JP5272712B2 - Vehicle steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular steering apparatus capable of approximating a steering reaction characteristic to the steering reaction characteristic of a conventional steering apparatus. <P>SOLUTION: The vehicular steering apparatus includes: a first steering angle calculation unit 19a for calculating a first steering angle by adding a value multiplying a torsion angle by a first coefficient to a reaction motor rotation angle; a second steering angle calculation unit 20a for calculating a second steering angle by adding a value multiplying the torsion angle by a second coefficient larger than the first coefficient to the reaction motor rotation angle; a turning control unit 19 for controlling a turning motor based on the first steering angle; and a reaction control unit 20 for controlling a reaction motor 5 based on the second steering angle. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a so-called steer-by-wire vehicle steering apparatus in which a steering wheel and a steering mechanism that steers steering wheels are mechanically separated.

In Patent Literature 1, in a steer-by-wire system, the target turning angle of the front wheels is calculated based on the steering angle of the steering wheel, and the actual turning angle is matched with the calculated target turning angle. While controlling the motor, the reaction force motor is controlled based on the calculated target turning angle.
JP 2004-314891 A

  However, in the above prior art, since the response of the steering reaction force to the driver's steering operation is determined by the response of the target turning angle to the driver's steering operation as well as the steering angle, the vehicle behavior ( The steering reaction force characteristic is different from that of a conventional steering device (a steering device in which a steering wheel and a steering mechanism are mechanically coupled) having a higher response of the steering reaction force than the response of the steering angle). Give a sense of incongruity.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a vehicle steering apparatus capable of bringing the steering reaction force characteristic close to the steering reaction force characteristic of a conventional steering apparatus. is there.

In order to achieve the above object, in the present invention, the first steering angle is calculated based on the reaction motor rotation angle and the torsion bar torsion angle, and the output torque of the steered motor is controlled based on the first steering angle. both the you that, than the first steering angle based on the torsion angle of the reaction motor rotation angle and the torsion bar to calculate a large second steering angle, and controls the output torque of the reaction force motor on the basis of the second steering angle .

  Therefore, in the present invention, since the reaction force steering angular velocity is larger than the steering steering angular velocity, the response of the steering reaction force is faster than the response of the steering angle (that is, the phase of the steering reaction force is the steering angle). Is more advanced than the phase). For this reason, the responsiveness of the steering reaction force is higher than the responsiveness of the vehicle behavior, and the steering reaction force characteristic can be brought close to the steering reaction force characteristic of the conventional steering device.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

First, the configuration will be described.
FIG. 1 is an overall configuration diagram of a steer-by-wire system to which a vehicle steering apparatus according to a first embodiment is applied. The vehicle steering apparatus according to the first embodiment includes a handle 1 and front wheels (steering wheels) 2 and 2. This is a so-called steer-by-wire (SBW) system in which the steering mechanism 3 that steers the vehicle is mechanically separated.

  The column shaft 4 that supports the handle 1 has a reaction force motor 5 that applies a steering reaction force to the handle 1, a rotation angle sensor 6 that detects the rotation angle of the column shaft 4, and a steering torque based on the twist angle of the column shaft 4. A steering torque sensor 7 for detecting the reaction force and a reaction force motor angle sensor 8 for detecting the rotation angle of the reaction force motor 5 are provided. The steering torque sensor 7 is a sensor that detects a torsion angle of a torsion bar provided on the column shaft 4 and detects torque based on the detected torsion angle.

  The steering mechanism 3 includes first and second steering motors 9a and 9b for applying a steering torque for turning the front wheels 2 and 2 to the pinion gears 13a and 13b, respectively. First and second steered motor angle sensors 10a and 10b that detect the rotational angles of the first and second steered motors 9a and 9b as steered angles that are rotational angles, and the front wheels 2 as lateral forces of the front wheels 2 and 2 , 2 are provided with first and second tire lateral force sensors 12a, 12b for detecting a force input in the axial direction of the rack 11. The first steering motor 9a is mechanically connected to the front wheels 2 and 2 via the pinion gear 13a and the rack 11 and the second steering motor 9b is mechanically connected to the front wheels 2 and 2 via the rack 11; 1, the turning angle of the front wheels 2 and 2 can be detected by detecting the rotation angle of the second turning motors 9a and 9b.

The reaction motor 5 and the first and second steering motors 9a and 9b are controlled by the first, second and third controllers 14, 15 and 16, respectively.
The second controller 15 includes a column shaft rotation angle from the rotation angle sensor 6, a steering torque from the steering torque sensor 7, a reaction force motor angle from the reaction force motor angle sensor 8, and the first and second tire sideways. The tire lateral force from the force sensors 12a and 12b is input. In addition, vehicle information such as wheel speed is input to the second controller 15 via a CAN communication line (not shown).

  The second controller 15 generates a target turning angle of the front wheels 2 and 2 based on the reaction force motor angle from the reaction force motor angle sensor 8 and the vehicle speed from the CAN communication line, and the first and third controllers 14 and 16. Send to. The first controller 14 generates a command current that eliminates the deviation between the target turning angle sent from the second controller 15 and the actual turning angle of the front wheels 2 and 2 detected by the first turning motor angle sensor 10a. 1 Output to the steered motor 9a to control the steered angle. The third controller 16 outputs a command current that eliminates the deviation between the target turning angle sent from the second controller 15 and the actual turning angle of the front wheels 2 and 2 detected by the second turning motor angle sensor 10b. 2 Outputs to the steered motor 9b and controls the steered angle.

  The second controller 15 also includes a reaction force motor angle from the reaction force motor angle sensor 8, a tire lateral force from the first and second tire lateral force sensors 12a and 12b, and first and second turning motors 9a and 9b. A target steering reaction force applied to the steering wheel 1 is generated based on the current value of the vehicle and the vehicle speed from the CAN communication line, and a current for detecting the target current based on the target steering reaction force and the current supplied to the reaction force motor 5 is detected. The command current is calculated so that the deviation from the actual current detected by a sensor (not shown) becomes zero, and the calculated command current is output to the reaction force motor 5 to control the steering reaction force.

  The first, second, and third controllers 14, 15, and 16 are supplied with power from the battery 17. The first, second, and third controllers 14, 15, and 16 share input / output information with each other via the communication line 18, and even if a failure occurs in the second controller 15, the remaining The first and third controllers 14 and 16 generate the target turning angle and the target steering reaction force, and the first and second steering motors 9a and 9b and the two first and third controllers 14 and 16 Control of the reaction force motor 5 can be continued.

When a failure occurs in both the first and second turning motors 9a and 9b, or when a failure occurs in the reaction force motor 5, the second controller 15 uses a backup clutch or the like to connect the column shaft 4 and the pinion shaft. 13 is mechanically connected to enable manual steering by the driver.
The second controller 15 adjusts the rotation angle of the column shaft 4 to a neutral position (a position corresponding to a turning angle of zero) based on the column shaft rotation angle detected by the rotation angle sensor 6 when the ignition is on.

FIG. 2 is a control block diagram of steering control and reaction force control according to the first embodiment.
Hereinafter, for the sake of simplicity, the first and second steered motors 9a and 9b are referred to as the steered motor 9 and the first and second steered motor angle sensors 10a, unless it is necessary to explain each separately. 10b is referred to as the steering motor angle sensor 10, and the first, second, and third controllers 14, 15, and 16 are referred to as the controller 15.

The controller 15 includes a turning control unit (steering control unit) 19 and a reaction force control unit (reaction force control unit) 20.
The turning control unit 19 includes a first steering angle calculation unit (first steering angle calculation means) 19a, a target turning angle generation unit 19b, and a motor drive unit 19c.

The first steering angle calculation unit 19a is configured to perform a first steering angle (after-operation) based on the reaction force motor angle from the reaction force motor angle sensor 8 and the torsion angle of the torsion bar provided in the steering torque sensor 7. The steering angle for calculating the target turning angle is calculated using the following formula.
First steering angle = reaction force motor angle + K1 × twist angle K1 is a coefficient (first coefficient), and in the first embodiment, K1 = 0.5.

In general, the torque sensor detects torque by converting the torsion angle of the torsion bar into torque. Therefore, the torsion angle of the torsion bar can be directly detected, or can be calculated from the torque converted from the torsion angle and the torsion characteristic of the torsion bar using the following relational expression. In any case, the steering torque sensor 7 is a torsion angle detecting means for detecting torsion of the torsion bar directly or indirectly.
Torsion bar torsion angle = steering torque / torque sensor spring constant Here, the torque sensor spring constant is an eigenvalue of the torsion bar and has been previously determined by experiments or the like.

The target turning angle generator 19b adds the steady steering control amount based on the variable gear ratio map and the differential steering control amount based on the differential steering map to generate a target turning angle.
First, the steady steering control amount is calculated with reference to the variable gear ratio map from the steering angle estimated by the first steering angle calculation unit 19a.

  In the variable gear ratio map, the steady steering control amount is calculated by multiplying the input first steering angle by a predetermined steering gear ratio (the ratio of the steering angle to the turning angle, which is a predetermined ratio). In the variable gear ratio map, the steady steering control amount corresponding to the first steering angle is stored in advance as a map, and the steady steering control amount corresponding to the first steering angle input with reference to the map is calculated. May be. The steering gear ratio in this variable gear ratio map depends on the vehicle speed. For example, the steering gear ratio is reduced (lower the steering angle relative to the turning angle) in the low vehicle speed range, and the turning performance is improved. The driving stability may be improved by increasing the ratio (increasing the steering angle relative to the turning angle).

Next, the steering angle is time-differentiated to calculate a steering angular velocity (first steering angular velocity), and a first differential steering control amount is calculated from the steering angular velocity with reference to a differential steer map. Here, the differential steer map is set so that the first differential steer control amount is a value obtained by multiplying the steering angular velocity by a predetermined differential gain. That is, the differential steer map is a map that outputs a differential steer control amount that is a value obtained by multiplying the steering angular velocity by a predetermined differential gain that is determined in advance. Therefore, the differential steer control amount corresponding to the steering angular velocity may be stored in advance as a map in the differential steer map, and the differential steer control amount may be calculated with reference to the map for the input steering angular velocity. The differential steer control amount has an upper limit set by a certain limit value. The differential gain is a positive gain obtained in advance through experiments and simulations.
The motor drive unit 19c calculates a command current based on a deviation between the target turning angle generated by the target turning angle generation unit 19b and the actual turning angle (actual turning angle), and calculates the calculated command current. Based on the current supplied to the steered motor 9, the steered motor 9 is controlled so that the target steered angle matches the actual steered angle (actual steered angle).

The reaction force control unit 20 includes a second steering angle calculation unit (second steering angle calculation means) 20a, a virtual target turning angle generation unit 20b, a target reaction force generation unit 20c, and a motor drive unit 20d.
Similar to the first steering angle calculation unit 19 a, the second steering angle calculation unit 20 a is a torsion bar twist angle calculated from the reaction force motor angle from the reaction force motor angle sensor 8 and the steering torque from the steering torque sensor 7. Based on the above, a second steering angle (a steering angle for calculating a virtual target turning angle to be described later is calculated.
Obtained as second steering angle = reaction motor angle + K2 × twist angle.
K2 is a coefficient (second coefficient) larger than the coefficient K1, and in the first embodiment, K1 = 0.8.

  The virtual target turning angle generation unit 20b adds the steady steering control amount based on the variable gear ratio map and the differential steering control amount based on the differential steer map by the same method as the target turning angle generation unit 19b. A target turning angle is generated. That is, the steady steering control amount is calculated based on the second steering angle and the variable gear ratio map, and the differential steering control amount is obtained by multiplying the second steering angular velocity obtained by differentiating the second steering angle by a predetermined differential gain. calculate. The variable gear ratio map and differential steer map of the virtual target turning angle generator 20b are the same as those of the target turning angle generator 19b.

  The target reaction force generation unit 20c is based on the virtual target turning angle generated by the virtual target turning angle generation unit 20b, and the vehicle speed, the tire lateral force, and the turning motor current (first and second turning motors 9a and 9b). ) To generate a target steering reaction force.

In the first embodiment, when the steering angle is θ, the steering angular velocity that is the first derivative of the steering angle θ is dθ / dt, and the steering angular acceleration that is the second derivative of the steering angle θ is d ² θ / dt ^2. The target steering reaction force Th is calculated with reference to the following equation (1).
Th = Ih * d ² θ / dt ² + Ch * dθ / dt + Kh * θ + Th * (δ ^* -δ) + Fh * CF + Lh * AP… (1)
Ih is an inertia coefficient, Ch is a damping coefficient, Kh is a spring coefficient, Th is a feedback coefficient, Fh is a tire lateral force coefficient, CF is a tire lateral force detected from the first and second tire lateral force sensors 12a and 12b, Lh is the turning axial force coefficient, and AP is the turning axial force converted from the turning motor current.

  Here, the first term on the right side is an inertia term that simulates the inertia component of the steering reaction force generated according to the steering angular acceleration. The second term is a damping term that simulates the viscous component of the steering reaction force generated according to the steering angular velocity. The third term is a spring term (rigidity term) that simulates the spring component of the steering reaction force generated according to the rotation angle of the handle 1. The fourth term is a feedback term that simulates a feedback component of the steering reaction force generated according to the deviation between the target turning angle and the actual turning angle. The fifth term is a tire lateral force term that simulates the tire lateral force component of the steering reaction force generated according to the tire lateral force. The sixth term is a self-aligning torque term that simulates the self-aligning torque component of the steering reaction force generated according to the self-aligning torque.

In the above equation (1), the parameters Ih, Ch, kh, Th, Fh, Lh that determine the reaction force characteristics (reaction characteristics that control the steering reaction force with respect to the steering wheel operation) are all coefficients dependent on the vehicle speed. By setting so as to become a larger value as the vehicle speed becomes higher, traveling stability at high speed traveling can be ensured. The parameters Ih, Ch, kh, Th, Fh, and Lh can be realized by previously storing the parameters in association with the vehicle speed through experiments, simulations, or the like, and determining the parameters according to the vehicle speed.
The motor drive unit 20d supplies the reaction force motor 5 with a current based on the target steering reaction force generated by the target reaction force generation unit 20c, so that the motor 5 outputs a steering reaction force that matches the target steering reaction force. To do. .

Next, the operation will be described.
[Steering reaction force response improvement]
In a conventional steering device in which a steering wheel and a steering mechanism are mechanically connected by a steering shaft, a steering reaction force rises first with respect to a driver's steering input, and the turning angle changes with a delay. In other words, the conventional steering device has a steering reaction force characteristic in which the response of the steering reaction force is higher than the response of the vehicle behavior determined by the response of the turning angle to the change of the steering angle.

  Therefore, in the SBW system in which the steering wheel and the steering mechanism are mechanically separated, when the driver who is used to the conventional steering device steers, the steering reaction force is not given to the driver due to the difference in the steering reaction force characteristics. It is desirable to bring the characteristics closer to conventional steering reaction force characteristics. In general, the higher the response of the steering reaction force, the better the information for the driver. On the other hand, the response of the turning angle should be moderate enough that the turning angle control does not vibrate. Is preferred.

However, in the conventional SBW system, since the target steering reaction force of the reaction force control is generated based on the target turning angle of the turning control, the response of the steering reaction force to the steering input of the driver is the same as the turning angle. It will be decided by the response of the target turning angle. For this reason, the response of the steering reaction force cannot be made higher than the response of the vehicle behavior (steering angle), and the driver feels uncomfortable.
In addition, as described above, the response of the steering reaction force to the driver's steering input is determined by the response of the target turning angle as well as the turning angle. Therefore, the response of the steering reaction force is improved in order to improve information for the driver. When the response of the target turning angle is increased in order to increase the turning angle, the turning angle control becomes vibrational, and it is difficult to tune the response of the steering reaction force.

  On the other hand, in the vehicle steering system of the first embodiment, the target turning angle used for the turning control and the target turning angle (virtual target turning angle) used for the reaction force control are respectively different systems (target turning angles). The coefficient K2 (= 0.8) generated by the generation unit 19b and the virtual target turning angle generation unit 20b) and used for calculating the second steering angle by the second steering angle calculation unit 20a on the reaction force control side is steered. The value is larger than the coefficient K1 (= 0.5) used for calculating the first steering angle in the first steering angle calculation unit 19a on the control side.

  Therefore, as shown in FIG. 3, the differential steer control amount generated by the virtual target turning angle generation unit 20b is larger than the differential steer control amount generated by the target turning angle generation unit 19b. That is, the phase of the steering reaction force can be advanced from the phase of the turning angle.

  Therefore, as shown in FIG. 4, the response of the steering reaction force is compared with the response of the steering reaction force in the conventional control that generates the target steering reaction force of the reaction force control based on the target turning angle of the steering control. , Can be raised more. That is, the response of the steering reaction force can be made higher than the response of the vehicle behavior (steering angle). In addition, since the response of the steering reaction force and the response of the vehicle behavior (steering angle) can be changed individually by changing the magnitudes of the coefficients K1 and K2, the response of the vehicle behavior is made appropriate. However, the response of the steering reaction force can be increased. As a result, the response of the steering reaction force of the SBW system can be made higher than the response of the vehicle behavior like a conventional steering device, and the response of the steering reaction force is higher than that of a conventional steering device. The desired response characteristic can be approached.

  Further, in the first embodiment, the target steering angle generation unit 19b and the virtual target steering angle generation unit 20b generate the steady steering control amount and the differential steering control amount with reference to the same variable gear ratio map and the differential steering map. doing. In other words, the same map is used for the steering control and the reaction force control, and only the steering angle (first steering angle, second steering angle) input to the map is different, so the response of the steering reaction force is determined as the steering angle. It is possible to advance more reliably than the responsiveness of.

Next, the effect will be described.
The vehicle steering apparatus according to the first embodiment has the following effects.
(1) A steering wheel 1 operated by a driver, a steering mechanism 3 that is mechanically separated from the steering wheel 1 and connected to the front wheels 2 and 2 to steer the front wheels 2 and 2, and a steering mechanism 3 Steering motors 9 a and 9 b for applying a steering torque, a reaction force motor 5 for applying a steering reaction force to the column shaft 4 that supports the handle 1, and a reaction force motor angle for detecting the rotation angle of the reaction force motor 5 A sensor 8, a steering torque sensor 7 as a torsion angle detecting means for detecting a torsion angle of a torsion bar provided between the handle 1 on the column shaft 4 and the reaction force motor 5, and a reaction force motor rotation angle The first steering angle calculation unit 19a for calculating the first steering angle by adding a value obtained by multiplying the twist angle by the first coefficient, and the reaction force motor rotation angle from the first coefficient with respect to the twist angle. Is a value multiplied by a large second coefficient. A second steering angle calculation unit 20a that calculates the second steering angle by adding, a steering control unit 19 that controls the steering motors 9a and 9b based on the first steering angle, and a reaction force based on the second steering angle And a reaction force control unit 20 that controls the motor 5. As a result, the response of the steering reaction force is higher than the response of the vehicle behavior, and the steering reaction force characteristic can be brought closer to the steering reaction force characteristic of a conventional steering device.

  (2) The turning control unit 19 adds a value obtained by multiplying the first steering angle by a predetermined ratio and a value obtained by multiplying the first steering angular velocity, which is a differential value of the first steering angle, by a predetermined differential gain. A target turning angle generator 19b that generates a target turning angle based on the value, and controls the turning motors 9a and 9b based on the target turning angle generated by the target turning angle generator 19b; The force control unit 20 is based on a value obtained by adding a value obtained by multiplying the second steering angle by a predetermined ratio and a value obtained by multiplying the second steering angular velocity, which is a differential value of the second steering angle, by a predetermined differential gain. A virtual target turning angle generation unit 20b that generates a virtual target turning angle is provided, and the reaction force motor 5 is controlled based on the virtual target turning angle generated by the virtual target turning angle generation unit 20b. In other words, by increasing the steering rigidity of the reaction force control over the steering rigidity of the steering control, the phase of the steering reaction force can always be advanced with respect to the phase of the vehicle behavior, and a good balance of steering-steering reaction force is achieved. Is obtained.

  (3) A target steering angle generator 19b multiplies the first steering angle by a predetermined ratio and a differential gain by which the first steering angular speed is multiplied, and a virtual target steering angle generator 20b multiplies the second steering angle. The predetermined ratio and the differential gain multiplied by the second steering angular velocity were set to the same ratio and gain ratio, respectively. As a result, the response of the steering reaction force can be more reliably advanced than the response of the turning angle.

1 is an overall configuration diagram of a steer-by-wire system to which a vehicle steering apparatus according to a first embodiment is applied. It is a control block diagram of steering control and reaction force control of Example 1. It is a time chart which shows the relationship between the virtual target turning angle of reaction force control when turning a steering wheel from a neutral position, and the target turning angle of turning control. 2 is a time chart of a steering reaction force showing an operation for improving the response of the steering reaction force according to the first embodiment.

Explanation of symbols

1 Handle 2 Front wheel (steering wheel)
3 Steering mechanism 4 Column shaft 5 Reaction force motor 6 Rotation angle sensor 7 Steering torque sensor 8 Reaction force motor angle sensors 9a and 9b Steering motors 10a and 10b Steering motor angle sensors 11 Racks 12a and 12b Tire lateral force sensor 13 Pinion shaft 14 1st controller 15 2nd controller 16 3rd controller 17 Battery 18 Communication line 19 Steering control part (steering control means)
19a 1st steering angle calculation part (1st steering angle calculation means)
19b Target turning angle generation part 19c Motor drive part 20 Reaction force control part (Reaction force control means)
20a Second steering angle calculation unit (second steering angle calculation means)
20b Virtual target turning angle generator 20c Target reaction force generator 20d Motor drive unit

Claims (4)

A handle operated by the driver;
A steering mechanism mechanically separated from the steering wheel and connected to the steered wheel to steer the steered wheel;
A steering motor for applying steering torque to the steering mechanism;
A reaction force motor that applies a steering reaction force to the column shaft that supports the handle;
A reaction force motor angle sensor for detecting the rotation angle of the reaction force motor;
A torsion angle detection means for detecting a torsion angle of a torsion bar provided at a position between the handle on the column shaft and the reaction force motor;
First steering angle calculation means for calculating a first steering angle based on the reaction force motor rotation angle and the twist angle;
Second steering angle calculation means for calculating a second steering angle larger than the first steering angle based on the reaction force motor rotation angle and the twist angle;
Steering control means for controlling the output torque of the steering motor based on the first steering angle;
Reaction force control means for controlling the output torque of the reaction force motor based on the second steering angle;
A vehicle steering apparatus comprising: The vehicle steering apparatus according to claim 1,
The steering control means controls the output torque of the steering motor based on a first steering angular velocity that is a differential value of the first steering angle,
The vehicle steering apparatus, wherein the reaction force control means controls an output torque of the reaction force motor based on a second steering angular velocity that is a differential value of the second steering angle. The vehicle steering apparatus according to claim 2,
The steering control means generates a target turning angle based on a value obtained by adding a value obtained by multiplying the first steering angle by a predetermined ratio and a value obtained by multiplying the first steering angular velocity by a predetermined differential gain. A target turning angle generation unit that controls the output torque of the turning motor based on the target turning angle generated by the target turning angle generation unit,
The reaction force control means determines a virtual target turning angle based on a value obtained by adding a value obtained by multiplying the second steering angle by a predetermined ratio and a value obtained by multiplying the second steering angular velocity by a predetermined differential gain. A vehicle steering system comprising a virtual target turning angle generation unit for generating, and controlling output torque of the reaction force motor based on the virtual target turning angle generated by the virtual target turning angle generation unit apparatus. The vehicle steering apparatus according to claim 3,
A predetermined ratio for multiplying the first steering angle by the target turning angle generator and a differential gain for multiplying the first steering angular speed, and a predetermined multiplier for multiplying the second steering angle by the virtual target turning angle generator. The vehicle steering apparatus, wherein the differential gain multiplied by the ratio and the second steering angular velocity are the same ratio and gain ratio, respectively.

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