JP5087920B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of enhancing steering feeling without providing a torque sensor in order to determine a target assistant force by determining the target assistance force based on a steering angle changing accompanied by the operation of a steering wheel. <P>SOLUTION: In the electric power steering device, the target assistance force is determined based on the operation of the steering wheel 30 of the vehicle, a motor 5 for steering assistance is driven according to the determined target assistance force to assist the steering. A steering angle changing accompanied by the operation of the steering wheel 30 and steering angular velocity and steering angular acceleration calculated from the steering angle are applied to an equation of motion to calculate required torque, and the target steering torque is calculated from the calculated required torque. Therefore, it is not required that the torque sensor is provided in order to determine the target assistance torque, and the steering feeling can be enhanced by constituting a steering shaft 3 by a hollow material or a solid material with high rigidity. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus configured to assist steering by calculating a target assisting force according to an operation of a steering member and driving a steering assisting motor to generate the target assisting force.

  In recent years, as a power steering device for a vehicle, an electric power steering device using an electric motor as an actuator for assisting steering has become widespread. This electric power steering device generally has a torque sensor arranged in the middle of a steering shaft that transmits an operation of a steering member such as a steering wheel to a steering mechanism, and generates a steering torque applied to the steering shaft according to the operation of the steering member. It is configured to detect a target assisting force based on the detected steering torque, and to drive and control a steering assisting motor so as to generate the target assisting force. 1).

The torque sensor is configured to detect torsion that occurs in the steering shaft due to the action of steering torque applied to the steering member. For the purpose of increasing this torsion and increasing the detection accuracy of the steering torque, In the middle, a connecting portion is provided in which the input shaft on the steering member side and the output shaft on the steering mechanism side are connected by a low-rigidity torsion bar. The relative angular displacement generated between the output shaft and the output shaft is detected by appropriate means.
JP 2004-338562 A

  In an electric power steering apparatus equipped with such a torque sensor, the torsion bar acts as a kind of damper, causing a situation where the road surface condition is not easily transmitted to the steering member, or a slight time delay when operating the steering member. As a result, there arises a problem that the steering mechanism reacts to cause the steering feeling to deteriorate.

  The present invention has been made in view of such circumstances, and by calculating the target auxiliary force based on the steering angle that changes in accordance with the operation of the steering member, a torque sensor having a low-rigidity torsion bar is not required, An object of the present invention is to provide an electric power steering apparatus capable of improving the steering feeling.

An electric power steering apparatus according to a first aspect of the present invention obtains a target auxiliary force based on an operation of a steering member of a vehicle, and drives a steering auxiliary motor according to the obtained target auxiliary force to assist the steering. In the steering device, a steering angle sensor that detects a steering angle that changes in accordance with an operation of the steering member, a calculation unit that calculates a steering angular velocity and a steering angular acceleration using the steering angle detected by the steering angle sensor, An auxiliary force calculating means for calculating the target auxiliary force using the steering angular velocity and the steering angular acceleration calculated by the calculating means and the steering angle detected by the steering angle sensor, the auxiliary force calculating means comprising: The elastic region where the steering wheel tire of the vehicle is steered while elastically deforming on the road surface, and the friction where the tire is steered while sliding against the road surface And determining the steering force required to steer the steering wheel using an equation of motion including an elastic term whose main element is the elastic force accompanying the elastic deformation of the tire. The target auxiliary force is calculated from the obtained steering force, and in the friction region, the steering wheel is adjusted using an equation of motion including a friction term whose main element is a friction force acting between the tire and the road surface. It obtains a steering force necessary to steer the characterized that you calculate the target assist force from a steering force determined.

An electric power steering device according to a second aspect of the invention obtains a target auxiliary force based on an operation of a steering member of a vehicle, and drives a steering auxiliary motor according to the obtained target auxiliary force to assist steering. In the steering apparatus, a steering angle sensor that detects a steering angle that changes in accordance with the operation of the steering member, and a relative steering angle is calculated by subtracting a predetermined reference steering angle from the steering angle detected by the steering angle sensor. Relative angle calculating means, calculating means for calculating relative steering angular velocity and relative steering angular acceleration using the relative steering angle calculated by the relative angle calculating means, and relative steering angular velocity and relative steering calculated by the calculating means. and an auxiliary power calculating means for calculating the target assist force using the relative steering angle calculated by the angular acceleration and the relative angle calculating means, the auxiliary The calculating means discriminates an elastic region where the steering wheel tire of the vehicle is steered while being elastically deformed on a road surface, and a friction region where the tire is steered while sliding against the road surface, In the elastic region, a steering force necessary for turning the steering wheel is obtained using an equation of motion including an elastic term having an elastic force accompanying elastic deformation of the tire as a main element, and the steering force is obtained from the obtained steering force. A target assist force is calculated, and in the friction region, it is necessary to steer the steering wheel using an equation of motion including a friction term whose main element is a friction force acting between the tire and the road surface. obtains a steering force, it characterized that you calculate the target assist force from a steering force determined.

According to a third aspect of the present invention, there is provided an electric power steering apparatus according to the present invention, wherein when the steering force obtained by the auxiliary force calculating means using the equation of motion is equal to or higher than a predetermined upper limit steering force, the target auxiliary force is calculated from the upper limit steering force. It is comprised so that force may be calculated.

According to a fourth aspect of the present invention, there is provided an electric power steering apparatus including a determining unit that determines that the steering member is turning back, and the relative angle calculating unit is configured such that the steering force calculated by the auxiliary force calculating unit is the upper limit steering. It is characterized in that the reference steering angle is reset when it is determined by the determination means that the vehicle is turning over in a state where the force is greater than or equal to a force.

An electric power steering apparatus according to a fifth aspect of the present invention includes a vehicle speed sensor that detects a traveling speed of the vehicle, and the equation of motion includes a dynamic friction term indicating dynamic friction generated according to an operation of the steering member, The force calculation means is configured to change at least one of the upper limit steering force, the elastic term, and the dynamic friction term according to the vehicle speed detected by the vehicle speed sensor.

According to the first aspect of the present invention, the necessary steering force is obtained by using the steering angle that changes with the operation of the steering member, the steering angular velocity and the steering angular acceleration calculated from the steering angle, and the target auxiliary force is obtained from the steering force. and an auxiliary force calculating means Ru determined, it is not necessary to provide a torque sensor to determine the target assist force, is possible to improve the steering feeling by forming the steering shaft by a high hollow material or solid material rigidity it can.

The auxiliary force calculating means determines whether the steering state is in the elastic region or the friction region, and when calculating the target auxiliary force, the elastic region includes an equation of motion including an elastic term whose main element is the elastic force of the tire. In the friction area, the equation of motion including the friction term with the frictional force acting between the tire and the road surface as the main element is used. Therefore , the target auxiliary force can be accurately obtained in each area, and the steering assist can be appropriately performed. It can be performed.

According to the second invention, the relative steering angle is calculated mainly by using the relative steering angle obtained by subtracting the predetermined reference steering angle from the steering angle, the relative steering angular velocity and the relative steering angular acceleration calculated from the relative steering angle. It obtains a steering force required proportionally, that comprise an auxiliary force calculating means for calculating a target assist force from the steering force. As a result, it is possible to improve the steering feeling by configuring the steering shaft with a highly rigid hollow material or solid material without providing a torque sensor. Further, as a reference steering angle, for example, the tire of the steering wheel is elastically deformed. By using the steering angle that is not in use, it is possible to accurately determine the target auxiliary force by obtaining the elastic force of the steering system that occupies the main part of the necessary steering force in consideration of the elastic behavior of the tire of the steering wheel. It is possible to assist steering appropriately.

The auxiliary force calculating means determines whether the steering state is in the elastic region or the friction region, and when calculating the target auxiliary force, the elastic region includes an equation of motion including an elastic term whose main element is the elastic force of the tire. In the friction area, the equation of motion including the friction term with the frictional force acting between the tire and the road surface as the main element is used. Therefore , the target auxiliary force can be accurately obtained in each area, and the steering assist can be appropriately performed. It can be performed.

According to the third invention, when the steering force obtained using the equation of motion is greater than or equal to a predetermined upper limit steering force, the target auxiliary force is calculated from the upper limit steering force. By determining the upper limit steering force based on the friction force acting between the tire of the steering wheel and the road surface, the target auxiliary force can be accurately obtained even when the elastically deformed tire is steered while sliding on the road surface. Therefore, steering assistance can be performed appropriately.

According to the fourth aspect of the invention, when it is determined that the steering member is turning back in a state where the steering force calculated by the auxiliary force calculation means is equal to or greater than the upper limit steering force, the reference steering angle is reset. Since the reset reference steering angle is applied to the equation of motion, the target assist force can be obtained with high accuracy, and steering assist can be performed appropriately.

According to the fifth aspect of the present invention, the upper limit steering force, at least one of the elastic section and the dynamic friction term, because they change depending on the running speed of the vehicle, it is possible to determine the target assist force accurately, appropriately Steering assistance can be performed.

  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. Needless to say, it is also possible to apply.

  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 a vehicle body (not shown). The pinion housing 20 has a known configuration including a pinion shaft 2 rotatably supported inside the pinion 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, 12 as steering wheels via separate tie rods 11, 11, and from one side of the pinion housing 20. An upper end of the pinion shaft 2 protruding outward is connected to a steering wheel 30 as a steering member via the 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 attached to the interior of a vehicle compartment (not shown) while maintaining an inclined posture with the front facing down via the column housing 31. The pinion shaft 2 is connected to the projecting end of the steering shaft 3 below the column housing 31, and the steering wheel 30 is fixed to the 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 movement in the axial length direction. By such movement of the rack shaft 1, the left and right front wheels 12, 12 are pushed and pulled through the respective tie rods 11, 11 to steer Is made.

  In the middle of the column housing 31 that supports the steering shaft 3, there is provided a steering angle sensor 4 that detects a steering angle that changes as the steering wheel 30 rotates, and is steered to a position below the steering angle sensor 4. An auxiliary motor 5 is attached.

  The steering angle sensor 4 can be configured as a rotation angle sensor that detects the rotation angle of the steering shaft 3. Since the steering wheel 30 is rotated by multiple rotations in both the left and right directions centered on the straight neutral position for steering, the steering angle sensor 4 can detect the absolute angle over the entire rotation range of the steering wheel 30. It is desirable that the rotation angle sensor is configured as follows. It is also possible to use a resolver that detects the rotation angle of the rotor of the steering assist motor 5 as a rotation angle sensor for obtaining the rotation angle of the steering shaft 3, that is, the steering angle sensor 4.

  The steering assist motor 5 is attached to the outside of the column housing 31 with its axis substantially orthogonal, and a worm fixed to an output end extending inside the column housing 31 is externally fixed to the steering shaft 3. The rotation of the motor 5 is engaged with the wheel, and the rotation of the motor 5 is decelerated by the worm and the worm wheel and transmitted to the steering shaft 3 to assist the steering performed as described above.

  The steering assisting motor 5 attached in this way is driven according to a control command given from the assist control unit 6 via the motor drive circuit 7. The assist control unit 6 is provided with a detected value of the steering angle by the steering angle sensor 4 and a detected value of the vehicle speed by the vehicle speed sensor 8 arranged at an appropriate part of the vehicle. Further, the steering assisting motor 5 is provided with a motor current sensor 50 for detecting a current flowing through the motor 5, and a detected value of the current from the motor current sensor 50 is also given to the assist control unit 6.

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 that are connected to each other via an internal bus 60, and is configured as an ECU that performs the following assist control by the operation of the CPU 61 in accordance with a control program stored in the ROM 62. Steering angle theta _h detected by the steering angle sensor 4, the motor current I _s, which is detected by the vehicle speed V and the motor current sensor 50 which is detected by the vehicle speed sensor 8 via the respective other input interface 64, 65, 66, It is adapted to be taken into the CPU 61.

Electric power steering apparatus according to the present invention, by using the steering angle theta _h which varies with the rotation operation of the steering wheel 30, determine the target assist torque T _a which is the torque converting the target assist force to be applied to the steering shaft 3, obtained are configured to determine the target assist torque T _a from the target drive current I _a to be supplied to the motor 5 for steering assistance.

First, a method is described for obtaining the target assist torque T _a with a steering angle theta _h. The equation of motion of the steering system including the steering wheel 30 to the front wheels 12 and 12 is expressed as follows.
T _n = J · α _h + C · ω _h + K · θ _h + T _h (1)
Here, J is the moment of inertia of the steering system, C is the viscous friction coefficient of the steering system, K is the elastic coefficient of the steering system, T _h is the torque determined by the dynamic friction of the steering system (hereinafter, referred to as dynamic friction torque). θ _h is a steering angle. ω _h is a steering angular velocity and is given as a first derivative value of θ _h . α _h is a steering angular acceleration and is given as a second-order differential value of θ _h .

T _n obtained by the equation of motion of such a steering system, the value obtained by the torque converting the steering force required in order to steer the front wheels 12, 12 (hereinafter, requires that the torque), and (1) to As shown, it can be expressed by an elastic term proportional to the steering angle θ _h , a viscosity term proportional to the steering angular velocity ω _h , an inertia term proportional to the steering angular acceleration α _h , and a dynamic friction term. θ _h is determined to be positive or negative depending on the direction of the steering wheel 30 from the straight neutral position. For example, the right direction from the straight neutral position is positive and the left direction is negative. The sign of T _h is determined in the same manner as θ _h .

Target assist torque T _a to be applied to the steering shaft 3 by the motor 5 for steering assistance is obtained by the following equation using the required torque T _n obtained by (1).
T _a = T _n −T _ha (2)
Here, T _ha is a steering input torque target value to be applied by the driver who rotates the steering wheel 30, and is a parameter appropriately set as a feeling of response of the steering wheel 30 according to the vehicle speed, as will be described later.

The target assist torque T _a which is determined by equation (2), as described below, in accordance with the operation state of the steering wheel 30, whether or not it is necessary to have to add as an auxiliary steering, is either added to the right or left direction It is determined.

For example, the operation state of the steering wheel 30 is divided into steering start, turning, steering, turning back, and steering end. The steering start is a state in which the steering wheel 30 is started to rotate right or left from the straight traveling neutral position. This state is determined when the steering angular velocity ω _h is not zero. If it is determined that the steering start, in the same direction as the rotation direction of the steering wheel 30, is determined to apply the target assist torque T _a.

Steering is a state in which the steering wheel 30 is held at a position that is rotated right or left from a straight traveling neutral position. This state is the steering angular velocity omega _h is 0, the motor current I _s is determined by non-zero. If it is determined that the steering hold is determined torque obtained by subtracting the frictional torque T _h from the previous target assist torque T _a to apply as the target assist torque T _a.

The end of steering is a state in which the steering wheel 30 is returned to and held in the straight traveling neutral position. This state is determined by the steering angular velocity omega _h and the motor current I _s is 0.

The incision is a state in which the steering wheel 30 is rotated in the same direction as the direction of the necessary torque T _n obtained by the expression (1), and the turning back is the steering wheel 30 in the direction opposite to the direction of the necessary torque T _n. Is rotating. It is determined that the required torque T _n and the steering angular velocity ω _h are not 0 in the state of cutting and turning back. Cut and crosscut are distinguished by the sign of the product of the steering angular velocity omega _h required torque T _n. That is, when the obtained product is positive, the cut is performed, and when the obtained product is negative, the cut is performed. If it is determined that the cut, in the same direction as the rotation direction of the steering wheel 30, is determined to apply the target assist torque T _a. If it is determined that the crosscut, in a direction opposite to the rotation direction of the steering wheel 30, is determined to apply the target assist torque T _a.

The assist control portion 6 according to the classified operational state as described above, determine the target assist torque T _a with a steering angle theta _h, be supplied to the motor 5 of the target assist torque T _a from a steering assist obtained The target drive current Ia to be _calculated is obtained. 3 and 4 are flowcharts showing the operation contents of the assist control unit 6. The assist control unit 6 first initializes N indicating the number of times of sampling (N = 1: step S1). Next, the steering angle θ _h (N) detected by the steering angle sensor 4, the vehicle speed V (N) detected by the vehicle speed sensor 8, and the motor current I _s (N) detected by the motor current sensor 50 are captured. (Steps S2, 3, 4).

Further, a difference calculation is performed using the steering angle θ _h (N) captured at the current sampling in step S2 and the steering angle θ _h (N−1) captured at the previous sampling in step S2. A steering angular velocity ω _h (N) is obtained (step S5). Next, the difference calculation is performed using the steering angular velocity ω _h (N) obtained by the difference calculation in step S5 and the steering angular velocity ω _h (N−1) obtained by the difference calculation at the previous sampling in step S5. The steering angular acceleration α _h (N) is obtained (step S6). The difference calculation in steps S5 and S6 in the case of N = 1 may be executed with the steering angle θ _h (N−1) = 0 and the steering angular velocity ω _h (N−1) = 0.

The assist control unit 6 determines whether or not the steering angular velocity ω _h (N) is 0 (step S7). If the steering angular velocity ω _h (N) is not 0 (step S7: YES), the assist control unit 6 proceeds to step S8 and performs steering. When the angular velocity ω _h (N) is 0 (step S7: NO), the process proceeds to step S11. It is determined whether or not the steering wheel 30 is operated under the determination condition of step S7. As a state in which the steering wheel 30 is operated, there may be steering start, cutting, or turning back. Further, as a state when the steering wheel 30 is not operated, there is a case where the steering is maintained or the steering is ended.

In step S8, the vehicle speed V (N) captured in step S3 is applied to the input torque target value map indicating the correspondence relationship between the steering input torque target value T _ha (N) and the vehicle speed V (N). A torque target value T _ha (N) is determined. The input torque target value map is set in advance so that the steering input torque target value T _ha increases or decreases according to the level of the vehicle speed V.

Next, the required torque T _n (N) is calculated using the equation (1), and the target auxiliary torque T _a (N) is calculated using the equation (2) (steps S9 and S10). Note that the target assist torque _Ta (N) calculated in this way is | T _a (N−1) | <| T _a (N) | when the operation state of the steering wheel 30 is steering start and infeed. Thus, the applied direction is the same as the rotation direction of the steering wheel 30. In the case of switching, | T _a (N−1) |> | T _a (N) |, and the direction to be added is opposite to the rotation direction of the steering wheel 30.

On the other hand, the assist control portion 6, in step S11, the motor current I _s (N) is determined whether 0 or not, if the motor current I _s (N) is not 0 (step S11: YES), the target assist torque T _a (N) = T _a (N−1) −T _h (Step S12). If the motor current I _s (N) is 0 (step S11: NO), the process ends without determining the target auxiliary torque T _a (N).

Based on the determination condition of step S11, it is determined whether the operation state of the steering wheel 30 is the steering holding or the steering end. As described above, in the case of steering, the motor current I _s (N) is not 0 (step S11: YES), and in the case of the end of steering, the motor current I _s (N) is 0 (step S11: NO). .

The assist controller 6 determines the target drive current I _a (N) based on the target assist torque T _a (N) calculated in step S10 or step S12 (step S13). Next, a deviation between the target drive current I _a (N) and the motor current I _s (N) flowing through the steering assist motor 5 is obtained, and PID calculation is performed on the deviation to obtain a motor voltage. A PWM signal based on the calculation result is given to the motor drive circuit 7 (step S14). The motor drive circuit 7 drives the motor 5 by the PWM signal given from the assist control unit 6 in step S14. The assist control unit 6 adds 1 to N (step S15), returns to step S2, and repeats a series of operations. As described above, the target drive current I _a (N) and the actual motor current I _s (N) can be matched to obtain the target auxiliary torque T _a (N) corresponding to the target drive current I _a (N). .

In the present embodiment, the assist control unit 6 applies the vehicle speed V (N) to the input torque target value map indicating the relationship between the vehicle speed V (N) and the steering input torque target value T _ha (N). Although T _ha (N) is obtained, the present invention is not limited to this, and the vehicle speed V (N) is applied to a function indicating the relationship between the vehicle speed V (N) and the steering input torque target value T _ha (N) for steering. Needless to say, the input torque target value T _ha (N) may be obtained.

  In the electric power steering apparatus according to the present invention configured as described above, the target auxiliary force is obtained using the steering angle that changes as the steering wheel 30 is operated, the steering angular velocity and the steering angular acceleration calculated from the steering angle. Since the corresponding target assist torque is calculated, it is not necessary to provide a torque sensor to obtain the target assist torque, and the steering feeling can be improved by configuring the steering shaft 3 with a rigid hollow material or solid material. In addition, the cost can be reduced.

  Further, the motion of the steering system including the steering wheel 30 to the front wheels 12, 12 includes an elastic term proportional to the steering angle, a viscosity term proportional to the steering angular velocity, and an inertia term proportional to the steering angular acceleration. 1) The torque required to steer the front wheels 12 and 12 is obtained using the equation of motion given as the equation, and the target auxiliary torque is calculated from the obtained required torque. Therefore, steering assistance can be performed appropriately.

  Another embodiment of the electric power steering apparatus will be described below. First, the equation of motion of the steering system used in the present embodiment will be described.

The front wheels 12 and 12 include a tire, and the expression (1) can be expressed by the following expression (3) having an elastic term whose main element is an elastic force accompanying elastic deformation of the tire. The elastic force of the tire is not the steering angle θ _h detected by the steering angle sensor 4, but a reference steering angle θ ₀ determined in relation to the elastic behavior of the tires of the front wheels 12, 12 as shown in the following equation (4): More specifically, it is proportional to the relative steering angle θ obtained by subtracting the reference steering angle θ ₀ , which is the steering angle when the tires of the front wheels 12 and 12 are not elastically deformed, from the steering angle θ _h .
T _n = J · α + C · ω + K · θ + T _h (3)
θ = θ _h −θ ₀ (4)
Here, ω is a relative steering angular velocity and is given as a first-order differential value of θ. α is a relative steering angular acceleration and is given as a second-order differential value of θ.

As long as the steering wheel 30 is not operated rapidly, the inertia term and the viscosity term in the equation (3) are very small values. Hereinafter, description will be made using the following equation in which the inertia term and the viscosity term in the equation (3) are omitted.
T _n = K · θ + T _h (5)

  By the way, when a force is applied to the front wheels 12 and 12 according to the rotation operation of the steering wheel 30 during driving of the vehicle, the tires of the front wheels 12 and 12 are elastically deformed by the frictional force acting between the ground contact surface and the road surface. Lateral force (hereinafter referred to as lateral force) is generated. When the lateral force is small, the frictional force acting between the ground contact surface of the tire and the road surface is larger, so it does not slip and a lateral force proportional to the deformation is generated. On the other hand, when the lateral force is larger than the frictional force, the tire slides against the road surface, and the lateral force applied to the tire becomes substantially constant. That is, the steering force required to steer the front wheels 12, 12 does not exceed the frictional force (upper limit steering force) when the tire starts to slide on the road surface.

When using an equation of motion of a steering system having an elastic term whose main element is the elastic force accompanying the elastic deformation of the tire, paying attention to such a state of the tire, the region where the tire is steered while being elastically deformed Necessary torque T _n needs to be considered in two areas: an area (hereinafter referred to as an elastic area) and an area where steering is performed while sliding on the road surface in a state where the tire is elastically deformed (hereinafter referred to as a friction area). There is. Since the main component of elastic deformation required torque T _n of the tire in the elastic region, the required torque T _n is given by the aforementioned equation (5).

On the other hand, the steering force required to steer the front wheels 12, 12 as described above in the friction region, since the tire can not exceed the frictional force at the start slipping relative to the road surface, the required torque T _n is It is given as a constant value as in the following equation.
T _n = T _t (6)
T _t is determined based on a value obtained by converting the frictional force acting between the ground contact surface of the tire and the road surface into a torque (hereinafter referred to as an upper limit torque). The upper limit torque T _t is, for example, a predetermined value obtained by measurement under the condition that, when the vehicle is stationary, the elastic coefficient of the elastic region of the tire and the torque at which the tire slides do not change due to external factors such as road surface friction changes. Can be used. Since the frictional force acting between the tire contact surface and the road surface changes depending on the vehicle speed, the upper limit torque T _t is set so as to increase or decrease according to the vehicle speed V. .

As described above, when the necessary torque T _n is less than T _t, it is determined that the tire is in the elastic region, and the necessary torque T _n is calculated from the equation (5). On the other hand, when the necessary torque T _n is _{equal to} or greater than T _t, it is determined that the tire is in the friction region, and the necessary torque T _n is calculated by the equation (6).

By the way, in the friction region, since the tire slides with respect to the road surface while maintaining a deformed state without newly elastically deforming, the reference steering angle θ ₀ changes as the steering wheel 30 rotates. . For this reason, when the tire switches from the friction region to the elastic region and the necessary torque T _n in the elastic region is calculated, a value obtained by adding the movement of the reference steering angle θ ₀ in the friction region is used as a new reference steering angle θ _0. It is necessary to use as.

However, when the steering angle θ _h increases, the tire becomes highly rigid, the elastic coefficient K increases, and the dynamic friction torque T _h increases mainly due to the tire contribution. Therefore, a value obtained by adding the change amount of the steering angle under the friction region to the reference steering angle θ ₀ in the elastic region cannot be used as the new reference steering angle θ ₀ . Therefore, when the tire is switched elastic region from friction region, reset the reference steering angle theta ₀ with the new modulus K and the dynamic friction torque T _h, using a reference steering angle theta ₀ which is the reset Therefore, it is necessary to calculate the required torque T _n in the elastic region (FIG. 5 is an explanatory diagram showing the concept of the reference steering angle θ ₀ and shows an example of steering).

The reference steering angle θ ₀ is expressed as follows:
θ ₀ = θ _hr − (T _tr −T _h ) / K (7)
Here, θ _hr is the steering angle θ _h at the time of turning back, and T _tr is the upper limit torque at the time of turning back.

6 and 7 are flowcharts showing the operation contents of the assist control unit 6 according to another embodiment. The assist controller 6 initializes N indicating the number of samplings (N = 1: step S21). Next, the steering angle θ _h (N) detected by the steering angle sensor 4, the vehicle speed V (N) detected by the vehicle speed sensor 8, and the motor current I _s (N) detected by the motor current sensor 50 are captured. (Steps S22, 23, 24).

Further, the relative steering angle θ (N) is obtained by subtracting the reference steering angle θ ₀ (N) from the steering angle θ _h (N) captured in step S22 (step S25). In addition, what is necessary is just to perform the calculation of step S25 in the case of N = 1 as reference | standard steering angle (theta) ₀ (N) = steering angle (theta) _h (N).

Next, a difference calculation is performed using the steering angle θ _h (N) captured at the current sampling in step S22 and the steering angle θ _h (N−1) captured at the previous sampling in step S22. The steering angular velocity ω _h (N) is obtained (step S26). Note that the difference calculation in step S26 in the case of N = 1 may be executed with the steering angle θ _h (N−1) = 0.

The assist control unit 6 determines whether or not the steering angular velocity ω _h (N) is 0 (step S27). If the steering angular velocity ω _h (N) is not 0 (step S27: YES), the assist control unit 6 proceeds to step S28 and performs steering. When the angular velocity ω (N) is 0 (step S27: NO), the process proceeds to step S33. The determination condition in step S27 is the same as the determination condition in step S7 in FIG.

In step S28, the elastic coefficient map showing the correspondence relationship between the steering angle θ _h (N) and the steering system of the modulus K (N), by applying the steering angle θ _h (N) taken in step S22 elasticity A coefficient K (N) is determined. Modulus map is previously set so as to increase or decrease the modulus K in accordance with the magnitude of the steering angle theta _h. Since the correspondence relationship between the steering angle θ _h and the elastic coefficient K of the steering system changes as the vehicle speed V changes, the assist control unit 6 selects a plurality of prepared elastic coefficient maps according to the vehicle speed V. Thus, the elastic modulus K is obtained.

Next, the steering angle θ _h (N) and the dynamic friction torque T _h in frictional torque map showing the correspondence between the (N), the steering angle is taken in step S22 θ _h (N) by applying the T _h (N ) Is determined (step S29). The dynamic friction torque map is set in advance such that T _h increases or decreases according to the magnitude of the steering angle θ _h . Similarly correspondence relationship between the steering angle theta _h and the dynamic friction torque T _h, in order to change with changes in vehicle speed V, the assist control portion 6, selected according to a plurality of dynamic friction torque map prepared in advance on the vehicle speed V T _h is obtained.

Further, the vehicle input speed V (N) taken in step S23 is applied to the input torque target value map showing the correspondence between the vehicle speed V (N) and the steering input torque target value T _ha (N), and the steering input torque target is obtained. The value T _ha (N) is determined (step S30). The input torque target value map is set in advance so that the steering input torque target value T _ha increases or decreases according to the level of the vehicle speed V.

The required torque T _n (N) is calculated by applying the elastic coefficient K (N) and the dynamic friction torque T _h (N) thus obtained to the equation (5) (step S31). Next, it is determined whether the product of the required torque T _n (N) calculated in step S31 and the steering angular velocity ω _h (N) obtained in step S26 is greater than 0 (step S32). When the product of the torque T _n (N) and the steering angular velocity ω _h (N) is greater than 0 (step S32: YES), the process proceeds to step S34, and the target auxiliary torque _Ta (N) at the time of cutting is calculated. . On the other hand, when the product of the necessary torque T _n (N) and the steering angular velocity ω _h (N) is 0 or less (step S32: NO), the process proceeds to step S35, and the target auxiliary torque _Ta (N) at the time of switching is obtained. calculate.

Based on the determination condition in step S32, it is determined whether the operation state of the steering wheel 30 is cut or turned. As described above, in the case of cutting, the sign of the steering angular velocity ω _h (N) and the required torque T _n (N) are the same (step S32: YES). In the case of switchover, the sign of the steering angular velocity ω _h (N) and the required torque T _n (N) are different (step S32: NO).

FIG. 8 is a flowchart showing a procedure for calculating the target auxiliary torque _Ta (N) at the time of cutting. The assist control unit 6 determines whether the necessary torque T _n (N) is less than the upper limit torque T _t (step S51). When the required torque T _n (N) is less than T _t (step S51: YES), the target auxiliary torque T _a (N (N) is obtained by using the required torque T _n (N) obtained by the expression (5). ) Is calculated (step S52), and the process returns. When the required torque T _n (N) is _{equal to} or greater than T _t (step S51: NO), the target auxiliary torque T _a (N (N) is calculated by using the required torque T _n (N) obtained by the expression (6). ) Is calculated (step S53), and the process returns.

Based on the determination condition in step S51, it is determined whether the tire is in the elastic region or the friction region. As described above, when it is in the elastic region (step S51: YES), the necessary torque T _n (N) is obtained from the equation (5), and when it is in the friction region (step S51: NO), the necessary torque T _n (N ) _Does not exceed T _t , so T _t is used as the necessary torque T _n (N) as shown in the equation (6). The upper limit torque T _t is set so as to become larger or smaller according to the slow speed of the vehicle speed as described above. The assist control unit 6 may be configured to obtain T _t by applying the vehicle speed V (N) to the upper limit torque map indicating the relationship between the vehicle speed V (N) and the upper limit torque T _t , or the vehicle speed V ( N) and the vehicle speed V (N) may be applied to a function indicating the relationship between the upper limit torque T _t and the T _t may be obtained.

FIG. 9 is a flowchart showing a calculation procedure of the target auxiliary torque _Ta (N) at the time of switching. The assist control unit 6 determines whether or not the necessary torque T _n (N−1) at the previous sampling is less than the upper limit torque T _t (step S61). When the required torque T _n (N−1) is less than T _t (step S61: YES), the process proceeds to step S62, and when the required torque T _n (N−1) is _{equal to} or greater than T _t (step S61: NO). The process proceeds to step S63. In step S63, the reference steering angle θ ₀ (N) is obtained using equation (7). Next, the relative steering angle θ (N) is obtained using equation (4) (step S64), and the process proceeds to step S62.

In step S62, the assist control unit 6 calculates the target assist torque T _a (N) by the equation (2) using the necessary torque T _n (N) obtained by the equation (5) and returns. Note that, based on the determination condition in step S61, it is determined whether the tire was in the elastic region or the friction region at the time of the previous sampling. This is because, as described above, when the tire switches from the friction region to the elastic region (step S61: NO), it is necessary to newly set the reference steering angle θ ₀ (N).

On the other hand, the assist control portion 6, in step S33, the motor current I _s (N) is determined whether 0 or not, if the motor current I _s (N) is not 0 (step S33: YES), the time of steering hold A target auxiliary torque is obtained by T _a (N) = T _a (N−1) −T _h (N−1) (step S36). If the motor current I _s (N) is 0 (step S33: NO), the process ends without determining the target auxiliary torque _Ta (N). The determination condition in step S33 is the same as the determination condition in step S11 in FIG.

After calculating the target assist torque T _a (N) as described above, the assist control portion 6, the target drive current based on the target assist torque T _a which is calculated in either step S34,35,36 (N) I _a (N) is determined (step S37). Next, a deviation between the target drive current I _a (N) and the motor current I _s (N) flowing through the steering assist motor 5 is obtained, and PID calculation is performed on the deviation to obtain a motor voltage. A PWM signal based on the calculation result is given to the motor drive circuit 7 (step S38). The motor drive circuit 7 drives the motor 5 by the PWM signal given from the assist control unit 6 in step S38. The assist controller 6 adds 1 to N (step S39), returns to step S22, and repeats a series of operations. As described above, the target drive current I _a (N) and the actual motor current I _s (N) can be matched to obtain the target auxiliary torque T _a (N) corresponding to the target drive current I _a (N). .

In the present embodiment, the assist control unit 6 applies the vehicle speed V (N) to the input torque target value map indicating the relationship between the vehicle speed V (N) and the input torque target value T _ha (N). _{Although ha} (N) is obtained, the present invention is not limited to this, and the steering input is applied by applying the vehicle speed V (N) to a function indicating the relationship between the vehicle speed V (N) and the steering input torque target value T _ha (N). Needless to say, the torque target value T _ha (N) may be obtained. Similarly for modulus K and the dynamic friction torque T _h, constitute the K and T _h by applying a steering angle theta _h related to the respective indicating function of the steering angle theta _h and K and T _h as determined respectively Needless to say.

  In the electric power steering apparatus according to the present invention configured as described above, a reference steering angle which is a steering angle in a state where the tires of the front wheels 12 and 12 are not elastically deformed is set, and this reference steering angle is set to the current level. A relative steering angle is obtained by subtracting from the steering angle, the required torque is obtained by applying the relative steering angle to an equation of motion including an elastic term proportional to the relative steering angle, and a steering input torque set in advance from the obtained necessary torque. The target auxiliary torque is calculated by reducing the target value. As a result, it is not necessary to provide a torque sensor for obtaining the target auxiliary torque, and the steering feeling can be improved and the cost can be reduced by configuring the steering shaft 3 with a highly rigid hollow material or solid material. . Furthermore, it is possible to obtain the target assist torque with high accuracy by obtaining the elastic term of the steering system that occupies the main part of the necessary torque, and to appropriately assist the steering.

In addition, when an upper limit torque T _t determined based on a value obtained by converting the frictional force acting between the tire contact surface and the road surface is converted into a torque and the required torque obtained using the equation of motion is _{equal to} or greater than T _t , Since the target auxiliary torque is calculated from T _t , the target auxiliary torque can be accurately obtained even in a state where the steering is performed while sliding on the road surface in a state where the tire is elastically deformed, Steering assistance can be performed appropriately.

Further, when it is determined that the steering wheel 30 is turning back in a state where the required torque calculated by the assisting force calculation means is _{equal to} or higher than the upper limit torque T _t , the reference steering angle is reset, Since the set reference steering angle is applied to the equation of motion, the target assist torque can be obtained with high accuracy, and steering assist can be performed appropriately.

Further, the elastic term and the dynamic friction term of the equation of motion are changed according to the steering angle. More particularly, in accordance with the magnitude of the steering angle, (3) and (5) from being changed respectively large and small and the elastic coefficient K and the dynamic friction torque T _h in the expression, to determine the target assist force accurately Therefore, steering assistance can be performed appropriately.

Furthermore, in accordance with a change in the vehicle speed, are respectively changed and the upper limit torque T _t and (3) and (5) elastic modulus is shown in formula K and the dynamic friction torque T _h as shown in equation (6). For example, since the upper limit torque T _t is changed according to the slow speed of the vehicle speed, the target assist force can be obtained with high accuracy, and steering assist can be performed appropriately.

In the present embodiment, although change both the elastic coefficient K and the dynamic friction torque T _h according to the steering angle, may be only one. Similarly, although the upper limit torque T _t , the elastic coefficient K, and the dynamic friction torque _Th are changed according to the vehicle speed, only one of them may be used.

  Furthermore, in the above embodiment, the rotation angle sensor that detects the rotation angle of the steering shaft 3 is used as the steering angle sensor 4, but the present invention is not limited to this. For example, the angle of the front wheels 12, 12 is detected. A sensor may be used as the steering angle sensor 4. Needless to say, the present invention can be implemented in variously modified forms within the scope of the matters described in the claims.

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 operation | movement content of an assist control part. It is explanatory drawing which shows the view of a reference | standard steering angle. It is a flowchart which shows the operation | movement content of the assist control part in other embodiment. It is a flowchart which shows the operation | movement content of the assist control part in other embodiment. It is a flowchart which shows the calculation procedure of the target auxiliary torque at the time of cutting. It is a flowchart which shows the calculation procedure of the target auxiliary torque at the time of switching.

Explanation of symbols

  4 Steering angle sensor, 5 Steering assist motor, 6 Assist control unit (calculating means, assisting force calculating means, relative angle calculating means, judging means), 8 vehicle speed sensor, 12 front wheel (steering wheel), 30 steering wheel ( Steering member)

Claims (5)

In an electric power steering device for obtaining a target auxiliary force based on an operation of a steering member of a vehicle, driving a steering auxiliary motor according to the obtained target auxiliary force, and assisting steering,
A steering angle sensor that detects a steering angle that changes in accordance with the operation of the steering member;
Calculating means for calculating a steering angular velocity and a steering angular acceleration using a steering angle detected by the steering angle sensor;
An auxiliary force calculating means for calculating the target auxiliary force using the steering angular velocity and steering angular acceleration calculated by the calculating means and the steering angle detected by the steering angle sensor ;
The auxiliary force calculating means includes
Discriminating between an elastic region where the tire of the steering wheel of the vehicle is steered while being elastically deformed on the road surface and a friction region where the tire is steered while sliding on the road surface;
In the elastic region, a steering force required to steer the steering wheel is obtained using an equation of motion including an elastic term whose main element is an elastic force accompanying elastic deformation of the tire, and from the obtained steering force Calculating the target assist force,
In the friction region, a steering force required to steer the steering wheel is obtained by using a motion equation including a friction term having a frictional force acting between the tire and the road surface as a main element. an electric power steering apparatus characterized that you calculate the target assist force from the steering force. In an electric power steering device for obtaining a target auxiliary force based on an operation of a steering member of a vehicle, driving a steering auxiliary motor according to the obtained target auxiliary force, and assisting steering,
A steering angle sensor that detects a steering angle that changes in accordance with the operation of the steering member;
A relative angle calculating means for calculating a relative steering angle by subtracting a predetermined reference steering angle from a steering angle detected by the steering angle sensor;
Calculating means for calculating a relative steering angular velocity and a relative steering angular acceleration using the relative steering angle calculated by the relative angle calculating means;
An auxiliary force calculating means for calculating the target auxiliary force using the relative steering angular velocity and relative steering angular acceleration calculated by the calculating means and the relative steering angle calculated by the relative angle calculating means ,
The auxiliary force calculating means includes
Discriminating between an elastic region where the tire of the steering wheel of the vehicle is steered while being elastically deformed on the road surface and a friction region where the tire is steered while sliding on the road surface;
In the elastic region, a steering force required to steer the steering wheel is obtained using an equation of motion including an elastic term whose main element is an elastic force accompanying elastic deformation of the tire, and from the obtained steering force Calculating the target assist force,
In the friction region, a steering force required to steer the steering wheel is obtained by using a motion equation including a friction term having a frictional force acting between the tire and the road surface as a main element. an electric power steering apparatus characterized that you calculate the target assist force from the steering force. The auxiliary force calculating means is configured to calculate the target auxiliary force from the upper limit steering force when the steering force obtained using the equation of motion is equal to or greater than a predetermined upper limit steering force. Item 3. The electric power steering device according to Item 2 . A determination unit configured to determine that the steering member is turning back; and the relative angle calculation unit is configured to perform the determination in a state where the steering force calculated by the auxiliary force calculation unit is equal to or greater than the upper limit steering force. 4. The electric power steering apparatus according to claim 3 , wherein the reference steering angle is reset when it is determined by the means that the vehicle is turning back. A vehicle speed sensor for detecting a traveling speed of the vehicle, wherein the equation of motion includes a dynamic friction term indicating dynamic friction generated according to an operation of the steering member;
The auxiliary force calculation means according to the detected vehicle speed by the vehicle speed sensor, the upper steering force, according to claim 3 or 4 is arranged to change at least one of the elastic section and the dynamic friction term Electric power steering device.

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