JP2005170185A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize a motor driving circuit, and to reduce the cost thereof by eliminating necessity of providing a fail safe relay in an electric power steering device provided with two motors. <P>SOLUTION: In the electric power steering device having a first and a second motors Ma and Mb arranged on a steering torque transmitting route, a first motor driving circuit Ca is provided with a first fuse 47a between the firt motor Ma, and a second motor driving circuit Cb is provided with a second fuse 47b between the second motor Mb. When the first motor driving circuit Ca or the second motor driving circuit Cb is failed, the first fuse 47a or the second fuse 47b corresponding to the failed circuit is fused for disconnection to prevent inappropriate operation of the motor connected to the failed motor driving circuit. Since a fuse is compact and price thereof is low in comparison with a fail safe relay and special wiring for disconnection thereof is unnecessary, the first and the second motor driving circuits Ca and Cb can be miniaturized and the cost thereof can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, first and second motors are arranged on a steering torque transmission path for transmitting steering torque input to a steering handle to wheels, and the first and second motors are selectively driven to steer the wheels. The present invention relates to an electric power steering apparatus.

In the electric power steering device that generates assist torque in the motor according to the steering torque input to the steering wheel by the driver and assists the driver's steering operation with the assist torque, the assist by the motor is unnecessary because the steering torque is small. It is known from Patent Document 1 below that a switch (fail-safe relay) provided in a motor drive circuit is opened at a certain time to prevent the motor from operating inappropriately.
Japanese Patent Laid-Open No. 9-30433

  By the way, the fail safe relay has a large casing for housing the relay main body, and requires a signal line for turning on / off the relay main body, so the motor drive circuit including the fail safe relay is enlarged. There are problems that layout becomes difficult and causes cost increase.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to reduce the size and cost of a motor drive circuit by eliminating the need for a fail-safe relay of an electric power steering apparatus including two motors. .

  In order to achieve the above object, according to the first aspect of the present invention, the first and second motors arranged on the steering torque transmission path for transmitting the steering torque input to the steering handle to the wheels, A first motor drive circuit that has a plurality of switching elements to drive the first motor, a second motor drive circuit that has a plurality of switching elements to drive the second motor, and a steering torque input to the steering handle And a control means for controlling the driving of the first and second motors via the first and second motor drive circuits based on the steering torque detected by the steering torque sensor. In the apparatus, the first motor drive circuit includes a first fuse between the first motor and the second motor drive circuit includes a second fuse between the second motor. An electric power steering apparatus characterized by comprising is proposed.

  According to the invention described in claim 2, in addition to the configuration of claim 1, when the control means detects an abnormality in one of the first and second motor drive circuits, the abnormality is detected. An electric power steering apparatus is proposed in which the current flowing through the fuse of the motor drive circuit is increased to blow the fuse.

  According to the invention described in claim 3, in addition to the configuration of claim 2, an electric power steering apparatus is proposed in which the first and second motors are brushless motors.

  According to a fourth aspect of the invention, in addition to the configuration of the second or third aspect, the one motor drive circuit drives one motor in the first direction and balances the drive force. As described above, the electric power steering is characterized in that the current supplied to the one motor is increased and the fuse connected to the motor is blown in a state where the other motor driving circuit drives the other motor in the second direction. A device is proposed.

  According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect, an electric power steering device is proposed in which the fuse is blown when the vehicle is stopped.

  The first to fourth switching elements 46a to 46d of the embodiment correspond to the switching elements of the present invention, and the electronic control unit U of the embodiment corresponds to the control means of the present invention.

  According to the configuration of the first aspect, in the electric power steering apparatus in which the first and second motors are arranged on the steering torque transmission path, the first motor drive circuit includes the first fuse between the first motor and the first motor. Since the two-motor drive circuit includes the second fuse between the second motor and the second motor drive circuit, the first and second fuses corresponding to the failure of the first motor drive circuit or the second motor drive circuit are cut off. The motor connected to the failed motor drive circuit can be prevented from performing an inappropriate operation, and the function of the electric power steering apparatus can be maintained with a normal motor drive circuit. The fuse is smaller and cheaper than the fail-safe relay, and does not require special wiring to cut it, so that the first and second motor drive circuits can be reduced in size and cost. Can do.

  According to the configuration of the second aspect, since the current flowing through the fuse of the motor drive circuit in which the control means has become abnormal is increased, the fuse can be blown without the need for special wiring or a mechanical cutting device. .

  According to the configuration of the third aspect, since the first and second motors are brushless motors, it is possible to perform control without generating torque while energizing the motors, and to prevent the wheels from being steered by the motor torque. The fuse can be surely blown.

  According to the configuration of the fourth aspect of the present invention, the motor drive is performed from the state in which the motor on the side where the motor drive circuit has failed and the motor on the side where the motor drive circuit is normal are driven in opposite directions to balance the drive force of both motors. Since the current supplied to the motor on the side of the circuit failure is increased and the fuse connected to the motor is blown, the fuse can be easily blown only by slightly increasing the current from the balanced state.

  According to the configuration of the fifth aspect, since the fuse is blown when the vehicle is stopped, even if the wheels are steered by the blow of the fuse, the vehicle does not turn and the driver's uncomfortable feeling can be solved. it can.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on examples of the present invention shown in the accompanying drawings.

  1 to 8 show a first embodiment of the present invention. FIG. 1 is an overall perspective view of an electric power steering apparatus, FIG. 2 is an enlarged sectional view taken along line 2-2 of FIG. 1, and FIG. FIG. 4 is an enlarged sectional view taken along line 4-4 of FIG. 1, FIG. 5 is a diagram showing a motor drive circuit, FIG. 6 is a diagram for explaining the operation during normal rotation and reverse rotation of the motor, FIG. FIG. 8 is an operation explanatory diagram when the first switching element has an ON failure, and FIG. 8 is a flowchart for explaining the fuse blowing operation.

  As shown in FIG. 1, the upper steering shaft 12 that rotates integrally with the steering handle 11 is a pinion that protrudes upward from the first reduction gear 16 a via the upper universal joint 13, the lower steering shaft 14, and the lower universal joint 15. Connected to the shaft 17. Tie rods 19 and 19 projecting from the left and right ends of the steering gear box 18 connected to the lower end of the first reduction gear 16a are connected to knuckles (not shown) of the left and right wheels WL and WR. A first motor Ma is supported by the first speed reducer 16a, and an electronic control unit to which a signal from a steering torque sensor St housed in the first speed reducer 16a is input as the operation of the first motor Ma. Controlled by U. The steering gear box 18 is provided with a second reduction gear 16b, and the second motor Mb supported by the second reduction gear 16b is also controlled by the electronic control unit U.

  As shown in FIGS. 2 and 3, the first reduction gear 16a includes a lower case 21 integrated with the steering gear box 18, an intermediate case 23 coupled to the upper surface thereof with bolts 22 ..., and bolts 24 ... on the upper surface thereof. The pinion shaft 17 is rotatably supported by ball bearings 26 and 27 on the steering gear box 18 and the upper case 25. A pinion 28 provided at the lower end of the pinion shaft 17 meshes with a rack 30 provided on a rack bar 29 that is supported in the steering gear box 18 so as to be movable left and right. A pressing member 31 is slidably accommodated in a through hole 18 a formed in the steering gear box 18, and the pressing member 31 is attached to the rack bar 29 by a spring 33 disposed between the nut member 32 closing the through hole 18 a. By biasing toward the back, the rack 30 can be properly meshed with the pinion 28 while suppressing the deflection of the rack bar 29.

  A rotation shaft 34 of the first motor Ma extending inside the first reduction gear 16a is rotatably supported by the lower case 21 by a pair of ball bearings 35 and 36. A worm 37 provided on the rotation shaft 34 of the first motor Ma meshes with a worm wheel 38 fixed to the pinion shaft 17. The first reduction gear 16a and the first motor Ma constitute first assist torque input means 40a.

  As shown in FIG. 4, the structure of the second speed reducer 16b is similar to the structure of the first speed reducer 16a, but the second speed reducer 16b does not include the upper case 25, and the steering gear box 18 and the middle A short pinion shaft 17 is supported on the case 23 via ball bearings 26 and 27. A pinion 28 provided at the lower end of the pinion shaft 17 meshes with the rack 30 of the rack bar 29. The other structure of the second assist torque input means 40b composed of the second reduction gear 16b and the second motor Mb is the same as that of the first assist torque input means 40a.

  Therefore, when the first and second motors Ma and Mb are driven, the first and second reduction gears 16a are connected via the worm wheels 38 and 38 meshing with the worms 37 and 37 provided on the rotary shafts 34 and 34, respectively. 16b, the pinion shafts 17 and 17 rotate, and the common rack 30 meshing with the pinions 28 and 28 is driven, so that the steering torque applied to the steering handle 11 by the driver is applied to the first and second motors Ma and Mb. Assisted by.

  Next, the structure of the first motor drive circuit Ca that drives the first motor Ma according to a command from the electronic control unit U will be described with reference to FIG. The structure of the second motor drive circuit Cb that drives the second motor Mb is the same as the structure of the first motor drive circuit Ca.

  The first motor drive circuit Ca includes an H-bridge circuit 41, and the high-voltage terminal TH is connected to a positive pole 45a of an in-vehicle 12V battery 45 through a shunt resistor 42, a power relay 43, and a choke coil 44. The low voltage terminal TL is grounded and connected to the negative electrode 45 b of the battery 45. The first output terminal TM1 and the second output terminal TM2 of the H bridge circuit 41 are connected to the first motor Ma, the low voltage terminal TL and the first output terminal TM1 are connected by the first switching element 46a, and the low voltage terminal TL and The second output terminal TM2 is connected by the second switching element 46b, the high voltage terminal TH and the first output terminal TM1 are connected by the third switching element 46c, and the high voltage terminal TH and the second output terminal TM2 are connected by the fourth switching element 46d. Connected. The first to fourth switching elements 46a to 46d are configured by, for example, field effect transistors (FETs). A first fuse 47a (second fuse 47b) is disposed between one of the first output terminal TM1 and the second output terminal TM2 (first output terminal TM1 in the embodiment) and the first motor Ma.

  The power relay 43 that turns ON / OFF the supply of power from the battery 45 to the H-bridge circuit 41 is connected to the relay drive circuit 48 controlled by the electronic control unit U and turned ON / OFF.

  The shunt resistor 42 disposed between the power relay 43 and the H bridge circuit 41 is connected to a motor current detection circuit 49, and the motor current detection circuit 49 connected to the electronic control unit U has a potential difference between both ends of the shunt resistor 42. And the current supplied from the battery 45 to the H-bridge circuit 41 based on the resistance value of the shunt resistor 42.

  The potential VMN of the first output terminal TM1 and the potential VMP of the second output terminal TM2, that is, the potentials of both terminals of the first motor Ma are detected by the motor terminal voltage detection circuit 50 connected to the electronic control unit U. When the first motor Ma is not operating, the potential VMN of the first output terminal TM1 and the potential VMP of the second output terminal TM2 are pulled up to a pull-up voltage lower than the battery voltage.

  The first to fourth switching elements 46 a to 46 d of the H-bridge circuit 41 are duty-controlled by a switching element driving circuit 51 connected to the electronic control unit U. That is, as shown in FIG. 6A, when the first switching element 46a and the fourth switching element 46d at the diagonal positions are turned on, the first output terminal TM1 is connected to the low voltage terminal TL and becomes 0V. When the 2 output terminal TM2 is connected to the high voltage terminal TH and becomes 12V, the first motor Ma rotates forward. At this time, the current flowing through the first motor Ma can be controlled by controlling the duty ratio of one of the first switching element 46a and the fourth switching element 46d.

  As shown in FIG. 6B, when the second switching element 46b and the third switching element 46c at other diagonal positions are turned on, the second output terminal TM2 is connected to the low voltage terminal TL and becomes 0V. When the first output terminal TM1 is connected to the high voltage terminal TH and becomes 12V, the first motor Ma is reversely rotated. At this time, the current flowing through the first motor Ma can be controlled by controlling the duty ratio of one of the second switching element 46b and the third switching element 46c.

  The second motor Mb is also controlled in the same manner as the first motor Ma by the second motor drive circuit Cb. Of the first and second motors Ma and Mb, the first motor Ma is used as a main motor, and the second motor Mb backs up the first motor Ma as a sub motor when the first motor drive circuit Ca fails. The relationship between the main motor and the sub motor may be switched every time a predetermined time elapses or every time the ignition switch is turned on, so that the durability of the first and second motors Ma and Mb is made uniform. Can be

  Next, the operation of the embodiment of the present invention having the above configuration will be described.

  For example, when the first motor Ma is the main motor, it is assumed that the first switching element 46a has an ON failure as shown in FIG. In this state, as shown in FIG. 7B, when an ON command is output from the switching element drive circuit 51 to the second and third switching elements 46b and 46c to drive the first motor Ma, the first output terminal TM1. The second output terminal TM2 is short-circuited via the low-voltage terminal TL so that the first motor Ma cannot be rotated, and even if an attempt is made to drive the first motor Ma by an external force, the regenerative braking force acts to rotate. This makes it difficult to perform the function of the electric power steering device.

  In such a case, when the electronic control unit U detects a failure of the first motor drive circuit Ca, the second motor Mb is operated as a main motor instead of the first motor Ma in response to a command from the electronic control unit U. Although the function of the power steering device is maintained, when the second motor Mb is operated to perform steering, the first motor Ma is forcibly rotated from the outside by the driving force to generate a regenerative braking force. The regenerative braking force acts so as to resist the driving force of the second motor Mb. Therefore, the electronic control unit U makes the current supplied to the second motor Mb larger than the normal current, and generates a driving force that can cancel the regenerative braking force generated by the first motor Ma. Similar steering can be continued.

  When the vehicle eventually stops while continuing the steering by the electric power steering device in this way, the first motor Ma is blown by blowing the first fuse 47a connected to the first motor Ma in response to a command from the electronic control unit U. The regenerative braking force cannot be generated, and the steering by the electric power steering device can be continued only by driving the second motor Mb with a normal current. The reason why the first fuse 47a is blown when the vehicle is stopped is to prevent the driver from being unexpectedly steered by the driving force of the second motor Mb when the first fuse 47a is blown. .

  Next, a procedure for fusing the first fuse 47a connected to the first motor Ma after the vehicle stops will be described.

  For example, as shown in FIG. 7A, when the first switching element 46a has an ON failure, the first and fourth switching elements are switched from the electronic control unit U so as not to be affected by the ON failure. By outputting an ON command to 46a and 46d, the first motor Ma is driven in the first direction. At the same time, the second motor Mb is driven in the second direction by outputting an ON command from the electronic control unit U to the second and third switching elements 46b and 46c of the second motor drive circuit Cb, and the first motor The steering torque by Ma and the steering torque by the second motor Mb are balanced. In this state, if the current supplied to the first motor Ma is instantaneously increased, the first fuse 47a is blown by the current exceeding the limit value, and the first motor Ma can no longer generate the regenerative braking force, so that there is almost no load. Thus, the motor is driven from the outside, and the steering by the second motor Mb is not hindered.

  If the first fuse 47a is blown by blowing a large current at a stroke from a state in which no current flows to the first motor Ma, a very large current is required, making it difficult to blow the first fuse 47a. In a state where a predetermined amount of current is passed through the first motor Ma and the second motor Mb in advance to cancel the steering torque generated by each, the current of the first motor Ma is instantaneously increased to Since fusing, the first fuse 47a can be easily blown by reducing the amount of increase in current required at that time.

  As described above, when the first motor drive circuit Ca that drives the first motor Ma fails, the first fuse 47a is blown and the regenerative braking force of the first motor Ma inhibits the function of the electric power steering device. Therefore, a large and heavy fail-safe relay that has been necessary in the past and a signal line for turning on / off the fail-safe relay are not required, which can contribute to space and cost savings. In addition, in order to cut the fuse, it is only necessary to increase the current flowing therethrough and blow it, so that no special wiring or mechanical cutting device is required, and further space and cost can be saved.

  Next, the above-described fuse blowing operation will be described in more detail based on the flowchart of FIG.

  First, when there is a fuse blow request in step S1, by energizing the failure side motor by the failure side motor drive circuit in step S2, and by energizing the normal side motor by the normal side motor drive circuit in step S3, The steering torque output from the motor on the failure side and the motor on the normal side is balanced.

  In subsequent step S4, the duty ratio of the motor drive circuit on the failure side is increased from Duty to Duty ′ for a predetermined time Δt. As a result, if the current to the motor on the failure side does not become zero in step S5, it is determined that the fuse has not yet blown, and in step S6, Duty ′ is increased to Duty ′ + α. This operation is repeated until the fuse is blown. If the current to the faulty motor becomes zero in step S5, that is, if the fuse blows, the faulty motor drive circuit is stopped in step S7, and normal in step S8. The motor drive circuit on the side is stopped.

  In this way, in the state where the failure side motor and the normal side motor are driven in the opposite directions to cancel the steering torque, the duty ratio of the failure side motor is temporarily increased to blow the fuse. In addition to preventing the wheels from being steered at the time of fusing, the fuse can be blown in a short time by increasing the duty ratio momentarily. In addition, since the duty ratio is increased stepwise until the fuse is blown, it is possible to blow the fuse with the minimum necessary current.

  Next, a second embodiment of the present invention will be described.

  The second embodiment employs a three-phase brushless motor as the first and second motors Ma and Mb. Since the brushless motor can be energized so that no torque is generated even if a current is supplied, the fuse is blown if the first and second motors Ma and Mb are driven in the reverse direction to prevent the wheels from turning. There is no need, and only the motor in which an abnormality has occurred can be energized to blow the fuse.

  FIG. 9 (A) shows a waveform during normal energization of the three-phase AC current supplied to the three-phase brushless motor. The torque current Iq = constant and the field current Id = 0, and the motor generates a predetermined torque. To do. On the other hand, FIG. 9B shows a waveform at the time of energization of torque 0. By delaying the phase of each phase by 90 ° compared to the waveform at the time of normal energization, torque current Iq = 0, field current Id = The motor becomes constant and no torque is generated. For example, in the case of energization at position A in FIG. 9B, the V-phase current flowing through the V-phase coil and the W-phase current flowing through the W-phase coil merge and flow into the U-phase coil. Can be melted.

  As described above, when a brushless motor is used, it is possible to energize without generating torque. Therefore, if the first and second motors Ma and Mb are driven in the reverse direction to prevent the wheels from turning, it is necessary to blow the fuse. Thus, even when only a single motor is provided, it is possible to blow the fuse while preventing the wheel from turning.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

  For example, the first to fourth switching elements 46a to 46d are not limited to field effect transistors (FETs) and may be other types of switching elements such as insulated gate bipolar transistors (IGBTs).

  The positions at which the first and second motors Ma and Mb are arranged are not limited to the embodiment, and can be arranged at arbitrary positions on the steering torque transmission path from the steering handle 11 to the wheels WL and WR.

Overall perspective view of an electric power steering apparatus according to an embodiment 2-2 line enlarged sectional view of FIG. 3-3 sectional view of FIG. 4-4 enlarged cross-sectional view of FIG. Diagram showing motor drive circuit Action diagram for forward and reverse rotation of motor Action explanatory diagram when the first switching element has an ON failure Flowchart explaining the action of fuse fusing The figure which shows the waveform of the energization current to the three-phase brushless motor which concerns on 2nd Example

Explanation of symbols

11 Steering handle 46a First switching element (switching element)
46b Second switching element (switching element)
46c 3rd switching element (switching element)
46d Fourth switching element (switching element)
47a first fuse 47b second fuse Ca first motor drive circuit Cb second motor drive circuit Ma first motor Mb second motor St steering torque sensor U electronic control unit (control means)
WL wheel WR wheel

Claims (5)

First and second motors (Ma, Mb) disposed on a steering torque transmission path for transmitting the steering torque input to the steering handle (11) to the wheels (WL, WR);
A first motor driving circuit (Ca) having a plurality of switching elements (46a to 46d) and driving the first motor (Ma);
A second motor drive circuit (Cb) having a plurality of switching elements (46a to 46d) and driving the second motor (Mb);
A steering torque sensor (St) for detecting a steering torque input to the steering handle (11);
Control means (U) for controlling the driving of the first and second motors (Ma, Mb) via the first and second motor drive circuits (Ca, Cb) based on the steering torque detected by the steering torque sensor (St). )When,
In the electric power steering apparatus with
The first motor drive circuit (Ca) includes a first fuse (47a) between the first motor (Ma) and the second motor drive circuit (Cb) includes a second fuse between the second motor (Mb). An electric power steering apparatus comprising a fuse (47b).   When the control means (U) detects an abnormality in one of the first and second motor drive circuits (Ca, Cb), the control means (U) increases the current flowing through the fuse of the motor drive circuit in which the abnormality has occurred. The electric power steering apparatus according to claim 1, wherein the fuse is blown out.   The electric power steering apparatus according to claim 2, wherein the first and second motors (Ma, Mb) are brushless motors.   The one motor driving circuit drives one motor in the first direction, and the other motor driving circuit drives the other motor in the second direction so as to balance the driving force. 4. The electric power steering apparatus according to claim 2, wherein a current supplied to the motor is increased and blown to a fuse connected to the motor. 5.   The electric power steering apparatus according to claim 4, wherein the fuse is blown when the vehicle is stopped.

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