during gear shifting. An effective method for appropriately controlling regenerative braking in such a situation has not been proposed so far. Therefore, in an electric vehicle with a transmission, the motor cannot be actively used for regenerative braking.

In particular, when regenerative braking is performed on an electric vehicle having a transmission, the following problems occur due to the difference in the gear ratio depending on the gear position. For example, it is assumed that the accelerator is turned off while driving in the D range. At this time, the gear ratio between the motor and the wheels differs depending on the gear that is being set. Therefore, the braking force applied to the vehicle differs for each gear. For the driver, it is not possible to predict how much braking force will be generated when the accelerator is turned off.

The above problem will be described in comparison with a vehicle equipped with an engine equipped with a transmission. In an engine-equipped vehicle, a shift map as shown in FIG. 6A is set for transmission control. When the accelerator is off, upshifting to a specific gear position according to the travel range is performed as indicated by the arrow in the figure. Since the gear at the time of accelerator off is specified,
The braking force generated by the engine brake can also be predicted.

On the other hand, in an electric vehicle with a transmission, FIG.
The shift map shown in (b) can be adopted. The motor has a small difference in efficiency depending on the number of revolutions and is quiet even at high revolutions, so that there is no need to shift up when the accelerator is off as in an engine car. Rather, by suppressing shift-up as shown in the figure, kick-down during acceleration is unnecessary, and intermediate acceleration can be improved. However, the gear position differs before and after the shift line m even when one travel range is set. Since the driver does not know the gear position during traveling, the deceleration that occurs when the accelerator is off cannot be predicted.

Further, in an engine vehicle, it is possible to determine to some extent the gear position being set according to the degree of noise. On the other hand, in an electric vehicle, since the motor has low noise, it is difficult to determine the gear position based on the rotation sound.

As described above, in an electric vehicle with a transmission, the driver cannot predict the degree of braking force generated in the vehicle when the accelerator is turned off. Therefore, unexpectedly large braking force may be generated and the driving may be jerky.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a brake control device provided in an electric vehicle with a transmission, wherein a degree of braking force generated when an accelerator is turned off is given to a driver. An object of the present invention is to provide a control device that is predictable and can smoothly drive using a regenerative braking force.

[0012]

SUMMARY OF THE INVENTION A braking control device according to the present invention is a device for controlling braking of an electric vehicle provided with a transmission for changing a gear ratio between an electric motor and wheels. Speed ratio detecting means for obtaining a current gear ratio during the current driving, a deceleration request degree detecting means for obtaining a deceleration request degree indicating a braking action required of the vehicle based on a driving operation of the driver, and a detected speed ratio And a motor control means for generating a required regenerative torque required to achieve the required degree of deceleration, and generating the required regenerative torque in the electric motor, so that the same vehicle deceleration is generated even when the gear ratio is different. . Here, the transmission may be capable of setting a plurality of specific speed ratios, or may be a continuously variable transmission in which the speed ratio continuously changes.

As described above, according to the present invention, the degree of deceleration request indicating the braking action required of the vehicle is determined based on the driving operation of the driver. For example, the degree of deceleration request is a travel range set by the driver. The motor control means obtains a regenerative torque that achieves the required degree of deceleration using the gear ratio, and causes the motor to generate the determined regenerative torque. Accordingly, regardless of the current gear ratio, the actual braking force applied to the vehicle has a magnitude corresponding to the degree of deceleration request. The driver can predict the magnitude of the braking force or deceleration generated in the vehicle during regenerative braking without knowing the current gear ratio. Therefore, the driver can smoothly run the vehicle without the behavior of the vehicle being jerky due to the occurrence of the unexpectedly large deceleration.

The apparatus according to one aspect of the present invention includes a traveling range detecting means for detecting a traveling range set by a driver, wherein the degree of deceleration request is the set traveling range, and the motor control means In addition, the electric motor generates a regenerative torque capable of obtaining a deceleration according to the traveling range. Preferably, the vehicle further includes a brake operation detection unit that detects an operation state of a brake operation device operated by a driver, wherein the electric motor control unit has a deceleration corresponding to a travel range and a brake operation amount. The obtained regenerative torque is generated in the electric motor. When one driving range is set,
Even when the gear ratios are different, the deceleration of the vehicle is constant.
Therefore, the driver can predict the deceleration that occurs for his / her brake operation.

In the present invention, it is not necessary to apply the configuration of the present invention to all speed ratios that can be set in the transmission. For example, in an electric vehicle having a three-speed transmission, the braking force may be made constant for the second and third speeds by the above-described method, and such processing may not be performed for the first speed. Which shift speed is to be applied to the present invention is appropriately determined according to the specifications of the motor and the use of the electric vehicle.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings. FIG. 1 shows a drive system of an electric vehicle provided with the braking control device of the present invention. The brake control device of the present invention is provided integrally with the drive system control device.

In FIG. 1, a transmission 3 is connected to a motor 1 for generating a vehicle propulsion force. The transmission 3 has a well-known two-axis gear mechanism, and is of a forward two-speed and a reverse one-speed type. The transmission 3 is connected to the wheels 5 via a differential gear device (not shown). The power running torque generated by the motor 1 is transmitted to the wheels 5 via the transmission 3.

The motor 1 is connected to a battery 9 via an inverter 7. The inverter 7 is a current adjusting unit that includes a plurality of switching elements and adjusts a current supplied to the motor 1. The motor 1 is driven by a current supplied from the inverter 7.

The friction brake 11 is a device for braking the rotation of the wheels 5 by a frictional force. In the present embodiment, the friction brake 11 is a disk type, and includes a disk that rotates with the axle and a brake pad that makes frictional contact with the disk. The hydraulic pressure is transmitted to the friction brake 11 from the hydraulic cylinder 13 via the adjustment valve 15.
When the driver steps on the brake pedal 17, the hydraulic cylinder 1
3, hydraulic pressure is generated, the brake pad is pressed against the disk, and the rotation of the wheel 5 is braked by the frictional force between the two.

The drive system controller 20 controls the entire system, and includes a motor controller 22, a transmission controller 2
4, including a friction brake control unit 26; Each control unit may be integrated, or may be a separate electronic control device. The drive range selected by the driver is input from the shift lever device 28 to the drive system control device 20. By moving the shift lever, the driver can set the travel ranges P (parking), R (reverse), N (neutral), D, and L (forward). Further, information indicating the accelerator operation amount θ by the driver is input from the accelerator pedal 30 to the drive system control device 20. The accelerator operation amount θ increases / decreases in proportion to the accelerator depression amount, with 0% when the accelerator is off and 100% when the accelerator is fully open. Further, an electric signal indicating the oil pressure in the cylinder is input from the hydraulic cylinder 13 to the drive system control device 20. Based on the electric signal, the magnitude of the depression force on the brake pedal 17 is detected as the amount of brake operation by the driver. Note that, as a modification, the movement amount (stroke) of the brake pedal may be detected instead of the hydraulic pressure as the brake operation amount.

The drive system controller 20 receives a motor rotation speed n from a rotation sensor 32 provided in the motor 1 and a current value I of a supply current to the motor 1 from a current sensor 34. You. Further, information indicating the vehicle speed V is input to the drive system control device 20 from a vehicle speed sensor 36 provided on the output side of the transmission 3. The vehicle speed sensor 36 detects the rotation speed of the output shaft of the transmission 3.

The motor control unit 22 is a device that controls the motor 1 by supplying a switching signal to the inverter 7. The motor control unit 22 includes a well-known vector control unit and a well-known PWM control unit. The motor control unit 22 generates a switching signal based on input information and supplies the switching signal to the inverter 7.

When the accelerator is on, the motor control unit 22
Controls the motor 1 to generate a powering torque according to the accelerator operation amount. The motor control unit 22 stores a torque map in which the motor speed n and the accelerator operation amount θ% are associated with the power running torque to be generated by the motor. The motor control unit 22 determines a torque command value according to the torque map based on the input information of the rotation speed n and the accelerator operation amount θ%. The motor control unit 22 obtains a current command according to the determined torque command based on the motor speed n and the motor current I, and further generates a switching signal according to the current command. This switching signal is output to the inverter 7, and the switching element of the inverter 7 operates according to the switching signal. Thus, the DC current supplied from the battery 9 to the inverter 7 is converted into an AC current by the inverter 7 and supplied to the motor 1. Here, the switching signal is set based on the torque command value. Therefore, the motor 1 is driven by the current supplied from the inverter 7 to generate a torque corresponding to the command value determined by the motor control unit 22.

When the accelerator is turned off, the torque command value becomes regenerative (negative). The motor control unit 22 performs regenerative braking control by outputting a switching signal to the inverter 7. At this time, the motor 1 is rotated by the rotational force of the wheels 5 and operates as a generator. The generated current is converted into a DC current by an inverter 7 operating according to the switching signal, and the battery 9 is charged.
The regenerative torque is in the opposite direction to the power running torque, and the regenerative torque acts as a resistance to decelerate the vehicle.

Incidentally, the vehicle deceleration during regenerative braking corresponds to the wheel shaft deceleration torque generated on the wheel shaft. The wheel shaft deceleration torque is a product of a regenerative torque generated in the motor 1 and a gear ratio between the motor and the wheel. In 1st gear and 2nd gear,
The gear ratio is different. Therefore, when the regenerative torque corresponding to the travel range is generated one-to-one, the wheel shaft deceleration torque is different between the first speed travel and the second speed travel. In this,
The driver cannot predict the braking force when the accelerator is off. Therefore, as a feature of the present embodiment, the motor control unit 22 determines the required regenerative torque according to FIG. 2 and controls the motor 1 so that the required regenerative torque is generated.

The setting of FIG. 2 will be described. TD and TL are reference required deceleration torques. TD is a wheel axle deceleration torque to be generated when the D range, the accelerator is off, and the brake is off. TL is a similar wheel shaft deceleration torque, and L
It is for the range (TL> TD). F is a brake depression force obtained from the output of the hydraulic cylinder 13, and k is a proportional coefficient. Further, i1 is the gear ratio of the first speed, i2
Is the speed ratio of the second speed (the speed ratio is between the motor and the wheels).

In this embodiment, first, the required value of the wheel shaft deceleration torque is determined as the sum of the reference required deceleration torque (TD or TL) and the deceleration torque kF that is proportional to the brake depression force for each travel range. Then, the required regenerative torque to be generated by the motor 1 in order to obtain the wheel shaft deceleration torque described above is calculated back for each gear using the gear ratio.
The motor 1 is controlled so that the required regenerative torque set in this way is generated. Therefore, in the present embodiment, when one travel range is set, the same deceleration occurs during the first speed travel and the second speed travel. This deceleration increases and decreases in proportion to the brake pedal force.

Next, the transmission control unit 24 will be described. The transmission control unit 24 controls a shift change of the transmission 3 based on the shift map of FIG. As shown in FIG. 3, when the D range is set, the transmission control unit 24 maintains the transmission 3 at the first speed while the vehicle speed is lower than V1. When the vehicle speed reaches V1, the transmission control unit 24
Causes the transmission 3 to shift up to the second speed. When the vehicle speed decreases and reaches V2 (not shown), the vehicle is shifted down to the first speed.

When the L range is set, in principle, only the first speed is set, and no shift change is performed. However, the shift lever may be operated during high-speed traveling in the D range / second speed, and the traveling range may be changed to the L range. At this time, the second speed is maintained, and the shift down is performed until the vehicle speed reaches V3 (dotted line in the figure).

As is apparent from FIG. 3, the transmission control device of the present embodiment does not basically perform a shift change in accordance with the accelerator operation amount θ. As described above, the motor has little difference in efficiency depending on the number of rotations, and is quiet even at high rotations.
This is because there is no need to shift up when the accelerator is off as in an engine car. Rather, since no upshift is performed when the accelerator is off, kickdown during acceleration is not required, and intermediate acceleration can be improved.

Next, the friction brake control section 26 will be described. The friction brake control unit 26 controls the braking torque generated by the friction brake device 11. The friction brake control unit 26 outputs a control signal to the adjustment valve 15. The adjustment valve 15 adjusts the magnitude of the hydraulic pressure transmitted to the brake device 11 according to the control signal. That is, the adjustment valve 15 transmits only the hydraulic pressure of the magnitude indicated by the control signal to the friction brake device 11 among the hydraulic pressures transmitted from the hydraulic cylinder 13. The friction brake device 11
A braking force having a magnitude corresponding to the input hydraulic pressure is generated. Therefore, the friction brake control unit 26 can control the braking torque generated by the friction brake device 11 by outputting an appropriate control signal.

The friction brake control unit 26 follows a command from the motor control unit 22. In the motor control unit 22, the maximum regenerable torque that can be generated is determined for each motor speed n. When the required regenerative torque determined according to FIG. 2 is equal to or less than the maximum value, the motor control unit 22 does not request the friction brake control unit 26 to generate a friction brake force.

However, when the driver depresses the brake pedal strongly, the required regenerative torque exceeds the above-mentioned maximum value. It is necessary for the friction brake device 11 to take charge of the braking that is exceeded. Therefore, information indicating the difference between the required regenerative torque and the maximum regenerative torque is sent to the friction brake control unit 26. The friction brake control unit 26 causes the friction brake device 11 to generate a braking torque that can provide the same deceleration as the excess of the required regenerative torque.

Next, the operation of the brake control device according to the present embodiment will be described with reference to the flowchart of FIG. The motor control unit 22 determines whether the accelerator is off (S1).
0), if the accelerator is on, return. The motor control unit 22 causes the motor 1 to generate a powering torque according to the accelerator operation amount. When the accelerator is off, it is determined whether the traveling range is the L range based on the output of the shift lever device 28 (S12). If you are driving in the L range,
It is determined whether the current gear of the transmission 3 is the first speed (S14). This determination is based on information from the transmission control unit 24. In the case of the first speed, as shown in FIG. 2, the required regenerative torque T * to be generated in the motor 1 is set to (TL + k
F) / i1 is determined (S16). In the case of not the first speed, that is, in the case of the second speed, the required regenerative torque T *
= (TL + kF) / i2 (S18). As described above, TL is a predetermined reference required deceleration torque (for the L range), and i1 and i2 are the gear ratios between the motor and the wheels at the first speed and the second speed, respectively. F is a brake depression force obtained from the output of the hydraulic cylinder 13, and k is a proportional coefficient.

On the other hand, if the L range has not been set in step S12, it is determined in next step S20 whether the D range has been set. If it is not the D range, that is, if another range such as P (parking) is selected, the routine returns. When the D range is set, it is determined whether or not the current gear is the first speed (S22). In the case of the first speed, the regenerative torque T *
= (TD + kF) / i1 (S24), and in the case of the second speed, regenerative torque T * = (TD + kF) / i2 (S26). TD is a reference required deceleration torque for the D range.

The required regenerative torque determined in steps S16, S18, S24 or S26 is compared with the maximum regenerative torque Tmax (S28). As described above, the maximum regenerative torque Tmax is the maximum regenerative torque that the motor 1 can generate at the current rotational speed N. T * ≦ Tmax
If so, the motor control unit 22 controls the motor 1 to generate the regenerative torque T * (S30).

On the other hand, when T *> Tmax in step S28, a torque difference ΔT = T * −Tmax between the two is calculated,
It is sent from the motor control unit 22 to the friction brake control unit 26. The friction brake control unit 26 controls the friction braking force to generate a friction braking force such that a deceleration corresponding to ΔT is obtained (S32). Also, the motor control unit 22
Replaces the regenerative torque T * with Tmax (S34),
This T * (that is, Tmax) is generated by the motor 1 (S30), and the routine returns.

The configuration and operation of the braking control device according to the present embodiment have been described above. By such braking control, a regenerative torque as shown in FIG. 5 is generated. FIG. 5 shows the regenerative torque generated at the first speed and the second speed when the D range is set. In the first speed, as shown by the line p, a regenerative torque TD / i1 is generated when the accelerator is off. Then, the regenerative torque (TD + kF) / i1 is generated in proportion to the brake pressing force F. When the brake pedal force is F1, the regenerative torque reaches the allowable upper limit Tmax.
When the brake depression force is F1 or more, the regenerative torque is constant at Tmax. Similarly, at the second speed, the regenerative torque (TD +
kF) / i2 occurs. When the brake pedal force is F2 (F2 <
Above F1), the regenerative torque is a constant value Tmax.

The upper line r in FIG. 5 shows the wheel shaft deceleration torque generated on the wheel shaft. In the present embodiment, as shown, the wheel shaft deceleration torque is the same both during the first speed running and during the second speed running. In addition, as shown on the line r,
During first speed traveling, the friction brake device 11 operates in a region where the brake pedal force is larger than F1. Further, during the second speed traveling, the friction brake device 11 operates in a region where the brake depression force is larger than F2. As a result, even when the brake is strongly depressed, the generation of the wheel shaft deceleration torque proportional to the brake depression force is guaranteed.

As described above, according to the present embodiment, when one traveling range is set, the wheel axle deceleration torque is equal during the first traveling and the second traveling, that is,
Vehicle deceleration is equal. The driver can predict how much deceleration will occur in the vehicle when the accelerator is turned off. This is because the same magnitude of braking force is generated regardless of the gear position. Similarly, the deceleration when the brake is operated is the same in the first speed and the second speed. Therefore, unexpected deceleration does not occur when the accelerator is off or when the brake is operated, so that the vehicle can run smoothly.

In this embodiment, an electric vehicle in which two driving ranges D and L can be set and which has a forward two-speed transmission has been described. However, it goes without saying that the present invention is applicable to an electric vehicle having a transmission different from this type. For example, the present invention can be applied to a vehicle with a transmission capable of setting a larger number of gears. In this case, the generated deceleration can be the same in three or more gear stages for one travel range.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a required regenerative torque set by a motor control unit in the system of FIG. 1;

FIG. 3 is a diagram showing a shift map set in a transmission control unit in the system of FIG. 1;

FIG. 4 is a flowchart showing braking control by the system of FIG. 1;

FIG. 5 is an explanatory diagram showing regenerative torque generated in a motor of the system of FIG. 1;

FIG. 6 is an explanatory diagram showing a shift map set for a conventional vehicle equipped with an engine with a transmission and an electric vehicle with a transmission.

[Explanation of symbols]

1 motor, 3 transmission, 5 wheels, 7 inverter,
9 battery, 11 friction brake device, 13 hydraulic cylinder, 15 adjustment valve, 17 brake pedal, 20
Drive system controller, 22 Motor controller, 24
Transmission control unit, 26 friction brake control unit, 28 shift lever, 30 accelerator pedal, 32 rotation sensor, 34 current sensor, 36 vehicle speed sensor.

Claims (3)

[Claims] 1. A braking control device for controlling braking of an electric vehicle provided with a transmission for changing a transmission ratio between an electric motor and wheels, wherein the transmission determines a current transmission ratio between the electric motor and wheels. A ratio detecting means, a deceleration request degree detecting means for obtaining a deceleration request degree indicating a braking action required of the vehicle based on the driving operation of the driver, and a deceleration request degree based on the detected gear ratio. And a motor control means for obtaining a required regenerative torque required for the electric vehicle and generating the required regenerative torque in the electric motor. Control device. 2. The apparatus according to claim 1, further comprising: a traveling range detecting unit that detects a traveling range set by a driver; wherein the degree of deceleration request is a set traveling range; and the motor control unit. A brake control device for an electric vehicle, wherein a regenerative torque capable of obtaining a deceleration according to a travel range is generated in an electric motor. 3. The device according to claim 2, further comprising: a brake operation detecting unit configured to detect an operation state of a brake operating device operated by a driver, wherein the electric motor control unit is configured to operate according to a travel range and to apply a brake. A braking control device for an electric vehicle, wherein a regenerative torque capable of obtaining a deceleration according to an operation amount is generated in an electric motor.