Rotation sensor

The rotation sensor (10) has a cylindrical first rotor (11) made of an insulating magnetic material, having conductor layers (11a) arranged circumferentially, the first rotor being attached to a rotating first shaft (5a) at a predetermined axial position; a fixed core (12) having an exciting coil (12b), the core being fixed to a fixing member with a space secured in the axial direction with respect to the first shaft; a second rotor (13) having nonmagnetic metal bodies (13b) arranged circumferentially to oppose the conductor layers respectively, the second rotor being attached to a second shaft located adjacent to and rotating relative to the first shaft (5a) and being located between the first rotor (11) and the fixed core (12); and oscillating device connected to the exciting coil (12b), the oscillating device transmitting an oscillation signal of a specific frequency. The rotation sensor has rotation guides (11c,13c) for guiding rotation of the first and second rotors (11,13) respectively with respect to the fixed core (12).

FIELD OF THE INVENTION

The present invention relates to a rotation sensor.

BACKGROUND OF THE INVENTION

There is known, as a rotation sensor having a pair of rotors and a stator containing an exciting coil and detecting a running torque between two shafts rotating relative to each other, for example, one which is utilized for smooth electronic control of a steering device. The sensor detects a running torque in an automotive handle shaft having two rotating shafts rotating relative to each other and connected to each other through a torsion bar (see, for example, Examined Japanese Patent Publication(Kokoku) No. Hei 7-21433).

Here, in the conventional rotation sensor described above, the rotors are fixed beforehand to the rotating shafts respectively, and a rotation guide such as a bearing is interposed between the stator and each rotating shaft to achieve alignment of the rotating shafts of these two rotors with the central axis of the exciting coil in the stator.

However, according to the above constitution, the rotation sensor must be manufactured or assembled integrally with two rotating shafts rotating relative to each other to impose design limitation on a target to which the rotation sensor is attached, e.g., a steering device. In addition, the rotation sensor generally needs adjustment of sensitivity and output range, and when it is integrated into the rotating shafts, such adjustments are carried out after completion of assembly. Therefore, the resulting rotation sensor involves problems that the adjusting mechanisms are enlarged and complicated due to upsizing by integration into the rotating shafts.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a rotation sensor, which need not be manufactured integrally with rotating shafts but can be post-fitted thereto, which imposes no design limitation on a target to which the rotation sensor is attached, and which can be downsized.

In the present invention, in order to attain the above object, the rotation sensor contains a cylindrical first rotor made of an insulating magnetic material, having conductor layers arranged circumferentially, the first rotor being attached to a rotating first shaft at a predetermined axial position; a fixed core having an exciting coil, the core being fixed to a fixing member with a space secured in the axial direction with respect to the first shaft; a second rotor having nonmagnetic metal bodies arranged circumferentially to oppose the conductor layers respectively, the second rotor being attached to a second shaft located adjacent to and rotating relative to the first shaft and being located between the first rotor and the fixed core; and oscillating means connected to the exciting coil, the means transmitting an oscillation signal of a specific frequency; wherein the rotation sensor is provided with rotation guides for guiding rotation of the first rotor and the second rotor respectively with respect to the fixed core.

Preferably, the rotation guides are a first guide ring and a second guide ring formed on the first rotor and on the second rotor respectively and are engaged with the fixed core.

Preferably, the rotation guides are bearings interposed between the first rotor and the fixed core and between the second rotor and the fixed core, respectively.

These and other objects, aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

The present invention will be described below by way of embodiments realized in a rotation sensor for detecting a running torque, for example, in an automotive steering shaft to be transmitted from a main driving shaft to a driven shaft through a converting joint (torsion bar) referring toFIGS. 1to5.

A rotation sensor according to a first embodiment of the invention will be described first. The rotation sensor10is provided with a first rotor11, a fixed core12, a second rotor13and a relative rotation angle measuring device14and is attached to a steering shaft5. Here, the steering shaft5has a main driving shaft5aand a driven shaft5cconnected to each other through a torsion bar5b. The main driving shaft5ais oriented relative to the driven shaft5csuch that the former rotates at an angle of ±8° relative to the latter.

The first rotor11is formed to have a cylindrical shape using an insulating magnetic material prepared by admixing 10 to 70% by volume of powdery soft magnetic material to a thermoplastic synthetic resin having electrical insulating properties. The first rotor11is post-fitted to the rotating main drive shaft5aat an axial predetermined position. Such thermoplastic synthetic resins employable here include nylon, polypropylene (PP), polyphenylene sulfide (PPS), ABS resins, etc. Meanwhile, powdery soft magnetic materials employable here include Ni—Zn and Mn—Zn ferrite powders. The first rotor11has on the periphery six sheets of copper foils11aarranged circumferentially at predetermined intervals, for example, at 30°-central angle intervals, in FIG.1. The first rotor11has a flange11bformed at the top to extend radially outward. The flange11bhas a first guide ring11con the periphery.

The first guide ring11cis ring-shaped and is engaged with a step12f(to be described later) of the fixed core12to guide rotation of the first rotor11with respect to the fixed core12. For that reason, the first guide ring11cis made of the same material as used for a second guide ring13c(to be described later), for example, a metal such as a copper alloy and aluminum or a synthetic resin. The first guide ring11chas a multiplicity of protrusions11dformed on the periphery and on the upper and lower surfaces and arranged circumferentially so as to reduce friction with the fixed core12. It should be noted here that the first guide ring11cmay have ridges11eextended in the circumferential direction in place of the protrusions11dso long as the intended purpose is attained.

Meanwhile, the copper foils11amay be replaced with any other conductor layer such as of aluminum or silver, and these conductor layers including the copper foils11amay be embedded in the insulating magnetic material.

The fixed core12, which is located at the outermost position coaxially with the first rotor11with a very small gap of about several millimeters secured radially, is fixed to a fixing member (not shown) located in the vicinity of the steering shaft5by means of post-fitting. The fixed core12has a core body12a, an exciting coil12bhoused in the core body12aand a metallic shielding case (hereinafter simply referred to as “case”)12cfor containing the core body12a. The core body12ais made of the same insulating magnetic material as used for the first rotor11and has a ring shape with a groove12hfor containing the exciting coil12b. The exciting coil12bis connected to a signal processing circuit (not shown) with electric cables12d(seeFIG. 1) extended externally from the case12c. An alternating current is supplied from this signal processing circuit. The case12cis made of a metal such as aluminum and copper, having a property of shielding alternate current magnetic field and has a ring shape with a groove12efor containing the core body12a. Here, the case12chas on the inner surface thereof an upper step12fand a lower step12gwhich are engaged with the first and second guide rings11cand13crespectively.

The second rotor13is interposed between the first rotor11and the fixed core12, as shown inFIG. 1, and is post-fitted to the driven shaft5cwhich rotates relative to the main driving shaft5a. The second rotor13is made of a metal having a property of shielding alternate current magnetic field, such as aluminum and copper, and has at the bottom a mounting flange13ato be fixed to the driven shaft5c. The mounting flange13ahas six louver boards13bformed to rise from the periphery thereof parallel to the rotational axis Art and arranged circumferentially and equally at 60°-central angle intervals and to oppose the copper foils11arespectively.

Here, the second rotor13has on the periphery of the mounting flange13aa second guide ring13cformed integrally therewith, like the first rotor11. The second guide ring13cis ring-shaped and has a multiplicity of protrusions13dformed on the periphery and on the upper and lower surfaces and arranged circumferentially so as to be engaged with the step12g(to be described later) of the fixed core12under low friction and to guide rotation of the second rotor13with respect to the fixed core12. The second guide ring13cmay have ridges extended in the circumferential direction in place of the protrusions13d.

The rotation sensor10having the constitution as described above is incorporated into a steering device by means of post-fitting by attaching the first rotor11and the second rotor13to the main driving shaft5aand to the driven shaft5c, respectively, and fixing the fixed core12to the fixing member.

In the thus assembled rotation sensor10, a magnetic flux induced by the alternate current flowing through the exciting coil12bflows along a magnetic circuit formed of the insulating magnetic material of the core body12aand the first rotor11. Thus, the alternate current magnetic field traverses the copper foils11aof the first rotor11to induce an eddy current within the copper foils11a.

Here, the direction of the alternate current magnetic field excited by the eddy current is opposite to that of the alternate current flowing through the exciting coil12b. Consequently, the direction of the magnetic flux induced by the exciting alternate current of the exciting coil12bgenerated in such portions of the gap between the core body12aand the first rotor11, where the copper foils11aare present, and the direction of the magnetic flux induced by the eddy current are opposite to each other, so that the total magnetic flux density is reduced. On the contrary, in the portions of the gap where no copper foil11ais present, the magnetic flux induced by the exciting alternate current of the exciting coil12band the magnetic flux induced by the eddy current are of the same direction, so that the total magnetic flux density is increased. In other words, a nonuniform magnetic field is formed in the gap between the core body12aand the first rotor11.

Therefore, in the rotation sensor10, when the second rotor13rotates relative to the first rotor11, the louver boards13bformed at 60°-central angle intervals on the second rotor13traverse the nonuniform magnetic field. Here, the amount of total magnetic flux which the louver boards13btraverse changes under relative rotation of the first rotor11and the second rotor13, so that the intensity of the eddy current occurring in the louver boards13bchanges. Thus, in the rotation sensor10, impedance of the exciting coil12bfluctuates depending on the relative rotation angle between the first rotor11and the second rotor13.

In the rotation sensor10of this embodiment, the fluctuation of impedance in the exciting coil12bis measured by detecting the amount of phase shift in pulse signals.

Next, measurement of the relative rotation angle with the rotation sensor10will be described referring to FIG.2.FIG. 2is a circuit block diagram showing an embodiment of relative rotation angle measuring device14to be used in the rotation sensor10.

InFIG. 2, the measuring device14constitutes oscillating means of the rotation sensor10and has an oscillation circuit14awhich transmits an oscillation signal, a dividing circuit14bwhich divides the oscillation signal to output a pulse signal of a specific frequency, a shift amount circuit14dfor detecting a phase shift amount (to be described later), a converter14ffor converting the detected phase shift amount to a corresponding voltage value, a shift level adjusting section14hfor adjusting the shift level of that voltage value, an amplification circuit14jfor amplifying the voltage corresponding to the phase shift amount output from the converter14fand a relative rotation angle measuring section14mfor measuring a relative rotation angle based on the amplified voltage value.

The oscillation circuit14aoutputs a pulse signal of a specific frequency through the dividing circuit14bto a resonant circuit containing a resistor R, the exciting coil12band a condenser C as shown in FIG.2. The fluctuation in impedance of the exciting coil12bchanges the phases of the voltage signals at both ends of the condenser C. The voltage signals at both ends of the condenser C are output to the shift amount circuit14d.

The shift amount circuit14ddetects the phase shift amount of the voltage signal at each end of the condenser C. The converter14fconverts the detected phase shift amount to a corresponding voltage value, while the shift level adjusting section14hadjusts the voltage level of the signal output from the converter14fand outputs the adjusted voltage value to the amplification circuit14j. The amplification circuit14jamplifies the voltage level of the signal output from the converter14fto output the amplified voltage value to the relative rotation angle measuring section14m.

The relative rotation angle measuring section14mmeasures the relative rotation angle between two rotors11and13with high accuracy within the range of −8° to +8° based on the signal (voltage value) input from the amplification circuit14j.

Therefore, the rotation sensor10can determine the running torque acting between the main driving shaft5aand the driven shaft5cdepending on the relative rotation angle, based on the relationship between the running torque acting between these two shafts5aand5chaving been determined beforehand and the relative rotation angle between them.

Here, the components of the rotation sensor10including the first rotor11, the fixed core12and the second rotor13are incorporated by means of post-fitting into an intended target, for example, a steering device. Therefore, the rotation sensor10need not be manufactured integrally with the rotating shafts, nor it imposes design limitation on an intended target and can be downsized. Further, the rotation sensor10can be incorporated into the steering device after adjustment of sensitivity and output range.

In addition, the rotation sensor10has, on the first rotor11, the first guide ring11cto be engaged with the step12fof the fixed core12, and on the second rotor13, the second guide ring13cto be engaged with the step12gof the fixed core12. This facilitates rotation of the rotors11and13and improves reliability of the rotation sensor10in terms of operation.

Here, the rotation sensor of the present invention can be applied to a case where a plurality of rotation sensors are integrated into one body, for example, as in a rotation sensor20shown in FIG.4. The rotation sensor20contains two rotation sensors housed in a fixed case to be integrated into a single body. The rotation sensor20has a first rotation sensor for detecting the relative rotation angle between a rotating first shaft and a second shaft rotating relative to the first shaft, and a second rotation sensor which detects the relative rotation angle between the rotating first shaft and the fixed case.

The rotation sensor20has a first rotor21, a second rotor22and a fixed case23and is attached to an intended target, as shown in FIG.4. In the rotation sensor20, the inner wall of a flange23bextended from an inner barrel23aof the fixed case23is abutted against the periphery of an inner barrel22aof the second rotor22as illustrated in section A ofFIG. 4; whereas the inner wall of a lower cover23cof the fixed case23is abutted against the lower periphery of an inner barrel21aof the first rotor21as illustrated in section B ofFIG. 4, guiding rotation of the first rotor21and the second rotor22with respect to the fixed case23, respectively.

The first rotor21is made of a thermoplastic synthetic resin and has the inner barrel21ahaving a cylindrical form. A flange extended from the inner barrel21ahas a peripheral wall21f. The synthetic resin employable here includes, for example, nylon, polypropylene (PP) and polybutylene terephthalate (PBT), etc. As shown inFIG. 4, the first rotor21has a first ring member21dand a second ring member21eon the inner barrel21aand on the peripheral wall21frespectively. The first and second ring members21dand21eare formed into ring shapes using an insulating magnetic material prepared by admixing 10 to 70% by volume of powdery soft magnetic material to a thermoplastic synthetic resin having electric insulating properties. The thermoplastic synthetic resin employable here includes nylon, polypropylene (PP), polyphenylene sulfide (PPS), ABS resins, etc. Meanwhile, the powdery soft magnetic material employable here includes Ni—Zn and Mn—Zn ferrite powders. The first ring member21dhas on the periphery thereof copper foils21bformed at the same pitch as that of copper pieces22b(to be described later). The second ring member21ehas copper foils21cattached thereto at a central angle of up to 180° and arranged circumferentially on the periphery. Further, the first rotor21has a cylindrical screw member25aattached to the periphery of the flange. The first rotor21is provided with an arcuate copper thin plate29over the central angle of 180° on the upper surface of the flange.

The second rotor22is made of a thermoplastic synthetic resin and has the inner barrel22ahaving a cylindrical form. The inner barrel22ahas six copper pieces22battached thereto and arranged at 60°-central angle equal intervals. The same synthetic resins as used for the first rotor21can be employed here.

As shown inFIG. 4, the fixed case23has a first fixed core27and a second fixed core28. These cores27and28are assembled by housing exciting coils respectively into annular core bodies formed using the same insulating magnetic material as used for the ring members21dand21e. The fixed case23further contains a circuit board24, a displacement sensor25and a pitch sensor26.

The circuit board24is connected to the exciting coil of the first fixed core27and to that of the second fixed core28and has a transmitting circuit which transmits a signal of a specific frequency and which converts the signals detected by the first rotation sensor and the second rotation sensor into a relative rotation angle. As described above, the circuit board24processes the signals detected by the first rotation sensor and the second rotation sensor respectively.

The displacement sensor25detects a change in coil inductance based on the shift of a sliding core25e(to be described later) in the axial direction of the rotating shaft and detects revolution between the first rotor21and the fixed case23. The displacement sensor25contains the screw member25a, a thread portion25b, a slider25c, a thread portion25d, the sliding core25e, a coil25fand a core25g. The pitch sensor26detects if rotational positions of the first and second rotors21and22are within the angle of 180° in the positive direction or negative direction from the reference position.

In the rotation sensor20, the first ring member21dand the second ring member21eare opposed to the first fixed core27and to the second fixed core28respectively, and the first rotor21is attached rotatably to the second rotor22. In the rotation sensor20, six copper pieces22bare arranged between the first ring member21dand the fixed core27, and the second rotor22is rotatably attached to the fixed case23.

Here, the first rotation sensor contains the first ring member21d, the first fixed core27and the copper pieces22bto allow the circuit board24to transmit a signal of a specific frequency to the exciting coil and detects the relative rotation angle between the first rotor21and the second rotor22.

Meanwhile, the second sensor contains the second ring member21e, the displacement sensor25, the pitch sensor26and the second fixed core28to allow the circuit board24to output a signal of a specific frequency to the exciting coil and detects relative rotation angle between the first rotor21and the fixed case23.

The rotation sensor20having the constitution as described above is incorporated to an intended target, for example, into a steering device by means of post-fitting by attaching the first rotor21and the second rotor22to the first shaft and to the second shaft respectively. It should be noted here that in the rotation sensor20, the inner barrel21aof the first rotor21and the inner barrel22aof the second rotor22serve as guide rings corresponding to the first guide ring11cand the second guide ring13cof the rotation sensor10respectively.

Therefore, the rotation sensor20, like the rotation sensor10, need not be manufactured integrally with the rotating shafts nor imposes design limitation on the target to which the rotation sensor is to be attached and can be downsized.

Next, a rotation sensor according to a second embodiment of the present invention will be described. It should be noted here that the same or like elements as in the rotation sensor10of the first embodiment will be affixed with the same reference numbers respectively so as to avoid redundant descriptions.

The rotation sensor30contains a first rotor11, a fixed core12, a second rotor13and a relative rotation angle measuring device14(seeFIG. 2) as shown in FIG.5. In the revolution sensor30, a bearing16is interposed between the flange11bof the first rotor11and the step12fof the fixed core12, whereas another bearing17is interposed between the mounting flange13aof the second rotor13and the step12gof the fixed core12.

Therefore, in the rotation sensor30, since the first rotor11, the fixed core12and the second rotor13are incorporated to an intended target such as a steering device by means of post-fitting, like in the rotation sensor10, the rotation sensor30need not be manufactured integrally with rotating shafts nor imposes design limitation on the intended target and can be downsized easily.

It should be noted here, while the embodiments each described a rotation sensor for detecting running torque, the sensors can detect absolute rotation angles.

Furthermore, the rotation sensors according to the present invention can be applied not only to automotive steering shafts as described in the above embodiments but to any other shaft such as robot arms, so long as they are used for determining a relative rotation angle, rotation angles or a running torque between two rotating shafts rotating relative to each other.