A rear axle electric power steering system and method of design and control thereof

Abstract

The application relates to a rear axle electric power steering system and a design and control method thereof, which is based on the maximum rotation angle range of an output shaft of a rear axle electric circulating ball steering machine to determine the working angle of a rear axle steering vertical arm, then the working angle of the resistance torque of the rear axle steering machine is obtained to obtain a ratio; according to the ratio and design rule one, the length of the lower knuckle arm of the axle steering and the length of the rear axle steering vertical arm are determined to obtain size parameters; the initial included angle between the rear axle steering vertical arm and the vertical axis is obtained, and the final included angle parameter is obtained according to design rule two; through the above method, the most suitable length of the lower knuckle arm of the axle steering and the length of the rear axle steering vertical arm are obtained based on the maximum rotation angle of the output shaft of the rear axle electric circulating ball steering machine, so that the optimal transmission ratio of the output shaft of the rear axle electric circulating ball steering machine to the rear axle wheel is obtained, the torque of the rear axle steering vertical arm can be amplified and transmitted to the kingpin of the axle, and the electric circulating ball steering machine used in light trucks is applied to heavy trucks to realize rear axle steering.

Description

Technical Field

[0001] This application relates to the field of automotive rear axle steering technology, and in particular to a rear axle electric steering system and its design and control method. Background Technology

[0002] Most wheeled vehicles currently use front-wheel steering, including single-axle steering, single-axle and double-axle steering, or single-axle, double-axle, and triple-axle steering. Adding rear-wheel active steering to front-wheel steering shifts the vehicle's steering center forward, significantly reducing the minimum turning diameter and improving maneuverability. It also significantly reduces tire wear on the rear axle wheels, resulting in improved fuel economy.

[0003] Existing rear-axle active steering technology has limited applications in high-end passenger vehicles. The Porsche 911 Turbo and 911 GT3 models achieve rear-wheel steering through an adjustable-length linkage mechanism, with a maximum wheel angle of 3°. Some military vehicles and medium- and heavy-duty commercial vehicles possess rear-axle steering capabilities, but due to the heavy load on the rear axle and the significant ground resistance torque to overcome during steering, these systems are typically implemented using hydraulic steering. Currently, electric steering systems are only used in light commercial vehicles, and because their output torque is mostly below 2500 N·m, their application is limited to steering axles with axle loads below 2.5 tons. Therefore, electric steering systems are difficult to apply to heavy-duty vehicles.

[0004] Hydraulic steering systems require matching hydraulic steering pumps and gears, or hydraulic cylinders, hydraulic lines, hydraulic valves, and hydraulic oil tanks, resulting in numerous parts and complex layout. Electric steering systems, on the other hand, only require power and communication lines to achieve steering action, requiring fewer parts, having a compact layout, and being cleaner and more environmentally friendly. Both in terms of structural complexity and control reliability, electric steering systems have significant advantages. Therefore, it is necessary to provide a rear-axle steering system that reduces the torque requirements of the electric steering system on the rear-forward steering system, enabling the application of electric steering systems in medium and heavy-duty vehicles. Summary of the Invention

[0005] This application provides a rear axle electric steering system and its design and control method to solve the problem that electric steering gears are difficult to apply to hydraulic steering systems of heavy vehicles in related technologies.

[0006] Firstly, a design method for a rear axle electric power steering system is provided, which includes the following steps:

[0007] Obtain the maximum angle range of the output shaft of the rear axle electric recirculating ball steering gear, and determine the working angle of the rear axle steering drop arm based on the maximum angle range;

[0008] Obtain the working angle of the rear steering axle resistance torque and combine it with the working angle of the rear axle steering drop arm to obtain the ratio between the two; determine the lengths of the lower steering arm of the axle and the rear axle steering drop arm according to the ratio and design rule one to obtain the dimensional parameters.

[0009] Obtain the initial angle between the rear axle steering arm and the vertical axis, and obtain the final angle parameter according to design rule two;

[0010] The included angle parameter and dimensional parameter are used as the manufacturing parameters for the rear axle electric steering system.

[0011] In some embodiments, the lengths of the lower steering arm of the axle and the lower steering arm of the rear axle are determined according to the ratio and design rule one to obtain dimensional parameters, specifically including the following steps:

[0012] Obtain the first length range of the rear axle steering vertical arm and the second length range of the axle steering lower joint arm;

[0013] Select any value within the first length range as the initial value of the rear axle steering boom, and select any value within the second length range as the initial value of the axle steering lower boom.

[0014] The length of the lower steering arm of the axle is gradually increased while the length of the lower steering arm of the rear axle is shortened to obtain multiple sets of dimensional parameters;

[0015] Multiple sets of dimensional parameters with a ratio equal to the ratio of the lower steering arm of the axle to the lower steering arm of the rear axle are selected; then, the set of dimensional parameters with the longest lower steering arm of the axle is selected as the final dimensional parameters.

[0016] In some embodiments, the initial angle between the rear axle steering arm and the vertical axis is obtained, and the final angle parameter is obtained according to design rule two, specifically including the following steps:

[0017] Obtain the angle between the straight line where the rear axle steering arm is located when it is not steering and the vertical axis, and use this angle as the initial angle;

[0018] Then determine whether the first included angle and the second included angle are equal;

[0019] If they are equal, the initial included angle does not need to be adjusted, and the initial included angle is used as the final included angle parameter;

[0020] If they are not equal, the initial included angle is adjusted; the first included angle is the angle between the line where the rear axle steering arm is not turning and the line where the positive rotation limit position of the axle steering arm is located; the second included angle is the angle between the line where the rear axle steering arm is not turning and the line where the reverse rotation limit position of the axle steering arm is located.

[0021] Secondly, a rear axle electric steering system is provided, which includes a rear axle electric recirculating ball steering gear, a rear axle steering drop arm, a rear axle steering tie rod, a lower steering arm of the axle, and a rear axle;

[0022] The rear axle steering arm and the lower axle steering arm are manufactured according to the design method of the rear axle electric steering system as described in any one of the claims;

[0023] An auxiliary centering mechanism is installed on the rear axle.

[0024] In some embodiments, the vehicle ECU is also included, as well as angle sensors for mounting on the front and rear axle steering knuckles.

[0025] In some embodiments, the auxiliary centering mechanism and the rear axle steering tie rod are located on opposite sides of the rear axle width direction; the auxiliary centering mechanism includes two spring damping elements; the two spring damping elements are symmetrically arranged about the centerline of the axle as an axis of symmetry; one end of the spring damping element is connected to the extension of the lower steering arm of the axle, and the other end is connected to the middle of the rear axle, and there is a designed included angle between them; the extension and the spring damping element are located on the same side of the rear axle width direction.

[0026] In some embodiments, the spring damper has connecting cylinders with openings at both ends; the rear axle and the extension are both provided with mounting brackets for accommodating the connecting cylinders, and the mounting brackets are also provided with openings; the connecting cylinders and the mounting brackets are connected by bolts.

[0027] Thirdly, a control method for a rear axle electric steering system is provided, which includes the following steps:

[0028] Obtain the vehicle's real-time speed and make the following judgments:

[0029] If the real-time driving speed is greater than the set threshold, the output shaft of the rear axle electric recirculating ball steering gear will not rotate;

[0030] If the real-time driving speed is less than the set threshold, the output shaft of the rear axle electric recirculating ball steering gear will be rotated based on the two steering angle sensors and the set rules.

[0031] In some embodiments, the rotation of the output shaft of the rear axle electric recirculating ball steering gear is controlled based on two steering angle sensors and set rules, specifically including the following steps:

[0032] The real-time value of the front axle steering angle is obtained by a steering angle sensor installed on the front axle, and the real-time value of the rear axle steering angle is obtained by a steering angle sensor installed on the rear axle.

[0033] Based on the real-time value of the front axle steering angle, the target value of the rear axle steering angle is calculated using the vehicle ECU.

[0034] The output shaft of the rear axle electric recirculating ball steering gear is rotated according to the target value to change the rear axle steering angle.

[0035] In some embodiments, the specific steps for controlling the output shaft rotation of the rear axle electric recirculating ball steering gear according to the target value are as follows:

[0036] The target angle difference is calculated based on the target value and the real-time value of the rear axle steering angle;

[0037] The vehicle ECU controls the rotation of the output shaft of the rear axle electric recirculating ball steering gear to change the rear axle steering angle, and the changed angle is the target angle difference.

[0038] The beneficial effects of the technical solution provided in this application include:

[0039] This application provides a rear axle electric steering system and its design and control method. The system obtains the maximum angle range of the output shaft of the rear axle electric recirculating ball steering gear and determines the working angle of the rear axle steering drop arm based on this maximum angle range. It also obtains the working angle of the rear steering axle resistance torque and, combined with the working angle of the rear axle steering drop arm, obtains their ratio. Based on this ratio and design rule one, the lengths of the lower steering arm of the axle and the rear axle steering drop arm are determined to obtain dimensional parameters. Finally, the initial angle between the rear axle steering drop arm and the vertical axis is obtained, and the final angle is obtained according to design rule two. Parameters: The included angle and dimensional parameters are used as manufacturing parameters for the rear axle electric steering system. Based on the maximum rotation angle of the output shaft of the rear axle electric recirculating ball steering gear, the most suitable lengths of the lower steering arm and the rear axle steering drop arm are obtained. This yields the optimal transmission ratio from the output shaft of the rear axle electric recirculating ball steering gear to the rear axle wheel. The torque of the rear axle steering drop arm can be amplified and transmitted to the axle kingpin, thus enabling the use of a steering gear with a small steering torque to drive the rear axle steering. This allows the use of an electric recirculating ball steering gear for light trucks to drive vehicles with heavier axle loads to achieve rear axle steering. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A schematic diagram showing the connection between the rear axle electric steering system and the front axle steering system provided in an embodiment of this application;

[0042] Figure 2 A schematic diagram showing the relationship between the front axle steering angle and the rear axle steering angle provided in an embodiment of this application;

[0043] Figure 3 This is a three-dimensional structural diagram of the rear axle electric steering system provided in an embodiment of this application;

[0044] Figure 4 The control logic diagram of the rear axle electric steering system provided in the embodiments of this application is shown.

[0045] In the diagram: 1. Rear axle electric recirculating ball steering gear; 2. Rear axle steering drop arm; 3. Rear axle steering tie rod; 4. Lower steering arm of the axle; 5. Auxiliary centering mechanism; 6. Front axle; 7. Front axle steering gear; 8. Steering angle sensor; 9. Front axle steering tie rod. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] This application provides a rear axle electric steering system and its design and control method to solve the problem that electric steering gears are difficult to apply to hydraulic steering systems of heavy vehicles in related technologies.

[0048] Please see Figures 1-3 A design method for a rear axle electric power steering system, comprising the following steps:

[0049] Obtain the maximum angle range of the output shaft of the rear axle electric recirculating ball steering gear 1, and determine the working angle of the rear axle steering arm 2 based on the maximum angle range;

[0050] Obtain the working angle of the rear steering axle resistance torque and combine it with the working angle of the rear axle steering drop arm 2 to obtain the ratio between the two; determine the lengths of the lower steering arm 4 of the axle and the rear axle steering drop arm 2 according to the ratio and design rule 1 to obtain the dimensional parameters.

[0051] Obtain the initial angle between the rear axle steering arm 2 and the vertical axis, and obtain the final angle parameter according to design rule 2; use the angle parameter and dimensional parameter as the manufacturing parameters of the rear axle electric steering system.

[0052] Based on the maximum rotation angle of the output shaft of the rear axle electric recirculating ball steering gear 1, the most suitable lengths of the lower axle steering arm 4 and the rear axle steering drop arm 2 are obtained through the above method. This yields the optimal transmission ratio from the output shaft of the rear axle electric recirculating ball steering gear to the rear axle wheel, which can amplify and transmit the torque of the rear axle steering drop arm 2 to the axle kingpin. This enables the use of a steering gear with a small steering torque to drive the rear axle steering, and allows the use of an electric recirculating ball steering gear for light trucks to drive vehicles with heavier axle loads to achieve rear axle steering.

[0053] To better understand the innovative concept behind this design, please refer to the following explanation:

[0054] Because the front axle steering gear 7 uses a hydraulic recirculating ball steering gear, and the rear axle steering gear uses a rear axle electric recirculating ball steering gear 1, that is, a steerable electric recirculating ball steering gear; steerable electric recirculating ball steering gears are currently used in light trucks, with output torque mostly below 2000 N.m and suitable for axle loads below 3t.

[0055] See Figure 2 Since the rear steering axle is usually very close to the instantaneous center of steering, the steering angle relationship between the front and rear axle wheels can be calculated using automotive steering theory, as shown in Formula 1. The maximum steering angle of the front steering axle wheels is usually 40°-50°. Formula 1 can be used to calculate that the maximum steering angle of the rear steering axle wheels is usually 13°-20°, which is much smaller than that of the front steering axle.

[0056] Formula 1: a2=arcctg(L1 / L2*ctg(a1)), where a1 is the maximum turning angle of the front steering axle wheel, a2 is the maximum turning angle of the rear steering axle wheel, L1 is the distance from the center of the front wheel to the center of the center wheel; L2 is the distance from the center of the front and rear wheels to the center of the center wheel.

[0057] The output shaft angle of the rear axle electric recirculating ball steering gear 1 is typically ±45°, used to match the front steering axle with a maximum wheel turning angle of 40°-50°, but the maximum turning angle requirement for the rear steering axle is only 13°-20°. Its output shaft angle greatly meets the usage requirements; how to utilize this advantage in heavy-duty trucks is the problem we face.

[0058] Therefore, we propose a clever design method: by adjusting the transmission ratio from the output shaft of the rear axle electric recirculating ball steering gear 1 to the rear axle wheels, the torque of the rear axle steering arm 2 can be amplified and transmitted to the axle kingpin, thereby enabling the use of a light-duty electric recirculating ball steering gear to drive a vehicle with a heavier axle load for rear axle steering. By lengthening the lower axle steering arm 4 and shortening the length of the rear axle steering arm 2, a steering gear with a small steering torque can be used to drive the rear axle steering.

[0059] In some preferred embodiments, when adjusting the transmission ratio from the output shaft of the rear axle electric recirculating ball steering gear 1 to the rear axle wheels, the rotation angle of the rear axle steering drop arm 2 should be adjusted to within ±45°, close to but not exceeding it. The purpose is to maximize the working angle of the electric steering gear output shaft. Given a fixed maximum steering angle requirement for the rear steering axle vehicle, this reduces the torque demand on the electric steering gear, thus providing more torque margin for the steering gear. The length of the lower steering arm 4 is typically between 200-250 mm, and the length of the rear axle steering drop arm 2 is typically between 100-130 mm.

[0060] The following two points were mainly considered during the design process:

[0061] First point:

[0062] The lengths of the lower steering arm 4 and the rear steering drop arm 2 of the axle are determined according to the ratio and design rule 1 to obtain the dimensional parameters. The specific steps include:

[0063] Obtain the first length range of the rear axle steering arm 2 and the second length range of the axle steering lower arm 4;

[0064] Select any value within the first length range as the initial value of the rear axle steering boom 2, and select any value within the second length range as the initial value of the axle steering lower boom 4.

[0065] The length of the lower steering arm 4 of the axle is gradually increased, while the length of the lower steering arm 2 of the rear axle is shortened, in order to obtain multiple sets of dimensional parameters;

[0066] Multiple sets of dimensional parameters with a ratio equal to the ratio of the lower steering arm 4 of the axle to the lower steering arm 2 of the rear axle are selected; then, the set of dimensional parameters with the longest length of the lower steering arm 4 of the axle is selected as the final dimensional parameters.

[0067] It can be understood as:

[0068] The rear axle steering arm 2, rear axle steering tie rod 3, and axle steering lower link arm 4 form a four-bar steering mechanism. When the rear axle is fully loaded, the output torque of the rear axle electric recirculating ball steering gear 1 is amplified through this four-bar mechanism to drive the rear axle under full load. The lengths of the rear axle steering arm 2 and the axle steering lower link arm 4 must be determined to ensure that the output torque of the electric steering gear can be amplified to overcome the maximum resistance torque when the rear axle is fully loaded. Specifically, this is based on the working angle of the electric steering gear being approximately 90°±45°, and the working angle of the rear steering axle resistance torque being 33°-13° to +20°, with a ratio of 90° / 33° = 2.73.

[0069] Therefore, the ratio of lower steering arm 4 of the axle to lower steering arm 2 of the rear axle is approximately 2.73.

[0070] Second point:

[0071] Obtain the initial angle between the rear axle steering arm 2 and the vertical axis, and obtain the final angle parameters according to design rule 2. The specific steps include:

[0072] Obtain the angle between the straight line where the rear axle steering arm 2 is located when it is not steering and the vertical axis, and use this angle as the initial angle;

[0073] Then determine whether the first included angle and the second included angle are equal;

[0074] If they are equal, the initial included angle does not need to be adjusted, and the initial included angle is used as the final included angle parameter;

[0075] If they are not equal, the initial included angle is adjusted; the first included angle is the angle between the line where the rear axle steering arm 2 is not turning and the line where the positive rotation limit position of the axle steering arm 2 is located; the second included angle is the angle between the line where the rear axle steering arm 2 is not turning and the line where the reverse rotation limit position of the axle steering arm 2 is located.

[0076] This can be understood as follows: When adjusting the transmission ratio from the output shaft of the rear axle electric recirculating ball steering gear 1 to the rear axle wheels, the rotation angle of the rear axle steering arm 2 should be adjusted as close to ±45° as possible, but not exceeding it. The purpose is to maximize the working angle of the electric steering gear output shaft. Given a fixed maximum steering angle requirement for the rear steering axle, this reduces the torque demand on the electric steering gear, thus providing more torque margin for the steering gear. The length of the lower steering arm 4 of the axle is typically between 200-250mm, and the length of the rear axle steering arm 2 is typically between 100-130mm.

[0077] This application also proposes a rear axle electric steering system, comprising a rear axle electric recirculating ball steering gear 1, a rear axle steering drop arm 2, a rear axle steering tie rod 3, a lower steering arm 4, and a rear axle, characterized in that:

[0078] The rear axle steering arm 2 and the lower steering arm 4 are manufactured according to the design method of the rear axle electric steering system; an auxiliary centering mechanism 5 is installed on the rear axle.

[0079] The above-described rear axle electric steering system, specifically the rear axle electric recirculating ball steering gear 1, integrates a steering motor into a standard recirculating ball steering gear. This system is widely used in the steering systems of light trucks. An input steering angle electrical signal is sent to the steering motor, which then drives the recirculating ball steering gear to output a certain torque, thus achieving vehicle steering. Because a motor is used to achieve torque output, remote electronic control is easily possible, and the product structure is mature and its performance is reliable. However, due to the limited torque output of the motor, it has not yet been applied to heavy-duty commercial vehicles with heavy loads. This patented structure combines the advantages of a recirculating ball steering gear (facilitating remote electronic control) with the ability to amplify and transmit the output torque of the electric recirculating ball steering gear to the axle steering knuckle by adjusting the transmission ratio of the steering tie rod system, thereby achieving rear axle steering in heavy-duty vehicles.

[0080] In addition, using an electric recirculating ball steering gear to achieve rear axle steering eliminates the need for a separate hydraulic system for the rear axle steering system, including hydraulic pumps, hydraulic lines, hydraulic valves, etc. The electric recirculating ball steering gear can be powered only by the car's battery, which greatly simplifies the layout of the steering system and improves reliability.

[0081] On the other hand, assuming the rear axle steering system lacks a reliable centering mechanism, if the steering motor's electronic control system or the rear axle steering gear's hydraulic system suddenly fails while the vehicle is traveling at high speed, the rear steering axle may fail to automatically return to center because there is no tie rod connecting it to the front steering axle. This could cause the vehicle to fishtail at high speeds, leading to a safety accident, and should be completely eliminated. The addition of an auxiliary centering mechanism 5 to the rear axle is precisely to avoid this safety hazard.

[0082] In some preferred embodiments, the rear axle steering system also includes a vehicle ECU and angle sensors 8 for mounting on the front and rear axle steering knuckles.

[0083] The auxiliary centering mechanism 5 and the rear axle steering tie rod 3 are located on opposite sides of the rear axle width direction. The auxiliary centering mechanism 5 includes two spring damping elements. The two spring damping elements are symmetrically arranged about the centerline of the axle. One end of each spring damping element is connected to the extension of the lower steering arm 4 of the axle, and the other end is connected to the middle of the rear axle, forming a designed angle with the rear axle. The extension and the spring damping elements are located on the same side of the rear axle width direction. Both ends of the spring damping elements have perforated connecting cylinders. The rear axle and the extension are each provided with mounting brackets for accommodating the connecting cylinders, and the mounting brackets also have perforations. The connecting cylinders and mounting brackets are connected by bolts.

[0084] The structure of the spring damper is as follows Figure 3As shown, the characteristic is that the damping spring of the spring damping component has a very high stiffness when it extends or shortens rapidly; and a very low stiffness when it extends or shortens at low speed. The function of adding a damping spring is twofold: first, to filter out frequent wheel kingpin deviation caused by uneven tire force when the vehicle travels over bumpy, uneven roads, which affects the lifespan of the electric power steering system; and second, to prevent the rear axle steering wheels from failing to return to center due to sudden power outages or other malfunctions in the electric power steering system at high speeds, thus avoiding vehicle skidding and traffic accidents.

[0085] This application also proposes a control method for a rear axle electric steering system, which includes the following steps:

[0086] Step S01: Obtain the vehicle's real-time speed and make the following judgments:

[0087] Step S02: If the real-time driving speed is greater than the set threshold, the output shaft of the rear axle electric recirculating ball steering gear 1 will not rotate. In this step, the rear axle electric recirculating ball steering gear 1 does not actively steer. The steering of the rear axle wheels is completed by the lateral force of the rear axle tires when the whole vehicle is turned. The return to center is completed by the return torque provided by the rear axle kingpin caster angle and the return torque of the damping spring.

[0088] Step S03: If the real-time driving speed is less than the set threshold, the output shaft of the rear axle electric recirculating ball steering gear 1 is controlled to rotate based on the two steering angle sensors 8 and the set rules.

[0089] The rotation of the output shaft of the rear axle electric recirculating ball steering gear 1, based on two steering angle sensors 8 and set rules, specifically includes the following steps:

[0090] The real-time value of the front axle steering angle is obtained by the steering angle sensor 8 installed on the front axle, and the real-time value of the rear axle steering angle is obtained by the steering angle sensor 8 installed on the rear axle.

[0091] The target value of the rear axle angle is calculated based on the real-time value of the front axle angle using the vehicle ECU.

[0092] The output shaft of the rear axle electric recirculating ball steering gear 1 is controlled to rotate according to the target value in order to change the rear axle steering angle. The specific steps for controlling the output shaft of the rear axle electric recirculating ball steering gear 1 to rotate according to the target value are as follows: the target angle difference is calculated based on the target value and the real-time value of the rear axle steering angle; the output shaft of the rear axle electric recirculating ball steering gear 1 is controlled to rotate using the vehicle ECU to change the rear axle steering angle, and the changed angle is the target angle difference.

[0093] In summary, the rear axle electric recirculating ball steering gear 1 is fixed above the rear axle via a connecting bracket. The rotation of the rear axle electric recirculating ball steering gear 1 is remotely controlled by the vehicle's ECU via electrical signals, thereby rotating the output shaft of the rear axle steering gear and driving the rear axle to steer. The steering wheel input torque drives the front axle steering gear to rotate, thus driving the first axle to steer normally. The vehicle ECU compares and analyzes the angle values ​​from the front and rear axle angle sensors. If the rear axle angle is not coordinated with the front axle angle, the vehicle ECU sends a control signal to drive the steering motor to rotate a certain angle until the front and rear axle angles are coordinated. The rear axle return to center is achieved by two torques: one is the return torque provided by the damping springs connecting the left and right wheel kingpins; the other is the return torque provided by the rear axle kingpin caster angle.

[0094] When the vehicle speed exceeds 20 km / h, the rear axle electric recirculating ball steering gear 1 does not actively steer. During vehicle steering, the steering force of the rear axle wheels is provided by the lateral forces of the left and right wheels. When the vehicle is traveling straight, the wheel return force is achieved jointly by the return forces of the damping springs on both the left and right sides and the return force provided by the kingpin inclination angle of the axle. This ensures that the rear steering axle wheels can return to center at speeds exceeding 20 km / h, guaranteeing driving safety.

[0095] Advantages of this application:

[0096] (1) Remote control of the rear axle steering gear is achieved by installing the rear axle electric recirculating ball steering gear 1 on the rear axle axle; applied to the rear axle steering system of heavy trucks, compared with the hydraulic recirculating ball steering gear, the hydraulic system's supporting pipelines, steering pump, steering oil tank and other parts are eliminated, and the structure is compact, the performance is reliable and the price is cheap.

[0097] (2) Combining the small steering angle of the rear axle, by reducing the length of the rear axle steering arm and appropriately increasing the length of the rear axle steering lower arm, the transmission ratio of the rear axle steering mechanism is amplified, so that the torque of the rear axle electric recirculating ball steering gear 1 can be amplified, which can drive the heavy truck to achieve rear axle steering.

[0098] (3) Install steering angle sensors 8 on the front and rear axle steering knuckles to measure the wheel angle at any time in real time. The vehicle ECU calculates the target value of the rear axle angle based on the front axle angle and controls the rotation angle of the steering motor according to the result until the rear axle angle reaches the target value. This can accurately realize rear axle steering, coordinate the front and rear axle angles, and reduce the turning diameter and tire wear.

[0099] (4) The return torque is provided by using damping springs and rear axle kingpin tilting, which enables rear axle return to center at higher vehicle speeds (the limit set in this patent is greater than 20km / h) and in the event of a rear axle steering gear failure. The mechanical structure achieves rear axle steering return, eliminating the need for an electrical or hydraulic control system. The structure is simple and reliable, ensuring high-speed driving safety.

[0100] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0101] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0102] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A design method for a rear axle electric steering system, characterized in that, It includes the following steps: Obtain the maximum angle range of the output shaft of the rear axle electric recirculating ball steering gear (1), and determine the working angle of the rear axle steering arm (2) based on the maximum angle range; Obtain the working angle of the rear steering axle resistance torque, and take the ratio of the working angle of the rear axle steering arm (2) to the working angle of the rear steering axle resistance torque as the first ratio; determine the length of the lower steering arm (4) of the axle and the rear steering arm (2) according to the first ratio and design rule 1 to obtain the dimensional parameters; Obtain the initial angle between the rear axle steering arm (2) and the vertical axis, and obtain the final angle parameter according to design rule two; The included angle parameter and dimensional parameter are used as the manufacturing parameters for the rear axle electric steering system.

2. The design method of the rear axle electric steering system as described in claim 1, characterized in that, The lengths of the lower steering arm (4) and the lower steering arm (2) of the axle are determined according to the first ratio and design rule one to obtain the dimensional parameters. The specific steps include: Obtain the first length range of the rear axle steering arm (2) and the second length range of the axle steering lower arm (4); Select any value in the first length range as the initial value of the rear axle steering arm (2), and select any value in the second length range as the initial value of the axle steering lower arm (4); The length of the lower steering arm (4) of the axle is increased successively, and the length of the lower steering arm (2) of the rear axle is shortened to obtain multiple sets of dimensional parameters; Multiple sets of dimensional parameters are selected whose ratio of the lower steering arm (4) of the axle to the lower steering arm (2) of the rear axle is equal to the first ratio; then the set of dimensional parameters with the longest length of the lower steering arm (4) of the axle is selected as the final dimensional parameters.

3. The design method of the rear axle electric steering system as described in claim 1, characterized in that, Obtain the initial angle between the rear axle steering arm (2) and the vertical axis, and obtain the final angle parameters according to design rule two. The specific steps include: Obtain the angle between the straight line where the rear axle steering arm (2) is located when it is not steering and the vertical axis, and use this angle as the initial angle; Then determine whether the first included angle and the second included angle are equal; If they are equal, the initial included angle does not need to be adjusted, and the initial included angle is used as the final included angle parameter; If they are not equal, the initial included angle is adjusted; the first included angle is the angle between the line where the rear axle steering arm (2) is not turning and the line where the positive rotation limit position of the rear axle steering arm (2) is located; the second included angle is the angle between the line where the rear axle steering arm (2) is not turning and the line where the reverse rotation limit position of the rear axle steering arm (2) is located.

4. A rear axle electric steering system, comprising a rear axle electric recirculating ball steering gear (1), a rear axle steering drop arm (2), a rear axle steering tie rod (3), a lower steering arm (4), and a rear axle, characterized in that: The rear axle steering arm (2) and the lower axle steering arm (4) are manufactured according to the design method of the rear axle electric steering system as described in any one of claims 1-3; An auxiliary centering mechanism (5) is installed on the rear axle.

5. The rear axle electric steering system as described in claim 4, characterized in that: It also includes the vehicle ECU, as well as angle sensors (8) for mounting on the front and rear axle steering knuckles.

6. The rear axle electric steering system as described in claim 4, characterized in that: The auxiliary centering mechanism (5) and the rear axle steering tie rod (3) are located on both sides of the width direction of the rear axle, respectively. The auxiliary centering mechanism (5) includes two spring damping elements. The two spring damping elements are symmetrically arranged with the center line of the axle as the axis of symmetry. One end of the spring damping element is connected to the extension of the lower steering arm (4) of the axle, and the other end is connected to the middle of the rear axle, and there is a designed angle between them. The extension and the spring damping element are located on the same side of the width direction of the rear axle.

7. The rear axle electric steering system as described in claim 6, characterized in that: The spring damping component has connecting cylinders with openings at both ends; the rear axle and the extension are both provided with mounting brackets for accommodating the connecting cylinders, and the mounting brackets are also provided with openings; the connecting cylinders and the mounting brackets are connected by bolts.

8. A control method for a rear axle electric steering system as described in claim 5, characterized in that, It includes the following steps: Obtain the vehicle's real-time speed and make the following judgments: If the real-time driving speed is greater than the set threshold, the output shaft of the rear axle electric recirculating ball steering gear (1) will not rotate; If the real-time driving speed is less than the set threshold, the output shaft of the rear axle electric recirculating ball steering gear (1) is rotated based on the two steering angle sensors (8) and the set rules.

9. The control method for the rear axle electric steering system as described in claim 8, characterized in that, The rotation of the output shaft of the rear axle electric recirculating ball steering gear (1) is controlled based on two steering angle sensors (8) and set rules, specifically including the following steps: The real-time value of the front axle angle is obtained by the angle sensor (8) installed on the front axle, and the real-time value of the rear axle angle is obtained by the angle sensor (8) installed on the rear axle. Based on the real-time value of the front axle steering angle, the target value of the rear axle steering angle is calculated using the vehicle ECU. The output shaft of the rear axle electric recirculating ball steering gear (1) is rotated according to the target value to change the rear axle steering angle.

10. The control method for the rear axle electric steering system as described in claim 9, characterized in that, The specific steps for controlling the output shaft rotation of the rear axle electric recirculating ball steering gear (1) according to the target value are as follows: The target angle difference is calculated based on the target value and the real-time value of the rear axle steering angle; The output shaft of the rear axle electric recirculating ball steering gear (1) is rotated by the vehicle ECU to change the rear axle steering angle, and the changed angle is the target angle difference.

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