JP2003137112A - Wheel steering gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high operation efficiency during direction operation, low operation efficiency and steering stability during reverse operation, and restoration to a neutral position by thrust from a tire during a motor failure in a screw mechanism. SOLUTION: In a vehicular steering gear A, a reciprocating steering shaft 3 is used as a screw shaft 5a of a ball screw 5, and the steering shaft 3 is reciprocated for steering by rotating a nut 5b by a motor. Contact angles α1 and α2 between a ball 8 and a thread groove 6 of the steering shaft 3 are provided larger than contact angles θ1 and θ2 between the ball 8 and a thread groove 7 of the nut 5b.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ARS for an automobile.
The present invention relates to a wheel steering device applied to a system or the like.

[0002]

2. Description of the Related Art In a vehicle steered by front wheels, a system that monitors the wheel speeds of front wheels on both sides and electronically controls steering of rear wheel angles so that the vehicle body always has a target vehicle body slip angle (ARS system (Active Rear The steering wheel for the rear wheels used in this system is a steering wheel that is connected to the supporting member of the wheel and steered by forward and backward movements by rotating the electronically controlled motor. The screw mechanism is configured to be converted into a linear motion and moved back and forth through the screw mechanism, which is usually a sliding screw such as a trapezoidal screw.

[0003]

A slip screw such as a trapezoidal screw has a loss (loss) of 50% or less because the efficiency of the operation (normal operation) of converting a nut rotation torque applied from a motor into an axial thrust is generally less than that. large. Therefore, it is necessary to take measures such as increasing the size of the motor.

If a ball screw is used as the screw mechanism, the motor torque for rotating the nut is reduced, the motor capacity can be reduced, and the peripheral components and the like can be made compact. However, the screw characteristics required for steering the rear wheels are light when the nut of the ball screw is rotated by the motor (during normal operation), and when thrust is applied from the tire to the screw shaft via the axle (reverse operation). When)
Is required to be heavy. If it is light even in reverse operation, the torque generated in the rotor of the motor increases when the wheel steering device for the rear wheels receives an external force such as when the vehicle receives a side wind, and the steerability of the vehicle deteriorates. Is concerned. Therefore, conventionally, a sliding screw has been used instead of a ball screw.

The ball screw is also advantageous in the following points. That is, in the unlikely event that the motor fails and the nut cannot be rotated, it is necessary to return it to the neutral position by the thrust from the tire. A mechanism for forcibly returning by means is required. When a ball screw is used, the reverse operation efficiency is high, and therefore a separate mechanism is not required for the operation of returning to the neutral position by the thrust from the tire. As described above, the ball screw has various excellent properties when applied to a wheel steering device, but is practically applied to a wheel steering device in an ARS system or the like from the viewpoint of ensuring handleability due to its high reverse efficiency. Has not reached.

The application of a ball screw to a wheel steering device is adopted in a wheel steering device for main steering such as power steering. In such a wheel steering device for main steering, there has been proposed one in which a contact angle between a ball and a thread groove of a worm shaft and an angle difference between a ball and a thread groove of a nut are provided (Japanese Patent Laid-Open No. Sho 53-53). -105668 gazette). In this proposed example, in a power steering system such as a power steering, the contact angle between the ball and the thread groove of the nut is made larger than the contact angle between the ball and the thread groove of the worm shaft, thereby improving the reverse efficiency. That is, the frictional resistance is reduced. This is the above contact angle so as to improve the returning operability of the handle.

However, in the wheel steering device for main steering, the steering wheel and the wheels need to move in conjunction with each other, and the wheel steering device for the rear wheels in the ARS system in which the steering wheel and the wheels are not mechanically connected is: The required performance is different. The above-mentioned proposal requires only lowering the reverse efficiency than the normal efficiency, but in the case of the ARS system, it is necessary to keep the ball screw from rotating during reverse operation. In this case, it is difficult to take measures to make the contact angle difference.
It is necessary to design the lead angle of the ball screw to be smaller than the lead angle normally adopted. Request for reduction of reverse efficiency is
Eventually, a sliding screw will be adopted.

An object of the present invention is to provide a screw mechanism with high operating efficiency at the time of normal operation and low operating efficiency at the time of reverse operation so that steering stability is obtained.
It is an object of the present invention to provide a wheel steering device that can return to a neutral position by thrust from a tire when a motor fails.

[0009]

A vehicle steering system according to the present invention comprises a steering shaft for steering a wheel, a nut having a thread groove on the inner circumference facing a thread groove provided on the outer circumference of the steering shaft, and A wheel steering system comprising a plurality of balls arranged in a rolling path formed between a steering shaft and a nut, and steering the wheel by rotating the nut by a motor to advance and retract the steering shaft. The contact angle between the ball and the thread groove of the steering shaft is larger than the contact angle between the ball and the thread groove of the nut. Normally, the thread groove of a ball screw is
The thread groove contact angle of the nut and the thread groove contact angle of the shaft are made equal, and by such a design, both the normal operation efficiency and the reverse operation efficiency are high. According to the present invention, by providing an angle difference between the contact angle between the shaft and the nut and making the contact angle of the thread groove of the steering shaft larger than the contact angle of the thread groove of the nut, the normal operation efficiency of the ball screw is high and The operating efficiency is low. Therefore, the following three features can be obtained at the same time. That is ,. The operation efficiency at the time of normal operation is good, the loss is small, and the motor can be small.
． The efficiency at the time of reverse operation can be made smaller than that of a general ball screw, and therefore even when the vehicle steering device receives an external force such as a side wind, it is difficult for the rotor of the motor to rotate due to the external force. It is possible to ensure stable vehicle steering. ． Even if the reverse operation efficiency is reduced, since it is a ball screw, higher reverse operation efficiency can be obtained compared to a sliding screw, and even if the motor fails and the nut cannot be rotated, The thrust can return the nut to the neutral position. for that reason,
There is no need to provide another mechanism for forced recovery.

The lead angle of the rolling path is preferably 5 ° or less. In the ball screw, the efficiency is reduced when the lead angle is reduced, but the efficiency is remarkably reduced when the lead angle is 5 ° or less. For this reason, regarding the contact angle, the reverse angle can be further reduced by making the contact angle of the thread groove larger than the contact angle of the thread groove of the nut as described above and setting the lead angle to 5 ° or less. The reverse input from the wheels to the motor rotor can be reduced.

The wheel steering system having each of the above-mentioned configurations monitors the wheel speeds and steering amounts on both front wheels of the vehicle in which the main steering is performed by the front wheels,
It may be used as a device for steering the rear wheels in a system that electronically controls the steering of the rear wheels so as to improve the running stability of the vehicle according to the monitoring result. By applying the above-mentioned system to the wheel steering device for the rear wheels, each of the above-described actions becomes effective, and the steering property of the rear wheels can be improved by the wheel steering device having a compact structure, and when the motor fails, Coping is also easy.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. This wheel steering device A is equipped with a wheel 1
The steering shaft 3 for steering the
And a ball screw 5 for moving back and forth. The steering shaft 3 is connected to a support member 2 that supports the wheel 1 so as to be steerable, and is supported by a support means (not shown) provided on the vehicle body so as to be able to move back and forth. In this embodiment, the motor 4 and the ball screw 5 are coaxially arranged side by side. The support member 2 is composed of a knuckle arm or the like.

As shown in FIG. 2, the ball screw 5 has a thread groove 6 provided on the outer periphery of the steering shaft 3 and a thread groove of the steering shaft 3 provided on the inner periphery of a nut 5b loosely fitted to the steering shaft 3. A plurality of balls 8 are interposed between the screw shaft 7 and the screw groove 7 facing the screw shaft 6, and the steering shaft 3 partially or wholly serves as the screw shaft 5a. The ball screw 5 has a circulation path (not shown) for circulating the ball 8 interposed between the screw grooves 6 and 7.
This circulation path connects the both ends of the spiral rolling path 9 formed between the screw grooves 6 and 7 to form a circular path, and is a piece provided on the nut 5a, a return tube, or the like. It is composed of a circulation member (not shown).

The motor 4 is provided with a speed reducer and is composed of a motor section 4a and a speed reducer section 4b. Motor part 4
Reference numeral a denotes a rotor 10 and a stator 11, and the stator 11 is installed in the motor housing 12. The rotor 10 is formed in a cylindrical shape, and the steering shaft 3 penetrates therethrough in a loosely fitted state. The speed reducer unit 4b reduces the speed of rotation of the rotor 10 and transmits it to the nut 5b that serves as a motor output shaft and the like. For the speed reducer unit 4b, for example, a planetary gear type speed reducer is used. The motor 4 may not have the speed reducer section 4b. In that case, the nut 5b is directly connected to the rotor 10.

The sectional shapes of the thread grooves 6 and 7 of the ball screw 5 are, for example, a Gothic arch shape (a shape in which two arcs are combined at the groove bottom), as shown in an enlarged view in FIG. A contact angle and a lead angle are set for these thread grooves 6 and 7, as described below. Contact angles α ₁ , α ₂ (α ₁ = α ₂ ) between the ball 8 and the thread groove 6 of the steering shaft 3
Is the contact angle θ ₁ between the ball 8 and the thread groove 7 of the nut 5a,
It is larger than θ ₂ (θ ₁ = θ ₂ ). The degree of increase is appropriately designed according to the required performance. The size of the contact angle can be appropriately set by changing the curvatures of the arcs forming the cross sections of the screw grooves 6 and 7, or by changing the opening angles of the two arcs. The range of the contact angles α ₁ and α ₂ of the thread groove 6 on the shaft side is, for example, 35
It is set to ° to 40 °. The contact angles θ ₁ and θ ₂ of the thread groove 7 on the nut side are, for example, 50 ° to 55 °. Also,
When the contact angles α ₁ and α ₂ of the thread groove 6 are set to 30 ° to 45 °, the contact angle α ₁ and α ₂ are set to a range larger than this by about 10 ° to 20 °.
The contact angles θ ₁ and θ _{2 of the} thread groove 7 are set. The contact angles α ₁ , α ₂ , θ ₁ , and θ ₂ described above are target angles.

As shown in FIG. 2, the lead angle β of the rolling path 9
Is preferably smaller than an angle generally adopted, and is set to, for example, 5 ° or less. As a specific example, when the shaft diameter is 25 and the lead of the rolling passage 9 is 6 mm, the lead angle of the rolling passage 9 is 4 ° 12 '. Shaft diameter is φ25,
When the lead of the rolling passage 9 is 4 mm, the lead angle of the rolling passage 9 is 2 ° 48 '.

The operation of the above configuration will be described. 1 and 2, the rotation of the rotor 10 of the motor 4 is transmitted to the nut 5b of the ball screw 5, and the rotation of the nut 5a causes the steering shaft 3 forming the screw shaft 5a to move in the axial direction. By this axial movement, the direction of the wheel 1 is steered via the support member 2. Since the rotation of the motor 4 is transmitted to the steering shaft 3 via the ball screw 5, the operating efficiency is higher and the loss is smaller than that of the slide screw, and the motor 4 can be small in size. Although the ball screw 5 is used, the contact angles α ₁ and α ₂ of the thread groove 6 on the shaft side are larger than the contact angles θ ₁ and θ ₂ of the thread groove 7 on the nut side, so that the reverse efficiency is low. Even when the vehicle steering device A receives an external force such as when the vehicle receives a side wind, it is difficult for the rotor 11 of the motor 4 to rotate due to the external force.
It is possible to ensure stable vehicle steering.

The shaft side screw groove contact angles α ₁ and α ₂ are set to the nut 5
By making it larger than the contact angles θ ₁ and θ ₂ of the screw groove of a, the reverse efficiency can be improved by using a general ball screw (α ₁ = α ₂ = θ ₁ =
It can be reduced by, for example, about 10 to 20% compared to θ ₂ ). In order to improve the steering of the steering wheel, it is preferable to further reduce the reverse efficiency, and the lead angle β (Fig. 2) is set small. If the lead angle β is 5 ° or less,
As shown in FIGS. 5 and 6, both the normal efficiency and the reverse efficiency are significantly reduced. FIG. 5 and FIG. 6 are catalog values (“precision ball screw” manufactured by NTN Corporation) for general ball screws. When the lead angle β is reduced from 4 ° 12 'to 2 ° 48' as in the above specific example, the reverse efficiency is 10% from FIG.
It can be seen that it decreases to some extent. By taking the two measures of the contact angle and the lead angle, it becomes possible to reduce the reverse efficiency by, for example, 20 to 30% as compared with a general ball screw. By reducing the reverse efficiency in this way, the steering stability is ensured to a satisfactory level.

Although reducing the lead angle β reduces the positive efficiency, the contact angles α ₁ , α ₂ ,
By setting the relationship between θ ₁ and θ ₂ , the positive efficiency is, for example, 1
Since it is improved by about 0 to 20%, even if the lead angle β is reduced, the positive efficiency is not significantly reduced as compared with a general ball screw.

Further, in the case of the ball screw 5, the reverse efficiency also has a high value to some extent, so even if the motor 4 fails and the nut 5a cannot be rotated, the thrust force from the wheel 1 causes The nut 5a can be returned to the neutral position. Therefore, it is not necessary to provide a mechanism for forcibly returning the nut 5a to the neutral position.

FIG. 4 is a block diagram showing a conceptual configuration of an ARS system for an automobile which employs the vehicle steering system A having the above configuration. An automobile equipped with this ARS system is one in which main steering is performed by the front wheels 1F, 1F, and the rear wheels 1R,
The vehicle steering system A having the above configuration is used as a device for steering the 1R. In this ARS system, the control unit 13 includes a wheel speed sensor 14 and a steering angle sensor 15
The wheel speeds and steering amounts of the front wheels 1F, 1F are monitored via the, and the motor 4 of the vehicle steering system A is driven according to the monitoring result. As a result, the steering of the rear wheels 1R, 1R is electronically controlled so that the running stability of the vehicle is improved, for example, the target vehicle body slip angle is always maintained. It should be noted that the control unit 13 may use, as an input for controlling the rear wheel steering amount, other detected values such as yaw rate in addition to the wheel speed and the like.

As described above, when the vehicle steering system A having the above-mentioned structure is adopted in the ARS system of an automobile, the motor 4 is a small-sized wheel steering system A having a compact structure and the rear wheels 1R,
The steerability of 1R can be improved, and it becomes possible to deal with the case where the nut 5b of the wheel steering device A cannot be rotated due to the failure of the motor 4.

[0023]

According to the vehicle steering system of the present invention, a steering shaft for steering a wheel, a nut having a thread groove on the inner circumference facing a thread groove provided on the outer circumference of the steering shaft, the steering shaft and the nut. And a plurality of balls arranged in a rolling path formed between the ball and the ball, wherein the wheel is steered by rotating the nut by a motor to advance and retreat the steering shaft. The contact angle between the screw groove of the steering shaft and the steering shaft is larger than the contact angle between the ball groove and the screw groove of the nut.Therefore, in the screw mechanism section, high operation efficiency is obtained during normal operation, and the motor can be downsized, and At the time of operation, the operation efficiency is low and the steering stability is stable. Further, in the event of a motor failure, it is possible to return to the neutral position by the thrust from the tires, and there is no need to provide another mechanism for forcibly returning. If the lead angle of the rolling path is 5 ° or less, the operating efficiency will be significantly reduced, and the reverse efficiency will be further reduced in combination with the configuration in which the contact angle of the thread groove is larger than the contact angle of the thread groove of the nut. The steering stability is improved. The wheel steering device of the present invention performs main steering by monitoring front and rear wheel speeds and steering amount of a vehicle performed by front wheels, and electronically controls rear wheel steering so as to improve traveling stability of the vehicle according to the monitoring result. When used as a device for steering the rear wheels in the system, the motor is a small-sized and compact wheel steering device, which can improve the steerability of the rear wheels and can cope with a motor failure.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view of a vehicle steering system according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the vehicle steering system.

FIG. 3 is an enlarged sectional view of a ball screw rolling path in the vehicle steering system.

FIG. 4 is an explanatory diagram of an example of an ARS system using the vehicle steering system.

FIG. 5 is a graph showing the relationship between the lead angle of a ball screw and the positive efficiency.

FIG. 6 is a graph showing the relationship between the lead angle of a ball screw and the reverse efficiency.

[Explanation of symbols]

1, 1F, 1R ... Wheels 3 ... Steering shaft 4 ... Motor 5 ... Ball screw 5a ... Screw shaft 5b ... Nut 6 ... Screw shaft thread groove 7 ... Nut thread groove 8 ... Ball 9 ... Rolling path A ... Wheel steering Device α ₁ , α ₂ , θ ₁ , θ ₂ … Contact angle β: Lead angle

Claims (3)

[Claims] 1. A steering shaft for steering a wheel, a nut having a thread groove formed on the inner circumference thereof, the thread groove facing the thread groove provided on the outer periphery of the steering shaft, and a rolling shaft formed between the steering shaft and the nut. A wheel steering device, comprising: a plurality of balls arranged in a moving path, for steering a wheel by rotating the nut with a motor to advance and retreat the steering shaft, wherein: A wheel steering device characterized in that a contact angle is made larger than a contact angle between a ball and a thread groove of a nut. 2. The wheel steering system according to claim 1, wherein the lead angle of the rolling path is 5 ° or less. 3. A system for electronically controlling steering of rear wheels so as to improve the running stability of the vehicle according to a result of monitoring, by monitoring front and rear wheel speeds and steering amounts of a vehicle in which main steering is performed by front wheels. The wheel steering device according to claim 1 or 2, which is used in a device that steers rear wheels.