JP2006175925A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle steering device which miniaturizes the system, and at the same time, can realize a favorable fail-safe when the system fails in the vehicle steering device for which a steer-by-wire system is adopted. <P>SOLUTION: A first wheel 16 is mechanically combined with a steering wheel 12 through a steering transmission mechanism 14. In the meantime, a steering actuator 22 which operates depending on the steering state of the first wheel 16 is combined with the other second wheel 20. A driver can always steer the first wheel by his own will by directly steering the first wheel 16 which is combined with the steering transmission mechanism 14. In the meantime, the second wheel 20 which is combined with the steering actuator 22 is steered depending on the steering state of the first wheel 16, and also, depending on an steering angle which is calculated by an ECU 24 in response to the state of the vehicle. Thus, the steering being suitable for the traveling state or the turning state of the vehicle is performed by the first wheel 16 and the second wheel 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in a vehicle steering apparatus, that is, a vehicle steering apparatus that employs a so-called steer-by-wire system.

  In recent years, various systems relating to steering of automobiles, so-called steer-by-wire systems, have been developed for practical use. Conventional vehicles generally have a steering wheel and a steered wheel mechanically coupled through a mechanism such as a rack and pinion. However, in the steer-by-wire system, there is no such mechanical connection, and inputs from the driver, such as torque and steering angle, are detected by sensors, and in addition to information from other vehicle sensors, A suitable steering angle is obtained, the steering angle command value is sent to the steering actuator, and the wheels are actually steered (see, for example, Patent Document 1).

  In addition, there is a system in which a steering actuator is provided for each of the left and right steering wheels to arbitrarily realize different steering angles (see, for example, Patent Document 2).

By adopting such a steer-by-wire system, it is possible to easily control the attitude of the vehicle with high accuracy, and to prevent the steering wheel from feeling uncomfortable even when automatic steering is realized. become.
JP 2001-106111 A JP 2003-112650 A

  By the way, when adopting a steer-by-wire system, in order to ensure steering performance when the system fails, a coupling mechanism that mechanically couples the steering wheel and the steered wheels separately from the steer-by-wire system, or the like It is common to prepare a mechanism, a mechanism for so-called fail-safe.

  In this case, a steer-by-wire system is usually used. However, when the system fails, it is necessary to mechanically connect the steering wheel and the steered wheels using, for example, a clutch mechanism. As a result, a backup mechanism that is not normally used is included, and the system tends to be large and complicated.

  Further, in the conventional vehicle, the driver can know the traveling state of the vehicle by the steering reaction force. However, in the steer-by-wire system, since there is no mechanical coupling, the motor connected to the steering wheel is driven. Therefore, it is necessary to reproduce a virtual reaction force, and a good steering feeling cannot be easily obtained, and the system is further enlarged.

  Therefore, the present invention has been made in view of the above-described circumstances, and in a vehicle steering apparatus that employs a steer-by-wire system, the system is downsized and a good fail-safe in the event of a system failure is realized. An object of the present invention is to provide a vehicle steering apparatus that can perform the above-described operation.

  The vehicle steering apparatus of the present invention is a steering transmission mechanism that is mechanically connected to one of the left and right steering wheels, transmits the steering state of the steering means, and steers the first wheel. A steering actuator that is connected to a second wheel different from the first wheel and that steers the second wheel; and a control means that controls the steering actuator according to the steering state of the first wheel; , Including.

  According to this aspect, one of the left and right wheels is always mechanically coupled via the steering transmission mechanism. That is, since the fail-safe mechanism is configured by the mechanism that is normally used, it is not necessary to separately provide a fail-safe mechanism when the system fails, and the entire apparatus can be downsized. Further, since the steering means can always obtain the steering reaction force from the first wheel side, the driver can recognize the traveling state of the vehicle without providing a new reaction force generation mechanism.

  In the above configuration, the steering means may include a steering assist device that assists the steering force.

  Here, as the steering assisting device, for example, a device using a motor or hydraulic pressure can be used, and a device that can arbitrarily generate torque and assist in increasing or decreasing the steering force is preferable. According to this aspect, it is possible to arbitrarily control the steering force generated in the steering means and to provide an appropriate steering reaction force to the driver.

  Moreover, the said structure WHEREIN: The 1st wheel to which the said steering transmission mechanism was connected can be made to be a wheel by the side in which the steering means was provided.

  According to this aspect, the mechanical configuration related to the left and right wheels is separated, and interference between the mechanical components such as the engine and the mechanical components constituting the vehicle steering apparatus can be easily avoided. , The degree of freedom of layout of each component is improved.

  ADVANTAGE OF THE INVENTION According to this invention, in the vehicle steering device of the vehicle which employ | adopted the steer-by-wire system, size reduction and simplification of a system can be performed easily, ensuring a fail safe function sufficiently.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  In the vehicle steering apparatus of the present embodiment, either the left or right steering wheel is mechanically coupled to the steering means via the steering transmission mechanism. In the present embodiment, the steering wheel coupled with the steering transmission mechanism may be referred to as the first wheel. On the other hand, a steering actuator that is driven according to the steering state of the first wheel is coupled to the other steered wheel. In the present embodiment, the steered wheel coupled to the steered actuator may be referred to as a second wheel. The driver can always steer the first wheel at his / her own will by directly steering the first wheel coupled to the steering transmission mechanism. On the other hand, the 2nd wheel couple | bonded with the steering actuator steers arbitrarily according to the steering state of a 1st wheel, and according to the state of a vehicle, and the steering suitable for the driving | running state and turning state of a vehicle I do.

  FIG. 1 is a structural conceptual diagram illustrating the structural concept of a vehicle steering apparatus 10 according to the present embodiment. FIG. 1 shows the concept of a front wheel steering type vehicle. As described above, the vehicle steering apparatus 10 uses, as the steering means, one of the left and right steering wheels via the steering transmission mechanism 14 in which the steering wheel 12 is configured by a known rack and pinion mechanism, for example. One wheel 16 is connected. That is, when the driver steers the steering wheel 12, the rotational motion is converted into a reciprocating motion in the vehicle width direction by the steering transmission mechanism 14, and the tie rod 18 can be advanced and retracted to steer the first wheel 16.

  On the other hand, a steering actuator 22 driven by, for example, a motor is connected to the second wheel 20. Therefore, the second wheel 20 can perform turning based on the driving amount of the turning actuator 22. Based on information from the steering transmission mechanism 14 and other steering angle sensors arranged at any position between the steering wheel 12 and the tie rod 18, the control unit (ECU) 24 that controls the steering actuator 22 The turning angle of the second wheel 20 corresponding to the turning angle of one wheel 16 is calculated, and the driving amount of the turning actuator 22 is determined.

  The vehicle steering apparatus 10 of the present embodiment is equipped with an electric power steering system (EPS) 26 as a steering assist apparatus that assists the steering force of the steering wheel 12 operated by the driver. The EPS 26 includes a wheel gear 30 attached to a steering shaft 28 connected to the steering wheel 12, a worm gear 32 that meshes with the wheel gear 30, a motor 34 that rotationally drives the worm gear 32, and the like. At the time of steering, the motor 34 is driven to generate assist torque, thereby reducing the operating force of the steering wheel 12.

  The direction of the assist force and the magnitude of the assist force can be determined by the ECU 24, for example, based on a signal from the steering torque sensor and a signal from a vehicle speed sensor mounted on the vehicle. Usually, when the vehicle speed is low, the assist force is increased to reduce the steering resistance of the steering wheel 12 so that the steering wheel 12 can be easily rotated. On the contrary, when the vehicle speed is high, the assist force is reduced to increase the steering resistance of the steering wheel 12 to improve the steering stability and prevent sudden steering and the like. The wheel gear 30 may be attached to a steering column provided between the steering shaft 28 and the steering wheel 12.

  The vehicle steering apparatus 10 of the present embodiment configured as described above directly steers the first wheel 16 coupled to the steering transmission mechanism 14, so that the driver always steers the first wheel 16 at his / her own will. can do. On the other hand, the 2nd wheel 20 couple | bonded with the steering actuator 22 turns arbitrarily according to the steering state of the 1st wheel 16, or according to the state of a vehicle, and is suitable for the driving state and turning state of a vehicle. The wheel position is controlled. That is, one of the steered wheels, that is, the first wheel 16 can be mechanically steered at all times by the driver's will, and the second steered wheel, the second wheel 20, is electrically controlled by adopting a steer-by-wire system. The one wheel 16 can be arbitrarily controlled to be steered independently.

  FIG. 2 is a block diagram for explaining the relationship between various sensors and actuators to be driven with the ECU 24 as the center.

  As described above, the ECU 24 is provided with detection information from the steering angle sensor 36 and the steering torque sensor 38 in order to calculate the control amount of the motor 34 and the steering actuator 22 of the EPS 26. The rudder angle sensor 36 is disposed, for example, on a part of the tie rod 18 and can detect the rudder angle based on the advance / retreat amount and the advance / retreat direction of the tie rod 18. The steering torque sensor 38 is disposed on the steering shaft 28, the steering transmission mechanism 14, and the like. In addition, a vehicle speed sensor 40, a wheel speed sensor, and the like are connected to the ECU 24.

  The ECU 24 includes an EPS assist calculation unit 24 a and a turning angle calculation unit 24 b that calculates the turning angle of the second wheel 20. The EPS assist calculation unit 24a is based on the current vehicle speed acquired from the vehicle speed sensor 40, the steering direction obtained from the steering angle sensor 36, the current steering torque of the first wheel 16 obtained from the steering torque sensor 38, and the like. The target torque assist amount is calculated, and the EPS motor 34 is driven. In this case, only the first wheel 16 is assisted, and half the assist force is generated as compared with the conventional case of steering two steered wheels. Can be configured.

  Information from the steering angle sensor 36 and the steering torque sensor 38 is also provided to the turning angle calculation unit 24b, and the second wheel 20 is turned so as to be steered according to the turning state of the first wheel 16. The rudder actuator 22 is driven.

  As shown in FIG. 3, in general, when the vehicle 42 turns, in order to be able to turn smoothly without applying excessive force to the wheels, the axle of each wheel 44, 46, 48, 50 is used. The center line must pass through the turning center O of the vehicle. Further, when the rear axles of the rear wheels 48 and 50 are not steered, the turning center O exists on the extension line of the rear axle. Therefore, it is necessary to change the direction of the inner front wheel 44 larger than the outer front wheel 46 during turning. It was necessary to set which of the tie rod and knuckle arm so that the so-called Ackermann rate would be optimal.

  On the other hand, in the case of the present embodiment, the second wheel 20 is steered independently of the first wheel 16 by the control of the steering actuator 22, so that the first wheel 16 and the second wheel 20 are always optimum Ackermann. It can be steered to get the rate. That is, the turning angle calculation unit 24b of the ECU 24 calculates the turning direction and the ideal steering angle of the second wheel 20 based on the turning direction and the steering angle of the first wheel 16 obtained from the steering angle sensor 36. The steering actuator 22 is driven. As a result, according to the vehicle steering apparatus 10 of the present embodiment, it is possible to always set an optimal Ackermann rate, and it is possible to easily realize smooth steering.

  FIG. 4 shows a conceptual diagram of the structure of the steered actuator 22. The steered actuator 22 includes a brushless motor 52, a speed reducer 54, a trapezoidal screw 56, and the like. In the inner rotor 52a of the brushless motor 52, the sun gear included in the speed reducer 54 is fixed to the tip of the inner rotor 52a, and the rotation of the sun gear is decelerated by the two-stage planetary gear and transmitted to the trapezoidal screw 56 through the carrier. The The rotation of the trapezoidal female screw 56a is transmitted to the trapezoidal male screw 56b. The trapezoidal male screw 56 b is fixed to the rack 60. In addition, the rack 60 is restricted in rotation direction by a spline of the case 62. As a result, the rack 60 strokes in the left-right direction in FIG. 4 according to the rotation of the inner rotor 52a. Therefore, when the brushless motor 52 is rotationally controlled by the control from the ECU 24, the second wheel 20 is steered in a predetermined direction at a predetermined angle.

  In this embodiment, since the trapezoidal screw 56 is used for the drive transmission system of the steering actuator 22, the transmission efficiency of the force with respect to the input from the second wheel 20 side is low or zero. Further, it is possible to reduce the inadvertent swing of the second wheel 20 due to the road surface condition during traveling, and it is possible to improve traveling stability.

  By the way, in this embodiment, as shown in FIG. 1, the 1st wheel 16 to which the steering transmission mechanism 14 was connected is a wheel by which the steering wheel 12 which is a steering means was provided. By adopting such a layout, it becomes possible to make the mechanisms related to the left and right steered wheels 16, 20 independent of the left and right, for example, avoiding interference with an engine mount and the like, and improving the degree of freedom of vehicle layout. be able to. In other words, as in the conventional steer-by-wire system, the steer-by-wire system has a configuration in which the steered wheels and the steering means are completely separated, and the steered actuators for the left and right steered wheels are separated. The effect of improving the layout flexibility of the members can be maintained.

  In addition, since the steering wheel 12, which is a steering means, is mechanically connected to the first wheel 16 via the steering transmission mechanism 14, the steering actuator 22 and the ECU 24 fail and cannot function. Even in this case, the first wheel 16 can be steered by the steering wheel 12, and the vehicle can be quickly moved to a safe place. Specifically, when the steering actuator 22 fails and the operation is stopped, for example, the second wheel 20 is fixed so as to face the neutral position, that is, in the straight traveling direction by a reset mechanism using a biasing means such as a spring. To do. In this state, the vehicle is turned only by the wheel generation force generated by turning the first wheel 16 that can be steered by the steering wheel 12, and the vehicle is quickly moved to a safe place.

  Further, when the motor 34 of the EPS 26 fails and does not function, the steering of the first wheel 16 by the steering wheel 12 is not hindered by switching the motor 34 to a free state. At this time, the steering of the first wheel 16 is not possible with the assistance of the EPS 26 and can be steered only by increasing the steering resistance, and the second wheel 20 is driven by the turning actuator 22 according to the steering of the first wheel 16. Since the vehicle is steered, the vehicle can be quickly moved to a safe place. In this embodiment, since only the first wheel 16 is connected to the steering wheel 12, the steering resistance applied to the steering wheel 12 during the failure of the EPS 26 is applied to the left and right wheels during the normal EPS failure. Since the steering resistance is halved compared with the case where the steering resistance is applied, the steering wheel 12 can be steered with a small steering force, and the vehicle can be easily steered even during an EPS failure.

  As described above, since the vehicle steering apparatus 10 according to the present embodiment can always maintain the mechanical coupling of the first wheel 16, a separate mechanical coupling mechanism for backup, such as a clutch, like the conventional steer-by-wire system. There is no need to prepare a mechanism, and the system can be reduced in size and simplified.

  Furthermore, the vehicle steering apparatus 10 according to the present embodiment has a dual system configuration of mechanical control and electrical control as a steering system, and can easily ensure a steering function during a system failure.

  Further, since the steering wheel 12 always receives the reaction force from the first wheel 16, the reaction force from the actual wheel can be reflected in the steering reaction force against the steering wheel 12. That is, in the case of the conventional steer-by-wire system, it is necessary to generate a virtual steering reaction force from scratch. However, according to the vehicle steering device 10 of the present embodiment, the actual reaction force is always used to perform steering. Sensation can also be improved.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The configuration shown in each drawing is for explaining an example, and can be appropriately changed as long as the configuration can achieve the same function. For example, in FIG. 1, even if the mechanical connection between the steering wheel 12 and the first wheel 16 is configured by a steering mechanism using a mechanical wire, the same effect as in this embodiment can be obtained. In the present embodiment, the first wheel 16 to which the steering transmission mechanism 14 is connected has been described as a wheel on the steering wheel 12 side, but the first wheel 16 to which the steering transmission mechanism 14 is connected is different from the side on which the steering wheel 12 is disposed. Even if one wheel 16 is arranged and the second wheel 20 to which the steering actuator 22 is connected is arranged on the steering wheel 12 side, the same effect as in the present embodiment can be obtained. Moreover, the structure shown in FIG. 2 is an example, and if the motor 34 and the turning actuator 22 of the EPS 26 can be driven in the same manner as described above, the sensor to be used and the type of information to be used are arbitrary. Moreover, the structure in ECU24 is also arbitrary. In the present embodiment, the front wheel steering type vehicle has been described. However, the same effect can be obtained even if the technique of the present embodiment is applied to the rear wheel steering type vehicle.

  Furthermore, the power steering system and the steering actuator used in the present embodiment can be appropriately changed as long as they have similar functions. For example, a system or actuator using hydraulic pressure can be used. Effects can be obtained.

It is a composition conceptual diagram explaining the composition concept of the steering device for vehicles concerning this embodiment. It is a block diagram centering on ECU of the vehicle steering device which concerns on this embodiment. It is explanatory drawing explaining the Ackermann rate regarding the steering apparatus for vehicles. It is explanatory drawing explaining schematic structure of the steering actuator of the steering apparatus for vehicles which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle steering apparatus, 12 Steering wheel, 14 Steering transmission mechanism, 16 Steering wheel, 16 1st wheel, 18 Tie rod, 20 2nd wheel, 22 Steering actuator, 24 ECU, 24a EPS assist calculation part, 24b Steering angle Calculation unit, 26 EPS, 28 steering shaft, 30 wheel gear, 32 worm gear, 34 motor, 36 steering angle sensor, 38 steering torque sensor, 40 vehicle speed sensor.

Claims (3)

Steering means;
A steering transmission mechanism that is mechanically connected to one of the left and right steering wheels, transmits the steering state of the steering means, and steers the first wheel;
A steering actuator that is connected to a second wheel different from the first wheel and that steers the second wheel;
Control means for controlling the steered actuator according to the steered state of the first wheel;
A vehicle steering apparatus comprising:   The vehicle steering apparatus according to claim 1, wherein the steering means includes a steering assist device that assists a steering force.   The vehicle steering apparatus according to claim 1, wherein the first wheel to which the steering transmission mechanism is connected is a wheel on a side on which a steering unit is provided.

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