JP2008213674A - Electric power steering device and assembling method for electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of inconvenience caused by creep deformation at an engagement part of a large gear with a small gear by improvement of support structure of the large gear without increasing the assembling man-hours. <P>SOLUTION: A support plate 6 is fitted to a large diameter part 24 at one side of a gear housing 21, and at the inside of a gear chamber 50 in which an outer side of the support plate 6 is closed while mounting a sensor housing 20, a worm wheel 52 fitted to a midway of a steering shaft 1 is arranged while the steering shaft 1 is supported, at both ends, by bearings 56, 57 retained on the gear housing 20 and the support plate 6. The worm wheel 52 is engaged with a worm 51 connected to a steering assistance motor 3, and can be engaged/rotated in the loading state before assembling of the gear housing 20. Further, a window hole 60 facing to the engagement part of the worm 51 and the worm wheel 52 is provided on the support plate 6, and air for cooling can be blown to the engagement part. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus configured to transmit the rotation of a steering assist motor driven in accordance with steering to a steering shaft via a small gear and a large gear and assist the steering, and the electric power The present invention relates to a method for assembling a steering device.

  An electric power steering device using an electric motor as a source of steering assist force detects a steering torque applied to a steering member (steering wheel) for steering, and based on the detection result, an electric motor for steering assist is detected. It is configured to drive and apply the rotational force of the motor to the steering mechanism to assist steering, and can flexibly control the change of auxiliary force characteristics according to the running state of the vehicle, such as vehicle speed, steering angle, yaw rate, etc. In recent years, it has been installed in many vehicles.

  In the electric power steering apparatus, various types are adopted to transmit the rotation of the steering assist motor to the steering mechanism, and one of them is a column assist type electric power steering apparatus. This is a structure in which a steering assist motor is attached in the middle of a housing that accommodates and supports a steering shaft that communicates between a steering wheel and a steering mechanism, and the rotation of the motor is reduced and transmitted to the steering shaft via a gear reducer. (For example, refer to Patent Document 1).

The gear reducer is provided in order to obtain a sufficient steering assist force with a small output motor, and a worm gear reducer that can obtain a high reduction ratio in a small space is widely used. This worm gear reducer is made by engaging a worm (small gear) connected to an output end of a motor with a worm wheel (large gear) fitted and fixed in the middle of a steering shaft, together with a steering assist motor. Because it is arranged in the room, one or both teeth of the worm wheel and worm are made of resin, and the initial adjustment of the backlash is appropriately performed during assembly, thereby suppressing the generation of meshing noise and quiet operation Is realized.
JP 2002-54695 A

  However, in the electric power steering apparatus equipped with the worm gear reducer as described above, the backlash which is initially adjusted at the time of assembly is deformed by creep deformation after the worm wheel or the resin teeth of the worm rotate under the action of the operating load. May change, causing various problems such as increased meshing noise, tooth surface wear, and reduced transmission efficiency.

  These problems can be prevented by adjusting the backlash at the time of assembly in anticipation of the amount of creep deformation, but it is difficult to accurately estimate the amount of creep deformation of resin teeth, and a sufficient prevention effect can be expected. Absent.

  Therefore, in the prior art, a preliminary operation is performed in which the worm wheel and the worm are meshed and rotated under the load condition of the operating load, the resin teeth are creep-deformed in advance, and then slowly cooled by blowing air, and then backlash is performed. A method of performing assembly including adjustment is employed. This method utilizes the characteristics of the resin material that the amount of creep deformation is large while the amount of subsequent creep recovery is small, and suppresses the amount of creep deformation in the stress load state during normal operation, thereby achieving a good operating state. Can be realized.

  However, since the worm wheel and the worm are arranged inside a gear chamber that is sealed for lubrication and air for cooling cannot be blown, the preliminary operation described above is performed before the regular assembly. Since the worm wheel and the worm are engaged with each other using a jig, an assembling process for preliminary operation is separately required, resulting in an increase in the number of assembling steps.

  This problem similarly occurs in an electric power steering apparatus that uses a gear reducer including other gears such as a spur gear and a bevel gear for reduction transmission from the steering assist motor to the steering shaft. .

  The present invention has been made in view of such circumstances, and by preventing the large gears and the small gears from engaging with each other by improving the structure for supporting the large gears, it is possible to prevent the occurrence of problems caused by creep deformation without increasing the number of assembly steps. It is an object of the present invention to provide an electric power steering apparatus and an assembling method that can be performed.

  An electric power steering device according to a first aspect of the present invention includes a large gear fitted to a steering shaft, and a small gear meshed with the large gear and connected to a steering assist motor. Electric power for assisting steering by supporting both ends of the steering shaft by bearings on both sides and arranging the steering shaft inside the gear chamber, and transmitting the rotation of the motor at a reduced speed to the steering shaft via the small gear and the large gear. In the steering device, the gear chamber is configured such that an opening on one side of a large diameter portion provided in the middle of the housing that houses the steering shaft is closed by a lid member, and the meshing portion of the large gear and the small gear And a support plate disposed on the inner side of the lid member, and bearings on both sides of the large gear are held by the housing and the support plate, respectively.

  An electric power steering apparatus according to a second aspect of the present invention is characterized in that one or both of the large gear and the small gear in the first aspect have resin teeth.

  The method for assembling the electric power steering apparatus according to the third aspect of the present invention is the method for assembling the electric power steering apparatus according to the first or second aspect, wherein the steering shaft is supported by the bearings held on the housing and the support plate. In a temporarily assembled state in which the large gear and the small gear are engaged, the large gear and the small gear are rotated under a predetermined load condition, and then air is introduced from a window hole provided in the support plate. The meshing portion of the large gear and the small gear is cooled to cause creep deformation, and after adjusting the meshing state of the large gear and the small gear, the lid member is attached and the gear chamber is closed. .

  In the electric power steering apparatus according to the first aspect of the present invention, the one side of the large gear fitted to the steering shaft is supported by a support plate having a window hole facing the meshing portion of the large gear and the small gear. Therefore, the preliminary operation is performed without using a jig by rotating the small gear and the large gear meshingly without mounting the lid member for closing the gear chamber and cooling the meshing portion by blowing air from the window hole. It is possible to prevent the occurrence of defects due to creep deformation without increasing the number of assembling steps, and it is possible to maintain a good operating state with an initially adjusted backlash for a long period of time. .

  In the electric power steering apparatus according to the second aspect of the present invention, the meshing noise can be suppressed, but the gear having resin teeth with a large amount of creep deformation is adopted, so that the occurrence of problems due to creep deformation is prevented while being quiet. Can be realized.

  In the method for assembling the electric power steering apparatus according to the third aspect of the invention, the small gear and the large gear are meshed and rotated in a temporarily assembled state in which the steering shaft is supported by the bearing held by the housing and the support plate, and the window opened on the support plate. Preliminary operation to cause creep deformation by blowing air from the hole was carried out, and then the lid member was attached to finish the assembly, so the preliminary operation was performed in the middle of the original assembly procedure, and recombination was required As a result, the present invention has an excellent effect, for example, it is possible to complete the assembly without the occurrence of a failure and to prevent the occurrence of defects due to creep deformation during normal operation after the assembly without increasing the number of assembly steps. .

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. FIG. 1 is a longitudinal sectional view showing a configuration of a main part of an electric power steering apparatus according to the present invention, and shows a support structure of a steering shaft 1 that connects a steering member and a steering mechanism.

  The illustrated electric power steering apparatus includes a housing 2 that accommodates and rotatably supports a steering shaft 1, and a steering assist motor 3 that is attached to the outside of the housing 2, and the rotation of the motor 3 is controlled by the steering shaft 1. It is configured as a column assist type electric power steering device that assists steering by transmitting to

  The steering shaft 1 includes an upper (right side in the figure) input shaft 10 and a lower (left side in the figure) output shaft 11 that are coaxially connected via a low-rigidity torsion bar 12. The housing 2 that supports the steering shaft 1 includes a sensor housing 20 and a gear housing 21 that are connected in the vertical direction.

  An upper end portion of the input shaft 10 is extended into a cylindrical extension housing 22 fitted to the upper portion of the sensor housing 20, and is connected to a steering member (not shown) via a connecting shaft 13. Further, the lower end portion of the output shaft 11 protrudes outside the gear housing 21 and is connected to a steering mechanism (not shown) via a universal joint 14 that is partially shown in the drawing.

  With the above configuration, the rotation operation of the steering member for steering is transmitted to the steering mechanism via the connecting shaft 13, the input shaft 10, the output shaft 11, and the universal joint 14, and the steering is executed by the operation of the steering mechanism. Is done. At this time, the torsion bar 12 connecting the input shaft 10 and the output shaft 11 is twisted according to the steering torque applied to the steering member. Inside the sensor housing 20, a known torque sensor 4 for detecting the steering torque through a relative angular displacement generated between the input shaft 10 and the output shaft 11 with the torsion bar 12 being twisted is configured. .

A disc-shaped coupling flange 23 is provided around the outer periphery of the lower end portion of the sensor housing 20, and the gear housing 21 is provided with a disc-shaped large-diameter portion 24 that is open on the entire upper surface. The gear housing 21 is integrally connected to the opening of the large-diameter portion 24 by abutting the connection flange 23 and tightening a connection bolt (not shown).
Inside the large-diameter portion 24, a gear chamber 50 is formed in which an opening on one side is closed by a connecting flange 23 as a lid member.

  2 is a cross-sectional view taken along line II-II in FIG. As shown in the figure, a cylindrical worm cylinder 25 extending in a tangential direction is continuously provided at one place in the circumferential direction on the outer periphery of the large diameter portion 24 of the gear housing 21, and one side is closed by a connecting flange 23 as a lid member. A gear chamber 50 is formed inside the large diameter portion 24 and the worm cylinder 25. Inside the gear chamber 50, a worm gear speed reducer 5 including a worm (small gear) 51 and a worm wheel (large gear) 52 is configured.

  As shown in FIG. 2, the diameter of the worm cylinder 25 is increased coaxially and extended to one side, and a steering assist motor 3 is fixed to a motor seat 26 provided around the extended end. The worm 51 of the worm gear reducer 5 faces the communication part with the large diameter part 24 of the gear housing 21 in the middle part of the worm shaft 55 that is supported at both ends inside the worm cylinder 25 by bearings 53 and 54. It is provided integrally. The worm shaft 55 is extended to the mounting side of the motor 3 and is connected to the motor shaft 30 protruding into the worm cylinder 25.

  On the other hand, the worm wheel 52 of the worm gear reducer 5 is fitted and fixed in the middle of the output shaft 11 and is arranged inside the gear chamber 50 with both sides of the fixed position supported by bearings 56 and 57. The worm wheel 52 includes a metal boss portion 52a fitted to the output shaft 11, and a resin annular tooth portion 52b molded on the outside of the boss portion 52a. The teeth integrally formed on the outer periphery of 52b are meshed with the worm 51 at the communicating portion with the worm cylinder 25.

  The bearing 56 that supports one side (lower side) of the worm wheel 52 as described above is directly fitted and fixed to the cylindrical part that constitutes the lower half part of the gear housing 21. On the other hand, the bearing 57 that supports the other side (upper side) of the worm wheel 52 is indirectly fitted and fixed to the large diameter portion 24 constituting the upper half of the gear housing 21 via the support plate 6.

  3 is a cross-sectional view taken along line III-III in FIG. As shown in this figure, the support plate 6 is a thick disk fitted into the large diameter portion 24 from the opening side. As shown in FIG. 1, the support plate 6 is formed by a connecting flange 23 of the sensor housing 20 that closes the opening. It is held and positioned in the axial direction. As shown in FIG. 3, a window hole 60 is formed in the support plate 6 in the vicinity of the outer periphery, and the support plate 6 is fitted into the large-diameter portion 24 when the worm 51 and the worm wheel inside the gear chamber 50. Positioning is performed in the circumferential direction so that the formation position of the window hole 60 faces the meshing portion of 52.

  The window hole 60 shown in FIG. 3 is a hole having an oval cross section that is long in the circumferential direction. It can be selected appropriately under the condition of obtaining. Furthermore, the window hole 60 does not need to have a shape as a hole within the range of the support plate 6. It is also possible to form the window hole 60 by the inner surface of the diameter portion 24 and the notch.

  In such a support plate 6, a circular shaft support hole 61 penetrating the shaft center portion is formed, and a bearing 57 that supports the upper side of the worm wheel 52 is fitted and held in the shaft support hole 61, and is output. The corresponding position of the shaft 11 is supported. As shown in FIG. 1, the bearings 56 and 57 that support both sides of the worm wheel 52 are seal bearings in which a seal body is mounted on one side (outside) of the rolling element. The grease supplied for lubrication is configured to be sealed inside the gear chamber 50.

  In the electric power steering apparatus configured as described above, the steering assist motor 3 is driven and controlled in accordance with an operation command given from a control unit (not shown) based on the detection result of the steering torque by the torque sensor 4. The rotation of the motor 3 thus driven is decelerated at a predetermined reduction ratio at the meshing portion of the worm 51 and the worm wheel 52 and transmitted to the output shaft 11, and further to the steering mechanism via the universal joint 14. The steering performed by the operation of the steering mechanism is assisted.

  The steering torque detected by the torque sensor 4 is a torque acting on the input shaft 10 and the output shaft 11 via the connecting shaft 13 in accordance with the operation of the steering member, and the direction of the force applied to the steering member by the driver and Since it corresponds to the magnitude, appropriate steering assistance is performed by drive control of the steering assistance motor 3 based on the detection result of the steering torque. In addition, in the drive control of the motor 3 based on the detection result of the steering torque, an auxiliary force characteristic suitable for the driving state is realized by performing correction based on the detection result of the driving state such as the vehicle speed, the steering angle, and the yaw rate. Is possible.

  In the electric power steering apparatus shown in the embodiment, a worm gear speed reducer 5 having a worm 51 and a worm wheel 52 and having a large reduction ratio with a compact configuration is used. And the motor 3 and the worm gear reducer 5 can be disposed without difficulty in the middle of the steering shaft 1. Further, the worm wheel 52 of the worm gear speed reducer 5 has resin teeth formed on the outer periphery of the annular tooth portion 52b, and the worm teeth are meshed with the worm 51, so that the meshing noise is suppressed to a low level. Silent operation can be realized.

  On the other hand, the resin teeth of the worm wheel 52 have a large amount of creep deformation as described above, and there is a possibility that problems such as increased meshing noise, tooth surface wear, and reduced transmission efficiency due to this creep deformation may occur. Therefore, also in the electric power steering apparatus according to the present invention, the worm wheel 52 and the worm 51 are engaged with each other for the purpose of preliminarily deforming the resin teeth of the worm wheel 52 in the same manner as in the past. Preliminary operation is performed to rotate under load conditions.

  FIG. 4 is an explanatory diagram showing an implementation state of the preliminary operation. In the electric power steering apparatus according to the present invention, the lower bearing 56 of the worm wheel 52 is fitted and fixed to a cylindrical portion constituting the lower half of the gear housing 21, and the upper bearing 57 of the worm wheel 52 is a gear. The bearings 56 and 57 are fitted and held in shaft support holes 61 provided in the support plate 6 fitted in the large-diameter portion 24 that constitutes the upper half of the housing 21, and these bearings 56 and 57 are output at their respective positions. The shaft 11 is supported.

  Therefore, the support of the worm wheel 52 fitted and fixed to the output shaft 11 can be realized in a state where the support plate 6 is fitted into the large diameter portion 24 of the gear housing 21 as shown in FIG. The worm 51 is supported inside a worm cylinder 25 connected to the outer periphery of the large-diameter portion 24 of the gear housing 21, and the outer periphery of the worm wheel 52 is connected to the communication portion between the worm cylinder 25 and the large-diameter portion 24. Can mesh with teeth. Further, the steering assist motor 3 can be attached to the worm cylinder 25 as described above, and the motor 3 can be connected to the worm 50 so as to be capable of transmission.

  As described above, in the electric power steering apparatus according to the present invention, as shown in FIG. 4, the worm gear speed reducer 5 that reduces the transmission of the rotation of the steering assisting motor 3 to the output shaft 11 is not attached to the sensor housing 20. In this state, by applying an appropriate load to the output shaft 11 and rotating the motor 3, the above-described preliminary operation can be performed. In this preliminary operation, for example, the support plate 6 may be fixed and secured by a retaining ring 62 engaged with the large diameter portion 24 as shown in FIG.

  The support plate 6 that supports one side (upper side) of the worm wheel 52 is provided with a window hole 60 opened so as to face the meshing part of the worm 51 and the worm wheel 52. This window hole 60 is shown in FIG. As shown in FIG. 4, the air is used as an air introduction hole for blowing cooling air to the meshing portion of the worm 51 and the worm wheel 52. By carrying out the above preliminary operation, the resin teeth of the worm wheel 52 are in a state where the creep deformation caused by the meshing rotation under the load condition is recovered by being cooled by the air introduced from the window hole 60. By carrying out the backlash adjustment, the rotation of the worm 51 and the worm wheel 52 can be carried out satisfactorily without causing problems due to creep deformation such as increased meshing noise, tooth surface wear, and reduced transmission efficiency. it can.

  The electric power steering apparatus according to the present invention is assembled by attaching the sensor housing 20 indicated by a two-dot chain line in FIG. 4 and closing the opening of the large diameter portion 24 of the gear housing 21 after the above preliminary operation. The worm wheel 52 can be supported while being supported by the support plate 6. In FIG. 1, the retaining ring 62 used for retaining the support plate 6 during preliminary operation is removed, but the retaining ring 62 may be left after the sensor housing 20 is attached.

  As described above, in the present invention, it is possible to perform the preliminary operation in a temporarily assembled state in which the support plate 6 is attached and the worm wheel 52 is supported in the middle of the original assembly process, and a dedicated jig is used. The assembly process for preliminary operation is not necessary, and the number of assembly steps can be reduced.

  In the above embodiment, the case where the worm gear speed reducer 5 including the worm 51 and the worm wheel 52 is used for transmission from the steering assist motor 3 to the steering shaft 1 has been described. It can be similarly applied to an electric power steering apparatus provided with a gear reducer using other gears such as a spur gear and a bevel gear, and a preparatory operation for preventing the occurrence of defects due to creep deformation is assembled. It can be carried out without increasing man-hours.

It is a longitudinal cross-sectional view which shows the structure of the principal part of the electric power steering apparatus which concerns on this invention. It is a cross-sectional view by the II-II line of FIG. It is a cross-sectional view by the III-III line of FIG. It is explanatory drawing which shows the implementation state of preliminary operation.

Explanation of symbols

  1 Steering shaft, 2 housing, 3 motor, 6 support plate, 20 sensor housing (lid member), 24 large diameter part, 50 gear chamber, 51 worm (small gear), 52 worm wheel (large gear), 56, 57 bearing , 60 window holes

Claims (3)

A large gear fitted to the steering shaft and a small gear meshed with the large gear and connected to a steering assist motor are both supported by bearings on both sides of the large gear to support the steering shaft. In the electric power steering device that is arranged inside the chamber and assists steering by decelerating the rotation of the motor to the steering shaft via the small gear and the large gear,
The gear chamber is configured by closing an opening on one side of the large diameter portion provided in the middle of the housing that houses the steering shaft with a lid member;
It has a window hole facing the meshing part of the large gear and the small gear, and includes a support plate arranged on the inner side of the lid member,
The electric power steering apparatus characterized in that bearings on both sides of the large gear are respectively held by the housing and the support plate.   The electric power steering apparatus according to claim 1, wherein one or both of the large gear and the small gear have resin teeth. An assembly method of the electric power steering device according to claim 1 or 2,
After rotating the large gear and the small gear under a predetermined load condition in a temporarily assembled state in which the steering shaft is supported by a bearing held on the housing and the support plate and the large gear and the small gear are engaged with each other. The lid member after introducing air from a window hole provided in the support plate, cooling the meshing portion of the large gear and the small gear to cause creep deformation, and adjusting the meshing state of the large gear and the small gear And assembling the electric power steering apparatus, wherein the gear chamber is closed.

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