JP2010132036A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device being smoothly operated even at the lowest use allowance temperature. <P>SOLUTION: The steering device 12 is constituted such that a nut 44 formed with a female screw is thread-engaged with a male screw formed on a steering rod 32 and rotation force is given to the nut by a motor. A material having larger linear expansion coefficient than an inner race 52 of a bearing 50 for retaining the nut and the steering rod is used for the nut. A pressure-fitting margin of the nut to the inner race and a clearance of the male screw and the female screw are adjusted such that the pressure-fitting margin does not become 0 and the clearance does not become 0 even at the lowest use allowance temperature. A contraction amount difference of an outer diameter of the nut and an inner diameter of the inner race by temperature variation and a contraction amount difference of the male screw and the female screw are compensated to absorb variation of the clearance. Even at the lowest use allowance temperature, therefore, the nut is firmly retained to the inner race and smooth relative action of the nut and the steering rod is ensured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle steering apparatus.

In recent years, a so-called power steering system, that is, a system that assists steering of a wheel by an actuator disposed in a steering device is generally used. In addition, a so-called steer-by-wire type steering system, that is, a system that steers a wheel exclusively by the force of an actuator without depending on an operation force input to an operation member such as a steering wheel has been proposed. In these power steering systems and steer-by-wire type steering systems, a motor is used as a power source for the actuator of the steering device. In a certain type of steering device, the rotation of the motor rotates the nut, The rotation is converted into the movement of the steered rod in the axial direction, so that a steered force is applied to the wheels. In order to convert the rotation of the nut into movement of the steered rod in the axial direction, a screw mechanism including a male screw and a nut is used. In such a steering apparatus, when the component member in which the male screw is formed and the component member in which the female screw is formed use materials having different linear expansion coefficients, when the environmental temperature changes, the male screw and the female screw are respectively Expands or contracts to different degrees. In the following Patent Document 1, in the screwing of the male screw and the female screw used for adjusting the position of the steering shaft, a material having a larger linear expansion coefficient is used for the component member on which the male screw is formed than on the component member on which the female screw is formed. In such a case, a technique is disclosed in which expansion of the external thread when the temperature rises is released by a slit provided in the internal thread.
JP 2001-315648 A

  On the other hand, when the component in which the male screw is formed uses a material having a smaller linear expansion coefficient than the component in which the female screw is formed, a clearance is provided between the male screw and the female screw during assembly. However, when the environmental temperature decreases from the time of assembly, the clearance is reduced because the female screw is more contracted than the male screw. When this clearance is 0 or less, a large frictional force is generated between the male screw and the female screw, and smooth relative movement between the male screw and the female screw is hindered. An object of the present invention is to provide a steered device in which smooth relative motion between a male screw and a male screw is ensured even at a minimum temperature at which use is permitted (hereinafter sometimes referred to as “minimum allowable use temperature”). And

  In order to solve the above-described problem, a vehicle steering apparatus according to the present invention includes (A) a steering rod in which both ends are connected to left and right wheels and male threads are formed on the outer periphery, and (B) the A housing that holds the steered rod movably in its axial direction, (C) a nut formed on the inner periphery of the steered rod, and a screw that engages with the male screw of the steered rod, and (D) is fixed to the housing A radial bearing for holding the nut in the housing in a state in which the outer race and the inner race into which the outer peripheral portion of the nut is press-fitted are permitted, while the nut is allowed to rotate and the movement in the axial direction is prohibited. ) A vehicle steering device that includes an actuator that is held in a housing and moves the steering rod in the axial direction by applying a rotational force to the nut, the nut being more wire-line than the inner race and the steering rod. Expansion coefficient Even at the lowest temperature at which the turning device is allowed to be used, the press-fitting allowance between the outer periphery of the nut and the inner race does not become zero, and the clearance between the male screw and the female screw does not become zero. It is characterized by being set to.

  When the nut is made of a material having a larger linear expansion coefficient than the inner race, the shrinkage amount of the outer diameter of the nut is smaller than the shrinkage amount of the inner diameter of the inner race when the environmental temperature at which the steering device is used, that is, when the use temperature is lowered. Is also big. On the other hand, when the nut is made of a material having a larger linear expansion coefficient than the steered rod, when the operating temperature decreases, the amount of contraction in the radial direction of the female thread formed on the nut is the male thread formed on the steered rod. It is larger than the amount of shrinkage in the radial direction. Therefore, by adjusting the press-fitting allowance of the nut to the inner race and the clearance between the male screw and the female screw, the amount of change in the difference between the shrinkage of the nut outer diameter and the inner race inner diameter can be offset by the change in the press-fit allowance. By doing so, it is possible to absorb the change in the clearance corresponding to the offset. Utilizing this, even at the lowest allowable temperature, the allowance between the outer periphery of the nut and the inner race is not zero, and the clearance between the male screw and the female screw is not zero. Thus, a steering device is realized in which the nut is firmly held by the inner race and the smooth relative motion between the nut and the steering rod is ensured even at the lowest temperature permitted for use.

Embodiment of the Invention

  The “steering device” of the present invention may be used for a so-called power steering system, or may be used for a so-called steer-by-wire type steering system. Here, the power steering system means a system configured to assist the steering of the wheel by an actuator disposed in the steering device, and the steer-by-wire type steering system means a steering. Regardless of the operation force of the driver input to the operation member such as a wheel, the wheel is steered exclusively by the force of the actuator by controlling the actuator of the steering device based on the operation amount of the operation member. Means a system configured in

  The “male screw” and “female screw” constituting the steering device of the present invention are not limited as long as they do not interfere with the use of the steering device. The screw mechanism of the steered apparatus constituted by these male and female screws is required to have a small friction for smooth operation and to be strong for transmitting a large force. From this point of view, it is desirable to employ “trapezoidal screws” for the male screw and the female screw in the steering device of the present invention.

  The “radial bearing” which is a component of the steering device of the present invention is an inner race, that is, an inner ring into which a nut is press-fitted, and is held rotatably with respect to an outer race, that is, an outer ring fixed to a housing. There is no limitation on the type.

  The “actuator”, which is a component of the steering apparatus of the present invention, may employ, for example, an electric motor as a power source, or employ anything other than an electric motor such as a hydraulic motor as a power source. It may be a thing.

  Regarding the material of the “nut”, “steering rod”, which is a component of the steering device of the present invention, and “inner race”, which is a component of the bearing, for example, a copper alloy as the material of the nut, Medium carbon steel or high carbon steel can be used as the material for the steering rod, and bearing steel can be used as the material for the inner race. By adopting different types of materials for the nut and steered rod, smooth sliding between the male screw and the female screw is ensured, and by using different types of materials for the nut and inner race, The nut can be easily press-fitted into the inner race.

  “Press-fit allowance” is a tightening allowance when the nut is press-fitted into the inner race, that is, a value obtained by subtracting the inner peripheral radius of the inner race from the outer peripheral radius of the nut. In other words, the press-fitting allowance can be expressed as minus clearance. That is, the radius of the outer periphery of the nut is larger than the radius of the inner periphery of the inner race, and the clearance thereof is less than zero. Therefore, by providing a pressure margin and inserting the nut into the inner race, they are firmly fastened.

  The “minimum temperature at which the use of the steering device is allowed” means the lowest temperature that can be used in the design (hereinafter sometimes referred to as “the minimum allowable temperature for use”). For example, when the use of the steered device is permitted in a temperature range of −30 ° C. to 40 ° C., the minimum allowable temperature for use is −30 ° C.

  Hereinafter, an embodiment of the claimable invention will be described in detail with reference to the drawings. The claimable invention is not limited to the following embodiments, and can be implemented in various modes with various changes and improvements based on the knowledge of those skilled in the art.

≪A. Configuration of vehicle steering system >>
FIG. 1 schematically shows a steering system provided with a steering apparatus according to an embodiment of the present invention. In the present steering system, the operating device 10 and the steering device 12 according to the embodiment are mechanically separated. The present steering system detects an operation amount of the steering wheel 14 which is a steering operation member included in the operation device 10, determines a turning amount of the steering device 12 based on the detected operation amount, and the determination is made. By electrically controlling the steered device 12 based on the steered amount, the steered wheel 16 (hereinafter, referred to as the steered wheel 16) is driven solely by the driving force of the steered device 12 without depending on the operating force of the driver on the steering wheel 14. It is configured to steer a wheel (sometimes simply referred to as “wheel 16”). That is, this steering system is a so-called steer-by-wire type steering system.

  The operating device 10 includes a steering wheel 14, a shaft 18 having the steering wheel 14 attached to one end thereof, and an operation amount sensor 20 that detects an operation amount of the steering wheel 14 based on a rotational position of the shaft 18. . The operation amount sensor 20 has a structure that detects the rotational position of the shaft 18 with an optical rotary encoder and detects the operation amount based on the detected position.

  The steered device 12 includes a housing 30 and a steered rod 32 that is supported by the housing 30 in a state in which the housing 30 penetrates the housing 30 in the vehicle width direction and cannot rotate with respect to the housing 30. . The steered rod 32 is connected to a tie rod 36 via a ball joint 34 at each of both ends thereof. Each of the tie rods 36 is connected to a knuckle arm 40 fixed to a steering knuckle 38 that rotatably holds the left and right wheels 16. That is, the steered device 12 steers the wheels 16 by moving the steered rod 32 in the axial direction and turning the steering knuckle 38.

  FIG. 2 shows a cross section of the steering device 12. The steered rod 32 has a male screw portion 42 having a male screw formed on the outer peripheral portion. The steered device 12 includes a nut 44 having a female screw formed on the inner peripheral portion thereof and screwed into the male screw portion 42, and a nut. And a steering motor 46 as a power source that constitutes an actuator 47 for applying a rotational force to 44. The steered motor 46 is held by the housing 30 and rotates the nut 44 to move the steered rod 32 in the axial direction thereof. The nut 44 is press-fitted into the inner race 52 of the radial bearing 50, and the outer race 54 of the radial bearing 50 is fixed to the housing 30. Therefore, the nut 44 is rotatable with respect to the housing 30. The steered motor 46 is a so-called brushless motor. The steered motor 46 has a cylindrical shape that allows the steered rod 32 to pass therethrough and is rotatable, and a cylindrical motor shaft 48 provided in the vehicle width direction center of the housing 30. A stator 56 and a rotor 58 provided in a cylindrical shape on the outer peripheral portion of the motor shaft 48 so as to face the inner peripheral surface of the stator 56 are included. The stator 56 is mainly composed of coils, and the rotor 58 is mainly composed of permanent magnets.

  Note that the housing 30 is provided with a steered position sensor 60 that detects the position of the steered rod 32 moved in the vehicle width direction, that is, the steered position. The steered position sensor 60 is bonded to the steered rod 32 in an axially extending posture, and a scale tape 62 in which a large number of detected portions are formed at minute intervals, and the scale tape 62 is fixed to the housing 30. And an optical sensor 64 for detecting the detected portion.

  As shown in FIG. 1, the present steering system is controlled by an electronic control unit 66 (hereinafter sometimes simply referred to as “ECU”). The ECU 66 is mainly configured by a computer including a CPU, a ROM, a RAM, and the like. An operation amount sensor 20 and a steered position sensor 60 are connected to the ECU 66. When the wheel 16 is steered, the ECU 66 obtains the operation amount of the steering wheel 14 based on the detection signal of the operation amount sensor 20, determines the target turning amount based on the operation amount, and turns the steering position. Based on the detection position of the sensor 60, the steering motor 46 is driven to steer the wheels to the target turning amount.

≪B. Relationship between press-fitting allowance and clearance >>
Both the male screw formed on the male screw portion 42 of the steered rod 32 and the female screw formed on the inner peripheral portion of the nut 44 are trapezoidal screws. As shown in FIG. 3, a gap, that is, a clearance is provided between the male screw and the female screw.

  On the other hand, the nut 44 is press-fitted into the inner race 52 of the bearing 50 at the outer peripheral portion thereof. That is, the outer diameter of the nut 44 is larger than the inner diameter of the inner race 52, and the press-fitting allowance ΔF is indicated by a value obtained by subtracting the inner peripheral radius of the inner race 52 from the outer peripheral radius of the nut 44. The nut 44 and the inner race 52 are fastened by a tightening force corresponding to the press-fitting allowance.

The material of the nut 44 is a copper alloy having a linear expansion coefficient α _N of 17.7 × 10 ⁻⁶ / ° C., and the material of the steered rod 32 is carbon having a linear expansion coefficient α _R of 11.0 × 10 ⁻⁶ / ° C. Steel (S45C), and the material of the inner race 52 is a bearing steel having a linear expansion coefficient α _I of 12.5 × 10 ⁻⁶ / ° C. Therefore, the nut 44 has a larger linear expansion coefficient than the steered rod 32 and the inner race 52, and has a greater degree of expansion and contraction with respect to a temperature change than the steered rod 32 and the inner race 52.

As for this steering device 12, the use allowable minimum temperature is set to -30 degreeC, and the use allowable maximum temperature which is the maximum temperature which can be used is set to 40 degreeC. Therefore, the temperature difference between them, that is, the use temperature difference ΔT is set to 70 ° C. The inner race radius R _{I of} the inner race 52 and the outer radius R _N of the nut 44 are 25 mm. Under such dimensions, the inner radius R _I of the inner race 52 and the nut 44 at this operating temperature difference ΔT. the shrinkage of the difference ΔC between the radius R _N of the outer circumference can be calculated by the following equation,
ΔC = ΔT × (R _I × α _I −R _N × α _N )
The difference ΔC in the amount of contraction is about 9 μm. That is, if the operating temperature is 40 ° C., even if the inner radius R _I of the inner race 52 and the outer radius R _N of the nut 44 are set to the same value, at the lowest allowable temperature of −30 ° C. The radius R _N of the outer periphery of the nut 44 is smaller than the radius R _I of the inner race 52 by about 9 μm.

Therefore, when the operating temperature is 40 ° C., the nut 44 is press-fitted into the inner race 52 with a press allowance ΔF of 9 μm, that is, the outer radius R _N of the nut 44 is 9 μm larger than the inner radius R _{I of the} inner race 52. In the case of being press-fitted in a state, when the minimum allowable temperature for use is −30 ° C., the outer radius R _N of the nut 44 and the inner radius R _{I of the} inner race 52 at the minimum allowable temperature −30 ° C. Are exactly the same value, and the press-fit allowance ΔF becomes zero.

On the other hand, the radius R _S of the thread pitch circle between the male screw of the steered rod 32 and the female screw of the nut 44 is 15 mm. Under such dimensions, the clearance change ΔCL at the operating temperature difference ΔT is: Can be calculated by the following equation:
ΔCL = ΔT × R _S × (α _N −α _R )
The clearance change amount ΔCL is about 7 μm. In other words, if the clearance when the steering device 12 is used at a temperature of 40 ° C. is 7 μm, the clearance becomes approximately 0 μm at the lowest allowable temperature of −30 ° C., and the male screw and the female screw are smoothly screwed together. You will not be able to.

In view of the foregoing, and set the inner peripheral radius R _I of the inner race 52 as press-fitting margin ΔF becomes larger than 9μm at 40 ° C. is used allowable maximum temperature, the radius R _N of the outer circumference of the nut 44, and, In the state where the nut 44 is press-fitted into the inner race 52 at 40 ° C., the clearance between the male screw and the female screw is set to be larger than 7 μm. In this case, even if the allowable minimum temperature −30 ° C. is reached, the press-fit allowance ΔF does not become 0, and the nut 44 is firmly held by the inner race 52.

  At the maximum allowable temperature of 40 ° C., the nut 44 is compressed in the radial direction by the press-fitting allowance ΔF. From this state, even if the minimum allowable temperature for use is −30 ° C., the shrinkage difference ΔC is offset by the decrease in the press-fitting allowance ΔF, and therefore the radial shrinkage of the nut 44 is offset by the offset amount. As a result, the inner diameter of the nut 44 does not change much. That is, the amount of change ΔCL in the clearance between the male screw and the female screw is absorbed in proportion to the decrease in the press-fitting allowance ΔF. Incidentally, in this case, even when the allowable minimum temperature is −30 ° C., the clearance does not fall below 7 μm, and the smooth sliding between the male screw and the female screw, that is, the smooth movement between the nut 44 and the steered rod 32 is achieved. Relative motion is guaranteed.

  Therefore, by adjusting the press-fit allowance ΔF to the inner race 52 of the nut 44 and the clearance between the male screw and the female screw, the press-fit allowance ΔF does not become zero even at the lowest allowable temperature and the clearance between the male screw and the female screw. In which the nut 44 is firmly held by the inner race 52 and the smooth relative motion between the nut 52 and the steered rod 32 is ensured even at the lowest allowable temperature. The device 12 realizes it. In the above-described case, the clearance and the press-fitting allowance ΔF are set at the maximum allowable use temperature, but they may be set at any temperature.

It is a figure which shows the outline of the turning apparatus for vehicles which is an Example of claimable invention. It is a schematic diagram which shows the cross section of the said steering apparatus for vehicles. It is the schematic diagram which expanded a part of said steering apparatus for vehicles.

Explanation of symbols

  16: Steering wheel 30: Housing 32: Steering rod 42: Male thread part 44: Nut 46: Steering motor 47: Actuator 48: Motor shaft 50: Radial bearing 52: Inner race 54: Outer race

Claims (1)

Each of both ends are connected to the left and right wheels, and a steered rod with external threads formed on the outer periphery,
A housing for holding the steered rod movably in the axial direction thereof;
A female screw is formed on the inner periphery, and a nut that engages with the male screw of the steered rod;
An outer race fixed to the housing; and an inner race in which an outer peripheral portion of the nut is press-fitted; and the housing is allowed to rotate in the axial direction while allowing the nut to rotate. Radial bearings for holding
A vehicle steering apparatus comprising: an actuator that is held by the housing and moves the steering rod in the axial direction by applying a rotational force to the nut;
The nut is made of a material having a larger linear expansion coefficient than the inner race and the steered rod,
Even at the lowest temperature at which the steering device is allowed to be used, the allowance for press-fitting between the outer peripheral portion of the nut and the inner race is not zero, and the clearance between the male screw and the female screw is not zero. A vehicle steering apparatus characterized by being set.

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