vehicle

Abstract

We propose a technology that reduces the torque input from the wheels to the motor while maintaining the vehicle's driving stability. [Solution] The vehicle includes a motor for driving the wheels, a storage device that stores target rotation speed data which defines the target rotation speed of the motor according to the road surface friction coefficient, and a control device. The control device performs the following steps: when the wheels are slipping on a low-μ road which has a road surface friction coefficient lower than a reference value, it determines whether the wheels have moved to a high-μ road which has a road surface friction coefficient higher than the reference value; when it determines that the wheels have moved to the high-μ road, it identifies a target rotation speed corresponding to the road surface friction coefficient of the high-μ road from the target rotation speed data; and when it determines that the wheels have moved to the high-μ road, it performs the following steps: it reduces the rotation speed of the motor to the identified target rotation speed.

Description

Technical Field

[0001] The technology disclosed in this specification relates to vehicles.

Background Art

[0002] Patent Document 1 discloses a vehicle equipped with a motor and a control device. The vehicle travels by driving the motor. The control device corrects to reduce the required torque for the motor when the road surface changes from a low-μ road to a high-μ road during the vehicle's travel. Thereby, when the road surface changes from a low-μ road to a high-μ road, excessive torque is prevented from being input from the wheels to the motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If the required torque is reduced too much when the road surface changes from a low-μ road to a high-μ road, the running stability of the vehicle, such as the vehicle decelerating, decreases. On the other hand, if the reduction of the required torque is insufficient, the torque input from the wheels to the motor increases. In this specification, a technique for reducing the torque input from the wheels to the motor while maintaining the running stability of the vehicle is proposed.

Means for Solving the Problems

[0005] (Aspect 1) The vehicle disclosed herein includes a motor for driving wheels, a storage device that stores target rotation speed data defining a target rotation speed of the motor according to the road surface friction coefficient, and a control device, wherein the control device performs the steps of: determining whether the wheels have moved to a high-μ road having a road surface friction coefficient higher than the reference value when the wheels are slipping on a low-μ road having a road surface friction coefficient lower than the reference value; identifying a target rotation speed corresponding to the road surface friction coefficient of the high-μ road from the target rotation speed data if it is determined that the wheels have moved to the high-μ road; and reducing the rotation speed of the motor to the identified target rotation speed.

[0006] The inventors of this application have found that the appropriate value for the reduction in motor rotational speed changes depending on the road surface friction coefficient. In the above vehicle, a memory device stores target rotational speed data that defines the target rotational speed of the motor according to the road surface friction coefficient. When the road surface changes from a low-μ surface to a high-μ surface, the control device reduces the motor rotational speed to a target rotational speed corresponding to the road surface friction coefficient of the high-μ surface. Therefore, the torque input from the wheels to the motor can be reduced while maintaining the vehicle's driving stability. [Brief explanation of the drawing]

[0007] [Figure 1] This is a top-down view of the vehicle. [Figure 2] This is a flowchart of the operation process of the control device. [Figure 3] This graph shows the relationship between motor rotation speed and the torque generated by the motor. [Modes for carrying out the invention]

[0008] First, let's explain the problems that arise when a vehicle moves from a low-μ road surface (e.g., an icy road) to a high-μ road surface (e.g., a dry road). When a vehicle is traveling on a low-μ road, the wheels may slip. If a vehicle moves from a low-μ road to a high-μ road while its wheels are slipping, the vehicle will accelerate rapidly, and an excessive torque will be instantaneously input from the road surface to the motor through the wheels. When such an excessive torque is input, there is a risk that the drive mechanism (e.g., gears that make up the reduction gear) will be subjected to a load that exceeds its allowable limit. To address this problem, if control is implemented to reduce the motor speed when the vehicle moves from a low-μ road to a high-μ road, the torque applied from the road surface to the wheels can be reduced.

[0009] Figure 3 is a graph showing the relationship between motor rotational speed R and torque T generated in the motor. Figure 3 shows the torque generated in the motor when the motor is rotated at a constant rotational speed with the wheels not slipping (i.e., when the vehicle is traveling at a constant speed). As shown in Figure 3, in the region where the motor rotational speed R is low, the torque T increases as the rotational speed R increases. Also, in the region where the motor rotational speed R is higher than a predetermined value, the torque T is maintained at a high value. Furthermore, the intensity threshold L1 shown in Figure 3 is the allowable upper limit of torque T. If torque T exceeds the intensity threshold L1, excessive torque is applied to the motor and drive mechanism (e.g., the ring gear of a planetary gear reducer). Furthermore, the upper limit rotational speed Rth shown in Figure 2 is the rotational speed R at the intensity threshold L1. If the vehicle travels on a high-μ surface at a rotational speed exceeding the upper limit rotational speed Rth, torque T exceeding the intensity threshold L1 will be generated.

[0010] Next, the motor control method of the comparative example will be explained. The rotational speeds R1 and R2 in Figure 3 illustrate the rotational speed R of the motor in the comparative example vehicle. Note that rotational speed R2 is the target rotational speed when moving from a low-μ path to a high-μ path, and is set to a value slightly lower than the upper limit rotational speed Rth. Assume that the motor rotational speed R is R1 when the wheels of the comparative example vehicle are slipping on a low-μ path. In this case, the comparative example vehicle reduces the rotational speed R from R1 to R2 when moving from a low-μ path to a high-μ path. As a result, the torque T generated when moving from a low-μ path to a high-μ path is suppressed to a value less than the intensity threshold L1. In this way, the comparative example vehicle can suppress the generation of excessive torque.

[0011] Figure 3 shows a graph for the case where the road surface friction coefficient of a high-μ surface is constant. However, the graphs of rotational speed R and torque T change depending on the road surface friction coefficient of the high-μ surface. Therefore, the upper limit rotational speed Rth when the torque T reaches the intensity threshold L1 changes depending on the road surface friction coefficient of the high-μ surface. In the motor control method of the comparative example, a constant target rotational speed R2 is set so that the target rotational speed R2 is below the upper limit rotational speed Rth in all cases where the road surface friction coefficient of the high-μ surface is different, so the target rotational speed R2 may become lower than necessary. Therefore, when the vehicle moves from a low-μ surface to a high-μ surface, the motor rotational speed R may become lower than necessary, and driving stability may be impaired. [Examples]

[0012] The vehicle 100 shown in Figure 1 is an electric vehicle equipped with a motor 10. The vehicle 100 moves by driving the motor 10 with electricity stored in a battery (not shown).

[0013] Vehicle 100 has wheels 12, 14, 16, and 18 and a drive mechanism 20. Wheels 12 and 14 are the front wheels. Wheels 16 and 18 are the rear wheels. The drive mechanism 20 is a mechanism that transmits the rotation of the motor 10 to the wheels 12 and 14 and has a reduction gear (for example, a planetary gear reduction gear) and a differential. Wheels 12 and 14 rotate at a rotational speed reduced by a predetermined ratio (hereinafter referred to as the gear ratio M) relative to the rotational speed of the motor 10. The motor 10 is driven by electricity stored in a battery (not shown) and rotates the wheels 12 and 14 via the drive mechanism 20.

[0014] Vehicle 100 has wheel sensors 22-28. Wheel sensors 22-28 are located near each of the wheels 12-18. Wheel sensors 22-28 detect the rotational speed (i.e., wheel speed) of each of the wheels 12-18.

[0015] Vehicle 100 has a vehicle speed sensor 30. The vehicle speed sensor 30 is, for example, a GPS speedometer and detects the speed of vehicle 100 (i.e., vehicle speed).

[0016] The vehicle 100 has a storage device 32. The storage device 32 stores target rotational speed data that defines the target rotational speed R2. As mentioned above, the upper limit rotational speed Rth changes depending on the road surface friction coefficient of a high μ road, so the appropriate target rotational speed R2 also changes depending on the road surface friction coefficient. In this embodiment, the storage device 32 stores target rotational speed data that defines the target rotational speed R2 of the motor 10 for each road surface friction coefficient μ of a high μ road. The target rotational speed R2 is set to a value slightly below the upper limit rotational speed Rth in each case where the road surface friction coefficient is different.

[0017] Vehicle 100 has a control device 34. The control device 34 controls the motor 10. The control device 34 also receives input from the motor 10's rotation speed, the wheel rotation speeds detected by wheel sensors 22-28, and the vehicle speed detected by the vehicle speed sensor 30.

[0018] While the vehicle 100 is running, the control device 34 repeatedly executes the flowchart shown in FIG. 2. Steps S8 to S12 in FIG. 2 are input torque reduction operations, and steps S2 to S6 are determination processes for whether to execute the input torque reduction operation.

[0019] In step S2, the control device 34 substitutes the values corresponding to the following formula (1) to calculate the road surface friction coefficient μ1 of the road surface where the wheel 12 is located. Further, the control device 34 substitutes the values corresponding to the formula (1) to calculate the road surface friction coefficient μ2 of the road surface where the wheel 14 is located.

Equation

[0020] Furthermore, the control device 34 determines whether at least one of the calculated road surface friction coefficients μ1 and μ2 is lower than the reference value. That is, the control device 34 determines whether the vehicle 100 is running on a low-μ road. When the road surface friction coefficient μ1 and the road surface friction coefficient μ2 are higher than the reference value (NO in step S2), the control device 34 does not execute the input torque reduction operation.

[0021] If at least one of the road surface friction coefficients μ1 and μ2 is below the reference value (if YES in step S2), in step S4, the control device 34 calculates the normal value of the wheel speed of wheels 12 to 18 (i.e., the wheel speed when each wheel is not slipping) from the vehicle speed detected by the vehicle speed sensor 30. The control device 34 calculates the difference between the normal value of the wheel speed of wheels 12 to 18 and the wheel speed of wheels 12 to 18 detected by the wheel sensors 22 to 28 (hereinafter referred to as the wheel speed difference). The control device 34 determines whether the calculated wheel speed difference is equal to or greater than the specified value. If the calculated wheel speed difference is equal to or greater than the specified value, the control device 34 determines that one of the wheels 12 to 18 is slipping. If wheels 12 to 18 are not slipping (if NO in step S4), the control device 34 does not perform the input torque reduction operation.

[0022] If any one of the wheels 12 to 18 is slipping (if the answer is YES in step S4), in step S6, the control device 34 recalculates the road surface friction coefficients μ1 and μ2 of wheels 12 and 14 using the above formula (1). The control device 34 determines whether the road surface friction coefficient μ1 has risen to a value equal to or greater than the reference value, and whether the road surface friction coefficient μ2 has risen to a value equal to or greater than the reference value. If at least one of the road surface friction coefficients μ1 and μ2 has risen to a value equal to or greater than the reference value, the control device 34 determines that the road surface on which the vehicle 100 is traveling has changed from a low-μ road to a high-μ road. If the road surface on which the vehicle is traveling has not changed from a low-μ road to a high-μ road (if the answer is NO in step S6), the control device 34 does not perform the input torque reduction operation.

[0023] If the road surface being driven on changes from a low-μ surface to a high-μ surface (if the answer is YES in step S6), the control device 34 performs an input torque reduction operation in steps S8 to S12. In step S8, the control device 34 identifies the wheel whose road surface friction coefficient μ was equal to or greater than the reference value, and identifies the road surface friction coefficient μ (hereinafter referred to as road surface friction coefficient μa) of that wheel. After executing step S8, the control device 34 executes step S10.

[0024] In step S10, the control device 34 identifies a target rotational speed R2 corresponding to the road surface friction coefficient μa from the target rotational speed data stored in the memory device 32. After executing step S10, the control device 34 executes step S12.

[0025] In step S12, the control device 34 reduces the rotational speed of the motor 10 to the target rotational speed R2 identified in step S10. After executing step S12, the control device 34 terminates the input torque reduction operation.

[0026] As described above, in this embodiment, in the target rotation speed data stored in the memory device 32, an appropriate target rotation speed R2 is set for each high-μ road surface friction coefficient μ. The control device 34 reduces the rotation speed of the motor 10 to the target rotation speed R2 according to the high-μ road surface friction coefficient μa identified during driving. This prevents the rotation speed of the motor 10 from decreasing more than necessary, while making it possible to reduce the torque generated in the motor 10 to a value lower than the intensity threshold L1. As a result, the torque input from the wheels 12 and 14 to the drive mechanism 20 and the motor 10 can be reduced while maintaining the driving stability of the vehicle 100.

[0027] In the embodiment described above, vehicle 100 was a front-wheel drive vehicle. However, vehicle 100 may also be a rear-wheel drive vehicle. In that case, the relationship formula for the road surface friction coefficient μ is calculated based on the values ​​of wheels 16 and 18. Vehicle 100 may also be a four-wheel drive vehicle. In that case, the relationship formula for the road surface friction coefficient μ is calculated based on the values ​​of wheels 12 to 18.

[0028] Although embodiments have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness. [Explanation of symbols]

[0029] 10: Motor, 12-18: Wheels, 20: Drive mechanism, 22-28: Wheel sensors, 30: Vehicle speed sensor, 32: Memory device, 34: Control device, 100: Vehicle

Claims

[Claim 1] It is a vehicle, A motor that drives the wheels, A storage device that stores target rotational speed data that defines the target rotational speed of the motor according to the road surface friction coefficient, control device, Equipped with, The control device, The steps include determining whether the wheel has moved to a high-μ road surface having a road surface friction coefficient higher than the reference value when the wheel is spinning on a low-μ road surface having a road surface friction coefficient lower than the reference value, When it is determined that the wheel has moved onto the high-μ surface, the step of identifying a target rotational speed corresponding to the road surface friction coefficient of the high-μ surface from the target rotational speed data, A step of reducing the rotational speed of the motor to the specified target rotational speed, Execute vehicle.

Images