Vehicle control system

Abstract

The objective is to provide a vehicle control device that can appropriately suppress vehicle vibrations. [Solution] A vehicle control device comprising: a determination unit that determines whether the slip ratio of the vehicle's tires falls within a predetermined range in which the longitudinal force of the tires changes from increasing to decreasing as the slip ratio of the tires increases; and a setting unit that, in the case of a positive determination by the determination unit, sets a higher value for the frequency of vibrations to be suppressed in vibration damping control that suppresses vibrations of the vehicle than in the case of a negative determination by the determination unit.

Description

Technical Field

[0001] The present invention relates to a vehicle control device.

Background Art

[0002] Vibration control for suppressing vehicle vibrations is known. In vibration control, the frequency of vibrations to be suppressed is predetermined (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As the slip ratio of a tire increases, there is a range in which the vertical force of the tire changes from an increase to a decrease. If the slip ratio is within such a range, there is a possibility that vehicle vibrations cannot be appropriately suppressed even by the above vibration control.

[0005] Therefore, an object of the present invention is to provide a vehicle control device that can appropriately suppress vehicle vibrations.

Means for Solving the Problems

[0006] The above object can be achieved by a vehicle control device including a determination unit that determines whether or not the slip ratio of a vehicle tire is included in a predetermined range in which the vertical force of the tire changes from an increase to a decrease as the slip ratio of the tire increases, and a setting unit that sets a higher value for the frequency of vibrations to be suppressed in vibration control for suppressing vibrations of the vehicle when the determination unit makes an affirmative determination than when the determination unit makes a negative determination.

Effects of the Invention

[0007] According to the present invention, a vehicle control device that can appropriately suppress vehicle vibrations can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of the vehicle's configuration. [Figure 2] Figure 2A is a graph showing the relationship between the tire slip ratio and the tire longitudinal force, Figure 2B is a graph showing the case when the tire slip ratio fluctuates with a predetermined period, Figure 2C is a graph showing the fluctuation of the tire longitudinal force when the tire slip ratio fluctuates outside the predetermined range R, and Figure 2D is a graph showing the fluctuation of the tire longitudinal force when the tire slip ratio fluctuates within the predetermined range R such that it crosses the peak value P. [Figure 3] Figure 3 is a flowchart illustrating the vibration frequency setting control performed by the ECU. [Modes for carrying out the invention]

[0009] [Vehicle Outline] Figure 1 is a schematic diagram of Vehicle 1. Vehicle 1 is an electric vehicle equipped with a motor 2. Vehicle 1 comprises a motor 2, a propeller shaft 3, a differential gear 4, drive shafts 51 and 52, tires 61 and 62, a PCU (Power Control Unit) 7, a battery 8, and an ECU (Electric Control Unit) 10.

[0010] Motor 2 functions as a prime mover, outputting torque in response to power supply. Furthermore, Motor 2 also functions as a generator, generating electricity when Vehicle 1 is braking. The electricity generated by Motor 2 is supplied to Battery 8 via PCU 7.

[0011] Motor 2 is connected to tires 61 and 62 via propeller shaft 3, differential gear 4, and drive shafts 51 and 52. The vehicle 1 moves when the torque of motor 2 is transmitted to tires 61 and 62.

[0012] The ECU10 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and storage devices, and performs various controls by executing programs stored in the ROM and storage devices. The ECU10 is an example of a vehicle control device and functionally implements the determination unit and setting unit, which will be described in more detail later.

[0013] The ECU10 is electrically connected to an ignition switch 90, wheel rotation speed sensors 91 and 92, axle rotation speed sensor 93, accelerator pedal position sensor 94, and vehicle speed sensor 95. The ignition switch 90 detects the on / off state of the ignition. The wheel rotation speed sensors 91 and 92 detect the rotation speed of the tires 61 and 62, respectively (hereinafter referred to as wheel speed). The axle rotation speed sensor 93 detects the rotation speed of the propeller shaft 3. The accelerator pedal position sensor 94 detects the accelerator pedal position operated by the driver. The vehicle speed sensor 95 detects the vehicle speed of vehicle 1.

[0014] Figure 2A is a graph showing the relationship between the tire slip ratio and the tire's longitudinal force. The tire slip ratio is, for example, the difference between the tire's wheel speed and the vehicle speed divided by the vehicle speed. The tire's longitudinal force is the force acting in the longitudinal direction of the tire from the contact surface. As shown in Figure 2A, the tire's longitudinal force increases as the slip ratio increases. The longitudinal force reaches a peak value P at a given slip ratio. Beyond that point, the longitudinal force gradually decreases. Thus, there exists a predetermined range R in which the longitudinal force changes from increasing to decreasing as the slip ratio increases.

[0015] Figure 2B is a graph showing the case where the tire slip ratio fluctuates with a predetermined period. For example, when a vehicle accelerates suddenly, the slip ratio fluctuates periodically as shown in Figure 2B. Figure 2C is a graph showing the fluctuation of the longitudinal force of a tire when the tire slip ratio fluctuates outside the predetermined range R. The vehicle vibrates due to the fluctuation of the longitudinal force of the tire. When the tire slip ratio fluctuates outside the predetermined range R, the frequency of the slip ratio fluctuation and the frequency of the longitudinal force fluctuation coincide. For example, when the slip ratio fluctuates within a range smaller than the predetermined range R, the longitudinal force increases or decreases in accordance with the increase or decrease in the slip ratio. When the slip ratio fluctuates within a range larger than the predetermined range R, the longitudinal force decreases as the slip ratio increases, and increases as the slip ratio decreases.

[0016] Figure 2D is a graph showing the fluctuation of the longitudinal force of a tire when the tire slip ratio fluctuates within a predetermined range R, crossing the peak value P. When the slip ratio fluctuates within the predetermined range R, crossing the peak value P, the frequency of the longitudinal force fluctuation is approximately twice the frequency of the slip ratio fluctuation. For example, when the slip ratio increases from below the peak value P to above the peak value P, or when it decreases from above the peak value P to below the peak value P, the longitudinal force changes from increasing to decreasing. Thus, when the slip ratio fluctuates within the predetermined range R, the frequency of the longitudinal force fluctuation increases compared to when it fluctuates outside the predetermined range R. Consequently, the frequency of vibration of vehicle 1 also increases in this way.

[0017] Figure 3 is a flowchart illustrating the vibration frequency setting control performed by the ECU 10. The ECU 10 determines whether or not launch control has been started (step S1). Launch control is a control to suddenly accelerate a stationary vehicle 1. This is because, as mentioned above, the slip ratio is likely to fluctuate when the vehicle 1 is suddenly accelerated. If the answer in step S1 is No, this control is terminated. If the answer in step S1 is Yes, the ECU 10 determines whether or not the tire slip ratio falls within a predetermined range R (step S2). Here, the tire slip ratio may be, for example, the slip ratio of either tire 61 or 62, or the average slip ratio of tires 61 and 62. The slip ratio is calculated using the detected values ​​of the wheel rotation speed sensors 91 and 92 and the vehicle speed sensor 95. Step S2 is an example of the processing performed by the determination unit.

[0018] If the answer in step S2 is No, the ECU 10 sets the frequency of vibration to be suppressed by vibration damping control to frequency H1 (step S3). If the answer in step S2 is Yes, the ECU 10 sets the frequency of vibration to be suppressed by vibration damping control to frequency H2, which is higher than frequency H1 (step S4). For example, frequency H2 is set to twice frequency H1. Steps S3 and S4 are examples of processes performed by the setting unit. Vibration damping control is a control that reduces the maximum torque of motor 2 when, for example, the frequency of fluctuations in the rotational speed of the propeller shaft 3 becomes the frequency of the vibration to be suppressed as described above. As described above, by switching the frequency of vibration to be suppressed by vibration damping control depending on whether the slip ratio is within a predetermined range R, the vibration of vehicle 1 is appropriately suppressed.

[0019] In the above embodiment, vehicle 1, which is an electric vehicle, was used as an example, but the invention is not limited to this. For example, the vehicle may be an engine-powered vehicle equipped with an engine as a power source for driving. Alternatively, the vehicle may be a hybrid vehicle equipped with both an engine and a motor as power sources for driving. In the above embodiment, the motor 2 and tires 61 and 62 are directly connected, but the invention is not limited to this, and the contents of the above embodiment can also be applied to mechanisms that are connected via a clutch, transmission, etc.

[0020] As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0021] 1 Vehicle 10 ECU (Vehicle Control Device, Determination Unit, Setting Unit) 61, 62 Tires

Claims

[Claim 1] A determination unit that determines whether the slip ratio of the vehicle's tires falls within a predetermined range in which the longitudinal force of the tires changes from increasing to decreasing as the slip ratio of the tires increases, A vehicle control device comprising: a setting unit that, when the determination unit makes a positive determination, sets a higher value for the frequency of the vibration to be suppressed in the vibration damping control that suppresses the vibration of the vehicle than when the determination unit makes a negative determination.

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