JP5412782B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that is mounted on a vehicle such as an automobile and generates a steering assist force by a motor in accordance with a steering torque applied to a steering wheel by a driver.

As a test performed while the vehicle is traveling at high speed, there is a so-called release test. This test is performed to verify how much the vehicle itself has the ability to go from unstable to stable.
Due to the characteristics (hand-off characteristics) obtained by this test, the stability of vehicle behavior in crosswinds, puddles, continuous curves, etc. during normal driving, that is, the ability of the vehicle itself to autonomously resolve unstable behavior Can know.
This is important when the driver controls the vehicle, and shows how faithfully the vehicle itself can perform the vehicle behavior for a given steering while suppressing disturbance to the steering intended by the driver. One of the characteristics.

  On the other hand, when the vehicle is steered while traveling, the grounding portion that is in contact with the road surface of the tire tries to push back the force Ft in the direction in which the tire moves forward and the twist generated in the grounding portion by steering due to the weight of the vehicle. It is known that the reaction force Fc works. Fc is generally called a cornering force, and twisting of a tire ground contact portion is called a slip angle. Here, since Fc is generated at a position deviated from the center of the tire due to the influence of the tire shape or the like, it causes a moment force to reduce the slip angle generated by the steering. The moment force generated at this time is referred to as self-aligning torque. Therefore, the restoring force for returning the steering wheel to the original position, which is generated by setting the caster angle of the suspension, and the self-aligning torque are added to the steering force of the steering wheel. These forces acting on the driver's steering force can be reduced by performing power assist.

  If the vehicle is equipped with an electric power steering device that performs power assist, and the driver releases his / her hand from the steering wheel immediately after performing the right or left turning steering, the self-aligning torque, the restoring force described above, etc. In the case of a vehicle having a characteristic of suddenly returning the steering device to the neutral position due to the above, a vibration occurs that the vehicle is returned too far from the neutral position due to the moment of inertia of the electric motor (for example, patent document) 1). This vibration is gradually damped and the steering device converges to the neutral position.

JP 2005-41279 A

However, if the driver steers the vehicle to the right or left while driving at high speed and releases his hand from the steering wheel immediately after that, the rear portion of the vehicle may roll left and right together with the vibration described above. Since rolling also affects steering, there is a problem that vibrations do not converge as a result.
In view of such conventional problems, an object of the present invention is to improve the convergence of an electric power steering apparatus when a driver releases his / her hand from a steering wheel immediately after performing cutting steering.

The present invention is an electric power steering device that generates a steering assist force by a motor according to a steering torque,
And the steering angle detecting means for detecting a steering angle to be applied to the steering wheel, a behavior detection means for detecting the rolling of the vehicle rear portion, in synchronization with the right and left vibration of the steering angle at the time of convergence to the neutral position, and the vehicle If the rolling direction reaches a predetermined amount due to the reverse relationship between the left / right direction of the steering angle when viewed from above and the left / right direction of rolling when viewed from the rear of the vehicle , And a control means for losing the auxiliary force.

In the electric power steering apparatus configured as described above, the left and right direction of change of the steering angle when the vehicle is viewed from above in synchronization with the left and right vibration of the steering angle when converging to the neutral position, and the vehicle The direction in which the rolling changes to the right and left when viewed from behind is reversed, and when the rolling that reaches the predetermined amount occurs, the direction of the steering angle (right or left) is the opposite direction (left direction or This is a case where rolling of the rear part of the vehicle occurs in the right direction (so-called seesaw state). In such cases, convergence is hindered. Therefore, the control means reduces the influence of the steering assist on the rolling by losing the steering assist force. Thereby, convergence can be promoted. The “lost” may be “temporarily lost”.

Further, in the electric power steering apparatus, the behavior detection means is a displacement detection apparatus that is provided for each of the left and right rear suspension devices and detects whether or not the rear suspension device is compressed to a predetermined state. May be that rolling that reaches a predetermined amount occurs due to the left and right displacement detection devices being alternately detected.
In this case, the rolling that reaches a predetermined amount can be detected easily and reliably by the displacement of the rear suspension device.

The electric power steering device may include a vehicle speed sensor that detects a vehicle speed, and the control means may perform control to lose the steering assist force only when the vehicle speed reaches a predetermined value.
In this case, since the control is not performed when the vehicle speed is less than the predetermined value, it is possible to prevent the vehicle from performing unnecessary control in a speed region where there is a low possibility of being in a so-called seesaw state.

According to the electric power steering apparatus of the present invention, the convergence can be promoted by losing the steering assist force . Therefore, the convergence when the driver releases his / her hand from the steering wheel immediately after the turning steering is performed. Can be improved.

  Further, according to the electric power steering apparatus of the present invention, rolling in a so-called seesaw state can be converged, and unstable vehicle behavior can be converged and returned in a stable direction. As a result, it is possible to effectively prevent the vehicle from becoming unstable due to crosswinds, puddles, continuous curves, etc. during normal driving while holding the steering wheel. It is easy to realize a stable vehicle behavior against the vehicle.

  FIG. 1 is a diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. In the figure, the steering wheel 1 is connected to a first steering shaft 2. The first steering shaft 2 is connected to the second steering shaft 4 via a torsion bar 3. Torque due to rotation of the motor 5 can be applied to the second steering shaft 4. A pinion 6 is formed at the lower end of the second steering shaft 4, and the pinion 6 meshes with the rack 7. By moving the rack 7 in its axial direction (lateral direction in the figure), a steering angle can be given to the steered wheels (generally the front wheels) 8.

  The torque sensor 9 detects the twist of the torsion bar 3, that is, the relative rotational angle difference between the first steering shaft 2 and the second steering shaft 4 as a steering torque, and sends the output to an ECU (electronic control unit) 10. The ECU 10 is a unit for an electric power steering device. The steering angle sensor 11 detects the rotational displacement of the second steering shaft 4 corresponding to the steering angle of the steered wheels 8 and sends the output to the ECU 10. That is, the rudder angle sensor 11 constitutes an example of a rudder angle detection unit that detects a rudder angle to be given to the steered wheels 8. A vehicle speed signal is input from the vehicle speed sensor 12 to the ECU 10. Further, the ECU 10 drives the motor 5 to generate a necessary steering assist force based on the steering torque and the vehicle speed.

On the other hand, the left and right rear wheels 13 of the vehicle are respectively suspended by a rear suspension device 14. A reed switch 15 is provided in the vicinity of the coil spring 14 s constituting the rear suspension device 14, and its output is sent to the ECU 10.
FIG. 2 is a schematic diagram showing the positional relationship between the coil spring 14s and the reed switch 15 provided in the vicinity thereof. In FIG. 2A, a magnet 16 is fixed to a predetermined portion of the coil spring 14s. If the vehicle is horizontal and the road surface is flat, the coil spring 14s is in the state shown in (a), and the magnet 16 is not located in front of the reed switch 15. At this time, the reed switch 15 does not detect the magnetic field of the magnet 16, and therefore the output is off (not detected).

  When the rear part of the vehicle rolls left or right and sinks a predetermined amount, the coil spring 14s is compressed, and the state shown in FIG. At this time, the magnet 16 is located in the detection area in front of the reed switch 15. Accordingly, the reed switch 15 detects the magnetic field of the magnet 16 and the output is turned on (detected). Thus, when the left reed switch 15 is on and the right reed switch 15 is off as viewed from the rear of the vehicle, the rear of the vehicle is rolling leftward. Conversely, if the right reed switch 15 is on and the left reed switch 15 is off, the rear of the vehicle is rolling in the right direction.

Thus, the magnet 16 and the reed switch 15 provided in the rear suspension device 14 constitute a displacement detection device 17 that detects whether or not the coil spring 14s of the rear suspension device 14 has been compressed to a predetermined state. . Such a displacement detection device 17 constitutes an example of behavior detection means for detecting rolling at the rear of the vehicle.
According to such a configuration of the behavior detecting means, the rolling of the vehicle can be easily and reliably detected by the displacement of the rear suspension device 14.

  In the electric power steering apparatus (FIG. 1) configured as described above, when the driver rotates the steering wheel 1, the steering torque is detected by twisting the torsion bar 3 and sent to the ECU 10. The ECU 10 generates a necessary steering assist force by the motor 5 based on the steering torque and the vehicle speed.

Next, the convergence when the driver releases his hand from the steering wheel 1 immediately after performing the turning steering will be described.
FIG. 5 is a diagram showing the movement of the steering wheel 8 and the schematic operation when focusing on rolling among the behavior of the rear part of the vehicle. (A) is the schematic which shows four wheels at the time of a straight drive, (d) is the schematic which looked at the vehicle at that time from back. At this time, the lengths of the coil springs 14s in the left and right rear suspension devices 14 are equal to each other on the left and right.

  When the driver performs turning steering while driving at high speed (for example, 100 km / h) and releases his hand from the steering wheel immediately thereafter, the steering angle vibration (vibration when the steering angle converges) is caused by the function of the electric power steering device. Occur. (B), (c) is the schematic which exaggerated and showed the steering angle by the said vibration. (E) and (f) are schematic views of the vehicle behavior (rolling) that occurs due to the steering angles of (b) and (c), respectively, as seen from the rear.

In the case of (b), the steering wheel 8 has a steering angle to the right due to vibration during convergence. At this time, as shown in (e), the rear part of the vehicle rolls leftward. This rolling shortens the left coil spring 14s, and conversely lengthens the right coil spring 14s. When the left coil spring 14s is compressed by a predetermined amount, the reed switch 15 (FIGS. 1 and 2) is turned on.
In the case of (c), the steering wheel 8 has a steered angle to the left due to vibration during convergence. At this time, as shown in (f), the rear part of the vehicle rolls in the right direction. This rolling shortens the right coil spring 14s, and conversely lengthens the left coil spring 14s. When the right coil spring 14s is compressed by a predetermined amount, the reed switch 15 (FIGS. 1 and 2) is turned on.

The temporal relationship between the change in the steering angle of the steering wheel 8 and the rolling at the rear of the vehicle is, for example,
(1) When timing is off (asynchronous)
(2) Timing coincides (synchronization) and phase is the same (3) Timing coincides and phase is reversed. Here, in the cases (1) and (2), there is no particular problem, but (3) is an unfavorable state that prevents convergence.

  FIG. 3 is a diagram showing the relationship between the steering angle and the on / off operation of the reed switch in the case of (3) above. When the change in the steering angle due to vibration at the time of convergence to the neutral position is a sin waveform as shown in the figure, the reed switch is turned on within a predetermined range before and after the peak value of the steering angle. That is, the timing at which each reed switch is turned on is synchronized with the steering angle vibration. However, the steering angle and the ON operation of the reed switch are in opposite phase to each other. If the steering angle is right, the reed switch that rolls to the left and turns on is the left side when viewed from the rear of the vehicle. If the rudder angle is left, the reed switch that rolls to the right and turns on is the right side when viewed from the rear of the vehicle.

In this way, when rolling that reaches a predetermined amount occurs in synchronism with the left and right vibration of the rudder angle at the time of convergence to the neutral position and due to the opposite phase, the convergence is hindered and the vibration of the rudder angle is prevented. Does not attenuate easily (in some cases, the amplitude may increase). This is a so-called seesaw state.
Note that the above “synchronization” may include a case where there is a slight error in addition to perfect synchronization. For example, even when the middle of the ON period of the reed switch slightly deviates from the peak of the steering angle (for example, 10% or less of one cycle), it may be substantially synchronized.

Therefore, the operation of the electric power steering apparatus that promotes convergence when such a phenomenon that prevents convergence will occur will be described.
FIG. 4 is a flowchart illustrating an example of control executed by the ECU 10. This control is repeatedly executed. First, in step S1, the ECU 10 determines whether or not the driver is in a released state where the driver releases his hand from the steering wheel. This determination may be, for example, a state where the steering torque is released if the steering torque is a predetermined value or less (for example, 1 N or less). When it is determined that it is not in the hand-off state, the ECU 10 executes normal assist (steering assist) control (step S2).

  On the other hand, the ECU 10 when determining that it is in the hand-off state next determines whether or not the vehicle speed is equal to or higher than a predetermined value (for example, 100 km / h) (step S3). Here, when the vehicle speed is less than the predetermined value, normal assist control is executed (step S2). In other words, when the vehicle speed is less than the predetermined value, the subsequent steps S4 to S6 are not controlled. This is because when the vehicle speed is less than the predetermined value, a seesaw state that prevents convergence is unlikely to occur. That is, it is possible to prevent the vehicle from performing unnecessary control in a speed range where the possibility of entering the seesaw state is low. However, even in a low speed region where the possibility of the seesaw state is low, the subsequent steps S4 to S6 may be controlled (in this case, step S3 is unnecessary).

  Subsequently, the ECU 10 reads signals sent from the rudder angle sensor 11 and the pair of reed switches 15 (step S4), and determines whether or not the seesaw state is set (step S5). If it is not the seesaw state, the ECU 10 executes normal assist control (step S2). On the other hand, in the seesaw state, the ECU 10 turns off the assist (step S6). Here, turning off the assist means that the power supply to the motor 5 is cut off and the motor 5 is stopped.

  Since the energy for maintaining the vibration is lost by turning off the assist, the left-right vibration of the steering angle is attenuated, and the steering device tries to converge to the neutral position by the self-aligning torque. Thereafter, the assist-off state continues until convergence is completed, and rapid convergence is realized. Thus, by temporarily losing the steering assist force, the influence of the assist by the electric power steering device on the rolling can be reduced. Thereby, convergence can be promoted.

  When the driver steers, the ECU 10 proceeds from step S1 to step S2, and again executes assist control. Similarly, when the vehicle speed decreases or the seesaw state is canceled, the ECU 10 executes assist control.

  In the above-described embodiment, the process of assist-off (step S6) is performed. However, the steering assist force by the motor 5 can be temporarily reduced by methods other than “off”. For example, even if the steering assist force is not lost completely, if the steering assist force is temporarily reduced greatly, the burden of the rudder angle vibration will be burdened, and the influence of the assist by the electric power steering device on the rolling will be affected. Can be killed.

Moreover, it is also possible to obtain the same effect by using a motor with a brake and applying a brake to the rotation of the motor to temporarily reduce the steering assist force.
Furthermore, it is possible to obtain a similar effect by using a motor with a clutch to interrupt the transmission path of the rotational force of the motor and temporarily lose the steering assist force.

In the above-described embodiment, the configuration in which the displacement of the rear suspension device is detected by a reed switch is used as a means for detecting rolling. However, this is merely an example, and rolling may be detected by another device. For example, a proximity switch or an optical sensor may be used instead of the reed switch. Further, such a displacement detection device may be provided not inside the coil spring but inside a damper device (not shown) at the lower end of the coil spring.
Further, also in a suspension device having a structure that does not use a coil spring, the sinking of the rear portion of the vehicle can be detected in the same manner by the displacement of the elastic body and the change in the distance between the ground.
Furthermore, not only the configuration for detecting the displacement, but also a gyro sensor, for example, may be mounted to directly detect the behavior called rolling.

In the above-described embodiment, the convergence when the driver releases the hand immediately after performing the turning steering is described. However, the control for temporarily reducing the steering assist force is performed in other cases. Is also beneficial. For example, let us consider a case where left and right steering is repeated intermittently through a steering neutral state, such as a lane change after overtaking on an expressway, particularly when it is intermittently repeated with sporty steering (relatively fast steering). In such a case, it is easy to shift to the seesaw state, which may be a condition that makes the vehicle behavior unstable.
Rolling can be converged by performing control to temporarily reduce the steering assist force even under the above conditions, and unstable vehicle behavior can be converged and restored in a stable direction. Can do. That is, since the vehicle can be effectively prevented from becoming unstable, it is easy to realize a stable vehicle behavior with respect to steering intended by the driver.

It is a figure showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is the schematic which shows the positional relationship of the coil spring of a rear suspension apparatus, and the reed switch provided in the vicinity. It is a figure which shows an example of the relationship between a steering angle and ON / OFF operation | movement of a reed switch. It is a flowchart which shows an example of the control performed by ECU. It is a figure which shows the operation | movement of the steering wheel, and the outline operation | movement when paying attention to rolling among the behaviors of a vehicle rear part, (a) is a schematic diagram which shows four wheels at the time of a straight drive, (d) is at that time It is the schematic which looked at the vehicle from back. Also, (b) and (c) are schematic diagrams exaggerating the rudder angle due to vibration, and (e) and (f) are due to the rudder angles of (b) and (c), respectively. It is the schematic which looked at the behavior (rolling) of the vehicle which generate | occur | produced from back.

Explanation of symbols

5 Motor 8 Steering wheel 10 ECU (control means)
11 Steering angle sensor 12 Vehicle speed sensor 14 Rear suspension device 15 Reed switch 17 Displacement detection device

Claims (4)

An electric power steering device for generating a steering assist force by a motor according to a steering torque,
Rudder angle detecting means for detecting the rudder angle applied to the steered wheels;
Behavior detecting means for detecting rolling at the rear of the vehicle;
Synchronized with the left-right vibration of the rudder angle when converging to the neutral position, and the left-right change direction of the rudder angle when the vehicle is viewed from above and the left-right change direction of the rolling when viewed from the rear of the vehicle And a control means for losing the steering assist force when rolling that reaches a predetermined amount occurs due to the reverse relationship . The behavior detection means is a displacement detection device that is provided for each of the left and right rear suspension devices and detects whether the rear suspension device is compressed to a predetermined state,
The electric power steering apparatus according to claim 1, wherein the control means is configured such that rolling that reaches a predetermined amount is generated by alternately detecting the left and right displacement detection devices. It has a vehicle speed sensor that detects the vehicle speed,
3. The electric power steering apparatus according to claim 1, wherein the control unit performs control to lose the steering assist force only when the vehicle speed reaches a predetermined value.   The electric power steering apparatus according to any one of claims 1 to 3, wherein the control means temporarily loses the steering assist force when the steering assist force is lost.

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