JP2009180585A - Rotation angle detector and electrical power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotation angle detector for highly accurately detecting a rotation angle without therein providing an amplification circuit. <P>SOLUTION: The capacitance of a capacitor, which is connected between an exciting coil of a motor resolver and an MPU, and the inductance of the exciting coil are set so as to enhance the sharpness of a resonance circuit consisting of the capacitor and the exciting coil. The frequency f of an excitation signal is corrected so that a peak voltage value Vp of an exciting voltage of the exciting coil approximates to a target voltage value Vm, that is, the frequency f of the excitation signal is corrected so as to approximate to a changed resonance frequency of the resonance circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rotation angle detection device and an electric power steering device that detect a rotation position of a rotating body.

Conventionally, as a rotation angle detection device that detects a rotation position of a rotating body, for example, a motor, for example, a rotation angle detection device shown in Patent Document 1 below is known. In this rotation angle detection device, a sine wave signal generated by a sine wave generation device (excitation signal generation means) is amplified by an amplification circuit, inverted by an inverting circuit, and input as an excitation signal to the excitation coil of the resolver. Is done. Then, an output signal output from the resolver in response to the excitation signal is input to the angle detection means, so that the rotation angle of the rotating body is detected based on the output signal.
JP 2005-150873 A

By the way, the above-described amplifier circuit is provided between a microprocessor (hereinafter also referred to as MPU) functioning as an excitation signal generating means and an excitation coil of a resolver for the following reason.
That is, since the voltage level that can be handled by the MPU is limited, the upper limit value of the voltage of the excitation signal output from the MPU is limited. Further, since the voltage of the excitation signal output from the MPU is lowered by a filter in the middle, a sufficiently high excitation voltage cannot be applied to the excitation coil, and a large dynamic range cannot be ensured. Therefore, the amplifier circuit is provided between the MPU and the excitation coil, and the voltage of the excitation signal from the MPU is amplified and applied to the excitation coil to ensure a large dynamic range and detect the rotation angle with high accuracy. Yes.

  However, since it is necessary to provide an amplifier circuit between the MPU and the excitation coil in this way, the cost of components of the rotation angle detection device increases by the amount of the amplifier circuit, which is an obstacle to cost reduction.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a rotation angle detection device and an electric power steering capable of detecting a rotation angle with high accuracy without providing an amplifier circuit. To provide an apparatus.

In order to achieve the above object, in the rotation angle detection device according to claim 1, the resolver (35, 37, 44) for detecting the rotation angle (θm) of the rotating body (40, 43). A resolver for outputting a rotation angle signal corresponding to the rotation angle by an excitation signal input to the excitation coil (47a), an excitation signal generating means (61) for generating and outputting the excitation signal, A capacitor (66) connected between the exciting coil and the exciting signal generating means, a voltage detecting means (67) for detecting the exciting voltage (V _L ) of the exciting coil, and the rotation inputted from the resolver A rotation angle detector (60) for calculating the rotation angle based on an angle signal, wherein the rotation angle detector (60) includes a capacitance (C) of the capacitor and an inductance ( L) is set so as to increase the sharpness (Q) of the resonance circuit (80) including the capacitor and the excitation coil, and the excitation signal generation means has an amplitude value of the excitation voltage of the resonance circuit. A technical feature is that the frequency (f) of the excitation signal is controlled so as to approach a target voltage value (Vm) set to a resonance voltage or less.

  In the rotation angle detection device according to claim 1, the capacitance of the capacitor connected between the excitation coil and the excitation signal generation means and the inductance of the excitation coil increase the sharpness of the resonance circuit including the capacitor and the excitation coil. Is set to

  For this reason, for example, by inputting an excitation signal having a frequency equal to the resonance frequency of the resonance circuit to the excitation coil, the excitation voltage of the excitation coil is increased by utilizing the frequency resonance characteristic of the resonance circuit, and the required dynamic range is increased. Can be secured. Thereby, since the voltage applied to the exciting coil can be increased without providing an amplifier circuit, the rotation angle detecting device can be simplified and the cost can be reduced.

  In general, when the capacitance of the capacitor or the inductance of the exciting coil changes due to temperature change or aging of the rotation angle detector, the resonant frequency of the resonant circuit changes and the excitation voltage of the exciting coil decreases. It is assumed that

Therefore, correction of the excitation signal frequency so that the amplitude value of the excitation voltage is close to the target voltage value set below the resonance voltage of the resonance circuit, that is, the excitation signal frequency is close to the resonance frequency of the changed resonance circuit. By performing the correction, the voltage applied to the exciting coil can be kept high by always using the frequency resonance characteristic of the resonance circuit.
Therefore, the rotation angle can be detected with high accuracy without providing an amplifier circuit.

  According to the second aspect of the present invention, a plurality of maps showing the relationship between the frequency of the excitation signal and the amplitude value of the excitation voltage that changes according to the change in the frequency are provided for each resonance frequency that changes in the resonance circuit, and excitation signal generating means There is provided map selection means for selecting, from a plurality of maps, a map in which the frequency of the excitation signal output from is established and the amplitude value of the excitation voltage detected by the voltage detection means corresponding to the excitation signal is established. The excitation signal generation means controls the excitation signal frequency to be equal to the resonance frequency of the map selected by the map selection means.

  In this way, the map selection means selects a map in which the relationship between the excitation signal frequency output from the excitation signal generation means and the excitation voltage of the excitation coil is established. Since the resonance frequency corresponding to the selected map is equal to the resonance frequency of the resonance circuit that has changed due to temperature change or aging of the rotation angle detection device, the frequency of the excitation signal output from the excitation signal generating means is selected. By controlling so as to be equal to the resonance frequency of the map, the voltage applied to the exciting coil can be reliably increased by always using the frequency resonance characteristic of the resonance circuit.

  According to a third aspect of the present invention, the excitation signal generating means lowers the frequency of the excitation signal when the amplitude value of the excitation voltage is lower than the target voltage value, and the excitation signal when the amplitude value of the excitation voltage is higher than the target voltage value. The excitation signal is generated so as to increase the frequency of the signal.

  As described above, when the resonance frequency of the resonance circuit is changed as described above, when the excitation voltage decreases and the amplitude value of the excitation voltage becomes lower than the target voltage value, the excitation signal is controlled so as to suppress this voltage decrease. When the frequency is lowered and the excitation voltage rises and the amplitude value of the excitation voltage becomes higher than the target voltage value, the excitation signal frequency is increased to suppress this voltage rise, so the excitation voltage is set to the target voltage value. It can be maintained well.

  The electric power steering apparatus according to claim 4 includes a motor that outputs an assist force capable of assisting steering by the steering wheel, and the rotation angle of the motor is determined according to any one of claims 1 to 3. It detects with a detection apparatus and controls the said motor based on this rotation angle.

  As a result, it is possible to realize an electric power steering apparatus that enjoys the operations and effects of the inventions of claims 1 to 3 such that the rotation angle can be detected with high accuracy without providing an amplifier circuit. . Therefore, the cost reduction of the electric power steering apparatus can be achieved by adopting the rotation angle detection apparatus with reduced manufacturing costs.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the configuration of the electric power steering apparatus 20 according to the present embodiment will be described with reference to FIGS. FIG. 1 is a configuration diagram showing a configuration of an electric power steering apparatus 20 according to an embodiment of the present invention. FIG. 2 is an enlarged view of the inside of the ellipse along the alternate long and short dash line II shown in FIG. FIG. 3 is an enlarged view of the inside of the ellipse along the alternate long and short dash line III shown in FIG. FIG. 4 is a block diagram showing an electrical configuration of the ECU 60 that controls the electric power steering apparatus 20 of the present embodiment.

  As shown in FIGS. 1 to 4, the electric power steering apparatus 20 according to the present embodiment mainly includes a steering wheel 21, a steering shaft 22, a pinion shaft 23, a rack shaft 24, a torque sensor 30, a motor 40, The motor resolver 44, the ball screw mechanism 50, the ECU 60, and the like are configured. The steering state by the steering wheel 21 is detected by the torque sensor 30, and the assist force corresponding to the steering state is generated by the motor 40 to be steered by the driver. Is to assist. Note that steered wheels (not shown) are connected to both sides of the rack shaft 24 via tie rods or the like.

  That is, as shown in FIGS. 1 and 2, one end side of a steering shaft 22 is connected to the steering wheel 21, and the other end side of the steering shaft 22 is connected to a torque sensor 30 housed in a pinion housing 25. The input shaft 23 a and the torsion bar 31 are connected by a pin 32. Further, the output shaft 23b of the pinion shaft 23 is connected to the other end 31a of the torsion bar 31 by spline coupling.

  The input shaft 23a of the pinion shaft 23 is rotatably supported in the pinion housing 25 by a bearing 33a, and the output shaft 23b is also supported by a bearing 33b. Further, between the input shaft 23a and the pinion housing 25, The first resolver 35 and the second resolver 37 are provided between the output shaft 23b and the pinion housing 25, respectively. The first resolver 35 and the second resolver 37 constituting the torque sensor 30 can detect the rotation angle by the steering wheel 21, and include a sine wave phase output terminal 35s, a cosine wave phase output terminal 35c and the like, and a sine wave phase output terminal. 37s and a cosine wave phase output terminal 37c and the like are electrically connected to the ECU 60 (see FIG. 4).

  A pinion gear 23c is formed at an end portion of the output shaft 23b of the pinion shaft 23, and a rack groove 24a of the rack shaft 24 is coupled to the pinion gear 23c so as to be meshable. Thus, a rack and pinion type steering mechanism is configured.

  As shown in FIGS. 1 and 3, the rack shaft 24 is accommodated in a rack housing 26 and a motor housing 27, and a ball screw groove 24 b is formed in a spiral shape at an intermediate portion thereof. A cylindrical motor shaft 43 supported by a bearing 29 is provided around the ball screw groove 24 b so as to be rotatable coaxially with the rack shaft 24. This motor shaft 43 constitutes the motor 40 together with the stator 41, the excitation coil 42, etc., and the field generated by the excitation coil 42 wound around the stator 41 is generated on the outer periphery of the motor shaft 43 corresponding to the rotor. By acting on the permanent magnet 45 provided, the motor shaft 43 can be rotated.

  A ball screw nut 52 is attached to the inner periphery of the motor shaft 43, and the ball screw nut 52 is also formed with a ball screw groove 52a in a spiral shape. Therefore, a large number of balls 54 are movably interposed between the ball screw groove 52a of the ball screw nut 52 and the ball screw groove 24b of the rack shaft 24, whereby the rack shaft 24 is pivoted by the rotation of the motor shaft 43. A ball screw mechanism 50 that can move in the direction can be configured.

  In other words, the rotational torque of the motor shaft 43 rotating in the forward and reverse directions can be converted into the reciprocating motion in the axial direction of the rack shaft 24 by the ball screw mechanism 50 including both the ball screw grooves 24b and 52a. As a result, the reciprocating motion becomes an assist force that reduces the steering force of the steering wheel 21 via the pinion shaft 23 that forms a rack and pinion type steering mechanism together with the rack shaft 24.

  A motor resolver 44 capable of detecting the rotation angle (electrical angle) θm of the motor shaft 43 is provided between the motor shaft 43 of the motor 40 and the motor housing 27, and this motor resolver 44 is a sine wave phase output terminal. 44s, and is electrically connected to the ECU 60 via a cosine wave phase output terminal 44c (see FIG. 4).

  As shown in FIG. 4, the ECU 60 includes an MPU 61, a memory 62, an I / F circuit 63, and the like. The MPU 61 gives sinusoidal excitation signals to the first resolver 35 and the second resolver 37 from the output ports 60a and 60b. Thereby, the sine wave phase output signal from the sine wave phase output terminal 35 s of the first resolver 35, the cosine wave phase output signal from the cosine wave phase output terminal 35 c, and the sine wave phase output of the second resolver 37. The sine wave phase output signal from the terminal 37 s and the cosine wave phase output signal from the cosine wave phase output terminal 37 c are input to the ECU 60. An offset voltage is applied to the voltage of each output signal via the I / F circuit 63 of the ECU 60, which is input to the A / D converter side of the MPU 61 and A / D converted. The MPU 61 calculates the steering torque by detecting the rotation angle of the first resolver 35 and the second resolver 37 from each A / D converted output signal, and steers according to the steering torque and the rotation angle θm of the motor 40 described later. An assist command for assisting the force is output to the motor drive circuit 70 side. By supplying a motor voltage corresponding to the current command value to the motor 40 by the motor drive circuit 70, steering by the driver is assisted by the steering force generated by the motor 40.

FIG. 5 is a circuit diagram showing a configuration of the resonance circuit 80. FIG. 6 is a graph for explaining the principle of increasing the excitation voltage V _L by using the frequency resonance characteristics of the resonance circuit 80.
As shown in FIG. 5, the ECU 60 functions as a low-pass filter 64 that is a secondary filter using a resistor and a capacitor, a buffer 65, and a high-pass filter between the MPU 61 and the excitation coil 47a of the motor resolver 44. A capacitor 66 and a voltage sensor 67 for detecting a voltage applied to the exciting coil 47a are provided.

  The MPU 61 outputs a rectangular wave-shaped excitation signal whose frequency is corrected as will be described later. This rectangular wave-like excitation signal is converted into a sine wave by the low-pass filter 64 and impedance-converted by the buffer 65, and then the signal component having a frequency lower than the cutoff frequency is blocked by the capacitor 66, and the output port 60c. To the excitation coil 47a of the motor resolver 44. Thereby, a sine wave phase output signal from a sine wave phase output terminal 44s connected to a sine wave phase coil 47b described later, and a cosine wave phase output from a cosine wave phase output terminal 44c connected to the cosine wave phase coil 47c. The signal is fed back to the motor drive circuit 70 and input to the ECU 60. An offset voltage is applied to the voltage of each output signal via the I / F circuit 63 of the ECU 60, which is input to the A / D converter side of the MPU 61 and A / D converted. The MPU 61 calculates the rotation angle θm of the motor 40 described above from each A / D converted output signal.

Further, as shown in FIG. 5, a resonance circuit 80 is configured by the capacitor 66 and the excitation coil 47 a of the motor resolver 44. The resonance circuit 80 plays a role of ensuring a dynamic range required when the rotation angle θm is detected by increasing the excitation voltage _VL applied to the excitation coil 47a using the frequency resonance characteristic of the capacitor 66. Specifically, the sharpness Q at the time of resonance of the resonance circuit 80 is increased, and the amplitude value (voltage peak value) of the resonance voltage, which is a voltage applied to the exciting coil 47a at the time of resonance, is set to the target voltage value Vm, for example, 5V. The capacitance C of the capacitor 66 and the inductance L of the exciting coil 47a are set so that (see FIG. 6).

Thereby, as can be seen from FIG. 6, the frequency f of the excitation signal is applied to the excitation coil 47a using the frequency resonance characteristic of the resonance circuit 80 by bringing the frequency f of the excitation signal close to the resonance frequency fc shown in the following equation (1). The excitation voltage V _L can be increased.
fc = 1 / {(2π × (L × C) ^1/2 )} (1)

  Here, the electrical characteristics of the motor resolver 44 will be described with reference to FIG. FIG. 7 is an explanatory diagram for explaining the electrical characteristics of the motor resolver 44. FIG. 7 shows a single pole resolver (a signal for one rotation is output when the rotor is rotated once) as a model. As shown in FIG. 7, the motor resolver 44 is a so-called one-phase excitation two-phase output type resolver that outputs a sine wave phase output signal and a cosine wave phase output signal in response to a one-phase excitation signal. A rotor 46 attached to the motor shaft 43 so as to be eccentric with respect to the rotation center of the motor, and an annular stator 47 whose center axis coincides with the rotation center of the motor shaft 43. The stator 47 is provided with a plurality of coils at equal intervals along the circumferential direction. These coils include an exciting coil 47a that functions as an exciting coil, and a sine wave phase coil 47b that functions as a sine wave phase coil. The cosine wave phase coil 47c functions as a cosine wave phase coil with a phase shifted by 90 degrees with respect to the sine wave phase coil 47b. In FIG. 7, only one exciting coil 47a, sine wave phase coil 47b, and cosine wave phase coil 47c are shown.

  When the motor resolver 44 applies an excitation signal that periodically changes in a sinusoidal manner to the excitation coil 47a and rotates the rotor 46 with respect to the stator 47, the motor resolver 44 outputs a sinusoidal phase output signal from the sinusoidal phase coil 47b. The cosine wave phase coil 47c outputs a cosine wave phase output signal. At this time, since the rotor 46 is attached to the motor shaft 43 so as to be eccentric with respect to the rotation center of the motor shaft 43, the amplitudes of the sine wave phase output signal and the cosine wave phase output signal are the same as the stator of the rotor 46. Therefore, the rotation angle θm of the motor 40 can be detected from both output signals. Here, the “rotation angle detecting device” described in the claims includes a resolver that is one of the motor resolver 44, the first resolver 35, and the second resolver 37, and the ECU 60.

By the way, the frequency f of the excitation signal input to the excitation coil 47a is set to, for example, the resonance frequency (hereinafter referred to as the resonance frequency) obtained from the above equation (1) from the capacitance C of the capacitor 66 and the inductance L of the excitation coil 47a. , Which is also referred to as an initial resonance frequency fc _k ), the following problem occurs. That is, when the capacitance C of the capacitor 66 and the inductance L of the exciting coil 47a change due to temperature change or temporal change of the ECU 60, the resonance frequency fc changes according to this change. When the resonance frequency fc changes in this way, the excitation signal output at the frequency f equal to the initial resonance frequency fc _k cannot sufficiently use the frequency resonance characteristic, so that the amplitude value of the excitation voltage _VL is smaller than the target voltage value Vm. turn into.

Therefore, in the present embodiment, the voltage peak value Vp, which is the amplitude value of the excitation voltage _VL , is detected, and the frequency f of the excitation signal is corrected so as to approach the changed resonance frequency fc according to the voltage peak value Vp. Thus, the amplitude value of the excitation voltage V _L is maintained at the target voltage value Vm.

Hereinafter, the process of correcting the frequency f of the excitation signal by the ECU 60 will be described with reference to FIGS. FIG. 8 is a flowchart showing the flow of the frequency correction process of the excitation signal by the ECU 60 of the electric power steering apparatus 20 according to this embodiment. FIG. 9 is a graph showing the relationship among the excitation signal frequency f, voltage peak value Vp, and resonance frequency fc in each of the characteristic maps M _{1 to} M _n .

First, excitation signal output processing is performed in step S101 of FIG. 8, and an excitation signal of frequency f is output from the MPU 61. The frequency f of the excitation signal is set to be equal to the initial resonance frequency fc _k at the start of the frequency correction process.

Next, in step S103, excitation voltage value acquisition processing is performed. In this process, the excitation voltage V _L when the excitation signal from the MPU 61 is input to the excitation coil 47 a is detected by the voltage sensor 67 and stored in the memory 62.

The acquisition process is repeated until it is determined Yes in step S105 by the elapsed time t from the acquisition start time of the excitation voltage V _L has passed the acquisition time t _0. Here, the acquisition time t ₀ is set to a time sufficiently larger than the time corresponding to one cycle of the excitation signal, but is changed according to one cycle of the frequency-corrected excitation signal as will be described later. It may be set as follows.

If the elapsed time t elapses the acquisition time t ₀ during such repeated processing (Yes in S105), the voltage peak value Vp is equal to the maximum value among the excitation voltages stored in the memory 62 in step S107. Is set to be

Next, in step S109, it is determined whether or not the flag F = 0. Here, the flag F is set to any one of 0, 1, and 2, and F = 1 means that the frequency f of the excitation signal is _a resonance frequency in a characteristic map Ma described later. The state set equal to fc _a is shown. Also, the state is a flag F = 2, showing a state where the frequency f of the excitation signal is set equal to the resonance frequency fc _b of the characteristic map M _b which will be described later. Note that the flag F = 0 is set at the start of the frequency correction process.

Since the flag F is set to 0 at this stage (Yes in S109), in step S111, it is determined whether or not the difference between the target voltage value Vm and the voltage peak value Vp is larger than the threshold voltage δ. Here, the threshold voltage δ is set to a value determined to be 0 (zero) V, for example. When the resonance frequency fc has not changed from the initial resonance frequency fc _k and the target voltage value Vm and the voltage peak value Vp are considered equal (No in S111), the processing from step S101 is repeated.

Here, as a result of the resonance frequency fc changing due to the temperature change or aging change of the ECU 60 and the frequency resonance characteristic cannot be fully utilized, the amplitude value of the excitation voltage _VL becomes smaller than the target voltage value Vm. When the difference between the value Vm and the voltage peak value Vp becomes larger than the threshold voltage δ (Yes in S111), a characteristic map selection process is performed in step S113.

In this selection process, as shown in FIG. 9, among the _n characteristic maps M _{1 to} M _n stored in advance in the memory 62, the frequency f of the excitation signal output from the MPU 61 in step S101, and the step A characteristic map that satisfies the relationship with the voltage peak value Vp set in S107 is selected. At this stage, since the frequency f of the excitation signal is not corrected as will be described later, it is set to be equal to the initial resonance frequency fc _k .

Here will be described the characteristic map _M 1 ~M _n. The characteristic map M _k shows the relationship between the frequency f and the voltage peak value Vp when the resonance frequency fc is equal to the initial resonance frequency fc _k . The characteristic maps M _{1 to} M _n show the relationship between the frequency f and the voltage peak value Vp when the resonance frequency fc is changed to the resonance frequencies fc _{1 to} fc _n due to temperature change or temporal change of the ECU 60, respectively. Each is shown.

In the characteristic map selection process in step S113, when the frequency f of the excitation signal output from the MPU 61 in step S101 is equal to the initial resonance frequency fc _k and the voltage peak value Vp set in step S107 is Vp ₁ , frequency f = fc _k and characteristic voltage peak value Vp = Vp ₁ conditions (see point _{P 1} in FIG. 9) is a characteristic map which satisfies the maps _{M a} and the characteristic map _{M b} is selected. The resonance frequency fc _a of the characteristic map _{M a} is set to be smaller than the resonance frequency fc _b of the characteristic map _{M b} (see FIG. 9).

At this stage, as can be seen from FIG. 9, since it cannot be determined whether the resonance frequency fc of the resonance circuit 80 has changed to the resonance frequency fc _a or the resonance frequency fc _b , an excitation signal having a frequency equal to both resonance frequencies is generated. Each frequency is output and the frequency with the higher voltage peak value Vp is actually adopted.

Specifically, in step S115, the frequency f of the excitation signal is set to be equal to the resonant frequency fc _a in the selected characteristic map M _a in step S113. In step S117, after the flag F = 1 is set, the processing from step S101 is performed.

Then, since a flag F = 1, while being determined as No at step S109 it is determined as Yes at step S119, in step S121, the memory 62 is a voltage peak value Vp as Vp _a in stage Remembered.

Next, in step S123, the frequency f of the excitation signal is set to be equal to the resonant frequency fc _b in the selected characteristic map _{M b} at step S113. In step S125, after the flag F = 2 is set, the processing from step S101 is performed.

Since flag F = 2, if it is determined No in step S109 and if it is determined No in step S119, frequency correction processing is performed in step S127. In this correction process, so that the frequency f of the excitation signal is equal to the frequency corresponding to the high voltage peak value of the voltage peak value Vp _a stored in the memory 62 in the voltage peak value Vp and the step S121 in this stage It is corrected.

  Next, after setting the flag F = 0 in step S129, the processing from step S101 is repeated, and step S127 is continued until the difference between the target voltage value Vm and the voltage peak value Vp becomes larger than the threshold voltage δ. The excitation signal of the frequency f corrected in this way is output from the MPU 61.

  As described above, in the ECU 60 of the electric power steering apparatus 20 according to the present embodiment, the capacitance C of the capacitor 66 and the inductance L of the excitation coil 47a connected between the excitation coil 47a and the MPU 61 are as follows. The sharpness Q of the resonance circuit 80 including the capacitor 66 and the exciting coil 47a is set to be high.

Therefore, for example, by inputting an excitation signal having a frequency f equal to the resonance frequency fc of the resonance circuit 80 to the excitation coil 47a, the excitation voltage _VL of the excitation coil 47a is obtained by utilizing the frequency resonance characteristics of the resonance circuit 80. The required dynamic range can be secured. Thereby, since the voltage applied to the exciting coil 47a can be increased without providing an amplifier circuit, the rotation angle detecting device can be simplified and the cost can be reduced.

Further, the excitation signal frequency f is corrected so that the voltage peak value Vp of the excitation voltage _VL approaches the target voltage value Vm, that is, the excitation signal frequency f is corrected so as to approach the resonance frequency fc of the changed resonance circuit 80. By performing the above, the voltage applied to the exciting coil 47a can be kept high by always using the frequency resonance characteristic of the resonance circuit 80.
Therefore, the rotation angle θm can be detected with high accuracy without providing an amplifier circuit.

Further, the ECU 60 of the electric power steering apparatus 20 according to the present embodiment has a characteristic map showing the relationship between the frequency f of the excitation signal and the voltage peak value Vp of the excitation voltage _VL that changes in accordance with the change in the frequency f. M _{1 to} M _n are stored in the plurality of memories 62 for each resonance frequency fc changing in the resonance circuit 80. The ECU 60 also displays a characteristic map in which the frequency f of the excitation signal output from the MPU 61 and the voltage peak value Vp of the excitation voltage _VL detected by the voltage sensor 67 corresponding to the excitation signal are established. Select from M _{1 to} M _n . Then, the MPU 61 controls the excitation signal frequency f to be equal to the resonance frequency fc of the characteristic map selected as described above.

As described above, when a characteristic map that satisfies the relationship between the frequency f of the excitation signal output from the MPU 61 and the voltage peak value Vp of the excitation voltage _VL of the excitation coil 47a is selected, the selected characteristic map is supported. The resonance frequency fc is equal to the resonance frequency fc of the resonance circuit 80 that has changed due to a temperature change or a change with time of the rotation angle detection device. Therefore, by controlling the frequency f of the excitation signal output from the MPU 61 to be equal to the resonance frequency fc of the selected characteristic map, the frequency resonance characteristic of the resonance circuit 80 is always applied to the excitation coil 47a. The excitation voltage V _L can be reliably increased.

  Further, in the electric power steering apparatus 20 that employs the rotation angle detection apparatus according to the present embodiment, the rotation angle detection apparatus that can detect the rotation angle θm of the motor 40 with high accuracy without providing an amplification circuit. Thus, it is possible to realize the electric power steering apparatus 20 that enjoys the functions and effects of the above. Therefore, the cost reduction of the electric power steering device 20 can be achieved by adopting the rotation angle detection device with reduced manufacturing costs.

In addition, this invention is not limited to the said embodiment, You may actualize as follows, and even in that case, an effect | action and effect equivalent to the said embodiment are acquired.
(1) The frequency f of the excitation signal is not limited to be corrected to be equal to the resonance frequency fc of the characteristic map selected from any _{one of the} characteristic maps M _{1 to} M _n , and each characteristic map is adopted. It may be set as follows without doing.
That is, the capacitance C of the capacitor 66 and the inductance L of the exciting coil 47a are set so that the amplitude value of the resonance voltage in the resonance circuit 80 is larger than the target voltage value Vm. When the voltage peak value Vp set in step S107 is lower than the target voltage value Vm, the excitation signal frequency f is lowered. When the voltage peak value Vp is higher than the target voltage value Vm, the excitation signal frequency is decreased. An excitation signal is generated so as to increase f. Even in this case, the voltage peak value Vp of the excitation voltage _VL can be satisfactorily maintained at the target voltage value Vm.

  Further, the frequency f of the excitation signal may be changed randomly until the voltage peak value Vp set in step S107 matches the target voltage value Vm.

(2) The frequency f of the excitation signal output from the motor resolver 44 is not limited to the correction according to the voltage peak value Vp, but is output from the first resolver 35 by using the above-described excitation signal frequency correction processing. The frequency f of the excitation signal may be corrected according to the voltage peak value of the excitation voltage in the excitation coil of the first resolver 35. Further, the frequency f of the excitation signal output from the second resolver 37 may be corrected according to the voltage peak value of the excitation voltage in the excitation coil of the second resolver 37.

(3) In the ECU 60 having a D / A converter, the low-pass filter 64 may be eliminated and a pseudo sine wave excitation signal may be output from the D / A converter to the buffer 65.

(4) In the ECU 60 having the PWM output port, a primary low-pass filter may be adopted by using a rectangular wave DUTY variable signal output from the PWM output port instead of the low-pass filter 64.

(5) The low-pass filter 64 is not limited to a secondary filter using a resistor and a capacitor, and may be a filter using a coil and a capacitor, or may be a multistage of them.

(6) In the above embodiment, the rotation angle detection device including the ECU 60 and the motor resolver 44 is applied to a so-called rack-type electric power steering device that can transmit the assist force output from the motor 40 to the rack mechanism. However, the present invention is not limited to this. For example, a so-called column-type electric power steering system that can transmit the assist force output from the motor to the pinion shaft 23 via the reduction gear. You may apply to an apparatus.
Also, a so-called rack parallel type electric power steering device in which the rack shaft and the motor are arranged in parallel, a so-called pinion type electric power steering device in which the motor is arranged in the pinion portion having the pinion shaft 23, or a so-called You may apply to a dual pinion type electric power steering device.

It is a lineblock diagram showing the composition of the electric power steering device concerning the embodiment of the present invention. It is an enlarged view in the ellipse by the dashed-dotted line II shown in FIG. It is an enlarged view in the ellipse by the dashed-dotted line III shown in FIG. It is a block diagram which shows the electric constitution of ECU which controls the electric power steering device of this embodiment. It is a circuit diagram which shows the structure of a resonance circuit. It is a graph for demonstrating the principle which makes excitation voltage high using the frequency resonance characteristic of a resonance circuit. It is explanatory drawing for demonstrating the electrical property of a motor resolver. It is a flowchart which shows the flow of the frequency correction process of the excitation signal by ECU of the electric power steering device which concerns on this embodiment. It is a graph which shows the relationship between the frequency of the excitation signal in each characteristic map, a voltage peak value, and the resonance frequency.

Explanation of symbols

20 ... Electric power steering device 35 ... First resolver (resolver)
37 ... Second resolver (resolver)
40 ... motor (rotating body)
43 ... Motor shaft (rotating body)
44 ... Motor resolver (resolver)
47a ... excitation coil 60 ... ECU (rotation angle detector)
61 ... MPU (excitation means, rotation angle calculation means, abnormality determination means, correction means)
66 ... condenser 67 ... Voltage sensor 80 ... resonant circuit C ... capacitance f ... frequency fc ... resonant frequency fc k _... initial resonant frequency L ... inductance _{M 1 ~M n, M a,} M b, M k ... characteristic map V _L ... Excitation voltage Vm ... Target voltage value Vp ... Peak voltage value Q ... Sharpness θm ... Rotation angle

Claims (4)

A resolver for detecting a rotation angle of a rotating body, wherein the resolver outputs a rotation angle signal corresponding to the rotation angle by an excitation signal input to an excitation coil;
Excitation signal generating means for generating and outputting the excitation signal;
A capacitor connected between the excitation coil and the excitation signal generating means;
Voltage detection means for detecting an excitation voltage of the excitation coil;
Rotation angle calculation means for calculating the rotation angle based on the rotation angle signal input from the resolver;
A rotation angle detection device comprising:
The capacitance of the capacitor and the inductance of the exciting coil are set so as to increase the sharpness of the resonance circuit composed of the capacitor and the exciting coil,
The excitation signal generation means controls the frequency of the excitation signal so that the amplitude value of the excitation voltage approaches a target voltage value set to be equal to or lower than the resonance voltage of the resonance circuit. . A plurality of maps showing the relationship between the frequency of the excitation signal and the amplitude value of the excitation voltage that changes in accordance with the change of the frequency are provided for each resonance frequency that changes in the resonance circuit, and are output from the excitation signal generating means. Map selection means for selecting, from the plurality of maps, a map in which the frequency of the excitation signal and the amplitude value of the excitation voltage detected by the voltage detection means corresponding to the excitation signal are established;
The rotation angle detecting device according to claim 1, wherein the excitation signal generation unit controls the frequency of the excitation signal to be equal to a resonance frequency of a map selected by the map selection unit.   The excitation signal generating means lowers the frequency of the excitation signal when the amplitude value of the excitation voltage is lower than the target voltage value, and the excitation signal generation means when the amplitude value of the excitation voltage is higher than the target voltage value. The rotation angle detection device according to claim 1, wherein the excitation signal is generated so as to increase the frequency of the signal. It has a motor that outputs assist force that can assist steering by the steering wheel,
An electric power steering apparatus, wherein the rotation angle of the motor is detected by the rotation angle detection device according to any one of claims 1 to 3, and the motor is controlled based on the rotation angle.

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