Control device for an electric vehicle

Abstract

Provided is a control device for an electric vehicle that can suppress a decrease in vehicle drivability when the electric vehicle having left and right independent drive motors switches from turning travel to straight travel. The control device (30) for an electric vehicle is installed in an electric vehicle (1) having a left drive motor (22) and a right drive motor (22) that respectively output power to left and right drive wheels (2a, 2a). The control device includes: an indicated torque calculation unit (32) that calculates left and right indicated torques following a required torque; and a change rate adjustment unit (33) that adjusts respective upper limit change rates of the left and right indicated torques. Further, the change rate adjustment unit (33) makes the upper limit change rate belonging to the inner wheel side before the steering angle turns smaller than the upper limit change rate belonging to the outer wheel side before the steering angle turns, based on a turning operation of the steering angle using a steering unit.

Description

Technical Field

[0001] The present invention relates to a control device for an electric vehicle. Background Art

[0002] In recent years, electric vehicles having left and right independent traveling motors have been developed. Patent Document 1 discloses output control of a traveling motor in the case of a skid occurring when such an electric vehicle turns.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-49825 Summary of the Invention

[0004] When skidding is predicted, suppressing torque before skidding results in better drivability of the vehicle than suppressing torque after skidding. Conventionally, on a road surface with low frictional resistance, when switching from turning travel to straight travel, the drive wheel on the inner wheel side sometimes skids, reducing the drivability of the vehicle.

[0005] An object of the present invention is to provide a control device for an electric vehicle that can suppress a decrease in the drivability of the vehicle when an electric vehicle having left and right independent traveling motors switches from turning travel to straight travel.

[0006] The invention according to Technical Solution 1 provides a control device for an electric vehicle, installed in an electric vehicle having a steering unit, an accelerator operation unit, a left traveling motor and a right traveling motor that respectively output power to left and right drive wheels. The control device includes: a required torque calculation unit that calculates a required torque corresponding to an operation of the accelerator operation unit; an indicated torque calculation unit that calculates left and right indicated torques following the required torque; a change rate adjustment unit that adjusts upper limit change rates of the left and right indicated torques; and a drive control unit that controls the left traveling motor and the right traveling motor so that the calculated left and right indicated torques are respectively output from the left traveling motor and the right traveling motor. The change rate adjustment unit makes the upper limit change rate belonging to the inner wheel side before the steering angle rotation smaller than the upper limit change rate belonging to the outer wheel side before the steering angle rotation based on a predetermined steering angle rotation operation performed using the steering unit.

[0007] The invention according to Technical Solution 2 is based on the control device for an electric vehicle according to Technical Solution 1, characterized in that the control device is installed in an electric vehicle further equipped with load sensors that respectively detect loads on the left and right drive wheels. The change rate adjustment unit makes the upper limit change rate belonging to the inner wheel side before the steering angle rotation smaller than the upper limit change rate belonging to the outer wheel side before the steering angle rotation when the load on the drive wheel belonging to the inner wheel side before the steering angle rotation is below a load threshold based on a predetermined steering angle rotation operation performed using the steering unit.

[0008] The invention of Technical Solution 3 is a control device for an electric vehicle according to Technical Solution 1 or 2, characterized in that the indicated torque calculation unit further suppresses the left and right indicated torques based on the detection of the idling of one of the left and right drive wheels.

[0009] According to the present invention, when switching from turning driving to straight driving or the like, the change rate adjustment unit makes the upper limit change rate belonging to the inner wheel side smaller than the upper limit change rate belonging to the outer wheel side based on a predetermined steering angle turning operation. Therefore, it is possible to suppress the indicated torque of the drive wheel belonging to the inner wheel side from becoming a large value and causing a slipping situation when the load of the drive wheel belonging to the inner wheel side is still low during or after the steering angle turning operation. Therefore, when switching from turning driving to straight driving or the like, it is possible to suppress a decrease in the drivability of the electric vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a block diagram showing an electric vehicle according to an embodiment of the present invention.

[0011] Figure 2 is a timing chart showing an operation example when the electric vehicle according to the embodiment switches from turning driving to straight driving.

[0012] Figure 3 is a timing chart showing an operation example when the electric vehicle according to the comparative example switches from turning driving to straight driving.

[0013] (Description of Reference Numerals)

[0014] 1 Electric vehicle

[0015] 2a, 2a Left and right drive wheels

[0016] 10 Driving operation unit

[0017] 11 Accelerator pedal

[0018] 12 Brake pedal

[0019] 13 Steering wheel

[0020] 21 Inverter

[0021] 22, 22 Left and right driving motors

[0022] 24 Load sensor

[0023] 26 Wheel speed sensor

[0024] 30 Control device

[0025] 31 Required torque calculation unit

[0026] 32 Indicated torque calculation unit

[0027] 33 Rate adjustment unit

[0028] 35 Drive control unit

[0029] SL Slip Detailed implementation manner

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Figure 1 It is a block diagram of an electric vehicle showing an embodiment of the present invention.

[0031] The electric vehicle 1 of the present embodiment is an EV (Electric Vehicle), HEV (Hybrid Electric Vehicle), etc., and includes left and right drive wheels 2a, 2a, left and right traveling motors 22, 22 that output independent power to the left and right drive wheels 2a, 2a, inverters 21, 21 that drive the left and right traveling motors 22, 22 respectively, and a control device 30 that controls the traveling of the electric vehicle 1. The electric vehicle 1 further includes a driving operation unit 10 having an accelerator pedal 11, a brake pedal 12, and a steering wheel 13, wheel speed sensors 26, 26 that detect the respective wheel speeds of the left and right drive wheels 2a, 2a, and load sensors 24, 24 that detect the respective loads of the left and right drive wheels 2a, 2a. The detection results of the left and right wheel speed sensors 26, 26 are sent to the control device 30. The detection results of the left and right load sensors 24 are sent to the control device 30 via the load sensing receiving unit 24b. The accelerator pedal 11 is an example of the accelerator operation unit of the present invention. The steering wheel 13 is an example of the steering unit of the present invention.

[0032] The load sensor 24 is installed on the inner surface of the tire of the drive wheel 2a, measures the deformation generated in the tire during driving, and thereby estimates the load applied to the drive wheel 2a.

[0033] The control device 30 is composed of one ECU (Electronic Control Unit) or multiple ECUs. In the case of being composed of multiple ECUs, the multiple ECUs communicate with each other and cooperate. The control device 30 includes a ROM (Read Only Memory) that stores a control program and a CPU (Central Processing Unit) that performs calculation processing. The CPU realizes multiple functional modules by executing the control program. The multiple functional modules include a required torque calculation unit 31 that calculates the required torque based on the operation signal sent from the driving operation unit 10, an indicated torque calculation unit 32 that calculates the left and right indicated torques that follow the required torque while suppressing the sharp change of the torque, and a drive control unit 35 that controls the inverter 21 so that the calculated left and right indicated torques are respectively output from the left and right traveling motors 22, 22.

[0034] The required torque calculation unit 31 calculates, for example, the required torque corresponding to the operation amount of the accelerator pedal 11 or the brake pedal 12. If the driver makes a violent operation, the required torque changes sharply.

[0035] In the normal situation where the drive wheels 2a, 2a do not spin, the indicated torque calculation unit 32 calculates the indicated torque following the required torque at a rate of change not exceeding the upper limit rate of change. In addition, the indicated torque calculation unit 32 calculates the left and right indicated torques in such a way that the sum of the left and right indicated torques follows the required torque. The distribution ratio of the left and right indicated torques is 1:1 under the standard, but the distribution ratio can be changed based on predetermined conditions. By calculating the indicated torque in a manner that does not exceed the upper limit rate of change, even if the accelerator pedal 11 is violently operated, the output torque of the drive wheels 2a, 2a can be changed smoothly.

[0036] Moreover, the indicated torque calculation unit 32 has a traction control function of suppressing the output torque of the drive wheels 2a, 2a regardless of the required torque in the case where the drive wheels 2a, 2a spin, so that the slip ratio of the drive wheels 2a, 2a becomes below a predetermined value. The indicated torque calculation unit 32 can detect the spin of the drive wheels 2a, 2a using the outputs of the wheel speed sensors 26, 26 of the drive wheels 2a, 2a, etc.

[0037] Moreover, the indicated torque calculation unit 32 includes a rate adjustment unit 33 that adjusts the upper limit rates of change of the left and right based on predetermined conditions. The so-called left upper limit rate of change means the upper limit of the rate of change of the torque output from the left traveling motor 22 to the left drive wheel 2a, and the so-called right upper limit rate of change means the upper limit of the rate of change of the torque output from the right traveling motor 22 to the right drive wheel 2a. The adjustment of the upper limit rate of change can be achieved by limiting the time rate of change of the torque itself to the upper limit rate of change. For example, in the case of calculating the indicated torque following the required torque using the first-order lag filtering method, it can be achieved by adjusting the time constant of the first-order lag filtering method.

[0038] In the case where there is a predetermined steering angle turning operation using the steering wheel 13 and the loads applied to the left and right drive wheels 2a, 2a satisfy the predetermined conditions, the rate adjustment unit 33 makes the upper limit rate of change of the inner wheel before the steering angle turning smaller than the upper limit rate of change of the outer wheel before the steering angle turning. Or, it makes the upper limit rate of change of the inner wheel before the steering angle turning lower than the standard upper limit rate of change during straight running decrease.

[0039] The above-mentioned predetermined steering angle turning operation, for example, corresponds to such as Figure 2As shown in the steering angle θ column, when the absolute value |θ| of the steering angle is equal to or greater than the steering angle threshold θth1, the speed |Δθ| at which the steering angle is rotated becomes equal to or greater than the steering angle change rate threshold Δθth, and so on. The steering angle threshold θth1 and the steering angle change rate threshold Δθth are set to positive values. The steering angle threshold θth1 and the steering angle change rate threshold Δθth may be values that change according to parameters such as vehicle speed and road surface conditions that represent the ease of occurrence of slipping.

[0040] The above-mentioned predetermined condition regarding the load is equivalent to, for example, Figure 2 As shown in the wheel loads Pl and Pr columns, the load of the drive wheel 2a that is the inner wheel before the steering angle is rotated among the drive wheels 2a, 2a is equal to or less than the threshold load Pth1, and so on. The threshold load Pth1 may be a value that changes according to parameters such as vehicle speed and road surface conditions that represent the ease of occurrence of slipping.

[0041] <Action Example>

[0042] Figure 2 is a timing chart showing an action example when the electric vehicle of the embodiment switches from turning travel to straight travel. In Figure 2 , the lines of the left torque and the right torque shown in the motor torque column are lines indicating the left and right indicated torques. This is because the drive control unit 35 drives the left and right traveling motors 22 so that the motor torque coincides with the indicated torque.

[0043] The load center of the electric vehicle 1 moves back and forth during braking or acceleration and moves left and right during turning. When the load on the inner wheel side drive wheel 2a is low, if the steering angle is rotated quickly, the low load on the inner wheel side drive wheel 2a will continue for a short time under the action of the suspension.

[0044] Figure 2 The action example represents the action when quickly switching from turning travel to straight travel in a situation where the friction coefficient of the road surface (road surface μ) is low. During Figure 2 the period T1, the steering angle and vehicle speed during turning travel are large with respect to the required torque, and before the time shown in Figure 2 the drive wheels 2a, 2a spin, and thus traction control is executed. By the traction control, the left and right indicated torques are suppressed to low torques, and the required torque is greater than the value obtained by adding the left and right indicated torques.

[0045] When changing from a turning section to a straight section, if the driver quickly returns the steering wheel 13 from a steering angle greater than or equal to a certain value, at the timing t1 when the return starts, a situation occurs where the steering angle |θ| is greater than or equal to the steering angle threshold θth1 and the speed |Δθ| of the return steering angle θ becomes greater than or equal to the steering angle change rate threshold Δθth. The change rate adjustment unit 33 repeatedly performs a determination process on whether such a situation occurs. If such a situation is detected, the value of the load sensor 24 is then read, and it is determined whether the load (left tire load Pl) of the drive wheel 2a on the inner wheel side is not less than the threshold load Pth1. Then, if the determination result is yes, the change rate adjustment unit 33 sets the upper limit change rate on the inner wheel side to a value lower than the normal upper limit change rate. That is, the upper limit change rate on the outer wheel side remains the normal value, and the upper limit change rate on the inner wheel side is lower than the upper limit change rate on the outer wheel side.

[0046] At the end of the traction control period T1 and at the stage of starting to turn the steering angle θ, the slip rates of the drive wheels 2a, 2a become below a predetermined value, and the traction control ends. Then, the indicated torque calculation unit 32 starts to calculate so that the left and right indicated torques follow the left and right required torques. In Figure 2 In the operation example of, at the end of the traction control, the left and right indicated torques are suppressed to be lower than the required torque. Therefore, during the periods T2, T3 immediately after the traction control ends, the indicated torque calculation unit 32 increases the left and right indicated torques at a rate close to the upper limit change rate determined by the change rate adjustment unit 33. Here, the right upper limit change rate is the normal value, but the left upper limit change rate is set to a low value. Therefore, as Figure 2 shown in the periods T2, T3 of, the right indicated torque rises relatively sharply, but the left indicated torque rises gently. And it takes a relatively long time for the sum of the left and right indicated torques to be approximately the same as the required torque.

[0047] During the periods T4 before and after the operation of quickly turning the steering angle θ, the load of the drive wheel 2a that belongs to the inner wheel side before turning the steering will remain low. If a large torque is applied to the drive wheel 2a when the load is low, it will cause the drive wheel 2a to slip. However, in this embodiment, during the period T4, the indicated torque of the drive wheel 2a on the inner wheel side rises gently and does not increase rapidly. Therefore, even if the load of the drive wheel 2a on the inner wheel side remains low, the situation where the drive wheel 2a on the inner wheel side slips is suppressed.

[0048] After the change rate adjustment unit 33 reduces the upper limit change rate on the inner wheel side at the timing t1, based on appropriate conditions such as after a predetermined time or when the difference between the left and right indicated torques approaches within the threshold, the upper limit change rate on the inner wheel side is adjusted back to the normal value.

[0049] <Comparative Example>

[0050] Figure 3It is a timing chart showing an operation example when an electric vehicle of a comparative example switches from a turning drive to a straight drive. The electric vehicle of the comparative example does not have the function of the change rate adjustment unit 33 of the present embodiment. Figure 3 The operation example shows a case where the same driving operation as Figure 2 the operation example is performed.

[0051] As Figure 3 shown, when the steering angle θ is rotated to switch from a turning section to a straight section (period T11), the traction control that occurred in the turning section ends, and the indication torque calculation unit increases the left and right indication torques to follow the required torque. At this time, in the comparative example, the left and right upper limit change rates are normal values. Therefore, when, even though the steering angle θ has been rotated, there is a period T12 in which the load of the drive wheel 2a on the inner wheel side is maintained at a low load, sometimes during this period T12, the indication torque increases relatively quickly. If a large torque is output to the drive wheel 2a on the inner wheel side that maintains a low load, slipping SL of the drive wheel 2a occurs. If slipping SL occurs, then traction control is performed afterwards, and a short-term magnitude fluctuation D1 occurs in the torque of the drive wheel 2a on the inner wheel side. Due to such a fluctuation D1, the drivability of the electric vehicle is reduced.

[0052] On the other hand, in the electric vehicle 1 of the present embodiment, the occurrence of slipping SL as described above is suppressed, and the reduction in the drivability of the electric vehicle 1 when switching from a turning section to a straight section is suppressed.

[0053] In addition, in Figure 2 and Figure 3 the operation example, the operation when traction control occurs during turning drive is shown, and in this operation, the superiority of the present embodiment over the comparative example is shown. However, even when switching from a turning drive in which traction control never occurs to a straight drive, when the amount of depression of the accelerator pedal 11 is increased relatively quickly, the superiority of the present embodiment over the comparative example is similarly obtained. That is, as described above, if the amount of depression of the accelerator pedal 11 is increased rapidly when switching to a straight drive, in the electric vehicle of the comparative example, during the period when the load of the drive wheel on the inner wheel side is maintained at a low load, the indication torque becomes large, and the same behavior as the above-described slipping SL is likely to occur. On the other hand, in the electric vehicle 1 of the embodiment, during the period when the load of the drive wheel 2a on the inner wheel side is maintained at a low load, the indication torque of the drive wheel 2a increases gently, so it is difficult for the above-described slipping SL to occur. Therefore, the electric vehicle 1 of the present embodiment can also suppress the reduction in the drivability of the electric vehicle 1 during the above-described driving operation.

[0054] In addition, in the above-described embodiment, the indicated torque calculation unit 32 determines whether the load on the drive wheel 2a on the inner wheel side is equal to or less than the threshold load Pth1 based on the operation of the rapid turning steering angle, and reduces the upper limit change rate on the inner wheel side based on the result of this determination. However, for example, when a rapid turning steering angle operation is performed at a certain vehicle speed or higher, it is possible to estimate how long the reduction in the load on the drive wheel 2a on the inner wheel side will be maintained. Therefore, the comparison process between the load on the drive wheel 2a on the inner wheel side and the threshold load Pth1 can also be omitted, and when a rapid turning steering angle is made at a predetermined vehicle speed or higher, the upper limit change rate on the inner wheel side is always reduced by the change rate adjustment unit 33. In such a configuration, the same function as described above when switching from turning driving to straight driving is also achieved.

[0055] As described above, in the electric vehicle 1 according to the present embodiment, when a predetermined steering angle turning operation is performed by the steering wheel 13, the change rate adjustment unit 33 makes the upper limit change rate belonging to the inner wheel side smaller than the upper limit change rate belonging to the outer wheel side. Therefore, although the load on the drive wheel 2a belonging to the inner wheel side may be temporarily reduced due to a rapid turning steering angle, at this time, even if the required torque increases, the indicated torque of the drive wheel 2a belonging to the inner wheel side increases gently. Therefore, it is possible to suppress the slip of the drive wheel 2a where the load is eliminated, and thus it is possible to suppress the deterioration of the drivability of the electric vehicle 1.

[0056] Moreover, in the electric vehicle 1 according to the present embodiment, the change rate adjustment unit 33 confirms the load on the drive wheel 2a belonging to the inner wheel side based on the fact that the steering angle has been turned at a predetermined rapidity or more by the steering wheel 13. And, when the load is equal to or less than the threshold load Pth1, the change rate adjustment unit 33 adjusts the upper limit change rate. Therefore, it is possible to achieve the following control: the upper limit change rate is adjusted only when there is a high possibility of slip if not adjusted due to a low load, slip is suppressed, and at the same time, when the load has recovered and the possibility of slip is low, the adjustment of the upper limit change rate is omitted and the torque is quickly restored.

[0057] Moreover, in the electric vehicle 1 according to the present embodiment, the indicated torque calculation unit 32 has a traction control function of suppressing the indicated torque regardless of the required torque based on the detection of the idling of the drive wheel 2a. As shown in the operation example of Figure 2 and Figure 3 , if there is a traction control function, when switching from turning driving to straight driving, the required torque and the indicated torque will deviate due to traction control, and after switching to straight driving and ending the traction control, it is easy to occur Figure 3 the slip SL as shown. In the present embodiment, such a slip SL can be suppressed, so it is particularly effective for the electric vehicle 1 having a traction control function.

[0058] The above has described the embodiments of the present invention. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, an operation example of the electric vehicle 1 when the driver performs steering and throttle operations is shown. However, for example, the steering and throttle operations of the electric vehicle may be performed by an autonomous driving device. In this case, the forms of the steering unit and the throttle operation unit are not limited to the forms of a disk and a pedal. In addition, in the above embodiments, an electric vehicle having two left and right drive wheels that are independently driven has been described. However, the electric vehicle of the present invention may be an electric vehicle in which four drive wheels, front, rear, left, and right, are independently driven. In this case, it may be configured to adjust the upper limit change rate through two processes, namely, the calculation process of the indicated torque related to the two left and right drive wheels of the front wheels and the calculation process of the indicated torque related to the two left and right drive wheels of the rear wheels. In addition, in the above embodiments, a sensor mounted on the inner surface of the tire is shown as the load sensor. However, the method of measuring the load is not particularly limited. In addition to this, it may be a structure that measures the load of each drive wheel based on the deformation amount of the suspension of the drive wheel. In addition, in the above embodiments, the torque has been described as the calculation object. However, the torque may be replaced with the driving force. Since there is a predetermined relationship between the driving force and the torque, a structure with the driving force as the calculation object can be regarded as equivalent to a structure with the torque as the calculation object. In addition to this, the details shown in the embodiments can be appropriately changed without departing from the gist of the invention.

Claims

1. A control device for an electric vehicle, which is installed in an electric vehicle having a steering section, an accelerator operation section, a left traveling motor and a right traveling motor that respectively output power to left and right drive wheels, and is characterized in that: The control device includes: A required torque calculation unit that calculates a required torque corresponding to the operation of the accelerator operation section; An indicated torque calculation unit that calculates left and right indicated torques that follow the required torque; A change rate adjustment unit that adjusts upper limit change rates of the left and right indicated torques; And A drive control unit that controls the left traveling motor and the right traveling motor so that the calculated left and right indicated torques are respectively output from the left traveling motor and the right traveling motor, Based on a predetermined steering angle turning operation performed by the steering section, the change rate adjustment unit makes the upper limit change rate belonging to the inner wheel side before the steering angle turns smaller than the upper limit change rate belonging to the outer wheel side before the steering angle turns; The predetermined steering angle turning operation is a case where when the absolute value of the steering angle is equal to or greater than a steering angle threshold, the speed of turning the steering angle becomes equal to or greater than a steering angle change rate threshold; The steering angle threshold and the steering angle change rate threshold are positive values, and the steering angle threshold and the steering angle change rate threshold are values that change according to a parameter reflecting the ease of occurrence of slippage based on the vehicle speed or road surface condition.

2. The control device for an electric vehicle according to claim 1, characterized in that: The control device is installed in an electric vehicle further equipped with load sensors that respectively detect the loads of the left and right drive wheels, Based on a predetermined steering angle turning operation performed by the steering section, when the load of the drive wheel belonging to the inner wheel side before the steering angle turns is equal to or less than a load threshold, the change rate adjustment unit makes the upper limit change rate belonging to the inner wheel side before the steering angle turns smaller than the upper limit change rate belonging to the outer wheel side before the steering angle turns.

3. The control device for an electric vehicle according to claim 1 or 2, characterized in that: The indicated torque calculation unit also suppresses the left and right indicated torques based on the detection of the idling of one of the left and right drive wheels.

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