Rotation angle detecting device, and torque detecting device

The rotation angle detecting device includes a target of a spur gear shape made rotatable together with a rotary member and having a plurality of teeth of magnetic members protruding at a substantially equal pitch in the circumferential direction of the axis of the rotary member, and magnetic sensors arranged at positions to confront the teeth for outputting output signals according to the rotation of the rotary member. This device detects the angle of rotation of a rotary member with the output signals from the magnetic sensors. In the target of the spur gear shape, moreover, the two circumferential end portions of the crests of all the teeth are formed into angular portions.

BACKGROUND OF THE INVENTION

The present invention relates to a rotation angle detecting device to be used in an electric power steering device for a vehicle, for detecting the angle of rotation of a rotary member, and to a torque detecting device for detecting a torque to be applied to the rotary member.

As an auxiliary steering device mounted on a vehicle such as an automobile for assisting the steering operation of a driver, there is an electric power steering device for applying a steering assisting force such as the turning force of an electric motor. This electric power steering device is provided with an input shaft and an output shaft, which are so connected to a steering member and steering wheels sides respectively, as to rotate according to the steering operation of the driver. The steering device is provided with a rotation angle detecting device for detecting the respective rotation angles of the input and output shafts, and a torque detecting device for detecting the steering torque to be applied to the steering member by using the detection results of the detecting device. The steering device assists the steering operation by deciding an instruction value to the electric motor on the basis of the detected steering torque and by transmitting the motor turning force to a steering system through a reduction mechanism thereby apply the steering assisting force to the steering system (as referred to JP-A-2002-107112, for example).

Here, the rotation angle detecting device and the torque detecting device are provided with: a target so fixedly fitted on each of the input and output shafts as to rotate together and having a plurality of teeth made of a magnetic material; and a magnetic sensor including magnetoresistive elements for outputting output signals varying periodically according to the rotations of the corresponding input and output shafts. In the devices, the rotation angle can be detected based on the output signals (or its digitized signals, if necessary) from the magnetic sensor and by referring to a table, which is stored in advance with the rotation angle and the output signals of the magnetic sensor in a corresponding manner. On the other hand, the torque can be detected by determining the rotation angle difference (or the relative angle displacement) between the input shaft and the output shaft using the output signal (or its digitized signal, if necessary) from the magnetic sensor on the input shaft side and the output signal (or its digitized signal, if necessary) from the magnetic sensor on the output shaft side, and by calculating the relative angle displacement. In these devices, moreover, the target or the objective to be detected by the magnetic sensor uses a spur gear54, in which the side faces51of a tooth are formed into an involute curve (as seen in a top plan view, as in the following) and in which the two end portions53of a tooth crest52are formed into a smooth curve.

However, the involute-shaped gear54generally has a main object to effect the power transmission by a meshing engagement and is worked to form the two end portions53of the tooth crest52into the gentle curve having no angular portion because it is intended to eliminate a failure such as chip. Therefore, a problem is that it is difficult to make the shapes of all teeth identical in an excellent size precision. On the other hand, the output signals from the magnetic sensors are decided mainly by the distance from the tooth crest52so that the target is generally tested with the tooth pitch. In the case of the involute gear54, however, it is necessary to measure the tooth pitch L, as shown inFIG. 7, by supporting virtual corner portions61. This necessity raises a problem that the target or the objective of the sensor detection is hard to test.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of the background thus far described and has an object to provide a rotation angle detecting device capable of easily testing and a torque detecting device using the that device. Another object is to provide a rotation angle detecting device, which is not only easy in test but also inexpensive, and a torque detecting device using that device.

In order to solve the aforesaid object, the invention is characterized by having the following arrangement.(1) A rotation angle detecting device comprising:

a target having a spur gear shape rotatable together with a rotary member, the target including,a plurality of magnetic teeth protruding at a substantially equal pitch in a circumferential direction of an axis of the rotary member, wherein each of the magnetic teeth are defined by a pair of side faces, and a crest surface between the side faces in the circumferential direction, andangular portions formed at boundaries between the side faces and the crest surfaces of all of the teeth; and

magnetic sensors arranged so as to confront the plurality of teeth for outputting output signals according to a rotation of the rotary member, thereby to detect a rotation angle of the rotary member based on the output signals.(2) The rotation angle detecting device according to (1), wherein the side faces are flat.(3) The rotation angle detecting device according to (1), wherein a bottom land and the corresponding side faces which are disposed between the adjacent two teeth constitute an arcuate face recessed radially.(4) A torque detecting device comprising:

a rotation member including a first rotary shaft and a second rotary shaft connected coaxially to the first rotary shaft;

rotation angle detecting devices provided to the first and second rotary shafts, respectively, each of the rotation angle detecting devices including,a target having a spur gear shape rotatable together with a rotary member, the target including,a plurality of magnetic teeth protruding at a substantially equal pitch in a circumferential direction of an axis of the rotary member, wherein each of the magnetic teeth are defined by a pair of side faces, and a crest surface between the side faces in the circumferential direction, andangular portions formed at boundaries between the side faces and the crest surfaces of all of the teeth;

magnetic sensors arranged so as to confront the plurality of teeth for outputting output signals according to a rotation of the rotary member, thereby to detect a rotation angle of the rotary member based on the output signals; and

a torque detecting unit for detecting a torque to be applied to the rotary member based on signals outputted from the corresponding rotation angle detecting devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A rotation angle detecting device and a torque detecting device according to a preferred embodiment of the invention will be described with reference to the accompanying drawings. Here in the following description, the invention is applied to an electric power steering.

FIG. 1is a diagram schematically showing a construction of an essential portion of the electric power steering device including the rotation angle detecting device and the torque detecting device according to the embodiment of the invention. The electric power steering device is so mounted on an automobile, for example, that a steering shaft3is interposed between a steering member (or steering wheel)1and a pinion2. The steering shaft3is provided with: a torsion bar31disposed at the center of the steering shaft3; an input shaft32acting as a first rotary shaft and fixed to the input (upper) side of the torsion bar31; and an output shaft33acting as a second rotary shaft and fixed to the output (lower) side of the torsion bar31. The input shaft32and the output shaft33are arranged coaxially with each other and is connected to each other not directly but through the torsion bar31.

The steering member1is connected to the input shaft32so that the rotation of the steering member1by the steering operation of a driver is transmitted directly to the input shaft32.

A reduction mechanism having a worm5and a worm wheel4meshing with the worm5; and a steering assisting electric motor6having an output shaft, on which the worm5is mounted integrally rotatably therewith, and controlled by a control unit21are connected to the output shaft33. The rotation of the electric motor6is reduced and transmitted as a steering assisting force to the pinion2. The rotation of the pinion is converted into linear motions of a rack7thereby to steer steering wheels9through left and right tie rods8. The reduction mechanism and the electric motor6constitute an auxiliary steering unit for applying the steering assisting force to a steering system leading from the steering member1to the steering wheels9.

The input shaft32and the output shaft33are provided with targets and magnetic sensors, which are included in the rotation angle detecting device and the torque detecting device of the invention, for outputting output signals corresponding to the input and output shafts32and33which rotate according to the steering operation on the steering member1.

With reference toFIG. 2, a first target gear34of a spur gear shape is so fixedly fitted on the input shaft32as to rotate together. A pair of first magnetic sensors A1and B1are arranged at positions to confront the teeth of the target34and are spaced in the circumferential direction. Likewise, second and third target gears35and36are so fixedly fitted on the output shaft33as to rotate together. A pair of second magnetic sensors A2and B2are arranged at positions to confront the teeth of the target35and are spaced in the circumferential direction, and a pair of third magnetic sensors A3and B3are arranged at positions to confront the teeth of the target36and are spaced in the circumferential direction.

The first to third targets34to36are formed into the shape of a spur gear, in which a plurality of teeth of a magnetic material protrude at a substantially equal spacing in the circumferential direction. The tooth numbers of the first target34and the second target35are equal at N (e.g.,36), and the tooth number of the third target36is a prime (e.g.,35) (having no common divisor other than 1) to N.

The teeth of the targets34to36have angular portions at the two end portions in the circumferential direction on their crests. In the related art, specifically, the tooth side faces of the targets34to36are formed into an involute curve so that the two end portions of the tooth crests are not formed into the angular portions but into a gentle curve, but these angular portions are formed in the invention. As a result, the tooth pitch can be directly measured with reference to those angular portions so that the targets can be simply inspected.

More specifically, the target34is made arcuate not only at its tooth crest71but also at its bottom land72, as shown in FIG.3. Tooth side faces73are formed flat. The two circumferential end portions74of the tooth crest71, that is, the boundaries (or ridgelines) between the tooth crest71and the tooth side faces73are formed into the angular portions. As a result, a tooth pitch L can be directly measured with reference to the two angular end portions74, as shown in FIG.3.

This target34can be simply manufactured, for example, by subjecting a disc of a magnetic material to the gear cutting, press working or sintering treatment using a milling machine.

Here, the targets35and36can be likewise manufactured so that their description is omitted.

Reverting to FIG.1andFIG. 2, the first to third magnetic sensors A1and E1, A2and B2, and A3and B3, as arranged at positions to confront the first to third targets34to36, are arranged in three steps and two rows and are housed in a sensor box10. This sensor box10is fixed at a predetermined position of a vehicle body and can keep a gap at a predetermined distance between the first to third targets34to36and the first to third magnetic sensors A1and B1, A2and B2, and A3and B3. Here, the pair of first magnetic sensors A1and B1are arranged in the state spaced from each other. Likewise, the pair of second magnetic sensors A2and B2are arranged in the state spaced from each other, and the pair of third magnetic sensors A3and B3are arranged in the state spaced from each other.

The respective magnetic sensors A1to A3and B1to B3include elements such as magnetoresistive effect elements (or MR elements) characterized to have resistances varied by the action of a magnetic field, so that they output periodically varying voltage signals, period of which is defined mainly by the distance between the adjacent tooth crests of the confronted targets34to36. When the first target34rotates together with the input shaft32in accordance with the steering operation of the driver, the output signal is made into such a periodic signal mainly according to the distance between the first magnetic sensors A1and B1and the tooth crests as varies according to the variation (or angular displacement) of the rotation angle of the input shaft32and the target34. When the second target35rotates together with the output shaft33, the output signal is made into such a periodic signal mainly according to the distance between the second magnetic sensors A2and B2and the tooth crests as varies according to the variation of the rotation angle of the output shaft33and the target35. When the third target36rotates together with the output shaft33, the output signal is made into such a periodic signal mainly according to the distance between the third magnetic sensors A3and B3and the tooth crests as varies according to the variation of the rotation angle of the output shaft33and the target36. The gears having the shape of a spur gear (as referred toFIG. 3) which can manage the aforementioned tooth pitch L are employed as the targets34to36. Therefore, the periodic signal has no discrepancy so that a more precise output signal can be obtained.

Moreover, the first magnetic sensors A1and B1are arranged in such a spaced state that their output signals may establish a phase difference of π/2, for example, in the electrical angle, as shown inFIG. 4Likewise, the second magnetic sensors A2and B2are arranged in such a spaced state that their output signals may establish the phase difference of π/2, and the third magnetic sensors A3and B3are arranged in such a spaced state that their output signals may establish the phase difference of π/2. By thus shifting the phases of the output signals, even if nonlinear changes appear near the maximal and minimal values of the output waveform, the later-described control unit21can use, when the signal of one of the two magnetic sensors A1to A3and B1to B3is in the nonlinear region, the signal of the other in the linear region, thereby to prevent the respective rotation detecting precisions of the input and output shafts32and33from degrading.

The control unit21is provided with an operation unit21afor performing a predetermined arithmetic operation with the outputs (which are used after they were converted into digital signals by the not-shown A/D converters, if necessary, as in the following description on the operations) of the first to third magnetic sensors A1to A3and B1to B3, and a drive control unit21bfor controlling the drive of the electric motor6on the basis of the operation results of the operation unit21a. To this control unit21, there is inputted the signal of a vehicle speed detected by a vehicle speed sensor22, so that the control unit21decides the turning force to be generated by the electric motor6, in view of the running speed of the automobile. Moreover, the control unit21is provided with a (not-shown) data storage unit constructed of a nonvolatile memory or the like, which is suitably stored in advance with not only a program or tabulated information necessary for the drive control of the electric motor6but also the operation results of the respective portions of the unit21and the information indicating the running state of the automobile from the vehicle speed sensor22.

The operation unit21ais constituted to have: the function of a rotation angle detecting unit for detecting the respective rotation angles of the corresponding input and output shafts32and33with the output signals of the magnetic sensors A1to A3and B1to B3; the function of a torque detecting unit for detecting the steering torque to be applied to the steering member1, with the respective rotation angles detected by the rotation angle detector; and the function to determine the steering torque and the steering angle to be applied to the steering member1, by calculations with the detected respective rotation angles, thereby to decide the steering assisting force to be applied from the auxiliary steering unit, on the basis of the steering torque and steering angle determined. Specifically, the operation unit21aacquires the output signals of the magnetic sensor A1and B1, and A2and B3, for example, for a predetermined sampling period, and obtains the rotation angles of the corresponding input shaft32and output shaft33, and then determines the absolute values of the relative rotation angle of the input and output shafts32and33thereby to calculate the steering torque and steering angle to be applied to the steering member1. On the basis of the steering torque and steering angle calculated, moreover, the operation unit21adecides a command value to the electric motor6and instructs the drive control unit21b. Here, the operation unit21ais also enabled to determine the absolute value of the absolute rotation angle of the output shaft33and to calculate the steering torque and the steering angle by using the output signals of the magnetic sensors A3and B3.

On the basis of the command value instructed by the operation unit21a, the drive control unit21bfeeds the electric motor6with an electric current and drives the electric motor6. As a result, the electric power steering device of this embodiment can detect the steering operation of the driver and can apply the steering assisting force according to the operation.

The foregoing description has been made on the case the gears of a spur gear shape, as shown inFIG. 3, are used. However, the invention should not be limited thereto but may use gears shown inFIG. 5, for example. Specifically, the targets34to36maybe constructed such that their tooth crests81are arcuate, such that the face existing between the respective tooth crests81is an arcuate face82, which is radially recessed to have no boundary between the tooth side face and the bottom land, and such that their two circumferential end portions83of the tooth crest81, namely, the boundaries (or ridgelines) between the tooth crest81and the arcuate face82are formed into the angular portions. Here, these targets34to36can be simply manufactured by the gear cutting, press working or sintering treatment using the milling machine.

Moreover, there may be used a gear, as shown in FIG.6. Specifically, the targets34to36maybe constructed such that not only their tooth crests91but also their bottom lands92are made arcuate, such that their tooth side faces93are recessed inward of the teeth into an arcuate shape, and such that their two circumferential end portions94, namely the boundaries (or ridgelines) between the tooth crest91and the tooth side faces93are formed into the angular portions. Here, these targets34to36can be simply manufactured by the gear cutting, press working or sintering treatment using the milling machine.

In the foregoing description, the invention is applied to the electric power steering device having the auxiliary steering unit for applying the steering assisting force to the steering system with the reduction mechanism and the electric motor6. However, the rotation angle detecting device and the torque detecting device of the invention should not be limited thereto but can also be applied to a variety of detecting devices for detecting the rotation angle of a rotary member or the torque to be applied to the rotary member. The invention can be further applied to a hydraulic power steering device for controlling hydraulic valves on the basis of the steering torque, for example.

According to the rotation angle detecting device of the invention, as has been described hereinbefore, the two circumferential side end portions on the tooth crests are formed into the angular portions so that the rotation angle detecting device provided can be easily tested.

Especially in the rotation angle detecting device, in case the side faces of each tooth are flat or in case the portion between the crests of each tooth is radially recessed into the arcuate face, the manufacturing cost can be suppressed to lower the price of the rotation angle detecting device advantageously.

According to the torque detecting device of the invention, the rotation angle detecting device is incorporated so that the torque detecting device provided can be easily tested. Especially in case the side faces of each tooth are flat or in case the portion between the crests of each tooth is radially recessed into the arcuate face, the price of the torque detecting device is also advantageously lowered.