JP2013159334A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device that can provide a steering feeling almost the same as a manual steering mechanism not having a steering assistance mechanism when not using steering assistance.SOLUTION: A mechanism transmitting motive power of a motor carrying out steering assistance to a steering mechanism includes a mechanism producing a dead zone cutting off almost all transmission of the motive power, and a dead zone sensor detecting a state of the mechanism producing the dead zone. When not using steering assistance, a control device changes a rotation angle position of an output shaft of the motor carrying out steering assistance by using a signal from the dead zone sensor, and by this, the mechanism producing the dead zone is controlled to retain a state of cutting off almost all transmission of the motive power.

Description

  The present invention relates to an electric power steering apparatus that assists steering using an electric motor, and relates to the structure and control of a steering assist mechanism that prevents the steering assist mechanism from obstructing the movement of the steering mechanism when steering assist is not performed. .

  The mechanism for transmitting the power of the motor that assists the steering of the steering assist mechanism in the conventional electric power steering apparatus to the steering mechanism is configured to transmit a minute movement bidirectionally. Therefore, in a state where the control device stops the drive current of the electric motor when steering assist is not performed, the steering mechanism moves the steering assist mechanism even with a slight movement of the steering mechanism. Since there is a moving part, a frictional force works, and the steering assist mechanism acts to stop the movement of the steering mechanism.

  Therefore, when steering assistance is not performed, not only the driver's steering force is increased by the frictional force, but also in the steering that returns the vehicle from the turning state to the straight traveling state, only the self-aligning torque that the vehicle tries to return straight ahead. In steering, there is no need for steering assistance, such as the steering mechanism does not return straight to the straight position, or the vehicle travels almost straight, and the steering mechanism is slow and sometimes stops. Because the frictional force changes due to the dynamic friction part or static frictional part, the driver feels an unnatural change in the steering force, such as a manual steering mechanism without a steering assist mechanism. It was difficult to obtain a good steering feeling.

  Therefore, in order to solve these problems, in [Patent Document 1] and [Patent Document 2], among the plurality of frictional forces in the steering assist mechanism, the frictional force in the motor for assisting steering in particular is used as a power source. The frictional force of the transmission mechanism is increased, and the power is further boosted by the mechanism of deceleration, and the steering mechanism is stopped by a large force. Therefore, a friction clutch mechanism is provided on the output shaft of the motor that assists steering. When the steering assist is unnecessary, the transmission of power to the electric motor is cut off by the friction clutch mechanism so that the force of the steering assist mechanism to stop the steering mechanism is reduced.

  JP 61-37581 A   JP 11-59440 A

  However, the conventional technology that connects and cuts off the transmission of power by providing a friction clutch mechanism on the output shaft of the motor that assists steering improves the steering feeling when the transmission of power is cut off. However, when connecting or disconnecting the transmission of power, the motor and the friction clutch mechanism are accurately controlled to ensure that the driver does not feel unnatural changes in steering force. It is difficult to connect or cut off the transmission. Therefore, good steering feeling was not obtained in various situations.

  In view of the circumstances as described above, the present invention can smoothly switch between the state of assisting steering and the state of not assisting steering. When assisting steering, the conventional electric power is small and comfortable. To realize an electric power steering device that can obtain a steering feeling equivalent to that of a steering device and that can obtain a smooth and natural steering feeling that is almost equivalent to a manual steering mechanism that does not have a steering assistance mechanism when steering assistance is not performed. It is aimed at.

  In order to solve the above-described problem, an electric power steering apparatus according to the present invention has a mechanism that generates a dead zone that substantially interrupts transmission of the power in a mechanism that transmits the power of an electric motor that assists steering to a steering mechanism, A dead zone sensor that detects the state of the mechanism that generates the dead zone, and when the steering assist is not performed, the control device uses the signal from the dead zone sensor to change the rotational angle position of the output shaft of the motor. The mechanism for generating the dead zone is controlled so as to maintain a state in which the transmission of the power is substantially cut off.

  Further, in the control in which the mechanism that generates the dead band maintains a state in which the transmission of the power is substantially cut off, the control target state of the mechanism that generates the dead band is changed according to the direction and magnitude of the steering torque and the vehicle speed. It is.

  In addition, an elastic member is provided in a portion that connects and blocks the transmission of the power of the mechanism that generates the dead zone, and the elastic member is compressed to connect the transmission of the power and perform steering assistance. is there.

  According to the present invention, when assisting the steering, the control device controls the output torque of the electric motor for assisting the steering, similarly to the conventional electric power steering device, regardless of the state of the mechanism causing the dead zone. As a result, the steering feeling is small and comfortable, and the steering feeling equivalent to that of the conventional electric power steering device is obtained. When the steering assist is not performed, the control device uses the signal from the dead zone sensor to steer. By changing the rotational angle position of the output shaft of the motor that assists the steering according to the movement of the mechanism, the mechanism that generates the dead zone is controlled so as to keep the power transmission almost cut off. Natural, smooth steering that is almost unimpeded by the mechanism and almost equivalent to a manual steering mechanism that does not have a steering assist mechanism Iringu so as to obtain.

  In addition, in the control that maintains the state in which the mechanism that generates the dead band substantially cuts off the transmission of power, the control target state of the mechanism that generates the dead band is changed according to the direction and magnitude of the steering torque and the vehicle speed to generate the dead band. Since the power transmission of the mechanism to be controlled is controlled so as to reduce the impact at the portion where the power transmission is connected and cut off, the state where the steering assist is performed and the state where the steering assist is not performed can be smoothly switched.

  And, the mechanism that generates the dead zone includes an elastic member in the portion that connects and blocks the transmission of power, and gradually increases or decreases the force to assist steering by compressing or expanding the elastic member. In addition to the above effects, the state where the steering assist is performed and the state where the steering assist is not performed can be switched more smoothly.

  1 is a partial cross-sectional view of a steering assist mechanism 100 using the present invention as viewed from the axial direction of a steering shaft 20. FIG.   It is a figure explaining the positional relationship of the main components in the state where the position of the worm 110 in the axial direction is near the center between two bearings 160R and 160L.   It is a figure of the state which rotates the worm | warm 110 to the clockwise direction CW, and starts the steering assistance of the steering shaft 20 to the clockwise direction CW.   It is a figure of the state which rotates the worm | warm 110 in the counterclockwise direction CCW, and starts the steering assistance in the counterclockwise direction CCW.   It is a figure explaining the relationship between the worm 110 of the state which the worm 110 moved to the axial direction of right R, and the photo interrupter 60. FIG.   It is a figure explaining the relationship between the worm 110 of the state which the worm 110 moved to the left L axial direction, and the photo interrupter 60. FIG.   It is a figure explaining the basic characteristic and relationship of steering assist control and dead zone control of the present invention.   It is a flowchart which shows the outline of the control processing in the calculating part 41 of this invention.   1 is an overall configuration diagram of an electric power steering apparatus using the present invention.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 9 is an overall configuration diagram of an electric power steering apparatus using the present invention. In the electric power steering device, a steering assist device is attached to a manual steering mechanism in which the steered wheels 90R and 90L are steered when the steering wheel 10 is rotated. As for the position where the steering assist device is attached, the torque sensor 30 is attached to the side closer to the steering wheel 10 of the steering shaft 20, and the steering assist mechanism 100 is attached to the far side. And the control apparatus 40 is attached to these exteriors. The control device 40 includes a calculation unit 41 and a drive unit 42. The calculation unit 41 includes a microprocessor for executing a program and other peripherals such as an input interface from various sensors, an A / D converter, and a memory. An output interface to the LSI and the drive unit 42 is provided. A steering torque signal VT from the torque sensor 30, a dead zone signal VD from the dead zone sensor 200, and a vehicle speed signal VS from the vehicle speed sensor 50 are input to the input interface of the calculation unit 41. And the calculating part 41 outputs the signal which instruct | indicates the rotation direction of the electric motor 70, and the magnitude | size of an electric current to the drive part 42 from an output interface by the result processed according to those input signals. The drive unit 42 performs steering assistance by outputting to the electric motor 70 a PWM drive current 1 in response to an instruction from the calculation unit 41.

  FIG. 1 is a partial cross-sectional view of a steering assist mechanism 100 using the present invention as seen from the axial direction of a steering shaft 20. The steering assist mechanism 100 includes an electric motor 70, a mechanism including a worm 110 and a worm wheel 120 that transmits power by decelerating, a dead zone sensor 200, and the like, which are attached to the housing 101 and integrated. .

  The worm wheel 120 is attached to the steering shaft 20 rotatably supported by a bearing (not shown) attached to the housing 101, and rotates together with the steering shaft 20.

  There are flange portions 110c and 110e on both sides of the tooth portion 110z of the worm 110 in the axial direction, followed by shaft portions 110b and 110f. An elastic ring 140 is fitted to the shaft portions 110b and 110f so as to be in contact with the flange portions 110c and 110e, and bearings 160R and 160L are fitted on the outer sides thereof. The outer bearings of the two bearings 160R and 160L are fixed to the housing 101 by the retaining ring 104, the holding screw 106, and the fixing nut 108, and the teeth 110z of the worm 110 and the teeth 120z of the worm wheel 120 are engaged with each other. The worm 110 is supported so as to be rotatable around the axial center.

  FIG. 2 is a diagram showing the positional relationship of the main components in a state where the axial position of the worm 110 is near the center between the two bearings 160R and 160L. A gap fit in which the shaft portions 110b and 110f of the worm 110 and the inner diameter portions of the bearings 160R and 160L and the end portion 110a of the worm 110 and the inner diameter portion 71a of the output shaft 71 of the electric motor 70 shown in FIG. Further, the length M1 that is the distance between the two bearings 160R and 160L is the outer length when the two elastic rings 140 are in contact with the flange portions 110c and 110e of the worm 110. Since it is longer than M2, there are gaps GR and GL between the elastic ring 140 and the bearings 160R and 160L. Therefore, the worm 110 can be easily moved not only in the rotation around the axis center but also in the axial direction until the gap GR = 0 or the gap GL = 0.

  Further, as shown in FIG. 1, since the outer diameter portion of the end portion 110a of the worm 110 and the inner diameter portion 71a of the output shaft 71 of the electric motor 70 are fitted by a spline system having a gear section, the worm 110 has a shaft. The worm 110 and the output shaft 71 of the electric motor 70 rotate as a unit regardless of where they move within the movable range.

  The position of the worm 110 in the axial direction is detected by the photo interrupter 60 used as the dead zone sensor 200. As shown in FIG. 1, the photo interrupter 60 is attached to a circuit board 201 and is further fixed to the housing 101 by a support member 202. As shown in FIGS. 5 and 6, the photo interrupter 60 includes a pair of a light emitting element 62 and a light receiving element 63 housed in a case 61 having a U-shaped cross section. The W detection light 64 exits from the exit slit 61 a opened in the case 61, passes through the detection part inside the U-shape of the case 61, enters the entrance slit 61 b opened in the case 61, and reaches the light receiving element 63. It is like that. Since the end 110s of the worm 110 is disposed at a position that blocks a part of the detection light 64, the width of the detection light 64 that reaches the light receiving element 63 changes when the position of the worm 110 in the axial direction changes. As shown in FIG. 5, when the worm 110 moves in the right R axial direction, the width of the detection light 64 reaching the light receiving element 63 is the width WR. However, as shown in FIG. 6, the worm 110 extends in the left L axial direction. When it moves, the width of the detection light 64 that reaches the light receiving element 63 becomes the width WL and decreases. Then, the change in the width of the detection light 64 reaching the light receiving element 63 becomes a change in the amount of light received by the light receiving element 63, and further changes in the current passing through the light receiving element 63. Therefore, the axis of the worm 110 depends on the value of this current. You can know the position of the direction. As will be described later, in the embodiment of the present invention, the state of the mechanism that causes a dead band in the transmission of power can be detected based on the position of the worm 110 in the axial direction. Therefore, this current is used as the dead band signal VD. Output to.

  Next, regarding the movement of the worm 110 and the worm wheel 120 of the steering assist mechanism 100 in which the worm 110 is movable in the axial direction as described above, the position of the worm 110 in the axial direction is the gap GR as shown in FIG. A case where the output shaft 71 of the electric motor 70 is rotated from a state where> 0 and the gap GL> 0 and a case where the steering shaft 20 is rotated will be described.

  First, as shown in FIG. 2, the output shaft of the electric motor 70 is moved in a direction in which the worm 110 rotates in the clockwise direction CW of the XX section from the state where the axial direction of the worm 110 is the gap GR> 0 and the gap GL> 0. When the 71 is rotated, the teeth 110z of the worm 110 and the teeth 120z of the worm wheel 120 mesh with each other, and the worm 110 can be easily moved in the axial direction. While moving the helical tooth portion 110z along the tooth portion 120z of the worm wheel 120 in the left L axial direction. Then, as shown in FIG. 3, when the output shaft 71 of the electric motor 70 is further rotated in the direction in which the worm 110 further rotates in the clockwise direction CW of the XX section after the gap GL = 0, the worm 110 further moves to the left L Although the bearing 160L is fixed to the housing 101, the elastic ring 140 is compressed between the flange portion 110e of the worm 110 and the bearing 160L. Then, the tooth portion 110z of the worm 110 rotates the worm wheel 120 in the clockwise direction CW by the reaction force compressing the elastic ring 140 at that time, thereby assisting the steering shaft 20 in the clockwise direction CW.

  Similarly, as shown in FIG. 2, the electric motor 70 is moved in a direction in which the worm 110 rotates in the counterclockwise direction CCW of the XX cross section from the state where the axial direction of the worm 110 is the gap GR> 0 and the gap GL> 0. When the output shaft 71 is rotated, first, the worm 110 rotates while moving the helical tooth portion 110z along the tooth portion 120z of the worm wheel 120 in the right R axial direction. Then, as shown in FIG. 4, when the output shaft 71 of the electric motor 70 is rotated so that the worm 110 further rotates counterclockwise CCW of the XX cross section after the gap GR = 0, the worm 110 further moves to the right. The bearing 160R is fixed to the housing 101, but the elastic ring 140 is compressed between the flange portion 110c of the worm 110 and the bearing 160R. Then, the tooth portion 110z of the worm 110 rotates the worm wheel 120 in the counterclockwise direction CCW by the reaction force compressing the elastic ring 140 at that time to assist the steering shaft 20 in the counterclockwise direction CCW. .

  As described above, when assisting the steering shaft 20, the output shaft 71 of the electric motor 70 rotates the worm 110 in the clockwise direction CW or the counterclockwise direction CCW of the XX section. Even when steering assist is performed in the direction, the elastic ring 140 is compressed with a large force between the flange portions 110c and 110e of the worm 110 and the bearings 160R and 160L, and the reaction force becomes a force for assisting the steering. Therefore, the elastic ring 140 has a structure that does not permanently deform even when compressed by a large force. As shown in FIG. 5, the elastic ring 140 is composed of a relatively soft elastic material 141 such as rubber and a metal cage 142, which are integrated so as not to come off. As shown in FIG. 5, the elastic ring 140 when the gap GL> 0 has a thickness T0. When the worm 110 moves in the left L axial direction, first, the elastic material 141 comes into contact with the bearing 160L. When the gap GL = 0 and the worm 110 further moves in the left L axial direction, the flange portion 110e starts to compress the elastic member 141 in the thickness direction. The reaction force of the elastic ring 140 during compression is small at the beginning of compression and gradually increases because the cross-sectional shape of the elastic material 141 is a mountain shape. Then, as shown in FIG. 6, the thickness T1 is substantially the same as the thickness of the cage 142, and a large force for moving the worm 110 in the axial direction of the left L is before the elastic material 141 is permanently deformed. A metal cage 142 is received.

  Next, as shown in FIG. 2, when the steering shaft 20 is rotated in the clockwise direction CW when the position of the worm 110 in the axial direction is the clearance GR> 0 and the clearance GL> 0, the steering shaft 20 is integrated with the steering shaft 20. The tooth portion 120z of the rotating worm wheel 120 and the tooth portion 110z of the worm 110 mesh with each other, and the worm 110 can be easily moved in the axial direction, so the worm wheel 120 first moves the worm 110 to the right. Move in the axial direction of R. When the steering shaft 20 is further rotated clockwise CW after the gap GR = 0, the worm wheel 120 tries to move the worm 110 further in the right R axial direction, but the bearing 160R is attached to the housing 101. Since it is fixed, the worm wheel 120 cannot move the worm 110 in the axial direction after the franchic part 110 c of the worm 110 slightly compresses the elastic ring 140, and the tooth part 120 z is moved to the tooth part of the worm 110. By moving along the spiral of 110z, the worm 110 and the output shaft 71 of the electric motor 70 are rotated in the clockwise direction CW of the XX section.

  Similarly, as shown in FIG. 2, when the steering shaft 20 is rotated counterclockwise CCW when the worm 110 is in the state where the axial direction of the worm 110 is the clearance GR> 0 and the clearance GL> 0, the steering shaft 20 is integrated. The rotating worm wheel 120 first moves the worm 110 in the left L axial direction. When the steering shaft 20 is further rotated counterclockwise CCW after the gap GL = 0, the worm wheel 120 attempts to move the worm 110 further in the left L axial direction, but the bearing 160L is a housing. Since the flange portion 110e of the worm 110 slightly compresses the elastic ring 140, the worm wheel 120 cannot move the worm 110 in the axial direction and the tooth portion 120z is moved to the worm 110. By moving along the spiral of the tooth portion 110z, the worm 110 and the output shaft 71 of the electric motor 70 are rotated in the counterclockwise direction CCW of the XX cross section.

  As described above, regardless of whether the output shaft 71 or the steering shaft 20 of the electric motor 70 is rotated from the state where the axial direction of the worm 110 is the gap GR> 0 and the gap GL> 0, the worm 110 is firstly rotated. Starts moving in the axial direction. When the worm 110 moves in the axial direction without compressing the elastic ring 140 by the flange portions 110c and 110e, the frictional force at the portion where the worm 110 slides against other parts, or the movement of the worm 110 in the axial direction. A slight force that affects the movement of each other acts between the output shaft 71 of the electric motor 70 and the steering shaft 20 such as an inertial force when the rotation around the center of the shaft accelerates or decelerates. The change in the rotational angle position of the output shaft 71 or the steering shaft 20 is almost insensitive to the movement of the worm 110 only by moving the worm 110 in the axial direction. Therefore, in the present embodiment, the ability of the worm 110 to move in the axial direction is a mechanism that generates a dead zone that substantially blocks transmission of power from the electric motor 70 that assists steering. Hereinafter, as shown in FIG. 2, a state where the position of the worm 110 in the axial direction is the gap GR> 0 and the gap GL> 0 is expressed as “the worm 110 is located in the dead zone”.

  Next, steering assist control and dead zone control by the control device 40 of the electric power steering apparatus using the present invention configured as described above will be described.

  FIG. 7 is a diagram for explaining the basic characteristics and relationship of the steering assist control and the dead zone control of the present invention. First, in the steering assist control, when the steering torque TS is outside the dead zone control range F shown in FIG. 7 (1) steering assist control, the steering assist torque TA is large and the steering assist is required. This is done by controlling As a method, it is performed by increasing / decreasing the driving current 1 of the electric motor 70 as in the conventional electric power steering apparatus, and the steering assist torque TA is increased as the steering torque TS increases as in the steering assist characteristic curves Acw, Accw, When the steering torque TS exceeds a certain level, the steering assist torque TA is set to a preset maximum value. In this steering assist control, the position of the worm 110 in the axial direction is not controlled, and is left to the movement determined by the direction of assisting the steering, but the curve Hcw drawn by the broken line in FIG. As the steering assist torque TA increases as in Hccw, the worm 110 further increases the maximum deformation amount t (= thickness T0) of the elastic ring 140 from the position where the gap GR = 0 or the gap GL = 0 where the steering assist starts. -Move to the position of Rmax or Lmax where thickness T1). Although not shown, the characteristics of the steering assist control are changed depending on the vehicle speed. When the vehicle speed is slow, the dead zone control range F is narrowed, the steering assist torque TA is also sharply increased, and the maximum value is increased. As the vehicle speed increases, the dead zone control range F is expanded, the steering assist torque TA is gradually increased, and the maximum value is decreased. In addition, as for the subscript of any symbol of FIG. 7, cw is clockwise and ccw is counterclockwise.

  Next, in the dead zone control, when the steering torque TS is inside the dead zone control range F shown in FIG. 7 (1) steering assist control, when the steering torque TS is small and steering assist is unnecessary, FIG. ) As shown in dead zone control, this is performed by controlling the position of the worm 110 in the axial direction in accordance with the steering torque TS. As described above, when the worm 110 is located in the dead zone, it is in a dead state in which the transmission of power from either side is substantially cut off. Therefore, the steering shaft 20 is rotated by attaching the steering assist mechanism 100. Since the increase in the torque TS is slight, the movement of the steering mechanism is hardly hindered by the steering assist mechanism 100, which is almost the same as that of a manual steering mechanism vehicle that does not have the steering assist mechanism 100. However, as shown in FIG. 2, the range D (= length M1−length M2) in which the worm 110 can move in the axial direction without compressing the elastic ring 140 is as narrow as 1 mm or less, for example. The angle at which the worm wheel 120 can rotate in the state of being in the dead zone is very small. Therefore, in the dead zone control, the worm 110 is always located in the dead zone according to the rotation of the worm wheel 120 by utilizing the fact that the worm 110 moves in the axial direction even if the worm 110 rotates around the axis center. As described above, by changing the rotation angle position around the axis center of the worm 110 using the electric motor 70, the worm wheel 120 and the steering shaft 20 attached to the worm wheel 120 can rotate with almost no obstruction by the steering assist mechanism 100. The control is performed so as to eliminate the restriction of the angle.

  As shown in FIG. 2, when the steering shaft 20 is rotated clockwise CW from the state where the worm 110 is located in the dead zone as shown in FIG. 2, the worm wheel 120 causes the worm wheel 120 to move in the right R axial direction. However, since the change in the position of the worm 110 in the axial direction is detected by the dead zone sensor 200, the control device 40 sets the rotation angle position of the worm 110 on the output shaft 71 of the electric motor 70 in the clockwise direction in the XX section. Instead of CW, the worm 110 is moved in the left L axial direction by the distance the worm 110 has moved in the right R axial direction. Similarly, when the steering shaft 20 is rotated in the counterclockwise direction CCW, the worm wheel 120 moves the worm 110 in the left L axial direction. However, the control device 40 uses the output shaft 71 of the electric motor 70 to rotate the angular position of the worm 110. Is changed to the counterclockwise CCW of the XX section, and the worm 110 is moved in the right R axial direction by the distance that the worm 110 has moved in the left L axial direction. As described above, the dead zone control is performed by the rotation angle of the worm 110 by the output shaft 71 of the electric motor 70 in a direction that cancels the movement of the worm 110 in the axial direction even when the worm wheel 120 rotates and the worm 110 moves in the axial direction. The position is changed and the worm 110 is controlled so as to be always in the dead zone.

  Furthermore, in the dead zone control, not only the steering shaft 20 can rotate without being obstructed by the steering assist mechanism 100, but also when the dead zone control and the steering assist control are switched, the elastic ring 140 attached to the worm 110 is provided. The position of the worm 110 in the dead zone in the dead zone according to the direction and magnitude of the steering torque TS is indicated by the solid line in FIG. 7 (2) dead zone control so that the bearings 160R and 160L can be smoothly switched without colliding with each other. Control is performed like the drawn target position curve C. First, when the steering torque TS is small and the steering direction is unknown, the gap GR = gap so that the axial target position of the worm 110 becomes the center of the range D in which the worm 110 can move in the axial direction. Set to GL. When the steering torque TS is outside the range F0 and the steering direction becomes clear, the axial position of the worm 110 is transmitted according to the magnitude of the steering torque TS in preparation for the subsequent steering assistance. Are gradually changed so that the gap GR or the gap GL on the side to be a portion to be connected becomes narrower. Even during this control, the sliding portion inside the steering assist mechanism 100 is changed to dynamic friction or static friction, so that it is difficult to perform highly accurate position control. The position control in the axial direction of 110 is a control with a large position deviation with respect to the target position curve C. However, the dead zone control does not require highly accurate position control, and if the worm 110 is located in the dead zone, steering is performed. The auxiliary mechanism 100 has little influence on the rotation of the steering shaft 20.

  Switching from the dead zone control to the steering assist control is performed at Bcw or Bccw where the steering torque TS is the maximum value of the dead zone control range F as shown in FIG. 7 (1) steering assist control. The connection of the power transmission by the mechanism to be connected is different from the method by the contact with the slip, although the speed is different like the friction clutch mechanism, the part where the power transmission is connected is not slipped, and the part where the power transmission is connected The power transmission is connected as soon as contact is made.However, the mechanisms that generate the dead band even during the dead band control are not attached to each other and always move according to the movement of the steering mechanism. In addition to the small change in the rotational speed around the axis center of the worm 110 when connecting and starting the steering assist, as described above, in the dead zone control, the steering torque TS In accordance with the size, the axial position of the worm 110 is gradually changed to narrow the gap GR or the gap GL on the side to which power transmission is connected. Therefore, when the elastic ring 140 contacts the bearings 160R and 160L, Since the impact is small and the steering assist torque TA is gradually increased while compressing the elastic ring 140, the power transmission is smoothly connected and the steering assist control is started.

  Similarly, in the switching from the steering assist control to the dead zone control, when the steering assist torque TA is decreased in accordance with the decrease in the steering torque TS, the elastic ring 140 gradually expands while weakening the reaction force, and the expansion ends and the elastic ring 140 ends. Is separated from the bearings 160R and 160L, the transmission of power is substantially cut off and the steering assist is finished. In this way, the steering assist ends smoothly, and then the dead zone control is started.

  Next, the outline of the control process in the calculating part 41 of this invention is demonstrated based on the flowchart of FIG.

  First, when power is turned on to the control device 40, the microprocessor of the calculation unit 41 initializes the input / output interface and the memory and starts control (step S0).

  Next, the microprocessor performs steering torque measurement (step S11) based on the steering torque signal VT from the torque sensor 30 and vehicle speed measurement (step S12) based on the vehicle speed signal VS from the vehicle speed sensor 50, and FIG. It is determined whether or not steering assist is necessary compared with the steering assist characteristic of the control (step S13).

  If steering assistance is required (YES in step S13), the drive unit 42 is instructed to output to the electric motor 70 the drive current 1 that generates the steering assist torque TA corresponding to the steering torque and the vehicle speed (step S14). After that, the process returns to the steering torque measurement (step S11).

  When steering assistance is unnecessary (NO in step S13), the worm position is measured (step S21) based on the dead zone signal VD from the dead zone sensor 200, and the current position of the worm 110 in the axial direction and the dead zone control in FIG. These control target positions are compared to determine whether correction is necessary (step S22). If correction is required (YES in step S22), the drive unit 42 is instructed to output to the motor 70 the drive current 1 that moves the position of the worm 110 in the axial direction to the target position in the dead zone (step S23). After that, the process returns to the steering torque measurement (step S11). If correction is not necessary (NO in step S22), the process returns to the steering torque measurement (step S11) without doing anything.

  As described above, the electric power steering apparatus according to the present embodiment switches between the steering assist control and the dead zone control as an infinite loop until the power is turned off.

  The present invention is not limited to the above-described embodiment, and can be implemented in variously modified forms within the scope of the matters described in the claims. For example, the mounting position of the steering assist mechanism 100 can be realized by various methods and positions, such as being mounted near the pinion gear 21 or the rack shaft 80 as shown in FIG. Further, the mechanism for transmitting the power of the electric motor for assisting the steering can be realized by various methods such as various types of gears, screws, and belts. In addition, the mechanism system that generates a dead band that almost cuts off the transmission of power is not limited to mechanical play, but a fixed mechanism such as using elastic materials for the mechanism parts that transmit power or providing a mechanism with slackness. This can be realized by various methods that substantially cut off the transmission of power in this state. Therefore, more accurate control is required, but the relationship between the length M1 and the length M2 in FIG. 2 in the present embodiment, such as increasing the thickness T0 of the elastic ring 140, is always the gap GR = Similarly, the dead band control range is defined as a range in which the reaction force of the elastic ring 140 is small when the worm 110 moves in the axial direction and compresses the elastic ring 140 with zero and the gap GL = 0. The effect is obtained. In addition, the dead zone control does not change the rotation angle position of the output shaft by driving the motor itself that assists the steering, but rotates the output shaft of the motor that assists the steering by the dedicated motor added for the dead zone control. It can also be realized by changing the angular position. The dead zone sensor can also be realized by various types of sensors such as a magnetic sensor and a differential transformer.

DESCRIPTION OF SYMBOLS 10 Steering wheel 20 Steering shaft 30 Torque sensor 40 Control apparatus 50 Vehicle speed sensor 60 Photo interrupter 70 Electric motor 71 Output shaft 100 Steering assist mechanism 110 Worm 120 Worm wheel 140 Elastic ring 160L, 160R Bearing 200 Dead zone sensor

Claims (3)

  A mechanism for transmitting the power of a motor for assisting steering to a steering mechanism includes a mechanism for generating a dead band that substantially interrupts transmission of the power, and a dead band sensor for detecting a state of the mechanism that generates the dead band. When the steering assist is not performed, the control device changes the rotation angle position of the output shaft of the electric motor using a signal from the dead zone sensor, so that the mechanism that generates the dead zone substantially interrupts transmission of the power. An electric power steering device characterized by controlling to maintain.   In the control in which the mechanism that generates the dead band maintains the state in which the transmission of the power is substantially interrupted, the control target state of the mechanism that generates the dead band is changed according to the direction and magnitude of the steering torque and the vehicle speed. The electric power steering apparatus according to claim 1.   A portion for connecting and blocking the transmission of the power of the mechanism that generates the dead zone is provided with an elastic member, and the elastic member is compressed to connect the transmission of the power to assist steering. The electric power steering apparatus according to claim 1.

Images