JP2010036800A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of achieving stable steering feeling on a rough road. <P>SOLUTION: The power steering device is favorably used for changing a steering assist force according to vehicle speed. More specifically, a steering assist control means compares the case that a traveling passage is a rough road with the case that the traveling passage is not a rough road, and reduces the change in the steering assist force to the change of the vehicle speed. Thus, the steering assist according to the travel on a rough road can be executed, and the stable steering feeling can be achieved on the rough road. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power steering apparatus that performs steering assist.

  2. Description of the Related Art Conventionally, an electric power steering device (EPS: Electric Power Steering) that assists steering by a driver using a driving force of a motor has been proposed. For example, Patent Literature 1 proposes a power steering device that determines a rough road based on wheel speed and reduces the steering assist force when the road is determined to be a bad road. Patent Document 2 proposes a technique for performing steering assist based on a basic assist force determined from a steering torque and a vehicle speed, and a correction amount determined from wheel acceleration and the like. In addition, a technique related to the present invention is proposed in Patent Document 3.

Japanese Patent Laid-Open No. 6-92256 JP 2004-114910 A JP 7-228263 A

  However, with the techniques described in Patent Documents 1 to 3, it is difficult to achieve a stable steering feeling while traveling on a rough road. For example, when a change occurs in the steering assist force due to a change in wheel speed, steering angular velocity, etc. on a rough road, the steering force changes, making it difficult for the driver to feel steering reaction force (traction information), etc. was there. Therefore, the running performance on a rough road may be deteriorated.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a power steering device capable of realizing a stable steering feeling on a rough road.

  In one aspect of the present invention, a power steering device that changes a steering assist force according to a vehicle speed has a change in the vehicle speed when the travel road is a bad road compared to a case where the travel road is not the bad road. Steering assist control means for reducing the change in the steering assist force with respect to is provided.

  The power steering device is preferably used to change the steering assist force according to the vehicle speed. Specifically, the steering assist control means reduces the change in the steering assist force with respect to the change in the vehicle speed when the traveling road is a bad road as compared with the case where the road is not a bad road. As a result, it is possible to perform steering assist according to traveling on a rough road, and to realize a stable steering feeling on a rough road.

  In another aspect of the present invention, the power steering device that changes the steering assist force in accordance with the steering angle has the steering angle when the traveling road is a bad road as compared with the case where the traveling road is not the bad road. Steering assist control means for reducing the change of the steering assist force with respect to the change of the steering assist force is provided. This also makes it possible to realize a stable steering feeling on a rough road.

  In another aspect of the present invention, the power steering device that changes the steering assist force in accordance with the steering angular velocity has the steering angular velocity compared to the case where the traveling road is not the bad road when the traveling road is a bad road. Steering assist control means for reducing the change of the steering assist force with respect to the change of the steering assist force is provided. This also makes it possible to realize a stable steering feeling on a rough road.

  In another aspect of the present invention, the power steering device that changes the steering assist force according to the vehicle speed and the steering angle or the steering angular velocity is compared with a case where the traveling road is not a bad road when the traveling road is a bad road. And a steering assist control means for reducing a change in the steering assist force with respect to the vehicle speed and the steering angle or the change in the steering angular velocity. This also makes it possible to realize a stable steering feeling on a rough road.

  In the power steering apparatus described above, preferably, the steering assist control means switches a map used for controlling the steering assist force between when the traveling road is the rough road and when the traveling road is not the bad road. .

  Preferably, the steering assist control means determines that the travel road is the bad road when the shift range of the drive transmission is set to a low range.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Device configuration]
First, the overall configuration of the steering control system 50 to which the power steering apparatus according to the present embodiment is applied will be described. FIG. 1 is a schematic diagram showing the configuration of the steering control system 50.

  The steering control system 50 mainly includes a steering wheel 1, a steering shaft 2, a steering angle sensor 3, a motor 5, a rack and pinion unit 7, tie rods 8r and 8l, knuckle arms 9r and 9l, and wheels. (Front wheels) 10Fr, 10F1, a vehicle speed sensor 12, a transfer changeover switch 13, and a controller 20 are provided. In the following, “r” and “l” attached to the end of the reference numerals of the tie rods 8r and 8l, the knuckle arms 9r and 9l, and the wheels 10Fr and 10Fl will be omitted when they are used without distinction. And

  The steering control system 50 is configured by an electric power steering (EPS) system. Specifically, the steering control system 50 is mounted on a vehicle, performs drive control of a motor 5 that steers and drives a wheel 10 </ b> F that is a steered wheel, and steers the steered wheel according to an operation of the steering wheel 1. It is.

  The steering wheel 1 is operated by a driver (driver) to turn the vehicle. The steering wheel 1 is connected to the rack and pinion unit 7 via the steering shaft 2. The steering shaft 2 is provided with a steering angle sensor 3 and a motor 5. Hereinafter, the steering wheel is simply referred to as “steering”.

  The motor 5 is constituted by a reduction gear, an electric motor, or the like (not shown), and is controlled by a control signal S5 supplied from the controller 20. For example, the motor 5 generates a steering assist force (in other words, a steering assist torque) in accordance with the steering by the driver in order to assist the steering by the driver.

  The steering angle sensor 3 detects a steering angle corresponding to the operation of the steering 1 by the driver, and supplies a detection signal S3 corresponding to the detected steering angle to the controller 20. The vehicle speed sensor 12 detects the vehicle speed (for example, detects the wheel speed), and supplies a detection signal S12 corresponding to the detected vehicle speed to the controller 20.

  The transfer switch 13 is a switch configured to be able to switch the transfer setting (in other words, a switch configured to be able to switch the shift range in the drive transmission), and is operated by a driver. For example, it is operated to change the vehicle characteristics according to the road surface environment. Further, the transfer changeover switch 13 supplies the controller 20 with a signal S13 corresponding to the currently set state. Specifically, the transfer changeover switch 13 supplies a signal S13 corresponding to the shift range of the drive transmission. For example, the transfer switch 13 outputs a signal S13 corresponding to “low range” or the like. The “low range” is set by the driver when traveling on a rough road such as off-road.

  The rack and pinion unit 7 is configured by a rack, a pinion, or the like, and operates by transmitting rotation from the steering shaft 2. Further, a tie rod 8 and a knuckle arm 9 are connected to the rack and pinion unit 7, and a wheel 10 </ b> F is connected to the knuckle arm 9. In this case, when the tie rod 8 and the knuckle arm 9 are operated by the rack and pinion unit 7, the wheel 10F connected to the knuckle arm 9 is steered.

  The controller 20 includes a CPU, a ROM, a RAM, an A / D converter, and the like (not shown). The controller 20 corresponds to an ECU (Electronic Control Unit) in the vehicle. The controller 20 supplies a control signal S5 to the motor 5 mainly based on signals S3, S12, S13 and the like supplied from the steering angle sensor 3, the vehicle speed sensor 12, and the transfer changeover switch 13 described above. That is, the controller 20 performs control related to the steering assist force. Thus, the controller 20 functions as a steering assist control means in the present invention.

[Steering assist method]
Next, a steering assist method performed by the controller 20 described above will be described. In the present embodiment, the controller 20 reduces the change in the steering assist force with respect to the change in the vehicle speed and reduces the change in the steering angular speed when the road is a bad road as compared with the case where the road is not a bad road. The change in steering assist force is also reduced. Specifically, the controller 20 executes such a steering assist method when the traveling road is off-road. Specifically, the controller 20 switches the control map used for controlling the steering assist force depending on whether the travel path is off-road or when the travel path is not off-road. Hereinafter, a control map used when the travel path is off-road is referred to as an “off-road control map”, and a control map used when the travel path is not off-road is referred to as a “normal control map”.

  The reason for performing such a steering assist method is as follows. Normally, the steering assist force is controlled based on the vehicle speed, the steering angular velocity, and the like. Specifically, the steering assist force is controlled based on the normal control map in which the steering assist force is defined according to the vehicle speed and the steering angular velocity so that an appropriate steering assist force according to the vehicle speed and the steering angular velocity is applied. Is done. However, when such steering assist force is controlled during off-road driving, there is a possibility that a stable steering feeling cannot be realized. For example, if the wheel idling occurs during off-road driving or the steering is searched, if the steering assist force is controlled based on the normal control map, the steering force will change. In some cases, it becomes difficult for the driver to accurately obtain information on the steering reaction force (front wheel grip force). The reason why the steering assist force is controlled when the wheel idling occurs is that the vehicle speed on the control is changed when the wheel idling occurs by calculating the vehicle speed from the wheel speed. Further, search steering corresponds to steering (steering angle swing) performed in order to find the escape direction when the vehicle is stuck during off-road driving. In this case, if the front wheel grip force increases due to the steering operation, the steering reaction force increases, which is a guideline for determining the escape direction.

  In the present embodiment, in order to suppress the occurrence of the above-described problems, the steering assist force with respect to changes in the vehicle speed and the steering angular velocity when the travel path is off-road is compared to when the travel path is not off-road. Reduce changes in That is, the controller 20 controls the steering assist force in such a manner that the influence of the vehicle speed and the steering angular velocity on the steering assist force is reduced. Specifically, the controller 20 controls the steering assist force by using an off-road control map in which the change in the steering assist force with respect to the change in the vehicle speed and the steering angular velocity is small when the travel path is off-road. I do. This makes it possible to improve the steering stability performance during off-road driving. Specifically, a stable steering feeling can be realized. In addition, when the driver steers for the off-road, information on the steering reaction force (front wheel grip force) and the like can be accurately acquired by the driver.

  Next, the normal control map and the offload control map will be described in detail with reference to FIG. FIG. 2A shows an example of a normal control map, and FIG. 2B shows an example of an offload control map. 2A and 2B, the horizontal axis indicates the vehicle speed (km / h), and the vertical axis indicates the steering assist force.

  As shown in FIG. 2A, in the normal control map, the steering assist force is defined according to the vehicle speed and the steering angular velocity. Here, three examples of ω11, ω12, and ω13 (ω11 <ω12 <ω13) are shown as examples of the steering angular velocity. In FIG. 2A, the steering angular velocities ω11, ω12, and ω13 are indicated by solid lines, broken lines, and alternate long and short dash lines, respectively. In practice, the steering assist force is defined by, for example, three or more steering angular velocities. When steering assist is performed according to such a normal control map, a steering assist force corresponding to the vehicle speed and the steering angular velocity is applied.

  On the other hand, as shown by the thick solid line in FIG. 2B, it can be seen that the steering assist force is not affected at all by the steering angular velocity in the off-road control map. In addition, the off-road control map shows that the steering assist force is hardly affected by the vehicle speed. More specifically, during off-road driving, the vehicle speed tends to be in the range indicated by the broken line region R1 (for example, 30 km / h or less). However, at the vehicle speed in the range, the steering assist force is not affected by the vehicle speed at all. I understand that. When steering assist is performed according to such an off-road control map, a steering assist force that is uniquely determined regardless of the vehicle speed and the steering angular velocity is applied during off-road driving.

  Next, the steering assist control process in this embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a steering assist control process in the present embodiment. This processing is executed by the controller 20 when the driver steers the steering wheel 1.

  First, in step S101, the controller 20 acquires a vehicle speed and a steering angle. Specifically, the controller 20 acquires detection signals S3 and S12 from the steering angle sensor 3 and the vehicle speed sensor 12. In this case, the controller 20 obtains a steering angular velocity or the like from the acquired steering angle. Then, the process proceeds to step S102.

  In step S102, the controller 20 determines whether or not the shift range in the drive transmission is set to a low range. Here, the controller 20 determines whether or not the current traveling road is a bad road (off-road). Specifically, the controller 20 performs the determination based on the signal S13 supplied from the transfer switch 13.

  If it is the low range (step S102; Yes), the process proceeds to step S103. In this case, the controller 20 determines the off-road control map as a control map used for steering assist (step S103). Then, the process proceeds to step S105. On the other hand, when not in the low range (step S102; No), the process proceeds to step S104. In this case, the controller 20 determines the normal control map as a control map used for steering assist (step S104). Then, the process proceeds to step S105.

  In step S105, the controller 20 controls the steering assist force according to the control map determined in any one of steps S103 and S104. Specifically, the controller 20 determines a steering assist force to be applied by referring to either the normal control map or the off-road control map, and performs the steering assist with the steering assist force. Specifically, when the normal control map is set, the controller 20 refers to the control map to obtain the steering assist force corresponding to the vehicle speed and the steering angular velocity acquired in step S101. On the other hand, when the off-road control map is set, the controller 20 obtains a steering assist force that is uniquely determined from the control map regardless of the vehicle speed and the steering angular velocity. Next, the controller 20 controls the motor 5 by supplying a control signal S5 corresponding to the steering assist force to the motor 5 so that the steering assist force thus obtained is appropriately applied. Do. Then, the process ends.

  According to the steering assist control process described above, it is possible to appropriately perform the steering assist according to the off-road running, and it is possible to improve the steering stability performance in the off-road. Specifically, a stable steering feeling can be realized. Therefore, according to the present embodiment, it is possible to appropriately suppress deterioration in running performance during off-road.

  In the above, an off-road control map is shown in which the steering assist force changes to some extent according to the vehicle speed (see FIG. 2B), but the use of such a control map is not limited. In another example, an off-road control map in which the steering assist force does not change at all according to the vehicle speed may be used. FIG. 4 shows an example of an offload control map according to such a modification. In the off-road control map, as shown in FIG. 4, it can be seen that the steering assist force is not affected by not only the steering angular velocity but also the vehicle speed.

  In the above description, the off-road control map is shown in which the steering assist force is not affected by the steering angular velocity at all (see FIG. 2B), but the use of such a control map is not limited. In another example, an off-road control map in which the steering assist force is affected to some extent by the steering angular velocity may be used. That is, an off-road control map in which the steering assist force changes to some extent according to the steering angular velocity may be used. For example, an off-road control map may be used in which different steering assist forces are determined depending on whether the steering angular velocity is less than a predetermined value or the steering angular velocity is greater than or equal to a predetermined value.

  Further, in the above description, the embodiment has been described in which the change in the steering assist force with respect to the change in the steering angular velocity is reduced. However, the change in the steering assist force with respect to the change in the steering angle may be reduced. In this case, an off-road control map defined by the steering angle or an off-road control map defined by both the steering angular velocity and the steering angle can be used instead of the steering angular velocity. In addition, in the above description, the embodiment using the off-road control map in which the change in the steering assist force with respect to the change in the vehicle speed and the steering angular velocity (or the steering angle) is shown, but the present invention is not limited to this. In another example, an off-road control map may be used in which a change in the steering assist force is small with respect to a change in any one of the vehicle speed, the steering angular velocity, and the steering angle.

  In the above description, the embodiment is described in which the transfer changeover switch 13 is used to determine whether the road is off-road (bad road). However, the present invention is not limited to this. Moreover, it is not limited to determining whether it is such an off-road by determining whether the drive transmission is set to the low range. In another example, it can be determined whether or not the vehicle is off-road based on the output of a sensor other than the transfer selector switch 13. For example, it can be determined whether or not the vehicle is traveling off-road based on wheel speed, wheel acceleration, or the like.

[Modification]
Next, modified examples of the present invention will be described. The steering assist control in the embodiment described above is performed when traveling on an off road as a bad road. However, the steering assist control in the modified example is performed when traveling on a low μ road such as a snow road as a bad road. Is to be done. Specifically, in the modified example, when the traveling road is a low μ road such as a snow road, the steering assist force is made smaller than when the traveling road is not a low μ road such as a snow road. That is, steering assist control is performed so that the operation of the steering wheel 1 by the driver becomes heavy. Specifically, in the modification, when the traveling road is a snow road, the steering assist control is performed using the snow road control map as the control map. Such steering assist control is performed because the steering force tends to be lower than usual when traveling on a low μ road such as a snowy road. Therefore, by applying the steering assist force in a mode different from the normal time, This is to correct the decrease in the steering force.

  FIG. 5 shows an example of a snow road control map in a modified example. FIG. 5 shows the vehicle speed (km / h) on the horizontal axis and the steering assist force on the vertical axis. In the snow road control map, the steering assist force is defined according to the vehicle speed and the steering angular velocity. Here, three examples of ω21, ω22, and ω23 are shown as examples of the steering angular velocity. In FIG. 5, the steering angular velocities ω21, ω22, and ω23 are indicated by a solid line, a broken line, and an alternate long and short dash line, respectively. Note that ω21, ω22, and ω23 are “ω21 <ω22 <ω23”, and the relationship “ω21≈ω11”, “ω22≈ω12”, and “ω23≈ω13” are compared with the above-described ω11, ω12, and ω13. There shall be.

  As shown in FIG. 5, it is understood that the steering assist force is generally smaller in the snow road control map than in the normal control map (see FIG. 2A). When steering assist is performed according to such a snowy road control map, the operation of the steering wheel 1 by the driver tends to be heavy.

  FIG. 6 is a flowchart showing a steering assist control process in the modification. This process is also executed by the controller 20 described above when the driver steers the steering 1. In addition, since the process of step S201, S204, S205 is the same as the process of step S101, S104, S105 of the steering assist control process shown in FIG. 3, the description is abbreviate | omitted. Here, only the processing of steps S202 and S203 will be described.

  In step S202, the controller 20 determines whether or not the user is set to a snowy road mode for running on a snowy road. Specifically, the controller 20 performs the determination by acquiring a signal from the snow mode switch. Instead of performing the determination based on the signal from the snow mode switch, the determination may be performed based on the signal from the traction change switch. Such a traction change switch and a snow mode switch are operated by a driver in order to change vehicle characteristics in accordance with changes in road surface environment.

  When it is a snowy road mode (step S202; Yes), a process progresses to step S203. In this case, the controller 20 determines the snow road control map as a control map used for steering assist (step S203). Then, the process proceeds to step S205. On the other hand, when it is not the snowy road mode (step S202; No), the process proceeds to step S204. In this case, the controller 20 determines the normal control map as a control map used for steering assist (step S204). Then, the process proceeds to step S205.

  According to the steering assist control process according to the modified example described above, it is possible to appropriately perform the steering assist in accordance with the snowy road traveling, and to improve the steering stability performance on the snowy road. Specifically, a stable steering feeling can be realized.

  The present invention is not limited to the application to the electric power steering apparatus as shown in FIG. 1, but can also be applied to a power steering apparatus using hydraulic pressure (for example, a hydraulic power steering variable flow rate pump). The present invention can also be applied to steer-by-wire systems.

  Furthermore, although the example which switches the map used for control of steering assist force by the case where a driving road is a bad road and the case where it is not a bad road was shown above, it is not limited to this. In another example, an arithmetic expression used for obtaining the steering assist force can be changed depending on whether the traveling road is a bad road or a bad road.

1 is a schematic configuration diagram of a steering control system to which a power steering apparatus according to an embodiment is applied. 2 shows an example of a normal control map and an offload control map. It is a flowchart which shows the steering assist control process in this embodiment. The modification of the control map for offloading is shown. An example of the control map for snowy roads is shown. It is a flowchart which shows the steering assist control process in a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Steering angle sensor 5 Motor 7 Rack and pinion part 10F Wheel 12 Vehicle speed sensor 13 Transfer change switch 20 Controller 50 Steering control system

Claims (6)

A power steering device that changes a steering assist force according to a vehicle speed,
A power steering system comprising: a steering assist control means for reducing a change in the steering assist force with respect to a change in the vehicle speed when the travel road is a bad road compared to a case where the travel road is not the bad road. apparatus. A power steering device that changes a steering assist force according to a steering angle,
A power having a steering assist control means for reducing a change in the steering assist force with respect to a change in the steering angle when the travel road is a bad road compared to a case where the travel road is not the bad road. Steering device. A power steering device that changes a steering assist force according to a steering angular velocity,
A power having a steering assist control means for reducing a change in the steering assist force with respect to a change in the steering angular velocity when the travel road is a bad road compared to a case where the travel road is not the bad road. Steering device. A power steering device that changes a steering assist force according to a vehicle speed and a steering angle or a steering angular velocity,
Steering assist control means for reducing a change in the steering assist force with respect to a change in the vehicle speed and the steering angle or the steering angular velocity when the driving road is a bad road as compared with a case where the driving road is not the bad road. A power steering apparatus comprising:   5. The steering assist control unit according to claim 1, wherein the map used for controlling the steering assist force is switched between a case where the travel path is the rough road and a case where the travel path is not the rough road. A power steering device according to claim 1.   The power steering apparatus according to any one of claims 1 to 5, wherein the steering assist control unit determines that the travel path is the rough road when the shift range of the drive transmission is set to a low range. .

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