JP3364673B2 - Vehicle steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system for steering a vehicle in response to a driver's operation. 2. Description of the Related Art Steering of a vehicle is performed by operating a steering means disposed inside a vehicle compartment, for example, by rotating a steering wheel to steer a steering wheel (generally, a front wheel). Is transmitted to a steering mechanism arranged outside the vehicle compartment. In recent years, an actuator for assisting steering such as a hydraulic cylinder and an electric motor is arranged in the middle of the steering mechanism, and the actuator is driven based on a detection result of an operating force applied to a steering wheel for steering. 2. Description of the Related Art A power steering device (power steering device), which is configured to assist the operation of a steering mechanism in accordance with the rotation of a steering wheel with a force generated by an actuator to reduce a driver's labor burden for steering, has become widespread. ing. However, in such a conventional steering apparatus for a vehicle, a mechanical connection between a steering wheel, which is a steering means, and a steering mechanism is required, and the position of the steering wheel in the vehicle interior is limited. There is a problem that the connection to the steering mechanism outside the vehicle compartment is limited, and even if the steering wheel is arranged to be connectable, complicated connection is required to realize the connection. This requires a structure, which is a factor that hinders weight reduction of the vehicle and simplification of the assembly process. [0004] Japanese Utility Model Publication No. 2-29017 discloses a vehicle steering apparatus which is a linkless power steering apparatus for solving such a problem.
This steering apparatus for a vehicle arranges a steering wheel separately from a steering mechanism, and, like a steering assist actuator in a power steering apparatus, includes an electric motor as a steering actuator in the middle of the steering mechanism. The electric motor is controlled by a steering angle control means including a microprocessor based on a detection result of an operation direction and an operation amount of the steering wheel.
The steering wheel is operated according to the operation of the steering wheel. [0005] A steering wheel not mechanically connected to the steering mechanism is provided with a reaction force actuator having an electric motor. The reaction force actuator drives and controls the motor based on the detection result of the vehicle speed and the steering angle of the steering wheel, based on the reaction force instruction signal output by the steering angle control means. It becomes large or small according to the size and applies a reaction force toward the neutral position. Thus, the steering can be performed with a feeling equal to or higher than that of a general vehicle steering device (connection type steering device) in which the steering wheel and the steering mechanism are mechanically connected. [0006] The linkless vehicle steering system constructed as described above replaces the steering wheel, such as a lever and a pedal, in addition to the above-mentioned objects of increasing the degree of freedom in arranging the steering wheel and reducing the weight of the vehicle. The present invention is useful for the development of automobile technology in the future, such as the realization of new steering means and the realization of an automatic driving system according to driving information such as detection of guidance signs on the road surface and reception of satellite information. [0007] In a conventional vehicle steering system in which a steering mechanism and a steering wheel are mechanically connected to each other, mechanical friction and reverse friction applied to wheels from a road surface are reduced. The response becomes dull because the inertial force becomes a drag and absorbs a part of the reverse input. On the other hand, in a linkless vehicle steering system in which the steering mechanism and the steering wheel are not mechanically connected, the influence of friction torque and inertia force is reduced so that the operation of the wheel is not absorbed, and the high-speed response of the steering control is achieved. In addition, rigidity is enhanced by including an integral element in the control operation. Here, when the wheel comes into contact with a curb or the like during high-speed running and the steering angle of the wheel changes due to the reverse input, the reverse input causing the change is large, and the integral element is added to the steering angle control means. In the one used, vibration occurs due to the time delay,
It may disturb the stable running of the vehicle. [0009] As a countermeasure against such a disturbance, a "vehicle route holding control device" (Japanese Patent Publication No. 53-1033) for compensating for a path deviation caused by the disturbance.
No. 4), a "disturbance compensating device for removing a vehicle from a course" by automatically turning back and steering to deviate from the course caused by a cross wind or other disturbance (Japanese Patent Laid-Open No. Sho 50)
No. -35826) is disclosed, but these are:
This is to compensate for the deviation of the course or the deviation from the course, and there is a possibility that the deviation from the course cannot be avoided. On the other hand, the vehicular steering apparatus according to the present invention intends to suppress the deviation before the vehicle deviates from the course. The present invention has been made in view of the above circumstances, and in a linkless vehicle steering system, when a wheel receives a reverse input from a road surface, the steering angle of a steering mechanism is increased or decreased. An object of the present invention is to provide a vehicle steering device capable of performing stable running even at high speed against large disturbance to wheels by suppressing the rotation of a motor for a moment. According to the present invention, there is provided a steering apparatus for a vehicle, wherein the steering means is not mechanically connected to a steering mechanism for changing the direction of wheels, and a steering angle of the steering means is detected. Steering angle detecting means, and a steering angle control means for driving a motor having a polyphase winding by a polyphase current to increase or decrease the steering angle of the steering mechanism in accordance with the steering angle detected by the steering angle detecting means. In the vehicle steering system provided with the above, by the reverse input received by the wheel from the road surface, the axial force detecting means for detecting the axial force received by the shaft for changing the direction of the wheel, and the axial force detecting means Comparing means for comparing the axial force with a predetermined value; and superimposing a direct current on one or more of the multiphase currents when the comparing means determines that the axial force is larger than the predetermined value. Means for controlling the increase or decrease of the steering angle. It is characterized in that the effect of the reverse input is suppressed. In this vehicle steering system, the axial force detecting means detects the axial force applied to the shaft for changing the direction of the wheel by the reverse input applied to the wheel from the road surface. When the comparing means determines that the axial force is larger than a predetermined value determined by the allowable value, the superimposing means sets one or more of the multiphase currents for driving the motor for increasing or decreasing the steering angle of the steering mechanism. By superimposing a direct current on the phase, the rotation of the motor is momentarily suppressed, and the influence of the reverse input to the control for increasing or decreasing the steering angle is suppressed. The steering control system, which is the steering angle control means, has some response to disturbance (reverse input). However, to make the response of the steering control system slow to large disturbance reduces the control gain. As a result, the rigidity of the wheel is reduced, and the steering angle easily changes due to disturbance. Therefore, when a disturbance exceeding the allowable value of the steering control system is involved, a direct current is superimposed on one or more phases of the polyphase current for driving the motor, thereby giving a resistance to the rotation of the motor. When a direct current is superimposed on one or more phases of the polyphase current for driving the motor, a fixed magnetic field is generated by the direct current, and the fixed magnetic field attracts the rotor of the motor to suppress the rotation. . When the fixed magnetic field is stronger than the rotating magnetic field generated by the multi-phase current, the rotation of the rotor stops and the steering angle of the wheel is fixed. That is, the rigidity of the wheel with respect to disturbance increases. As a result, stable running is possible even during high-speed running against a large disturbance (reverse input) to the wheels, and if DC current is superimposed instantaneously at high speed, the steering angle increase / decrease control is affected. Never. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment. FIG. 1 is a block diagram showing a configuration of an embodiment of a vehicle steering system according to the present invention. This vehicle steering device includes a steering mechanism 1 for causing a pair of steering wheels 10, 10 arranged on the left and right sides of a vehicle body (not shown) to perform a steering operation, and a steering mechanism separately provided from the steering mechanism 1. Steering wheel 2 as means, and electric motor 3 for applying a reaction force to steering wheel 2
A reaction force control unit 7 that uses a microprocessor to drive and control the electric motor 3, a steering mechanism control unit 8 that drives and controls the steering motor 5 arranged in the middle of the steering mechanism 1, and a microprocessor that uses the microprocessor. A steering control unit (steering angle control means) 4 comprising: a steering motor 5 which is a three-phase brushless motor driven by the operation of the steering control unit 4 in accordance with the operation of the steering wheel 2; 1 is operated. As is well known, the steering mechanism 1 includes both ends of a steering shaft 11 that extends in the left-right direction of the vehicle body and slides in the axial direction, and knuckle arms 12 that support the wheels 10, 10.
12 are connected by separate tie rods 13, 13, respectively.
The tie rods 13 and 1 are moved by sliding the steering shaft 11 in both directions.
The knuckle arms 12, 12 are pushed and pulled via 3 to steer the wheels 10, 10 to the left and right. This steering is performed by the steering motor 5, which is coaxially formed in the middle of the steering shaft 11. The rotation is converted into sliding of the steering shaft 11 by an appropriate motion conversion mechanism. The rotation of the steering shaft 11 around the axis thereof is restricted by rotation restricting means (not shown) interposed between the steering shaft 11 and the steering shaft housing 14. And the steering (steering of the steering wheels 10, 10) according to the rotation of the steering motor 5 is performed. The current flowing through the steering motor 5 is detected by a current sensor 8a and provided to the steering control unit 4. The steering angles of the wheels 10 and 10 thus steered are determined by the relative sliding position between the steering shaft housing 14 on one side of the steering motor 5 and the steering shaft 11 as a medium.
6 and a steering angle sensor 16
Is supplied to the steering control unit 4 together with the output of the rotary encoder 15 that detects the rotational position of the steering motor 5. The tie rods 13, 13 are provided with axial force sensors 9, 9 (axial force detecting means) for detecting a road surface reaction force received by the wheels 10, 10 from a road surface and an axial force applied by a reverse input received from a curb or the like on the road surface. Each output of the axial force sensors 9 is provided to the steering control unit 4. An electric motor 3 for applying a reaction force to the steering wheel 2 is fixedly attached to a casing that supports the rotating shaft 30, and its rotational movement is performed by an electromagnetic clutch 3a and by a worm gear mechanism 3b. The rotation direction is converted and transmitted to the rotation shaft 30. The steering wheel 2 is coaxially fixed to a protruding end on one side of the rotating shaft 30, and the protruding end on the other side is connected to an appropriate portion of a vehicle body (not shown) by a torsion spring 31 having a predetermined elasticity. I have. The electric motor 3 is driven in both forward and reverse directions by energization from the reaction force control unit 7 in response to a reaction force instruction signal given from the steering control unit 4, and the steering wheel 2 attached to one end of the rotating shaft 30. Then, an operation of applying a force (reaction force) in a direction opposite to the operation direction is performed. Therefore, it is necessary to apply a steering torque against the reaction force generated by the electric motor 3 to the rotation operation of the steering wheel 2. The steering torque applied to the steering wheel 2 in this manner is detected by the torque sensor 32. You. The output of the torque sensor 32 is provided to the steering control unit 4. The operation amount (steering angle) of the steering wheel 2 is determined by a rotary encoder 33 serving as a steering angle detecting means.
Is detected including the operation direction. This detection result is provided to the steering control unit 4. Further, a current flowing through the electric motor 3 is detected by a current sensor 7 a and provided to the steering control unit 4. The torsion spring 31 interposed between the other end of the rotating shaft 30 and a part of the vehicle body causes the rotating shaft 30 to rotate due to its elasticity when the rotating operation performed as described above is stopped. Thus, the steering wheel 2 returns to a predetermined neutral position. This return is necessary for returning the steering wheel 2 in accordance with the return operation of the wheels 10, 10 in the straight traveling direction that occurs on the mechanically separated steering mechanism 1 side. As described above, the steering state actually occurring on the steering mechanism 1 side is given to the steering control unit 4 as an input from the rotary encoder 15 and the steering angle sensor 16. The operation state of the steering wheel 2 is given as an input from a torque sensor 32 and a rotary encoder 33, respectively. In addition, the steering control unit 4 is provided with a vehicle speed sensor 6 for detecting the traveling speed of the vehicle. Output is given. The output of the vehicle speed sensor 6 is also provided to a reaction force control unit 7. On the other hand, the output of the steering control unit 4 is, as described above, a reaction force control unit 7 for applying a reaction force to the steering wheel 2 and a steering for causing the steering mechanism 1 to perform a steering operation. The reaction force control unit 7 and the steering mechanism control unit 8 perform different control operations in response to an instruction signal from the steering control unit 4. The steering control unit 4 determines the reaction force to be applied to the steering wheel 2 to be large or small according to the level of the vehicle speed given as an input from the vehicle speed sensor 6, for example. A reaction force control for giving a reaction force instruction signal to the force control unit 7 is performed. The steering control unit 4 recognizes the operation angle including the operation direction of the steering wheel 2 based on the input from the rotary encoder 33 and recognizes the operation angle based on the input from the steering angle sensor 16 attached to the steering mechanism 1. The steering angle deviation from the actual steering angle is calculated, and the steering angle deviation is corrected so as to be larger or smaller according to the vehicle speed given as an input from the vehicle speed sensor 6 to obtain the target steering angle. The steering control operation for driving the steering motor 5 is performed until the angle is obtained. At this time, the input from the steering angle sensor 16 is used as a feedback signal for checking whether or not the steering motor 5 has reached a desired rotational position. The steering control unit 4 includes axial force sensors 9 and 9
When each output is larger than a predetermined value, a DC current superimposition instruction signal for superimposing a DC current on two phases of a three-phase current for driving the steering motor 5 which is a three-phase brushless motor is provided. This is given to the steering mechanism control unit 8. The steering mechanism control unit 8 receives the DC current superimposition instruction signal and superimposes the DC current on the two phases of the current for driving the steering motor 5. FIG. 2 is a block diagram showing the configuration of the steering motor 5, which is a three-phase brushless motor, and its drive circuit and gate control circuit included in the steering mechanism control unit 8. The steering motor 5 detects a stator 5a in which coils A, B, and C are star-connected, a rotor 5b that is rotated by a rotating magnetic field generated by the coils A, B, and C, and a rotational position of the rotor 5b. Rotor position detector (rotary encoder) 1
5 is provided. The drive circuit 8b of the steering motor 5 includes a transistor Q1, Q2 connected in series between a DC power supply terminal and a ground terminal, and a diode D connected in series in the reverse direction.
1 and D2 are connected in parallel. The transistors Q3 and Q4 connected in series and the diodes D3 and D4 connected in series in the reverse direction are connected in parallel. Transistors Q5 and Q6 connected in series and diodes D5 and D6 connected in series in the reverse direction are connected in parallel. A common connection node of the transistors Q1 and Q2 and a diode D1
A star-connected coil A is connected to the common connection node of D2.
Is connected to the other terminal U. Transistor Q3
The other terminal V of the star-connected coil B is connected to the common connection node of Q4 and the common connection node of diodes D3 and D4. The other terminal W of the star-connected coil C is connected to the common connection node of the transistors Q5 and Q6 and the common connection node of the diodes D5 and D6. The rotation position of the rotor 5b detected by the rotor position detector 15 is notified to the gate control circuit 8c.
The gate control circuit 8c is supplied with an instruction signal of a rotation direction and an output level and a direct current superimposition instruction signal from the steering control unit 4. The gate control circuit 8c controls the transistors Q1 to Q4 according to the instruction of the rotation direction and the rotation position of the rotor 5b.
Turn on / off each gate of Q6, for example, UV, U-
The path of the current flowing through the stator 5a is switched as in W, VW, VU, WU, WV, and UV to generate a rotating magnetic field. The rotor 5b is a permanent magnet, and rotates by receiving a rotating force from the rotating magnetic field. The current value as the output level is determined by turning on / off the transistors Q1 to Q6 by PW
Increase / decrease control is performed by M (Pulse Width Modulation) control. The diodes D1 to D6 are connected to the transistor Q1.
This is for absorbing noise generated by turning on / off Q6. The operation of the steering apparatus for a vehicle according to the present invention having such a configuration will be described below with reference to a flowchart showing the operation. FIG. 3 is a flowchart showing the operation of the steering control unit 4 of the vehicle steering system according to the present invention. The steering control unit 4 reads from the axial force sensors 9 and 9 the axial force received by the tie rods 13 and 13 (the shaft for changing the direction of the wheels) due to the reverse input that the wheels 10 and 10 receive from the road surface (S10). . Next, when the read axial force is equal to or more than the predetermined value (S12), the steering control unit 4 provides a direct current superimposition instruction signal to the gate control circuit 8c included in the steering mechanism control unit 8 (S14). When the read axial force is less than the predetermined value (S12), the steering control unit 4 returns as it is,
Move to another control operation. Normally, the gate control circuit 8c turns on / off the gates of the transistors Q1 to Q6 in accordance with the rotation direction instruction from the steering control unit 4 and the rotation position of the rotor 5b, The rotating magnetic field is generated by switching the path of the current flowing through 5a. When a direct current superimposition instruction signal is received from the steering control unit 4, for example, the transistors Q3 and Q6 are turned on longer than usual, and the coils B and C are turned on.
DC current to At this time, transistors Q4 and Q5
Are not turned on, and the transistors Q1 and Q2 are turned on / off according to the rotational position of the rotor 5b. When a direct current is applied to the coils B and C,
A fixed magnetic field is generated by the DC current, and the fixed magnetic field attracts the rotor 5b of the brushless motor 5 to suppress its rotation. When the fixed magnetic field is stronger than the rotating magnetic field generated by the polyphase current, the rotation of the rotor 5b stops, and the steering angle of the wheel is fixed. FIG. 4 is an explanatory diagram for explaining a case where a direct current is applied to the coils B and C. In FIG. 4, when the center direction of each of the coils A, B, and C is the direction of the bar OA, the bar OB, and the bar OC, the angle between these three lines is 120 °.
It becomes. Here, the bar OA is defined as the X axis on the XY coordinates. The currents flowing through the coils A, B, and C are represented by i _A , i _B , i _C
In the case of a three-phase brushless motor, i _A = asi
nωt, i _B = asin (ωt + 4π / 6), i _C = a
The current i of the coil A, such as sin (ωt + 8π / 6)
_With respect to _A , the currents i _B and i _C of the coils B and C flow currents whose phases are delayed by 120 ° and 240 ° (however, the current i _A
Its phase will vary depending on the position of the rotor 5b, where the phase of the current i _A is considered as 0). At this time, each of the coils A, B, and C has a magnetic flux → B _A , → B _B , → B
_C (→ B represents a vector) occurs, its _{intensity, | → B A | = ki} A = kasinωt ( direction, direction of the bar _{OA) | → B B | =} ki B = kasin (ωt + 4π / 6)
(The direction is the direction of the bar OB) | → B _C | = ki _C = kasin (ωt + 8π / 6)
(The direction is the direction of the bar OC) (where k is a proportional constant including the number of turns of the coil and the like). Now, assuming that the total magnetic flux vector of each of the coils A, B, C is → B, then → B = → B _A + → B _B + → B _C. When the X-direction component B _X and the Y-direction component _BY are calculated, B _X = casinωt− (1/2) casin (ωt +
4π / 6)-(1/2) kasin (ωt + 8π / 6)
= (3/2) kasinωt [0036] ^{_{B Y = (3 1/2 / 2}} ) kasin (ωt +
^{4π / 6) - (3 1/2} / 2) kasin (ωt + 8π /
6) = (3/2) kacosωt, and the magnetic flux vector → B has a constant magnitude (= (3 /
2) A rotating magnetic field of ka) results. In a normal operation, the permanent magnet of the rotor 5b is driven by the rotating magnetic field, and the rotation is maintained. Now, when a DC current (magnitude δ) is superimposed on the two phases of coils B and C, i _B = asin (ωt + 4π / 6) + δ i _C = asin (ωt + 8π / 6) + δ Total flux vector by A, B, C →
B ′ is: → B ′ = → B _A + → B _B ′ + → B _C ′ where | → B _B ′ | = kasin (ωt + 4π / 6)
_{+ Kδ | → B C '|} = kasin (ωt + 8π / 6) + kδ next, X direction component B _X' and Y-direction component B _Y 'are each _{B X' = (3/2) kasinωt} -kδ B Y '= ( 3/2) kacosωt, and the magnetic flux vector → B ′ has a magnitude (3/2) ka
And the DC magnetic field in the −X direction are superimposed. Therefore, the rotor 5b, which is a permanent magnet, is given a rotational driving force by the rotating magnetic field and is attracted in the -X direction. This attractive force is
The drag becomes a drag that hinders the rotation of the rotor, and the rotation becomes impossible under the condition of drag> rotational driving force, and the rotor 5b is bound in one direction. In the vehicle steering system according to the present invention, by utilizing the binding force, the rotation of the steering motor 5 due to the reverse input received when the wheel contacts the curb or the like is suppressed. Note that the steering motor 5 may be a step motor. According to the vehicle steering system of the present invention,
Stable running is possible even during high-speed running against large disturbances (reverse input) to the wheels. In addition, if DC current is superimposed instantaneously at high speed, the increase / decrease control of the steering angle at normal times is affected. I will not give.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a vehicle steering system according to the present invention. FIG. 2 is a block diagram illustrating a configuration of a three-phase brushless motor, a drive circuit thereof, and a gate control circuit. FIG. 3 is a flowchart showing an operation of a steering control unit of the vehicle steering system according to the present invention. FIG. 4 is an explanatory diagram for explaining a case where a direct current is applied to two phases of a three-phase brushless motor. [Description of Signs] 1 Steering mechanism 2 Steering wheel (steering means) 4 Steering control unit (steering angle control means, superimposing means, comparing means) 5 Steering motor (brushless motor, motor) 5a Stator 5b Rotor 8 Steering Picking mechanism controller (superimposing means) 9 Axial force sensor (axial force detecting means) 13 Tie rod 15 Rotary encoder (rotor position detector) 16 Steering angle sensor 30 Rotary shaft 33 Rotary encoder (Steering angle detecting means)

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-105100 (JP, A) JP-A-4-54772 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 5/04 B62D 6/00

Claims (1)

(57) [Claim 1] Steering means not mechanically connected to a steering mechanism for changing the direction of wheels, steering angle detecting means for detecting a steering angle of the steering means, A steering apparatus for a vehicle, comprising: steering angle control means for driving a motor having a polyphase winding with a polyphase current to increase or decrease the steering angle of the steering mechanism according to the steering angle detected by the steering angle detection means. In the above, an axial force detecting means for detecting an axial force applied to a shaft for changing the direction of the wheel by a reverse input received by the wheel from a road surface, and comparing the axial force detected by the axial force detecting means with a predetermined value. And a superimposing means for superimposing a DC current on one or more phases of the multi-phase current when the comparing means determines that the axial force is larger than the predetermined value. To reduce the effect of the reverse input on A steering device for a vehicle, comprising: