JPH0234476A - Rear-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To avoid high power consumption to prevent battery failure by restricting steering of rear wheels comparing the steering to the steering under the condition where battery voltage is normal, when the voltage of battery or power supply of an electric motor in a rear wheel steering means is reduced. CONSTITUTION:In a rear wheel steering device which is provided with a rear wheel steering means 22 for steering rear wheels 6L, 6R by an electric motor 32, and which controls the rear wheels steering by means of the rear wheel steering means 22 using a control means 24, a power supply voltage detecting means 90 for supplying power to the electric motor 32 is provided. In the control means 24, a regulating unit 24a for receiving output signals from the power supply voltage detecting means 90 is provided to restrict the steering of the rear wheels 6L, 6R by the electric motor 32 when the detected power supply voltage is reduced below the normal level, camparing the detected power supply voltage to the condition where the power supply voltage is normal. Thus, when the power supply voltage is reduced, the sterring angle is reduced or steering volume is reduced to avoid high power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle that steers the rear wheels using an electric motor.

(Prior Art) Vehicles include two-wheel steering (2WS) vehicles that steer the front wheels and four-wheel steering (4WS) vehicles that steer the rear wheels as well as the front wheels.

As a rear wheel steering device for the above-mentioned four-wheel steering vehicle, a so-called electric motor type device in which the rear wheels are steered by an electric motor is known, for example, as described in Japanese Utility Model Application Publication No. 82-25277.

In such an electric motor type, the electric motor is generally configured to use a battery mounted on the vehicle as a power source, and to operate by receiving power from the power source.

(Problems to be Solved by the Invention) By the way, the battery serving as the power source cannot always maintain a predetermined voltage (normal voltage), and the voltage may drop due to various causes.

When the voltage of the battery decreases in this way, the rotational speed and torque of the electric motor decrease, resulting in the inconvenience that proper rear wheel steering (steering according to predetermined characteristics) becomes difficult. That is, if the rotational speed of the electric motor decreases, the steering speed of the rear wheels decreases, and if the torque of the electric motor decreases, it becomes impossible to steer the rear wheels at a large steering angle, making it difficult to properly steer the rear wheels. Note that electric motor-type rear wheel steering devices are usually equipped with a centering spring, etc. that always biases the rear wheels toward a neutral position (straight-ahead position). The centering spring must be bent significantly, which requires a correspondingly large amount of torque.

Further, if the rear wheel steering by the electric motor is continued when the battery voltage has decreased, the battery will run out, and there is also the problem that various other devices using the battery as a power source may be affected.

In view of the above-mentioned circumstances, an object of the present invention is to provide a rear wheel steering device for a vehicle that can perform proper rear wheel steering using an electric motor as much as possible while preventing the battery from running out even when the battery voltage decreases. It's about doing.

(Means for Solving the Problems) In order to achieve the above object, the rear wheel steering device for a vehicle according to the present invention provides a rear wheel steering system in which rear wheels 6L and 6R are steered by an electric motor 32, as shown in FIG. means 22; control means 24 for controlling the steering of the rear wheels 6L and 6R by the rear wheel steering means 22; power supply voltage detection means 90 for detecting the voltage of a power supply supplying electric power to the electric motor 32; When the power supply voltage detected by the power supply voltage detection means 90 provided at 24 falls from the normal state, the electric motor 3
A regulating portion 24a that regulates the steering of the rear wheels 6L and 6R by
It is characterized by comprising the following.

Restricting the steering of the rear wheels by the electric motor means limiting the steering in order to avoid consumption of large amounts of electric power, such as reducing the steering angle, reducing the steering range, Do not steer in the following cases).

(Function) If the voltage of the battery, which is the power source for the electric motor, drops, for example, if rear wheel steering is immediately stopped, the battery will not run out and problems associated with it will not occur, and proper rear wheel steering will not be performed. As a result, there are no problems such as an unexpected steering condition of the rear wheels and a significant decrease in maneuverability, but on the other hand, the benefits of four-wheel steering cannot be enjoyed at all from the time the rear wheel steering is stopped. .

However, in the present invention, when the battery voltage decreases, rear wheel steering is restricted rather than being canceled.

If rear wheel steering is regulated in response to voltage drops in this way, large amounts of power consumption due to rear wheel steering can be avoided, and as a result, even if rear wheel steering is performed when battery voltage is low, the battery will not run out and related inconveniences will be avoided. It can be avoided.

Further, even if there are regulations, the rear wheels are steered within the limits of the regulations, so the benefits of four-wheel steering can still be enjoyed, albeit within a limited range.

In addition, since rear wheel steering is regulated, large electric power is not required for rear wheel steering. Therefore, rear wheel steering is properly controlled according to its characteristics within the regulated range, and unexpected rear wheel steering conditions can be avoided. Occurrence can be prevented.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic diagram showing an example of a four-wheel steering system equipped with an embodiment of the present invention.

The four-wheel steering system shown in Fig. 2 has left and right front wheels 2L and 2R.
The vehicle includes a front wheel steering device 4 for steering the left and right rear wheels 6L and a rear wheel steering device 8 for steering the left and right rear wheels 6L and 6R.

The front wheel steering device 4 includes a front wheel steering shaft 14 that extends in the vehicle width direction and has both ends connected to a pair of left and right front wheels 2L, 2H via a pair of left and right tie rods IOL, IOR and knuckle arms L2L, 12R. and a steering shaft 20 having a pinion 16 at one end that meshes with rack teeth (not shown) formed on the steering shaft 14 and a steering wheel 18 at the other end. The front wheels 2L and 2R are steered by displacing the front wheel steering shaft 14 in the vehicle width direction by operating the steering wheel 1B.

The rear wheel steering device 8 includes a rear wheel steering means 22 for steering the rear wheels 6L and 6R, and a control means 2 for controlling the rear wheel steering means 22.
4, and various information for controlling the rear wheel steering means such as the vehicle speed detecting means 2B and the front wheel steering angle detecting means 28 are transmitted to the control means 24.
and the electric motor 32 described below.
and a battery voltage detection means 90 for detecting the voltage of a battery 88, which is the power source of the battery.

The rear wheel steering means 22 includes a rear wheel steering shaft 30 and a servo motor 32 which is an electric motor.

The rear wheel steering shaft 30 extends in the vehicle width direction, and has both ends connected to a pair of left and right rear wheels 6L via a pair of left and right tie rods 34L, 34R and knuckle arms 3fiL, 36R.
, 6R, and the rear wheels 6L, 6R are steered by stroke displacement of the rear wheel steering shaft 30 in the vehicle width direction. Also,
This rear wheel steering shaft 30 is provided with a centering spring means 38 which is a neutral position return means for urging the shaft 30 to return to the neutral position.

Stroke displacement of the rear wheel steering shaft 30 in the axial direction is performed by the servo motor 32. That is, the servo motor 32 is a step motor, and the brake means 40. Rotation is transmitted to the pawl screw means 46 through a driving force transmission system consisting of a clutch means 42 and a reduction gear 44, and the rear wheel steering shaft is rotated through the pawl screw means 46 against the biasing force of the centering spring means 38. 30 from a neutral position, that is, it is configured to cause a stroke displacement.

The brake means 40 locks the driving force transmission system between the servo motor 32 and the rear wheel steering shaft 30 to maintain the rear wheel steering shaft 30 in a predetermined displacement state. That is,
During steady steering (when the target rear wheel steering angle does not change), it is necessary to maintain the rear wheel steering shaft 30 at a predetermined displacement state.
This is done by the brake means 40 rather than the servo lock by the servo motor 321, thereby saving power consumption. The brake means 40 in this embodiment is constituted by an electromagnetic brake that locks the output shaft of a servo motor.

The clutch means 42 disconnects the driving force transmission system between the servo motor 32 and the rear wheel steering shaft 30 when a predetermined abnormality occurs, thereby freeing the rear wheel steering shaft 30, thereby moving the steering shaft 30 toward the centering spring. The means 38 returns it to the neutral position to bring it into the 2WS state, thereby providing a so-called fail-safe.

The clutch means 42 in this embodiment is a normal oven (disconnection when no current is applied) type electromagnetic clutch 4 arranged in series.
2A and a normally closed (connected when not energized) type electromagnetic clutch 42B.

The reason why the clutch means 42 is constituted by two clutches, the normal oven type electromagnetic clutch 42A and the normally closed type electromagnetic clutch 42B arranged in series, is to improve disconnection reliability and save power consumption. This is to aim for.

In other words, by installing two clutches in series, even if one clutch cannot be disconnected due to seizure, etc., the drive power transmission system can be disconnected by the other clutch, which greatly improves disconnection reliability. It will be planned. Furthermore, if two devices are provided in series, for example, if both devices are of normally open type, both devices must be energized during normal times (when no abnormality occurs), which doubles the power consumption. On the other hand, if both of them are of the normally closed type, the problem of power consumption will be eliminated, but the disconnection will become impossible if, for example, the clutch power supply fails. Therefore, by making one of them a normally closed type, it is possible to save power consumption, and by making the other one a normal oven type, it is possible to improve disconnection reliability in the event of a power supply failure.

The pole screw means 46 includes a pole nut 48;
A pole screw 50 carved into the steering shaft 30 and both 48.
The pole nut 48 is fixed to a gear 54 that meshes with the reduction gear 44 and rotates integrally with the gear 54, and cannot be displaced in the axial direction of the steering shaft 30. When the pole nut 48 is rotated by the servo motor 32, the steering shaft 30 is stroked in the axial direction accordingly.

The centering spring means 38 includes a pair of stoppers 56 and 58 provided on the steering shaft 30 at a predetermined interval, and is disposed within the two stoppers 58 and 58 that are loosely fitted on the steering shaft 30. A pair of spring receivers 60.82 whose movement in the expansion direction is regulated by 56.58, and both spring receivers 8
Centering spring 6 arranged in a compressed state between 0.62
4, and both spring receivers 60 and 82 are connected to both stoppers 56.
．． 58, the stopper 56.5
Similarly to 8, the casing-side stopper portions ee and es are provided which abut against both spring receivers 60.82 in order to restrict the movement of both spring receivers 80.82 in the expansion direction, and the compressive load of the centering spring 64 ( Steering shaft 3 due to preset load)
0 is always biased towards the neutral position.

The rear wheel steering by the servo motor 32 is controlled by the control means 24.
It is controlled by the control section 24b inside. The control section 24b
The basic control of rear wheel steering is so-called vehicle speed-sensitive control, which uses vehicle speed and front wheel steering angle as control parameters, and steers the rear wheels in accordance with the front wheel steering. (rudder angle) is changed according to vehicle speed.

An example of changing the steering ratio according to the vehicle speed is as shown in FIG. 3. When the control characteristics shown in the figure are applied, the rear wheel steering angle relative to the front wheel steering angle changes in the same phase direction as the vehicle speed increases, for example, vehicle speed 4 (ll!).
The phase changes from the opposite phase to the same phase with n/h as the boundary, and this situation is shown in FIG. In the illustrated control characteristics, a dead zone is provided in the anti-phase steering region where the vehicle speed is less than 40 KIn/h, in which the rear wheels are not steered until the front wheel steering angle reaches a predetermined value θ1.

In order to perform such rear wheel steering control, the control section 24b
Signals from the vehicle speed detection means 26, the front wheel steering angle detection means 28, and the rotary encoder 72 that detects the rotational position of the servo motor 32 are input to the control section 24b.
Then, a target rear wheel steering angle is calculated based on the front wheel steering angle and the vehicle speed, and a control signal corresponding to the required rear wheel steering angle is output to the servo motor 32.

The rotary encoder 72 constantly monitors whether or not the servo motor 32 is operating properly, that is, under feedback control, the rear wheels 6L and 6R are operated.
The vehicle is now being steered.

The control section 24b also controls the operation of the brake means 40 and the clutch means 42 in addition to the servo motor 32. As described above, the brake means 40 is controlled by locking the output shaft of the servo motor during steady steering so as to control the rear wheel steering shaft 3.
0 is maintained at a predetermined displacement state, and as described above, the clutch means 42 is controlled to be in a disconnected state when a predetermined abnormality occurs, and the rear wheel steering shaft 30 is returned to the neutral position by the centering spring means 38 for fail-safe purposes. It is done as much as possible.

The control means 24 includes ON/O signals from a neutral clutch switch 76, an inhibitor switch 78, a brake switch 80, and an engine switch 82.
It is configured so that an FF signal and a signal from the alternator terminal 84 indicating the presence or absence of power generation are input. 86 is a warning lamp that is turned on when an abnormality occurs.

The control means 24 is provided with a control section 24b and a regulating section 24a, which control rear wheel steering according to the basic control characteristics shown in FIGS. 3 and 4. The regulating portion 24a regulates the steering of the rear wheels by the servo motor 32 when the battery voltage drops from a normal state compared to when the battery voltage is normal.

The above-mentioned normal battery voltage refers to a voltage state in which no particular problem occurs even if the rear wheel steering is controlled according to the basic control characteristics shown in Figs. 3 and 4 above. For example, in the case of a 12V battery, for example, IOV or higher can be said to be normal.

Rear wheel steering when the battery voltage is normal is performed according to the basic control characteristics, and therefore the servo motor 3
2 means that the steering of the rear wheels is restricted compared to the steering based on the basic control characteristics described above.

Furthermore, restricting the steering means, as described above, restricting the rear wheel steering in order to avoid the consumption of large amounts of power by steering the rear wheels, that is, restricting the steering that consumes a large amount of electric power to be stopped.

Various modes of regulation can be considered, and for example, a mode of reducing the steering angle or reducing the steering area can be adopted.

To reduce the steering angle, set a coefficient f (V) that varies between 1 and 0 depending on the battery voltage, as shown in Fig. 5, and set the target rear wheel steering angle determined by the following formula. The rear wheels may be controlled according to θRT. However, θRTN in the formula below is the basic target rear wheel steering angle based on the above basic control characteristics.

θRT-f (V)XθRTN According to this control, the battery voltage decreases to 8V
〜IOV, f is determined according to the voltage
When the target rear wheel steering angle is decreased by (V) and the battery voltage becomes 8V or less, rear wheel steering is stopped,
The state becomes 2WS. If the rear wheel steering angle is made smaller, the amount by which the centering spring 64 is not bent becomes smaller, and power consumption can be reduced accordingly.

Examples of ways to reduce the steering range include prohibiting rear wheel steering at low vehicle speeds when the voltage is below a predetermined voltage, and reducing the rear wheel steering angle when the front wheel steering angle is above a predetermined value. Can be done.

As a specific example of the former aspect, for example, if the vehicle speed is 40 KIn
It is conceivable to prohibit rear wheel steering in a reverse phase steering region of 11 h/h or less, or to prohibit rear wheel steering when the vehicle speed is 11 h/h or less. Rear wheel steering at low vehicle speeds has a large road resistance, especially when the vehicle speed is below 1/la/h, the rear wheel steering is in a stationary state or a state close to that when the vehicle is stopped, so the road resistance is extremely large, so in such cases Large power consumption can be avoided by prohibiting rear wheel steering.

As a specific example of the latter aspect, it is conceivable to change the control characteristics as shown in FIG. 6, for example, when the voltage becomes lower than a predetermined voltage. The characteristics shown in FIG. 6 are such that when the front wheel steering angle θF is less than the predetermined value θ2, the rear wheels are steered according to the basic control characteristics described above, and when the front wheel steering angle θ exceeds the predetermined value θ2, the rear wheels are steered. This is to prevent the steering angle θ8 from increasing. Note that the broken line in the figure indicates the characteristics before the change. Rear wheel steering when the front wheels have a small steering angle greatly exhibits the benefits of 4WS, so in that area the rear wheels should be steered according to the basic control characteristics, and from then on, large rear wheel steering should be prohibited. This makes it possible to avoid large power consumption without significantly impairing the benefits of 4WS.

Note that when the battery voltage decreases and a predetermined rotational speed cannot be obtained, the current consumption increases, and as a result, the current of the motor may be limited. This current restriction is to protect the motor protection circuit 1, and regulates the upper limit current value that can flow through the motor, and may come into play even when the load becomes abnormally large.

When the above current limit is activated, the rear wheels will be steered to the target steering angle using the current at the limit value (upper limit), but the fact that the current limit is activated means that higher output torque and rotational speed are required. This means that the steering of the rear wheels is delayed. This follow-up delay of the rear wheels is not a problem if the steering is in only one direction, but if the steering is repeated in the vicinity of neutral, there is a possibility that the phase will be reversed when in-phase control is required. Therefore, in order to avoid such a possibility, it is better to avoid steering the rear wheels any more when the current limit is activated.

(Effects of the Invention) As described above, in the vehicle rear wheel steering device according to the present invention, when the voltage of the battery, which is the power source of the electric motor, decreases, the rear wheel steering device according to the present invention can perform rear wheel steering compared to steering when the battery voltage is normal. Since the steering is configured to be regulated, the consumption of a large amount of electric power can be avoided by regulating the steering, and thereby a dead battery can be avoided. In addition, since the rear wheels are steered within the regulated range, you can still enjoy the benefits of 4WS, and since steering within the regulated range does not require large amounts of power, it is possible to control according to the characteristics within the regulated range. , it is possible to prevent the occurrence of unexpected rear wheel steering conditions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview of the present invention, FIG. 2 is a schematic diagram showing an example of a four-wheel steering device equipped with an embodiment of the present invention, and FIGS. 3 and 4 are shown in FIG. A diagram showing an example of the basic rear wheel steering control characteristics of the embodiment, FIG. 5 is a diagram showing an example of the coefficient f (V) used when decreasing the steering angle, and FIG. 6 is a diagram showing an example of the coefficient f (V) used when decreasing the steering angle. FIG. 6L, 6R...Rear wheel 22...Rear wheel steering means 2
4... Control means 24a... Regulation part 32.
...Electric motor 90...Power supply voltage detection means group

Claims (1)

[Scope of Claims] Rear wheel steering means for steering the rear wheels by an electric motor, control means for controlling the steering of the rear wheels by the rear wheel steering means, and a power source for detecting the voltage of a power source that supplies electric power to the electric motor. voltage detection means, and when the power supply voltage detected by the power supply voltage detection means provided in the control means drops from a normal state, the steering of the rear wheels by the electric motor is reduced compared to when the power supply voltage is normal. A rear wheel steering device for a vehicle, comprising: a regulating section that regulates the vehicle.