JP5313729B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus, and more particularly to a technique for variably controlling a damping force of a steering system according to a road surface state.

  In an electric power steering device that generates an auxiliary steering force by an assist motor, the basic auxiliary steering force is set based on the driver's steering torque, and the steering is suppressed based on the rotation speed (steering angular velocity) of the steering wheel. There is one that improves the steering feeling by setting the damping force. However, since such an electric power steering apparatus sets the auxiliary steering force based on the steering torque and the steering angular velocity, which are parameters that are not related to each other, for example, when traveling on a low μ road, the road surface reaction force is reduced. The steering torque decreases and the basic auxiliary steering force decreases, but the damping force does not change. Therefore, the damping force is excessive with respect to the basic auxiliary steering force, and the steering operability and the steering feeling may be impaired. is there.

  In order to prevent the damping force from becoming excessive with respect to the basic auxiliary steering force, when driving on low μ roads where the road surface reaction force decreases, the motor reaction force is applied to compensate for the road surface reaction force, thereby reducing the steering torque. Some have been suppressed (for example, Patent Document 1). According to the invention described in Patent Document 1, since the basic auxiliary steering is maintained at a normal value on a low μ road, an excessive damping force is prevented.

JP-A-11-147482

  However, the invention described in Patent Document 1 has a problem that the driver cannot detect the change in the road surface state from the change in the steering torque in order to suppress the change in the steering torque according to the road surface state.

  The present invention has been made in view of the above problems, and by controlling the damping force according to the road surface state without suppressing the change of the steering torque according to the road surface state, It is an object of the present invention to provide an electric power steering device that can sense a change in road surface state without impairing the feeling.

  In order to solve the above problems, the first invention is an electric power steering device (1) mounted on a vehicle and generating an auxiliary steering force by an actuator (9), wherein the steering speed of a steering wheel (2) is controlled. Steering speed detecting means (11) for detecting, steering torque detecting means (12) for detecting steering torque generated by operation of the steering wheel, and base auxiliary steering force for setting a base auxiliary steering force based on the steering torque Setting means (22), damping force setting means (31) for setting a damping force for damping steering based on the steering speed, and road surface state estimating means (33, 34) for estimating the road surface state of the traveling road surface of the vehicle. 35), damping force correcting means (33, 34, 35) for correcting the damping force according to the road surface condition, And having an auxiliary steering force setting means and (21) to set the assist steering force on the basis of the over scan auxiliary steering force to said damping force.

  According to this configuration, since the damping force is variably controlled according to the road surface condition, the damping force is prevented from becoming excessive with respect to the auxiliary steering force.

  A second invention is an electric power steering device (1) mounted on a vehicle and generating an auxiliary steering force by an actuator (9) and used in a rack and pinion type steering device, wherein the steering wheel (2) Steering speed detecting means (11) for detecting steering speed, steering torque detecting means (12) for detecting steering torque generated by operation of the steering wheel, and base for setting base auxiliary steering force based on the steering torque Auxiliary steering force setting means (22), a damping force setting means (31) for setting a damping force for damping steering based on the steering speed, and a rack for estimating a load applied in the axial direction of the rack shaft as a rack axial force Axial force estimating means (33) and a damping force for correcting the damping force based on the rack axial force Positive means (42), characterized by having a said base steering assist force and the steering assist force setting means for generating the auxiliary steering force based on said damping force (21).

  According to this configuration, since the damping force is variably controlled based on the rack axial force correlated with the road surface state, the damping force is prevented from being excessive with respect to the auxiliary steering force.

  According to a third invention, in the second invention, a vehicle speed detecting means for detecting a vehicle speed of the vehicle, a steering angle detecting means (11) for detecting a steering angle of the steering wheel, and a standard acting on the rack shaft A load is stored as a standard rack axial force in advance corresponding to the vehicle speed and the steering angle, and corresponds to the vehicle speed detected by the vehicle speed detection means and the steering angle detected by the steering angle detection means. A standard rack axial force calculating means (33) for setting a standard rack axial force, and when the rack axial force is smaller than the standard rack axial force, the damping force correcting means includes the standard rack axial force and the rack. The damping force is reduced as the difference from the axial force increases.

  According to this configuration, the damping force can be controlled according to the road surface μ by correcting the damping force based on the difference between the rack axial force and the standard rack axial force.

  In a fourth aspect based on the second aspect, a steering angle detecting means (11) for detecting a steering angle of the steering wheel, and a rack shaft for calculating the rack axial force with respect to the change amount of the steering angle as a rack axial force gain. Force gain setting means (41), wherein the damping force correction means corrects the damping force based on the rack axial force gain.

  According to this configuration, it is not necessary to set the standard rack axial force, so the configuration becomes simple.

  In a fourth aspect based on the fourth aspect, the damping force correction means reduces the damping force as the rack axial force gain decreases.

  According to this configuration, the damping force can be variably controlled by making the rack axial force gain correspond to the road surface μ.

  In a sixth aspect based on the second to fifth aspects, the rack axial force estimating means estimates the rack axial force when a steering direction of the steering wheel coincides with a direction of the auxiliary steering force. It is characterized by doing.

  According to this configuration, since the rack axial force is estimated when the steering torque is stable, the rack axial force can be estimated with high accuracy.

  According to the above configuration, since the damping force is variably controlled according to the road surface condition, the damping force is prevented from becoming excessive with respect to the auxiliary steering force.

It is a mimetic diagram showing the steering device for vehicles concerning a 1st embodiment. It is a block diagram which shows the steering control apparatus which concerns on 1st Embodiment. It is a block diagram which shows the damping compensation current setting part of FIG. It is a data map which shows the damping correction coefficient which concerns on 1st Embodiment. It is a flowchart which shows the setting procedure of the damping compensation current which concerns on 1st Embodiment. It is a graph which shows the restoring force added to a steering wheel. It is a block diagram which shows the damping compensation current setting part which concerns on 2nd Embodiment. It is a graph which shows the relationship between a road surface state, a steering angle, and a rack axial force. It is a data map which shows the damping correction coefficient which concerns on 2nd Embodiment. It is a flowchart which shows the setting procedure of the damping compensation current which concerns on 2nd Embodiment.

  Hereinafter, two embodiments in which the electric power steering apparatus 1 of the present invention is applied to a vehicle steering apparatus will be described in detail with reference to the drawings.

  The first embodiment will be described below. FIG. 1 is a schematic diagram showing a vehicle steering apparatus according to the first embodiment. As shown in FIG. 1, an electric power steering apparatus 1 includes a pinion 4 connected to a steering wheel 2 via a steering shaft 3, and a rack 5 that meshes with the pinion 4 and reciprocates in the vehicle width direction. An and pinion mechanism is provided. Both ends of the rack shaft 5 are connected to a knuckle arm 8 that supports left and right front wheels 7 as steering wheels via tie rods 6, and the left and right front wheels 7 rotate according to the rotation operation of the steering wheel 2. It is to be steered. An assist motor (actuator) 9 is coaxially mounted on the rack shaft 5, and the steering force of the driver is reduced by the torque generated by the assist motor 9.

  The steering shaft 3 is provided with a steering angle sensor 11 for detecting the steering angle θ of the steering wheel 2, and in the vicinity of the pinion 4, a steering torque sensor (steering torque detection means for detecting a steering torque T acting on the pinion 4 is provided. ) 12 is provided. A vehicle speed sensor 13 for detecting the vehicle speed V is provided at an appropriate position of the vehicle body. Further, the assist motor 9 is provided with a resolver 15 that detects a motor rotation angle φ and a motor current sensor 16 that detects a motor current I flowing through the assist motor 9.

  The output signals of the steering angle sensor 11, the steering torque sensor 12, the vehicle speed sensor 13, the resolver 15, and the motor current sensor 16 are steering control devices (EPS-ECUs) for comprehensively controlling the operation of the electric power steering device 1. 21 is input.

  The steering control device 21 includes a microcomputer, ROM, RAM, peripheral circuits, input / output interfaces, various drivers, and the like, and controls for driving and controlling the assist motor 9 based on the output signals of the sensors 11 to 15. A target value (target current It) is determined and input to the drive circuit 19 of the assist motor 9. The drive circuit 19 is composed of an FET bridge circuit or the like, and supplies power to the assist motor 9 based on the target current It determined by the steering control device 21, thereby controlling the output torque of the assist motor 9 and assisting. A steering force is applied to the rack shaft 5.

  FIG. 2 is a block diagram illustrating the steering control device 21 according to the embodiment. As shown in FIG. 2, the steering control device 21 includes a base current setting unit (base auxiliary steering force setting means) 22, an inertia compensation current setting unit 23, a damping compensation current setting unit 25, an adder 26, and a subtraction. The target current It of the assist motor 9 calculated based on the output signals of the sensors 11 to 16 is output to the drive circuit 19.

  The base current setting unit 22 detects the steering wheel operation by the driver, and calculates the base current Ia that is the basis of the target current It according to the operation amount. Based on the steering torque detected by the steering torque sensor 12 and the vehicle speed detected by the vehicle speed sensor 13, the base current setting unit 22 calculates the base current Ia using a known method. The base current Ia is input to the adder 26 and the subtracter 28 in order and corrected.

  The inertia compensation current setting unit 23 calculates an inertia compensation current Ib for canceling out the inertia moment of the assist motor 9 and the steering system. The inertia compensation current setting unit 23 calculates a time differential value of the steering torque T detected by the steering torque sensor 12, and based on the time differential value of the steering torque T and the vehicle speed V detected by the vehicle speed sensor 13, a known value is known. The inertia compensation current Ib is calculated using the method. The inertia compensation current Ib is input to the adder 26 and used for correcting the base current Ia.

  The damping compensation current setting unit 25 sets a damping compensation current Id for damping (attenuating) steering. The damping compensation current Id is input to the subtractor 28 and used for correcting the base current Ia.

  The base current Ia set by the base current setting unit 22 is corrected by the inertia compensation current Ib and the damping compensation current Id when passing through the adder 26 and the subtractor 28 to become the target current It.

  Next, the damping compensation current setting unit 25 will be described in detail. FIG. 3 is a block diagram showing the damping compensation current setting unit 25 of FIG. The damping compensation current setting unit 25 includes a damping compensation current base value setting unit (damping force setting unit) 31, a return / return determination unit 32, a rack axial force estimation unit (rack axial force estimation unit) 33, and a standard rack axial force. A setting unit (standard rack axial force calculation means) 34, a damping correction coefficient setting unit 35, a memory 36, and a multiplier 37 are provided.

  The damping compensation current base value setting unit 31 sets the damping compensation current base value Idb corresponding to the damping force to be generated based on the steering angular velocity ω calculated by differentiating the steering angle θ detected by the steering angle sensor 11. . The damping compensation current base value Idb may be set using a predetermined arithmetic expression, a data map, or the like based on the steering angular velocity ω. The damping compensation current base value Idb is input to the multiplier 37.

  Based on the steering angular velocity ω calculated by differentiating the steering angle θ detected by the steering angle sensor 11 and the steering torque T, the forward / return determination unit 32 determines the rotation direction of the steering wheel 2 from the sign of each value. It is determined whether or not the direction of the steering torque T matches. The case of coincidence is forward steering, and the case of non-coincidence is return steering. In the case of forward steering, the determination result S is output to the rack axial force estimation unit 33.

  The rack axial force estimation unit 33 estimates the load applied in the axial direction of the rack shaft 5 as the rack axial force Fr. The load applied in the axial direction of the rack shaft 5 includes a steering force by the driver's steering wheel operation, a steering assist force by the assist motor 9, and a road surface reaction force received from the road surface. Since the road surface reaction force decreases as the road surface μ decreases, the rack axial force Fr decreases. The estimation of the rack axial force Fr is performed only when the forward steering is performed based on the forward determination result S input from the forward / return determination unit 32. The rack axial force estimation unit 33 uses a known method based on the steering torque T, the motor current I, and the motor rotation speed ωm calculated by differentiating the motor rotation angle φ detected by the resolver 15. The rack axial force Fr is calculated (see, for example, JP-A-11-49000). When the rack axial force Fr is estimated, the rack axial force estimating unit 33 outputs the rack axial force Fr to the damping correction coefficient setting unit 35.

  The standard rack axial force setting unit 34 determines the rack axial force at an arbitrary vehicle speed V and steering angle θ when the road surface is in a standard state (for example, a dry asphalt road that is a high μ road) as a standard rack axial force Frs. Set as. The standard rack axial force setting unit 34 refers to a data map in which the standard rack axial force Frs is set corresponding to the vehicle speed V and the steering angle θ based on the vehicle speed V and the steering angle θ, thereby making the standard rack axial force Frs. Set. The standard rack axial force Frs is output to the damping correction coefficient setting unit 35.

  The damping correction coefficient setting unit 35 sets a correction coefficient K1 for correcting the damping compensation current base value Idb. The damping correction coefficient setting unit 35 calculates the rack axial force difference ΔFr by subtracting the rack axial force Fr estimated by the rack axial force estimating unit 33 from the standard rack axial force Frs set by the standard rack axial force setting unit 34. Then, referring to the data map shown in FIG. 4, the damping correction coefficient K1 corresponding to the rack axial force difference ΔFr is set. FIG. 4 is a data map showing the damping correction coefficient K1 according to the first embodiment. As shown in FIG. 4, the damping correction coefficient K1 is a numerical value in the range of 0 to 1, and is set so as to decrease as the rack axial force difference ΔFr increases. That is, since the rack axial force Fr decreases as the road surface μ decreases, the rack coefficient F1 is set so that the correction coefficient K1 decreases as the road surface μ decreases.

  The damping correction coefficient K1 is output to the multiplier 37 and stored in the memory 36. When the rack axial force Fr is not received from the rack axial force estimation unit 33, the damping correction coefficient setting unit 35 does not perform the calculation process of the damping correction coefficient K1, and multiplies the damping correction coefficient K1 stored in the memory 36. To 37.

  The multiplier 37 multiplies the damping compensation current base value Idb by the damping correction coefficient K1 to calculate the damping compensation current Id. The damping compensation current Id is input to the subtractor 28.

  The damping compensation current setting unit 25 described above calculates the damping compensation current Id according to the flowchart shown in FIG. FIG. 5 is a flowchart showing a procedure for setting the damping compensation current according to the first embodiment. First, the damping compensation current base value setting unit 31 sets the damping compensation current base value Idb based on the steering angular velocity ω (S1). Next, it is determined whether or not forward steering is performed by the forward / return determination unit 32 (S2).

  In the case of forward steering, the rack axial force estimation unit 33 calculates the rack axial force Fr (S3), and the standard rack axial force setting unit 34 sets the standard rack axial force Frs (S4). Then, the damping correction coefficient setting unit 35 calculates the rack axial force difference ΔFr from the rack axial force Fr and the standard rack axial force Frs (S5), and the damping correction coefficient K1 is set based on the rack axial force difference ΔFr ( S6). Then, in the multiplier 37, a damping compensation current Id is calculated by multiplying the damping compensation current base value Idb by the damping correction coefficient K1 (S7).

  If the determination in step S2 is not forward steering, the process proceeds to step S7 without setting the rack axial force Fr, rack axial force difference ΔFr, and damping correction coefficient K1, and the previous damping correction coefficient K1 stored in the memory 36 is set. Is multiplied by the damping compensation current base value Idb to calculate the damping compensation current Id. The initial value of the damping correction coefficient K1 is set to 1. When the damping correction coefficient K1 has never been set, the damping compensation current base value Idb is multiplied by 1.

  The effect of 1st Embodiment comprised as mentioned above is demonstrated. In the first embodiment, since the damping compensation current Id is set based on the rack axial force Fr, the damping force can be set according to the road surface condition. Since the rack axial force Fr changes according to the road surface reaction force, the road surface state (road surface μ) can be estimated from the rack axial force Fr. The rack axial force estimation unit 33 that estimates the rack axial force Fr, the standard rack axial force setting unit 34 that sets the standard rack axial force Frs, and the rack axial force Fr and the standard rack axial force Frs are compared. The damping correction coefficient setting unit 35 that calculates the difference ΔFr functions as a road surface state estimation unit.

  Since the rack axial force Fr is small on a low μ road where the road surface reaction force is small and large on a high μ road where the road surface reaction force is large, a damping compensation current is obtained when the rack axial force Fr is small (ie, on a low μ road). By decreasing Id and increasing the damping compensation current Id when the rack axial force Fr is large (that is, in the case of a high μ road), the damping force can be set according to the road surface condition.

  FIG. 6 is a graph showing the restoring force applied to the steering wheel. FIG. 6A shows the restoring force when the vehicle equipped with the vehicle steering apparatus according to the first embodiment travels on a high μ road. ) Shows a restoring force when a vehicle equipped with the vehicle steering device according to the first embodiment travels on a low μ road, and (c) shows a conventional vehicle steering device (without correcting the damping force). It shows the restoring force when the vehicle that has been driven on a low μ road. As shown in FIGS. 6A and 6B, when the road changes from a high μ road to a low μ road, the road surface reaction force decreases and the steering torque gradient decreases. At this time, since the damping force is set based on the rack axial force that changes in accordance with the road surface μ, the hysteresis of the restoring force becomes small. Therefore, the steering angle θ0 at which the steering torque T becomes 0 can be maintained substantially constant during traveling on the low μ road and when traveling on the high μ road. Therefore, even on a low μ road, the steering can return to the neutral point by self-aligning.

  On the other hand, as shown in FIG. 6 (c), when the damping force is not corrected, the damping force remains large despite the small steering torque gradient, so the hysteresis is large and the steering torque T becomes zero. The steering angle θ0 is larger than when traveling on a high μ road. That is, a phenomenon occurs in which the steering torque becomes 0 when the steering angle is large, and the steering 2 cannot return to the neutral point.

  Next, a second embodiment will be described. The second embodiment differs from the first embodiment only in the configuration of the damping compensation current setting unit. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  FIG. 7 is a block diagram showing a damping compensation current setting unit 40 according to the second embodiment. As shown in FIG. 7, the damping compensation current setting unit 40 includes a damping compensation current base value setting unit 31, a return / return determination unit 32, a rack axial force estimation unit 33, a rack axial force gain setting unit (rack axial force Gain setting means) 41, damping correction coefficient setting unit 42, memory 36, and multiplier 37. Since the damping compensation current base value setting unit 31, the return / return determination unit 32, the rack axial force estimation unit 33, the memory 36, and the multiplier 37 have the same configuration as that of the first embodiment, the description thereof is omitted.

  Based on the steering angle θ and the rack axial force Fr estimated by the rack axial force estimating unit 33, the rack axial force gain setting unit 41 determines the amount of change in the rack axial force Fr relative to the amount of change in the steering angle θ. Set as gain Gr. FIG. 8 is a graph showing the relationship between the road surface condition, the steering angle, and the rack axial force. As shown in FIG. 8, when the steering angle θ is increased, the lateral force generated in the tire is increased by turning the front wheel 7 with respect to the traveling direction of the vehicle, and a force in the vehicle width direction is applied to the front wheel 7. Therefore, the rack axial force Fr increases. At this time, if the steering angle θ is the same, the higher the road surface friction coefficient, the greater the force in the vehicle width direction applied to the front wheels 7. Therefore, the rack axial force gain Gr, which is the change amount of the rack axial force Fr with respect to the change amount of the steering angle θ (that is, the slope of each straight line in FIG. 8) changes according to the road surface condition, and the higher the μ road. growing. The rack axial force gain setting unit 41 outputs the rack axial force gain Gr to the damping correction coefficient setting unit 42 when the rack axial force Fr is input and the rack axial force gain Gr is set.

  The damping correction coefficient setting unit 42 sets a correction coefficient K2 for correcting the damping compensation current base value Idb. The damping correction coefficient setting unit 42 sets a damping correction coefficient K2 corresponding to the rack axial force gain Gr with reference to the data map shown in FIG. FIG. 9 is a data map showing the damping correction coefficient K2 according to the second embodiment. As shown in FIG. 9, the damping correction coefficient K2 is a numerical value in the range of 0 to 1, and is set to decrease as the rack axial force gain Gr decreases. Further, in consideration of the road surface estimation error due to the rack axial force gain Gr, the damping correction coefficient K2 is made smaller than 1 from the state where the value α ′ is decreased from the rack axial force gain Grs when the road surface is in the standard state. The data map is set.

  The damping correction coefficient K2 is output to the multiplier 37 and stored in the memory 36. If the rack axial force Gr is not received from the rack axial force gain setting unit 41, the damping correction coefficient setting unit 42 does not calculate the damping correction coefficient K2, and multiplies the damping correction coefficient K2 stored in the memory 36. Output to the device 37.

  The damping compensation current setting unit 40 according to the second embodiment calculates the damping compensation current Id according to the flowchart shown in FIG. FIG. 10 is a flowchart showing a procedure for setting a damping compensation current according to the second embodiment. First, the damping compensation current base value setting unit 31 sets the damping compensation current base value Idb based on the steering angular velocity ω (S11). Next, it is determined whether or not forward steering is performed by the forward / return determination unit 32 (S12).

  In the case of forward steering, the rack axial force estimation unit 33 calculates the rack axial force Fr (S13), the rack axial force gain setting unit 41 sets the rack axial force gain Gr (S14), and the damping. In the correction coefficient setting unit 42, a damping correction coefficient K2 is set based on the rack axial force gain Gr (S15). Then, in the multiplier 37, a damping compensation current Id is calculated by multiplying the damping compensation current base value Idb by the damping correction coefficient K2 (S16).

  If the determination in step S12 is not forward steering, the process proceeds to step S16 without setting the rack axial force Fr, rack axial force gain Gr, and damping correction coefficient K2, and the previous damping correction coefficient K2 stored in the memory 36 is set. Is multiplied by the damping compensation current base value Idb to calculate the damping compensation current Id. The initial value of the damping correction coefficient K2 is set to 1. If the damping correction coefficient K1 has never been set, the damping compensation current base value Idb is multiplied by 1.

  By configuring as in the second embodiment, it is not necessary to compare the rack axial force Fr with the standard rack axial force Frs, thereby eliminating the need to prepare a data map in which the standard rack axial force Frs is set.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, in the present embodiment, the rack axial force Fr is estimated based on the motor current I, the steering torque T, and the motor rotational speed ωm. However, a rack axial force sensor is provided on the rack shaft 5 to detect the rack axial force. May be actually measured.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering wheel, 5 ... Rack shaft, 9 ... Assist motor (actuator), 11 .... Steering angle sensor, 12 .... Steering torque sensor (steering torque detection means), 13 ..Vehicle speed sensor, 15 ..Resolver, 16 ..Motor current sensor, 21 ..Steering control device (auxiliary steering force setting means), 22 ..Base current setting section (base auxiliary steering force setting means), 23. Inertia compensation current setting unit, 25, 40... Damping compensation current setting unit, 31 .. Damping compensation current base value setting unit (damping force setting means), 33 .. Rack axial force estimation unit (rack axial force estimation means), 34 ··· Standard rack axial force setting unit (standard rack axial force calculation means), 35, 42 ·· Damping correction coefficient setting unit, 41 · · Rack axial force gain Tough (rack axial force gain setting means),

Claims (3)

An electric power steering device mounted on a vehicle for generating an auxiliary steering force by an actuator and used for a rack and pinion type steering device,
Steering speed detection means for detecting the steering speed of the steering wheel;
Steering torque detection means for detecting steering torque generated by operation of the steering wheel;
Base auxiliary steering force setting means for setting a base auxiliary steering force based on the steering torque;
A damping force setting means for setting a damping force that attenuates steering based on the steering speed;
Rack axial force estimating means for estimating a load applied in the axial direction of the rack shaft as a rack axial force;
Steering angle detecting means for detecting the steering angle of the steering wheel;
Rack axial force gain setting means for calculating a rack axial force gain that is a change amount of the rack axial force with respect to a change amount of the steering angle based on the steering angle and the rack axial force;
Damping force correcting means for correcting the damping force based on the rack axial force gain ;
An electric power steering apparatus comprising: an auxiliary steering force setting unit that sets the auxiliary steering force based on the base auxiliary steering force and the damping force. 2. The electric power steering apparatus according to claim 1 , wherein the damping force correction unit decreases the damping force as the rack axial force gain decreases. The rack shaft force estimating means, the steering direction of the steering wheel, when the direction of the auxiliary steering force are matched to claim 1 or claim 2, wherein the estimating the rack shaft force The electric power steering apparatus as described.

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