JP2007015495A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device eliminating a sense of incongruity in steering at starting and acceleration traveling by detecting existence of acceleration of a vehicle without using an exclusive sensor and without delaying, and by performing correction of a reduction amount of steering assistant force based on the detection result. <P>SOLUTION: A detection value of a rotation speed of an engine by an engine rotation sensor 8 is given to an assist control part 6 for driving/controlling a motor 5 for steering assistance so as to obtain target assistance force determined on the basis of steering torque detected by a torque sensor 4 and a vehicle speed detected by a vehicle speed sensor 7. The existence of acceleration of the vehicle is determined on the basis of the detection value, and the target assistance force is reducedly corrected at the acceleration to drive the motor 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that assists steering by a rotational force of a motor that is driven and controlled based on a detection result of steering torque applied to a steering member.

  An electric power steering device that drives a steering assist motor in response to a rotation operation of a steering member such as a steering wheel and applies the generated force of the motor to a steering mechanism to assist steering, generates a steering torque applied to the steering member. The target assist force is detected based on the detected steering torque, and the motor is driven and controlled to generate the target assist force.

  Further, it has been conventionally known that a good steering feeling can be realized by correcting the target assist force calculated as described above in accordance with the vehicle speed. This correction increases the target assist force by increasing the target assist force when driving at low speed or stopping the vehicle, and increases the steering assist force generated by the motor for assisting the steering operation. In some cases, the target assist force is corrected by reducing the steering assist force so that the steering member operated by the driver is given appropriate rigidity to achieve stable running without wobbling (for example, , See Patent Document 1).

In the electric power steering apparatus disclosed in Patent Document 1, a dedicated sensor for detecting the vehicle speed is not required by obtaining the vehicle speed using the engine speed detected by the alternator.
Japanese Patent Laid-Open No. 9-48359

  However, when the control for increasing or decreasing the steering assist force is performed according to the slow speed of the vehicle as described above, there is a problem that the steering at the time of start and acceleration is uncomfortable. That is, when starting and accelerating, the load applied to the steering wheel (front wheel) decreases because the load balance of the vehicle shifts to the rear side, and the force required for steering is reduced, whereas when starting from a stopped state Or, when accelerating under low speed, the steering assist force generated by the steering assist motor is corrected to increase according to the low vehicle speed, and the steering member feels too light and the steering is unstable. It becomes.

  The above-mentioned uncomfortable feeling of steering is solved by detecting the presence or absence of acceleration of the vehicle and reducing the target assist force including correction according to the vehicle speed while in the acceleration (including start) state. There is a problem that a dedicated sensor (longitudinal acceleration sensor) for detecting the presence / absence of this is required, resulting in a complicated apparatus configuration. Further, the vehicle speed detected by the vehicle speed sensor can be differentiated and used to detect the presence or absence of acceleration. However, in this case, the detection is delayed and a sufficient elimination effect cannot be obtained.

  The present invention has been made in view of such circumstances, and detects the presence or absence of acceleration of a vehicle without using a dedicated sensor and without delay, and based on the detection result, the amount of steering assist force is reduced. It is an object of the present invention to provide an electric power steering device that can eliminate the uncomfortable feeling of steering during starting and accelerating running by performing correction.

  An electric power steering apparatus according to a first aspect of the present invention determines a target assist force based on a steering torque applied to a steering member of a vehicle and a traveling speed of the vehicle, and is used for steering assist to generate the target assist force. In the electric power steering apparatus for driving and controlling the motor, an engine rotation sensor that detects a rotation speed of the engine of the vehicle, a determination unit that determines whether the vehicle is accelerated based on a detection result of the engine rotation sensor, And correction means for reducing the target assisting force in accordance with the determination of acceleration by the determining means.

  According to a second aspect of the present invention, there is provided the electric power steering apparatus according to the first aspect of the invention, wherein the means for calculating the rate of change of the steering torque and the correction when the rate of change calculated by the means exceeds a preset lower limit value. Means for canceling the weight reduction correction by the means.

  In the electric power steering apparatus according to the first aspect of the invention, since the presence or absence of acceleration is determined based on the engine speed detected by the engine rotation sensor, the presence or absence of acceleration is detected without delay without using a dedicated sensor. Since the target assist force is corrected to decrease in accordance with this detection, it is possible to effectively eliminate the uncomfortable feeling of steering during start and acceleration travel, and to perform stable steering.

  In the electric power steering apparatus according to the second aspect of the invention, the rate of change of the steering torque applied to the steering member is calculated, and when the rate of change is large, the target auxiliary force reduction correction according to the acceleration determination is stopped. Therefore, it is possible to secure a large steering assist force when torque steer is generated due to start or acceleration, and there is no possibility that the operation of the steering member to resist this torque steer is obstructed. The present invention has an excellent effect that steering during acceleration can be performed more stably.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to the present invention. Although this figure shows an application example to a vehicle equipped with a rack and pinion type steering mechanism, the present invention is applied to a vehicle equipped with another type of steering mechanism such as a ball screw type steering mechanism. It goes without saying that it is possible.

  The rack-and-pinion type steering mechanism includes a rack shaft 1 that is supported in an axially movable manner in a rack housing 10 that extends in the left-right direction of a vehicle body (not shown), and a pinion that crosses the rack housing 10 in the middle. The housing 20 has a known configuration including a pinion shaft 2 rotatably supported within the housing 20.

  Both ends of the rack shaft 1 projecting outward from both sides of the rack housing 10 are connected to left and right front wheels 12 and 12 as steering wheels via respective tie rods 11 and 11, and projecting to the outside of the pinion housing 20. The upper end of the pinion shaft 2 is connected to a steering wheel 30 as a steering member via a steering shaft 3. A pinion (not shown) is formed at the lower part of the pinion shaft 2 extending into the pinion housing 20, and the pinion is formed on the outer surface of the rack shaft 1 at an appropriate length at the intersection with the rack housing 10. Meshed with the rack teeth.

  The steering shaft 3 is rotatably supported inside a cylindrical column housing 31, and is fixed to the interior of a vehicle compartment (not shown) while maintaining a tilted posture with the front facing down through the column housing 31. The pinion shaft 2 is connected to the protruding end of the steering shaft 3 below the column housing 31, and the steering wheel 30 is fixed to the protruding end.

  With the above configuration, when the steering wheel 30 is rotated for steering, this rotation is transmitted to the pinion shaft 2 via the steering shaft 3, and the rotation of the pinion shaft 2 is engaged with the pinion and the rack teeth. The movement of the rack shaft 1 is converted into the movement of the rack shaft 1 in the portion, and by such movement of the rack shaft 1, the left and right front wheels 12, 12 are pushed and pulled via the respective tie rods 11, 11 and steered. Is made.

  In the middle of the column housing 31 that supports the steering shaft 3, there is provided a torque sensor 4 that detects a steering torque applied to the steering shaft 3 by the rotation operation of the steering wheel 30, and the steering assist is located below the torque sensor 4. A motor 5 is attached.

  The torque sensor 4 divides the steering shaft 3 to be detected into two upper and lower axes, connects these two axes coaxially by a torsion bar having a known torsion characteristic, and twists the torsion bar by the action of the steering torque. Accordingly, it has a known configuration in which the relative angular displacement generated between the two axes is detected by appropriate means.

  The steering assist motor 5 is attached to the outside of the column housing 31 with its axis substantially orthogonal, and, for example, a worm fixed to an output end extending inside the column housing 31 is fixed to the steering shaft 3 by external fitting. The rotation of the motor 5 is transmitted to the steering shaft 3 after being decelerated by the worm and the worm wheel. With this configuration, the rotation of the steering assisting motor 5 is transmitted to the steering shaft 3 at a reduced speed, and a rotational force is applied to the pinion shaft 2 connected to the lower end of the steering shaft 3. Steering performed as described above is assisted.

  The steering assist motor 5 is not limited to the position shown in the figure, and is configured to transmit to the steering shaft 3, the pinion shaft 2, or the rack shaft 1 as long as it is below the torque sensor 4 that detects the steering torque. It can be attached at an appropriate position. When the transmission is configured to the rack shaft 1, motion conversion means such as a ball screw mechanism is required to convert the rotation of the motor 5 into movement in the axial direction of the rack shaft 1.

  The steering assist motor 5 attached in this way is driven according to a control command given from the assist control unit 6 via a drive circuit (not shown). The assist control unit 6 is provided with a detected value of the steering torque by the torque sensor 4, and is also provided with a detected value of the vehicle speed from a vehicle speed sensor 7 disposed at an appropriate part of the vehicle, and is further attached to the engine of the vehicle. A detected value of the rotation speed of the engine is given from the engine rotation sensor 8 that has been made.

  FIG. 2 is a block diagram of the assist control unit 6. The assist control unit 6 includes a CPU 61, a ROM 62, and a RAM 63 connected to each other by an internal bus 60, and is configured as an ECU that performs the following assist control by the operation of the CPU 61 according to a control program stored in the ROM 62. The detected value of the steering torque by the sensor 4, the detected value of the vehicle speed by the vehicle speed sensor 7, and the detected value of the engine speed by the engine speed sensor 8 are taken into the CPU 61 via the input interfaces 64, 65, 66. is there.

  FIG. 3 is a flowchart showing the operation content of the assist control unit 6. The assist controller 6 takes in the steering torque T detected by the torque sensor 4 and the vehicle speed V detected by the vehicle speed sensor 7 at a predetermined sampling period (steps 1 and 2), and then these steering torque T and vehicle speed V. Is used to calculate the target value (target assist force) of the steering assist force to be generated (step 3).

  The calculation of the target auxiliary force in step 3 is performed by, for example, applying the detected value of the steering torque T acquired from the torque sensor 4 to the control map stored in the ROM 62 to obtain the reference auxiliary force, and using this reference auxiliary force as the vehicle speed. This is performed according to a procedure for correcting the increase / decrease according to the slow speed of the vehicle speed V acquired from the sensor 7. A plurality of control maps showing the relationship between the steering torque and the target assisting force are prepared for each vehicle speed, and the steering torque T is applied to the control map selected according to the detection result of the vehicle speed V, so that the correction by the vehicle speed V is performed. It can also be performed by a procedure for obtaining a target auxiliary force including a term. Such a calculation operation of the target assist force is a conventionally known operation, and is shown by a single subroutine block in FIG. 3, and detailed description thereof is omitted.

  After completing the calculation of the target assist force as described above, the assist control unit 6 performs an acceleration correction operation for correcting the amount of the target assist force that has been obtained previously by using the engine speed N detected by the engine rotation sensor 8. (Step 4), a control command is issued to the steering assist motor 5 to generate the obtained target assist force, and the motor 5 is driven (Step 5).

FIG. 4 is a flowchart showing the contents of the acceleration correction operation. In this operation, the assist control unit 6 first calculates the steering torque change rate ΔT (step 11). This calculation is performed by a difference calculation using the current steering torque T _x captured in step 1 and the steering torque T _X-1 captured at the previous sampling. The previous steering torque T _X-1 may be stored in the RAM 63 as a work area.

Next, the assist control unit 6 compares the calculated ΔT with a preset lower limit change rate δ (step 12). As a result of this comparison, if it is determined that ΔT is equal to or greater than δ (step 12: NO), the process returns to step 13 and subsequent steps, that is, without correcting the target assisting force for reduction.

  This operation is particularly necessary in order to reduce the influence of torque steer that occurs when starting and accelerating in vehicles such as front-wheel drive vehicles and four-wheel drive vehicles where steering wheels also serve as drive wheels for traveling. It is. Torque steer is caused by the unavoidable imbalance of the driving force transmitted to the left and right driving wheels, and the steering force and the steering force change during acceleration and start when the driving force changes greatly. It is a phenomenon that invites you.

  The step 12 is provided for determining whether or not torque steer is generated. When the rate of change ΔT of the steering torque T is large (step 12: NO), torque steer is generated and this is countered. It is determined that the steering wheel 30 is being operated. In this case, the process returns without correcting the reduction in the target assisting force, so that the sufficient steering assisting force is maintained by the steering assisting motor 5 driven in step 5, which resists torque steer. There is no hindrance to the operation of the steering wheel 30 that should be performed.

On the other hand, as a result of the comparison in step 12, if it is determined that the steering torque change rate ΔT is smaller than the lower limit change rate δ (step 12: YES), that is, if it is determined that torque steer has not occurred, The assist control unit 6 takes in the engine rotation speed N detected by the engine rotation sensor 8 (step 13), and compares this rotation speed N with a reference rotation speed N ₀ preset according to the vehicle speed V ( Step 14). As a result of this comparison, when the current rotation speed N exceeds the reference rotation speed N ₀ (step 14: YES), it is determined that acceleration is in progress, and an acceleration correction amount is set based on the detected value of the rotation speed N. (Step 15), the target auxiliary force is reduced by this acceleration correction amount (Step 16), and the process returns. If the current rotational speed N is equal to or lower than the reference rotational speed N ₀ (Step 14: NO), It is determined that the vehicle is not accelerating, and the process returns without correcting the target assist force to reduce the amount.

  In this way, the assist control unit 6 detects that the engine rotation speed is increased by the engine rotation sensor 8 while paying attention to the fact that the rotation speed of the engine increases during acceleration traveling with the accelerator operation compared to during constant speed traveling and deceleration traveling. The presence or absence of acceleration is determined based on the rotational speed N of the engine, and the target assist force is reduced according to this determination. Therefore, the steering wheel 30 has an appropriate rigidity feeling during acceleration traveling when the grounding load of the steering wheel is reduced. Can be provided, and stable steering can be performed.

  Here, since the rotational speed N of the engine increases prior to the actual acceleration of the vehicle, the presence or absence of acceleration can be determined without delay, and the engine rotation sensor 8 is used for controlling the drive system of the vehicle. This is an indispensable sensor, and the presence or absence of acceleration can be determined without using a dedicated sensor.

  The acceleration correction amount set in step 15 is preferably set as a value that increases appropriately as the rotational speed N increases, but may be set as a constant value regardless of the rotational speed N. Good.

It is a mimetic diagram showing the composition of the electric power steering device concerning the present invention. It is a block diagram of an assist control part. It is a flowchart which shows the operation | movement content of an assist control part. It is a flowchart which shows the content of the acceleration correction operation.

Explanation of symbols

4 Torque sensor 5 Motor 6 Assist control unit 7 Vehicle speed sensor 8 Engine rotation sensor
30 Steering wheel (steering member)

Claims (2)

In an electric power steering apparatus that determines a target assist force based on a steering torque applied to a steering member of a vehicle and a traveling speed of the vehicle, and drives and controls a motor for assisting steering to generate the target assist force.
An engine rotation sensor for detecting a rotation speed of the engine of the vehicle;
Determination means for determining the presence or absence of acceleration of the vehicle based on a detection result of the engine rotation sensor;
An electric power steering apparatus comprising: correction means for reducing and correcting the target auxiliary force according to the determination of acceleration by the determination means.   The means for calculating the rate of change of the steering torque, and means for canceling the reduction correction by the correcting means when the rate of change calculated by the means exceeds a preset lower limit value. Electric power steering device.

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