JP3927531B2 - Control device for vehicle steering system - Google Patents

Description

  The present invention relates to a control device for a vehicle steering device mounted on an automobile or the like.

  In the electric power steering control device, in order to calculate the target value of the drive current of the assist motor that assists the steering torque by the driver, the road surface reaction force torque estimated value is calculated. For example, in Japanese Patent Laid-Open No. 2003-127888 (Prior Art 1), a friction term is determined as a disturbance from a road surface reaction force torque signal in terms of a steering shaft obtained based on a steering torque by a driver and an assist torque by an assist motor. What is removed and the road surface reaction force torque estimated value is obtained is disclosed.

  However, what is disclosed in the prior art 1 is to remove the hysteresis of the road surface reaction force torque signal in terms of the steering axis with the friction term as a steady-state disturbance, so that the road surface reaction torque against the high frequency disturbance. The estimation accuracy of the estimated value deteriorates.

  In order to cancel out high-frequency disturbances, it is also considered to low-pass filter the road surface reaction force torque signal converted to the steering axis. In this low-pass filter processing, the road surface reaction force against the actual road reaction torque change There is a problem that a phase delay or a gain shift occurs in the estimated torque value.

  On the other hand, an estimated value of the road surface reaction force torque in terms of steering shaft is obtained from a primary low-pass filter of one or more stages, and the time constant of this low-pass filter is changed according to the steering speed of the steering wheel. Japanese Unexamined Patent Publication No. 2001-122146 (prior art 2), and the one that changes the time constant of the low-pass filter according to the vehicle speed is disclosed in Japanese Patent Laid-Open No. 2001-239951 (prior art 3). Yes.

  However, the technique disclosed in Prior Art 2 has a disadvantage that the estimation accuracy of the road surface reaction force torque estimated value decreases when the vehicle speed increases. Further, the technique disclosed in the prior art 3 has a disadvantage that the estimation accuracy of the road surface reaction force torque estimated value is lowered when the steering speed of the steering wheel is increased.

  Therefore, in the previous application by the same inventors as this application, Japanese Patent Application No. 2002-124701, the road surface reaction force torque signal converted to the steering shaft is subjected to one or more primary low-pass filters to obtain the road surface reaction force torque estimation value. Among them, a method has been proposed in which the time constant of low-pass filter processing is changed according to both the steering speed of the steering wheel and the vehicle speed.

JP 2003-127888 A JP 2001-122146 A JP 2001-239951 A Application for Japanese Patent Application No. 2002-124701

  However, since the previous application requires a gradient between the road surface reaction torque and the steering angle of the steering wheel, it is necessary to measure the ratio between the road surface reaction torque and the steering angle of the steering wheel. In addition, even if the same model is used, the ratio of road reaction torque to the steering angle of the steering wheel must be re-measured when the front wheel load of the car changes due to changes in the grade of the car. Remains.

  This application improves such a problem, and even when a high-frequency disturbance is generated in the road surface reaction force torque converted to the steering shaft, the vehicle steering device can accurately obtain the road surface reaction force torque estimated value. A control device is proposed.

A control apparatus for a vehicle steering system according to the present invention generates a steering wheel that is steered by a driver, a steering shaft that is coupled to the steering wheel, and an assist torque that is coupled to the steering shaft and assists the steering torque of the driver. A control device for a vehicle steering apparatus having a steering mechanism having an assist motor, and further a steering shaft reaction force torque signal corresponding to a steering shaft reaction force torque acting on the steering shaft based on a road surface reaction force torque And a road surface reaction force torque calculation means for calculating an estimated value of the road surface reaction force torque, the road surface reaction force torque calculation means being a low pass filter means for filtering the steering shaft reaction force torque signal. And time constant calculating means for calculating the time constant of the low-pass filter means, Constant computing means, a differential output of the steering shaft reaction torque signal, based on the friction torque signal representing the frictional torque of the steering mechanism, characterized by calculating said time constant.

  In the control device for a vehicle steering system according to the present invention, the steering shaft reaction force torque signal is filtered by the low-pass filter means, so that the road surface reaction force torque estimated value can be obtained with high accuracy from the steering shaft reaction force torque including disturbance. . The time constant of the low-pass filter means is calculated based on the differential output of the steering shaft reaction force torque signal and the friction torque signal representing the friction torque of the steering mechanism, so that the gradient measurement of the road surface reaction force torque and the steering angle of the steering wheel is performed. In addition, when using a gain output that is proportional to the ratio of the road reaction torque and the steering angle, the gain output can be obtained more easily, and the road surface can be reduced with less measurement man-hours. An estimated reaction force torque can be obtained.

  Several embodiments of a vehicle steering control device according to the present invention will be described below with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 shows the overall configuration of a control device for a vehicle steering system according to Embodiment 1 of the present invention. The first embodiment is an electric power steering control device mounted on an automobile.
The control device for a vehicle steering apparatus according to the first embodiment includes a steering mechanism 10, and the steering mechanism 10 includes a handle 1, a steering shaft 2, a steering gear box 3, a torque sensor 4, and an assist motor. 5, a rack and a pinion mechanism 6.

  In FIG. 1, a handle 1 is a steering handle of an automobile that is steered by an automobile driver, and is connected to an upper end of a steering shaft 2. A steering torque Thdl by the driver is applied to the steering wheel 1, and this steering torque Thdl is transmitted to the steering shaft 2. The torque sensor 4 is coupled to the steering shaft 2 and generates a steering torque detection signal Thdl (s) corresponding to the steering torque Thdl. The steering motor 5 is an electric motor, which is also coupled to the steering shaft 2 via a reduction gear, and applies an assist torque Tassist that assists the steering torque Thdl to the steering shaft 2.

  The steering gear box 3 is provided at the lower end of the steering shaft 2. A combined torque obtained by adding the steering torque Thdl and the assist torque Tassist applied to the steering shaft 2 is multiplied several times through the steering gear box 3, and the tire 7 is operated through the rack and pinion mechanism 6.

The overall operation of the first embodiment will be described.
The control device of FIG. 1 has an EPS (Electric Power Steering) control unit 8 electrically combined with the steering mechanism 10. The control unit 8 receives a steering torque detection signal Thdl (s) from the torque sensor 4, a motor drive current detection signal Imtr (s) from the assist motor 5, and a motor drive voltage detection signal Vmtr (s). Is done. The control unit 8 supplies a control signal Imtr (t) to the assist motor 5. This control signal Imtr (t) is a drive current target for the assist motor 5.

  In FIG. 1, symbol Talign is a road surface reaction force torque applied to the tire 7, and Ttran is a steering shaft reaction force torque acting on the steering shaft 2 based on the road surface reaction torque Talign. The steering shaft reaction force torque Ttran is a road surface reaction force torque converted to the steering shaft 2. Tfrp is the friction torque of the steering mechanism 10 and is the friction torque of the steering mechanism 10 excluding the friction torque Tmfric in the assist motor 5.

  The electric power steering control device shown in FIG. 1 detects the steering torque Thdl when the driver turns the steering wheel 1 as a steering torque detection signal Thdl (s) by the torque sensor 4, and the steering torque detection signal Thdl (s) ) To generate an assist torque Tassist that assists the steering torque Thdl. The control unit 8 detects a detection signal Imtr (s) that detects the drive current Imtr of the assist motor 5, a detection signal Vmtr (s) that detects the drive voltage Vmtr of the assist motor 5, and a steering torque detection signal Thdl (s). Based on the control signal, a control signal Imtr (t) for generating the assist torque Tassist is calculated, and the control signal Imtr (t) is supplied to the assist motor 5.

Dynamically, the sum of the steering torque Thdl and the assist torque Tassist rotates the steering shaft 2 against the steering shaft reaction torque Ttran. Further, since the inertia term of the assist motor 5 also acts when the handle 1 is rotated, the steering shaft reaction force torque Ttran is given by the following equation (1).
Ttran = Thdl + Tassist−J × dω / dt (1)
However, the inertia torque of the assist motor 5 is assumed to be J × dω / dt.

The assist torque Tassist by the assist motor 5 is given by the following equation (2).
Tassist = Ggear × Kt × Imtr (2)
Here, Ggear is the gear ratio of the reduction gear between the assist motor 5 and the steering shaft 2.

The steering shaft reaction force torque Ttran is the sum of the road surface reaction force torque Talign and the total friction torque Tfric in the steering mechanism 10, and is given by the following equation (3).
Ttran = Talign + Tfric
= Talign + (Ggear × Tmfric + Tfrp) (3)
However, Tmfric is the friction torque in the assist motor 5, Tfrp is the friction torque of the steering mechanism 10 excluding the friction torque Tmfric in the assist motor 5, and Tmfric + Tfrp = Tfric.

  The control unit 8 of the electric power steering control device calculates a target value for the drive current Imtr of the assist motor 5 and generates a control signal Imtr (t). Current control is performed so that the actual drive current Imtr of the assist motor 5 matches the control signal Imtr (t), and the assist motor 5 has a torque constant and a gear ratio (from the motor 5 to the steering shaft). A predetermined torque multiplied by 2) is generated to assist the steering torque Thdl when the driver steers.

Next, estimation of the road surface reaction torque using the low-pass filter operation will be described.
First, steering is performed in various scenes such as a curve and a lane change, and the steering pattern is regarded as a ramp having a constant speed within a predetermined time range. In this case, when the time change rate of the road surface reaction torque Talign is Tgrad, the road surface reaction torque Talign and the steering shaft reaction torque Ttran are expressed by the following equations (4) and (5), respectively. Here, s is a Laplace transform variable.
Talign = Tgrad / s ² (4)
Ttran = Tgrad / s ² + {(Ggear × Tmfric + Tfrp) / s} (5)

Here, the road surface reaction force torque estimated value Talign-est obtained by filtering a signal proportional to the steering shaft reaction force torque Ttran by a low-pass filter operation is given by the following equation (6).
Talign-est = Ttran × 1 / (τest × s + 1)
= [Tgrad / s ² + {(Ggear × Tmfric + Tfrp) / s}] × 1 / (τest × s + 1) (6)

At this time, the estimation error E (s) between the road surface reaction force torque Talign and the road surface reaction force estimated value Talign-est, which are state quantities to be estimated, is expressed by the following equation (7).
E (s) = Tgrad / s ² − {Tgrad / s ² + (Ggear × Tmfric + Tfrp) / s}
× {1 / (τest × s + 1)}
= {Tgrad × τest− (Ggear × Tmfric + Tfrp)} / s {(τest × s + 1) (7)

Therefore, when the time constant τest of the low-pass filter operation can be expressed by the following equation (8), the estimation error E (s) becomes zero.
τest = {Ggear × Tmfric + Tfrp} / Tgrad (8)

Here, the time change rate Tgrad of the road surface reaction force torque Talign is equivalent to the time change rate of the steering shaft reaction force torque, and is expressed by the following equation (9).
Tgrad = dTalign / dt = dTtran / dt (9)

Therefore, the optimum value of the time constant τest of the low-pass filter operation is determined by the following equation (10).
τest = (Ggear × Tmfric + Tfrp) / (dTalign / dt)
= (Ggear × Tmfric + Tfrp) / (dTtran / dt) (10)
The optimum road reaction force torque estimated value Talign-est is obtained by low-pass filtering a signal proportional to the steering shaft reaction force torque Ttran using the optimum low-pass filter operation time constant τest given by the equation (10). It is done.

  FIG. 2 is a block diagram illustrating the control unit 8 and the control circuit 20 of the assist motor 5 according to the first embodiment. The control unit 8 is indicated by a block 8 in the chain line. The control unit 8 includes a vehicle speed detector 11, a steering torque detector 12, a motor speed detector 13, a motor acceleration detector 14, a road surface reaction force torque detector 30, an assist torque determining block 16, a motor. A current determiner 17.

  The vehicle speed detector 11 receives the vehicle speed V and outputs a vehicle speed signal V (s). The steering torque detector 12 includes the torque sensor 4, receives the steering torque Thdl, and outputs a steering torque detection signal Thdl (s). The motor speed detector 13 receives the rotational speed of the assist motor 5 and outputs a motor speed signal Smtr (s). The motor acceleration detector 14 differentiates the motor speed signal Smtr (s) and outputs a motor acceleration signal Amtr (s).

  The road surface reaction force torque detector 30 receives the steering shaft reaction force torque Ttran, and outputs a road surface reaction force torque estimated value Test-align. The assist torque determination block 16 includes a vehicle speed signal V (s), a steering torque signal Thdl (s), a road surface reaction force torque estimated value Talign-est, a motor speed signal Smtr (s), and a motor acceleration signal Amtr (s). ), An assist torque signal Tassist (s) corresponding to the assist torque Tassist generated by the assist motor 5 is generated. The motor current determiner 18 receives the assist torque signal Tassist (s) and outputs a current target value Imtr (t) for the motor drive current for generating the assist torque Tassist.

  The control circuit 20 of the assist motor 5 is built in the assist motor 5 and includes a comparator 21, a motor driver 22, and a motor current detector 23. The motor current detector 23 outputs a motor drive current signal Imtr (s) corresponding to the actual drive current Imtr of the assist motor 5. The comparator 21 compares the current target value Imtr (t) with the motor drive current signal Imtr (s). The motor driver 22 drives the assist motor 5 so that the difference between the current target value Imtr (t) and the drive current signal Imtr (s) is zero.

  FIG. 3 is a block diagram showing details of the road surface reaction force torque detector 30. The road surface reaction force torque detector 30 has signal output means 31 for outputting a steering shaft reaction force torque signal Ttran (s) and road surface reaction force torque calculation means 32 for calculating a road surface reaction force torque estimated value Talign. The signal output means 31 is a detection means such as a load cell provided on the steering shaft 2, for example, receives the steering shaft reaction force torque Ttran and outputs a steering shaft reaction force torque signal Ttran (s) proportional thereto.

  The road surface reaction force torque calculation means 32 excludes the differentiation calculator 33, the first friction torque signal generator 34 that generates the friction torque signal Tmfric (s) corresponding to the friction torque Tmfric of the assist motor 5, and the assist motor 5. A second friction torque signal generator 35 for generating a friction torque signal Tfrp (s) corresponding to the friction torque Tfrp of the steering mechanism 10, a time constant calculator 36 for calculating a time constant τest of the low pass filter operation, and a low pass filter means. 37.

  The differential calculator 33 receives the steering shaft reaction force torque signal Ttran (s) and outputs the differential output Ttran (d). The time constant calculator 36 receives the differential output Ttran (d), the friction torque signal Tmfric (s), and the friction torque signal Tfrp (s), and sets the time constant τest for the low-pass filter means 37 based on the equation (10). To calculate. The low-pass filter means 37 has its time constant τest determined by the time constant calculator 36, filters the steering shaft reaction force torque signal Ttran (s), and outputs a road surface reaction force torque estimated value Talign-est. .

  The control unit 8 shown in FIG. 2 and the road surface reaction force torque detector 30 shown in FIG. 3 are mainly composed of a microcomputer. The low-pass filter means 37 also realizes an operation equivalent to the filter operation of the low-pass filter by a microcomputer without using the low-pass filter as hardware.

  The steering shaft reaction torque Ttran is detected by attaching a detector such as a load cell to the steering shaft 2, and the signal output means 31 outputs a steering shaft reaction torque signal Ttran (s). 8 includes a motor acceleration detector 14 configured to receive the drive current detection signal Imtr (s) of the assist motor 5 and the steering torque detection signal Thdl (s), and to output the motor acceleration signal Amtr (s). Therefore, from these drive current detection signal Imtr (s), steering torque detection signal Thdl (s) and motor acceleration signal Amtr (s), the steering shaft reaction force torque signal Ttran (s ) Can also be calculated.

  Also, the time constant for the low-pass filter means 37 must always be positive from the viewpoint of control stability. Therefore, in the first embodiment, it is assumed that the absolute value of the time constant τest obtained by Expression (10) is the time constant of the low-pass filter means 37. In each of the embodiments after the second embodiment, the time constant τest takes the absolute value in the same manner.

  In the first embodiment, the speed signal Smtr (s) of the assist motor 5 is detected by the motor speed detector 13, but as shown in Japanese Patent Laid-Open No. 11-139339, the following equation (11 ).

  Next, the operation of the first embodiment will be described based on the flowchart of FIG. FIG. 4 includes steps S101 to S105 between the start and the end. First, in step S101, the steering shaft reaction force torque signal Ttran (s) from the steering shaft reaction force torque signal output means 31 is read into the memory of the microcomputer constituting the control unit 8. In the next step S102, the differential calculator 33 calculates the differential output Ttran (d) of the steering shaft reaction force torque signal Ttran (s).

  In the next step S103, the differential output Ttran (d) from the differential calculator 32, the friction torque signal Tmfic (s) from the first friction torque signal device 34, and the friction from the second friction torque signal device 35 are shown. Based on the torque signal Tfrp (s), the time constant calculator 36 calculates the time constant τest of the low-pass filter operation according to the equation (10). In the next step S104, the low pass filter means 37 uses the time constant τest from the time constant calculator 36 to low pass filter the steering shaft reaction force torque signal Ttran (s) from the steering shaft reaction force torque signal output means 31. As a result, the road surface reaction force torque estimated value Talign-est is output.

  As described above, the first embodiment obtains the road surface reaction force torque estimated value Talign-est by filtering the steering shaft reaction force torque signal Ttran (s) by the low pass filter means 37. Since the time constant τest is calculated based on the differential output Ttran (d) of the steering shaft reaction force torque signal Ttran (s) and the friction torque signal Tfic of the steering mechanism 10, the road surface reaction force torque Ttran and the steering angle of the steering wheel are calculated. It is no longer necessary to measure the ratio to the road surface, and the man-hours involved in this measurement can be reduced, and even if the front wheel load of the car changes due to changes in the car grade, etc. It is not necessary to re-measure the ratio with the steering angle of the steering wheel, and it is possible to effectively obtain the road surface reaction force torque estimated value Test-align and realize effective steering control.

  FIG. 5 shows an example of a road surface reaction force torque estimated value Talign-est according to the first embodiment. The horizontal axis is time (sec), and the vertical axis is road surface reaction torque (Nm). A thick solid line characteristic T1 indicates a change in the actual road reaction torque, a thin solid line characteristic T2 indicates a change in the steering shaft reaction torque Ttran including a disturbance applied to the characteristic T1, and a dotted line characteristic T3 indicates The road surface reaction force torque estimated value Test-align obtained in the first embodiment is shown. By filtering the steering shaft reaction force torque signal Ttran (s) with a low-pass filter operation, as shown in FIG. 5, even if the steering shaft reaction force torque Ttran including the disturbance is applied, the robust road surface reaction that eliminates the disturbance is removed. The estimated force torque value Test-align can be obtained.

Embodiment 2. FIG.
In the first embodiment, the time constant τest in the low-pass filter means 37 is determined by using the differential output Ttran (d) of the steering shaft reaction force torque signal Ttran (s) and the friction torque signal Tmfric ( s) and the friction torque signal Tfrp (s) of the steering mechanism 10 excluding the assist motor 5, the second embodiment calculates the time constant τest by a calculation different from that of the first embodiment. To do.

The time constant τest is given in the equation (8), and the denominator of the equation (8) includes the time change rate Tgrad of the road surface reaction torque Talign. This time change rate Tgrad is expressed by the following equation (12).
Tgrad = dTalign / dt = (dTalign / dα) (dα / dt) (12)
In this equation (12), α is a vehicle state quantity that can be regarded as a proportional relationship to the road surface reaction torque Talign in the linear region. Such a vehicle state quantity α corresponds to the steering angle of the steering wheel of the vehicle, the yaw rate of the vehicle, the lateral acceleration Gy of the vehicle, the side slip angle of the vehicle, the cornering force of the vehicle, and the like.

In the second embodiment, the time constant τest is calculated using the vehicle state quantity α. When the steering angle θ of the vehicle handle 1 is used as the vehicle state quantity α, (dTalign / dα) in the equation (12) is a gain proportional to the ratio between the road surface reaction torque Talign and the steering angle θ. Is expressed as Kalign-gainθ, the time constant τest can be expressed by the following equation (13).
τest = (Ggear × Tmfric + Tfrp) / Kalign-gain θ × (dθ / dt) (13)
In the second embodiment, for example, the time constant τest is calculated using this gain Kalign-gainθ. If the vehicle speed changes, the ratio between the road surface reaction torque Talign and the steering angle θ changes accordingly. In the second embodiment, for example, the road surface reaction torque Talign and the steering when the vehicle speed corresponds to 40 km / h are used. If the ratio of the angle θ is obtained, this value is set as a representative value and set as the gain Kalign-gain θ, thereby reducing the man-hour for measuring the ratio of the road surface reaction torque to the steering angle.

  FIG. 6 shows a road surface reaction force torque detector 30A used in the second embodiment, and this road surface reaction force torque detector 30A uses road surface reaction force torque calculation means 32A. Compared to the road surface reaction force torque detector 30 shown in FIG. 3, a handle angle detector 38 is added, and a gain output means 39 is added to the road surface reaction force torque calculation means 32A. The handle angle detector 38 generates a steering angle signal θ (s) corresponding to the steering angle θ of the handle 1 in FIG. 1, and the gain output means 39 outputs a ratio gain Kalign-gain θ. In FIG. 6, the differential calculator 33 differentiates the steering angle signal θ (s) from the steering wheel angle detector 15 and outputs the differential output θ (d). This differential output θ (d) is (dθ / dt) in equation (13). The time constant calculator 36A in the second embodiment calculates the time constant τest from the differential output θ (d), the gain output Ralign-gainθ, and the friction torque signals Tmfric (s) and Tfrp (s). Other steering reaction force torque signal output means 31, first and second friction torque signal devices 34 and 35, and low-pass filter means 37 are the same as in FIG.

  FIG. 7 is a flowchart showing the operation of the second embodiment. This flowchart has steps S201 to S206 between the start and the end. The operation will be described based on this flowchart.

  First, at step S201, the steering shaft reaction force torque signal Ttran (s) is read into the memory of the microcomputer constituting the control unit 8. In the next step S202, the steering angle signal θ (s) is subsequently read into the memory. In the next step S203, the differential output θ (d) of the steering angle signal θ (s) is calculated by the differential calculator 33. In the next step S204, the time constant calculator 36 calculates the time constant τest. In the second embodiment, this time constant τest is obtained from the differential output θ (d) from the differential calculator 33, the gain Kalign-gainθ of the ratio from the gain output means 39, and the first friction torque signal device 34. The friction torque signal Tmfric (s) and the friction torque signal Tfrp (s) from the second friction torque signal device 35 are used to calculate according to the equation (13).

  In the next step S205, the steering shaft reaction force torque signal Ttran (s) is passed through the low-pass filter means 37, and the steering shaft reaction force torque signal Ttran (s) is low-pass filtered based on the time constant τest from the time constant calculator 36. To do. As a result, in step S206, the road surface reaction force torque estimated value Talign-est is output.

  In the second embodiment, the steering angle signal θ (s) is differentiated by the differential calculator 31. However, if the signal corresponding to the steering wheel angular velocity can be directly obtained, the differential calculator 33 can be omitted.

When the steering angle signal θ (s) cannot be detected, the steering angle θ can be calculated from other vehicle state quantities. For example, the steering angle θ can be calculated from the lateral acceleration Gy by the following equation (14).
θ = Gy (β1 × s ² + β2 × s + β3) / α1 × s ² + α2 × s + α3) (14)
However,
α1 = I _z × M
α2 = {(C _f + C _r ) Iz + (C _f L _f ² + C _r L _r ² ) M} / V
α3 = C _f C _r L ² (1 + AV ² ) / V ²
β1 = I _z C _f
β2 = C _f C _r LL _r / V
β3 = C _f C _r L
Incidentally _{I z} is yaw inertia, M is vehicle weight, V is the vehicle speed, _{C f} is a front wheel cornering power, _{C r} is the rear wheel cornering power, _{L f} is the front axle distance between centers of gravity, _{L r} is the rear axle distance between centers of gravity, L Is the wheelbase, and A is the vehicle stability factor.

In addition, if the gain Kalign-gainθ of the ratio between the road surface reaction torque Talign and the steering angle θ cannot be obtained, it can be implemented by obtaining a gain proportional to the ratio of the road surface reaction torque Talign and other vehicle state quantity α. It becomes. For example, the time constant τest of the low-pass filter operation can be obtained from the following equation (15) using the gain Kalign-gainGy proportional to the ratio of the road surface reaction torque Talign and the lateral acceleration Gy.
Est = (Ggear × Tmfric + Tfrp) / Kalign-gain Gy × (dGy / dt) (15)

Even if this lateral acceleration Gy is not detected, it can also be calculated from the following equation (16) derived from equation (14).
Gy = θ (α1 × s ² + α2 × s + α3) / (β1 × s ² + β2 × s + β3) (16)

  Further, the vehicle state quantity α using the steering angle θ and the alternative vehicle state quantity using the lateral acceleration Gy have been described, but other vehicle state quantities α such as the vehicle yaw rate, the vehicle skid Similarly, the time constant τest of the low-pass filter operation for obtaining the road surface reaction force torque estimated value Talign-est can be calculated using corners, vehicle cornering forces, and the like.

  Thus, in the second embodiment, the time constant τest of the low-pass filter operation for obtaining the road surface reaction force torque estimated value Talign-est is a vehicle state quantity α that is proportional to the road surface reaction force torque Talign in the linear region. The differential output of the vehicle state quantity α can be easily calculated by multiplying the gain. Further, the time constant τest of the low-pass filter operation can be easily changed by the gain. Therefore, the man-hour for determining the time constant τest is reduced, and it is not necessary to measure the ratio of the road surface reaction force torque to the steering angle as in the first embodiment, and the man-hour associated with this measurement can be reduced. In addition, even if the front wheel load of the car changes due to changes in the grade of the car even if it is the same model, there is no need to re-measure the ratio of the road reaction torque to the steering angle, and the road reaction torque effectively By obtaining the estimated value Talign-est, effective steering control can be realized.

Embodiment 3 FIG.
In the second embodiment, while calculating the time constant τest of the low-pass filter operation, the gain of the ratio from the gain output means 39 is used as a constant value for the calculation, but in the third embodiment, the gain of this ratio is used. It is designed to change according to the vehicle speed.
In the third embodiment, the vehicle state quantity α that is proportional to the road surface reaction force torque Talign in the linear region includes the steering angle of the steering wheel of the vehicle, the yaw rate of the vehicle, the lateral acceleration Gy of the vehicle, the side slip angle of the vehicle, The cornering force of the vehicle can be used, but the one using the steering angle of the steering wheel of the vehicle will be described.

In the description of the second embodiment, it has been described that the gain of the ratio between the road surface reaction torque Talign and the steering angle θ changes according to the vehicle speed. In the second embodiment, the gain of this ratio is treated as a constant value with the ratio corresponding to, for example, 40 km / h as a representative value, but in the third embodiment, a more accurate road surface reaction force torque estimated value Talign-est is obtained. Therefore, the gain of this ratio is a function that changes according to the vehicle speed. If the function that changes according to the vehicle speed V is Kalign-θ (V), this is given by the following equation (17). This function Kalign-θ (V) is a ratio of the road surface reaction torque Talign and the steering angle θ, and changes according to the vehicle speed.
Kalign-θ (V) = (1/1 + AV ² ) × (V ² / L) × Tvel (17)
However, Tvel is a reference gain calculated from the ratio of the road surface reaction torque Talign and the steering angle θ according to an arbitrary vehicle speed.

  In the third embodiment, the road surface reaction force torque Talign and the vehicle state quantity α, for example, the function gain Kalign-θ (V) of the ratio of the steering angle θ, the road surface reaction force torque Talign corresponding to an arbitrary one vehicle speed and the steering. Based on the reference gain Tvel calculated from the ratio of the angle θ, the calculation is simply performed according to the equation (17).

When the function Kalign-θ (V) that changes according to the vehicle speed is used, the time constant τest of the low-pass filter operation for calculating the road surface reaction force torque estimated value Talign-est is expressed by the following equation (18). Desired.
Τest = (Ggear × Tmfric + Tfrp) / Kalign-θ (V) × (dθ / dt) (18)

  The function Kalign-θ (V) is a quadratic function of the vehicle speed V as shown in Expression (17). If it is difficult to obtain this quadratic function in terms of mounting, the approximation by the linear function The time constant τest of the low-pass filter operation for easily calculating the road surface reaction force torque estimated value Talign-est is obtained. FIG. 8 is a graph showing the relationship between the linear function and the quadratic function. The horizontal axis represents the vehicle speed (Km / h), and the vertical axis represents the torque gradient (Nm / rad). A thick solid line characteristic K1 indicates a quadratic function gain of the function Kalign-θ (V), and a thin solid line characteristic K2 indicates a linear function gain thereof. As is apparent from FIG. 8, this linear function gain approximates the quadratic function gain. In FIG. 8, a cross indicates a gain at a vehicle speed of 40 (Km / h) used as the reference gain Tvel in the third embodiment.

  FIG. 9 shows a road surface reaction force torque detector 30B used in the third embodiment. The road surface reaction force torque detector 30B uses road surface reaction torque calculation means 32B. The road surface reaction force torque detector 30B has a vehicle speed detector 11 added to the road surface reaction force torque detector 30A shown in FIG. 6, and a gain calculator 40 is added to the road surface reaction force torque calculation means 32B. Has been. The vehicle speed detector 11 is the same as that shown in FIG. 2 and generates a vehicle speed signal V (s) according to the vehicle speed V. The gain calculator 40 is a gain output means and is used in place of the gain output means 39 of FIG. A vehicle speed signal V (s) from the vehicle speed detector 11 is input to a gain calculator (gain output means) 40. The gain calculator (gain output means) 40 uses the reference gain Tvel as a function of the vehicle speed V. A certain gain Kalign-θ (V) is calculated and output. The time constant calculator 36B in the third embodiment uses the time constant τest based on the differential output θ (d), the gain output Kalign-θ (V), and the friction torque signals Tmfric (s) and Tfrp (s). Is calculated.

FIG. 10 is a flowchart showing the operation of the third embodiment. This flowchart includes steps S301 to S308 between the start and the end.
First, in step S301, the steering shaft reaction force torque signal Ttran (s) is read into the memory of a microcomputer constituting the control unit 8. In the next step S302, the steering angle signal θ (s) is subsequently read into the memory. In the next step S303, the vehicle speed signal V (s) is read into the memory. In the next step S304, the differential output θ (d) of the steering angle signal θ (s) is calculated by the differential calculator 33. In the next step S305, a gain Kalign-θ (V) that is a function of the vehicle speed V is calculated based on the vehicle speed signal V (s).

In the next step S306, the time constant calculator 36 calculates the time constant τest. In the third embodiment, this time constant τest is the differential output θ (d) from the differential calculator 33, the function gain Kalign-θ (V) from the gain calculator (gain output means) 40, and the first The friction torque signal Tmfric (s) from the friction torque signal device 34 and the friction torque signal Tfrp (s) from the second friction torque signal device 35 are used to calculate according to the equation (18).
In the next step S307, the steering shaft reaction force torque signal Ttran (s) is passed through the low-pass filter means 37, and the steering shaft reaction force torque signal Ttran (s) is low-pass filtered based on the time constant τest from the time constant calculator 36. To do. As a result, in step S308, the road surface reaction torque estimation value Talign-est is output.

  Thus, in the third embodiment, in order to obtain a more accurate road surface reaction torque estimation value Talign-est, the gain of the ratio between the road surface reaction force torque Talign and the vehicle state quantity α, for example, the steering angle θ is set according to the vehicle speed. And the function gain is simply calculated based on the reference gain calculated corresponding to any one vehicle speed, so the road surface reaction force torque estimated value Talign-est can be calculated more accurately. Moreover, it can be easily obtained.

  In the third embodiment, the vehicle state quantity α using the steering angle θ is specifically described. However, as in the second embodiment, the vehicle state quantity α is regarded as proportional to the road surface reaction force torque Talign in the linear region. Other vehicle state quantities α that can be used, such as the yaw rate of the vehicle, the lateral acceleration Gy of the vehicle, the side slip angle of the vehicle, the cornering force of the vehicle, etc. Also in this case, the road surface reaction torque Talign and the gain of these ratios are function gains that change according to the vehicle speed, and this function gain is simply based on the reference gain calculated corresponding to any one vehicle speed. The same effect can be obtained by calculating.

Embodiment 4 FIG.
In the third embodiment, a gain proportional to the ratio of the road surface reaction torque Talign and the vehicle state quantity α is set as a function that changes according to the vehicle speed, and this function gain is set to a reference gain calculated corresponding to an arbitrary vehicle speed. In this embodiment, the reference gain can be obtained more simply from the front axle load of the vehicle without any special measurement.

The road surface reaction torque Talign can be mechanically expressed by the following equation (19).
Talign = (ζn + ζc) C _f β _f (19)
Where ζ n is a pneumatic trail, ζ c is a caster trail, and β _f is a side slip angle of the front wheel of the vehicle.

Cornering power C _f represents the slope of the cornering force generated in the tire. Since the cornering force is a frictional force between the tire and the contact surface, the magnitude is determined by the load applied to the tire and the coefficient of friction between the tire and the road surface. This means that the cornering force is determined by the load applied to the tire when the same road surface condition is assumed. That is, the cornering power can also be determined by the load. Also, the effect of different cornering power depending on the type of tire can be ignored.

Further, when βf is proportional to the steering wheel angle θ in the linear region and ζn and ζc are also regarded as constant values, the equation (17) can be simplified as the following equation (20).
(Talign / θ) = Kalign−θ (V) = (1/1 + AV ² ) (V ² / L) Kw (20)
Here, Kw is a gain corresponding to the front axle load.

In a general vehicle, as shown in FIG. 11, the gain of the ratio between the road surface reaction torque and the tire angle at each vehicle speed is determined by the front axle load. This means that the function of the ratio of the road surface reaction torque and the steering angle θ according to each vehicle speed can be approximated by the front axle load. The thick solid line characteristic G1 in FIG. 11 indicates the ratio of the road surface reaction torque Talign to the tire angle for each vehicle type at a vehicle speed of 60 (Km / h). The horizontal axis indicates the front load, and the vertical axis indicates the torque gradient (Nm / rad).
A thin solid line G2 in FIG. 11 indicates an upper limit value for the characteristic G1, and a thin solid line G2 indicates a lower limit set value for the characteristic G1. As described above, the ratio of the road reaction torque and tire angle at each vehicle speed varies depending on the type of tire and the length of the pneumatic trail, but the ratio of the road reaction torque and tire angle for each front axle load. The gain is desirably set in a range between the upper limit G2 and the lower limit G3. However, this is not the case with vehicles having special tires and the steering mechanism 10.

  Thus, according to the fourth embodiment, the road surface reaction force torque corresponding to each vehicle speed V necessary for calculating the time constant τest of the low-pass filter operation for calculating the road surface reaction force torque estimated value Talign-est. The gain of the ratio between Talign and the vehicle state quantity α can be easily obtained from the front axle load without any special measurement.

  In the fourth embodiment, in addition to the steering angle θ, as in the second embodiment, another vehicle state quantity α that can be regarded as proportional to the road surface reaction torque Talign in the linear region, for example, Vehicle yaw rate, vehicle lateral acceleration Gy, vehicle side slip angle, vehicle cornering force, and the like can also be used. Also in this case, the gain of the ratio between the road surface reaction torque Talign and the vehicle state quantity α corresponding to each vehicle speed V can be easily obtained from the front axle load without special measurement.

Embodiment 5 FIG.
The fifth embodiment uses a road surface reaction force torque detector 30C. This road surface reaction force torque detector 30C is configured such that the time constants τest1 and τest2 calculated by the two time constant calculators 361 and 362 are selected by the switching calculator 41 and given to the low-pass filter means 37. is there. The first time constant calculator 361 is, for example, the time constant calculator 36 of the first embodiment, and the time constant calculated by the time constant calculator 36 is τest1. The second time constant calculator 362 is the time constant calculator 36A of the second embodiment, and the time constant calculated by the time constant calculator 36A is τest2. The switching calculator 41 is configured to select and output the larger one of the time constants τest1 and τest2 or the smaller one.

  According to the fifth embodiment, since the time constants τest1 and τest2 from the two time constant calculators 361 and 362 are selected, an appropriate time constant is selected according to the situation, and the steering shaft reaction force torque signal Ttran ( By filtering s) with the low-pass filter means 37, a more appropriate road surface reaction torque estimation value Talign-est can be obtained.

In the fifth embodiment, when one of the time constants τest1 and τest2 from the two time constant calculators 361 and 362 becomes an inappropriate value due to malfunction or large noise, the remaining appropriate It is also possible to select the other time constant.
Alternatively, the first time constant calculator 361 may be the time constant calculator 34B according to the third embodiment, and the second time constant calculator 362 may be the time constant calculator according to the fourth embodiment.

  Further, the first time constant calculator 361 is any one of the time constant calculators selected from the time constant calculators 36, 36A, and 36B of the first to fourth embodiments, and the second time constant calculator is used. The unit 322 may be another time constant calculator selected from the time constant calculators 36, 36A, and 36B of the first to fourth embodiments, and may be used in any combination. In this case, the first time constant calculator 361 corresponds to one state quantity in the vehicle state quantity α, and the second time constant calculator 362 corresponds to another vehicle state quantity α. It can also be. It is also possible to combine more than two more time constant calculators.

Embodiment 6 FIG.
The sixth embodiment uses a road surface reaction force torque detector 30D. This road surface reaction force torque detector 30D is provided with a limiter calculator 42 at the output of the time constant calculator 360 to cut an output level exceeding a predetermined level of the time constant τest output from the time constant calculator 360. Is. The limiter calculator 42 gives the limit output τest (l) of the time constant τest to the low-pass filter means 37.

  In the sixth embodiment, the time constant calculator 360 can be any of the time constant calculators 34, 34A, and 34B in the first to fourth embodiments, and a plurality of time constant calculators 360 can be used as in the fifth embodiment. For example, the two time constant calculators 361 and 362 and the switching calculator 41 may be combined.

  According to the sixth embodiment, the time constant τest can be cut at a level below zero, and the divergence of the time constant τest can be suppressed.

  The vehicle steering control device according to the present invention can be used, for example, as a power steering control device for an automobile.

1 is a perspective view showing the overall configuration of Embodiment 1 of a vehicle steering control device according to the present invention. FIG. 2 is a block diagram showing an overall control circuit of the first embodiment. FIG. 2 is a block diagram showing a road surface reaction torque detector used in the first embodiment. 3 is a flowchart showing the operation of the first embodiment. 6 is a graph illustrating an example of a change in road reaction force torque with respect to time corresponding to the first embodiment. The block diagram which shows the road surface reaction force torque detector used in Embodiment 2 of the vehicle steering control apparatus by this invention. 9 is a flowchart showing the operation of the second embodiment. 6 is a graph showing a vehicle speed and a function gain corresponding to the vehicle speed according to the second embodiment. The block diagram which shows the road surface reaction force torque detector used in Embodiment 3 of the vehicle steering control apparatus by this invention. 10 is a flowchart showing the operation of the third embodiment. FIG. 9 is a graph showing a road surface reaction force torque and tire angle ratio gain for each front axle load corresponding to the third embodiment. The block diagram which shows the road surface reaction force torque detector used in Embodiment 5 of the vehicle steering control apparatus by this invention. The block diagram which shows the road surface reaction force torque detector used in Embodiment 6 of the vehicle steering control apparatus by this invention.

Explanation of symbols

1: steering wheel, 2: steering shaft, 3: steering gear box,
4: torque sensor, 5: assist motor, 7: tire, 8: control unit,
11: Vehicle speed detector, 12: Steering torque detector, 13: Motor speed detector,
14: motor acceleration detector, 16: assist torque determination block,
17: Motor current determiner,
20: Motor control circuit, 21: Comparator, 22: Motor driver, 23: Motor current detector,
30, 30A, 30B, 30C, 30D: road surface reaction torque detector,
31: Steering reaction force torque signal output means,
32, 32A, 32B: road reaction force torque calculating means, 33: differential calculator,
34, 35: friction torque signal device,
36, 36A, 36B, 360, 361, 362: time constant calculator,
37: Low-pass filter means, 38: Handle angle detector,
39, 40: gain output means, 41: switching calculator, 42: limiter calculator.

Claims (11)

A vehicle equipped with a steering mechanism having a steering wheel steered by a driver, a steering shaft coupled to the steering wheel, and an assist motor coupled to the steering shaft and generating an assist torque for assisting the steering torque by the driver. A control device for a steering device, further comprising a signal output means for generating a steering shaft reaction force torque signal corresponding to a steering shaft reaction force torque acting on the steering shaft based on a road surface reaction force torque, and the road surface reaction force Road surface reaction force torque calculation means for calculating an estimated value of torque is provided , and the road surface reaction force torque calculation means calculates a low-pass filter means for filtering the steering shaft reaction force torque signal and a time constant of the low-pass filter means. Time constant calculating means, and the time constant calculating means includes the steering shaft reaction force torque. A differential output of the click signal, based on said friction torque signal representing the frictional torque of the steering mechanism, the control device of a vehicle steering system, characterized by calculating said time constant.   2. The control apparatus for a steering apparatus for a vehicle according to claim 1, wherein the assist motor is coupled to the steering shaft via a speed reducer, and the friction torque signal causes the friction torque of the assist motor to be reduced to the speed reducer. And a second friction torque signal corresponding to the friction torque of the steering mechanism excluding the friction torque of the assist motor. Control device for the device.   The control device for a vehicle steering system according to claim 1, further comprising: a ratio between the road surface reaction torque and a vehicle state quantity that can be considered to be proportional to the road surface reaction torque in a linear region. Gain output means for outputting a proportional gain output, wherein the time constant calculating means calculates the time constant based on the differential output, the friction torque signal, and the gain output. A control device for a vehicle steering system.   4. The control apparatus for a vehicle steering apparatus according to claim 3, wherein the gain output is output from the gain output means as a function that changes according to a vehicle speed.   5. The control apparatus for a vehicle steering apparatus according to claim 4, wherein the gain output is output from the gain output means as a function that changes as a linear function or a quadratic function according to a vehicle speed. A control device for a vehicle steering system.   5. The control apparatus for a vehicle steering apparatus according to claim 4, wherein the gain output is a function that changes according to a vehicle speed using a reference gain, and the reference gain corresponds to a road surface reaction corresponding to an arbitrary vehicle speed. A control device for a vehicle steering device, wherein the control device is calculated from a ratio between a force torque and the vehicle state quantity.   7. The control device for a vehicle steering apparatus according to claim 3, wherein a steering angle of the steering wheel is used as the vehicle state quantity.   5. The control apparatus for a vehicle steering apparatus according to claim 4, wherein the gain output is calculated using a reference gain, and the reference gain is set using a front axle load of the vehicle. Steering device control device.   The control apparatus for a vehicle steering system according to claim 1, wherein the time constant calculation means includes two time constant calculators and switching means for switching outputs of the two time constant calculators. The one time constant calculator is configured as a time constant calculator that calculates the time constant from the differential output of the steering shaft reaction force torque signal and the friction torque signal of the steering mechanism, and the other time constant calculator In addition to the differential output of the steering shaft reaction force torque signal and the friction torque signal of the steering mechanism, it can be considered that the road surface reaction force torque is proportional to the road reaction force torque in a linear region. A control device for a vehicle steering system, wherein the control device is configured as a time constant calculator that calculates the time constant based on a gain output proportional to a ratio to a vehicle state quantity.   The control apparatus for a vehicle steering system according to claim 1, wherein the time constant calculation means includes two time constant calculators and switching means for switching outputs of the two time constant calculators. In addition to the differential output of the steering shaft reaction force torque signal and the friction torque signal of the steering mechanism, the two time constant calculators are proportional to the road surface reaction force torque and the road surface reaction force torque in a linear region. A control device for a vehicle steering system, comprising: a time constant calculator that calculates the time constant based on a gain output proportional to a ratio with a vehicle state quantity that can be regarded as 2. The control apparatus for a vehicle steering apparatus according to claim 1, further comprising a limiter unit connected to an output of the time constant calculation unit, and the limiter unit outputs a time constant output from the time constant calculation unit. A control device for a vehicle steering system, characterized by limiting the length.

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