Electric power steering system of commercial vehicle

Abstract

The utility model discloses an electric power-assisted steering system of a commercial vehicle, which comprises a steering control power transmission mechanism and a steering power-assisted power transmission mechanism, and is characterized in that the system realizes independent and cooperative transmission of power of steering control and power of steering power-assisted power through a steering output shaft which is designed and optimized; the middle of the steering output shaft protrudes outwards in the radial direction, the upper portion of the steering output shaft is provided with a gear sector to receive power of the steering control power transmission mechanism, the lower portion of the steering output shaft is provided with a circular hole, and a planetary gear mandrel is arranged in the circular hole and serves as a planet carrier to receive power of the steering power-assisted power transmission mechanism, so that superposition coupling of the power is achieved. By adopting a circulating ball and planetary gear type electric power-assisted steering gear structure, the main power output by a power-assisted steering motor does not pass through a circulating ball screw nut mechanism with weak bearing capacity and directly acts on an output shaft. Performance limitation of an existing old-fashioned electric recirculating ball steering gear is avoided, and large-torque steering is achieved.

Description

Technical Field

[0001] The utility model relates to a power steering system, in particular to an electric power steering system for commercial vehicles. Background Art

[0002] With the rapid development of the information age and the remarkable improvement of communication technology, the electrification, intelligence, networking and even driverless technology of commercial vehicles have become an irreversible development trend in the industry. Under this transformation background, the demand of commercial vehicles for intelligent driving and efficient steering functions is increasing day by day, urgently calling for a more intelligent and electronically controlled pure electric power steering system (EPS) to meet the dual needs of the market and technology.

[0003] For a long time, commercial vehicles generally adopt a hydraulic power steering system (HPS) as their steering solution. Although HPS is known for its powerful power assistance ability, its power assistance characteristics are fixed during manufacturing and it is difficult to flexibly meet the dual challenges of the lightness requirement for low-speed or in-place steering and the vehicle stability during high-speed driving. In addition, from the perspective of energy efficiency, the HPS system significantly increases the fuel consumption of commercial vehicles, which is estimated to account for about 3%-8% of the total vehicle fuel consumption, especially the energy consumption is more prominent during high-speed driving, seriously restricting the improvement of fuel economy.

[0004] Subsequently, although technologies such as electric hydraulic power steering (EHPS) and electro-hydraulic coupling power steering (EHCPS) have been improved on the basis of HPS, their essence still depends on hydraulic power and they have not fundamentally got rid of the inherent defects of the HPS system, such as high energy consumption and slow response, and it is difficult to meet the development needs of the intelligence and electronic control of commercial vehicles.

[0005] In view of the above technical bottlenecks, research institutions and enterprises at home and abroad have invested a large amount of resources in developing an electric power steering system for commercial vehicles (CV-EPS) that can implement active steering intervention control. However, the successful application of the current EPS system in the passenger vehicle field has not been smoothly extended to the commercial vehicle field. The main reason is that the traditional EPS system is limited by its too small steering output torque and it is difficult to meet the specific needs of commercial vehicles for large steering forces.

[0006] To overcome this problem, the industry urgently needs a large-torque electric power steering system (CV-EPS) designed specifically for commercial vehicles, which should have the characteristics of high efficiency, high precision and large torque output. Compared with the traditional hydraulic system, the pure electric power steering system (EPS) stands out with its advantages of no hydraulic components, simple structure, rapid response and high energy efficiency, and becomes an ideal choice for the upgrade of the commercial vehicle steering system.

[0007] However, in the pursuit of high torque output, how to ensure the stable and reliable operation of the EPS system while overcoming the problem of insufficient load-bearing capacity of the existing steering transmission mechanism has become the key to R & D. For this reason, innovations in this field have emerged continuously. For example, complex designs such as planetary gear reduction mechanisms are adopted to achieve high torque output, but these solutions are often accompanied by challenges such as complex structures and high costs. Summary of the Invention

[0008] The purpose of the present utility model is to provide a commercial vehicle electric power steering system, aiming to achieve the high torque steering requirements of the commercial vehicle CV-EPS system in a more concise and efficient manner. This design not only reduces the manufacturing cost but also significantly enhances the market competitiveness of the product, providing strong technical support for the intelligent and electrified transformation of commercial vehicles.

[0009] The present utility model is implemented by the following technical solutions: A commercial vehicle electric power steering system includes a steering control power transmission mechanism and a steering assist power transmission mechanism. It is characterized in that: The system realizes the independent and coordinated transmission of the power of steering control and steering assist through an optimized steering output shaft. The middle part of the steering output shaft protrudes radially outwards, and a tooth sector is provided on the upper part. The tooth sector meshes with the steering control power transmission mechanism to receive the power of the steering control power transmission mechanism. The lower part is a protruding part, and a round hole is provided in the protruding part. A planetary gear core shaft is arranged in the round hole, so that the protruding part also serves as a planet carrier to receive the power of the steering assist power transmission mechanism, thereby realizing the superposition and coupling of power.

[0010] Further, the steering control power transmission mechanism includes a steering gear input shaft, a screw rod, a nut and a steering output shaft. Among them, the screw rod and the nut form a circulating ball screw nut transmission mechanism through internally installed steel balls, and the linear motion of the nut drives the steering output shaft to rotate through a rack and pinion transmission mechanism.

[0011] Further, thrust angular contact ball bearings are installed at the shaft necks at both ends of the screw rod, and bearing supports are used to adjust the clearance and axial preload of the thrust angular contact ball bearings to ensure the smooth and precise fixed-axis rotation of the screw rod.

[0012] Further, the steering assist power transmission mechanism includes a steering assist motor, a pinion, a cylindrical gear, a pinion shaft, a large cylindrical gear, a sun gear, a planetary gear, an internal gear ring and a steering output shaft, forming a three-stage transmission. Among them, the rotation of the sun gear drives the steering output shaft to rotate through the planetary gear and the planetary gear core shaft, realizing the three-stage deceleration and torque increase of the motor output torque.

[0013] Further, the pinion and the cylindrical gear adopt a cylindrical helical gear design to improve the transmission efficiency and reduce the noise. At the same time, angular contact ball bearings are installed at both ends of the pinion shaft to bear the axial force.

[0014] Furthermore, the rotation angle range of the steering output shaft is approximately ±45°, and the internal gear ring is not a complete full circle, with a size of 1 / 3 or 1 / 2 of a full circle.

[0015] Furthermore, a large oil seal and a bushing bearing are provided between the left end of the steering output shaft and the housing, and the right end is connected to the large end cover through an adjusting screw and a bushing bearing. By rotating the adjusting screw, the meshing clearance of the rack and pinion transmission mechanism can be adjusted to improve the accuracy of steering control.

[0016] The beneficial effects of the electric power steering system for commercial vehicles of the present utility model include:

[0017] By adopting the structure of a recirculating ball + planetary gear type electric power steering gear, the driving force output by the steering assist motor does not pass through the recirculating ball screw and nut mechanism with relatively weak load-bearing capacity, but directly acts on the output shaft. This avoids the performance limitations of the existing old-fashioned electric recirculating ball steering gear and realizes large-torque steering.

[0018] The "steering assist" of the recirculating ball + planetary gear type electric power steering gear structure is a three-stage gear transmission with extremely high efficiency, and its total efficiency can reach 90 - 95%.

[0019] The structure of the recirculating ball + planetary gear type electric power steering gear optimizes and improves the structure of the pinion output shaft, and has the function of bearing the planet carrier in the planetary gear reduction mechanism. The optimized steering output shaft can receive both the steering control hand force and the large steering assist torque transmitted by the motor through three-stage speed reduction and torque increase.

[0020] In addition, it also has the characteristics of light weight and small volume, and is easy to install and arrange on the vehicle.

[0021] In the structure of the recirculating ball + planetary gear type electric power steering gear, the screw nut + rack and pinion reduction mechanism responsible for the steering control function inside does not bear the transmission of the driving force and is subjected to less force, so the wear amount during use is extremely small, and it can maintain a small free clearance of the steering wheel for a long time, and the steering control is accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. The following drawings are only some embodiments of the present utility model. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0023] Figure 1 It is a schematic diagram of an electric power steering system for commercial vehicles;

[0024] Figure 2 is Figure 1 the A - A sectional view;

[0025] Figure 3 is the schematic diagram of the mating relationship of the steering output shaft;

[0026] Figure 4 is the schematic diagram of the steering output shaft;

[0027] In the figure, 1 - steering input shaft, 2 - dust seal, 3 - upper cover, 4 - deep groove ball bearing, 5 - torque sensor, 6 - housing, 7 - small oil seal, 8 - bearing support, 9 - thrust angular contact ball bearing, 10 - screw, 11 - nut, 12 - large oil seal, 13 - steering output shaft, 14 - sun gear, 15 - large cylindrical gear, 16 - large end cover, 17 - adjusting screw, 18 - planetary gear, 19 - angular contact ball bearing, 20 - pinion shaft, 21 - small cylindrical gear, 22 - pinion at the motor output end, 23 - steering assist motor, 24 - controller, 25 - locknut, 26 - internal gear ring, 27 - planetary gear core shaft, 28 - bushing bearing. Specific embodiments

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are some, but not all, of the embodiments of the present utility model. Usually, the components of the embodiments of the present utility model described and illustrated herein can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present utility model provided in the drawings is not intended to limit the scope of the claimed present utility model, but merely represents selected embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts fall within the scope of protection of the present utility model.

[0030] As Figures 1-3 shown, a commercial vehicle electric power steering system adopts the layout structure of a recirculating ball + planetary gear type electric power steering gear, including a steering control power transmission mechanism and a steering assist power transmission mechanism.

[0031] The steering control power transmission mechanism of the present utility model is realized through two - stage transmission of "screw - nut + rack - pinion". A torque sensor 5 is provided between the steering gear input shaft 1 and the screw 10 for monitoring the steering resistance. The steering gear input shaft 1 and the upper cover 3 are rotationally supported and dust - proofed through a deep groove ball bearing 4 and a dust seal 2.

[0032] At both ends of the screw rod 10, paired thrust angular contact ball bearings 9 are installed, which are respectively placed in the bearing seat holes of the housing 6 and the bearing support 8. By rotating the bearing support 8, the clearance and axial pre-tightening force of the thrust angular contact ball bearing 9 can be adjusted to ensure the stable and accurate fixed-axis rotation of the screw rod 10. A small oil seal 7 is also provided between the bearing support 8 and the screw rod 10 to prevent oil leakage.

[0033] The screw rod 10 and the nut 11 with internal steel balls form a circulating ball screw-nut transmission mechanism. The nut 11 is a special rack nut, and its internal spiral raceway transmits the axial thrust through the steel balls, causing the nut 11 to move linearly along the axis when the screw rod 10 rotates. A tooth fan structure is provided on the steering output shaft 13, and the linear motion of the nut 11 drives the rotation of the steering output shaft 13 through the rack and pinion transmission mechanism, thereby realizing the power transmission of the steering control.

[0034] To ensure the steering accuracy, a large oil seal 12 and a bushing bearing 28 are provided between the left end of the steering output shaft 13 and the housing 6, and the right end is connected to the large end cover 16 through an adjusting screw 17 and a bushing bearing 28. Since the fan teeth on the steering output shaft 13 are continuously modified tapered tooth fans, the axial position can be adjusted by rotating the adjusting screw 17 to adjust the meshing clearance of the rack and pinion transmission mechanism, compensate for the machining error, and improve the accuracy of the steering control. After adjustment, use a hexagon nut to tighten to ensure stability.

[0035] The steering assist power transmission mechanism of the present utility model includes three-stage transmission. The steering assist motor 23 meshes with the cylindrical gear 21 through the pinion 22 at its output end, constituting the first-stage transmission for reducing the output torque of the motor and increasing the torque. The cylindrical gear 21 is nested and fixedly connected to the pinion shaft 20 to form a double gear structure that rotates synchronously. To improve the transmission efficiency and reduce the noise, the pinion 22 and the cylindrical gear 21 are preferably designed as cylindrical helical gears. Due to the helical tooth structure of the cylindrical gear 21, the pinion shaft 20 needs to bear the axial force, so angular contact ball bearings 19 are installed at both ends to bear this force. A tightening plug 25 is provided between the left angular contact ball bearing 19 and the housing 6, and the clearance and axial pre-tightening force of the bearing can be adjusted by rotating the tightening plug 25.

[0036] The pinion shaft 20 further meshes with the large cylindrical gear 15 to constitute the second-stage transmission. The large cylindrical gear 15 is nested and fixedly connected to the sun gear 14 of the planetary reduction mechanism to form another set of double gears that rotate synchronously. The sun gear 14 is connected to the steering output shaft 13 through a bushing bearing 28, and at the same time, the combined double gear of the large cylindrical gear 15 and the sun gear 14 is axially limited by a shaft retaining ring. The sun gear 14 can rotate freely around the steering output shaft 13.

[0037] The sun gear 14, the planet gear 18, the internal gear ring 26 and the steering output shaft 13 with a special structure together constitute the third-stage transmission - a simplified planetary gear reduction mechanism. The internal gear ring 26 is fixed to the inner wall of the housing 6. The rotation of the sun gear 14 drives the planet gear 18 to perform a circular motion around the axis of the planet gear core shaft 27 and the steering output shaft 13, and then drives the steering output shaft 13 to rotate through the planet gear core shaft 27. This design realizes the three-stage deceleration and torque increase of the motor output torque, which is directly transmitted to the steering output shaft 13, bypassing the traditional recirculating ball screw nut + rack and sector reduction mechanism.

[0038] The key to the fact that the utility model can independently transmit the power of steering control and steering assist to the steering output shaft 13 lies in the optimized design of the structure of the steering output shaft 13. The middle part of the steering output shaft 13 protrudes radially outwards, as Figure 3 shown. The upwardly protruding part is machined with a rack and sector, and the downwardly protruding part is machined with a circular hole with the planet gear core shaft 27 placed inside, which can also serve as a planet carrier. Thus, the steering output shaft 13 can receive the power transmitted by both the rack and sector and the planetary gear reduction mechanisms at the same time, and perfectly superimpose and couple them into the output torque of the steering gear. This is the basis of the overall structural layout of the new recirculating ball + planetary gear type electric power steering gear.

[0039] Due to the characteristics of the commercial vehicle steering gear itself: the rotation angle of the steering output shaft is approximately ±45°, without a full-circle rotation. Therefore, the utility model cleverly utilizes this characteristic and designs a steering output shaft 13 with a special structure. When the planet carrier functional part protruding downwards and the rack and sector functional part protruding upwards of the steering output shaft 13 rotate within the ±45° angle range, the functional movement areas of the two do not interfere with each other. Thus, the recirculating ball screw nut + rack and sector (steering control reduction mechanism) and the planetary gear (steering assist reduction mechanism) can be organically combined into one body. They are closely related and cooperate with each other.

[0040] In the above embodiments, the basic principles, main features and advantages of the utility model are described. Those skilled in the art should understand that the utility model is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the utility model. Without departing from the spirit and scope of the utility model, any modifications and changes made by those skilled in the art that do not depart from the spirit and scope of the utility model shall fall within the protection scope of the appended claims of the utility model.

Claims

1. A commercial vehicle electric power steering system, comprising a steering control power transmission mechanism and a steering power transmission mechanism, characterized in that: The system realizes the independent and coordinated transmission of steering control and steering assistance power by means of an optimized steering output shaft (13). The middle portion of the steering output shaft (13) is radially convex outward, and the upper portion is provided with a gear fan, which meshes with a steering control power transmission mechanism to receive the power of the steering control power transmission mechanism. The lower portion is a protruding portion, and the protruding portion is provided with a circular hole, and the circular hole has a planetary gear core shaft (27) built therein, so that the protruding portion is also used as a planet carrier to receive the power of the steering assistance power transmission mechanism, thereby realizing the superposition coupling of power.

2. The electric power steering system for commercial vehicles according to claim 1, characterized in that: The steering control power transmission mechanism comprises a steering gear input shaft (1), a screw rod (10), a nut (11) and a steering output shaft (13), wherein the screw rod (10) and the nut (11) form a circulating ball screw nut transmission mechanism via a built-in steel ball, and the linear motion of the nut (11) drives the steering output shaft (13) to rotate via a rack and pinion transmission mechanism.

3. The electric power steering system for commercial vehicles according to claim 2, characterized in that: Thrust angular contact ball bearings (9) are installed at the journals at both ends of the screw (10), and the bearing support (8) is used to adjust the clearance and axial preload of the thrust angular contact ball bearing (9) to ensure smooth and accurate fixed-axis rotation of the screw (10).

4. The electric power steering system for commercial vehicles according to claim 1, characterized in that: The steering power transmission mechanism comprises a steering power motor (23), a pinion (22), a cylindrical gear (21), a pinion shaft (20), a large cylindrical gear (15), a sun gear (14), a planetary gear (18), an inner gear ring (26) and a steering output shaft (13), forming a three-stage transmission, wherein the rotation of the sun gear (14) drives the steering output shaft (13) to rotate via the planetary gear (18) and the planetary gear core shaft (27), thereby realizing a three-stage reduction in torque of the motor output torque.

5. The electric power steering system for commercial vehicles according to claim 4, characterized in that: The pinion gear (22) and the cylindrical gear (21) are designed as cylindrical helical gears to improve transmission efficiency and reduce noise. At the same time, angular contact ball bearings (19) are installed at both ends of the pinion gear shaft (20) to withstand axial force.

6. The electric power steering system for commercial vehicles according to claim 4, characterized in that: The rotation angle range of the steering output shaft (13) is approximately ±45°, and the inner gear ring (26) is not a complete circle, but has a size of 1 / 3 or 1 / 2 of a complete circle.

7. The electric power steering system for commercial vehicles according to claim 1, characterized in that: A large oil seal (12) and a bushing bearing (28) are provided between the left end of the steering output shaft (13) and the housing (6), and the right end is connected to the large end cover (16) via an adjusting screw (17) and a bushing bearing (28). The meshing clearance of the rack and pinion transmission mechanism can be adjusted by rotating the adjusting screw (17), thereby improving the accuracy of steering control.

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