JPH054270B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a four-wheel steering system for a vehicle.

(Prior art) Regarding a four-wheel steering system that controls the steering of the rear wheels in accordance with the steering of the front wheels of a vehicle, for example, as described in Japanese Patent Application Laid-open No. 59-81272, there is a method for steering the front wheels. The ring gear of the differential is engaged with the pinion of the steering shaft, and one side gear of the differential is connected to the motor, and the other side gear is connected to the rear wheel steering shaft. Techniques for controlling motors to change the steering phase and steering ratio of front and rear wheels are well known.

By the way, if a stepping motor is used as the motor for changing the steering ratio as described above, it is possible to control the steering ratio with high precision. However, this stepping motor becomes inoperable when the excitation coil winding is disconnected, and the steering ratio cannot be changed thereafter.

(Object of the Invention) The present invention is an apparatus in which the steering ratio of the front and rear wheels is made variable by a stepping motor, and in which the stepping motor can be driven even if the coil winding is disconnected, the steering ratio is changed. This is an attempt to improve the reliability of ratio control.

(Structure of the Invention) As shown in FIG. 1, the rear wheels 3 of the vehicle 1 are steered in accordance with the steering of the front wheels 2, and the steering ratio is sent from the control section 4 via the stepping motor drive section 6. The stepping motor 5 is actuated by a signal corresponding to the operating state, and the stepping motor 5 changes from the opposite phase to the same phase. In the stepping motor driving section 6, each coil winding has an inverted phase, and the excitation current of each coil winding has two directions, positive and negative. A drive controller unit 7 controls the reverse phase of the coil winding and the remaining coil windings to drive the stepping motor when the coil winding is broken, and reduces the frequency of the drive pulse of the stepping motor 5 when the coil winding breaks. The drive pulse frequency generating section 8 is provided with a driving pulse frequency generating section 8 that generates a driving pulse frequency. That is, the stepping motor 5 is driven by exciting the inverted phase of the disconnected coil winding to a polarity opposite to the normal state, but this compensates for the decrease in the output of the stepping motor 5 due to the switching of the current direction of this inverted phase. Therefore, the frequency of the drive pulse is lowered to ensure the necessary torque for changing the steering ratio.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 2 to 11. Note that the same reference numerals are used for components in the embodiment that correspond to those shown in FIG.

Embodiment 1 This embodiment is shown in FIGS. 2 to 10, and is an example in which the steering of the front wheels 2 is mechanically transmitted to the rear wheels 3.

First, the left and right front wheels 2, 2 are connected to the Katsukuru arm 9,
9, connected to both ends of the relay rod 11 via tie rods 10,10. relay rod 11
The shaft 13 from the handle 12 is easily 1
4 and pinion 15, and when the handle 12 is rotated, the relay rod 11 moves left and right to steer the left and right front wheels 2, 2.

On the other hand, the left and right rear wheels 3 and 3 are also equipped with Natsukuru arm 1.
It is connected to both ends of a relay rod 18 via tie rods 17 and 17, and is configured to be steered by moving the relay rod 18 left and right. This relay rod 18 moves in conjunction with the movement of the front wheel side relay rod 11, and the movement is assisted by hydraulic pressure.

Specifically, the front end of an operating rod 19 extending in the front-rear direction is connected to the relay rod 11 on the front wheel side by engaging a rack 20 and a pinion 21, and the rear end of this working rod 19 is connected to the relay rod 11 on the front wheel side. It is connected to a control rod 23 extending from the relay rod 18 on the rear wheel side via a steering ratio changing mechanism 22 that changes the steering ratio. The operating rod 19 rotates in response to the steering of the front wheels 2, and the control rod 23 slides left and right at the steering ratio determined by the steering ratio changing mechanism 22, so that the rear wheels 3 are steered. It's getting old.

The steering ratio is changed by operating the stepping motor 5.
The operation is controlled by a control circuit 24 that outputs a control signal in response to an output from a vehicle speed sensor 32 that detects the vehicle speed. Further, a steering ratio detection means 29 for detecting a steering ratio is attached to the steering ratio changing mechanism 22 to output a steering ratio signal to the control circuit 24.
4 is connected to a power source 26 via an ignition switch 25.

Further, the relay rod 18 on the rear wheel side passes through a power cylinder 27 fixed to the vehicle body, and the inside of the power cylinder 27 is divided into two hydraulic chambers 30a and 30b by a piston 28 fixed to the relay rod 18. Both hydraulic chambers 30a, 30b are connected to an oil pipe 3.
1a and 31b to a control valve 33, and the control valve 33 is connected to an oil supply pipe 35 from a reservoir tank 34 and an oil return pipe 3.
6 is connected. control valve 33
detects the direction of movement of the control rod 23, and connects the oil supply pipe 35 to one of the hydraulic chambers 30a, 30b and the oil return pipe 36 to the other of the hydraulic chambers 30a, 30b according to the direction of movement. , an oil pump 3 interposed in the oil supply pipe 35
The hydraulic pressure from the relay rod 18 is controlled to a pressure corresponding to the shifting force of the control rod 23, and the hydraulic pressure introduced into the power cylinder 27 controls the shifting force of the relay rod 18, that is, the steering force of the rear wheels 3, 3. assist.

The oil pump 37 is driven by the engine, and the hydraulic chambers 30a, 30b are provided with springs 38, 38 for biasing the relay rod 18 to a neutral position, that is, a zero rear wheel steering position.

The specific structure of the steering ratio changing mechanism 22 will be explained based on FIG. is indicated by l ₁ . The steering ratio changing mechanism 22 includes a holder 40 rotatably supported by the vehicle body 39 about a perpendicular line l ₂ orthogonal to the movement axis l ₁ .
A swing arm 41 is swingably held on a swing shaft 42 . This swing axis 42 is located at the intersection of the movement axis _l1 and the orthogonal line _l2 , and its swing axis _l3 extends in a direction orthogonal to the orthogonal line _l2 .

One end of a connecting rod 43 is connected to the control rod 23 through a ball joint 44, and the other end of this connecting rod 43 is connected to the tip of the swing arm 41 through a ball joint 45. There is. This connecting rod 43 includes a rotation imparting arm 4 having a rotation shaft 46 on the movement axis _l1 .
7 is connected via a ball joint 48, and an actuating rod 19 extending from the relay rod 11 on the front wheel side is connected to the rotating shaft 46 by the bevel gear 4.
They are connected by a mesh of 9 and 50. The rotation imparting arm 47 is a cylinder 5 integrated with the rotation shaft 46.
1, and is allowed to move forward and backward in a direction perpendicular to the rotation axis 46.

Then, a worm 52 is provided on the output shaft of the stepping motor 5 of the steering ratio changing mechanism 22, and this worm 52 meshes with a worm wheel 53 provided on the rotating shaft of the holder 40. The steering ratio is changed by the operation of the motor 5, and the steering ratio is detected from the rotation angle of the holder 40 by a steering ratio detection means 29 attached to the holder 40.

That is, in the steering ratio changing mechanism 22, the steering of the front wheels 2 is transmitted to the swing arm 41 via the actuating rod 19, the rotation imparting arm 47, and the connecting rod 43, and the swing arm 41 is aligned with the swing axis. l ₃
Swings (rotates) around the center. Then, when this swing axis _l3 coincides with the movement axis _l1 of the control rod 23 due to the swing angle setting of the honda 40 by the stepping motor 5, the swing locus of the tip of the swing arm 41 is Even if the front wheels 2 are steered in a plane perpendicular to the axis of movement _l1 , no force is generated to shift the control rod 23 via the connecting rod 43, so the rear wheels 3 are not steered (no steering occurs). ratio is zero).

On the other hand, when the stepping motor 5 operates and the swing axis _l3 is tilted downward to the right with respect to the movement axis _l1 as shown in FIG _. When the front wheels 2 are steered, the swing arm 41 swings to connect the connecting rod 4.
3 generates a force that causes the control rod 23 to shift from side to side, and the rear wheels 3 are steered in the same phase as the front wheels 2. Furthermore, when the swing axis _l3 is tilted in the opposite direction, the rear wheels 3 are steered in the opposite phase. In other words, the stepping motor 5 rotates the holder 40 to
By changing the inclination angle of l ₃ , the swing trajectory of the swing arm 41 is changed, and the steering angle of the rear wheels 3 relative to the steering angle of the front wheels 2 is changed. In other words, the steering ratio is changed from minus (opposite phase) to plus ( the same phase).

In addition, in the case of this example, the holder 40 has a swing shaft 4
Arms 54, 54 supporting both ends of the vehicle are connected in a U-shape.
Stoppers 55, 55 are provided which come into contact with the base end of the swing shaft 42 and restrict the rotation angle of the swing shaft 42.

Now, the concrete structure of the stepping motor 5 is shown in FIG. That is, this stepping motor 5 has ten rotating teeth 58 on a rotor 57 fixed to an output shaft 56, and eight rotating teeth on a stator 59.
The fixed teeth 60 are provided. In the case of this example, the rotating teeth 58 are composed of a permanent magnet (N pole),
Four sets of coil windings 61A, 61B, 61, 61 called A phase, B phase, phase, and phase of the stepping motor drive section 6 are wound around each fixed tooth 60, and each of these coil windings is sequentially excited. By exciting the fixed tooth 60 to the south pole through an electric current, the rotor 57 rotates 9 degrees in one step. In this case, the A phase coil winding 61A
and phase coil and winding 61, B phase coil winding 61
B and the phase coil winding 61B are out of phase with each other by 90 degrees (angle), and have an inverted phase relationship with each other.
In other words, the rotor 5 when one side is excited to the N pole
The relationship is such that the effect on rotor 57 is equivalent to the effect on rotor 57 when the other is excited to the S pole.

The configuration of a control system for controlling the driving of the stepping motor 5 is shown in FIG. 6, and the circuit configuration of the stepping motor driving section 6 is shown in FIG.

In the above control system, the control section 4 includes a characteristic switching means 62, a turning angle calculation section 63, a drive controller section 7, and a drive pulse frequency generation section 8. The characteristic switching means 62 receives the output from the vehicle speed sensor 32 and outputs a steering ratio characteristic switching signal (vehicle speed signal) to the steering angle calculation section 63. The steering angle calculating section 63 selects and calculates one of the steering ratio characteristic lines shown in FIG. A control signal regarding the rotation direction and the number of drive pulses of 5 is output.

The drive controller section 7 basically receives the above control signal and outputs excitation signals EA, E, EB, and E to the coil windings 61A, 61, 61B, and 61 of each phase of the stepping motor drive section 6. Furthermore, each phase coil winding disconnection detection signal DA, D, DB,
When D is received, current direction switching signals C _AA and C _BB are output to the stepping motor drive unit 6 so that current flows in the opposite direction to the coil winding that is in a reverse phase relationship with the broken coil winding. This point will be explained in detail later in relation to the stepping motor drive section 6.

The drive pulse frequency generator 8 determines how many seconds the stepping motor 5 is operated in steps, for example, in the case of a two-phase excitation method, the excitation signal (EA, EB) →
(EB, E) → (E, E) → (E, EA)
The timer T is used to determine the number of seconds at which switching is performed, and upon receiving a reset (initialization) signal _S1 from the drive controller 7, it outputs a timeout (switching) signal _S2 after T time, and then resets the drive controller. signal
The operation of receiving S ₁ is repeated. The stepping motor 5 has a characteristic that the output torque decreases as the frequency of the drive pulse increases, and the timer T is set so that the frequency of the drive pulse does not exceed the limit torque required for changing the steering ratio. The setting of this timer T will be explained in detail later.

Further, the steering angle calculation section 63 includes the steering ratio detection means 2
9, the actual steering ratio is compared with the steering ratio obtained from the above steering ratio characteristic line, and the actual steering ratio is made to match the calculated steering ratio. A correction means for outputting a correction control signal to the drive controller section 7 is provided. This correction means does not operate all the time, but normally changes the steering ratio using open-loop control. For example, the correction means performs feedback control at a set vehicle speed, such as when the vehicle speed is zero or when the vehicle speed is such that the steering ratio is zero. Let's do it.

Now, in FIG. 7 showing the circuit configuration of the stepping motor drive unit 6, 65 is a bipolar drive circuit using an A-phase and phase bridge system, which switches the direction of current from the A-phase coil winding 61A power source 26.
A first switching circuit 68 connecting PNP and NPN transistors 66 and 67, and a similar transistor 6
The phase coil winding 61 is connected between the second switching circuit 71 and a first switching circuit 74 including similar transistors 72 and 73. 75 is the A phase excitation signal EA and the (A,) phase current direction switching signal
C A NAND circuit which receives _{the AA} and sends a switch signal to the first PNP transistor 66 of the A phase;
This is an AND circuit that receives C _AA and sends a switch signal to the first NPN transistor 67 of the A phase. The transistors 72 and 73 on the phase side also have the same structure as on the A phase side.
A NAND circuit 78, an inverting element 80, and an AND circuit 79 are connected. Further, 81 is a diode that prevents reverse voltage to the base of the second PNP transistor 69, and 82 is an on-delay circuit for the second PNP transistor 69, which is composed of an integrating circuit made up of a resistor 83 and a capacitor 84, and a discharging diode 86. On the second NPN transistor 70 side, there is also a similar reverse voltage prevention diode 87, an integrating circuit consisting of a resistor 88 and a capacitor 89, and a discharge diode 90.
It has an on-delay circuit 91 consisting of. and,
Disconnection detection signals DA and D are obtained from the first switching circuits 68 and 74 for the A phase and phase, respectively.

Similarly, B-phase coil windings 61B, 61
is also incorporated into the bipolar drive circuit 92 based on the bridge method. This drive circuit 92 has substantially the same configuration as that for the A phase and the A phase, and detailed illustration and explanation thereof will be omitted.

In the A-phase and phase drive circuits 65, the drive controller section 7 outputs the current direction switching signal _CAA as an L (low) signal when normal, and as an H (high) signal when abnormal. First, under normal conditions, when the A-phase excitation signal EA (H signal) is output from the drive controller section 7, the output of the NAND circuit 75 is H, so the PNP transistor 66 of the first switching circuit 68 is turned off, and the AND circuit Since the output of 76 is H, the NPN transistor 67 is turned on, and the output of the second switching circuit 71 is turned on.
PNP transistor 69 is turned on and NPN transistor 70 is turned off. Therefore, the current flows through the A-phase coil winding 61A from the second switching circuit 71 side to the first switching circuit 68 side as indicated by the arrow I _o , and the A-phase is excited to the S pole. In the case of two-phase excitation, (A,
The two phases (B), (B,), . . . are sequentially excited, and the rotor 57 of the stepping motor 5 rotates one step at a time.

For example, when the phase coil winding 61 is disconnected, the phase disconnection detection signal D, which would normally be output as an H signal due to the power supply voltage, becomes
Since the power supply voltage is not transmitted through the phase coil winding 61, an L signal is generated and a disconnection is detected on the drive controller section 7 side. In other words, when the phase excitation signal E is output, the phase disconnection detection signal D is output, and the current direction switching signal C _AA of (A,) is L
It switches from to H.

Therefore, this time, the first switching circuit 68 on the A phase side is
The PNP transistor 66 is turned on, the NPN transistor 67 is turned off, the PNP transistor 69 of the second switching circuit 71 is turned off, the NPN transistor 70 is turned on, and the A-phase coil winding 61A is connected to the reverse direction I _a
A current flows, and the A phase is excited to the N pole. This A
The phase is the inversion phase of the phase, and the N pole of the A phase and the S pole of the phase
Since the poles have the same effect on the rotor,
When the phase excitation signal E is output, the A phase plays the role of the phase excitation signal E, and the stepping motor 5 operates smoothly. Then, when the phase excitation signal E becomes L,
The A phase disconnection detection signal D is not output, and (A,)
Phase current direction switching signal C _AA returns to normal L, and A
The phase is excited to the south pole by the excitation signal EA.

The on-delay circuits 82 and 91 delay the on-signal transmitted to the transistors 69 and 70 of the second switching circuit 71 when switching the current direction, and simultaneously both transistors 69 and 70 are turned on and destroyed. prevent this from happening. That is, the ninth
As shown in the figure, when the current direction switching signal C _AA switches from L to H, the PNP transistor 69 of the second switching circuit 71 turns off from H to L, but the NPN transistor 70 is connected to the capacitor 89 of the integrating circuit. The rise from L to H is delayed until the charge accumulates,
Both the PNP and NPN transistors 69 and 70 are never turned on at the same time. Conversely, when the switching signal C _AA switches from H to L, the integration circuit on the PNP transistor 69 side delays the rise from L to H.

Incidentally, the delay in the rising of the current when switching the current direction leads to a decrease in the drive current of the stepping motor 5, and as a result, when the coil winding of the stepping motor 5 is disconnected, as shown in FIG. Dynamic torque decreases compared to normal. However, as shown in the figure, this torque has a characteristic that it increases as the drive pulse frequency decreases, and when the drive pulse frequency decreases when the wire is disconnected.
By lowering f from f ₁ to f ₂ , the torque F required for changing the steering ratio can be secured as in the normal state.

The drive pulse frequency generator 8 controls the drive pulse frequency, and generates excitation signals (EA, EB) → (EB, E) → (E, E) →
Timer T=n・t (t=constant) for switching...
This is a programmable timer in which the n value can be rewritten. In this case, as n increases, T increases, the drive pulse frequency decreases, and the torque increases. Then, in response to a disconnection detection signal (DA, D, etc.) from the stepping motor drive unit 6, the drive controller unit 7 sends a signal S to the drive pulse frequency generator 8, which rewrites the n value when a disconnection is detected, and resets the n value when normal. It is designed to output _o . In this driving pulse frequency generating section 8, from the viewpoint of accelerating the responsiveness of steering ratio change, the timer T is controlled to be the highest frequency at which the above-mentioned required torque F can be obtained. n ₁ as the n value of and n ₂ (n ₁ > n ₂ ) as the n value at the time of coil winding breakage are stored in advance, and upon receiving the n value rewriting signal, n = n ₂ ,
Decrease the frequency of the drive pulse.

Therefore, in this embodiment, the coil winding 6 of the stepping motor drive unit 6 that changes the steering ratio is
When one of 1A, 61, 61B, and 61 is disconnected, the coil winding, which is in an inverted phase relationship with the disconnected wire, is excited to the opposite polarity than normal, and the drive pulse frequency decreases, causing the current direction to change. Therefore, the rotor 57 of the stepping motor 5 rotates in the same manner as when there is no disconnection, and the steering ratio can be changed by rotating the swing shaft 42 without any problem.

Since this embodiment uses a two-phase excitation method, when a coil winding breakage signal is input, the stepping motor 5 is driven by controlling the coil winding corresponding to the reverse phase of the broken coil winding and the other coil windings. However, in the case of the one-phase excitation method, only the inverted phase of the broken coil wire is excited to the opposite polarity to drive the stepping motor 5.

Embodiment 2 This embodiment is shown in FIG. 11, and is an example in which the steering control of the rear wheels 3 in conjunction with the steering of the front wheels 2 is performed electrically.

That is, the four-wheel steering system of this example includes a bundle steering angle sensor 9 provided on the steering shaft 13.
3. A controller 94 that receives the steering wheel angle signal from the steering wheel angle sensor 93 and the vehicle speed signal from the vehicle speed sensor 32 and outputs a control signal to the stepping motor driving section 6, and a drive from the stepping motor driving section 6. It includes a stepping motor 5 that steers the rear wheels 3 in response to a signal.

In this example, the stepping motor 5 is connected to a pinion 97 that meshes with a rack 96 of the rear wheel side relay rod 18 via a transmission mechanism 95 consisting of a pair of bevel gears.
The hydraulic control valve 33
is designed to detect the rotational direction and rotational force of the pinion 97 and change the oil passage and oil pressure. Further, a rear wheel steering angle sensor 98 is attached to the stepping motor 5, and a coil winding disconnection detection means 99 is provided in the stepping motor drive unit 6, and the rear wheel steering angle signal and the disconnection detection signal are sent to the controller 94. It is designed to output to. The controller 94 also includes front wheels 2 and rear wheels 3.
a display means 100 for graphically displaying the steering mode of the rear wheels 3, a control mode changeover switch 101 for setting the steering mode of the rear wheels 3, an energizing line 102 for operation that supplies electricity from the battery via the ignition switch, and a steering wheel steering angle memory. A current-carrying wire 103 is connected thereto.

Then, the controller 94 includes a steering angle calculating section 104 that calculates a rear wheel turning amount from the front wheel turning amount calculated from the steering wheel steering angle signal and a steering ratio calculated from the vehicle speed signal and outputs a control signal. In response to this control signal, it outputs an excitation signal for each coil winding to the stepping motor drive unit 6, and in response to a computer detection signal for each coil winding, it outputs a current direction switching signal to the stepping motor drive unit 6. A drive pulse frequency generating section 8 receives signals from the drive controller section 7 to reduce the drive pulse frequency, and detects the steering ratio from each steering wheel steering signal and each rear wheel steering signal. Rudder angle calculation unit 10
4 and steering detection means 105 for outputting a detection signal for steering ratio feedback correction.

Therefore, in the case of this example, the steering angle calculation unit 104
Steering control of the rear wheels 3 including steering ratio change control is performed, and the stepping motor 5 not only changes the steering ratio but also performs actual steering of the rear wheels 3.

The control mode changeover switch 101 also has an auto mode in which the rear wheels 3 are steered in an opposite phase to the front wheels 2 in a low vehicle speed range, and an auto mode in which the rear wheels 3 are steered in a phase opposite to the front wheels 2.
This is a switch for the driver to select and manually set the club mode in which the wheels are steered in the same phase as the wheels, and the steering ratio in each mode also changes depending on the vehicle speed.

In each of the above embodiments, the steering ratio is changed depending on the vehicle speed and the vehicle speed and setting mode, but the steering ratio can be changed by combining these factors with other factors such as lateral acceleration acting on the vehicle body. Change control may also be performed. Furthermore, the steering ratio may be changed by controlling only one of the lateral acceleration, the control mode changeover switch 101, and the steering angle, or by a combination of these.

(Effects of the Invention) According to the present invention, even if the coil winding of the stepping motor drive section is disconnected, the stepping motor is output by controlling the coil winding of the inverted phase and controlling the drive pulse frequency to decrease. Since the steering ratio can be driven without causing a decrease in the steering ratio, reliability of steering ratio change control in four-wheel steering can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention, Figs. 2 to 10 are related to Embodiment 1, Fig. 2 is an overall block diagram of a four-wheel steering device, and Fig. 3 shows a part of the steering ratio changing mechanism. A plan view shown in cross section, Figure 4 is taken along A-A in Figure 3.
Figure 5 is a cross-sectional view of the stepping motor, Figure 6 is a control system diagram, Figure 7 is a stepping motor drive circuit diagram, Figure 8 is a steering ratio characteristic diagram, and Figure 9 is a diagram of steering ratio characteristics.
The figure is a transistor switch operation characteristic diagram, No. 10.
The figure is an output characteristic diagram of a stepping motor, and FIG. 11 is an overall configuration diagram of a four-wheel steering system according to a second embodiment. 1...Vehicle, 2...Front wheel, 3...Rear wheel, 4...
Control unit, 5... Stepping motor, 6... Stepping motor drive unit, 7... Drive controller unit, 8... Drive pulse frequency generation unit.

Claims (1)

[Claims] 1. In a vehicle where the rear wheels are steered in response to the front wheels being steered, and the steering ratio of the rear wheels to the front wheels is variable between the opposite phase and the same phase depending on the driving condition, the above steering ratio is made variable. A stepping motor, a stepping motor drive unit in which each coil winding has an inverted phase and the excitation current of each coil winding has two directions, positive and negative; and a control section that controls a motor drive section to drive the stepping motor, and when a coil winding of the stepping motor drive section is disconnected, the control section controls the reverse phase of the disconnected coil winding and the remaining coils. A four-wheel steering system for a vehicle, comprising: a drive controller section that controls windings to drive a stepping motor; and a drive pulse frequency generator section that reduces the frequency of drive pulses of the stepping motor. .