JP2006213085A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device without forcing complicated operation to a driver, by effectively restraining torque steering generated in a vehicle using a steering wheel and a driving wheel in common. <P>SOLUTION: Longitudinal acceleration α is calculated by taking in a detecting result of a vehicle speed, and this longitudinal acceleration α exceeds a positive lower limit value α<SB>0</SB>, and when there is fear of generating the torque steering, an assist correction quantity A becoming large in response to an increase in the longitudinal acceleration α is calculated, and target assist force being a target value of driving control of a steering assisting motor is increasingly corrected by this assist correction quantity A. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering device that assists steering by a rotational force of a motor that is driven and controlled based on a detection result of a steering torque applied to a steering member, and more particularly, a front wheel drive vehicle, a four wheel drive vehicle, etc. The present invention relates to an electric power steering apparatus equipped in a vehicle in which steering wheels also serve as driving wheels for traveling.

  An electric power steering device that drives a steering assist motor in accordance with a rotation operation of a steering member such as a steering wheel and assists steering by applying the generated force of the motor to a steering mechanism is a steering torque applied to the steering member. Is detected by a torque sensor, a target value of the steering assist force is obtained based on the detected steering torque, and the motor is driven and controlled to generate the target assist force. At this time, various changes can be made by correcting the target auxiliary force based on the detection result of the running state that affects the steering, such as the vehicle speed, the lateral acceleration, the yaw rate, etc., and driving the motor using the corrected target auxiliary force. Appropriate steering assistance is performed under running conditions.

On the other hand, in a vehicle in which steering wheels also serve as driving wheels for driving, such as front-wheel drive vehicles and four-wheel drive vehicles, the change in the drive force is particularly caused by the inevitable unbalance of the drive force transmitted to each of them. A phenomenon in which the steering force and the holding force change at the time of a large acceleration and at the time of start change, leading to disturbance of the course, so-called torque steer occurs. Conventionally, an electric power steering apparatus has been proposed in which such torque steer is regarded as a phenomenon affecting steering and control is performed to reduce the phenomenon (see, for example, Patent Document 1).
JP-A-11-263233

  In the electric power steering apparatus disclosed in Patent Document 1, the vehicle front and rear acceleration exceeds a predetermined value, and the steering wheel as a steering member is swung around at the time of acceleration that may cause torque steer. The aim is to reduce torque steer by increasing the gain of the convergence control performed for the purpose of braking by a steering assist motor.

  However, the control performed in Patent Document 1 is a control that suppresses the swinging of the steering wheel due to the reverse input applied from the steering mechanism side when torque steer occurs, and the reverse input to the driver who operates the steering wheel is performed. Since the degree of experience is only mitigated and it is not possible to suppress the occurrence of torque steer itself, the driver operating the steering wheel must perform a complicated operation to eliminate the disturbance of the course due to the occurrence of torque steer. Will still be forced.

  The present invention has been made in view of such circumstances, and can effectively suppress torque steer generated in a vehicle in which both a steered wheel and a drive wheel are combined, forcing a driver to perform complicated operations. It is an object to provide an electric power steering device that does not.

  An electric power steering apparatus according to a first aspect of the present invention is a torque sensor for detecting a steering torque applied to a steering member of a vehicle, a target auxiliary force is determined based on the detected torque of the torque sensor, and the target auxiliary force is determined. And an assist control unit that controls driving of a steering assist motor to generate the electric power steering device that assists steering of a steering wheel that also serves as a driving wheel by the generated force of the motor, and detects longitudinal acceleration of the vehicle. The apparatus includes: an acceleration detection unit; and a correction unit that sets an assist correction amount based on a detection result of the acceleration detection unit, and corrects the target assist force by the assist correction amount.

  In the electric power steering apparatus according to the second invention of the present invention, the assist correction amount according to the first invention is in an acceleration state in which the longitudinal acceleration detected by the acceleration detecting means is a positive value exceeding a predetermined lower limit value. , And is set as a value that increases as the longitudinal acceleration increases.

  In the electric power steering apparatus according to the first aspect of the present invention, the target assist force that is the control target value of the steering assist motor is increased and corrected based on the longitudinal acceleration of the vehicle detected by the acceleration sensor. The steering assist motor is driven to generate a large target assist force according to the torque detected by the torque sensor due to the reverse input applied from the steering mechanism side, and the torque steering is suppressed by this generated force. Stable travel is possible without forcing the driver to perform complicated operations.

  In the electric power steering apparatus according to the second aspect of the invention, the increase in the target assist force is not corrected until the longitudinal acceleration exceeds the lower limit value. Therefore, the assist control based on the large target assist force is performed during deceleration or moderate acceleration. In addition, there is no possibility that the steering feeling will deteriorate, and at the time of sudden acceleration exceeding the lower limit value, assist control based on the target assist force that increases as the longitudinal acceleration increases is executed, so torque steer generation is more effective The present invention has excellent effects, such as being able to be suppressed and stable running.

  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. In addition, in this figure, although the example applied to a vehicle provided with a rack and pinion type steering mechanism is shown, the present invention is a vehicle provided with another type of steering mechanism such as a ball screw type steering mechanism. Needless to say, it can also be applied to the above.

  The rack and pinion type steering mechanism crosses the rack housing 10 in the middle of the rack housing 10, which is supported in an axially movable manner in a rack housing 10 that extends in the left-right direction of the vehicle body (not shown). The pinion housing 20 has a known structure including a pinion shaft 2 rotatably supported inside, and both ends of the rack shaft 1 projecting outward on both sides of the rack housing 10 are connected to separate tie rods 11, 11. The upper end of the pinion shaft 2 that is connected to the left and right front wheels 12 and 12 as steering wheels and protrudes outside the pinion housing 20 is connected to the steering wheel 30 as a steering member via the steering shaft 3. Yes.

  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 passenger compartment (not shown) while maintaining an inclined posture with the front facing down through the column housing 31. The pinion shaft 2 is connected to the downward projecting end of the column housing 31, and the steering wheel 30 is fixed to the upward projecting 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. In this part, the rack shaft 1 is converted into a movement in the axial direction, and by this movement, the left and right front wheels 12, 12 are pushed and pulled through the respective tie rods 11, 11, and steering is performed.

  The front wheels 12 and 12 that are steered in this way are also drive-coupled to an engine (not shown) via separate drive shafts 13 and 13, and are also used as driving wheels for traveling that are driven by power transmission from the engine. is doing. The front wheels 12 and 12 that also serve as steering wheels and drive wheels have a general configuration in front-wheel drive vehicles and four-wheel drive vehicles, and a detailed description of the drive system is omitted.

  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, and these two axes are connected coaxially by a torsion bar having a known torsion characteristic, and the torsion bar is twisted by the action of the steering torque. With this, there is a known configuration for detecting the relative angular displacement generated between the two axes by an appropriate means.

  Further, the steering assisting motor 5 is attached to the outside of the column housing 31 with its axis substantially orthogonal, and, for example, a worm fixed to the output end extending inside the column housing 31 is externally fixed to the steering shaft 3. The rotation of the motor 5 is transmitted to the steering shaft 3 by being decelerated by the worm and the worm wheel. According to this configuration, the rotation of the steering assist 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. Accordingly, the 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. Needless to say, 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 by the vehicle speed sensor 7 disposed at an appropriate part of the vehicle.

  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. An EEPROM 64 is provided for storing a control map used for the assist control operation and constant values such as various correction values by external writing. The detected value of the steering torque by the torque sensor 4 and the detected value of the vehicle speed by the vehicle speed sensor 7 are taken into the CPU 61 via the input interfaces 65 and 66.

  The assist controller 6 takes in the steering torque from the torque sensor 4 and applies this steering torque to the control map stored in the EEPROM 64 to determine the target value (target auxiliary force) of the steering auxiliary force to be generated. A control command is issued to the steering assist motor 5 to generate an assist force, and an assist control operation for driving and controlling the motor 5 is performed. A plurality of control maps used for determining the target assist force are prepared according to the vehicle speed, and are selected and used according to the detection result of the vehicle speed taken from the vehicle speed sensor 7. As a result, the assist force characteristics can be varied depending on the vehicle speed. For example, when the road surface reaction force applied to the front wheels 12 and 12 is low, the steering assist force is kept low, and the steering wheel 30 has a sense of rigidity. It gives stable steering without wobbling, while at the time of stop and low speed driving with large road surface reaction force, the steering assist force is increased as much as possible to lightly operate the steering wheel 30 for steering. An appropriate steering state can always be obtained regardless of the vehicle speed, such as reducing the labor load required.

  Further, the assist control unit 6 corrects the target assist force determined as described above based on the longitudinal acceleration of the vehicle in order to reduce torque steer generated when steering the front wheels 12 and 12 that also serve as drive wheels. Perform the action. FIG. 3 is a flowchart showing the content of the correction processing operation based on the longitudinal acceleration.

  This correction processing operation is performed in parallel with the above-described target assist force determination processing, and the assist control unit 6 takes in a vehicle speed detection value given from the vehicle speed sensor 7 (S1), and uses this vehicle speed detection value to The longitudinal acceleration α is calculated (S2). The calculation of the longitudinal acceleration α in S2 is performed by, for example, a differential process of obtaining a difference between the captured vehicle speed detection value and the previous vehicle speed detection value stored in the RAM 63 and dividing this difference by the sampling period. The longitudinal acceleration is a positive value when in the acceleration state and a negative value when in the deceleration state.

  It is also possible to provide an acceleration sensor that detects longitudinal acceleration, and to perform the following correction processing operation using the detected value of the acceleration sensor. This type of acceleration sensor is normally installed in a vehicle that performs, for example, traction control and ABS (Anti-Lock Brake System) control, and this acceleration sensor can be used.

Next, the assist control unit 6 determines whether the calculated longitudinal acceleration α is positive or negative (S3). If the longitudinal acceleration α is a negative value (including 0) (S3: NO), the vehicle is in a deceleration state. And the process ends without performing the following correction process. When the longitudinal acceleration α is a positive value (S3: YES), the magnitude relationship between the calculated longitudinal acceleration α and a predetermined lower limit value α ₀ is examined (S4), and the longitudinal acceleration α is determined to be the lower limit value α. If it is ₀ or less (S4: NO), it is determined that the degree of acceleration is small, and the process is terminated without performing the following correction process.

On the other hand, when the longitudinal acceleration α exceeds the lower limit α ₀ (S4: YES), the assist correction amount A is obtained by applying the longitudinal acceleration α to a predetermined correction function F (α) (S5). The assist correction amount A is added to the target assist force determined as described above based on the steering torque and the vehicle speed, and is used for increasing the target assist force (S6).

  The correction function F (α) is set as an increasing function that increases in an appropriate form such as proportionality or power proportionality as the variable α increases, and the assist correction amount A calculated in S5 is The acceleration α increases as the acceleration α increases.

FIG. 4 is an explanatory diagram showing an example of the assist correction amount A determined as described above. The assist correction amount A is a value during deceleration, constant speed travel, and lower limit value α ₀ when the longitudinal acceleration α is a negative value. During acceleration traveling at the following longitudinal acceleration α, the value is maintained at zero, and during acceleration traveling at the longitudinal acceleration α exceeding the lower limit value α ₀ , the value is determined by the correction function F (α). In this figure, the correction function F (α) is set as a square proportional increase function as shown in the following equation.
F (α) = k (α−α ₀ ) ²

In the electric power steering apparatus according to the present invention, when the torque is detected by the torque sensor 4 during acceleration traveling exceeding the lower limit value α ₀ as a result of the above correction processing operation being performed by the assist control unit 6, this detected torque Then, the target assist force determined based on the vehicle speed is increased and corrected, and assist control for driving the steering assist motor 5 is performed to obtain the corrected target assist force, whereby the torque generated as described above is performed. Steer can be reduced.

  When the left and right front wheels 12 and 12 that also serve as drive wheels are steered, torque steer is caused by an unbalance of the drive force transmitted to the front wheels 12 and 12 through the separate drive shafts 13 and 13, respectively. This is a phenomenon in which the rudder force changes and the course is disturbed. This phenomenon occurs remarkably at the time of acceleration and start when the driving force greatly changes. When such torque steer occurs, a reverse input is applied to the steering shaft 3 via the rack shaft 1 and the pinion shaft 2, and the torque sensor 4 detects a torque corresponding to the reverse input, and based on this detected torque. Thus, the steering assist motor 5 is driven, and the generated force of the motor 5 is applied in a direction to reduce the torque steer.

  In the electric power steering apparatus according to the present invention, the target assist force is increased and corrected by the assist correction amount A determined as described above at the time of acceleration at which torque steer is generated or at the time of start. The generated force of the motor 5 driven on the basis is sufficiently larger than that in the normal assist control, so that the torque steer generated as described above can be effectively reduced.

  Further, as described above, the assist correction amount A obtained by the increasing function increases as the longitudinal acceleration α increases, and the target assisting force at the time of acceleration and starting is increased according to the degree of acceleration. Or the torque steer which generate | occur | produces notably at the time of sudden start is further reduced effectively. At this time, the driver who operates the steering wheel 30 only feels the force obtained by subtracting the generated force of the motor 5 from the reverse input by torque steer, and easily performs steering or holding under acceleration and starting conditions. It is possible to correct the turbulence of the course caused by torque steer with a margin, and stable running without wobbling becomes possible.

Further, since the increase correction of the target assist force as described above is performed on the condition that the longitudinal acceleration α exceeding the preset lower limit value α ₀ is detected, the increase in the amount during the gentle acceleration traveling where torque steer does not occur. Assist control based on the corrected target assist force is performed, and it is possible to avoid the possibility that an unnecessary change in steering feeling will occur.

  In the above embodiment, the assist correction amount A is obtained by applying the longitudinal acceleration α to the increasing function. However, a correction map that appropriately determines the relationship between the longitudinal acceleration α and the assist correction amount A is used. It is good also as a structure which prepares and determines the assist correction amount A according to this correction map. In this case, the relationship between the longitudinal acceleration α and the assist correction amount A can be determined in an appropriate form such as a stepwise increase, and the occurrence of torque steer can be effectively reduced.

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 content of the correction | amendment process operation | movement based on a longitudinal acceleration. It is explanatory drawing which shows an example of assist correction amount.

Explanation of symbols

4 Torque sensor 5 Motor 6 Assist control unit 7 Vehicle speed sensor
12 Front wheel (steering wheel)
30 Steering wheel (steering member)

Claims (2)

A torque sensor that detects a steering torque applied to a steering member of a vehicle, and assist control that determines a target auxiliary force based on the detected torque of the torque sensor and controls the steering assist motor to generate the target auxiliary force. An electric power steering device that assists steering of a steering wheel that also serves as a driving wheel by the generated force of the motor,
Acceleration detecting means for detecting longitudinal acceleration of the vehicle;
An electric power steering apparatus comprising: a correction unit that sets an assist correction amount based on a detection result of the acceleration detection unit, and corrects the target auxiliary force by an increase amount based on the assist correction amount.   The assist correction amount is set as a value that increases as the longitudinal acceleration increases when the longitudinal acceleration detected by the acceleration detecting unit is in an acceleration state where the acceleration is a positive value exceeding a predetermined lower limit. The electric power steering device according to Item 1.

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