JP2008279808A - Vehicle steering gear - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize a vehicle steering gear. <P>SOLUTION: A steering shaft 3 is composed of an upper shaft 6, a lower shaft 7, an input shaft 8, and an output shaft 9. The upper shaft 6, the lower shaft 7, and the input shaft 8 are mutually connected to rotate together, and the input shaft 8 and the output shaft 9 are mutually connected to rotate relatively through a torsion bar 11. A rotor 21 of an electric motor 5 is connected with the output shaft 9 to rotate together. A rotation position of the rotor 21 is obtained by performing predetermined computation by using a rotation position of the lower shaft 7 detected by an input shaft rotation position detection device 18 and steering torque detected based on amount of relative rotation displacement of the input shaft 8 and the output shaft 9. Since a rotor rotation position detection device for detecting a rotation position of the rotor 21 is not arranged in the inside of the electric motor 5, the vehicle steering gear 1 is miniaturized in the axial direction X1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vehicle steering apparatus used in a vehicle such as an automobile.

As a vehicle steering device used for vehicles such as automobiles, an electric power steering device including an electric motor is known.
As this type of vehicle steering apparatus, there is a so-called direct drive type vehicle steering apparatus in which the output torque of an electric motor is directly transmitted to a steering shaft without passing through a reduction mechanism (see, for example, Patent Document 1).
JP 2005-145436 A

  The vehicle steering device is desired to be small because it is arranged in a vehicle interior that is a limited space. On the other hand, in the direct drive type vehicle steering apparatus, the output torque of the electric motor is not amplified by the speed reduction mechanism, so that an electric motor with a large output is required. Therefore, a large electric motor is often used in the direct drive type vehicle steering apparatus, which is contrary to the demand for downsizing.

  The present invention has been made based on such a background, and an object thereof is to downsize a vehicle steering apparatus.

  In order to achieve the above object, the present invention provides an input shaft (6, 7, 8) having a steering member (2) connected to one end and the other end of the input shaft connected via a torsion bar (11). An output shaft (9), a steering torque detecting means (12) for detecting a steering torque based on the relative rotational displacement of the input shaft and the output shaft, and a rotor (21) that can rotate coaxially with the output shaft. The steering assisting electric motor (5), the input shaft rotational position detecting means (18) for detecting the rotational position of the input shaft, and the rotational position and steering of the input shaft detected by the input shaft rotational position detecting means. A vehicle steering apparatus comprising: a rotor rotational position calculating means (33) for obtaining the rotational position of the rotor based on the steering torque detected by the torque detecting means. 1).

According to the present invention, the rotational position of the rotor can be detected using the outputs of the input shaft rotational position detecting means and the steering torque detecting means. That is, it is not necessary to arrange the rotor rotational position detecting means for detecting the rotational position of the rotor inside the electric motor, so that the electric motor can be downsized in the axial direction, and as a result, the vehicle steering device can be downsized. can do.
Further, the input shaft rotation position detecting means may be disposed to face the input shaft in the radial direction of the input shaft. In this case, the vehicle steering apparatus can be further miniaturized by efficiently using the space around the input shaft by disposing the input shaft rotation position detecting means around the input shaft having a sufficient space.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an electric power steering apparatus 1 according to an embodiment of the present invention. FIG. 2 is a schematic enlarged sectional view of a part of the electric power steering apparatus 1.
Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 to which a steering member 2 such as a steering wheel is coupled, a cylindrical steering column 4 that rotatably supports the steering shaft 3, and a steering shaft. 3 and a steering assisting electric motor 5 that are coaxially connected to each other.

The steering shaft 3 is constituted by a plurality of shafts extending linearly. That is, the steering shaft 3 is constituted by the upper shaft 6, the lower shaft 7, the input shaft 8 and the output shaft 9. Each of the shafts 6 to 9 is a cylindrical shaft extending linearly, and is disposed on the same axis.
A steering member 2 is connected to one end (upper end in FIG. 1) of the upper shaft 6 so as to be able to rotate together. Further, a steering mechanism 10 made of, for example, a rack and pinion mechanism is connected to one end (lower end in FIG. 1) of the output shaft 9 via an intermediate shaft (not shown). The steering member 2 and the steering mechanism 10 are mechanically connected via a steering shaft 3 and the like.

In the following, the steering member 2 side along the axial direction X1 of the steering shaft 3 is defined as the upper side, and the steering mechanism 10 side is defined as the lower side.
On the inner periphery of the lower end portion of the upper shaft 6, the upper end portion of the lower shaft 7 is, for example, serrated. The upper shaft 6 and the lower shaft 7 are coupled so as to be able to rotate together and to be relatively movable in the axial direction X1 of the steering shaft 3.

On the other hand, the input shaft 8 and the output shaft 9 are connected via a torsion bar 11 so as to be relatively rotatable. The torsion bar 11 is inserted through the inner periphery of the input shaft 8 and the output shaft 9. An upper end portion and a lower end portion of the torsion bar 11 are coupled to the input shaft 8 and the output shaft 9 so as to be able to rotate together.
The lower end portion of the input shaft 8 is fitted into the inner periphery of the upper end portion of the output shaft 9. Further, the upper end portion of the input shaft 8 is connected to the lower end portion of the lower shaft 7. The input shaft 8 and the lower shaft 7 can rotate together. That is, the upper shaft 6, the lower shaft 7 and the input shaft 8 can be rotated together. In the present embodiment, these three shafts 6 to 8 function as input shafts.

When rotational torque (steering torque) about its axis is input to the input shaft 8 via the steering member 2, the upper shaft 6 and the lower shaft 7, the torsion bar 11 is elastically torsionally deformed with a magnitude proportional to the steering torque. However, the rotational torque is transmitted to the output shaft 9. As a result, the output shaft 9 rotates about its axis.
A torque sensor 12 (steering torque detection means) provided in the vicinity of the fitting portion between the input shaft 8 and the output shaft 9 is based on a change in magnetic resistance caused by relative rotation of the input shaft 8 and the output shaft 9. The steering torque input to is detected. Specifically, the torque sensor 12 detects the change amount delta R of the change in magnetic resistance caused by the relative rotation of the input shaft 8 and the output shaft 9, and the steering torque T is calculated from the detected value and the following formula 1. Is detected.

(Formula 1) T = Ct * Delta R (Ct is a proportional constant)
Further, since the magnetic resistance change amount delta R is a value proportional to the relative rotational displacement amount delta θ of the input shaft 8 and the output shaft 9, the magnetic resistance change amount delta R uses the relative rotational displacement amount delta θ. Is represented by the following formula 2.
(Formula 2) Delta R = Cr * Delta θ = Cr (θi−θo)
Cr represents a proportional constant, θi represents the rotational position (absolute position) of the input shaft, and θo represents the rotational position (absolute position) of the output shaft.

Therefore, when the above formula 2 is substituted into the above formula 1, the following formula 3 is obtained.
(Formula 3) T = C (θi−θo) (C = Ct * Cr)
The torque detection result of the torque sensor 12 is input to an ECU 13 (Electronic Control Unit).
When the steering member 2 is operated (rotated), the shafts 6 to 9 rotate in the same direction while the input shaft 8 and the output shaft 9 rotate relative to each other. This rotation is transmitted to a pinion shaft (not shown) and converted into an axial movement of a rack shaft (not shown) that meshes with the pinion shaft. Thereby, the turning of a steered wheel (not shown) is achieved.

The steering column 4 includes a cylindrical upper column 14 and a lower column 15 that extend linearly, and a cylindrical sensor housing 16 in which the torque sensor 12 is accommodated on the inner periphery. The upper column 14, the lower column 15, and the sensor housing 16 are disposed on the same axis.
The upper column 14 and the lower column 15 are connected so as to be relatively movable in the axial direction of the steering column 4 (in FIG. 1, the same direction as the axial direction X1). When the upper column 14 and the lower column 15 are relatively moved in the axial direction X1, resistance is applied to one or both of the upper column 14 and the lower column 15. The upper end of the sensor housing 16 is fitted to the inner periphery of the lower end of the lower column 15. The sensor housing 16 and the lower column 15 are fixed to each other.

  The steering shaft 3 is inserted through the inner periphery of the upper column 14, the lower column 15 and the sensor housing 16. The steering shaft 3 is rotatably supported by the steering column 4 via a plurality of bearings. A hollow annular space S extending in the axial direction X1 surrounding the steering shaft 3 and surrounded by the upper column 14 and the lower column 15 is formed above the sensor housing 16 in the axial direction X1.

  The steering column 4 is fixed to the vehicle body side member 100 with a predetermined fixing strength by a first bracket 17 fixed to the upper column 14. Specifically, the first bracket 17 is attached to the vehicle body side member 100 via, for example, a breakable synthetic resin pin 17a. If an impact of a predetermined value or more is applied to the first bracket 17 during a vehicle collision, the pin 17a is broken and the upper column 14 and the vehicle body side member 100 are released from being fixed. As a result, the steering member 2, the upper shaft 6, the upper column 14, and the like can move downward in the axial direction X <b> 1 with respect to the vehicle body side member 100.

  Further, an input shaft rotational position detection device 18 as an input shaft rotational position detecting means for detecting the rotational position (absolute position) of the lower shaft 7 which is a part of the input shaft is disposed on the inner periphery of the lower column 15. Has been. Specifically, an annular rotor 19 is connected to the outer periphery of the lower shaft 7 so as to be able to rotate along with it, and the stator 20 is fixed to the inner periphery of the lower column 15 so as to surround the rotor 19. The input shaft rotational position detection device 18 includes a rotor 19 and a stator 20.

  The input shaft rotational position detector 18 can detect the rotational position of the lower shaft 7 based on the relative rotational displacement amount of the rotor 19 and the stator 20. Further, the input shaft rotation position detection device 18 can detect the rotation position θi of the input shaft 8 by detecting the rotation position of the lower shaft 7. The detection value (θi) detected by the input shaft rotational position detection device 18 is input to the ECU 13.

Note that the input shaft rotational position detection device 18 is not limited to the above, and other rotational position detection devices such as a rotary encoder may be used.
With reference to FIG. 2, the electric motor 5 according to the present embodiment is a brushless motor. The electric motor 5 includes a cylindrical rotor 21 that coaxially surrounds the steering shaft 3, an annular stator 22 that coaxially surrounds the rotor 21, and a cylindrical motor housing 23 that houses the rotor 21 and the stator 22. Including.

The rotor 21 holds a plurality of permanent magnets 24 on the outer periphery thereof. The outer periphery of the rotor 21 is a magnetic pole in which the N pole and the S pole are alternately switched. The rotor 21 is coupled to the output shaft 9 so as to be able to rotate together. The output shaft 9 functions as a rotating shaft of the electric motor 5.
The stator 22 includes an annular stator core 25 and a plurality of coils 26 wound around the stator core 25. The stator core 25 is held by the motor housing 23 at a position where the inner peripheral surface thereof faces the outer peripheral surface of the rotor 21. Although not shown, the stator core 25 includes an annular yoke and a plurality of teeth protruding inward in the radial direction from the inner periphery of the yoke. The plurality of coils 26 are wound around a plurality of teeth, respectively. Electric power from a power supply source (not shown) is supplied to each coil 26. Supply of electric power to each coil 26 is controlled by the ECU 13.

The motor housing 23 includes a cylindrical peripheral wall portion 27 that coaxially surrounds the steering shaft 3, and an annular lid member 28 fixed to the lower end portion of the peripheral wall portion 27. The stator core 25 is coaxially fixed to the inner peripheral surface of the peripheral wall portion 27. Further, the lower end portion of the sensor housing 16 is fixed to the upper end portion of the peripheral wall portion 27.
The lid member 28 has a peripheral edge fixed to the lower end of the peripheral wall 27. The output shaft 9 is inserted through an insertion hole provided at the center of the lid member 28. Further, a second bracket 29 fixed to the vehicle body side member 100 is fixed to the lid member 28. The motor housing 23 is fixed to the vehicle body side member 100 by the second bracket 29.

  The electric motor 5 is controlled by the ECU 13. That is, the ECU 13 controls the electric motor 5 based on the torque detection result of the torque sensor 12, the vehicle speed detection result of the vehicle speed sensor 30 (see FIG. 1), and the like. When the ECU 13 controls the electric motor 5, output torque as steering assist force is directly transmitted from the electric motor 5 to the steering shaft 3. Thus, the steering assist force is transmitted to the steering mechanism 10 to assist the driver's steering.

Next, the control of the electric motor 5 by the ECU 13 will be described in detail.
FIG. 3 is a block diagram relating to the control of the electric motor 5 by the ECU 13.
Referring to FIGS. 1 and 3, ECU 13 includes a control circuit 31 that performs a predetermined calculation and a drive circuit 32 that controls the supply of electric power to electric motor 5. In addition, the control circuit 31 includes a rotor rotation position calculation unit 33 as a rotor rotation position calculation unit that calculates the rotation position (absolute position) of the rotor 21 and a target current value calculation that calculates a target current value to be supplied to the electric motor 5. Part 34.

  The rotor rotational position calculation unit 33 calculates the rotational position of the rotor 21 based on the steering torque T input from the torque sensor 12 and the rotational position θi of the input shaft 8 input from the input shaft rotational position detector 18. Ask. Specifically, for example, the rotor rotational position calculation unit 33 calculates the rotational position of the output shaft 9 based on the following expression 4 obtained by transforming the expression 3 and the input steering torque T and the rotational position θi. Obtain θo.

(Formula 4) θo = θi−T / C
That is, the rotational position θo of the output shaft 9 is obtained based on the rotational position θi of the input shaft 8 and the steering torque T. Further, in the present embodiment, the rotor 21 and the output shaft 9 are connected so as to be able to rotate together, so that the rotational position of the rotor 21 is obtained by obtaining the rotational position θo of the output shaft 9. .

  On the other hand, the target current value calculation unit 34 is based on the steering torque input from the torque sensor 12, the vehicle speed input from the vehicle speed sensor 30, etc., and the steering assist force (electric motor 5) transmitted from the electric motor 5 to the output shaft 9. Is calculated and calculated. Then, the target current value calculation unit 34 calculates and obtains a target current value corresponding to the obtained magnitude of the steering assist force.

  The drive circuit 32 receives the rotational position of the rotor 21 obtained by the rotor rotational position computing unit 33 and the target current value obtained by the target current value computing unit 34. Then, the drive circuit 32 supplies the electric motor 5 with the current having the target current value by, for example, PWM control. Specifically, the energization state of the coil 26 is controlled by switching ON / OFF of a semiconductor switching element such as an FET based on the rotational position of the rotor 21. Further, the current value supplied to the electric motor 5 is detected by a current detection device (not shown), and the current value supplied to the electric motor 5 is corrected based on this detected value. The value is controlled to be the target current value. As a result, the steering assist force having the magnitude obtained by the target current value calculation unit 34 is transmitted to the output shaft 9 to assist the driver's steering.

  As described above, in this embodiment, the rotational position of the rotor 21 can be detected by the input shaft rotational position detection device 18, the torque sensor 12, and the ECU 13. That is, in this embodiment, since it is not necessary to provide a device such as a resolver for detecting the rotational position of the rotor inside the electric motor as in the prior art, the electric motor 5 can be downsized in the axial direction X1, As a result, the electric power steering device 1 can be reduced in size in the axial direction X1.

  In addition, an input shaft rotational position detection device 18 for detecting the rotational position of the lower shaft 7 that is a part of the input shaft is disposed above the electric motor 5 in the axial direction X1, and the lower shaft 7 and the lower column 15 The electric power steering device 1 can be further downsized in the axial direction X1 by efficiently using the space S.

  The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims. For example, in the above-described embodiment, the example in which the rotational position of the rotor 21 is obtained using the above equation 4 has been described, but the method for obtaining the rotational position of the rotor 21 is not limited to this. For example, the rotational position of the rotor 21 may be obtained using an expression other than the above expression 4, or a known torque sensor other than the torque sensor described above may be used as the torque sensor 12.

  For example, when a torque sensor that can directly detect the relative rotational displacement amount delta θ between the input shaft 8 and the output shaft 9 is used, the relative rotation is determined from the rotational position θi of the input shaft 8 detected by the input shaft rotational position detector 18. By subtracting the displacement amount delta θ, the rotational position of the rotor 21 can be obtained (θo = θi−delta θ). In this case, the calculation for obtaining the rotational position of the rotor 21 is easy.

  Moreover, although the above-mentioned embodiment demonstrated the example which detects the rotational position of the lower shaft 7 by the input shaft rotational position detection apparatus 18, it is not restricted to this. For example, the input shaft rotational position detection device 18 may be disposed around the upper shaft 6 to detect the rotational position (absolute position) of the upper shaft 6. That is, the input shaft rotational position detection device 18 only needs to detect the rotational position of any shaft (the upper shaft 6, the lower shaft 7, or the input shaft 8) that constitutes the input shaft. Further, when a steering member rotation position detection device (corresponding to a steering angle sensor) for detecting the rotation position of the steering member 2 is provided, the input shaft rotation position detection device 18 may not be provided. That is, the steering member rotational position detection device may be used as the input shaft rotational position detection means.

  In the above-described embodiment, the example in which the present invention is applied to the so-called column assist type electric power steering apparatus 1 in which the output torque of the electric motor 5 is transmitted to the steering shaft 3 has been described. For example, the present invention may be applied to other vehicle steering devices such as a so-called pinion assist type electric power steering device.

1 is a schematic cross-sectional view showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. It is a schematic expanded sectional view of a part of the electric power steering device. It is a block diagram regarding control of the electric motor by ECU.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device (vehicle steering device), 2 ... Steering member, 5 ... Electric motor, 6 ... Upper shaft (input shaft), 7 ... Lower shaft (input shaft) , 8 ... Input shaft (input shaft), 9 ... Output shaft, 11 ... Torsion bar, 12 ... Torque sensor (steering torque detecting means), 18 ... Input shaft rotational position detecting device ( Input shaft rotation position detection means), 21... Rotor, 33... Rotor rotation position calculation unit (rotor rotation position calculation means)

Claims (2)

An input shaft having a steering member connected to one end;
An output shaft connected to the other end of the input shaft via a torsion bar;
Steering torque detection means for detecting steering torque based on the relative rotational displacement of the input shaft and the output shaft;
An electric motor for assisting steering including a rotor that can rotate coaxially with the output shaft;
Input shaft rotational position detecting means for detecting the rotational position of the input shaft;
A vehicle steering apparatus comprising: a rotor rotational position calculating means for obtaining a rotational position of the rotor based on a rotational position of the input shaft detected by the input shaft rotational position detecting means and a steering torque detected by the steering torque detecting means.   2. The vehicle steering apparatus according to claim 1, wherein the input shaft rotation position detecting means is disposed to face the input shaft in the radial direction of the input shaft.

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