JP2010083313A - Rack thrust estimation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress estimation of rack thrust in such an operating region that an error of an estimated value of the rack thrust becomes large, and to provide the highly accurate rack thrust. <P>SOLUTION: In a rack thrust estimation device 10, a front wheel slip angle calculating unit 10a calculates a front wheel slip angle βf, an additional turning determining unit 10b determines whether a steering wheel 2 is in an additional turning state (θh×(dθh/dt)>0) or not, a front wheel slip angle determining unit 10c determines whether ¾βf¾>Cbf or not, and a rack thrust calculating unit 10d estimates the rack thrust Fr when the steering wheel 2 is in the additional turning state and ¾βf¾>Cbf. Thus, estimation of the rack thrust Fr in such the operating region that an S/N ratio lowers is excluded, and the highly accurate rack thrust Fr is provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rack thrust estimation device that accurately estimates rack thrust.

  In recent years, various control techniques for traction control, braking force control, torque distribution control, and the like have been proposed and put into practical use in vehicles. Many of these techniques use a road surface friction coefficient for calculation or correction of a necessary control amount, and it is necessary to estimate an accurate road surface friction coefficient in order to reliably execute the control. As an apparatus for estimating such a road surface friction coefficient, since a road surface friction coefficient can be estimated with a relatively small number of parameters with good response, an apparatus for estimating a road surface friction coefficient by estimating a rack thrust has been proposed.

  For example, in Patent Document 1, by utilizing the fact that the road surface reaction force at a certain vehicle speed and a certain steering angle changes depending on the road surface friction coefficient, the road surface reaction force for a certain road speed and a certain steering angle is stored in advance as a reference road surface friction coefficient. A technique for estimating a road surface friction coefficient by comparing with a road surface reaction force calculated by calculation has been disclosed. In this technology, the road surface reaction force is considered to be equal to the rack thrust, and the sum of the thrust assisted by the electric power steering motor and the steering steering thrust is used as the rack thrust to estimate the road surface friction coefficient based on the derived evaluation function. It has become.

  In FIG. 1, reference numeral 1 indicates a steering mechanism of a general electric power steering, and a driver's steering force input from a handle (steering wheel) 2 is applied to a rack 5 via a steering shaft 3 and a pinion 4. Accordingly, the wheel and the tire 6 are steered through a tie rod and a knuckle arm (not shown). The assist torque generated by the electric power steering motor 7 is transmitted to the steering shaft 3 through the speed reducer 8 to assist the driver's steering force.

It is known that such an operation of the steering mechanism 1 can be described by the equations of motion shown in the following equations (1) to (4) by handling the pinion 4, the rack 5, the wheel, and the tire 6 as one inertial object. (See, for example, Non-Patent Document 1).
Th = Jh · (d ² θh / dt ² ) + Ch · (dθh / dt) + Kh · (θh−θs)
... (1)
Rm · (Tm−Jm · (d ² θm / dt ² ) −Cm · (dθm / dt))
−Kh · (θh−θs) = (Jw · (d ² θw / dt ² ) + Cw · (dθw / dt)
-Ta) / Rs (2)
θm = Rm · θs (3)
θw = θs / Rs (4)
Here, Th is the steering torque input by the driver through the handle 2, Jh is the moment of inertia of the handle 2, Ch is the viscous friction coefficient (damping coefficient) of the handle 2, Kh is the elastic coefficient of the steering shaft (torsion bar) 3, θh Is the steering angle (steering wheel angle) on the steering shaft 3 side, θs is the steering angle (front wheel steering angle) on the wheel side of the steering shaft 3, Rm is the gear ratio from the electric power steering motor 7 to the steering shaft 3, and Tm is Assist torque generated by the electric power steering motor 7, Jm is the moment of inertia of the electric power steering motor 7, Cm is the viscous friction coefficient (attenuation coefficient) of the electric power steering motor 7, θm is the rotation angle of the electric power steering motor 7, Jw , Cw is the moment of inertia when the pinion 4, the rack 5, the wheel, and the tire 6 are handled as one inertia, Friction coefficient (damping coefficient), θw is the steering angle of the wheel, Ta is the torque around the steering shaft (moment around the kingpin) acting on the wheel from the road surface according to the lateral movement of the vehicle, and Rs is the gear ratio of the pinion. .

If the above formulas (1) to (4) are arranged for the moment around the kingpin (which is rack thrust when divided by the knuckle arm length) Ta, the following formula (5) can be obtained.
Rs, Rm, Tm + Rs, Kh, (θh-θs)
− (Rs · Rm ² · Jm + Jw / Rs) · (d ² θs / dt ² )
− (Rs · Rm ² · Cm + Cw / Rs) · (dθs / dt) = − Ta (5)
In this equation (5), the terms Rs, Rm, and Tm are terms of motor torque of the electric power steering motor 7, and the term of Rs, Kh, (θh−θs) is a steering torque sensor provided on the steering shaft 3. (Rs · Rm ² · Jm + Jw / Rs) · (d ² θs / dt ² ) (Rs · Rm ² · Jm + Jw / Rs) indicates equivalent inertia. In the term (Rs · Rm ² · Cm + Cw / Rs) · (dθs / dt), (Rs · Rm ² · Cm + Cw / Rs) represents equivalent attenuation.
JP 2001-341658 A Tsutomu Tashiro, Shigeyuki Hosoe; "Design Method for Driving Power and Electric Power Steering Control to Improve Vehicle Lateral Motion Characteristics", Proceedings of the Japan Opportunity Society (C), Vol.73, No.728, pp.1110-1118, (2007).

  As is clear from the above equation (5), in order to accurately estimate the moment around the kingpin (which becomes the rack thrust when divided by the knuckle arm length) Ta, it is disclosed in the aforementioned Patent Document 1, In addition to the assist torque Tm generated by the electric power steering motor 7 and the steering torque information Kh · (θh−θs) from the steering torque sensor, the front wheel steering angular speed (dθs / dt) (or the rotational angular speed of the electric power steering motor 7 ( dθm / dt)) must be obtained with high accuracy, and the method disclosed in Patent Document 1 has a problem that the rack thrust cannot be obtained with high accuracy. On the other hand, even if the front wheel rudder angular velocity (dθs / dt) can be obtained with high accuracy, the equivalent damping varies due to the friction of the steering mechanism, etc., so that it is affected by temperature conditions, component variations, etc. There is a problem that cannot be secured.

  The present invention has been made in view of the above circumstances, and provides a rack thrust estimation device capable of suppressing rack thrust estimation in an operation region in which an error in the estimated value of rack thrust becomes large and obtaining accurate rack thrust. It is intended to provide.

  The present invention relates to a rack thrust estimating apparatus for a vehicle equipped with an electric power steering device, a steering torque detecting means for detecting a steering torque, a motor torque detecting means for detecting a motor torque of the electric power steering, and an increase in steering. The increase determination means for determining whether or not the steering is being performed, and when it is determined that at least the increase in the steering is performed, a rack of the steering mechanism is used by using the steering torque and the motor torque. A rack thrust estimating means for estimating the rack thrust acting on the shaft and prohibiting the estimation of the rack thrust when it is determined that the steering is not increased is provided.

  According to the rack thrust estimating apparatus of the present invention, it is possible to suppress the estimation of the rack thrust in the operation region where the error of the estimated value of the rack thrust becomes large, and to obtain a highly accurate rack thrust.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 show an embodiment of the present invention, FIG. 1 is a configuration diagram of a steering mechanism and a rack thrust estimation device for estimating rack thrust, FIG. 2 is a functional block diagram of the rack thrust estimation device, and FIG. It is a flowchart of a rack thrust estimation program.

  In the steering mechanism 1 in this embodiment, as described above with reference to FIG. 1, the driver's steering force input from the steering wheel (steering wheel) 2 is transmitted to the rack 5 via the steering shaft 3 and the pinion 4. The wheel and the tire 6 are steered through a tie rod and a knuckle arm (not shown). The assist torque generated by the electric power steering motor 7 is transmitted to the steering shaft 3 through the speed reducer 8 to assist the driver's steering force.

  Further, the steering mechanism 1 detects a steering wheel angle sensor 12 that detects a steering wheel angle θh, a steering torque sensor 13 that detects a steering torque Th, and a current value (hereinafter abbreviated as a motor current) IEPS of an electric power steering motor 7. An electric power steering motor current sensor 14 is provided. Further, the vehicle is provided with a vehicle speed sensor 11 for detecting the vehicle speed V, and these vehicle speed V, steering wheel angle θh, steering torque Th, and motor current IEPS are input to the rack thrust estimation device 10.

  The rack thrust estimation device 10 performs steering addition according to the rack thrust estimation program described later based on each input signal described above, and the absolute value of the front wheel slip angle is equal to or greater than a preset threshold value. On the other hand, the rack thrust Fr is estimated, while if the steering is not increased, the estimation of the rack thrust Fr is prohibited. That is, as shown in FIG. 2, the rack thrust estimating apparatus 10 is mainly composed of a front wheel slip angle calculating unit 10a, a cut increase determining unit 10b, a front wheel slip angle determining unit 10c, and a rack thrust calculating unit 10d.

The front wheel slip angle calculation unit 10 a receives the vehicle speed V from the vehicle speed sensor 11 and the handle angle θh from the handle angle sensor 12. Then, for example, the front wheel slip angle βf is calculated by the following equation (6) and output to the front wheel slip angle determination unit 10c.
βf = β + (lf / V) · γ−δf (6)
Here, lf is the distance between the front shaft and the center of gravity, δf is the front wheel actual steering angle (= θh / n: n is the ratio of the steering wheel angle θh and the actual steering angle), β is the vehicle slip angle, and is expressed by the following equation (7) Γ is a yaw rate and is obtained by the following equation (8).
β = ((1- (m / (2 · (lf + lr))) · (lf / (lr · kr)) · V ² )
/ (1 + A · V ² )) · (lr / (lf + lr)) · δf (7)
γ = (1 / (1 + A · V ² )) · (V / (lf + lr)) · δf (8)
Here, m is the vehicle mass, lr is the distance between the rear axle and the center of gravity, and kr is the rear wheel equivalent cornering power. A is a stability factor of the vehicle, and is calculated by, for example, the following equation (9).
A = − (m / (2 · (lf + lr) ² ))
((Lf · kf−lr · kr) / (kf · kr)) (9)
Here, kf is the front wheel equivalent cornering power.

  The increase determination unit 10b is provided as an increase determination unit, and the handle angle θh is input from the handle angle sensor 12. Then, it is determined whether or not the steering wheel 2 has been increased, and the determination result is output to the rack thrust calculation unit 10d.

In the present embodiment, it is determined that the steering wheel 2 is increased when the following expression (10) is established.
θh · (dθh / dt)> 0 (10)
The steering wheel angular velocity (dθh / dt) is a value obtained by the following equation (11).

(Dθh / dt) = (θh (n−1) −θh (n)) / Δt (11)
Here, θh (n−1) is the previous value of θh, θ (n) is the current value of θh, and Δt is the sampling time.

  The front wheel slip angle determination unit 10c receives the front wheel slip angle βf from the front wheel slip angle calculation unit 10a. Then, for example, it is determined whether or not the absolute value | βf | of the front wheel slip angle is larger than a preset threshold value Cbf, and the determination result is output to the rack thrust calculation unit 10d.

The rack thrust calculation unit 10d is provided as rack thrust estimation means, and determines steering torque Th from the steering torque sensor 13, motor current IEPS from the electric power steering motor current sensor 14, and increase determination from the increase determination unit 10b. The determination result of whether or not | βf |> Cbf is input from the front wheel slip angle determination unit 10c. When the handle 2 is in the increased state (θh · (dθh / dt)> 0) and | βf |> Cbf, for example, the rack thrust Fr is calculated and output by the following equation (12). To do. On the other hand, when the steering wheel 2 is not in the increased state, that is, when the steering wheel 2 is in the back-turned state (θh · (dθh / dt) <0) or the steering holding state (θh · (dθh / dt) = 0). Calculation of the rack thrust Fr is prohibited.
Fr = ζ1 · (2 · π / hs) · Tp (12)
Here, ζ1 is the rack & pinion efficiency, hs is the rack & pinion specific stroke, and Tp is the pinion gear torque, which is calculated by the following equation (13).
Tp = Th + ζ2 · ηw · Tm (13)
Here, ζ2 is the efficiency of the worm gear, ηw is the worm gear ratio, Tm is the motor torque of the electric power steering motor 7, and is calculated by the following equation (14).

Tm = sign (Th) · km · 3 ⁻¹ / ² · IEPS (14)
Here, sign (Th) represents a sign of the steering torque Th, and km represents a motor torque constant.

  Next, a rack thrust estimation program executed by the rack thrust estimation apparatus 10 will be described with reference to the flowchart of FIG.

  First, in step (hereinafter abbreviated as “S”) 101, necessary parameters, that is, vehicle speed V, steering wheel angle θh, steering torque Th, and motor current IEPS are read.

  Next, the process proceeds to S102, where the front wheel slip angle calculation unit 10a calculates the front wheel slip angle βf by the above-described equation (6).

  Next, the process proceeds to S103, where it is determined whether or not the handle 2 has been increased (θh · (dθh / dt)> 0). If the increase has been performed, the process further proceeds to S104. Then, it is determined whether or not | βf |> Cbf. If | βf |> Cbf, the rack thrust estimating apparatus 10 calculates the rack thrust Fr according to the above-described equation (12) and calculates the current rack. The thrust is Fr (n).

  On the other hand, if it is determined in S103 that the steering wheel 2 has not been increased (when θh · (dθh / dt) ≦ 0) or if | βf | ≦ Cbf in S104, the process proceeds to S106. Then, the rack thrust Fr (n-1) set last time is set to the rack thrust Fr (n) of this time.

  After setting the current rack thrust Fr (n) in S105 or S106, the process proceeds to S107, where the current rack thrust Fr (n) is output, and the process proceeds to S108 where the current rack thrust Fr (n) is set. Exit the program as the previous rack thrust Fr (n-1).

  That is, generally, the electric power steering 7 outputs an assist torque (motor torque) Tm proportional to the steering torque Th. However, when the steering wheel 2 is returned, if the assist torque Tm proportional to the steering torque Th is continuously output, the return of the steering wheel 2 becomes worse, so that the assist torque Tm is controlled to decrease. Therefore, the rack thrust Fr is reduced when the steering wheel is turned back, and the output of the rack thrust Fr is stopped because the value of the Rs / Rm / Tm term in the above equation (5) decreases and the S / N ratio decreases. To do.

In the present embodiment, whether the steering wheel 2 is increased or not is determined by the sign of the product of the steering wheel angle θh and the steering wheel angular velocity (dθh / dt). , (17) may be determined that the steering wheel 2 has been increased.
Th · (dθm / dt)> 0 (15)
The rotational angular velocity (dθm / dt) of the electric power steering motor 7 is a value obtained by the following equation (16).

(Dθm / dt) = (θm (n−1) −θm (n)) / Δt (16)
βf · (dβf / dt)> 0 (17)
The front wheel slip angular velocity (dβf / dt) is a value obtained by the following equation (18).

    (Dβf / dt) = (βf (n−1) −βf (n)) / Δt (18)

  These utilize the fact that the sign of the steering torque Th is equal to the sign of the rack thrust Fr and the sign of the front wheel lateral force Fy, and can be approximated by Fy = −kf · βf.

  Similarly, the assist torque (motor torque) Tm is reduced even in a range where the steering torque Th is small, and the value of the Rs / Rm / Tm term is decreased in the above-described equation (5), so that the S / N ratio is lowered. Therefore, the output of the rack thrust Fr is stopped.

  In the embodiment of the present application, as described above, Fy = −kf · βf can be approximated. Therefore, when | βf | ≦ Cbf, the rack thrust force Fr is not calculated, but | Th | ≦ When CTh (CTh is a preset threshold value), the rack thrust Fr may not be calculated.

  Note that whether to use the above-mentioned formulas (10), (15), or (17), and whether to use | βf |> Cbf or | Th |> CTh is mounted on the vehicle. The sensor can be freely selected.

  In the present embodiment, the rack thrust Fr is calculated by the above-described equation (12), but may be calculated by other methods.

  As described above, according to the present embodiment, the steering is increased and the absolute value of the front wheel slip angle | βf | (or the absolute value of steering torque | Th |) is equal to or greater than a preset threshold value. In this case, since the estimation of the rack thrust Fr is executed, it is possible to suppress the estimation of the rack thrust Fr in the operation region where the error of the estimated value of the rack thrust becomes large and obtain the rack thrust Fr with high accuracy.

Configuration diagram of steering mechanism and rack thrust estimation device for estimating rack thrust Functional block diagram of rack thrust estimation device Flow chart of rack thrust estimation program

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering mechanism 2 Steering wheel 3 Steering shaft 4 Pinion 5 Rack 6 Wheel, tire 7 Electric power steering motor 8 Reducer 10 Rack thrust estimation apparatus 10a Front wheel slip angle calculation part 10b Increase / decrease determination part (Increase determination means)
10c Front wheel slip angle determination unit 10d Rack thrust calculation unit (rack thrust estimation means)
11 Vehicle speed sensor 12 Handle angle sensor 13 Steering torque sensor 14 Electric power steering motor current sensor

Claims (6)

In a rack thrust estimation device for a vehicle equipped with an electric power steering device,
Steering torque detection means for detecting steering torque;
Motor torque detecting means for detecting the motor torque of the electric power steering;
An increase determination means for determining whether or not an increase in steering is being performed;
When it is determined that at least the steering is increased, the rack torque acting on the rack shaft of the steering mechanism is estimated using the steering torque and the motor torque, and the steering is increased. Rack thrust estimating means for prohibiting the estimation of the rack thrust when it is determined that is not performed,
A rack thrust estimating device for a vehicle, comprising:   The rack thrust estimation means estimates the rack thrust when the steering is increased and the absolute value of the steering torque is equal to or greater than a preset threshold value. The rack thrust estimation apparatus of the vehicle as described.   The rack thrust estimating means performs the estimation of the rack thrust when the steering is increased and the absolute value of the front wheel slip angle is equal to or larger than a preset threshold value. Item 4. A rack thrust estimation device for a vehicle according to Item 1.   4. The steering increase determination means according to claim 1, wherein when the sign of the steering wheel angle value and the steering wheel angular velocity value is the same, it is determined that the steering steering increase is being performed. The vehicle rack thrust estimation apparatus according to one of the above.   4. The increase determination unit according to claim 1, wherein when the signs of the front wheel slip angle value and the front wheel slip angular velocity value are the same, it is determined that the steering increase is performed. The rack thrust estimation apparatus for a vehicle according to any one of the above.   2. The turning increase determination means determines that the turning increase of the steering is performed when the sign of the steering torque value and the value of the motor rotation speed value of the electric power steering are the same. The rack thrust estimation apparatus for a vehicle according to any one of claims 3 to 4.

Images