Variable damper control method

Abstract

To provide a variable damper control method which enables improvement of road-hugging property of a tire and vibration resistance to realize traveling of a vehicle which achieves high road surface following performance during traveling on a bad road.SOLUTION: In a vehicle, one of a front wheel and a rear wheel is driven by an in-wheel motor housed in the wheel, the other is driven by an on-board motor provided at a vehicle body, and at least the wheel driven by the in-wheel motor is attached to a suspension device having a variable damper capable of adjusting a damping force. In a variable damper control method of the vehicle, the variable damper adjusts the damping force according to a wheel speed of the wheel driven by the in-wheel motor.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for controlling a variable damper, and more particularly to a method for controlling a variable damper attached to a wheel of a vehicle equipped with an in-wheel motor. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in order to improve the driving stability of a vehicle when the vehicle is traveling on a rough road, a control method is known in which an electronic suspension is provided in the vehicle and the damping force of the electronic suspension is adjusted.

[0003] For example, the vehicle suspension control device disclosed in Patent Document 1 includes a vertical acceleration detection means for detecting the acceleration of the vehicle in the vertical direction, a rough road determination function for determining whether the road on which the vehicle is traveling is rough or not based on the vertical acceleration detected by the vertical acceleration detection means, and a rough road sensitive control function for setting the damping force of the suspension mechanism of the vehicle to a harder state when the road on which the vehicle is traveling is determined to be rough, and the vehicle suspension control device includes a driving wheel speed detection means for detecting the wheel speed of the driving wheels, and a driven wheel speed detection means for detecting the wheel speed of the driven wheels, and the suspension control means is equipped with a spin determination function for determining whether the driving wheels are spinning or not based on the difference between the wheel speed of the driving wheels detected by the driving wheel speed detection means and the wheel speed of the driven wheels detected by the driven wheel speed detection means, and a rough road spin sensitive control function for setting the damping force of the suspension mechanism to a relatively softer state when the road on which the vehicle is traveling is determined to be rough and spinning is occurring at the driving wheels. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-336109 Summary of the Invention [Problem to be solved by the invention]

[0005] Regarding electric vehicles (EVs) that are driven by an electric motor such as a motor, there are known on-board motor types in which a motor is mounted on the vehicle body like a vehicle equipped with a conventional internal combustion engine, and the rotational force of the motor is transmitted to each wheel to obtain driving force, as well as in-wheel motor types in which a motor is housed in the wheels of the vehicle to drive the wheels.

[0006] In-wheel motor type electric vehicles have various advantages, such as less energy loss caused by conventional gears and drive shafts because much of the driving force from the electric motor is transmitted directly to the wheels, and no need to place these gears, drive shafts, etc. on the vehicle body, making it easier to reduce the vehicle weight and ensure sufficient passenger compartment volume.

[0007] However, it is known that in-wheel motor type electric vehicles, since the motor is housed in the wheel, the weight of the wheel increases, and the so-called unsprung load increases, resulting in a decrease in ride comfort and maneuverability. In addition, when the unsprung loads of the front and rear wheels are different, for example, when the front wheels are driven by an on-board motor type and the rear wheels are driven by an in-wheel motor type, the vibration of the rear wheels increases and the tire ground contact deteriorates when traveling on a rough road such as a Belgian road, which is a paved road with rectangular stones. In addition, in the case of such vehicles, the weight of the rear wheels increases, so the unsprung vibration when traveling on a rough road also increases, and the sprung vibration also deteriorates, so there has been a demand for suppressing these vibrations when traveling on a rough road to improve the tire ground contact and vibration resistance.

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide a variable damper control method that controls a variable damper provided on a vehicle in which either the front or rear wheels are driven by an in-wheel motor, and the other of the front or rear wheels is driven by an on-board motor, thereby improving tire ground contact and vibration resistance, thereby realizing vehicle driving with high road surface tracking when driving on rough roads. [Means for solving the problem]

[0009] The variable damper control method of the present invention, which solves the above-mentioned problems, is a method for controlling a variable damper of a vehicle in which either one of the front or rear wheels is driven by an in-wheel motor housed in the wheel, and the other is driven by an on-board motor provided on the vehicle body, and at least the wheel driven by the in-wheel motor is attached to a suspension device having a variable damper capable of adjusting the damping force, and the variable damper adjusts the damping force in accordance with the wheel speed of the wheel driven by the in-wheel motor. Effect of the Invention

[0010] According to the variable damper control method of the present invention, a determination is made based on the wheel speed of a wheel driven by an in-wheel motor as to whether the wheel is pressed against the road surface or is floating, and the damping force of the variable damper is adjusted according to the state. This improves tire contact with the road when traveling on rough roads and reduces vibrations, making it possible to drive with high road surface tracking even on rough roads. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a vehicle equipped with a variable damper for performing a variable damper control method according to an embodiment of the present invention; [Diagram 2] 1 is a diagram showing a suspension device having a variable damper for performing a variable damper control method according to an embodiment of the present invention; [Diagram 3] FIG. 2 is a block diagram showing a basic control block of a variable damper control method according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing a control law of a variable damper control method according to an embodiment of the present invention. [Diagram 5] 4 is a graph showing the relationship between wheel input load and travel distance in a simulation of a vehicle traveling on a rough road to which a variable damper control method according to an embodiment of the present invention is applied. [Figure 6] 5 is a graph showing the results of a sensory evaluation by a driver of a vehicle to which a variable damper control method according to an embodiment of the present invention is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of a control method for a variable damper according to the present invention will be described with reference to the drawings. Note that the following embodiment does not limit the invention according to each claim, and all combinations of features described in the embodiment are not necessarily essential to the solution of the invention.

[0013] FIG. 1 is a schematic diagram of a vehicle equipped with a variable damper that performs the variable damper control method of an embodiment of the present invention, FIG. 2 is a diagram showing a suspension device having a variable damper that performs the variable damper control method of an embodiment of the present invention, FIG. 3 is a block diagram showing the basic control blocks of the variable damper control method of an embodiment of the present invention, FIG. 4 is a diagram showing the control law of the variable damper control method of an embodiment of the present invention, FIG. 5 is a graph showing the relationship between wheel input load and traveling distance simulating rough road driving of a vehicle to which the variable damper control method of an embodiment of the present invention is applied, and FIG. 6 is a graph showing the results of a sensory evaluation by a driver of a vehicle to which the variable damper control method of an embodiment of the present invention is applied.

[0014] As shown in Fig. 1, the variable damper control method according to this embodiment is executed by an electronic control unit 7 mounted on a vehicle 1. The vehicle 1 has front wheels 2F arranged on the left and right sides of the front of the vehicle 1 and rear wheels 2R arranged on the left and right sides of the rear of the vehicle 1. The front wheels 2F and rear wheels 2R have friction brake devices 3 that brake the rotation of the wheels by frictional force.

[0015] The front wheels 2F are driven by an on-board motor 4 mounted on the vehicle body, and the rear wheels 2R are driven by an in-wheel motor 5 housed in the rear wheels 2R. The front wheels 2F are equipped with a steering mechanism (not shown) that tilts the front wheels 2F in the steering direction in response to the operation of a steering wheel 6 located in the driver's seat, and function as steering wheels. The steering mechanism may employ various conventionally known configurations, for example, a by-wire system having a steering actuator may be used.

[0016] The steering actuator is wired so that it can receive signals from an electronic control unit 7, which receives signals from an operation unit 6a having a steering wheel 6 operated by the driver and performs predetermined processing, and controls the front wheels 2F to a steering angle corresponding to the steering wheel 6 operated by the driver.

[0017] The electronic control unit 7 is also connected to the on-board motor 4 and the in-wheel motor 5, and when the driver operates the accelerator pedal 9a, controls the on-board motor 4 and the in-wheel motor 5 to apply driving force in accordance with the amount of operation of the accelerator pedal 9a. When the driver operates the brake pedal 9b, the electronic control unit 7 controls the friction brake device 3, the on-board motor 4, and the in-wheel motor 5 to operate as regenerative braking means in accordance with the brake operation.

[0018] The friction brake device 3 has a disk-shaped brake disc 3a attached coaxially to the axles of the front wheels 2F and the rear wheels 2R, and a caliper 3b equipped with brake pads that grip the brake disc 3a in the axial direction. The caliper 3b is connected to a master cylinder (not shown) that is actuated by the driver's operation of the brake pedal 9b, and generates frictional force by being pressed against the brake disc 3a by the amplification effect of hydraulic pressure, air pressure, etc., of the master cylinder. In addition, the friction brake device 3 can adjust the degree of pressing of the caliper 3b so as to adjust the frictional force between the brake pads and the brake disc 3a as necessary, regardless of the pedaling force applied to the brake pedal 9b by the driver, upon receiving a signal from the electronic control unit 7.

[0019] The on-board motor 4 and the in-wheel motor 5 rotate so that the vehicle 1 moves forward or backward in the traveling direction in response to a signal from the electronic control unit 7 according to the opening degree of the accelerator pedal 9a operated by the driver. In addition, during braking when the brake pedal 9b is operated, the on-board motor 4 and the in-wheel motor 5 input shaft rotation conversely to operate as a generator, and are also used as a regenerative braking device that converts kinetic energy into electrical energy and recovers or consumes it to use for braking.

[0020] The electronic control unit 7 has a microprocessor as a control means, and is operated by power supply from a battery (not shown). The electronic control unit 7 receives signals from the operation unit 6a, the brake pedal 9b, the accelerator pedal 9a, etc., processes the various signals, and transmits signals to drive the on-board motor 4 and the in-wheel motor 5 at a predetermined rotation speed.

[0021] The front wheels 2F and rear wheels 2R are attached to an active suspension system 10. As shown in Fig. 2, the active suspension system 10 is attached between each wheel (for example, the rear wheel 2R) and the vehicle body, and absorbs vibrations and shocks input from the road surface, maintains the posture of the vehicle body, and ensures running stability. The active suspension system 10 has an active suspension 31 and a variable damper 32.

[0022] The active suspension 31 includes a spring, which is a compression coil spring, and a vehicle height adjustment actuator 31a that suppresses the movement of the spring that oscillates and is capable of adjusting the height of the vehicle body from the ground.

[0023] The vehicle height adjustment actuator 31a includes, for example, a ball screw mechanism in which a ball screw and a ball screw nut are screwed together, and generates a damping force from the resistance force of a motor that generates electricity by the vertical expansion and contraction of the ball screw mechanism. The damping force can be adjusted by the driving force of the ball screw mechanism that expands and contracts up and down when electricity is applied to the motor. By driving the motor in this way to expand and contract the ball screw mechanism up and down, the overall length of the active suspension 31 can be expanded and contracted, and the height of the vehicle body from the ground can be adjusted by changing the distance between the wheels and the vehicle body.

[0024] The variable damper 32 is a rotary damper that utilizes a damping force generated by magnetorheological resistance. The variable damper 32 is connected to the electronic control unit 7 and includes a variable damper actuator 32a that can adjust the damping force by current control.

[0025] The variable damper actuator 32a is supported by, for example, a bearing or the like so that the rotating shaft can rotate relative to the main body case. A coil and a rotor are built into the main body case, and the rotating shaft is attached to the rotor. There is a gap around the rotor, and this gap is filled with magnetic fluid. When a current is passed through the coil of such a variable damper actuator 32a, the viscous resistance of the filled magnetic fluid increases, generating a force that hinders the rotation of the rotor. By controlling the current input to the coil in this way, the variable damper actuator 32a can adjust the damping force of the variable damper 32.

[0026] Such a variable damper 32 can generate a damping force electrically, and therefore has excellent responsiveness, and can suppress vibration of the vehicle body even when there are high-frequency bumps on the road surface while traveling. In addition, since the viscous resistance of the magnetic fluid can be adjusted steplessly, it is possible to control the current to a minimum in order to generate the required torque, and power consumption can be reduced.

[0027] The active suspension device 10 is connected to an electronic control unit 7 and configured to transmit the amount of expansion and contraction of the active suspension 31 and the damping force of the variable damper 32 to the electronic control unit 7. A vehicle height sensor 8 is also attached to the vehicle 1. The vehicle height sensor 8 is a sensor that can measure the distance from the underside of the vehicle 1 to the road surface, and an optical sensor or an ultrasonic distance sensor, for example, is preferably used. The vehicle height data measured by the vehicle height sensor 8 is transmitted to the electronic control unit 7 and processed.

[0028] Next, a control method for the variable damper 32 according to this embodiment will be described. The control method for the variable damper 32 according to this embodiment controls the damping force of the variable damper 32 of the active suspension device 10 attached to the rear wheel 2R of the vehicle 1 described above.

[0029] As shown in Figure 3, the electronic control unit 7 includes a tire load determination unit 21 that acquires the wheel rotation speeds of the front wheels 2F and the rear wheels 2R and determines the loads on the front wheels 2F and the rear wheels 2R, a suspension stroke speed determination unit 22 that acquires the suspension stroke of the active suspension 31 and determines the suspension stroke speed, a target damping force calculation unit 23 that calculates a target damping force from the tire load and suspension stroke speed obtained from the tire load determination unit 21 and the suspension stroke speed determination unit 22, and a damping force control device 24 that controls the variable damper 32 to achieve the calculated target damping force.

[0030] The damping force control device 24 may be constantly in operation, but is preferably set to operate, for example, when it is determined that the vehicle 1 is traveling on a rough road with large bumps. The determination of whether or not the vehicle 1 is traveling on a rough road may be set to operate when the vehicle height data obtained by the vehicle height sensor 8 exceeds a predetermined fluctuation range, or the determination of whether or not the vehicle 1 is traveling on a rough road may be made by performing image processing on image data of the road surface obtained by an in-vehicle camera (not shown).

[0031] The target damping force calculation unit 23 compares the wheel speeds of the front wheels 2F and rear wheels 2R based on the tire load determined by the tire load determination unit 21. Also, since the stroke direction can be known from the suspension stroke speed determined by the suspension stroke speed determination unit 22, it is determined whether the variable damper 32 is in an extended or contracted state. The target damping force calculation unit 23 calculates the target damping force of the variable damper 32 based on the control law shown in Fig. 4 according to the wheel speed and the state of the variable damper.

[0032] That is, when the wheel speed of the rear wheel 2R is lower than the wheel speed of the front wheel 2F and the variable damper 32 is in an extended state, the rear wheel 2R is pressed against the road surface while traveling on a rough road. At this time, the rear wheel 2R is in an overloaded state and the tire contact with the ground is deteriorated, so that the target damping force is maximized so that the damping force becomes large in order to suppress the extension of the variable damper 32.

[0033] Thereafter, when the variable damper 32 transitions to a contracted state, the rear wheel 2R during traveling on a rough road is lifted off the road surface, and the overload on the rear wheel 2R is alleviated. At this time, in order to promote the contraction of the variable damper 32, the target damping force is set to a minimum so that the damping force is reduced.

[0034] Next, when the wheel speed of the rear wheel 2R is higher than the wheel speed of the front wheel 2F and the variable damper 32 is in a contracted state, the rear wheel 2R is lifted off the road surface while traveling on a rough road. At this time, the rear wheel 2R is in a state of insufficient load, and the tire contact with the ground is deteriorated. At this time, the target damping force is maximized so that the damping force becomes large in order to suppress the contraction of the variable damper 32.

[0035] Thereafter, when the variable damper 32 transitions to an extended state, the rear wheel 2R approaches the road surface while traveling on a rough road, and the load deficiency of the rear wheel 2R is improved. At this time, the target damping force is set to a minimum so that the damping force is reduced in order to promote the extension of the variable damper 32.

[0036] In this way, by switching the control law based on the wheel speeds of the front wheels 2F and rear wheels 2R and the state of the variable damper 32, the in-wheel motor 5 is provided and the damping force of the variable damper 32 of the rear wheel 2R is controlled so that the wheel speed of the rear wheel 2R, which has a large unsprung weight, matches the wheel speed of the front wheel 2F, which has a light unsprung weight. This improves the road surface following ability of the rear wheel 2R when traveling on rough roads, suppresses slippage, improves tire ground contact, and suppresses unsprung and over-sprung vibrations.

[0037] Next, we will explain the results of a simulation of the relationship between wheel input load and driving distance, simulating driving on rough roads with a vehicle to which the variable damper control method of this embodiment is applied, and the results of a sensory evaluation by a driver of a vehicle to which the variable damper control method of this embodiment is applied.

[0038] As shown in Fig. 5, it can be confirmed that the wheel input load is reduced in the example in which the variable damper control method according to this embodiment is applied, compared to the comparative example in which a vehicle having a conventional damper is simulated. In addition, the reduction in the wheel input load indicates that unsprung vibration is suppressed. It can also be confirmed that the amplitude of the tire input load is reduced, which confirms that the tire contact performance is improved.

[0039] Next, a sensory test was conducted to compare the vehicle to which the control method for the variable damper according to the present embodiment is applied with a conventional vehicle, and to evaluate how the driver felt the vibration of the vehicle. In the sensory test, the driver quantified and evaluated how the driver felt the vibration of the vehicle while driving the vehicle on a predetermined driving section.

[0040] As shown in FIG. 6, the sensory test evaluated the degree of vibration sensation felt by the driver when he felt continuous large vibrations and the degree of impact sensation felt by the driver when he felt large vibrations, using numerical values. The road surface used in the sensory test was a rough road similar to the Belgian road used in the simulation in FIG. 5, and the vehicle actually ran on it, and the vibration sensation was evaluated in the area of ​​section A, and the impact sensation was evaluated in the area of ​​section B. In addition, in the evaluation of the vibration sensation, the average value of the wheel input load in the section A in FIG. 5 was plotted on the vertical axis, and the degree of the driver's sensation was plotted on the horizontal axis. In addition, in the evaluation of the impact sensation, the maximum value of the wheel input in the section B in FIG. 5 was plotted on the vertical axis, and the degree of the driver's sensation was plotted on the horizontal axis, similar to the vibration sensation.

[0041] As shown in Fig. 6, it can be confirmed that the sensory evaluation of the vibration sensation of the Example is improved by 0.6 points compared to the Comparative Example, and the sensory evaluation of the impact sensation is improved by 0.2 points. That is, according to the variable damper control method of this embodiment, the score of the vibration sensation and the impact sensation is improved to an average of 2.4 points, 2.6 points in the vibration sensation region and 2.2 points in the impact sensation region, compared to a conventional vehicle, and the sensory test results also confirmed that the vehicle vibration is less noticeable than before.

[0042] In this way, according to the variable damper control method of this embodiment, it is possible to improve the tire ground contact of the rear wheel 2R equipped with the in-wheel motor 5 and reduce unsprung vibration, thereby making it possible to provide a vehicle with high road surface tracking performance when traveling on rough roads.

[0043] Furthermore, since a vehicle using the variable damper control method according to this embodiment is equipped with the active suspension unit 10 as described above, vehicle posture information can be obtained from the stroke amount obtained from each active suspension unit 10 attached to each wheel and from a horizontal sensor or the like attached to the vehicle, and it is also possible to correct the damping force appropriately according to the posture.

[0044] Furthermore, it is also possible to correct the damping force based on data on the stroke amount and damping force of the active suspension system 10 so that the resistance force of the suspension becomes constant.

[0045] By using such various correction means, it is possible to further improve the tire ground contact and reduce vibration.

[0046] In the above embodiment, the wheel speed is controlled by comparing the wheel speeds of the front and rear wheels, but the damping force may be controlled based on the magnitude relationship between the rear wheels equipped with in-wheel motors 5 and the vehicle speed. In the above embodiment, the variable damper control method according to this embodiment is applied to a vehicle 1 in which the front wheels 2F are driven by an on-board motor 4, but the variable damper control method may be applied to a vehicle in which the front wheels 2F are also driven by in-wheel motors 5 and the rear wheels are driven by an on-board motor 4. It is clear from the claims that such modified or improved embodiments are also included within the technical scope of the present invention. [Explanation of symbols]

[0047] 1 vehicle, 2F front wheel, 2R rear wheel, 4 on-board motor, 5 in-wheel motor.

Claims

1. A method for controlling a variable damper of a vehicle in which either one of a front wheel or a rear wheel is driven by an in-wheel motor housed in the wheel and the other is driven by an on-board motor provided on a vehicle body, and at least the wheel driven by the in-wheel motor is attached to a suspension device having a variable damper capable of adjusting a damping force, comprising: A method for controlling a variable damper, comprising the steps of: adjusting a damping force of the variable damper in accordance with a wheel speed of a wheel driven by the in-wheel motor.

2. 2. The method for controlling a variable damper according to claim 1, A method for controlling a variable damper, characterized in that the variable damper adjusts the damping force by comparing a wheel speed of a wheel driven by the in-wheel motor with a wheel speed of a wheel driven by the on-board motor.

3. 2. The method for controlling a variable damper according to claim 1, A method for controlling a variable damper, comprising the steps of: adjusting the damping force of the variable damper by comparing a wheel speed of a wheel driven by the in-wheel motor with a vehicle speed of the vehicle.

4. 3. The method for controlling a variable damper according to claim 1, further comprising the steps of: The method for controlling a variable damper, wherein the vehicle has front wheels driven by an on-board motor and rear wheels driven by the in-wheel motor.

5. 2. The vehicle control method according to claim 1, A method for controlling a variable damper, comprising the steps of: correcting a damping force of the variable damper based on posture information of the vehicle.

6. 2. The method for controlling a variable damper according to claim 1, A method for controlling a variable damper, comprising the steps of: adjusting the damping force of the variable damper so as to keep the resistance force of the suspension device constant.

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