Commercial vehicle steer-by-wire

Abstract

The application belongs to the technical field of commercial vehicles and relates to a commercial vehicle steer-by-wire device which comprises a first steering device and a second steering device working independently of each other; the first steering device and the second steering device are connected with right-side tires and left-side tires through steering bridges respectively; the first steering device and the second steering device both comprise an EPS controller, an assisting motor, a first steering device shell, a screw nut transmission mechanism, a worm wheel arranged outside the screw nut transmission mechanism, a worm cooperating with the worm wheel and connected with the assisting motor at one end, a second steering device shell, a pull rod, a ball pin mechanism and a displacement sensor; the application cancels the traditional T-shaped steering bridge mechanism, adopts two independently working steering devices arranged symmetrically, assists the left and right steering tires respectively, avoids steering side slip and reduces tire wear. Meanwhile, the arrangement mode of the sensor is changed, the response of the steering device is more sensitive, the feedback angle signal is more instant, the application is applied to the field of unmanned driving and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to a steer-by-wire system for commercial vehicles. It belongs to the field of automotive technology. Background Technology

[0002] Commercial vehicle steering systems, such as Figure 1 As shown, a typical steering system consists of a steering wheel, column, universal joint, intermediate shaft, recirculating ball steering gear, drop arm, tie rod, bend arm, and steering wheel. To reduce driver workload, the recirculating ball steering gear in the system is equipped with a power assist device, such as EPS (Electric Power Steering). In the industry's development, steering gears equipped with EPS power assist can achieve autonomous driving capabilities. This involves using specific control algorithms to interact with the steering gear's EPS controller, allowing the EPS controller to fulfill autonomous driving commands as required.

[0003] However, in practical applications, existing steering systems have the following problems that cannot be overcome:

[0004] 1. In this type of steering system, the angle sensor of the EPS controller is installed near the steering wheel. Due to mechanical transmission clearances and stiffness of the steering system, there is a discrepancy between the actual tire turning angle and the actual steering wheel turning angle. During vehicle operation, the transmission clearance constantly changes due to wear of mechanical parts and cannot be eliminated through compensation. Simultaneously, the stiffness is constantly changing due to the vehicle's load and cannot be eliminated through compensation either. Therefore, the steering wheel angle cannot accurately reflect the tire turning angle, causing the autonomous driving system to be unable to quickly determine the vehicle's operating status and respond to steering commands issued by the control system.

[0005] 2. The front axle steering system of commercial vehicles often uses a trapezoidal mechanism. During steering, the left and right tires rotate at inconsistent angles, leading to tire slippage, discontinuous steering angles, and abrupt changes in steering direction. This is detrimental to the execution of autonomous driving commands and the assessment of the vehicle's overall operating status. When the vehicle is running, if... Figure 2 As shown, the ideal state is that when the car turns along the turning radius R, the turning angles A and B of the left and right tires are fully... This prevents the tires from slipping and wearing out, and also prevents sudden changes in steering angle during autonomous driving applications.

[0006] 3. Existing commercial vehicle steering systems rely on mechanical transmission between the steering wheel and tires for angular movement. In applications requiring high torque output, a high gear ratio is necessary to transmit the torque. However, a high gear ratio results in excessive steering wheel turns, significantly reducing driving comfort. Furthermore, the gear ratio for mechanical motion transmission is typically a fixed linear relationship, which cannot meet the vehicle's non-linear handling requirements for the steering system.

[0007] In conclusion, existing commercial vehicle steering systems cannot meet the requirements of autonomous driving and high-end handling, and need to be improved. Summary of the Invention

[0008] This invention proposes a steer-by-wire system for commercial vehicles that can quickly respond to steering angle commands, provide feedback on tire angle, and adjust the steering angle function based on the ideal steering wheel-to-tire angle-to-speed ratio curve to achieve free speed ratio control.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A steer-by-wire system for commercial vehicles includes a first steering gear and a second steering gear that operate independently of each other; the first steering gear and the second steering gear are respectively connected to the right tire and the left tire via a steering axle.

[0011] The first steering gear and the second steering gear both include an EPS controller, a power assist motor, a first steering gear housing, a lead screw and nut transmission mechanism, a worm wheel disposed outside the lead screw and nut transmission mechanism, a worm cooperating with the worm wheel and having one end connected to the power assist motor, a second steering gear housing, a tie rod, a ball pin mechanism, and a displacement sensor.

[0012] The lead screw and nut transmission mechanism includes a lead screw, a lead screw nut, a reverser, and steel balls. There is an annular groove raceway between the lead screw and the lead screw nut. The steel balls roll in the raceway. Through the action of the reverser, the lead screw and nut transmission mechanism is formed.

[0013] In the process of transmitting motor motion, when the motor rotates, it drives the worm to rotate, which in turn drives the worm wheel to rotate, which in turn drives the lead screw nut to rotate. The rotation of the lead screw nut drives the lead screw to move, and finally converts the rotational motion of the motor into the linear motion of the lead screw, which acts on the bending arm of the tire, causing the tire to turn and completing the steering function of the steering gear.

[0014] The first steering gear housing and the second steering gear housing are provided with mounting holes, and both the first steering gear and the second steering gear are fixed to the steering axle through the mounting holes and bolts.

[0015] Thrust bearings are arranged at both ends of the lead screw nut. The outer ring of the thrust bearing is installed in the first steering gear housing and the second steering gear housing to support the lead screw nut.

[0016] A displacement sensor is arranged on the lead screw.

[0017] The worm gear is supported and fixed at both ends by a first deep groove ball bearing and a second deep groove ball bearing, and its axial movement is fixed by a retaining ring and a locking ring.

[0018] The EPS controller is equipped with an ECU chip and logic circuits for controlling the movement of the motor. Based on the speed and angle requirements transmitted by the steering wheel, it controls the speed and torque of the motor. The motor movement is transmitted to the steering tires through motion transmission to complete the steering function. The EPS controller can calculate the turning angle of the whole vehicle based on the displacement value measured by the displacement sensor and send the turning angle information through the CAN network.

[0019] The EPS controller controls the motor's rotation angle using a PID control algorithm, the functional relationship of which is:

[0020]

[0021] In the formula: Kp—proportional gain; Tt—integral time constant; TD—differential time constant; α(t)—the required rotation angle; e(t)—measurement error.

[0022] The first and second steering gears respectively assist the left and right wheels of the vehicle. The first and second steering gears operate independently, controlling the left and right tire steering angles of the vehicle to achieve the desired steering effect. .

[0023] The displacement of the lead screw and the steering of the steering wheel satisfy the following relationship:

[0024]

[0025] In the formula, θ: steering wheel angle, R: radius of the bending arm, S: displacement of the lead screw, and I: initial speed ratio. This is a type of steer-by-wire system for commercial vehicles. A displacement sensor is installed between the lead screw and the second steering gear housing. When there is relative movement between the lead screw and the second steering gear housing, the displacement sensor can measure the relative displacement between them and calculate the displacement.

[0026] The motor is a dual-winding redundant motor, with two sets of windings, and correspondingly, two sets of MOSFETs drive the motor to rotate.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention provides a steer-by-wire system that can execute steering commands from the steering wheel or autonomous driving systems more quickly, while providing more accurate feedback on the actual turning angle of the entire vehicle. During driving, the vehicle experiences no sideslip or sudden changes in steering angle, making it better suited for use in the field of autonomous driving for commercial vehicles. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of a traditional commercial vehicle steering system;

[0031] Figure 2 This is a diagram showing the relationship between the left and right tire angles and the turning radius R when a car is turning.

[0032] Figure 3 This is a schematic diagram of the structure of a steer-by-wire system for commercial vehicles according to the present invention;

[0033] Figure 4 This is a schematic diagram of a rod-nut transmission mechanism for a commercial vehicle steer-by-wire system according to the present invention;

[0034] Figure 5 This is a schematic diagram of the arrangement of the steering gear in the overall vehicle steering system of a steer-by-wire system for commercial vehicles according to the present invention.

[0035] Figure 6 This is a schematic diagram illustrating the operating principle of a steer-by-wire system for commercial vehicles according to the present invention.

[0036] Figure 7 This is a schematic diagram of a dual-winding motor drive circuit in a steer-by-wire system for commercial vehicles according to the present invention.

[0037] Figure 8 This invention relates to a schematic diagram of the worm gear mounting and fixing in a steer-by-wire system for commercial vehicles.

[0038] Figure 9 This is a block diagram of the angle control of a steer-by-wire system for commercial vehicles according to the present invention.

[0039] Figure 10 This is a flowchart illustrating the angle control calculation of a steer-by-wire system for commercial vehicles according to the present invention.

[0040] In the diagram: 1-Steering wheel; 2-Column; 3-Universal joint; 4-Intermediate shaft; 5-Recirculating ball steering gear; 6-Drop arm; 7-Tie rod; 8-Curved arm; 9-Steering wheel; 3.1-EPS controller; 3.2-Power steering motor; 3.3-First steering gear housing; 3.4-Steel ball; 3.5-Lead screw; 3.6-Worm gear; 3.7-Worm wheel; 3.8-Reversing device; 3.9-Lead screw nut; 3.10-Thrust bearing; 3.11-Second steering gear housing; 3.12-Tie rod; 3.13-Ball pin mechanism; 3.14-Displacement sensor; 3.6.1-First deep groove ball bearing; 3.6.2-Snap ring; 3.6.3-Second deep groove ball bearing; 3.6.4-Locking ring. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] Commercial vehicle steering systems, such as Figure 1 As shown, it typically consists of components such as a steering wheel (1), column (2), universal joint (3), intermediate shaft (4), recirculating ball steering gear (5), drop arm (6), tie rod (7), bend arm (8), and steering wheel (9). To reduce driver workload, the recirculating ball steering gear in the system is equipped with a power assist device, such as EPS (Electric Power Steering) for automobiles. A commercial vehicle steer-by-wire system includes a first steering gear and a second steering gear that operate independently; the first and second steering gears are respectively connected to the right tire and left tire via a steering axle.

[0043] Both the first and second steering gears include an EPS controller 3.1, a power assist motor 3.2, a first steering gear housing 3.3, a lead screw and nut transmission mechanism, a worm gear 3.7 disposed outside the lead screw and nut transmission mechanism, a worm 3.6 cooperating with the worm gear 3.7 and connected at one end to the power assist motor 3.2, a second steering gear housing 3.11, a tie rod 3.12, a ball pin mechanism 3.13, and a displacement sensor 3.14;

[0044] The lead screw and nut transmission mechanism includes a lead screw 3.5, a lead screw nut 3.9, a reverser 3.8, and steel balls 3.4. There is an annular groove raceway between the lead screw 3.5 and the lead screw nut 3.9, and the steel balls 3.4 roll within the raceway. Through the action of the reverser, the lead screw and nut transmission mechanism is formed. Two thrust bearings 3.10 are installed on the exterior of both ends of the lead screw and nut. The outer rings of the thrust bearings are installed inside the first and second steering gear housings, and the inner rings are installed at both ends of the nut, fixing and supporting the lead screw and nut so that it can only rotate, not axially or radially.

[0045] The input end of the worm gear is connected to the motor, and simultaneously, a worm wheel engages with it, which is mounted on the lead screw nut. (See attached image.) Figure 6 As shown, in the motor motion transmission process, when the motor rotates, it drives the worm to rotate, which in turn drives the worm wheel to rotate, which in turn drives the lead screw nut to rotate. The rotation of the lead screw nut drives the lead screw to move, and finally converts the rotational motion of the motor into the linear motion of the lead screw, which acts on the bent arm of the tire, causing the tire to turn and completing the steering function of the steering gear.

[0046] The first steering gear housing has support holes for mounting and fixing the worm gear, as shown in the attached figure. Figure 8 As shown, the two ends of the worm gear are supported and fixed by a first deep groove ball bearing 3.6.1 and a second deep groove ball bearing 3.6.3, and axial movement is fixed by a retaining ring 3.6.2 and a locking ring 3.6.4. The worm gear can only rotate. The first steering gear housing and the second steering gear housing are provided with mounting holes, and both the first steering gear and the second steering gear are fixed to the steering axle through the mounting holes and bolts.

[0047] A displacement sensor is arranged on the lead screw.

[0048] The worm gear is supported and fixed at both ends by a first deep groove ball bearing and a second deep groove ball bearing, and its axial movement is fixed by a retaining ring and a locking ring.

[0049] The EPS controller is equipped with an ECU chip and logic circuits for controlling the movement of the motor. Based on the speed and angle requirements transmitted by the steering wheel, it controls the speed and torque of the motor. The motor movement is transmitted to the steering tires through motion transmission to complete the steering function. The EPS controller can calculate the turning angle of the whole vehicle based on the displacement value measured by the displacement sensor and send the turning angle information through the CAN network.

[0050] The EPS controller controls the motor's rotation angle using a PID control algorithm, the functional relationship of which is:

[0051]

[0052] In the formula: Kp—proportional gain; Tt—integral time constant; TD—differential time constant; α(t)—the required rotation angle; e(t)—measurement error.

[0053] The first and second steering gears respectively assist the left and right wheels of the vehicle. The first and second steering gears operate independently, controlling the left and right tire steering angles of the vehicle to achieve the desired steering effect. Where A is the turning angle of the outer wheel of the car, B is the turning angle of the inner wheel of the car, L is the track width of the car, and s is the wheelbase of the car.

[0054] The displacement of the lead screw and the steering of the steering wheel satisfy the following relationship:

[0055]

[0056] In the formula, θ: steering wheel angle, R: radius of the bending arm, S: displacement of the lead screw, and I: initial speed ratio. This is a type of steer-by-wire system for commercial vehicles. A displacement sensor is installed between the lead screw and the second steering gear housing. When there is relative movement between the lead screw and the second steering gear housing, the displacement sensor can measure the relative displacement between them and calculate the displacement.

[0057] To meet the requirements for emergency stopping in case of malfunction, the motors of both steering gears are dual-winding redundant motors, and the control principle diagram of each motor is attached. Figure 7 As shown, the driving MOSFETs are divided into two groups, each driving a motor rotor with one winding. When one motor winding fails, the other winding can continue to be used. During normal driving and steering, the first and second steering gears have a total of four windings; if one fails, the other three can still function normally. This meets the requirements for emergency stopping in fault conditions.

[0058] When a car is turned, the ratio between the steering wheel angle and the tire steering angle is called the steering speed ratio. Preferably, in this invention, the ratio between the steering wheel angle and the tire steering angle is variable and satisfies the following relational expression.

[0059] -----1

[0060] (In the formula, θ: steering wheel angle, R: radius of the bend arm, S: displacement of the lead screw, I: initial speed ratio.)

[0061] The derivation principle of this function is as follows:

[0062] The steering angle between the steering wheel and the wheels satisfies the formula:

[0063] -------2

[0064] (Where: θ: steering wheel angle, α: tire angle, I: initial speed ratio)

[0065] And from

[0066] --------------3

[0067] Substituting Formula 3 into Formula 2 and rearranging, we get...

[0068] --------4

[0069] The above equation is the relationship between θ and S. Integrating Equation 4...

[0070]

[0071] The above is the derivation process of the function in Formula 1 used in this invention.

[0072] During the process of the steering gear rotating in accordance with the speed ratio of the steering wheel, the steering angle that needs to be adjusted satisfies the following relationship.

[0073] --------5

[0074] The source of Formula 5 is as follows:

[0075] As attached Figure 9 As shown, there is an error between the actual value of the controlled rotation angle α and the theoretical value.

[0076] To keep the error e(t) within a controllable range, proportional, integral, and derivative control are introduced during the control process. (See attached diagram) Figure 9 The block diagram shown has the following transfer function expression:

[0077] --------------6

[0078] Perform an inverse Laplace transform on Equation 6

[0079] When the software calculation program is working, its adjustment process is as follows: Figure 10 As shown, calculate respectively , , Sum these three data points and then make a judgment. If the value matches the theoretical value, the loop exits; otherwise, data collection and calculation continue.

[0080] Combining formulas 3 and 5, we can obtain

[0081] ---------7

[0082] Formula 7 transforms the control of the steering angle into the control of the lead screw's displacement. By using the lead screw's displacement sensor to collect real-time data, the steering angle can be precisely controlled.

[0083] When the steering wheel inputs a steering angle command, the controller plans the value of S based on the relationship between S and θ given in Formula 1, and calculates S(t) using Formula 7 to complete the steering command.

[0084] In autonomous driving applications, the steering angle α needs to be controlled by the upper-level control command of the vehicle. Compared with steering wheel control, the only difference is that the input signal is changed from the steering wheel to the upper-level controller of the vehicle. The upper-level command plans the value of α, the steering unit receives the command, calculates S(t) according to Formula 7, and completes the steering command.

[0085] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A steer-by-wire system for commercial vehicles, characterized in that: It includes a first steering gear and a second steering gear that operate independently of each other; the first steering gear and the second steering gear are respectively connected to the right tire and the left tire via a steering axle. Both the first steering gear and the second steering gear include an EPS controller, a power assist motor, a first steering gear housing, a lead screw and nut transmission mechanism, a worm wheel disposed outside the lead screw and nut transmission mechanism, a worm cooperating with the worm wheel and having one end connected to the power assist motor, a second steering gear housing, a tie rod, a ball pin mechanism, and a displacement sensor. The lead screw and nut transmission mechanism includes a lead screw, a lead screw nut, a reverser, and steel balls. There is an annular groove raceway between the lead screw and the lead screw nut, and the steel balls roll in the raceway. A displacement sensor is arranged on the lead screw; The EPS controller is equipped with an ECU chip and a logic circuit for controlling the movement of the motor. Based on the speed and angle requirements transmitted by the steering wheel, it controls the speed and torque of the motor. The motor movement is transmitted to the steering tires through a motion transmission method to complete the steering function. The EPS controller can calculate the turning angle state of the whole vehicle based on the displacement value measured by the displacement sensor and send the turning angle information through the CAN network. The displacement of the lead screw and the steering of the steering wheel satisfy the following relationship: ； In the formula, θ: steering wheel angle, R: radius of the bend arm, S: displacement of the lead screw, and I: initial speed ratio.

2. The steer-by-wire system for commercial vehicles according to claim 1, characterized in that: The first steering gear housing and the second steering gear housing are provided with mounting holes, and both the first steering gear and the second steering gear are fixed to the steering axle through the mounting holes and bolts.

3. A steer-by-wire system for commercial vehicles as described in claim 1 or 2, characterized in that: Thrust bearings are arranged at both ends of the lead screw nut.

4. A steer-by-wire system for commercial vehicles as described in claim 1 or 2, characterized in that: The worm gear is supported and fixed at both ends by a first deep groove ball bearing and a second deep groove ball bearing, and its axial movement is fixed by a retaining ring and a locking ring.

5. The steer-by-wire system for commercial vehicles according to claim 1, characterized in that: The EPS controller controls the motor's rotation angle using a PID control algorithm, the functional relationship of which is: ； In the formula: K p —Proportional gain, T t —Integral time constant; T d — Differential time constant; α(t) — Rotation angle to be performed; e(t) — Measurement error.

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