A control method for a small unmanned drive-by-wire chassis

Abstract

This invention discloses a control method for a small, unmanned, drive-by-wire chassis. The vehicle controller incorporates interfaces for target speed, target acceleration, and longitudinal distance error, integrating longitudinal control functionality into the drive-by-wire chassis. Through closed-loop feedback control of vehicle speed and longitudinal distance, coupled with feedforward control using acceleration, the drive-by-wire chassis offers advantages such as precise control, strong adaptability, and low energy consumption. Furthermore, the drive-by-wire chassis incorporates a compound braking function, utilizing the motor for energy recovery when vehicle deceleration is low and supplementing mechanical braking only when deceleration is insufficient, significantly improving the vehicle's economic efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned driving control, and in particular to a control method for a small unmanned driving wire-controlled chassis. Background Art

[0002] With the rapid development of artificial intelligence and unmanned driving, there are more and more small unmanned vehicles with special purpose requirements, such as logistics vehicles, sweepers and security vehicles. These vehicles often perform unmanned driving tasks in specific operating scenarios and are characterized by small vehicle size, simple road environment and low speed.

[0003] The current development approach for small autonomous vehicles typically involves the vehicle manufacturer providing the complete by-wire chassis and exterior design, while the autonomous driving system is provided by other autonomous driving solution providers. During operation, the autonomous driving system transmits signals through the various communication interfaces of the by-wire chassis to control the vehicle's driving and steering functions. Currently, the autonomous driving control method typically involves the autonomous driving system transmitting requested throttle and brake opening percentages, which the by-wire chassis converts and then transmits requested torque to the drive motor and brake pressure to the brake controller. This control approach means that lateral and longitudinal closed-loop control is directly performed by the autonomous driving system, while the by-wire chassis serves merely as an actuator to respond to the autonomous driving system's requests. The drawback of this approach is that the autonomous driving system requires extensive testing and control parameter calibration for the by-wire chassis, resulting in poor compatibility and a long development cycle. At the same time, when the unmanned driving system performs longitudinal closed-loop control, it is unable to coordinate the distribution between the electric braking of the drive motor and the mechanical braking, because this low-level control can only be completed by the wire-controlled chassis. Therefore, such small unmanned vehicles often only use mechanical braking when braking, without energy recovery. This undoubtedly increases the vehicle's driving energy consumption, reduces the vehicle's cruising range, and affects the operating efficiency of the small unmanned vehicle. Summary of the Invention

[0004] The present invention provides a control method for a small unmanned drive-by-wire chassis, the main purpose of which is to solve the problems existing in the prior art.

[0005] The present invention adopts the following technical solutions:

[0006] A control method for a small unmanned drive-by-wire chassis comprises the following steps:

[0007] (1) The vehicle controller obtains the target vehicle speed V through the unmanned driving system t Target acceleration A t and longitudinal distance error E s ;

[0008] (2) The vehicle controller obtains the actual vehicle speed Va , with the speed error E v Perform PID closed-loop control of the vehicle speed loop, using the longitudinal distance error E s Perform PID closed-loop control of the position loop and use the target acceleration A t Calculate the wheel force F(t) required by the vehicle to perform feedforward compensation, thereby achieving longitudinal control;

[0009] (3) During vehicle braking, the vehicle controller calculates the maximum wheel force F according to the wheel force F(t) e (r), if |F(t)|≤F e (r), mechanical braking is not requested and electric braking is used for energy recovery; if |F(t)|>F e (r), the mechanical brake is controlled to intervene to supplement the braking force, thereby achieving dynamic braking force distribution.

[0010] Furthermore, in step (1), the vehicle controller is provided with a target speed interface, a target acceleration interface and a longitudinal distance error interface, and the unmanned driving system sends the target speed V to the vehicle controller according to the driving plan. t and / or target acceleration A t , and decide whether to send the longitudinal distance error E to the vehicle controller s , when the longitudinal distance error E is not sent s When s =0.

[0011] Furthermore, if the unmanned driving system only sends the target speed V t , then the vehicle controller controls the target speed V t Differentiate to obtain the corresponding target acceleration A t ; If the unmanned driving system only sends the target acceleration A t , the vehicle controller integrates the target acceleration to obtain the corresponding target speed V t .

[0012] Furthermore, in step (2), the output of the speed loop is F v (t), which is calculated as follows:

[0013]

[0014] Where: K p1 , K i1 and K d1 are the PID control parameters of the speed loop.

[0015] Furthermore, in step (2), the output of the position loop is F s (t), which is calculated as follows:

[0016]

[0017] Where: K p2 , K i2 and K d2 is the PID control parameter of the position loop.

[0018] Going further, with F s (t) is used as the speed error compensation and is combined with the speed error E v The output correction of the closed-loop control part of the speed loop is F b (t):

[0019]

[0020] Going further, the calculation formula for the wheel force F(t) required by the vehicle is:

[0021] F(t)=F b (t)+F f

[0022] Where: F f is the theoretical wheel force.

[0023] Furthermore, in step (3), during the vehicle braking process, the maximum torque T(r) currently available to the motor is first calculated in real time, and then the maximum wheel force F corresponding to the maximum torque T(r) is obtained. e (r):

[0024]

[0025] Where: T m is the calibrated peak torque of the motor, P m is the calibrated peak power of the motor, r b is the motor speed corresponding to the boundary between the constant torque zone and the constant power zone, and r is the current actual motor speed;

[0026]

[0027] Where: i0 is the main reduction ratio and R is the tire radius.

[0028] Furthermore, if |F(t)|≤F e (r), the vehicle controller sends a torque command T to the drive motor and does not request mechanical braking;

[0029]

[0030] Furthermore, if |F(t)|>F e(r), the vehicle controller sends a pressure request P to the brake controller, thereby allocating the remaining braking force demand to the mechanical brake;

[0031] P=F m *β

[0032] F m =|F(t)-[-F e (r)]|

[0033] Where: β is the conversion coefficient between the calibrated braking pressure and the wheel side braking force.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention improves upon existing technologies by integrating longitudinal control functions into a drive-by-wire chassis. By testing and solidifying control parameters during development and design, it is possible to produce a mature, adaptable drive-by-wire chassis product with precise control performance indicators. This significantly reduces the difficulty of matching unmanned driving systems and shortens the development cycle.

[0036] 2. The present invention performs feedback closed-loop control on vehicle speed and longitudinal distance, and adds acceleration for feedforward control, thereby achieving the advantages of precise speed and distance control and fast vehicle response speed.

[0037] 3. The unmanned drive-by-wire chassis of the present invention has a compound braking function, which can fully use the motor to recover energy when the vehicle deceleration is small, and only supplement mechanical braking when the deceleration is insufficient, greatly improving the vehicle's economic level.

[0038] 4. The unmanned driving wire-controlled chassis of the present invention sets three interfaces: target vehicle speed, target acceleration and longitudinal distance error. The unmanned driving system can select the corresponding interface according to needs, which provides great convenience for the matching of the unmanned driving system and has the characteristics of high versatility, good control effect and low energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described below with reference to the accompanying drawings. In order to fully understand the present invention, many details are described below, but for those skilled in the art, the present invention can be implemented without these details.

[0041] Reference Figure 1An unmanned drive-by-wire chassis includes an unmanned driving system, a vehicle controller, a drive motor, and a brake controller. The unmanned driving system communicates only with the vehicle controller via CAN, not directly with the drive motor or brake controller. The vehicle controller receives the unmanned driving system's longitudinal control target and performs closed-loop control. Simultaneously, the vehicle controller sends a torque request to the drive motor and a brake pressure request to the brake controller via CAN.

[0042] The following is a detailed description of the control method for the aforementioned small unmanned drive-by-wire chassis, including the following steps:

[0043] 1. The vehicle controller obtains the target vehicle speed V through the unmanned driving system t Target acceleration A t and longitudinal distance error E s .

[0044] The vehicle controller is equipped with a target speed interface, a target acceleration interface and a longitudinal distance error interface. The unmanned driving system transmits the target speed V t Target acceleration A t The target speed V is the speed of the vehicle and the longitudinal distance error E is sent to the vehicle controller, which uses these three signals as control input to control the vehicle to follow the target. t and target acceleration A t As the basic interface, the unmanned driving system can choose to send two signals simultaneously, or choose to send only one, but cannot send neither signal. t , the vehicle controller will generate the corresponding target acceleration A by differentiating the target speed t ; If the unmanned driving system only sends the target acceleration A t The vehicle controller will generate the corresponding target speed V by integrating the target acceleration. t . Longitudinal distance error E s It is an optional interface. If the unmanned driving system sends it normally, the vehicle controller can control the wire-controlled chassis to achieve a higher position control accuracy. If it is not sent, it is considered as E s =0, the vehicle controller can only control the target speed V t Or target acceleration A t Follow along.

[0045] 2. The vehicle controller obtains the actual vehicle speed V a , with the speed error E v Perform PID closed-loop control of the vehicle speed loop, using the longitudinal distance error E s Perform PID closed-loop control of the position loop and use the target acceleration A tThe wheel force F(t) required by the vehicle is calculated, and feedforward compensation is performed to achieve longitudinal control.

[0046] 1. The speed loop is the target speed V sent by the vehicle controller to the unmanned driving system. t The actual vehicle speed V a The difference between them is the speed error E v Perform PID closed-loop control, actual vehicle speed V a The speed error is calculated by collecting the actual motor speed and combining it with the calibrated vehicle power chain parameters (such as the main reduction ratio, tire radius, etc.). v , the output of the speed loop is F v (t), then:

[0047] E v =V t -V a

[0048]

[0049] Where: K p1 , K i1 , K d1 These are the PID control parameters of the vehicle speed loop and need to be tested and calibrated on the wire-controlled chassis.

[0050] 2. The position loop is the longitudinal distance error E sent directly by the vehicle controller to the unmanned driving system s Perform PID closed-loop control and set the output of the position loop to F s (t), then:

[0051]

[0052] Where: K p2 , K i2 , K d2 The PID control parameters of the position loop need to be tested and calibrated on the wire-controlled chassis. If the unmanned driving system does not send the longitudinal distance error E s , then F s (t) = 0. F s (t) is used as the speed error compensation, and the speed error E v The output of the closed-loop control part is corrected by F b (t) is:

[0053]

[0054] 3. Feedforward control is performed by the VCU by receiving the target acceleration A sent by the unmanned driving system t , combined with the calibrated vehicle parameters and the vehicle driving equation, the theoretical wheel force F is calculated f, and then superimposed with the feedback control and output, the final control output is the wheel side force F(t):

[0055] F(t)=F b (t)+F f

[0056] The physical meaning of the wheel force F(t) is: when F(t)>0, it is characterized as the driving force on the vehicle wheel; when F(t)<0, it is characterized as the braking force on the vehicle wheel.

[0057] 4. When the vehicle is in the driving state (F(t)>0), the vehicle controller sends a torque command T to the drive motor:

[0058]

[0059] Where: i0 is the main reduction ratio, R is the tire radius, and the wire-controlled chassis has no gearbox, so the gearbox ratio is not considered.

[0060] 3. During vehicle braking, the vehicle controller calculates the maximum wheel force F according to the wheel force F(t) e (r), if |F(t)|≤F e (r), mechanical braking is not requested and electric braking is used for energy recovery; if

[0061] |F(t)|>F e (r), the mechanical brake is controlled to intervene to supplement the braking force, thereby achieving dynamic braking force distribution.

[0062] 1. During the vehicle braking process (F(t)<0), the vehicle controller calculates the current maximum available torque T(r) of the motor in real time:

[0063]

[0064] Where: T m is the calibrated peak torque of the motor, P m is the calibrated peak power of the motor, r b is the motor speed corresponding to the boundary between the constant torque zone and the constant power zone, and r is the current actual motor speed.

[0065] The maximum torque T(r) currently available from the motor corresponds to the maximum wheel force F that the motor can provide. e (r) is:

[0066]

[0067] Where: i0 is the main reduction ratio, R is the tire radius, and the wire-controlled chassis has no gearbox, so the gearbox ratio is not considered.

[0068] 2. During braking, if |F(t)|≤Fe (r), it indicates that electric braking is sufficient to provide vehicle deceleration. At this time, the vehicle controller sends a torque command T to the drive motor and does not request mechanical braking. Energy recovery is completely achieved through electric braking.

[0069]

[0070] 3. During braking, if |F(t)|>F e (r) indicates that the electric brake can no longer provide sufficient braking force and the mechanical brake needs to be controlled to intervene to supplement the braking force.

[0071] At this time, the vehicle controller sends torque T = -T(r) to the drive motor and allocates the remaining braking force to the mechanical brake. The wheel braking force F required by the mechanical brake m for:

[0072] F m =|F(t)-[-F e (r)]|

[0073] Then the pressure request P sent by the vehicle controller to the brake controller is:

[0074] P=F m *β

[0075] Where: β is the conversion coefficient between the calibrated braking pressure and the wheel side braking force.

[0076] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A control method for a small unmanned drive-by-wire chassis, characterized by: The unmanned drive-by-wire chassis includes an unmanned driving system, a vehicle controller, a drive motor and a brake controller. The unmanned driving system only communicates with the vehicle controller through CAN, and does not directly communicate with the drive motor and the brake controller. The vehicle controller receives the longitudinal control target of the unmanned driving system and performs closed-loop control. At the same time, it sends a required torque command to the drive motor and a brake pressure request command to the brake controller via CAN communication. The control method includes the following steps: (1) The vehicle controller obtains the target vehicle speed V through the unmanned driving system t Target acceleration A t and longitudinal distance error E s The vehicle controller is equipped with a target speed interface, a target acceleration interface and a longitudinal distance error interface. The unmanned driving system transmits the target speed V t Target acceleration A t and longitudinal distance error E s The three signals are sent to the vehicle controller, which uses them as control inputs to control the vehicle to follow the target. (2) The vehicle controller obtains the actual vehicle speed V a , with the speed error E v Perform PID closed-loop control of the vehicle speed loop, using the longitudinal distance error E s Perform PID closed-loop control of the position loop and use the target acceleration A t , calibrated vehicle parameters and vehicle driving equation to calculate the theoretical wheel force F f , and then output the wheel force F(t) required by the vehicle after superposition with the feedback control, so as to perform feedforward compensation and thus realize longitudinal control; The output of the speed loop is F v (t), which is calculated as follows: Where: K p1 , K i1 and K d1 is the PID control parameter of the speed loop; The output of the position loop is F s (t), which is calculated as follows: Where: K p2 , K i2 and K d2 is the PID control parameter of the position loop; F s (t) is used as the speed error compensation, and the speed error E v The output of the closed-loop control part of the speed loop is corrected to F b (t): The calculation formula for the wheel force F(t) required by the vehicle is: F(t)=F b (t)+F f The physical meaning of the wheel force F(t) is: when F(t)>0, it is characterized as the driving force on the vehicle wheel; when F(t)<0, it is characterized as the braking force on the vehicle wheel; (3) During vehicle braking, the vehicle controller calculates the maximum wheel force F according to the wheel force F(t) e (r), if |F(t)|≤F e (r), mechanical braking is not requested and electric braking is used for energy recovery; if |F(t)|>F e (r), the mechanical brake is controlled to intervene to supplement the braking force, thereby achieving dynamic braking force distribution.

2. The control method of a small unmanned drive-by-wire chassis according to claim 1, characterized in that: In step (1), the unmanned driving system sends the target speed V to the vehicle controller according to the driving plan. t and / or target acceleration A t , and decide whether to send the longitudinal distance error E to the vehicle controller s , when the longitudinal distance error E is not sent s When s =0.

3. The control method of a small unmanned drive-by-wire chassis according to claim 2, characterized in that: If the unmanned driving system only sends the target vehicle speed V t , then the vehicle controller controls the target speed V t Differentiate to obtain the corresponding target acceleration A t ; If the unmanned driving system only sends the target acceleration A t , the vehicle controller integrates the target acceleration to obtain the corresponding target speed V t .

4. The control method of a small unmanned drive-by-wire chassis according to claim 1, characterized in that: In step (3), during the vehicle braking process, the maximum torque T(r) currently available to the motor is first calculated in real time, and then the maximum wheel force F corresponding to the maximum torque T(r) is obtained. e (r): Where: T m is the calibrated peak torque of the motor, P m is the calibrated peak power of the motor, r b is the motor speed corresponding to the boundary between the constant torque zone and the constant power zone, and r is the current actual motor speed; Where: i0 is the main reduction ratio and R is the tire radius.

5. The control method of a small unmanned drive-by-wire chassis according to claim 4, characterized in that: If |F(t)|≤F e (r), the vehicle controller sends a torque command T to the drive motor and does not request mechanical braking; 6. The control method of a small unmanned drive-by-wire chassis according to claim 4, characterized in that: If |F(t)|>F e (r), the vehicle controller sends a pressure request P to the braking system, thereby allocating the remaining braking force demand to the mechanical brake; P=F m *b F m =|F(t)-[-F e (r)]| Where: β is the conversion coefficient between the calibrated braking pressure and the wheel side braking force.

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