Method for reducing mechanical shock load of steering system

Abstract

The invention discloses a method for reducing the mechanical impact load of a steering system. The method comprises the steps that S1, the motor rotor acceleration torque Ta of the steering system is monitored and calculated in real time; s2, judging whether the acceleration torque Ta of the motor rotor meets a preset condition or not; if a preset condition is met, entering the step S3, otherwise, returning to the step S1; step S3, outputting a target torque request TRML; the value of the target torque request TRML is determined according to an expected minimum target level lambda for reducing the external impact load and an external impact load value; the direction of the target torque request TRML is the same as the direction of the motor rotor speed n. Impact damage of external impact loads to the steering system and an internal key part worm gear under the special driving working condition can be reduced, the service life of the worm gear is guaranteed and even prolonged, the reliability of the steering system is improved, and the noise vibration performance of the steering system and the hand feeling of a driver are improved.

Description

Technical Field

[0001] The invention relates to the technical field of automobile steering systems, and in particular to a method for reducing the mechanical impact load of a steering system. Background Art

[0002] The service conditions and road load cycles of the vehicle during its life cycle determine that the design of the steering system must meet the vehicle's service conditions and road load requirements. In some special operating conditions, such as driving on washboard roads, speed bumps, or potholes and bumps caused by aging or natural environmental factors, the tires will be stimulated by the vibration impact of these special roads and introduce the excitation into the steering system through the steering knuckle and steering rod. In addition, in extreme driving operations such as high-speed emergency avoidance steering, such as in the J-Turn test used to evaluate vehicle handling and stability, due to the very fast steering speed, the tires are subjected to severe impact from the ground and transmit this impact to the steering system to which they are mechanically connected.

[0003] At present, the widely used electric power steering systems in automobiles include dual-gear, single-gear and column-type electric power steering systems. These steering systems generally use a worm gear servo reduction mechanism at the output end of the drive motor to transmit the torque and rotational motion of the motor. Taking into account factors such as processing and manufacturing, cost and noise performance, the worm is usually made of steel, while the worm wheel is usually made of low-cost, easy-to-process and good friction-reducing plastic. However, when the steering system is subjected to a high external load impact and transmitted to the worm wheel through the internal mechanical connection, the high-frequency and high-amplitude impact load will cause the worm wheel to bear a large stress instantly, which is easy to cause local yield; and repeated impacts will cause fatigue cracks in the worm wheel, especially in stress concentration areas such as the root of the tooth, which may cause the gear teeth to break in severe cases; at the same time, high-frequency and high-amplitude impacts will destroy the lubricating oil film, increase the wear rate of the tooth surface, and thus affect the stability and efficiency of the transmission. Especially for worm wheels made of plastic, due to their low strength and toughness, the above phenomenon is more likely to occur, which will have a serious impact on the service life of the worm wheel and the vibration and noise performance of the steering system.

[0004] In order to reduce the damage of external impact load to the worm gear and to maximize the service life of the worm gear and improve the vibration and noise performance of the steering system, measures can be taken from the mechanical design aspect: such as selecting worm gear materials with high strength and good toughness, optimizing the tooth shape and tooth root transition curve to improve the impact resistance, adding buffer and shock absorbing devices in the system to absorb the impact energy and thus reduce the direct impact on the worm gear and steering system. However, these will undoubtedly increase the cost of the entire product in terms of materials, processing and manufacturing, and parts, and the optimization effect only from the mechanical aspect is limited, and cannot effectively reduce the impact damage to the worm gear. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a technical solution for reducing the mechanical impact load of the steering system. The technical solution of the present invention uses software to monitor the characteristic changes of the motor rotor acceleration torque to identify the external impact load under special working conditions. When the impact load exceeds the limit level, the motor is controlled to generate corresponding torque to offset the impact.

[0006] In order to solve the above technical problems, the present invention provides a method for reducing the mechanical impact load of a steering system, comprising:

[0007] Step S1, real-time monitoring and calculation of the motor rotor acceleration torque T of the steering system a ;

[0008] Step S2, determining the motor rotor acceleration torque T a Whether the preset conditions are met; if the preset conditions are met, go to step S3, otherwise return to step S1;

[0009] Step S3: Output the target torque request T RML ;

[0010] The target torque request T RML The value of is determined according to the expected minimum target level λ for reducing the external impact load and the external impact load value; the target torque request T RML The direction of is the same as the direction of the motor rotor speed n.

[0011] Preferably, the external impact load value is obtained by any of the following methods: Method 1, using the motor rotor acceleration torque T a Method 2: obtain the rack force by real-time monitoring of the steering system; Method 3: obtain the rack force by measuring the steering system’s sensor device.

[0012] Preferably, in step S2, the preset conditions include:

[0013] Condition 3, |T in the preset direction a |≥T2 duration reaches t1; wherein T2 is a higher threshold value of the motor rotor acceleration torque for identifying a preset driving condition, wherein t1 is a preset time interval;

[0014] Condition 4, |T in the opposite direction a | <T2;

[0015] Condition 5, |T in the preset direction a |≥T2 duration is less than t2; where t2 is the preset target torque request T RML The shortest duration of action.

[0016] Preferably, in step S1, the motor rotor acceleration torque Ta The calculation method of a T is: T = J﹡α, where J is the sum of the inertia of the rotating parts on the rotor shaft, and α is the angular acceleration of the motor rotor.

[0017] Preferably, in the step S2, the judgments of Condition 1 and Condition 2 are first executed, and after Condition 1 and Condition 2 are satisfied, the judgments of Condition 3 to Condition 5 are started;

[0018] Condition 1: The rotor speed n, the driver state, and the motor torque M satisfy the preset conditions;

[0019] Condition 2: |T a | < T1 in the preset direction.

[0020] Preferably, the preset condition for the rotor speed n is: N1 < n < N2, where N1 is the preset lower limit of the rotor speed and N2 is the preset upper limit of the rotor speed.

[0021] Preferably, the preset condition for the motor torque M is: M1 < M < M2, where M1 is the lower limit of the torque that the motor can output, and M2 is the upper limit of the torque that the motor can output.

[0022] Preferably, the preset condition for the driver state is driver enable.

[0023] Compared with the prior art, the present invention can reduce the impact damage of the external impact load on the steering system and the key internal component worm gear under special driving conditions, ensure or even improve the service life of the worm gear, improve the reliability of the steering system, and improve the noise and vibration performance of the steering system and the driver's feel. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0025] Figure 1 It is a schematic structural diagram of a worm gear and worm drive type electric power steering system;

[0026] Figure 2 It is a functional architecture diagram of the method for reducing the mechanical impact load of the steering system in Embodiment 1;

[0027] Figure 3 It is a schematic longitudinal cross-sectional view of a typical washboard road;

[0028] Figure 4 It is a schematic diagram of the external load impact transmission process in the steering system;

[0029] Figure 5 It is a schematic flow chart of the method for reducing the mechanical impact load of the steering system in Embodiment 1;

[0030] Figure 6 The force analysis of the worm gear before and after the impact load is reduced in Example 1;

[0031] Figure 7 is the variation of the motor rotor acceleration torque with time under the washboard road condition and the corresponding T RML Status diagram of torque request;

[0032] Figure 8 is the variation of the motor rotor acceleration torque with time under J-Turn condition and the corresponding T RML Status diagram of torque request;

[0033] Fig. 9 Schematic diagram of the vehicle's motion trajectory under J-Turn conditions. DETAILED DESCRIPTION

[0034] The following describes the implementation methods of the present invention through specific specific embodiments, and those skilled in the art can fully understand other advantages and technical effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through different specific implementation methods, and the details in this specification can also be applied based on different viewpoints, and various modifications or changes can be made without deviating from the overall design concept of the invention. It should be noted that the following embodiments and the features in the embodiments can be combined with each other in the absence of conflict. The following exemplary embodiments of the present invention can be implemented in a variety of different forms and should not be interpreted as being limited to the specific embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary specific embodiments to those skilled in the art.

[0035] Example 1

[0036] An exemplary worm gear electric power steering system is as follows: Figure 1As shown, its working principle is that the steering wheel 1 is connected to the input shaft 4 of the steering gear through the steering column 2 and the intermediate shaft 3, and the steering gear 6 and the rack 7 form a meshing transmission in the toothed area 7-2 at the sensor end to drive the rack to move linearly along its axial direction; the input shaft 4 is integrated with a torque and angle sensor 5 for detecting the torque and angle signal of the driver rotating the steering wheel 1, and the signal is transmitted to the electronic control unit 9 of the drive motor 10 through the wiring harness 8; the electronic control unit 9 performs comprehensive processing and calculation on the received signal, and sends a command to the drive motor 10 to control the motor to output a certain torque The output torque of the driving motor 10 is transmitted to the worm wheel 12 through the worm 11. Since the servo gear 13 is fixedly connected to the worm wheel 12 and meshes with the rack 7 in the toothed area 7-1 at the servo end, the motor torque is amplified twice and transmitted to the rack 7 and converted into the force of the axial movement of the rack. At the same time, the rotational motion of the motor is converted into the linear motion of the rack 7 through the servo mechanisms 11, 12 and 13. The steering rod 14 connected to the rack 7 at both ends with spherical joints realizes spatial motion, drives the tire connected to it to rotate around a certain axis, and finally completes the electric power steering function.

[0037] It should be noted that the above Figure 1 The system shown in the figure is called a dual-gear electric power steering system in the industry. In addition, the drive units 9 and 10 and the worm gear servo mechanisms 11, 12 and 13 can also be flexibly arranged at the steering column 2 position or the steering gear 6 position to adapt to different vehicle requirements. The corresponding two arrangements are respectively called column-type electric power steering systems and single-gear electric power steering systems. The common feature of the above three types of steering systems is that they all use a worm gear servo transmission mechanism. At the same time, the present invention is also applicable to a wire-controlled steering system in which the lower steering actuator uses a worm gear servo transmission mechanism.

[0038] In order to reduce the external impact load on the steering system under special working conditions, this embodiment provides a method for reducing the mechanical impact load of the steering system, including:

[0039] Step S1, real-time monitoring and calculation of the motor rotor acceleration torque T of the steering system a ;

[0040] Step S2, determining the motor rotor acceleration torque T a Whether the preset conditions are met; if the preset conditions are met, go to step S3, otherwise return to step S1;

[0041] Step S3: Output the target torque request T RML ;

[0042] The target torque request T RMLThe value of is determined according to the expected minimum target level λ for reducing the external impact load and the external impact load value; the target torque request T RML The direction of is the same as the direction of the motor rotor speed n.

[0043] If we take a washboard road as an example, the excitation of the washboard road is transmitted to the outer tie rod of the steering system through the vehicle tires and steering knuckles. As a result, the outer tie rod alternately jumps up and presses down in the Z-axis direction, which in turn causes a reciprocating impact on the steering system. This impact is transmitted to the motor rotor through the mechanical transmission components inside the steering system, causing the rotor to generate an acceleration. Therefore, the characteristics related to the change in rotor acceleration can be quantified to identify the washboard road condition. The present invention reflects the impact force generated by the washboard road condition on the system by monitoring the change in the motor rotor acceleration torque. The motor rotor acceleration torque T a The calculation is as follows:

[0044] T a =J﹡α

[0045] in,

[0046] J is the inertia of the rotating parts on the rotor shaft, which is related to the specific design of the servo mechanism and can be obtained through three-dimensional digital model measurement. It is generally calculated as follows:

[0047] J = rotor inertia + worm inertia + (2 gear hub inertia) + coupling rotation inertia (including the inertia of the bearing inner ring and 50% of the bearing rolling element)

[0048] α is the angular acceleration of the rotor, obtained by differentiating the rotor speed n.

[0049] Step S2 is used to determine the motor rotor acceleration torque T a Whether the preset conditions (i.e., change characteristics) are met, and these change characteristics are used to determine whether the current vehicle is in a washboard road condition and whether the external impact load exceeds the tolerance threshold of the steering system or the worm gear, thereby determining whether to activate the target torque request T to reduce the mechanical impact load. RML .

[0050] To perform the above method, the following can be used as an example: Figure 2 The functional architecture shown.

[0051] When the vehicle is traveling in a straight line Figure 3 On the washboard road shown in the figure, the tire is stimulated by the impact of the uneven road surface, and its position in the z direction will change, such as Figure 4As shown. The two side steering tie rods are mechanically connected to the tires through the steering knuckles, so they will be subjected to tensile or compressive forces and alternately move up and down in the z direction. At the same time, the two side steering tie rods also transmit this impact load to the inside of the system, directly acting on the rack, causing the rack to reciprocate in its axial direction, and the servo gear and the steering gear meshing with the rack also generate rotational movements. On the one hand, at the servo gear end, the worm gear fixedly connected to the servo gear reciprocally rotates and impacts the worm on the motor rotor shaft, causing the worm (or rotor) to generate motion acceleration; on the other hand, at the steering gear end, the impact will cause a change in the input shaft torque, which is then transmitted to the steering wheel through mechanical connection, affecting the driver's feel.

[0052] Specifically, in step S2, the following exemplary preset conditions and the judgment steps as Figure 5 shown are used to judge whether the vehicle is in a special working condition that requires outputting the target torque request T RML , such as driving conditions like washboard roads, J-Turns, etc.

[0053] First, judge condition 1. Condition 1: The rotor speed n, the driver state, and the motor torque M meet the preset conditions; the preset condition for the rotor speed n is: N1 < n < N2, where N1 is the preset lower limit of the rotor speed and N2 is the preset upper limit of the rotor speed, which is related to the motor selection of the specific product, with the unit of rpm. The preset condition for the motor torque M is: M1 < M < M2, where M1 is the lower limit of the torque that the motor can output, and M2 is the upper limit of the torque that the motor can output, which is related to the motor selection of the specific product, with the unit of Nm. The preset condition for the driver state is that the driver is enabled.

[0054] After satisfying condition 1, jump to condition 2 for judgment; otherwise, within the current ignition cycle, set the requested torque to 0 Nm.

[0055] Condition 2: Judgment of the low threshold of the rotor acceleration torque. |T a | in the preset direction has dropped below T1 or has always been less than T1. If condition 2 is satisfied, jump to condition 3 for judgment; otherwise, exit the target torque request (remain in the inactive state). Where T1 is the lower threshold of the motor rotor acceleration torque used to identify the preset driving conditions (such as washboard roads, J-Turns, etc.), which is determined through steering system tests and / or vehicle tests and calculations during the development process, with the unit of Nm.

[0056] Condition 3: Judgment of the high threshold of the rotor acceleration torque. |T a|≥T2 lasts for t1, satisfying Condition 3, jump to Condition 4 for judgment; otherwise, exit the target torque request (remain inactive). Where T2 is the higher threshold of the motor rotor acceleration torque for identifying preset driving conditions (such as washboard road, J-Turn, etc.), which is determined by measurement and calculation through steering system tests and / or vehicle tests during development, with the unit of Nm. Where t1 is the preset time interval (i.e., the time interval from |T a |≥T2 to T RML torque activation), which is determined by steering system tests and / or vehicle tests during development, with the unit of ms.

[0057] Condition 4, time trigger restart judgment, |T a |<T2 in the opposite direction, satisfying the above conditions, jump to Condition 5; otherwise, the time trigger restarts and jumps to Condition 3 for judgment.

[0058] Condition 5, target torque request time threshold judgment, the duration of |T a |≥T2 in the preset direction is less than t2; satisfying Condition 5, activate the target torque request T RML (i.e., Step S3), and jump to Condition 4 for continuous judgment; otherwise, exit the target torque request (remain inactive), and jump to Condition 1 to start judgment again. Where t2 is the shortest time for the preset target torque request T RML to act, which is determined by steering system tests and / or vehicle tests during development, with the unit of ms.

[0059] In Step S3, the value of the target torque request T RML is determined according to the expected minimum target level λ for reducing external shock loads and the external shock load value. Among them, the magnitude of the external shock load is not limited to being characterized by the acceleration torque Ta generated by the motor rotor when being impacted, and can also be obtained through a rack force calculation program for real-time monitoring of the external load situation of the steering system, or by measurement methods such as using suitable sensing devices installed on the vehicle or inside the steering system.

[0060] The direction of the target torque request T RML is determined such that the acting force direction on the worm gear is opposite to the shock load direction of the worm gear due to external excitation, so as to reduce or offset all or part of the shock load. As determined by the force analysis of the worm gear as shown in Figure 6 , the direction of T RML should be the same as the direction of the motor rotor speed n, that is, the same as the direction of the external shock load or the motor rotor acceleration torque T a direction.

[0061] The motor rotor acceleration torque T for washboard road condition and J-Turn test condition is given below. a The activation state and direction of the

[0062] like Figure 7 The figure shows the change of the motor rotor acceleration torque with time and the corresponding T under the washboard road condition. RML Status of the torque request.

[0063] like Figure 8 The figure shows the change of the motor rotor acceleration torque over time and the corresponding T under the J-Turn test condition (simulating emergency avoidance steering driving behavior). RML The state of torque request. The vehicle motion trajectory corresponding to this working condition is as follows Fig. 9 shown.

[0064] The present invention has been described in detail above through specific implementation modes and embodiments, but these do not constitute limitations of the present invention. Without departing from the principles of the present invention, those skilled in the art may also make many variations and improvements, which should also be regarded as the protection scope of the present invention.

Claims

1. A method for reducing mechanical impact loads of a steering system, characterized in that: Including: Step S1, real-time monitoring and calculation of the motor rotor acceleration torque T of the steering system a ; Step S2, determining the motor rotor acceleration torque T a Whether the preset conditions are met; if the preset conditions are met, go to step S3, otherwise return to step S1; Step S3: Output the target torque request T RML ; The target torque request T RML The value of is determined according to the expected minimum target level λ for reducing the external impact load and the external impact load value; the target torque request T RML The direction is the same as the motor rotor speed n.

2. The method for reducing the mechanical impact load of a steering system according to claim 1, characterized in that: The external impact load value is obtained by any of the following methods: Method 1, using the motor rotor acceleration torque T a Method 2: obtain the rack force by real-time monitoring of the steering system; Method 3: obtain the rack force by measuring the steering system’s sensor device.

3. The method for reducing the mechanical impact load of a steering system according to claim 1, characterized in that: In the step S2, the preset conditions include: Condition 3, |T in the preset direction a |≥T2 duration reaches t1; wherein T2 is a higher threshold value of the motor rotor acceleration torque for identifying a preset driving condition, wherein t1 is a preset time interval; Condition 4, |T in the opposite direction a | <T2; Condition 5, |T in the preset direction a |≥T2 duration is less than t2; where t2 is the preset target torque request T RML The shortest duration of action.

4. The method for reducing mechanical impact load of a steering system according to claim 1, characterized in that: In step S1, the motor rotor acceleration torque T a The calculation method is: T a =J﹡α, where J is the sum of the inertia of the rotating parts on the rotor shaft, and α is the angular acceleration of the motor rotor.

5. The method for reducing mechanical impact loads of a steering system according to claim 3, characterized in that: In the step S2, first judge conditions 1 and 2, and start to judge conditions 3 to 5 after conditions 1 and 2 are satisfied; Condition 1, the rotor speed n, the driver state and the motor torque M meet the preset conditions; Condition 2, |T in the preset direction a | <T1。 6. The method for reducing mechanical impact load of a steering system according to claim 5, characterized in that: The preset condition for the rotor speed n is: N1 < n < N2, where N1 is the preset lower limit of the rotor speed and N2 is the preset upper limit of the rotor speed.

7. The method for reducing mechanical impact load of a steering system according to claim 5, characterized in that: The preset condition for the motor torque M is: M1 < M < M2, where M1 is the lower limit of the torque that the motor can output and M2 is the upper limit of the torque that the motor can output.

8. The method for reducing mechanical impact load of a steering system according to claim 5, characterized in that: The preset condition for the driver state is that the driver is enabled.

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