JP2012183987A - Electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering apparatus of a compact structure having sufficient steering auxiliary force during stationary steering without increasing the scale of a system.SOLUTION: In an electric power steering apparatus connected to a steering system, including a motor 18 generating steering auxiliary torque to the steering system via a reduction gear, controlling the motor on the basis of a steering torque of the steering system or a vehicle speed, and generating steering assist torque, the reduction gear comprises first reduction gears 18b, 20 and second reduction gears 18c, 21 having different speed reduction ratios. The electric power steering apparatus includes a switching means 13 switching the first and second reduction gears 18b, 20, 18c, 21.

Description

  The present invention relates to an electric power steering apparatus.

  In an electric power steering apparatus for a vehicle such as an automobile, the steering force required when the automobile is completely turned off is generally larger than that during normal driving. Therefore, general electric power steering is designed so that the steering assist force does not become insufficient when the required specification of the electric motor for assisting the steering force is completely cut. In particular, a large vehicle requires a large, high-output electric motor, and the size of the electric power steering device cannot be avoided. In order to avoid such an increase in the size of the electric motor, there is an electric power steering device that uses two small electric motors as shown in Patent Document 1 so that the steering assist force is not insufficient.

JP-A-5-155343

  However, when two electric motors are used, each electric motor can be reduced in size. However, when this electric power steering device is mounted on a vehicle, the two electric motors are prevented from interfering with other components. There was a problem that it was necessary and the degree of freedom of mounting on the vehicle was low. Accordingly, it is an object of the present invention to provide an electric power steering device that does not have a small steering assist force at the time of set-up without increasing the size of the system.

  In order to solve the above problems, the invention according to claim 1 is provided with a motor that generates a steering assist torque via a speed reducer in the steering system, and controls the motor based on a steering torque and a vehicle speed of the steering system. In the electric power steering apparatus that generates the steering assist torque, the speed reducer includes a first speed reducer and a second speed reducer having different speed reduction ratios, and switching means for switching between the first speed reducer and the second speed reducer is provided. This is the gist.

  According to the present invention, practically sufficient steering force can be obtained by switching the magnitude of the steering assist force by switching the reduction gear. That is, when the vehicle is traveling on the road, the first reduction gear with a small reduction ratio is used to reduce the steering assist force, and when the vehicle is completely turned off, the second reduction device with a large reduction ratio is set to increase the steering assistance force. Therefore, a large motor for increasing the steering assist force is unnecessary, and an electric power steering device can be obtained in which the steering assist force is not insufficient at the time of turning off.

  According to a second aspect of the present invention, the first speed reducer is constituted by a first drive gear and a first driven gear, the second speed reducer is constituted by a second drive gear and a second driven gear, The gist of the switching means is to change the reduction ratio by meshing the first drive gear and the first driven gear or the second drive gear and the second driven gear. That is, in the present invention, the reduction ratio of the steering assist is a simple configuration in which the first and second drive gears and the driven gear are directly connected to realize the first and second steering assist reduction ratios. Can be achieved. Also. Therefore, an electric power steering apparatus in which the number of parts is small and the system is miniaturized can be obtained.

  Further, in the invention described in claim 3, the first drive gear and the second drive gear are provided in series with the motor shaft of the motor, and the first driven gear and the second driven gear are related to the steering system. The summary is summarized. That is, since the drive gear is configured in series with one motor shaft and is coaxial, it can be driven by one motor. On the other hand, since the driven gear is directly provided in the steering system, it is possible to reliably assist the steering force with a simple structure. In addition, the speed reducer has a simple structure, and the system can be miniaturized with an increase in axial length being minimized.

  The gist further includes speed detecting means for detecting the vehicle speed, and the switching means switches based on the vehicle speed. In other words, the present invention includes a device for detecting a state of cut-off from the vehicle speed, and further includes an operation unit for operating the reduction ratio switching mechanism. Since the transmission path can be easily changed in two stages with a simple structure, it is possible to reliably operate the steering assist for the cut-off and secure the steering assist force.

  According to the present invention, since the magnitude of the steering assist force can be switched by switching the reduction gears in two stages, even in a large vehicle, a compact system in which the steering assist force is not insufficient at the time of set-up without increasing the size of the system. An electric power steering device having a simple structure can be provided.

It is a mimetic diagram showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is a partial sectional view showing a schematic structure of a power auxiliary transmission mechanism, and shows a state in the first reduction gear position. It is a partial cross section figure which shows schematic structure of a power auxiliary transmission mechanism, and has shown the state in a 2nd reduction gear position.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, and an intermediate shaft. 5, a pinion shaft 7 connected via a universal joint 6, and a rack shaft 8 as a steered shaft having a rack 8 a that meshes with a pinion 7 a provided near the end of the pinion shaft 7. The rack shaft 8 extends in the left-right direction of a vehicle such as an automobile. The pinion shaft 7 and the rack shaft 8 constitute a steering mechanism 9 composed of a rack and pinion mechanism.

  The rack shaft 8 is supported in a housing (not shown) fixed to the vehicle body through a plurality of bearings (not shown) so as to be capable of linear reciprocation along the axial direction of the rack shaft 8. A tie rod 10 is coupled to each end of the rack shaft 8. Each tie rod 10 is connected to a corresponding steered wheel 11 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, this rotation is converted into a linear motion in the axial direction of the rack shaft 8 by the pinion 7a and the rack 8a. Thereby, the turning of the steered wheel 11 is achieved.

  The electric power steering apparatus 1 includes a steering assist mechanism 12 for applying a steering assist force to the steering mechanism 9 and a reduction ratio switching mechanism 13 that can change the steering assist force of the steering member 2. Yes. The steering shaft 3 is disposed between the steering member 2 and the reduction ratio switching mechanism 13, and is disposed between the input shaft 14 that rotates according to the steering of the steering member 2, and the reduction ratio switching mechanism 13 and the intermediate shaft 5. And an output shaft 15 that rotates in conjunction with the operation of the steering mechanism 9.

  The steering assist mechanism 12 includes an electric motor 18 such as a brushless motor, and a speed reduction mechanism 19 to which output rotation of the electric motor 18 is input. The speed reduction mechanism 19 is, for example, a hypoid gear speed reduction mechanism, and is a first driven gear 20 connected to the motor shaft 18a of the electric motor 18 so as to be integrally rotatable, and a first driven gear connected to the output shaft 15 so as to be integrally rotatable. 20 includes a second driven gear 21 made of a hypoid gear that meshes with the first and second drive gears 18b and 18c provided on the motor shaft 18a. As described above, the speed reduction mechanism 19 includes the first drive gear 18b and the first driven gear 20 as the first speed reducer, and the second drive gear 18c and the second driven gear 21 as the second speed reducer. The first and second driven gears 20 and 21 are attached to the input shaft 14 and the output shaft 15 by spline fitting so as to be integrally rotatable, and can be moved in the axial direction X10 by the reduction ratio switching mechanism 13.

The electric motor 18 is connected to the steering mechanism 9 through the speed reduction mechanism 19, the output shaft 15, and the intermediate shaft 5 so that power can be transmitted. The output (steering assisting force) of the electric motor 18 is transmitted to the output shaft 15 via the speed reduction mechanism 19 to assist the driver's steering.
The electric power steering apparatus 1 also includes a torque sensor 22 and a vehicle speed sensor 23 for controlling the electric motor 18. The torque sensor 22 is provided around the input shaft 14. The torque sensor 22 is, for example, a sensor that detects torsion of the output shaft 15 according to the torque acting on the input shaft 14. By detecting the twist of the output shaft 15, the torque acting on the output shaft 15 is detected. The vehicle speed sensor 23 is provided on a wheel such as the steered wheel 11 of the vehicle, and detects the vehicle speed.

  The electric power steering apparatus 1 includes a control unit 24 including a CPU, a RAM, and a ROM. The control unit 24 is provided to control the operation of the electric motor 18. A torque sensor 22 and a vehicle speed sensor 23 are connected to the control unit 24, respectively. Detection signals from these sensors 22 and 23 are input to the control unit 24. The control unit 24 is connected to the electric motor 18 via the driver 25.

  The control unit 24 sets a target drive amount of the electric motor 18 based on input signals from the torque sensor 22 and the vehicle speed sensor 23, and the deviation between the actual drive amount and the target drive amount of the electric motor 18 becomes zero. Thus, the electric motor 18 is controlled. As a result, a predetermined force is generated in the electric motor 18. This force is transmitted to the output shaft 15 via the speed reduction mechanism 19 and further applied to the steering mechanism 9. As a result, the steering of the steering member 2 by the driver is assisted, and the driver can easily rotate the steering member 2 with a small force.

  FIG. 2 is a partial cross-sectional view showing a schematic configuration of the reduction ratio switching mechanism 13. As shown in FIG. 2, the input shaft 14 and the output shaft 15 are arranged coaxially with their tips opposed to each other. The reduction ratio switching mechanism 13 includes a first driven gear 20 connected to the input shaft 14 so as to be integrally rotatable, and a second driven gear 21 connected to the output shaft 15 so as to be integrally rotatable.

  The diameter of the first driven gear 20 is smaller than the diameter of the second driven gear 21 and the reduction ratio is small. The first and second driven gears 20 and 21 are formed with tooth portions 20a and 21a in the axial direction of the steering shaft 3, respectively.

  The reduction ratio switching mechanism 13 includes a housing 31 having a disk portion 31 a formed so as to pass through the input shaft 14, a biasing member 32 that biases the first and second driven gears, and a solenoid 33. The housing 31 is fixed to the column bracket (not shown) and is attached so as not to rotate integrally with the input shaft 14.

  The biasing member 32 is provided between the one end surface 31 b of the disk portion 31 a and the first driven gear 20. The biasing member 32 is a spring such as a coil spring, for example. A plurality (two in the present embodiment) of urging members 32 are arranged at equal intervals in the circumferential direction of the disk portion 31a. One end of each biasing member 32 biases the one end face 31b, and the other end biases one end face 20c of the first driven gear 20 toward the output shaft 15 side.

The solenoid 33 is provided in the disk portion 31a. The solenoid 33 is provided to displace the first and second driven gears 20 and 21 in the axial direction X10. The solenoid 33 includes a solenoid housing 33a fixed to the outer periphery of the disk portion 31a, and a rod 33b supported by the solenoid housing 33a so as to be movable back and forth in the axial direction X10.
A hook 33c is formed at the tip of the rod 33b and is engaged with a recess 20d formed in the first driven gear 20. Accordingly, the first and second driven gears 20 and 21 can be moved in the axial direction X10 of the steering shaft 3 by moving the rod 33b forward and backward by the solenoid 33.

  By supplying electric power to the solenoid 33, the rod 33b is displaced to one X11 side in the axial direction X10. As a result, the first and second driven gears 20 and 21 are displaced toward one X11 side in the axial direction X10 of the steering shaft 3 against the biasing force of the biasing member 32, and are positioned at the second position P2. . On the other hand, when electric power is not supplied to the solenoid 33, the first and second driven gears 20 and 21 are displaced toward the other X12 side in the axial direction X10 by the urging force of the urging member 32 to the first position P1. It is supposed to be located. Therefore, the first and second driven gears are always urged by the urging member 32, and there is no backlash with the first and second drive gears.

  An operation member 34 is connected to the solenoid 33. The operation member 34 includes, for example, a button 34a. When the driver operates the button 34a, the solenoid 33 is supplied with power from a power source (not shown) and the power supply from the power source is cut off. It is possible to switch between the current state and the current state. In addition, this power supply is supplied to the control unit 24 when detection signals from the torque sensor 22 and the vehicle speed sensor 23 respectively connected determine that the vehicle is stopped and not running.

  In FIG. 2, the first driven gear 20 is located at the first position P1. When the first driven gear 20 is located at the first position P <b> 1, the tooth portion 18 b of the drive gear 18 is engaged with the tooth portion 20 a of the first driven gear 20. At this time, the tooth portion 18b of the drive gear 18 and the first driven gear are directly connected (coupled so as to be integrally rotatable), and a steering assist force acts at a reduction ratio of the first reduction gear.

  For example, when the vehicle is traveling on a road, the input member 26 is positioned at the first position P1. At this time, the steering assist force is smaller than the steering force of the input shaft 14 when the vehicle is stopped. As a result, a natural steering feeling can be obtained when the vehicle changes lanes on the road.

  In FIG. 3, the second driven gear 21 is located at the second position P2. When the second driven gear 21 is located at the second position P <b> 2, the tooth portion 18 b of the drive gear 18 is engaged with the tooth portion 21 a of the first driven gear 21. At this time, the tooth portion 18b of the drive gear 18 and the second driven gear are directly connected (coupled so as to be integrally rotatable), and a steering assist force acts at a reduction ratio of the second reduction gear.

  For example, when the vehicle is put in a parking lot, the driver presses the button 34a of the reduction ratio switching mechanism 13 so that the displacement member 29 is displaced to the second position P2. At this time, since the second reduction ratio is larger than the first reduction ratio, the rotational operation force of the steering member 2 can be reduced. As a result, it is possible to reduce the force with which the driver turns the steering member 2 when the vehicle is put in the parking lot.

  As described above, according to the present embodiment, when the first reduction gear assists the power between the input shaft 14 and the output shaft 15, the second reduction gear reduces the input shaft 14 and the output shaft 15. The speed reduction ratio can be changed in two stages when power is assisted between the two. For example, it is possible to stop the vehicle on the parking frame of the parking lot with less effort by increasing the reduction ratio when the vehicle is parked compared to when the vehicle is traveling on the road. Since the reduction in the reduction ratio of the member 2 reduces the sense of inertia, the steering assist force does not become too large, and a natural steering feeling can be realized. Thus, by achieving two-step reduction ratio switching, which is a simple and inexpensive configuration, a practically sufficient steering assist force variable effect can be obtained.

  Furthermore, the steering assist reduction ratio can be easily changed in two stages with a simple configuration in which the driver operates the reduction ratio switching mechanism 13. Further, in order to realize the first reduction gear ratio, the first drive gear and the second reduction gear ratio may have a simple configuration in which the second drive gear is directly connected. Therefore, the electric power steering device 1 can be made more cost-effective.

  In addition, the first and second reduction gear ratios can be realized with a simple configuration in which the first and second drive gears 18b and 18c are engaged with the first and second driven gears 20 and 21 and with no backlash. Therefore, the reduction mechanism is excellent in quietness without generation of rattling noise due to gear backlash caused by assembly, dimensional errors, and wear during use. Further, as the reduction ratio switching mechanism, a gear mechanism different from that described in each of the above embodiments may be used. That is, an electric power steering apparatus including a displacement member that is displaced to a first position P1 and a second position P2 according to a driver's operation, and a steering assist transmission path is changed according to the displacement of the displacement member. The present invention can be applied.

  Further, in each of the above-described embodiments, the column assist type steering assist mechanism 12 that applies the steering assist force from the output shaft 15 of the steering shaft 3 to the steering mechanism 9 has been described, but the present invention is not limited thereto. For example, the present invention can be applied to an electric power steering device that applies a steering assist force from the pinion shaft 7 or the rack shaft 8 to the steering mechanism 9.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Steering member, 9 ... Steering mechanism, 13 ... Reduction ratio switching mechanism, 14 ... Input shaft, 15 ... Output shaft, 18 ... Electric motor, 18a ... Motor shaft, 18b ... First drive Gears 18c Second drive gear 19 Reduction mechanism 20 First driven gear 21 Second driven gear

Claims (4)

  An electric power steering device that includes a motor that is coupled to a steering system and that generates a steering assist torque via a speed reducer and that controls the motor based on the steering torque and vehicle speed of the steering system and generates the steering assist torque. The electric power steering apparatus according to claim 1, wherein the speed reducer comprises a first speed reducer and a second speed reducer having different speed reduction ratios, and switching means for switching between the first speed reducer and the second speed reducer.   The first reduction gear comprises a first drive gear and a first driven gear, the second reduction gear comprises a second drive gear and a second driven gear, and the switching means comprises the first drive gear and the first driven gear. An electric power steering device, wherein a reduction ratio is changed by meshing one drive gear and the first driven gear or the second drive gear and the second driven gear.   3. The first drive gear and the second drive gear are provided in series with the motor shaft of the motor according to claim 1, and the first driven gear and the second driven gear are engaged with the steering system. An electric power steering device.   4. The electric power steering apparatus according to claim 1, further comprising speed detection means for detecting a vehicle speed, wherein the switching means is switched based on the vehicle speed.

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