Calculation method for the steering angle of the parking brake wheel of an all-wheel independent steering vehicle

Abstract

This paper proposes a method for calculating the wheel steering angle of a parking brake in a vehicle with all-wheel independent steering. The method is applicable to vehicles with four-wheel independent steering capabilities, where the wheel steering angle is no less than ±90°, and the wheel steering units can self-lock when there is no steering signal. The method includes: when the vehicle needs to park, retrieving vehicle parameters and collecting external road information; calculating the required steering angles for the front and rear wheels according to the method; and controlling the front and rear wheels to rotate to the specified steering angles. This achieves stable parking under various road conditions without relying on traditional mechanical friction and locking parking brake mechanisms. This method ensures that the vehicle has sufficient residual traction at different inclines to resist wind interference from different directions, while reducing system assemblies and costs, and ensuring parking safety for such vehicles without a parking brake device.

Description

Technical Field

[0001] This invention relates to a novel parking brake method, and more particularly to a method for calculating the wheel steering angle of a parking brake vehicle with all-wheel independent steering. This method is used to calculate the target steering angle of each wheel and control the wheels to achieve a fixed-angle steering motion, thereby replacing the traditional parking brake system to achieve self-locking of the vehicle's movement on a slope, thus realizing the ability to stably resist gravity and wind or other disturbances from different directions to stabilize the vehicle on a slope. Background Technology

[0002] With the continuous development of new energy vehicle technology, wheel corner module technology with large-angle steering function is gradually gaining attention in the industry due to its advantages of high integration and high flexibility. However, the independence and integration of wheel corner modules limit the layout of traditional braking devices. In addition, since electromechanical brakes require the design of additional braking devices for parking brakes, it is not conducive to the integrated layout of vehicles. Therefore, it is considered to utilize the existing vehicle structure to realize the parking function to replace the parking brake device, thereby further reducing the overall vehicle weight and improving the vehicle integration.

[0003] Analysis of the working principle of parking brake function through wheel steering reveals that it achieves parking by interlocking the lateral forces of the four wheels. Therefore, compared to traditional parking methods that utilize all wheel traction, this method inherently requires some traction to cancel each other out to maintain vehicle posture, thus reducing the vehicle's resistance to external disturbances. Further considering actual parking conditions, the parking device should ensure that the vehicle does not roll away due to road slope or wind disturbances. Furthermore, due to the different front and rear axle load distribution, the front and rear wheel angles are crucial to the distribution of vehicle traction. Therefore, a wheel angle algorithm should be designed to ensure that the vehicle retains sufficient residual traction at different slopes to resist wind disturbances from different directions. Summary of the Invention

[0004] This invention proposes a control method for realizing the vehicle parking brake function by utilizing the independent steering function of the wheels, and develops a set of calculation methods for the front and rear axle wheel rotation angles that can ensure that the vehicle still has sufficient residual adhesion under different slopes to resist wind disturbances from different directions, thereby realizing the ability to stably resist gravity and wind or other disturbances from different directions to stabilize on slopes.

[0005] The technical solution of this invention is: a method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle, used to calculate the target steering angle of each wheel and control the wheels to achieve a fixed-angle steering motion, thereby replacing the traditional parking brake system to achieve vehicle movement self-locking and stable parking on slopes, characterized in that:

[0006] When the vehicle needs to be started and parked, vehicle parameters are retrieved and external road information is collected. The required steering angles of the front and rear wheels of the vehicle are calculated according to the wheel angle calculation method. The independent steering units of each wheel control the front and rear wheels to rotate to the required steering angle, thereby completing the process of starting the vehicle and parking. When the vehicle needs to be released from parking, the independent steering units of each wheel control the front and rear wheels to rotate to the initial state without steering angle, thereby completing the process of releasing the vehicle from parking.

[0007] The vehicle described therein should have a four-wheel independent steering function with a wheel steering angle of ±90° when parked, and should also ensure that the steering unit can automatically lock when there is no steering signal;

[0008] The vehicle parameters mentioned therein should include the vehicle's center of gravity position, wheelbase, front and rear track width, wheel radius, transmission ratio, aerodynamic information of the vehicle body, and curb weight, which are pre-stored in the storage unit.

[0009] The external road information mentioned therein should include the slope information and road surface adhesion information of the vehicle parking position collected and calculated by vehicle sensors;

[0010] The wheel angle calculation method mentioned above should ensure that the resultant force and resultant torque on the vehicle are balanced when parking under extreme working conditions, and ensure that the vehicle still has sufficient residual adhesion when parking on different slopes to resist the risk of movement caused by wind disturbance from different directions.

[0011] Preferably, the feature of resisting wind disturbances from different directions is as follows:

[0012] The first design objective of the algorithm for resisting wind disturbances from different directions is to ensure that the vehicle's remaining adhesion can withstand the same maximum wind speed in different directions as much as possible. The first design objective is the optimal solution of the wheel angle calculation method. However, if the first design objective cannot be guaranteed, the wheel angle calculation method should ensure that the second design objective is met, that is, to increase the vehicle's resistance to lateral wind disturbances as much as possible while ensuring that the vehicle's adhesion is sufficient to resist longitudinal slope.

[0013] Preferably, the specific vehicle start-up and parking process includes:

[0014] Detect whether the driver or autonomous driving decision unit sends a parking start signal; if detected, execute the parking start action.

[0015] Control all vehicle braking devices to activate and maintain braking status until a release command is issued;

[0016] The vehicle parameter information pre-stored in the storage unit is retrieved, and external road information is collected and calculated using vehicle sensors.

[0017] The required steering angles for the front and rear wheels of the vehicle are calculated using the wheel angle calculation method described above.

[0018] Control the steering unit to perform steering actions until each wheel reaches the steering angle calculated by the wheel angle calculation method;

[0019] A release command is issued to all service braking devices of the vehicle, the service braking is terminated, the vehicle completes the parking action, and a parking end signal is uploaded.

[0020] Preferably, the specific process of releasing the vehicle from parking includes:

[0021] Detect whether the driver or the autonomous driving decision unit has issued a signal to release the parking brake; if detected, execute the action to release the parking brake.

[0022] Control all vehicle braking devices to activate and maintain braking status;

[0023] Control the steering unit to rotate each wheel until the wheel returns to its initial state with no turning angle;

[0024] Once the vehicle completes the parking release action, it uploads a parking release signal, maintains the braking state of the vehicle's service braking device, and relinquishes control of the service braking to cooperate with further instructions from the driver or autonomous driving decision unit.

[0025] Preferably, the acquisition of the slope information of the vehicle parking position is characterized by:

[0026] The road slope information of the current parking position is calculated by relying on the acceleration signal detected by the acceleration sensor installed on the vehicle body; or the road slope information is detected by the tilt sensor installed on the vehicle body; and the information is stored in the storage unit.

[0027] Preferably, the acquisition of the road surface adhesion at the vehicle parking position is characterized by:

[0028] The adhesion coefficient of the road surface before parking can be estimated or stored in the storage unit based on the vehicle's motion state before parking, and retrieved directly from the storage unit when parking is started.

[0029] Alternatively, the road surface adhesion coefficient can be estimated by using the drive motor after the vehicle is parked.

[0030] Preferably, the road surface adhesion coefficient is estimated via a drive motor after the vehicle is parked, characterized by:

[0031] Upon detecting a vehicle start-up parking signal, the vehicle performs road surface adhesion coefficient estimation;

[0032] The vehicle uses the first set of service brakes to apply full braking to the first set of wheels to limit the movement of the vehicle body;

[0033] The vehicle gradually increases the driving torque to the second set of wheels via the drive motors of the corresponding wheels or axles until slippage of the second set of wheels is detected, and the driving torque of the motor at this moment is recorded. And stop applying the driving torque;

[0034] The vehicle brakes the second set of wheels using the second set of service brakes;

[0035] Retrieve the vehicle center of gravity position information, vehicle curb weight, wheel radius and vehicle transmission system transmission ratio pre-stored in the storage unit, and retrieve the calculated road slope information;

[0036] According to the formula:

[0037]

[0038]

[0039] Calculate the vertical load on the second group of wheels, where This refers to the vertical load on the front axle wheels. For the vertical load on the rear axle wheels For curb weight, Take the local gravitational acceleration as 9.8. The distance from the center of gravity to the front axle. The distance from the center of gravity to the rear axle. For the height of the center of mass, Road slope;

[0040] According to the formula for calculating the road surface adhesion coefficient:

[0041]

[0042] Estimate the current road adhesion coefficient, where The road adhesion coefficient, The transmission ratio of the transmission system. The radius of the wheel;

[0043] The calculated road adhesion coefficient The data is stored in the storage unit, and the road adhesion coefficient estimation is completed.

[0044] The first group of wheels should consist of three wheels that ensure the vehicle does not move during the estimation of the centroid road adhesion coefficient.

[0045] Preferably, the wheel angle calculation method is characterized by:

[0046] Retrieve vehicle center of gravity position information, front and rear wheel track information, vehicle aerodynamic parameters, road slope information and road surface adhesion coefficient stored in the storage unit;

[0047] The first formula, which takes into account the slope, is used to maximize resistance to wind disturbances from different directions, and the second formula, which considers moment balance, is combined as follows:

[0048]

[0049]

[0050] Calculate the pre-angle values ​​of the front and rear axle wheels. and ,in The road surface adhesion coefficient, To account for the distance from the center of gravity to the front axle due to the shift of the center of gravity under slope, To account for the distance from the center of mass to the rear axle due to the shift of the center of mass under slope, and The track width is the distance between the front and rear axles;

[0051] The obtained front and rear axle wheel angle pre-values and Substitute the following into the formula for judging a vehicle's ability to withstand wind disturbances from different directions at a constant wind speed:

[0052]

[0053] If the result is greater than or equal to the ratio of longitudinal to transverse wind force at a constant wind speed ,in and These are the longitudinal and lateral air drag coefficients. and To determine the longitudinal and lateral frontal areas, the pre-determined steering angles of the front and rear axles are selected. and As the final target steering angle for the front and rear axle wheels and If the obtained result is less than the ratio of longitudinal to transverse wind force at a constant wind speed... Then, combining the second formula with the third formula that ensures the vehicle can withstand wind disturbances from different directions at a constant wind speed:

[0054]

[0055] Calculate the final target steering angles of the front and rear axle wheels. and ;

[0056] The final target steering angles of the front and rear axle wheels obtained by the calculation unit and Stored in the storage unit and output to the wheel steering unit;

[0057] The first formula and the second formula are combined to satisfy the second design objective, the second formula and the third formula are combined to satisfy the first design objective, and the judgment formula is used to determine whether the vehicle can achieve the first design objective under the current working conditions.

[0058] Preferably, the front and rear axle wheel rotation angle outputs are characterized in that:

[0059] The steering angles of the four wheels of the vehicle should satisfy the formula:

[0060]

[0061] in The turning angle of the left front wheel. The turning angle of the right front wheel. For the left rear wheel's turning angle, This is the turning angle of the right rear wheel. All the above angles are positive in the counterclockwise direction.

[0062] Beneficial effects

[0063] This invention utilizes the advantage of independent steering of each wheel in a vehicle with a corner module-controlled wire-guided skateboard chassis, and achieves motion self-locking by using the relative alignment of the wheels. It can realize the parking braking function without setting up a parking brake device, increasing the vehicle integration and reducing the system structure and overall vehicle weight.

[0064] The wheel rotation angle calculation method described in this invention can reasonably calculate the front and rear axle wheel rotation angles to ensure that the vehicle still has sufficient residual adhesion under different slopes to resist wind disturbances from different directions. This method can effectively increase the vehicle's adaptability to different parking conditions and reduce the probability of the vehicle slipping under extreme conditions. As long as the road surface adhesion conditions are good, it can effectively guarantee the stable parking requirements under extreme wind interference conditions. Attached Figure Description

[0065] Figure 1 This is a schematic diagram illustrating the independent wheel steering mechanism for parking brake operation in the parking brake wheel steering angle calculation method for an all-wheel independent steering vehicle described in this invention.

[0066] Figure 2 This is a flowchart of the parking process in the parking brake wheel steering angle calculation method for an all-wheel independent steering vehicle described in this invention.

[0067] Figure 3 This is a flowchart illustrating the parking brake release process in the parking brake wheel steering angle calculation method for an all-wheel independent steering vehicle described in this invention.

[0068] Figure 4 Flowchart of the method for estimating the road adhesion coefficient after parking in the parking brake wheel steering angle calculation method for all-wheel independent steering vehicles described in the invention.

[0069] Figure 5 Flowchart of the method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle as described in the invention Detailed Implementation

[0070] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0071] The technical solution of this invention is: a method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle, used to calculate the target steering angle of each wheel and control the wheels to achieve a fixed-angle steering motion, thereby replacing the traditional parking brake system to achieve vehicle movement self-locking and stable parking on slopes, characterized in that:

[0072] When the vehicle needs to be parked, vehicle parameters are retrieved and external road information is collected. Based on the proposed calculation method, the required steering angles for the front and rear wheels are calculated, and the front and rear wheels are controlled to rotate to the specified steering angles, thereby completing the vehicle parking process. Figure 1 ;

[0073] The parking vehicle mentioned above should have a wheel steering angle of not less than The vehicle should feature 90° independent four-wheel steering, automatically locking the steering unit in the absence of a steering signal. The steering mechanism should be steer-by-wire, with decoupling between wheel steering and steering wheel rotation. The vehicle should be equipped with an autonomous driving decision-making unit with some intelligent decision-making capabilities to assist the driver in achieving parking braking through independent wheel steering. To ensure accurate calculation parameters, the vehicle should have a storage unit pre-stored with vehicle parameters and sensors for measuring external road parameters. The vehicle should also have an independently operable service braking device to facilitate the collection of external road information.

[0074] The vehicle parameters mentioned therein should include the vehicle's center of gravity position (distance from center of gravity to front axle, distance from center of gravity to rear axle, and height from center of gravity to ground), wheelbase, front and rear axle track, wheel radius, transmission ratio (if the drive motor is direct drive, the transmission ratio is recorded as 1), aerodynamic information (longitudinal and lateral air resistance coefficients and longitudinal and lateral frontal areas of the vehicle), and the vehicle's equipment weight.

[0075] The external road information mentioned therein should include the slope information and road surface adhesion of the vehicle parking position collected and calculated by vehicle sensors, wherein the vehicle sensors should include a vehicle acceleration sensor to measure the road slope and a drive motor measurement unit to collect the motor output torque and rotation angle;

[0076] The wheel angle calculation method described above should ensure that the vehicle can maintain a balance of resultant force and resultant torque under extreme working conditions, and that the vehicle can still retain sufficient residual adhesion to resist wind disturbances from different directions at different slopes. The first design objective for resisting wind disturbances from different directions is that the maximum wind speed that the vehicle can resist in different directions should be as similar as possible. The first design objective is the optimal solution of this design algorithm. However, if the first design objective cannot be guaranteed, the design algorithm should satisfy the second design objective, that is, to increase the vehicle's resistance to lateral wind disturbances as much as possible while ensuring that the vehicle's adhesion is sufficient to resist longitudinal slopes. It is worth mentioning that, even if the first design objective cannot be satisfied, the existence of the premise of resultant torque balance allows the vehicle to simultaneously ensure that its resistance to longitudinal wind disturbances is not lower than its resistance to lateral wind disturbances when satisfying the second design objective. Therefore, the second design objective can satisfy the design purpose of maximizing the vehicle's resistance to wind disturbances from different directions.

[0077] The specific parking process of the vehicle mentioned above, such as Figure 2 Its features are:

[0078] Step 1: The parking control unit detects the vehicle parking signal issued by the driver or the upper-level autonomous driving decision unit. If the driver or the autonomous driving decision unit issues a parking signal, the parking control unit begins to execute the parking action, and the vehicle enters the parking state.

[0079] Step 2: All vehicle service brake devices are activated and maintained in a braking state. If the vehicle service brake device is a hydraulic brake device, the braking pressure should be increased to the first braking pressure and maintained. If the vehicle service brake device is an electromechanical brake device, the brake motor should apply torque to the first braking torque and maintain it until the parking control unit issues a release command to the service brake device.

[0080] Step 3: Retrieve vehicle parameter information pre-stored in the vehicle storage unit, namely center of gravity position, wheelbase, front and rear axle track, wheel radius, transmission ratio of the transmission system, aerodynamic information and the equipment weight of the vehicle, and collect and calculate external road information, namely parking position road information and road surface adhesion, through vehicle sensors, namely vehicle acceleration sensors and drive motor sampling unit, and transmit the above data to the vehicle calculation unit for further calculation.

[0081] Step 4: The vehicle's computing unit receives the vehicle parameter information and collected external road information from the storage unit, and calculates the required steering angles of the front and rear wheels of the vehicle using a calculation method that ensures the vehicle has sufficient remaining adhesion to resist wind disturbances from different directions at different slopes.

[0082] Step 5: The vehicle's parking brake actuator sends a steering command to the steering unit. The steering unit receives the steering command and executes the steering action until the wheels reach the steering angle calculated by the calculation unit. The four steering units of the vehicle can be executed simultaneously or sequentially in a certain order. No explicit constraints are imposed here. After the steering unit finishes execution, it returns a steering end signal to the parking control unit.

[0083] Step 6: After receiving the steering end signal returned by the steering unit, the parking brake actuator of the vehicle issues a brake release command to all service brake devices of the vehicle, and all service brakes end the service braking. If the vehicle service brake device is a hydraulic brake device, the brake pressure is unloaded. If the vehicle service brake device is an electromechanical brake device, the brake motor should stop outputting braking torque.

[0084] Step 7: The vehicle completes the parking action, and the parking brake center of gravity unit uploads the parking end signal to the autonomous driving decision unit. After receiving the parking end signal, the autonomous driving decision unit feeds back to the driver in an appropriate form to remind the driver that the parking is complete.

[0085] The process of releasing the vehicle from parking, such as Figure 3 Its features are:

[0086] Step 1: The vehicle parking control unit detects the vehicle parking release signal sent by the driver or the upper-level autonomous driving decision unit. If the driver or the autonomous driving decision unit sends the parking release signal, the parking control unit enters the parking release state, and the vehicle executes the parking release action.

[0087] Step 2: The vehicle parking control unit sends a braking signal to all service braking devices. All service braking devices of the vehicle are activated and maintain the braking state. If the vehicle service braking device is a hydraulic braking device, the braking pressure should be increased to the second braking pressure and maintained. If the vehicle service braking device is an electromechanical braking device, the brake motor should apply torque to the second braking torque and maintain it. The first braking pressure and torque and the second braking pressure and torque are all preset values. They can be the same or different, and no constraint is imposed here.

[0088] Step 3: The vehicle parking brake control unit sends a steering return signal to the vehicle steering unit. The wheel steering unit rotates the wheel until the wheel returns to a state with no turning angle. The four steering units of the vehicle can be executed simultaneously or sequentially in a certain order. No explicit constraints are made here. After the steering unit finishes execution, it returns a steering end signal to the parking control unit.

[0089] Step 4: After receiving the steering end signal from the steering unit, the vehicle parking brake control unit completes the parking release action and uploads the parking release signal to the upper-level autonomous driving decision unit. The upper-level autonomous driving decision unit reminds the driver that the parking status has been released by appropriate driving.

[0090] Step 5: The vehicle service brake device maintains the braking state, and the vehicle parking brake unit returns the service brake control to the driver or the upper-level autonomous driving decision unit to cooperate with further instructions from the driver or the autonomous driving decision unit.

[0091] The acquisition of the slope information of the vehicle parking position is characterized by:

[0092] After the vehicle driver or autonomous driving decision unit issues a parking signal, the computing unit calculates the road slope information of the current parking position based on the acceleration signal detected by the acceleration sensor installed on the vehicle body, and stores it in the storage unit.

[0093] The method for obtaining the road surface adhesion at the vehicle parking position is characterized by:

[0094] After the vehicle driver or autonomous driving decision unit issues a parking signal, the computing unit can estimate the adhesion coefficient of the road surface before parking based on the motion state of the vehicle stored in the storage unit before parking.

[0095] Alternatively, after the vehicle is parked, the calculation unit may use the drive motors corresponding to the second set of wheels in conjunction with the first set of service braking devices to estimate the road surface adhesion coefficient.

[0096] The aforementioned method involves estimating the road surface adhesion coefficient via a drive motor after the vehicle is parked, such as... Figure 4 Its features include:

[0097] Step 1: The vehicle pavement coefficient calculation unit performs the pavement adhesion coefficient estimation operation;

[0098] Step 2: The vehicle road surface coefficient calculation unit issues a braking command to the first group of service brakes, and the first group of service brakes brakes the first group of wheels to limit the movement of the vehicle body;

[0099] Step 3: The vehicle road surface coefficient calculation unit issues a drive command to the drive motor corresponding to the second group of wheels. The drive motor gradually increases the driving torque on the second group of wheels until the drive motor angle detection unit detects that the second group of wheels is rotating. The drive torque sampled by the drive motor torque detection unit at this moment is recorded. And stop applying driving torque, wherein the selection of the first group of wheels and the second group of wheels should not overlap, and the selection of the first group of wheels should ensure that the first group of service brakes can still ensure that the vehicle does not move after the second group of wheels rotates;

[0100] Step 4: The vehicle road surface coefficient calculation unit issues a braking command to the second group of vehicle service brakes, and the second group of vehicle service brakes brakes the second group of wheels.

[0101] Step 5: The vehicle pavement coefficient calculation unit retrieves the vehicle center of gravity position information, vehicle curb weight, wheel radius and vehicle transmission system transmission ratio pre-stored in the storage unit, and retrieves the calculated road slope information.

[0102] Step 6: The vehicle pavement coefficient calculation unit calculates the vehicle vertical load formula.

[0103]

[0104]

[0105] Calculate the vertical load on the second group of wheels, where This refers to the vertical load on the front axle wheels. For the vertical load on the rear axle wheels For curb weight, Take the local gravitational acceleration as 9.8. The distance from the center of gravity to the front axle. The distance from the center of gravity to the rear axle. For the height of the center of mass, This refers to the road slope.

[0106] Step 7: The vehicle road surface coefficient calculation unit calculates the road surface adhesion coefficient according to the formula:

[0107]

[0108] Estimate the current road adhesion coefficient, where The road adhesion coefficient, The transmission ratio of the transmission system. The radius is the wheel radius.

[0109] Step 8: The vehicle road surface coefficient calculation unit stores the calculated road adhesion coefficient in the storage unit, ends the road adhesion coefficient estimation action, and hands over the driving braking control to the autonomous driving decision unit.

[0110] The method for calculating the steering angle described therein is characterized in that, as Figure 5 ,include:

[0111] Step 1: The vehicle calculation unit detects the calculation signal issued by the vehicle parking control unit, and the calculation unit retrieves the vehicle center of gravity position information, front and rear wheel track information, vehicle aerodynamic parameters, road slope information and road surface adhesion coefficient stored in the storage unit, which are pre-stored or collected.

[0112] Step 2: The vehicle calculation unit combines the first formula, which takes into account the slope, to maximize resistance to wind disturbances from different directions, and the second formula, which considers torque balance:

[0113]

[0114]

[0115] Calculate the pre-angle values ​​of the front and rear axle wheels. and ,in The road surface adhesion coefficient, To account for the distance from the center of gravity to the front axle due to the shift of the center of gravity under slope, To account for the distance from the center of mass to the rear axle due to the shift of the center of mass under slope, and The track width is the distance between the front and rear axles.

[0116] The first formula requires finding the maximum value of the function in order to satisfy the second design goal, which is to increase the vehicle's resistance to lateral wind disturbances as much as possible while ensuring that the vehicle's adhesion is sufficient to resist the longitudinal slope. The essence of the second formula is to ensure that the ratio of the lateral force arm of the front and rear axle wheels is the same as the ratio of the adhesion of the front and rear axle wheels, so as to ensure that the front and rear axle wheels can still maintain the vehicle's torque balance when the adhesion limit is reached.

[0117] Step 3: The calculation unit calculates the pre-values ​​of the front and rear axle wheel steering angles. and Substitute the following into the formula for judging a vehicle's ability to withstand wind disturbances from different directions at a constant wind speed:

[0118] If the result is greater than or equal to the ratio of longitudinal to transverse wind force at a constant wind speed ,in and These are the longitudinal and lateral air drag coefficients. and If the longitudinal and transverse windward areas are given, proceed to step 4; if the result is less than the ratio of longitudinal to transverse wind force at a constant wind speed... Then proceed to step 5. The judgment formula reflects the resultant force distribution of wind disturbances caused by different wind directions at a constant speed. Therefore, substituting the judgment formula is to determine whether the first design objective can be guaranteed under the current operating conditions. If the result of the judgment formula is less than... If the current situation meets the first design objective, then the front and rear axle wheel angles should be calculated based on the first design objective. If the result of the judgment formula is greater than or equal to... If the first design objective cannot be met under the current working conditions, the front and rear axle wheel angles should be calculated based on the second design objective.

[0119] Step 4: The vehicle calculation unit then selects the pre-values ​​of the front and rear axle wheel steering angles. and As the final target steering angle for the front and rear axle wheels and ;

[0120] Step 5 describes the vehicle calculation unit: combining the second formula with the third formula that ensures the vehicle can withstand wind disturbances from different directions at a constant wind speed.

[0121]

[0122] Find the front and rear axle wheel angles and The design principle of the second formula is to ensure that the balance boundary that the vehicle can reach is consistent with the resultant force distribution of wind disturbance caused by different wind directions at constant speed, so as to make full use of the wheel adhesion to resist external wind disturbance.

[0123] Step 6: The vehicle parking brake control unit calculates the front and rear axle wheel angles obtained by the calculation unit. and The data is stored in the storage unit and output to the wheel steering unit to complete the calculation of the front and rear axle wheel angles.

[0124] The front and rear axle wheel angle outputs described herein are characterized in that:

[0125] The steering angles of the four wheels of the vehicle should satisfy the formula:

[0126]

[0127] in The turning angle of the left front wheel. The turning angle of the right front wheel. For the left rear wheel's turning angle, This refers to the steering angle of the right rear wheel; all angles are positive in the counter-clockwise direction.

[0128] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for calculating the steering angle of the parking brake wheels in an all-wheel independent steering vehicle, used to calculate the target steering angle of each wheel and control the wheels to achieve a fixed-angle steering motion, replacing the traditional parking brake system to achieve vehicle movement self-locking and stable parking on slopes, characterized in that... Includes the following steps: When the vehicle needs to be started and parked, vehicle parameters are retrieved and external road information is collected. The vehicle parameters include the vehicle's center of gravity position, wheelbase, front and rear track width, wheel radius, transmission ratio, aerodynamic information of the vehicle body, and curb weight, which are pre-stored in the storage unit. The external road information includes the slope information of the vehicle's parking position and the road surface adhesion condition, which are collected and calculated by the vehicle's sensors. The required steering angles for the front and rear wheels of a vehicle are calculated using a wheel angle calculation method, which specifically includes: The first formula, which takes into account the slope, maximizes the resistance to wind disturbances from different directions. And the second formula considering torque balance : ； ； Calculate the pre-angle values ​​of the front and rear axle wheels. and ;in The road surface adhesion coefficient, To account for the distance from the center of gravity to the front axle due to the shift of the center of gravity under slope, To account for the distance from the center of mass to the rear axle due to the shift of the center of mass under slope, and The track width is the distance between the front and rear axles; The pre-values ​​of the front and rear axle wheel rotation angles and Substitute the formula for judging a vehicle's ability to resist wind disturbances from different directions at a constant wind speed into the equation. : ； If the calculation result is greater than or equal to the ratio of longitudinal to transverse wind force at a constant wind speed ,in and These are the longitudinal and lateral air drag coefficients. and To determine the longitudinal and lateral windward areas, the pre-values ​​of the front and rear axle wheel rotation angles are selected. and As the final target steering angle for the front and rear axle wheels and ; If the calculation result is less than the ratio Then, combining the second formula... The third formula ensures that the vehicle can withstand wind disturbances from different directions at a constant wind speed as much as possible. : ； The final target steering angles of the front and rear axle wheels can be obtained by simultaneously solving the equations. and ; The front and rear wheels are controlled to rotate to the final target turning angle by the independent steering units of each wheel, thereby completing the vehicle starting and parking process; The vehicle is equipped with four-wheel independent steering, with a wheel steering angle of ±90° when parked, and ensures that the independent steering unit can automatically lock when there is no steering signal.

2. The method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle according to claim 1, characterized in that, The aforementioned features for resisting wind disturbances from different directions are as follows: The first design objective of the algorithm for resisting wind disturbances from different directions is to ensure that the vehicle's remaining adhesion can withstand the same maximum wind speed in different directions as much as possible. The first design objective is the optimal solution of the wheel angle calculation method. However, if the first design objective cannot be guaranteed, the wheel angle calculation method ensures that the second design objective is met, that is, to increase the vehicle's resistance to lateral wind disturbances as much as possible while ensuring that the vehicle's adhesion is sufficient to resist longitudinal slope.

3. The method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle according to claim 1, characterized in that, The specific vehicle start-up and parking process includes: Detect whether the driver or autonomous driving decision unit sends a parking start signal; if detected, execute the parking start action. The vehicle's braking system is activated and maintained in a braking state until a release command is issued. The vehicle parameter information pre-stored in the storage unit is retrieved, and external road information is collected and calculated using vehicle sensors. The required steering angles for the front and rear wheels of the vehicle are calculated using the wheel angle calculation method described above. Control the independent steering unit to perform steering actions until each wheel reaches the steering angle calculated by the wheel angle calculation method; A release command is issued to all service braking devices of the vehicle, the service braking is terminated, the vehicle completes the parking action, and a parking end signal is uploaded.

4. The method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle according to claim 1, characterized in that, The specific process of releasing the vehicle from parking includes: Detect whether the driver or the autonomous driving decision unit has issued a signal to release the parking brake; if detected, execute the action to release the parking brake. Control all service braking devices of the vehicle to activate and maintain braking status; Control the independent steering unit to rotate each wheel until the wheel returns to its initial state with no turning angle; Once the vehicle completes the parking release action, it uploads a parking release signal, maintains the braking state of the service braking device, and relinquishes control of the service braking to cooperate with further instructions from the driver or autonomous driving decision unit.

5. The method for calculating the parking brake wheel steering angle of an all-wheel independent steering vehicle according to claim 1, characterized in that, The acquisition of the slope information of the vehicle parking position is characterized by: The road slope information of the current parking position is calculated by relying on the acceleration signal detected by the acceleration sensor installed on the vehicle body; or the road slope information is detected by the tilt sensor installed on the vehicle body; and the information is stored in the storage unit.

6. The method for calculating the steering angle of the parking brake wheels of an all-wheel independent steering vehicle as described in claim 1, characterized in that, The acquisition of the road surface adhesion at the vehicle's parking position includes: The adhesion coefficient of the road surface before parking is estimated or stored in the storage unit based on the vehicle's motion state before parking, and retrieved directly from the storage unit when parking is started. Alternatively, the road surface adhesion coefficient can be estimated by using the drive motor after the vehicle is parked.

7. The method for estimating the road surface adhesion coefficient via a drive motor after the vehicle is parked, as described in claim 6, is characterized by: Upon detecting a vehicle start-up parking signal, the vehicle performs road surface adhesion coefficient estimation; The vehicle uses the first set of service brakes to apply full braking to the first set of wheels to limit the movement of the vehicle body; The vehicle gradually increases the driving torque to the second set of wheels via the drive motors of the corresponding wheels or axles until slippage of the second set of wheels is detected, and the driving torque of the motor at this moment is recorded. And stop applying the driving torque; The vehicle brakes the second set of wheels using the second set of service brakes; Retrieve the vehicle center of gravity position information, vehicle curb weight, wheel radius and vehicle transmission system transmission ratio pre-stored in the storage unit, and retrieve the calculated road slope information; According to the formula: ； ； Calculate the vertical load on the second group of wheels, where This refers to the vertical load on the front axle wheels. For the vertical load on the rear axle wheels For curb weight, Take the local gravitational acceleration as 9.

8. The distance from the center of gravity to the front axle. The distance from the center of gravity to the rear axle. For the height of the center of mass, Road slope; According to the formula for calculating the road surface adhesion coefficient: ； Estimate the current road adhesion coefficient, where The road adhesion coefficient, The transmission ratio of the transmission system. The radius of the wheel; the calculated road adhesion coefficient Stored in the storage unit, and the road adhesion coefficient estimation is completed; The first group of wheels selected ensures that the vehicle does not move during the estimation of the centroid road adhesion coefficient.

8. The method for calculating the steering angle according to claim 1, characterized in that, When the final target steering angle of the front and rear axle wheels is output, the steering angles of the four wheels of the vehicle satisfy the formula: ； in For the left front wheel's turning angle, The turning angle of the right front wheel. For the left rear wheel's turning angle, This is the turning angle of the right rear wheel. All the above angles are positive in the counterclockwise direction.

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