JP5131513B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of determining abnormality of a transmission mechanism. <P>SOLUTION: The electric power steering device is provided with a deceleration mechanism comprising a belt/pulley mechanism, a steering angle sensor for detecting a steering angle of a steering wheel, and a rotation speed sensor for detecting a rotation speed of a rotating shaft of an electric motor. The steering angle and the rotation speed are input to an ECU (step S1). The steering angle is differentiated by the ECU, and a steering speed is calculated. The ECU calculates a slip ratio of a belt from the rotation speed and the steering speed (step S2), and the slip ratio is compared with a prescribed threshold (step S3). When the slip ratio exceeds the threshold, it is determined that abnormality (slip of the belt) is generated in the deceleration mechanism (step S4), and a signal for informing a driver of the abnormality is output by an abnormality informing part (step S5). <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus.

Some electric power steering devices include a speed reduction mechanism. For example, Patent Document 1 below discloses an electric power steering apparatus including a speed reduction mechanism that includes a pair of pulleys and a belt stretched between the pair of pulleys. The output of the electric motor is transmitted to the steering mechanism via the speed reduction mechanism.
JP 2004-314770 A

However, when the output of the electric motor is transmitted to the steering mechanism via the speed reduction mechanism including the pair of pulleys and the belt, the belt may slip.
In addition, for example, when a speed reduction mechanism including a plurality of gears is used as the speed reduction mechanism, the gear may be chipped.
The present invention has been made based on such a background, and an object thereof is to provide an electric power steering apparatus capable of determining an abnormality in a transmission mechanism.

In order to achieve the above object, the present invention provides a sensor (24, 25) for detecting the steering angle of the steering member (4) or the steering torque input to the steering member, and the steering speed using the detected value of the sensor. Steering speed detecting means ( 53) for detecting, a steering assisting electric motor (19) having a rotating shaft (18), and a transmission mechanism (21, 21a) for transmitting output rotation of the electric motor to the steering shaft (12) And a rotation speed detection means (23) for detecting the rotation speed of the rotation shaft of the electric motor, and a comparison between the steering speed detected by the steering speed detection means and the rotation speed detected by the rotation speed detection means, An electric power steering apparatus (1) comprising: a control means (22) for determining abnormality of the transmission mechanism.

According to the present invention, it is possible to determine the abnormality of the transmission mechanism based on the comparison between the steering speed and the rotation speed. Specifically, when the rotational speed is larger than a predetermined value obtained from the steering speed, it can be determined that there is an abnormality.
Further, in the present invention, there are cases where the abnormality notifying means (27) is provided, and the control means may output a signal for notifying the abnormality notifying means of the abnormality when it is determined to be abnormal. In this case, the control means outputs a signal for informing the abnormality so that the abnormality can be notified to the driver by the abnormality informing means.

In the present invention, the control means may reduce the output of the electric motor to a predetermined value (including zero) when it is determined as abnormal. In this case, by lowering the output of the electric motor, it is possible to give a sense of incongruity to the driver's steering and notify the abnormality.
In the present invention, the transmission mechanism may include a pair of toothed pulleys (35, 36) and a toothed belt (37) connecting between the pair of toothed pulleys. In this case, an abnormality such as slippage of the toothed belt can be determined based on a comparison between the steering speed and the rotational speed.

In the present invention, the transmission mechanism may include a pair of gears (55, 56) that mesh with each other. In this case, an abnormality such as a missing tooth of each gear can be determined based on a comparison between the steering speed and the rotational speed.
In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention.
Referring to FIG. 1, an electric power steering apparatus 1 according to this embodiment is a so-called rack assist type electric power steering apparatus, and includes a steering mechanism 2 including a rack and pinion mechanism, and a steering assist force ( A steering assist mechanism 3 for providing an assist torque.

  The steering mechanism 2 includes a steering shaft 5 connected to a steering wheel 4 as a steering member, an intermediate shaft 7 connected to the steering shaft 5 via a universal joint 6, and an intermediate shaft 7 connected to the intermediate shaft 7 via a universal joint 8. The pinion shaft 9 has a rack 11 that meshes with a pinion 10 provided at the tip of the pinion shaft 9 and has a rack shaft 12 as a steering shaft extending in the left-right direction of the vehicle.

  Tie rods 13 are coupled to both ends of the rack shaft 12, and each tie rod 13 is coupled to a steering wheel 14 via a knuckle arm (not shown). When the steering wheel 4 is operated and the steering shaft 5 rotates, this rotation is converted into an axial movement of the rack shaft 12 along the left-right direction of the vehicle by the pinion 10 and the rack 11. Thereby, steering of the steering wheel 14 is achieved.

The pinion shaft 9 is divided into an input shaft 15 and an output shaft 16. These input / output shafts 15 and 16 are connected to each other on the same axis via a torsion bar 17.
The steering assist mechanism 3 includes an electric motor 19 having a rotation shaft 18 (see FIG. 2), a conversion mechanism 20 for converting rotation of the rotation shaft 18 into axial movement of the rack shaft 12, and rotation of the rotation shaft 18. A reduction mechanism 21 as a transmission mechanism for decelerating and transmitting to the conversion mechanism 20 is provided.

The electric motor 19 is controlled by an ECU 22 (Electronic Control Unit). The rotational speed of the rotary shaft 18 of the electric motor 19 is detected by a rotational speed sensor 23 such as a resolver bar built in the electric motor 19.
Further, the electric power steering apparatus 1 includes a steering angle sensor 24 that detects the steering angle of the steering wheel 4 and a torque sensor that detects a steering torque based on a relative rotational displacement amount between the input and output shafts 15 and 16 via the torsion bar 17. 25 and a vehicle speed sensor 26 for detecting the speed of the vehicle. The steering angle sensor 24 and the torque sensor 25 are arranged around the pinion shaft 9. Values detected by these sensors 24, 25, and 26 including the rotational speed sensor 23 are input to the ECU 22.

  The ECU 22 determines an assist torque to be applied to the steering mechanism 2 based on the input steering torque, vehicle speed, and the like, and controls the electric motor 19 based on the assist torque. Further, the ECU 22 determines an abnormality of the vehicle based on various input values, and notifies the driver of the abnormality by the abnormality notifying unit 27 connected to the ECU 22. The abnormality notification unit 27 can notify the driver of the abnormality by, for example, lighting a buzzer or an abnormality notification lamp.

  FIG. 2 is an enlarged view of a main part of the steering assist mechanism 3. Referring to FIG. 2, the electric motor 19 includes the rotation shaft 18, the rotation speed sensor 23, and a motor housing 28, and the rotation shaft 18 is disposed so as to be parallel to the rack shaft 12. . The motor housing 28 is fixed to a cylindrical second housing 30 that accommodates the rack shaft 12 via a cylindrical first housing 29. An input shaft 32 is connected to the rotary shaft 18 via a joint 31. The input shaft 32 is rotatably held by the first housing 29 via bearings 33 and 34 disposed at each end thereof.

  The speed reduction mechanism 21 is a speed reduction mechanism including a belt / pulley mechanism, and includes a toothed input pulley 35, a toothed output pulley 36 having a larger diameter than the input pulley 35, and input / output pulleys 35, 36. And a toothed belt 37 stretched over. The input pulley 35 is connected to an intermediate portion in the axial direction of the input shaft 32 so as to be integrally rotatable. The output pulley 36 is disposed so as to surround the rack shaft 12 as a steering shaft.

  The conversion mechanism 20 is a conversion mechanism including a ball screw mechanism, and includes a ball nut 38 as a rotating cylinder surrounding the rack shaft 12. The ball nut 38 is screwed into a ball screw groove 39 formed on the outer periphery of the rack shaft 12 via a ball 40. The ball nut 38 is rotatably supported by the second housing 30 via a bearing 41. The output pulley 36 is fitted on the outer periphery of the ball nut 38 so as to be integrally rotatable. Specifically, the output pulley 36 is sandwiched between a step portion 42 formed on the outer periphery of the ball nut 38 and a fixing screw 44 screwed into a screw portion 43 formed on the outer periphery of the ball nut 38. It is fixed to.

  When the rotating shaft 18 of the electric motor 19 rotates, the input shaft 32 and the input pulley 35 rotate accordingly. The rotation of the input shaft 32 and the input pulley 35 is transmitted to the output pulley 36 through the belt 37, and the output pulley 36 and the ball nut 38 rotate at a lower speed than the rotation of the input shaft 32 and the input pulley 35. The rotation of the ball nut 38 is converted into an axial movement of the rack shaft 12 via the ball 40. Thereby, steering of the steering wheel 14 is assisted.

FIG. 3 is a block diagram for explaining an example of the electrical configuration of the electric power steering apparatus 1. FIG. 4 is a flowchart showing the flow of processing in one example of the electrical configuration, and FIG. 5 is a diagram showing the relationship between the steering speed and the reference rotation speed.
Referring to FIG. 3, the ECU 22 determines an assist torque using a control map stored in advance based on the steering torque, the vehicle speed, and the like, and an electric motor 19 based on the determined assist torque. A target current determining unit 46 for determining a target value of the supply current to the output, an output current control unit 47 for controlling the output current so that the supply current becomes a target value, and PWM (Pulse Width Modulation) control of the electric motor 19, for example. And a motor current detection circuit 49 for detecting a supply current.

The steering torque detected by the torque sensor 25 and the vehicle speed detected by the vehicle speed sensor 26 are input to the assist torque determination unit 45. The current value detected by the motor current detection circuit 49 is fed back and controlled so that the supplied current becomes the target value.
The ECU 22 calculates the slip ratio of the belt 37 based on the comparison between the steering speed of the steering wheel 4 and the rotational speed of the rotating shaft 18 of the electric motor 19, and the slip ratio calculating section 50 calculates the slip ratio. An abnormality determination unit 51 that determines an abnormality of the transmission mechanism (abnormal slip of the belt 37) based on a comparison between the slip ratio thus made and a predetermined threshold, and an abnormality notification unit 27 when the abnormality determination unit 51 determines that an abnormality has occurred. And a signal output unit 52 for outputting a signal for notifying the abnormality.

  The steering angle detected by the steering angle sensor 24 is input to a steering speed calculation unit 53 provided in the ECU 22. The steering speed calculator 53 calculates (differentiates) the input steering angle to obtain the steering speed. Then, the steering speed obtained by the steering speed calculator 53 is input to the slip ratio calculator 50. Further, the rotational speed of the rotary shaft 18 detected by the motor rotational speed sensor 23 is input to the slip ratio calculation unit 50.

  Referring to FIGS. 4 and 5, ECU 22 performs the process shown in the flowchart of FIG. 4 at a predetermined cycle. That is, in step S1, the steering angle of the steering wheel 4 and the rotational speed of the rotary shaft 18 are input. Next, in step S2, the steering angle A is differentiated to obtain the steering speed A, and the relationship between the steering speed and the reference rotational speed of the rotary shaft 18 is obtained using a map (see FIG. 5) stored in advance. A reference rotational speed C corresponding to the steering speed A is obtained. A difference (BC) between the reference rotation speed C and the input rotation speed B is obtained, and a slip ratio D corresponding to the ratio of the difference (BC) to the reference rotation speed C is obtained. That is, D = (BC) / C.

  Next, it is determined whether or not the determined slip ratio D exceeds a predetermined threshold D1 (step S3). When the determined slip ratio D exceeds the threshold D1 (D> D1), It is determined that there is an abnormality (step S4). In step S5, a signal for informing the abnormality notifying unit 27 of the abnormality is output. On the other hand, when the slip ratio D is smaller than the threshold value D1 in step S3 (D <D1), the process returns to step S2 again, and the slip ratio is calculated based on the steering angle and the rotational speed input at a predetermined cycle. To do.

  As described above, in the present embodiment, the abnormality of the speed reduction mechanism 21 is determined based on the comparison between the steering speed of the steering wheel 4 and the rotation speed of the rotating shaft 18 of the electric motor 19. Can notify the driver of the abnormality. As a result, it is possible to notify the driver of the abnormality of the speed reduction mechanism 21 at an early stage and prompt the speed reduction mechanism 21 to return to a normal state.

Further, the abnormality can be determined by the existing configuration (the electric motor 19, the ECU 22, and the steering angle sensor 24) without providing a new configuration for determining the abnormality of the speed reduction mechanism 21.
FIG. 6 is a block diagram for explaining another example of the electrical configuration of the electric power steering apparatus 1. FIG. 7 is a flowchart showing the flow of processing in another example of the electrical configuration. 6 and FIG. 7, the same components as those shown in FIG. 3 and FIG. 4 described above are denoted by the same reference numerals as those in FIG. 3 and FIG.

  The electrical configuration in FIG. 6 is mainly different from the electrical configuration in FIG. 3 in that the ECU 22 is provided with a torque correction unit 54, and the assist torque determined by the assist torque determination unit 45 is the torque correction unit. 54 to be input. When the abnormality determination unit 51 determines that there is an abnormality, a signal for correcting and decreasing the assist torque is input from the abnormality determination unit 51 to the torque correction unit 54, and the corrected assist torque is the target current determination unit 46. Is input. If the abnormality determination unit 51 does not determine that there is an abnormality, the assist torque input to the torque correction unit 54 is input to the target current determination unit 46 without being corrected.

In the ECU 22, the process shown in the flowchart of FIG. 7 is performed at a predetermined cycle. That is, in step S10, the steering torque and the vehicle speed are input to the assist torque determination unit 45. Next, in step S11, assist torque is determined based on the input steering torque, vehicle speed, and the like.
On the other hand, the steering speed and the rotational speed are input to the slip ratio calculation unit 50 in step S12, and the slip ratio is calculated in step S13. In step S14, it is determined whether or not the calculated slip ratio exceeds a threshold value.

  When the slip ratio calculated in step S14 is smaller than the threshold (in the case of No), in step S15, the assist torque determined in step S11 is input to the target current determination unit 46, and the target current is determined. . In step 16, the electric motor 19 is driven and controlled, and the assist torque determined in step S <b> 11 is applied to the steering mechanism 2.

  On the other hand, when the slip ratio calculated in step S14 exceeds the threshold value (in the case of Yes), in step S17, the assist torque determined in step S11 is reduced to a predetermined value (including zero). Next, in step 15, the assist torque corrected in step S17 is input to the target current determination unit 46, and the target current is determined. In step 16, the electric motor 19 is driven and controlled, and the assist torque corrected in step S <b> 17 is applied to the steering mechanism 2.

  At this time, the assist torque applied to the steering mechanism 2 is smaller than the assist torque determined in step S11. Therefore, the driver feels uncomfortable in steering. That is, when the abnormality determination unit 51 determines that an abnormality has occurred in the speed reduction mechanism 21, the assist torque is decreased from the original value to cause the driver to feel uncomfortable, thereby driving the abnormality. Can tell.

  The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims. For example, in the above-described embodiment, the example in which the steering angle of the steering wheel 4 is detected by the steering angle sensor 24 has been described. However, as described above, based on the relative rotational displacement amount between the input / output shafts 15 and 16. In the case of the torque sensor 25 that detects the steering torque, the steering speed of the steering wheel 4 may be obtained using a signal related to the steering angle output from the torque sensor 25 as shown in FIG.

  In the above-described embodiment, the case where the speed reduction mechanism 21 is composed of a belt / pulley mechanism has been described. However, as shown in FIG. 9, the speed reduction mechanism 21a including a pair of gears 55 and 56 that mesh with each other is used. Also good. In this case, based on a comparison between the steering speed of the steering wheel 4 and the rotational speed of the rotary shaft 18 of the electric motor 19, the ECU 22 determines an abnormality such as a missing tooth of the gears 55 and 56, and this abnormality is determined by the driver. Can tell.

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 principal part enlarged view of a steering assist mechanism. It is a block diagram for demonstrating an example of the electrical constitution of an electric power steering device. It is a flowchart which shows the flow of the process in an example of the said electrical structure. It is a figure which shows the relationship between a steering speed and a reference | standard rotation speed. It is a block diagram for demonstrating the other example of the electric structure of an electric power steering apparatus. It is a flowchart which shows the flow of the process in the other example of the said electric structure. It is a block diagram for demonstrating another example of the electric constitution of an electric power steering device. It is a principal part enlarged view of the steering assist mechanism which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 12 ... Rack axis | shaft (steering axis), 18 ... Rotation axis, 19 ... Electric motor, 21, 21a ... Deceleration mechanism (transmission mechanism), 23 ... Rotational speed sensor (rotational speed detection means) 24 ... steering angle sensor ( sensor ) 25 ... torque sensor ( sensor ) 27 ... abnormality notification unit (abnormality notification means) 35 ... input Pulley (toothed pulley), 36 ... output pulley (toothed pulley), 37 ... belt (toothed belt), 53 ... steering speed calculation unit (steering speed detecting means), 55 ... gear 56 ... gears

Claims (5)

A sensor for detecting a steering angle of the steering member or a steering torque input to the steering member;
Steering speed detection means for detecting the steering speed using the detection value of the sensor ;
An electric motor for steering assistance having a rotating shaft;
A transmission mechanism for transmitting the output rotation of the electric motor to the steering shaft;
A rotational speed detecting means for detecting the rotational speed of the rotating shaft of the electric motor;
An electric power steering apparatus comprising: control means for determining abnormality of the transmission mechanism based on a comparison between the steering speed detected by the steering speed detecting means and the rotational speed detected by the rotational speed detecting means.   2. The electric power steering apparatus according to claim 1, further comprising an abnormality notifying unit, wherein the control unit outputs a signal for notifying the abnormality notifying unit of the abnormality when it is determined to be abnormal.   3. The electric power steering apparatus according to claim 1, wherein the control means reduces the output of the electric motor to a predetermined value (including zero) when it is determined as abnormal. 4. The electric power steering apparatus according to claim 1, wherein the transmission mechanism includes a pair of toothed pulleys and a toothed belt connecting the pair of toothed pulleys. The electric power steering apparatus according to claim 1, wherein the transmission mechanism includes a pair of gears that mesh with each other.

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