Virtual differential lock control method for drive-by-wire chassis system

Abstract

The invention relates to the field of drive-by-wire chassis control systems, in particular to a drive-by-wire chassis system virtual differential lock control method which comprises the steps that when a virtual differential lock function key is pressed down, the wheel speeds of left and right driving wheels of a vehicle are obtained, and the real-time wheel speed difference is obtained; when the real-time wheel speed difference is larger than the preset wheel speed difference, the virtual differential speed function is started, the wheel speed of the wheel with the smaller wheel speed in the left driving wheel and the right driving wheel serves as the target wheel speed, the wheel speed of the wheel with the larger wheel speed serves as the control wheel speed, the wheel speed of the corresponding wheel is reduced by braking the wheel with the larger wheel speed, and the driving force is transferred to the wheel with the smaller wheel speed. The characteristic that the EMB can flexibly and independently control the braking force of the wheels for a long time is utilized, and the effect of the differential lock is achieved through the control algorithm of the virtual differential mechanism. The method can meet the requirements of cross-country escape of vehicles, and does not need to increase extra hardware cost.

Description

Technical Field

[0001] The present invention relates to the technical field of drive-by-wire chassis control systems, and in particular to a control method for a virtual differential lock of a drive-by-wire chassis system. Background Art

[0002] With the increasing requirements for intelligent and integrated vehicle chassis, the development of wire-controlled chassis has become a consensus in the industry, among which the electromechanical brake system (EMB) is becoming the mainstream of the development of wire-controlled brake systems. The electromechanical brake system is a wire-controlled device that decouples the brake actuator and the driver's pedal. The motor drives the transmission mechanism to push the friction plate on the brake against the brake disc to generate sufficient braking force, thereby obtaining the desired braking torque. An independent electromechanical brake will be installed on each wheel, and the wire-controlled chassis controller integrates and controls four electromechanical brakes to achieve the braking function.

[0003] Distributed independent control can flexibly and long-term control the braking force of a single wheel according to the specific vehicle usage scenario. While improving safety redundancy, it also broadens the vehicle's usage scenarios and the vehicle's control boundaries to a certain extent.

[0004] The function of differential lock is to improve the vehicle's ability to pass on bad roads. That is, when one of the drive axles of the vehicle is idling, the differential can be quickly locked, so that the two drive axles become rigidly connected. In this way, the power output of the left and right wheels of the vehicle will be consistent, which helps the vehicle get out of trouble. In order to achieve this goal, it is usually necessary to add additional hardware to the vehicle differential to achieve the above effect, but it requires additional costs. Therefore, how to achieve the effect of differential lock through more flexible control without increasing costs is a problem that technicians in this field need to consider. Summary of the invention

[0005] The purpose of the present invention is to provide a virtual differential lock control method for a wire-controlled chassis system, which can achieve the effect of differential lock without increasing additional hardware costs by flexibly and long-term applying braking force to the wheels with a higher vehicle speed, so as to solve the problem of vehicle escape from difficulties in off-road conditions.

[0006] The technical solution of the present invention is: a method for controlling a virtual differential lock of a wire-controlled chassis system, comprising:

[0007] When the virtual differential lock function button is pressed, the wheel speeds of the left and right drive wheels of the vehicle are acquired, and the real-time wheel speed difference is obtained; when the real-time wheel speed difference is greater than the preset wheel speed difference, the virtual differential function is activated, and the wheel speed of the wheel with the smaller wheel speed among the left and right drive wheels is used as the target wheel speed, and the wheel speed of the wheel with the larger wheel speed is used as the control wheel speed. By braking the wheel with the larger wheel speed to reduce the speed of the corresponding wheel, the driving force is transferred to the wheel with the smaller wheel speed.

[0008] Preferably, when the wheel with the smaller wheel speed is selected as the target wheel speed:

[0009] V Tar =min(V xL ,V xR );

[0010] When the wheel speed of the wheel with the larger wheel speed is selected as the control wheel speed:

[0011] V reg =max(V xL ,V xR );

[0012] The real-time wheel speed difference is:

[0013] e=V reg -V Tar ;

[0014] Among them, V xL is the wheel speed of the left wheel; V xR is the right wheel speed; e is the wheel speed difference.

[0015] Preferably, the acquired wheel speed is the wheel speed of the driving wheel, and is the left and right wheels on the same driving shaft.

[0016] Preferably, according to the tire dynamics equation:

[0017] Jω=F x r+(M drv -M Brk );

[0018] Among them, F x is the friction of the ground, and its value can be estimated approximately by the wheel slip rate and the adhesion coefficient of the current road surface; J represents the rolling inertia of the wheel; M drv is the driving torque of the wheel; M Brk is the braking torque of the wheel; r is the wheel radius, ω is the wheel rotation speed;

[0019] It can be seen that when the virtual differential function is activated and braking is performed, the wheel speed of the wheel with a larger wheel speed decreases; for the wheel with a smaller wheel speed, the driving torque increases and the wheel speed increases. Therefore, the real-time wheel speed difference e can be approached to zero by braking the wheel with a larger wheel speed.

[0020] Preferably, when the real-time wheel speed difference is less than or equal to the preset wheel speed difference and the maintenance time is greater than or equal to t, the virtual differential lock function is temporarily stopped.

[0021] Preferably, the wire-controlled chassis system used therein includes a wire-controlled chassis controller, an electromechanical brake and a wheel speed sensor.

[0022] Preferably, the electronic mechanical brakes are respectively mounted on the wheels at both ends of the drive shaft and can be controlled individually; the wheel speed sensors are respectively mounted on the wheels at both ends of the drive shaft and can monitor the wheel speeds individually;

[0023] The drive-by-wire chassis controller includes a fault diagnosis module, a wheel speed monitoring module and a PID controller.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) The present invention intends to utilize the characteristics of EMB that can flexibly and long-term control the braking force of the wheels individually, and achieve the effect of differential lock through the control algorithm of the virtual differential. It can not only meet the needs of off-road vehicle escape, but also does not require additional hardware costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0027] Figure 1 It is a flow chart of the virtual differential lock control method of the wire-controlled chassis system of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments:

[0029] like Figure 1 As shown, the present invention is applied to the electronic mechanical braking system of the automobile's wire-controlled chassis. In the existing intelligent vehicle chassis, the electronic mechanical brake is electrically connected to the driver's brake pedal and mechanically decoupled; each wheel is provided with a separate electronic mechanical brake, and the corresponding wheel can be braked separately during braking. The technical solution of the present invention is based on the existing electronic mechanical braking system of the wire-controlled chassis. When driving in off-road conditions or needing to get out of trouble, the rotation speed of the slipping or idling wheels can be reduced by separately braking the wheels at both ends of the drive shaft, so that more driving force is distributed to the relative wheels to increase their torque and achieve the purpose of getting out of trouble. Specifically: A virtual differential lock control method for a wire-controlled chassis system is:

[0030] When the driver determines that the vehicle is in an off-road condition or needs to get out of trouble, he can input the need to lock the front axle or rear axle through the human-machine interface, or press the corresponding function button. The wheel speed sensor set on the wheel obtains the wheel speed of the left and right driving wheels of the vehicle in real time, and uploads it to the wheel speed detection module in the wire-controlled chassis controller to obtain the real-time wheel speed difference. By comparing the real-time wheel speed difference with the preset wheel speed difference, when the real-time wheel speed difference is less than the preset wheel speed difference, the virtual differential lock function is not started; when the real-time wheel speed difference is greater than the preset wheel speed difference, the virtual differential function is started, and the wheel speed of the wheel with the smaller wheel speed of the left and right driving wheels is used as the target wheel speed, and the wheel speed of the wheel with the larger wheel speed is used as the control wheel speed. Through the electronic mechanical brake on the wheel with the larger wheel speed, the wheel with the larger wheel speed is braked to reduce the corresponding wheel speed. At this time, the driving force of the engine is transferred to the wheel with the smaller wheel speed, so that the wheel speed on the smaller wheel increases, and the corresponding torque also increases.

[0031] Specifically: When the wheel with the smaller wheel speed is selected as the target wheel speed:

[0032] V Tar =min(V xL ,V xR );

[0033] When the wheel speed of the wheel with the larger wheel speed is selected as the control wheel speed:

[0034] V reg =max(V xL ,V xR );

[0035] The real-time wheel speed difference is:

[0036] e=V reg -V Tar ;

[0037] Among them, V xL is the wheel speed of the left wheel; V xR is the right wheel speed; e is the wheel speed difference.

[0038] It should be noted that the wheel speed obtained is the wheel speed of the driving wheel, and is for the left and right wheels on the same driving shaft. In this embodiment, taking an ordinary passenger car as an example, in a four-wheel drive car, you can choose to lock the front axle or the rear axle; for a two-wheel drive car, if the front axle is driven, you can only choose to lock the front axle, and if it is rear axle driven, you can only choose to lock the rear axle.

[0039] Under the premise that the driver inputs the locking demand or presses the corresponding function key, when the real-time wheel speed difference is less than or equal to the preset wheel speed difference, the virtual differential lock function is not triggered; when the real-time wheel speed difference is greater than the preset wheel speed difference, the virtual differential lock is triggered, and after adjusting the real-time wheel speed difference to be less than or equal to the preset wheel speed difference, the maintenance time is calculated. When the maintenance time is greater than or equal to t, the virtual differential lock function is temporarily stopped. At this time, the real-time wheel speed difference is continuously monitored.

[0040] Furthermore, the technical solution of this embodiment is further explained based on the tire dynamics equation:

[0041] Jω=F x r+(M drv -M Brk );

[0042] Among them, F x is the friction of the ground, and its value can be estimated approximately by the wheel slip rate and the adhesion coefficient of the current road surface; J represents the rolling inertia of the wheel; M drv is the driving torque of the wheel; M Brk is the braking torque of the wheel; r is the wheel radius, and ω is the wheel rotation speed.

[0043] It can be seen that when the virtual differential function is activated and braking is performed, for the wheel with a larger wheel speed, the wheel speed decreases, the braking torque increases, the driving torque decreases, and the power output by the engine is transferred to the wheel with a smaller wheel speed; for the wheel with a smaller wheel speed, the driving torque increases and the wheel speed increases. Therefore, under ideal conditions, by braking the wheel with a larger wheel speed, the wheel sets of the two wheels on the drive shaft can be the same, that is, the real-time wheel speed difference e is zero. However, in actual conditions, the real-time wheel speed difference is difficult to maintain at zero, or the car has been out of trouble before the real-time wheel speed difference reaches zero, so a preset wheel speed difference is set so that the real-time wheel speed difference approaches zero.

[0044] The control-by-wire chassis system used in the virtual differential lock control method in this embodiment includes a control-by-wire chassis controller, an electromechanical brake and a wheel speed sensor. The electromechanical brakes are respectively installed on the wheels at both ends of the drive shaft and can be controlled separately; the wheel speed sensors are respectively installed on the wheels at both ends of the drive shaft and can monitor the wheel speed separately. The control-by-wire chassis controller includes a fault diagnosis module, a wheel speed monitoring module and a PID controller.

[0045] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A virtual differential lock control method for a drive-by-wire chassis system, characterized in that: include: When the virtual differential lock function button is pressed, the wheel speeds of the left and right driving wheels of the vehicle are obtained, and the real-time wheel speed difference is obtained; When the real-time wheel speed difference is greater than the preset wheel speed difference, the virtual differential function is activated, and the wheel speed of the wheel with the smaller wheel speed among the left and right driving wheels is used as the target wheel speed, and the wheel speed of the wheel with the larger wheel speed is used as the control wheel speed. The larger wheel speed is braked to reduce the wheel speed of the corresponding wheel, and the driving force is transferred to the smaller wheel speed.

2. The method for controlling a virtual differential lock of a drive-by-wire chassis system according to claim 1, characterized in that: When the wheel with the smaller wheel speed is selected as the target wheel speed: V Tar =min(V xL ,V xR ); When the wheel speed of the larger wheel speed is selected as the control wheel speed: V reg =max(V xL ,V xR ); The real-time wheel speed difference is: e=V reg -V Tar ; Among them, V xL is the wheel speed of the left wheel; V xR is the right wheel speed; e is the wheel speed difference.

3. The method for controlling a virtual differential lock of a drive-by-wire chassis system according to claim 2, characterized in that: The wheel speed obtained is the wheel speed of the driving wheel, and it is the left and right wheels on the same driving shaft.

4. The method for controlling a virtual differential lock of a drive-by-wire chassis system according to claim 3, characterized in that: According to the tire dynamics equation: Jω=F x r+(M drv -M Brk ); Among them, F x is the friction of the ground, and its value can be estimated approximately by the wheel slip rate and the adhesion coefficient of the current road surface; J represents the rolling inertia of the wheel; M drv is the driving torque of the wheel; M Brk is the braking torque of the wheel; r is the wheel radius, ω is the wheel rotation speed; It can be seen that when the virtual differential function is activated and braking is performed, the wheel speed of the wheel with a larger wheel speed decreases; for the wheel with a smaller wheel speed, the driving torque increases and the wheel speed increases. Therefore, the real-time wheel speed difference e can be approached to zero by braking the wheel with a larger wheel speed.

5. The method for controlling a virtual differential lock of a drive-by-wire chassis system according to claim 1, characterized in that: When the real-time wheel speed difference is less than or equal to the preset wheel speed difference and the maintenance time is greater than or equal to t, the virtual differential lock function is temporarily stopped.

6. A method for controlling a virtual differential lock of a drive-by-wire chassis system according to any one of claims 1 to 5, characterized in that: The wire-controlled chassis system used includes a wire-controlled chassis controller, an electromechanical brake and a wheel speed sensor.

7. A control method for a virtual differential lock of a drive-by-wire chassis system according to claim 6, characterized in that: The electronic mechanical brakes are respectively installed on the wheels at both ends of the drive shaft and can be controlled separately; the wheel speed sensors are respectively installed on the wheels at both ends of the drive shaft and can monitor the wheel speed separately; The drive-by-wire chassis controller includes a fault diagnosis module, a wheel speed monitoring module and a PID controller.

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