Machining method suitable for worm of electric steering gear of medium-heavy commercial vehicle

Abstract

The invention discloses a machining method suitable for a worm of an electric steering gear of a medium-heavy commercial vehicle. The machining method comprises the steps that (1) a worm blank with teeth to be machined is taken; (2) tooth profile trimming is conducted in the tooth profile direction of the worm blank, wherein two mismatched quadratic curve rack tools are used for replacing a rack tool with an arc tooth profile; (3) tooth profile displacement is conducted on the worm in the longitudinal direction, namely displacement machining is conducted by moving the axis of a worm workpiece and the center distance of a cutter according to a certain function, the tooth thickness of a part of a meshing area in the middle of a worm shaft is increased, the tooth thickness of other positions is small, and therefore displacement of a contact area can be reduced, edge contact is avoided, transmission errors are reduced, and the service life of the worm is prolonged. Large vibration and noise are avoided; and (4) the worm is machined and formed. The high-load worm gear has the advantages that the high-load requirement can be met, transmission can be smoother, and abnormal vibration and noise do not exist.

Description

Technical Field

[0001] This invention relates to the field of electric steering technology, and more specifically to a method for machining a worm gear suitable for electric steering systems in medium and heavy-duty commercial vehicles. Background Technology

[0002] Currently, the electric steering reduction mechanism used in light commercial vehicles is a ZI-type worm gear mechanism, where the normal tooth profile of the worm is a typical involute profile. Its meshing method with the worm wheel is point contact, resulting in high contact stress, low contact strength, and high friction loss. The actual transmission efficiency is less than 80%, and the load of the reduction mechanism is limited to a relatively small load range. Due to space constraints, this reduction mechanism cannot be extended in a series, i.e., from electric steering systems for light commercial vehicles to electric steering systems for medium and heavy commercial vehicles. To solve this problem, it is necessary to improve the structure and increase the load capacity of the electric steering reduction mechanism. The typical ZC1 worm gear has a concave arc tooth profile, while the worm wheel has a convex arc tooth profile, forming a transmission method where concave and convex arc tooth profiles mesh. This design increases the combined radius of curvature of the meshing line, reduces the contact stress per unit meshing tooth surface, and improves the contact strength, thereby increasing the load capacity of the reduction mechanism. However, the transmission function of this arc-shaped tooth profile is a discontinuous linear function, and the transmission between adjacent teeth is accompanied by high acceleration, resulting in large vibrations and noises. This drawback is unacceptable in the automotive industry. Therefore, a worm gear transmission device is needed that can solve the high load requirements while also ensuring smooth transmission and eliminating abnormal vibrations and noise. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a worm gear processing method suitable for electric steering gears of medium and heavy-duty commercial vehicles, which can meet the high load requirements, provide smoother transmission, and eliminate abnormal vibration and noise.

[0004] To solve the above problems, the present invention adopts the following technical solution: A method for machining worm gears for electric power steering systems in medium and heavy-duty commercial vehicles, specifically including the following machining steps: 1) Take the worm gear blank to be machined; 2) Tooth profile trimming of the worm blank: Replace the rack cutter with a circular arc tooth profile using two mismatched quadratic curve rack cutters, based on the ZC1 worm design principle: , , The tooth profile parameter equation of a quadratic curve rack cutter can be expressed as: 3) Longitudinal tooth profile displacement of the worm: that is, by moving the axis of the worm workpiece and the center distance of the tool according to a certain function, displacement machining is performed to increase the tooth thickness in a part of the meshing area in the middle position of the worm shaft, while the tooth thickness in other positions is smaller. 4) The worm gear is machined and shaped.

[0005] A further technical solution is that K is selected from 0.65 to 0.7 based on the optimization process of displacement design according to the relationship between the ZC1 worm tooth thickness and the paired worm wheel and the relevant stiffness.

[0006] The beneficial effects of the worm gear machining method for electric steering systems of medium and heavy-duty commercial vehicles proposed in this invention are: 1. It has a simple structure, low cost, no special requirements for processing and testing equipment, and high manufacturability; 2. The tooth profile of this worm gear is based on the circular arc tooth structure of the ZC1 worm gear, with tooth profile modification and axial displacement, which greatly improves the load of the worm gear reduction mechanism, making the application of electric steering gear in medium and heavy-duty commercial vehicles an option. 3. The worm gear tooth profile adopts tooth profile trimming and axial displacement, which can reduce the displacement of the contact area, avoid edge contact, reduce transmission error, make transmission smooth, and avoid generating large vibrations and noise. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings required for the work described in 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.

[0008] Figure 1 This is a schematic diagram of a worm gear for electric steering systems of medium and heavy-duty commercial vehicles, which is machined and then installed inside the steering gear according to the present invention. Figure 2 This is a cross-sectional view of the rack cutter in the normal direction of a method for machining worm gears for electric steering systems of medium and heavy-duty commercial vehicles according to the present invention. Figure 3 This is a schematic diagram showing the measured value of the span of the worm gear tooth groove in a worm gear machining method applicable to medium and heavy-duty commercial vehicles according to the present invention.

[0009] Figure 1-3 In the middle: 1-reduction mechanism housing, 2-paired worm gear, 3-bearing, 4-shock absorption device, 5-ZC1 worm gear with tooth profile trimming and axial displacement. Detailed Implementation

[0010] The preferred embodiments of the present invention will be described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the scope of protection of the present invention.

[0011] See Figure 1-3 As shown, a method for machining worm gears for electric power steering systems in medium and heavy-duty commercial vehicles specifically includes the following machining steps: 1) Take the worm gear blank to be machined; 2) Tooth profile trimming of the worm blank: Replace the rack cutter with a circular arc tooth profile using two mismatched quadratic curve rack cutters, based on the ZC1 worm design principle: , , The tooth profile parameter equation of a quadratic curve rack cutter can be expressed as: 3) Longitudinal tooth profile displacement of the worm: that is, by moving the axis of the worm workpiece and the center distance of the tool according to a certain function, displacement machining is performed to increase the tooth thickness in a part of the meshing area in the middle position of the worm shaft, while the tooth thickness in other positions is smaller. This can reduce the displacement of the contact area, avoid edge contact, reduce transmission error, and avoid generating large vibrations and noise. 4) The worm gear is machined and shaped.

[0012] K is selected based on the optimization process of displacement design according to the relationship between the ZC1 worm tooth thickness and the mating worm wheel and the relevant stiffness. At present, the worm wheel material is engineering plastic. Under normal circumstances, K is taken as 0.6, but in order to appropriately improve the strength of the worm wheel teeth, the range of K value is selected as 0.65 to 0.7.

[0013] In this embodiment, the specific connection structure of the worm gear with tooth profile modification and axial displacement suitable for medium and heavy-duty commercial vehicles in the electric steering system is as follows: Figure 1 As shown, bearings 3 are installed on the left and right sides of the housing 1 of the reduction mechanism. The paired worm gears 2 are rotatably connected to the housing 1 of the reduction mechanism. The ZC1 worm 5 with tooth profile trimming and axial displacement is rotatably connected to the two bearings 3 at the left and right ends, and the right end is connected to the output end of the power motor. Its middle end has teeth that mesh with the paired worm gears 2. Through meshing connection, the motor output drives the paired worm gears 2 to rotate. A shock-absorbing device 4 is also installed on the inner side of the ZC1 worm 5 with tooth profile trimming and axial displacement near the two bearings 3.

[0014] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived without creative effort should be covered within the scope of protection of the present invention.

Claims

1. A method for machining worm gears in electric power steering systems of medium and heavy-duty commercial vehicles, specifically including the following machining steps: 1) Take the worm gear blank to be machined; 2) Tooth profile trimming of the worm blank: Replace the rack cutter with a circular arc tooth profile using two mismatched quadratic curve rack cutters, based on the ZC1 worm design principle: , , The tooth profile parameter equation of a quadratic curve rack cutter can be expressed as: 3) Longitudinal tooth profile displacement of the worm: that is, by moving the axis of the worm workpiece and the center distance of the tool according to a certain function, displacement machining is performed to increase the tooth thickness in a part of the meshing area in the middle position of the worm shaft, while the tooth thickness in other positions is smaller. This can reduce the displacement of the contact area, avoid edge contact, reduce transmission error, and avoid generating large vibrations and noise. 4) The worm gear is machined and shaped.

2. The method for machining a worm gear suitable for electric steering systems in medium and heavy-duty commercial vehicles according to claim 1, characterized in that: The value of K is selected from 0.65 to 0.7 based on the optimization process of displacement design according to the relationship between the ZC1 worm tooth thickness and the paired worm wheel and the relevant stiffness.

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