JP4088678B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus that assists steering by a motor.
[0002]
[Prior art]
As an electric power steering device, a torque sensor that detects steering torque is attached to the input shaft to which the steering wheel is fixed, and assist torque corresponding to the steering torque detected by the torque sensor is generated by the electric motor to reduce the steering force. It is generally known what to do. In such an electric power steering apparatus, the vehicle speed is detected and the assist torque corresponding to the steering torque is adjusted.
[0003]
Currently, various techniques for improving the running performance of a vehicle by not only performing steering assist with an electric power steering apparatus but also actively adjusting the assist amount have been proposed. For example, Japanese Patent Laid-Open No. 2000-238654 proposes a technique for improving the running performance of a vehicle using the target slip angle of the vehicle and the value of the slip angle derivative. In this technology, a lateral acceleration sensor, a vehicle speed sensor, and a yaw rate sensor are used to estimate a slip angle differential value that is an index of a slip state of the vehicle. Steering is made heavy by determining to start and reducing the assist amount. Alternatively, the sign of the lateral acceleration (or slip angle differential value) is reversed and added to the assist torque to advance the phase of the steering reaction force and ensure stability during high-speed traveling.
[0004]
[Problems to be solved by the invention]
However, in the method of increasing the rudder when the slip angle differential value exceeds a predetermined limit value, the slip angle differential value does not exceed the limit value in a region that does not exceed the limit such as sudden steering during a high-speed lane change. Because it does not exceed, the control that makes the steering heavy does not work, and the convergence and stability do not increase. On the other hand, in the method using the sign of the lateral acceleration being reversed, the vehicle weight and the vehicle speed are not taken into consideration, so that the convergence and stability when the vehicle travels at a high speed is not increased. Further, even when the steering is gently performed at a low speed, if the slip angle differential value is increased, there is a disadvantage that the assist amount is reduced and the steering becomes heavy.
[0005]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering apparatus that can improve the convergence at the time of high-speed lane change.
[0008]
[Means for Solving the Problems]
  Claim1In the electric power steering apparatus including an assist control unit that detects the steering state and drives the motor according to the steering state to assist in the steering direction, the slip angle differential value calculation that calculates the slip angle differential value is provided. Means,
  The present invention is technically characterized by comprising slip angle compensation control means for reducing the assist amount by the assist control unit based on the calculated slip angle differential value, vehicle speed and vehicle weight.
[0009]
  Claim1In the electric power steering apparatus, the assist amount is reduced based on the calculated slip angle differential value, the vehicle speed, and the vehicle weight. Therefore, even in a high-speed lane change in which the slip angle differential value does not become so large, steering is performed according to the slip angle differential value, that is, the slip angle differential value, the vehicle speed, and the vehicle weight (vehicle inertia) so as to suppress a sudden change in the slip angle. Since it is heavier, it is possible to improve convergence and stability.
[0010]
  Claim2Then, since the slip angle compensation control means does not reduce the assist amount by the assist control unit when the slip angle differential value is smaller than the neutral dead zone value in the predetermined range, the deterioration of the steering feeling due to the change to the unintended assist torque is prevented. be able to.
[0011]
  Claim3Then, the slip angle compensation control means does not reduce the assist amount by the assist control unit when the vehicle speed is lower than a predetermined threshold value. That is, the deterioration of the steering feeling is prevented by not performing the control at a low speed at which the slip angle differential value cannot be accurately obtained by calculation.
[0012]
  Claim4In the electric power steering system, since the slip angle differential value is calculated in consideration of the road surface μ, the slip angle differential value is compared with the road surface μ in the fine weather when the road surface μ is raining. It becomes a big value. Thereby, the convergence property on a low μ road can be improved.
[0013]
  Claim5In the electric power steering apparatus, the slip angle differential value is calculated in consideration of the braking force and the driving force. The vertical load on the front and rear wheels also changes depending on the braking force and driving force, and the yaw rate, slip angle, and slip angle differential value change, so the braking force and driving force during turning can be reduced by considering the braking force and driving force. The state change can be corrected.
[0014]
  Claim6The invention is an electric power steering apparatus provided with a transmission ratio variable means for varying a transmission ratio by driving an electric motor in the middle of a steering transmission system for connecting a steering wheel and a steering wheel,
  A steering angle sensor that detects a steering angle input from the steering wheel to the transmission ratio variable means and outputs a steering angle signal;
  Slip angle differential value calculating means for calculating the slip angle differential value;
  A speed sensor that detects the vehicle speed and outputs a vehicle speed signal;
  A rotation angle determination means for determining a rotation angle of the electric motor based on the vehicle speed signal and the steering angle signal, so that the slip angle differential value does not exceed a predetermined value;
  It is a technical feature to have.
[0015]
  Claim6Then, the rotation angle of the electric motor is determined so that the slip angle differential value does not exceed the predetermined value, and the transmission ratio between the steering wheel and the steering wheel is adjusted, so that the slip angle differential value does not exceed the predetermined value. The vehicle can be prevented from slipping.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 is a block diagram showing a configuration of an electric power steering apparatus 10 according to the first embodiment. The electric power steering apparatus 10 includes a torque sensor 22 for detecting steering torque, and a control apparatus that calculates a motor command torque (steering assist amount) based on the steering torque from the torque sensor 22 and the vehicle speed from the vehicle speed sensor 24. 30 and a motor drive circuit 26 that obtains a current command value corresponding to the motor command torque and controls energization of the motor M.
[0019]
The torque sensor 22 is disposed on the input shaft 12 connected to the steering steering 14 of the vehicle. The output of the motor M is decelerated by the speed reducer 16 and transmitted to the rack and pinion gear 18 for steering the front wheels.
[0020]
The control system of the control device 30 and the motor drive circuit 26 is shown in the block diagram of FIG. The output from the torque sensor 22 (steering torque: voltage value) is converted into a digital value via the A / D conversion 32, and the torque value is calculated in the torque calculation 34. Noise is removed from the calculated torque value by the low-pass filter 36 and is input to the assist control 60 via the addition node 38. On the other hand, the vehicle speed (pulse signal) from the vehicle speed sensor 24 is input to the vehicle speed calculation 42 via the I / F 40, and the calculated vehicle speed is input to the assist control 60. On the other hand, the output from the low-pass filter 36 is phase-compensated by the phase compensation 46 via the differentiation 44 and input to the assist control 60 via the addition node 38. The phase compensation 46 advances the phase by differentiating the steering torque value by the differentiation 44 to compensate for the steering assist delay. That is, when the command value is calculated based on the detected value, it takes a certain time to complete the calculation, and this fixed time becomes a delay of the command value with respect to the detected value, and the command value is obtained based on the current detected value. The steering assist cannot be properly controlled. For this reason, the phase compensation 46 advances the phase of the steering torque.
[0021]
The contents of the assist control 60 are shown in FIG. A command torque value is determined by the assist map 62 according to the steering torque from the addition node 38. That is, when the steering torque is large, a high command torque value is determined, and when the steering torque is small, a low command torque value is determined and output to the multiplication node 68 side. Further, in the electric power steering apparatus according to the first embodiment, when the steering torque is smaller than a predetermined value, a “dead zone” is provided so that motor control according to the steering torque is not performed. In other words, by providing a dead zone, the feeling of rigidity in the vicinity of the steering neutral at the time of middle and high speed traveling is enhanced, and the steering feeling is enhanced. When the steering torque is smaller than the steering torque Ts, the command torque is output as 0. When the steering torque is larger than the predetermined steering torque Tm, a constant command torque value (maximum motor output) is output as the maximum value.
[0022]
The vehicle speed value from the vehicle speed sensor 24 is weighted according to the vehicle speed by the vehicle speed gain map 64. By searching the vehicle speed gain map according to the vehicle speed, for example, “1” is output when the vehicle speed is 0 km / h, and “0.2” is output when the vehicle speed is 100 km / h. As a result, when steering is performed by weighting the steering assist amount according to the vehicle speed, the steering is light at low speed and, on the contrary, the steering is heavy at high speed. A vehicle speed weighting value from the vehicle speed gain map 64 is output to the multiplication node 68 side, and the above-described command torque is corrected according to the vehicle speed.
[0023]
As shown in FIG. 2, the command torque value from the assist control 60 is applied to the current command limiter 50 via the addition node 48. In the current command limiter 50, the command torque value exceeding the maximum output of the motor M is limited.
[0024]
The command torque value from the current command limiter 50 is applied to the PI control 100 via the subtraction node 52. The contents of the PI control 100 are shown in FIG. In the PI control 100, a Gp gain is added to the command torque value and applied to the addition node 102, and the command torque value is differentiated and a Gi gain is added and applied to the addition node 102. On the other hand, the current of the motor M is applied to the subtraction node 52 via the low pass filter 112 and the A / D conversion 114. In the PI control 100, PI feedback control is performed so that the actual motor current input via the A / D conversion 114 becomes the command torque value (command current value).
[0025]
The command torque value from the PI control 100 is applied to the motor drive circuit 26. The PWM calculation 27 of the motor drive circuit 26 performs PWM control by applying current to the bases of the transistors Tr1, Tr2, Tr3, Tr4 so that the motor M generates an output corresponding to the command torque value.
[0026]
The motor U-phase potential is applied to the non-inverting input of the differential amplifier 136 via the low-pass filter 122 and the A / D converter 124. The motor V-phase potential is applied to the inverting input of the differential amplifier 136 via the low-pass filter 132 and the A / D converter 134. The voltage between the motor terminals is output from the differential amplifier 136 and applied to the subtraction node 54. The motor current input via the A / D conversion 114 described above is multiplied by (LS + R) 138 and applied to the subtraction node 54 as a motor electromotive force, and the motor back electromotive force is output from the subtraction node 54. Here, LS in (LS + R) to be multiplied represents a differential value of the motor inductance, and R represents a resistance of the motor.
[0027]
The counter electromotive force from the subtraction node 54 is divided by the amplifier 56 with the counter electromotive force constant Ke to obtain the angular velocity of the motor, and the amplifier 58 is further divided with the reduction ratio Gi of the reducer 16 to The angular velocity ω is applied to the steering wheel return compensation control 80, the damper compensation control 90, and the stop damper control 140. Here, the angular velocity ω of the steering wheel is estimated by calculation, but the angular velocity can also be detected by a steering angle sensor.
[0028]
The steering wheel return compensation control 80 performs control for compensating for the characteristics of the electric power steering apparatus in which the return of the rudder due to the reaction force of the road surface is slowed by the frictional resistance between the motor M and the speed reducer 16 at a low speed. The contents of the steering wheel return compensation control 80 are shown in FIG. The handle return amount is determined by the handle return map 82 according to the angular velocity of the handle. That is, when the angular velocity of the handle is large, the return amount of the large handle is determined, and when the angular velocity is small, the return amount of the small handle is determined and output to the multiplication node 88 side. In the steering wheel return map 82 of the electric power steering apparatus according to the first embodiment, similarly to the assist map 62 described above, when the angular velocity is smaller than a predetermined value, the motor control according to the angular velocity is not performed. A "dead zone" is provided. In addition, when the angular velocity is higher than a predetermined angular velocity, a fixed steering wheel return amount is output as a maximum value.
[0029]
The vehicle speed value from the vehicle speed sensor 24 is weighted according to the vehicle speed by the vehicle speed gain map 84. By searching the vehicle speed gain map according to the vehicle speed, for example, “1” is output when the vehicle speed is 0 km / h, and “0.2” is output when the vehicle speed is 40 km / h. As a result, the steering wheel return amount is increased at low speeds, and the return amount is decreased at medium and high speeds. A vehicle speed weighting value from the vehicle speed gain map 84 is output to the multiplication node 88 side, and the return amount of the steering wheel described above is corrected according to the vehicle speed. The output of the handle return compensation control 80 is applied to the summing node 48.
Note that the steering wheel return compensation control 80 may determine the steering wheel return amount according to the angular velocity of the motor M instead of the angular velocity of the steering wheel.
[0030]
On the other hand, the damper compensation control 90 shown in FIG. 2 compensates for the quick return of the rudder due to the reaction force of the road surface at medium and high speeds. This is to prevent the rudder from returning too much due to the inertia of the motor M and the speed reducer 16 once the rudder begins to return. The contents of the damper compensation control 90 are shown in FIG. The damper amount is determined by the damper map 92 according to the angular velocity of the steering wheel. That is, when the angular velocity of the handle is large, a large damper amount (small handle return amount) in the direction opposite to the rotation direction of the handle is determined, and when the angular velocity is small, a small damper amount (large handle return amount) is determined. It is output to the multiplication node 98 side. Similarly to the assist map 62 described above, the damper map 92 is provided with a “dead zone” that prevents the motor control corresponding to the angular velocity from being performed when the angular velocity is smaller than a predetermined value. Further, when the angular velocity is higher than the predetermined angular velocity, a constant damper amount is output as the maximum value.
[0031]
The vehicle speed value from the vehicle speed sensor 24 is weighted according to the vehicle speed by the vehicle speed gain map 94. By searching the vehicle speed gain map according to the vehicle speed, for example, “0” is output when the vehicle speed is 0 km / h, and “0.6” is output when the vehicle speed is 40 km / h. Thereby, the damper amount is increased at high speed, and the damper amount is decreased at low speed. A vehicle speed weighting value from the vehicle speed gain map 94 is output to the multiplication node 98 side, and the return amount of the steering wheel described above is corrected according to the vehicle speed. The damper amount corrected by the vehicle speed is applied to the addition node 48 shown in FIG. 2 to compensate the command torque value from the assist control 60.
The damper compensation control 90 may determine the amount of damper according to the angular velocity of the motor M instead of the angular velocity of the steering wheel.
[0032]
As shown in FIG. 2, the steering torque differential value and the vehicle speed value are input to the torque inertia compensation control 70. The torque inertia compensation control 70 reduces the feeling of inertia that the rudder is severed at the start of turning and once the rudder is turned off. The contents of the torque inertia compensation control 70 are shown in FIG. The inertia compensation amount is determined by the inertia compensation map 72 according to the steering torque differentiated by the differentiation 44. That is, when the steering torque differential value is large, a high inertia compensation amount is determined, and when the steering torque is small, a low inertia compensation amount is determined and output to the multiplication node 78 side.
[0033]
The vehicle speed value from the vehicle speed sensor 24 is weighted corresponding to the vehicle speed by the interpolation coefficient map 74. For example, “0.7” is output when the vehicle speed is 0 km / h, “1.0” is output when the vehicle speed is 40 km / h, and “0.6” is output when the vehicle speed is 70 km / h. . Thereby, the inertia compensation amount is small at low speed, large at medium speed, and small at high speed. The weighting value from the interpolation coefficient map 74 is output to the multiplication node 78 side, and the above-described inertia compensation amount is corrected according to the vehicle speed. The inertia compensation amount corrected by the vehicle speed is applied to the addition node 48 shown in FIG. 2 to compensate the command torque value from the assist control 60.
[0034]
The motor angle from a sensor (not shown) attached to the motor M is obtained by dividing the reduction ratio Gi of the reduction gear 16 by the amplifier 160 to obtain the steering wheel angle. Further, the steering gear ratio Gst is obtained by the amplifier 162. Divided and input as an actual steering angle to state quantity estimation 150 based on the two-wheel vehicle model. In the state quantity estimation 150 based on the two-wheel vehicle model, the lateral acceleration detected by the lateral acceleration sensor 164 and the longitudinal acceleration detected by the longitudinal acceleration sensor 166 are input together with the vehicle speed signal, and the target slip angle is based on these values. A differential value is obtained.
[0035]
The target slip angle differential value from the state quantity estimation 150 based on the two-wheel vehicle model is provided with a dead zone for a minute value and a limit for a large value in a slip angle differential value map 152. That is, when the target slip angle differential value is smaller than a predetermined value corresponding to the dead zone near the center of the steering wheel, a “dead zone” is provided so that motor control according to the slip angle differential value is not performed. This is to prevent deterioration of the steering feeling due to a change to an unintended assist torque by not reducing the assist amount when the slip angle differential value is smaller than the neutral dead zone value within a predetermined range. On the other hand, a target slip angle differential value larger than the maximum value that can be assumed is limited to the maximum value by a limiter. As a result, when the value of the vehicle speed, the steering angle, or the like becomes inappropriate due to a sensor abnormality and the target slip angle differential value becomes a very large value, control based on these values is prevented.
[0036]
The target slip angle differential value from the slip angle differential value map 152 is obtained by integrating the vehicle weight m and the vehicle speed v by the mv · dβ / dt calculation 154 and adding the gain Gain by the amplifier 156, thereby compensating torque. The phase of the target slip angle differential value is adapted to the phase lag of and is subtracted from the command torque value from the assist control 60 at the addition node 48.
[0037]
That is, when the slip angle is generated by turning, lane change or the like, the assist amount is reduced and the steering is made heavy so as to suppress the generation of the change in the slip angle (slip angle differential value). In particular, in the present embodiment, the assist amount is reduced based on a value obtained by multiplying the target slip angle differential value by the vehicle speed. Therefore, even in a high-speed lane change in which the slip angle differential value does not become so large, steering is performed according to the slip angle differential value, that is, the slip angle differential value, the vehicle speed, and the vehicle weight (vehicle inertia) so as to suppress a sudden change in the slip angle. Since it is heavier, it is possible to improve convergence and stability.
[0038]
Here, there is also a change in slip angle during general turning, and the vehicle tries to turn by the slip angle, so if you try to suppress the slip angle carelessly by making the steering heavy, it is difficult to turn and difficult to steer It becomes a vehicle characteristic. For this reason, by making the compensation amount proportional to the vehicle weight and the vehicle speed, the convergence of the high-speed lane change is mainly enhanced.
[0039]
Furthermore, in this embodiment, by adding the vehicle weight to the compensation, a compensation amount corresponding to the lateral force that changes in proportion to the vehicle weight can be calculated, and the variation in the convergence of the vehicle that changes depending on the vehicle weight can be calculated. Can be relaxed.
[0040]
Here, with reference to FIG. 6 and FIG. 7, the target slip angle differential value calculation in the state quantity estimation 150 by the two-wheel vehicle model will be described.
The equations (1) and (2) in FIG. 7 are two-wheel dynamic vehicle equation of motion, and FIG. 6 is a two-wheel dynamic vehicle equation of motion for analyzing the motion by replacing four wheels with two wheels. It is explanatory drawing for demonstrating.
By steering operation, an actual steering angle δ is generated between the vehicle front direction X and the steered wheels, and a vehicle center-of-gravity point slip angle (slip angle) β is generated between the vehicle traveling direction and the vehicle front direction X. The vehicle actually turns by the slip angle β. Here, when the slip angle differential value dβ / dt, that is, the amount of change in the slip angle β is large, slip occurs.
[0041]
For this reason, in this embodiment, the slip angle differential value dβ / dt is obtained by the equations (1) to (6) shown in FIG. 7 and the above control is performed, thereby improving the convergence and stability of the vehicle. Here, the vehicle lateral acceleration is detected by a lateral acceleration sensor 164 shown in FIG. 2, and the vehicle longitudinal acceleration is detected by a longitudinal acceleration sensor 166.
[0042]
Here, the cornering power of each wheel can be approximated by (3) and (4) by the lateral acceleration and the road surface μ. Further, load movement by braking force and driving force can be approximated by (5) and (6). In the electric power steering apparatus of the first embodiment, since the slip angle differential value is calculated in consideration of the road surface μ, the road surface when the slip angle differential value is clear when the road surface μ such as rainy weather is reduced. Larger value than μ. Thereby, the convergence property on a low μ road can be improved. In addition, the vertical load on the front and rear wheels also changes depending on the braking force and driving force, and the yaw rate, slip angle, and slip angle differential value change. Force state changes can be corrected.
[0043]
Subsequently, the processing in the control device 30 for the calculation in the amplifier 160, the amplifier 162, the state quantity estimation 150 by the two-wheel vehicle model, the slip angle differential value map 152, the mv · dβ / dt calculation 156, and the amplifier 156 shown in FIG. This will be described in more detail with reference to the flowchart of FIG. The process of FIG. 8 is repeated by the control device 30 with a cycle time of 5 ms.
[0044]
The control device 30 divides the reduction ratio Gi and the steering gear ratio Gst of the speed reducer 16 from the motor rotation angle, calculates the actual steering angle (S12: amplifiers 160 and 162), and dead zone processing to remove noise. (S14). Next, the vehicle state quantity (target slip angle differential value) is calculated from the actual rudder angle and the vehicle speed as described above with reference to FIGS. 6 and 7 (S16: state quantity estimation 150 using a two-wheel vehicle model). ).
[0045]
When dead zone processing is applied to the target slip angle differential value and the slip angle differential value is smaller than the neutral dead zone value within a predetermined range, the assist amount is not reduced, so that the steering feeling caused by a change in unintended assist torque can be reduced. Deterioration is prevented (S18: slip angle differential value map 152). This also changes the slip angle during general turning, and the vehicle tries to turn according to the slip angle, so if you try to suppress the slip angle carelessly by making the steering heavy, the steering will be difficult to turn. It becomes difficult vehicle characteristics. For this reason, a slight slip angle differential value is used to prevent heavy steering.
[0046]
Then, the target slip angle differential value is subjected to low-pass filter processing to remove high-frequency noise (S20). Then, the vehicle weight m and the vehicle speed v are added to the target slip angle differential value, and the control amount is calculated (S22). Then, the gain is multiplied by the control amount to adjust the control amount (S24).
[0047]
Next, it is determined whether the vehicle speed is equal to or higher than a predetermined value (for example, 10 km / h) (S26), and if it is less than 10 km / h (S26: No), the assist torque adjustment based on the slip angle differential value is not performed. Steering feeling is prevented from being deteriorated by not performing control at low speed when the slip angle differential value cannot be accurately obtained by calculation. On the other hand, in the case of 10 km / h or more (S26: Yes), the assist torque is adjusted based on the calculated value (S28).
[0048]
Here, a test result by the electric power steering apparatus of the first embodiment will be described with reference to FIGS. 9 and 10. Here, when the steering wheel is returned smoothly during a high-speed lane change (lane change with a vehicle speed of 80 km / h, lane change, steering speed 2 rad / s), the steering angle [rad] -time [sec] of FIG. The graph shows the lateral acceleration [G] -time [sec] in the graph of FIG. As shown in FIG. 9, when the control of the present embodiment is performed, it can be seen that the handle returns smoothly when 3 seconds have elapsed, and the stability is improved. Further, as shown in FIG. 10, when the control according to the present embodiment is performed, it can be seen that there is no overshoot of the lateral acceleration at the elapse of 3 seconds, the convergence is improved, and the occupant does not feel the shaking.
[0049]
In the first embodiment described above, compensation is performed using the target slip angle differential value, but a front wheel slip angle differential value can also be used. At this time, it is also possible to obtain the front wheel slip angle differential value using the actual yaw rate in addition to the actual steering angle and vehicle speed.
[0050]
In the first embodiment, the steering torque is detected as the steering state, and the assist control is performed according to the steering torque. However, the assist control is performed according to the steering angle or the steering angular velocity instead of the steering torque. May be. Further, the vehicle speed information or the like is not directly from the sensor, and the calculated value of the slip angle differential value can be acquired through CAN, Bean, J1950, or the like. In the first embodiment, the control amount is obtained by adding the vehicle weight m and the vehicle speed v to the target slip angle differential value in S22. However, the present invention is not limited to this, and the target slip angle differential value, the vehicle weight m and the vehicle speed are calculated. The relationship of v may be stored in advance as a map.
[0051]
[Second Embodiment]
In 1st Embodiment mentioned above, the structure of this invention was used for the assist torque adjustment of an electric power steering device. On the other hand, the second embodiment relates to an electric power steering apparatus provided with a transmission ratio variable means for varying a transmission ratio by driving an electric motor in the middle of a steering transmission system that connects a steering wheel and a steering wheel. Is.
[0052]
As shown in FIG. 11, the electric power steering apparatus 210 mainly includes a steering wheel 214, a first steering shaft 212, a second steering shaft 213, a steering gear box 218, a steering angle sensor 216, a vehicle speed sensor 224, and an output. It is composed of an angle sensor 217, an ECU 230, and a gear ratio variable unit 222.
[0053]
That is, one end of the first steering shaft 212 is connected to the steering wheel 214, and the input side of the gear ratio variable unit 222 is connected to the other end side of the first steering shaft 212. The variable gear ratio unit 222 is composed of a motor, a speed reducer, and the like. One end side of the second steering shaft 213 is connected to the output side, and the other end side of the second steering shaft 213 is connected to the steering gear box 218. The input side is connected. The steering gear box 218 is configured to convert the rotational motion input by the second steering shaft 213 into the axial motion of the rod 215 and output it by a rack and pinion gear or the like (not shown). The rotation angle (steering angle) of the first steering shaft 212 is detected by the steering angle sensor 216, the rotation angle (output angle) of the second steering shaft 213 is detected by the output angle sensor 217, and the vehicle speed is detected by the vehicle speed sensor 224. Thus, the ECU 230 can be input as a steering angle signal, an output angle signal, and a vehicle speed signal.
[0054]
With this configuration, in the gear ratio variable unit 222, the ratio of the output gear to the input gear is changed in real time according to the vehicle speed by the motor and the reduction gear, and the second steering with respect to the steering angle of the first steering shaft 212 is achieved. The output angle ratio of the shaft 213 is varied. That is, by inputting the steering angle signal from the steering angle sensor 216 and the vehicle speed signal from the vehicle speed sensor 224 to the ECU 230, the rotation angle of the motor of the gear ratio variable unit 222 that is uniquely determined according to the vehicle speed is set to the motor rotation angle. A motor voltage determined from the map and corresponding to the determined rotation angle command value is supplied to a motor drive circuit (not shown) via an amplifier circuit (not shown).
[0055]
As a result, the steering gear ratio corresponding to the vehicle speed is set so that the output angle of the gear ratio variable unit 222 is larger than the steering angle of the steering wheel when the vehicle is stopped or traveling at a low speed, and the steering wheel is steered when traveling at a high speed. The output angle of the gear ratio variable unit 222 can be set to be smaller with respect to the angle. That is, the gear ratio variable unit 222 is mainly configured to improve steering wheel handling.
[0056]
This ECU 230 calculates the target slip angle differential value in the same manner as in the first embodiment, and the gear ratio variable unit 222 causes the ratio of the output gear to the input gear so that the steering angle is equal to or less than the predetermined target slip angle differential value. Is changed in real time according to the vehicle speed, and the ratio of the output angle of the second steering shaft 213 to the steering angle of the first steering shaft 212 is varied.
[0057]
In the second embodiment, the rotation angle of the electric motor is determined so that the slip angle differential value does not exceed a predetermined value, and the transmission ratio between the steering wheel and the steering wheel is adjusted. For this reason, it is possible to prevent the vehicle from slipping by controlling the steered wheels so that the slip angle differential value does not exceed the predetermined value.
[0058]
[Third embodiment]
In 1st Embodiment mentioned above, the structure of this invention was used for the assist torque adjustment of an electric power steering device. On the other hand, the third embodiment relates to an SBW (steer-by-wire) type electric power steering apparatus that detects an operation of a steering wheel and drives an actuator by a control device to perform steering.
[0059]
As shown in FIG. 12, the electric power steering apparatus 310 mainly includes a steering wheel 314, a steering shaft 312, a steering angle sensor 326, a torque sensor 322, an actual steering angle sensor 374, a steering actuator 328, a shaft 315, a vehicle speed. The sensor 324 and the ECU 330 are included.
[0060]
That is, the steering angle is detected by the steering angle sensor 326 and the torque sensor 322, the ECU 330 determines the steering angle based on the detected value, the steering is performed by the steering actuator 328, and this is detected by the actual steering angle sensor 274.
[0061]
The ECU (steering angle determination means) 330 according to the third embodiment calculates a target slip angle differential value as in the first embodiment, and sets the steering angle so that the steering angle is equal to or less than a predetermined target slip angle differential value. The actual steering is performed by the steering actuator (steering wheel control means) 328 at the determined steering angle. For this reason, it is possible to prevent the vehicle from slipping by controlling the steered wheels so that the slip angle differential value does not exceed the predetermined value.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an electric power steering apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a control system of the electric power steering apparatus according to the first embodiment of the present invention.
3A is a block diagram of torque inertia compensation control in FIG. 2, and FIG. 3B is a block diagram of assist control.
4A is a block diagram of steering wheel return compensation control in FIG. 2, and FIG. 4B is a block diagram of damper compensation control.
FIG. 5 is a block diagram of PI control in FIG. 2;
FIG. 6 is an explanatory diagram for explaining a two-wheel dynamic characteristic vehicle motion equation for analyzing motion by replacing four wheels with two wheels.
FIG. 7 is a chart showing a two-wheel dynamic vehicle equation of motion.
FIG. 8 is a flowchart of a compensation process using a slip angle differential value.
FIG. 9 is a graph showing a steering angle-time at the time of a lane change by the electric power steering apparatus of the first embodiment and the electric power steering apparatus of the prior art.
FIG. 10 is a graph showing lateral acceleration-time at the time of a lane change by the electric power steering apparatus of the first embodiment and the electric power steering apparatus of the prior art.
FIG. 11 is a block diagram showing a configuration of an electric power steering apparatus according to a second embodiment of the present invention.
FIG. 12 is a block diagram showing a configuration of an electric power steering apparatus according to a third embodiment of the present invention.
[Explanation of symbols]
10 Electric power steering device
22 Torque sensor
24 Vehicle speed sensor
26 Motor drive circuit
28 ECU
30 Control device
48 addition nodes
60 Assist control
70 Torque inertia compensation control
80 Steering wheel return compensation control
90 Damper compensation control
140 Damper control at stop
148 Stop state determination unit
150 State quantity estimation by two-wheeled vehicle model
152 Slip angle differential value map
154 mv · dβ / dt calculation
214 Steering wheel
215 Rod
216 Steering angle sensor
222 Gear ratio variable unit (Transmission ratio variable means)
224 Vehicle speed sensor (speed sensor)
230 ECU (slip angle differential value calculation means, rotation angle determination means)
314 Steering wheel
315 Rod
322 Torque sensor (operation sensor)
324 Vehicle speed sensor (speed sensor)
326 Steering angle sensor (operation sensor)
328 Steering actuator (steering wheel control means)
230 ECU (steering angle determination means, slip angle differential value calculation means)

Claims (6)

In an electric power steering apparatus including an assist control unit that detects a steering state and drives a motor according to the steering state to assist in a steering direction.
Slip angle differential value calculating means for calculating the slip angle differential value;
An electric power steering apparatus comprising slip angle compensation control means for reducing an assist amount by the assist control unit based on the calculated slip angle differential value, vehicle speed, and vehicle weight. 2. The electric power steering apparatus according to claim 1 , wherein the slip angle compensation control means does not reduce an assist amount by the assist control unit when a slip angle differential value is smaller than a neutral dead zone value in a predetermined range. 3. The electric power steering apparatus according to claim 1, wherein the slip angle compensation control unit does not reduce an assist amount by the assist control unit when a vehicle speed is lower than a predetermined threshold value. . The electric power steering apparatus according to any one of claims 1 to 3 , wherein the slip angle differential value calculation means obtains a slip angle differential value in consideration of a road surface μ. The electric power steering apparatus according to any one of claims 1 to 4 , wherein the slip angle differential value calculation means obtains a slip angle differential value in consideration of a braking force and a driving force. An electric power steering apparatus provided with a transmission ratio variable means for changing a transmission ratio by driving an electric motor in the middle of a steering transmission system for connecting a steering wheel and a steering wheel,
A steering angle sensor that detects a steering angle input from the steering wheel to the transmission ratio variable means and outputs a steering angle signal;
Slip angle differential value calculating means for calculating the slip angle differential value;
A speed sensor that detects the vehicle speed and outputs a vehicle speed signal;
A rotation angle determination means for determining a rotation angle of the electric motor based on the vehicle speed signal and the steering angle signal, so that the slip angle differential value does not exceed a predetermined value;
An electric power steering apparatus comprising:

Images