JPH0558310A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To prevent a bad influence by external force from exerting upon reliability in a power assist mechanism unit by means of an electric motor arranged on a steering rod separately from a steering force transmitting mechanism unit. CONSTITUTION:A steering force transmitting mechanism unit 7 to transmit steering force from a steering wheel is provided on a rack shaft 5. On a steering body 3 to hold this rack shaft as well as in a position different from the transmitting mechanism unit, there is provided a body 14 of a power assist mechanism unit 11 by means of an electric motor 10. A worm shaft 20 being held in a position close to the rack shaft so as to be movable and a ball screw mechanism 24 consisting of a nut member 23 connected to this by means of a ball screw are provided in this mechanical unit body. A motor side rotation transmitting shaft 27 having a gear 26 being meshed with a rotation transmitting gear 25 on the nut member is supported so as to be rotatable. The worm shaft and a steering rod are connected to each other by means of a connecting arm 31 having a worm connecting ball joint unit 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus using an electric motor as a steering assisting force generating means for reducing an operating force (steering force) of a steering wheel.

[0002]

2. Description of the Related Art In recent years, various types of electric power steering devices of this type have been proposed. For example, the operation assisting force transmission system from the electric motor is provided at a position different from the steering force transmitting mechanism by the rack and pinion mechanism that transmits the steering force from the steering wheel to the steered wheels on the rack shaft as the steering rod. Structures such as Japanese Patent Publication No. 63-2830 and Japanese Utility Model Publication No. 2-21346 are known. With such a structure, the degree of freedom in assembling the electric motor and the steering assist force transmission system to the steering mechanism is increased, and the assemblability to a vehicle having many space constraints can be improved. It will be possible.

Further, as a solution to the above-mentioned problem in space, for example, Japanese Patent Laid-Open No. 59-50864 and Japanese Utility Model Laid-Open No. 63-15271 disclose a steering body for slidably holding a rack shaft. There is also known a structure in which a rotor or a stator that constitutes an electric motor is arranged around and the rotation thereof is directly or indirectly transmitted by a ball screw mechanism interposed between the rotor and the rack shaft. Has been.

Further, Japanese Patent Laid-Open No. 60-25853 and Sho 62-
In 146678, a motor is attached in parallel to the side of the steering body, and a gear coupling or a coupling member is provided between a nut member that is ball-screwed on a rack shaft or a motor shaft and a shaft on the other side. It is known that the structure is such that they are connected to each other.

[0005]

However, in the electric power steering apparatus using the electric motor as described above, the steering force transmission mechanism portion for the rack shaft and the pinion is provided in a part of the steering body. At the same time, a mechanism for transmitting a steering assist force to the electric motor and the rack shaft is simply attached to a position different from this. Therefore, in such a conventional structure, consideration is not given to the reliability of operation of this device, workability and assembly of each part, workability during maintenance and inspection, etc. There are many unsolved problems in realizing the steering system, and there is room for improvement.

[0006] For example, Japanese Examined Patent Publication No. Sho 63-2830 and Japanese Utility Model No. 2
In the structure disclosed in Japanese Patent Publication No. 21346, the amount of protrusion of the electric motor and its steering assist force transmission system arranged substantially orthogonal to the rack shaft from the steering body is large, and the motor is also supported on the vehicle body side. There was a problem that it was necessary.

Further, Japanese Patent Laid-Open No. 59-50864 and Sho 63-1
In the structure shown in Japanese Patent No. 5271, since the motor is assembled around the outer periphery of the steering body and installed integrally, not only the dedicated parts are required as the steering body, but also the motor can be There was a problem that the work for replacement was difficult. Further, in the former case where the rack shaft and the ball screw mechanism are coaxial with each other, if a force in the axial direction is applied to the rack shaft by kickback or the like, the ball screw mechanism may be twisted, resulting in an excessive load. When it works, there is a problem that the ball screw mechanism may not operate normally, and the wear also increases.

Further, Japanese Patent Laid-Open No. 60-25853 and Japanese Utility Model Laid-Open No. 62-
In the structure shown in Japanese Patent No. 146678, in the former case, since the ball screw mechanism exists on the rack shaft, similarly to the case described above, problems such as twisting and wear occur due to the acting force in the axial direction. Will end up. Further, in the latter case, the connecting member provided on the rack shaft is rotatably connected to a part of the nut member connected to the motor shaft by the ball screw through the connecting shaft. Therefore, there is no problem in the movement in the rotation direction by the connecting shaft, but the action force in the axial direction of the connecting shaft may cause twisting inside the ball screw mechanism, and Since the above reliability cannot be maintained, it is required to take some measures capable of eliminating these problems.

Further, in any of the above-mentioned conventional devices, it is necessary to use, as a steering body in which a normal steering force transmission system is incorporated, one having a shape and structure corresponding to each steering assist force transmission system. Therefore, there is a problem of versatility that parts cannot be shared with other models, and it is necessary to consider such a point.

[0010]

In order to meet such demands, an electric power steering apparatus according to the present invention has a steering force transmission mechanism portion in a part of a steering body slidably holding a steering rod. Is a power assist mechanism body attached to a different position, a worm shaft movably held in the power assist mechanism body at a position close to the steering rod in the power assist mechanism body, and a ball screw connection on the shaft. A ball screw mechanism composed of a nut member, a rotation transmission shaft rotatably supported in the power assist mechanism body having a gear meshing with a rotation transmission gear provided on the outer periphery of the nut member of the ball screw mechanism, An electric motor is mounted and fixed from the outside of the power assist mechanism body so that rotation can be transmitted to the rotation transmitting shaft. The Omu shaft and the steering rod, is obtained by connected by a connecting arm having a ball joint portion of the worm shaft coupling.

[0011]

According to the present invention, the steering force from the steering wheel is transmitted to the steering rod side by the steering force transmission mechanism provided in a part of the steering body, and the steering assist force from the electric motor is A gear of a rotation transmission shaft supported in a power assist mechanism body that is assembled to another position of the steering body, a rotation transmission gear on a nut member that meshes with the gear, and this nut member is connected by a ball screw. The worm shaft and a part of the worm shaft are transmitted to the steering rod as a linear motion by a connecting arm connected via a ball joint portion.

[0012]

1 and 2 show an embodiment of an electric power steering apparatus according to the present invention. In these figures, first, a schematic configuration of an electric power steering apparatus generally designated by reference numeral 1 will be briefly described with reference to FIG. 2. Reference numeral 2 is an input shaft connected to a steering handle (not shown) side. The tip is inserted into the body portion 3a of the steering body indicated by reference numeral 3. The pinion 4 provided at the tip of the input shaft 2 is slidably passed through the body main body 3a in a direction substantially orthogonal to the input shaft 2 on a rack shaft 5 as an output side steering rod. It is meshed with the rack 6. Here, steering wheels are provided on both ends of the rack shaft 5 via steering link mechanisms (not shown). Also,
In this embodiment, for example, a rack and pinion type steering gear mechanism 7 is illustrated as the steering force transmission mechanism portion from the steering wheel, but the details thereof are well known and a detailed description thereof will be omitted. ..

Further, reference numeral 8 in FIG. 2 detects the rotational torque of the input shaft 2 in the steering body body 3a,
A torque sensor for detecting a steering request transmitted from the steering wheel side is shown as an example in which a magnetostrictive torque detector disclosed in Japanese Patent Laid-Open No. 2-281115 is used. The output obtained by the sensor 8 is sent to the electric control system of the electric motor 10 which is a steering assist force generation source.

Now, the electric power steering apparatus 1 according to the present invention
According to the above, the rack and pinion type steering gear mechanism as a steering force transmission mechanism portion on one side of the steering body 3 that restrains the rotation of the rack shaft 5 which is the output side steering rod and holds it slidably only in the axial direction. The power assist mechanism portion 11 for transmitting the steering assist force by the electric motor 10 provided at a position different from that of FIG. 7 is characterized in that it is configured as shown in FIGS. 1 and 2.

That is, in the electric power steering apparatus 1 according to the present invention, the first and the second parts constituting the gear box are formed at the tip side portion of the pipe body 9 extending from the main body portion 3a of the steering body 3 to one side. A power assist mechanism body 14 including the second cases 12 and 13 is attached so as to project to one side of the rack shaft 5. In addition, 15 is an O-ring that seals an assembly portion between the first case 12 and the pipe body 9 that constitute the body 14, and 16 is a body 14 that is provided at the end of the pipe body 9 by press fitting. A fixing pin for fixing the second case 13 in a rotation-stopped state, 17 is a bellows-shaped boot provided from the end of the second case 13 to the connecting arm side described later, and 9a in the figure. Is a bush that slidably supports the rack shaft 5 at the end of the pipe body 9.

The power assist mechanism body 14 is
The worm shaft 20 is movably held in the axial direction at a position close to the rack shaft 5 in the inside thereof, and the ball 2 is provided in a thread groove 20a formed on the worm shaft 20.
2 is provided with a ball screw mechanism 24 including a nut member 23 having a screw groove 23a to which a ball screw connection is made. Further, the nut member 23 of the ball screw mechanism 24
A rotation transmission shaft 27 having a gear 26 that meshes with a rotation transmission gear 25 provided on the outer periphery is provided in the power assist mechanism body 1
4, the electric motor 10 is assembled and fixed from the outside of the power assist mechanism body 14 so as to be rotatably supported in the motor 4 and to transmit the rotation to the rotation transmission shaft 27. Reference numeral 28 in the drawing denotes a clutch portion provided so that the motor shaft (not shown) of the motor 10 and the rotation transmission shaft 26 can be connected. In addition, the rotation transmission gear 25 and the gear 2 described above
If 6 is a helical gear, for example, it is advantageous in ensuring the rotation transmission.

According to the present invention, the greatest feature is that the worm shaft 20 and the rack shaft 5 described above are connected by the connecting arm 31 having the ball joint portion 30 for connecting the worm shaft 20. There is. In the figure, 32 is a bellows-shaped boot interposed between the second case 13 constituting the body 14 and the connecting arm 31, and 33 is a state on the opposite side of the case 14 in which the amount of movement of the worm shaft 20 is secured. It is a cylindrical cover provided in
Is a bearing that rotatably supports the nut member 23 in the body 14.

According to this structure, the steering force from the steering wheel is transmitted to the rack shaft 5 side by the steering force transmission mechanism portion (steering gear mechanism 7) provided in a part of the steering body 3. In addition, the steering assist force from the electric motor 10 receives the gear 26 of the rotation transmission shaft 27 supported in the power assist mechanism body 14 assembled at different positions of the steering body 3 and the nut meshing with the gear 26. The rotation transmission gear 25 on the member 23, the worm shaft 2 to which the nut member 23 is connected by a ball screw
0, part of the worm shaft 20 is the ball joint 3
By a connecting arm 31 connected via 0, it is transmitted to the rack shaft 5 as a linear motion which is a steering assist force,
The necessary steering operation of the steered wheels is performed. Here, in the present embodiment, a case is shown in which the connecting arm 31 is assembled and fixed so as to intervene in the assembly portion of the ball joint mechanism portion 5a provided on one end side of the rack shaft 5.

According to the above construction, the worm shaft 20 is provided separately from the rack shaft 5, and the worm shaft is connected to the connecting arm provided on the steering rod side via the ball joint portion. The external force acting on the steering rod can be absorbed by the ball joint part, so that no unreasonable force or displacement is generated in the ball screw part between the nut member and the ball screw connected to the worm shaft. In addition, it is possible to prevent adverse effects such as axis misalignment and twisting, thereby improving the operational reliability of this device.
Here, in the present embodiment, the worm shaft 20 and the rotation transmission shaft 27 are arranged in parallel to the rack shaft 5 described above, but the present invention is not limited to this, and these three The axes of do not have to be parallel. In short, the worm shaft 20 may be arranged separately from the rack shaft 5, and the movement of the worm shaft 20 may be transmitted by the connecting arm 31 having the ball joint portion 30.

Further, according to the device 1 of the present invention, the electric motor 10 is detachably assembled and fixed to a part of the power assist mechanism body 14 which is detachably attached to a part of the steering body 3. Therefore, when an abnormality occurs in the motor 10 and the motor 10 needs to be replaced, the replacement work such as attachment and removal can be performed very easily. Further, the power assist mechanism 11 is connected to the rack shaft 5 side only by the connecting arm 30, and the structure for attaching the mechanism body 14 to the steering body 3 side may be simple, and the workability of each part may be improved. And the assemblability can be improved, and, for example, the motor 10 having an output required for the vehicle is selectively used, and the other body 3,
14 can be standardized, and the steering body 3 side can be used in common with those for other types.

Further, the workability and the assemblability of the power assist mechanism portion 11 can be improved to reduce the cost, the mechanism portion 11 can be downsized, and the motor 10 can be attached when the mechanism portion 11 is attached. The degree of freedom of the installation location and the like is large, the overall size and size of the apparatus 1 can be reduced, and an excellent layout configuration in terms of mountability in an actual vehicle can be freely selected.

The present invention is not limited to the structure of the embodiment described above, and the shape, structure, etc. of each portion can be freely modified or changed as necessary, and various modifications can be considered. For example, in the above-described embodiment, the rack shaft 5 of the rack and pinion type steering mechanism is used as the steering rod.
However, the present invention is not limited to this, and any conventionally known steering rod can be applied to exert the effect.

[0023]

As described above, according to the electric power steering apparatus of the present invention, the power assist is attached to a part of the steering body that holds the steering rod at a position different from the steering force transmission mechanism. A ball screw mechanism including a mechanism body, a worm shaft movably held in the mechanism body in the axial direction at a position close to a steering rod, and a nut member connected to the shaft by a ball screw. A rotation transmission shaft that has a gear that meshes with a rotation transmission gear provided on the outer periphery of the nut member and is rotatably supported in the mechanism body, and is assembled from the outside of the mechanism body so that rotation can be transmitted to this shaft. It is equipped with an electric motor that is fixed, and connects the worm shaft and steering rod by a connecting arm that has a ball joint for connecting the worm shaft. Since such coupling, despite a simple configuration, it exhibits various excellent effects listed below. (1) Since a worm shaft is provided separately from the steering rod, and this worm shaft is connected to the connecting arm provided on the steering rod side via the ball joint section, the external action that acts on the steering rod. The force can be absorbed by the ball joint part, which prevents unreasonable force and displacement in the ball screw part between the nut member that is connected to the worm shaft by the ball screw and the adverse effect such as misalignment and twisting. It can be prevented from being applied, which can improve the operational reliability of the device. (2) When an electric motor is attached and fixed to a part of the power assist mechanism part body attached to a part of the steering body, this motor needs to be replaced, etc. In the above, replacement work such as installation and removal can be performed extremely easily. (3) The connection of the power assist mechanism part to the steering rod side is only the connecting arm.
The structure for attaching to the steering body side is simple, and the workability and assembly of each part can be improved. For example, a motor having an output necessary for the vehicle is selectively used, and other bodies are standardized. It is also possible to use the steering body side in common with those for other types. (4) The workability and assemblability of the power assist mechanism can be improved to reduce the cost, the size of the mechanism can be reduced, and the installation location of the motor can be freely set when attaching the mechanism. It is also possible to freely select a layout configuration that is excellent in terms of mounting in an actual vehicle, achieving a small size and downsizing of the entire device.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part showing an embodiment of an electric power steering apparatus according to the present invention.

FIG. 2 is a schematic cross-sectional view showing a schematic configuration of the entire apparatus to which the present invention is applied.

[Explanation of symbols] 1 electric power steering device 2 input shaft 3 steering body 4 pinion 5 rack shaft 6 rack 7 steering force transmission mechanism section 10 electric motor 11 power assist mechanism section 14 power assist mechanism section body 20 worm shaft 22 ball 23 Nut Member 24 Ball Screw Mechanism 25 Rotation Transmission Gear 26 Gear 27 Rotation Transmission Shaft 30 Ball Joint 31 Connection Arm

Claims (1)

[Claims] 1. A power assist mechanism section for transmitting a steering assist force from an electric motor to a position different from a steering force transmission mechanism section for converting a steering force from a steering wheel into a steering force for steered wheels on a steering rod. In the electric power steering apparatus provided with, a power assist mechanism body attached to a part of a steering body that slidably holds the steering rod, and the steering rod in the power assist mechanism body. And a ball screw mechanism composed of a worm shaft that is movably held in the axial direction at a position close to the worm and a nut member that is connected to the worm shaft by a ball screw, and a rotation transmission provided on the outer periphery of the nut member of the ball screw mechanism A rotation transmission shaft that has a gear that meshes with a gear and is rotatably supported in the power assist mechanism body; An electric motor is provided which is assembled and fixed from the outside of the power assist mechanism body so that rotation can be transmitted to the rotation transmission shaft, and the worm shaft and the steering rod are connected to each other by a ball joint portion for connecting the worm shaft. An electric power steering apparatus, wherein the electric power steering apparatus is connected by a connecting arm having a.