JP7380288B2 - Torque measuring device and its assembly method - Google Patents

Description

The present invention relates to a torque measuring device for measuring torque applied to a torque transmission shaft and a method for assembling the same.

FIG. 7 shows a torque measuring device described in Japanese Unexamined Patent Publication No. 2012-98268. The torque measuring device includes a torque transmission shaft 1, a pair of encoders 2a, 2b, and a pair of sensors 3a, 3b. Each of the encoders 2a and 2b has detection surfaces 4a and 4b on the outer peripheral surface in which N poles and S poles are arranged alternately and at equal intervals in the circumferential direction. It is externally fitted and fixed at two positions spaced apart in the axial direction. Each of the sensors 3a, 3b has a detecting section 5a, 5b at its tip end facing the detected surface 4a, 4b, and changes the output signal according to the magnetic flux density passing through the detecting section 5a, 5b. That is, the output signals of the sensors 3a, 3b change periodically as the encoders 2a, 2b rotate together with the torque transmission shaft 1.

In the illustrated torque measuring device, when a torque transmission shaft 1 is elastically deformed in a torsional direction as torque is transmitted and a pair of encoders 2a and 2b are relatively displaced in a rotational direction, output signals from a pair of sensors 3a and 3b are generated. The phase difference between them changes. The phase difference between the output signals of the pair of sensors 3a and 3b has a correlation with the amount of elastic deformation of the torque transmission shaft 1 in the torsional direction. Further, the amount of elastic deformation of the torque transmission shaft 1 in the torsional direction has a correlation with the magnitude of the torque transmitted by the torque transmission shaft 1. Therefore, the torque measuring device is configured to determine the torque transmitted by the torque transmission shaft 1 based on the phase difference between the output signals of the pair of sensors 3a and 3b.

JP2012-98268A

The torque measuring device described in Japanese Patent Application Laid-open No. 2012-98268 utilizes the phase difference between the output signals of a pair of sensors to determine the torque transmitted by the torque transmission shaft. As the frequency difference increases, it becomes difficult to accurately determine torque. The reason for this will be explained below with reference to FIGS. 8 and 9.

As shown in FIG. 8, the sensor 3a (3b) used in the torque measuring device generally includes a magnetic detection element 6 such as a Hall element, and a controller for converting the output signal of the magnetic detection element 6 into a digital signal. 7 and an oscillator (oscillation circuit) 8.

The magnetic detection element 6 functions as a detection part of the sensor 3a (3b), and generates a sinusoidal analog signal as shown in FIG. 9(A) according to the magnetic flux density passing through it. Output. The analog signal of the magnetic detection element 6 is converted by the controller 7 into a pulse signal (rectangular wave signal) expressed in binary values of Hi and Low, as shown in FIG. 9(D). The controller 7 determines the magnitude relationship between the analog signal of the magnetic detection element 6 and the threshold value at time intervals determined by the oscillator 8.

Specifically, the oscillator 8 outputs a rectangular waveform clock signal as shown in FIG. 9(B). The frequency of the clock signal is called a clock frequency, and the frequency of the clock signal of each sensor is constant. The controller 7 uses the rising and falling timings of the clock signal to determine the magnitude relationship between the analog signal of the magnetic detection element 6 and the threshold value. Therefore, as shown in (C) and (D) of FIG. 9, the timing at which the analog signal of the magnetic detection element 6 actually exceeds the threshold value and the timing at which the controller 7 outputs a Hi signal to determine that the threshold value has been exceeded. There will be a time lag, that is, a delay time, that changes depending on the clock frequency.

On the other hand, it is known that variations in clock frequency exist even among sensors of the same product number due to manufacturing distortions and manufacturing errors of the oscillator. Therefore, there is a difference in delay time between the output signals of the pair of sensors due to the difference in clock frequency. Therefore, the phase difference between the output signals of the pair of sensors used to determine the torque includes a component (error) caused by the difference in delay time between the two sensors. If the phase difference between the output signals includes a large error (component caused by the difference in delay time), it will cause a decrease in torque measurement accuracy.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to realize a torque measuring device and a method for assembling the same, which can improve torque measurement accuracy.

A torque measuring device to be assembled according to the present invention includes a torque transmission shaft, a pair of encoders, a pair of sensors, and a computing unit.
The torque transmission shaft transmits torque during use.
The pair of encoders are supported by a member that rotates directly on the torque transmission shaft or in synchronization with the torque transmission shaft during use, and have detection surfaces whose characteristics alternately change in the circumferential direction. There is.
The pair of sensors are supported by parts that do not rotate even when in use, and have a detection section facing each detected surface of the pair of encoders, and output signals in response to changes in the characteristics of the detected surfaces. change.
The computing unit has a function of determining the torque transmitted by the torque transmission shaft based on a phase difference between the output signals of the pair of sensors.

An example of a characteristic change of the detection surface that changes the output signal of the sensor is, for example, when the sensor has N poles and S poles arranged alternately in the circumferential direction on the detection surface. An example of this is a change in magnetic properties, such as a change in the magnetic flux density passing through the sensor depending on the circumferential position of the opposing detection surfaces.

In the method for assembling a torque measuring device of the present invention, when assembling the torque measuring device having the above-described configuration, the absolute value of the clock frequency difference is selected from among a plurality of sensors that are candidates for use of the pair of sensors. is less than a predetermined threshold.

In the present invention, the threshold value can be determined as follows.
That is, a first relational expression representing the relationship between the clock frequency difference and the speed characteristic is determined in advance by using a plurality of sensor sets consisting of two sensors arbitrarily combined from among the plurality of sensors. Then, based on the first relational expression, the clock frequency difference is determined when the speed characteristic is set to an allowable limit value, and the clock frequency difference is set as the threshold value.
In this case, the first relational expression can be obtained by determining the clock frequency difference and the speed characteristic for each sensor group and linearly approximating the relationship between the clock frequency difference and the speed characteristic.
Further, in a state in which the torque measuring device is temporarily assembled using each of the sensor sets, the rotational speed of the torque transmission shaft is changed while applying a constant torque to the torque transmission shaft. A second relational expression representing the relationship between the rotational speed and the magnitude of the torque calculated by the arithmetic unit may be obtained, and the slope of the second relational expression may be taken as the speed characteristic.
In the present invention, the change in the characteristics of the detected surface can be a change in magnetic characteristics.

In the torque measuring device of the present invention, the clock frequency of each of the pair of sensors is f ₀ , f ₀ +Δf _clock [Hz], and the number of response clocks of each of the pair of sensors is c, The resolution when the rotation speed of the torque transmission shaft is N ₀ [rpm] is m ₀ [Nm], and the speed-dependent error when the rotation speed of the torque transmission shaft is N ₁ [rpm] is m ₁ [ Nm], the absolute value of the clock frequency difference Δf _clock can be set to a value that satisfies the following relational expression or less.

According to the present invention as described above, the clock frequency difference between a pair of sensors can be made equal to or less than a predetermined threshold value. Therefore, the difference in delay time between the output signals of a pair of sensors can be suppressed to a smaller value than when a pair of randomly selected sensors is used. As a result, it is possible to improve torque measurement accuracy.

FIG. 1 is a sectional view showing a torque transmission device according to a first example of the embodiment. FIG. 2 is a conceptual diagram of a pair of sensors and a computing unit used in the torque transmission device according to the first example of the embodiment. FIG. 3 is a diagram showing output signals of a pair of sensors, in which (A) shows the output signal before torque input, and (B) shows the output signal after torque input. FIG. 4 is a graph showing the relationship between the rotational speed of the torque transmission shaft and the torque output value calculated by the calculator. FIG. 5 is a graph showing the relationship between clock frequency difference and speed characteristics. FIG. 6 is a graph in which clock frequency differences and speed characteristics of nine sensor groups are plotted on coordinates and obtained by linear approximation. FIG. 7 is a side view showing an example of a conventional structure of a torque measuring device. FIG. 8 is a conceptual diagram of a sensor used in the torque measuring device. (A) of FIG. 9 is a diagram showing an analog signal outputted by the magnetic detection element, (B) of FIG. 9 is a diagram showing a clock signal outputted by the oscillator, and (C) of FIG. FIG. 9D is a diagram illustrating the reason why a delay time occurs based on the clock frequency, and FIG. 9D is a diagram illustrating a pulse signal output by the controller.

[First example of embodiment]
A first example of the embodiment will be described using FIGS. 1 to 6.
Hereinafter, the structure of the torque measuring device of this example will be explained, and then a method of selecting a sensor when assembling the torque measuring device will be explained.

The torque measuring device of this example is used by being incorporated into an automatic transmission for an automobile, and includes a housing (transmission case) 9, a torque transmission shaft 1a functioning as a counter shaft, and an input gear each functioning as a counter gear. 10 and an output gear 11, a pair of rolling bearings 12a and 12b, a first encoder 13 and a second encoder 14, a pair of sensor units 15a and 15b, and a computing unit 16.
In the following description, one side in the axial direction refers to the right side in FIG. 1, and the other side in the axial direction refers to the left side in FIG. 1.

The torque transmission shaft 1a is made of alloy steel such as carbon steel and has a hollow cylindrical shape, and is subjected to heat treatment such as hardening and tempering. In addition, in this example, the input gear 10 for inputting torque to the torque transmission shaft 1a is externally fitted and fixed to the other axially side portion of the torque transmission shaft 1a (left side portion in FIG. 1), and outputs torque. An output gear 11 is externally fitted and fixed to one axially side portion (the right side portion in FIG. 1) of the torque transmission shaft 1a. In addition, a pair of rolling bearings 12a and 12b connect both sides (one end and the other end) of the torque transmission shaft 1a between which the input gear 10 and the output gear 11 are fitted. It is rotatably supported with respect to the housing 9.

The input gear 10 and the output gear 11 are helical gears or spur gears made of alloy steel such as carbon steel, and are configured separately from the torque transmission shaft 1a. The fitting portions between the input gear 10 and the output gear 11 and the torque transmission shaft 1a include a cylindrical surface fitting portion to ensure concentricity (coaxiality) and an involute spline engagement portion to prevent relative rotation. A configuration is adopted in which the two are arranged adjacent to each other in the axial direction.

The pair of rolling bearings 12a and 12b are, for example, deep groove type, angular type ball bearings, tapered roller bearings, cylindrical roller bearings, radial needle bearings, self-aligning roller bearings, etc. (the illustrated example is a ball bearing), Each of them includes an annular outer ring 17a, 17b, an annular inner ring 18a, 18b, and a plurality of rolling elements 19. The outer rings 17a and 17b are stationary rings that do not rotate even during use, and are fixedly fitted into the housing 9. The inner rings 18a and 18b are rotary rings that rotate during use, and are externally fitted and fixed to the torque transmission shaft 1a. The rolling elements 19 are held by a retainer between an outer ring raceway formed on the inner peripheral surface of the outer rings 17a, 17b and an inner ring raceway formed on the outer peripheral surface of the inner rings 18a, 18b. They are freely placed. Moreover, when using angular contact ball bearings or tapered roller bearings as the rolling bearings 12a and 12b, the contact angles can be made opposite to each other.

The first encoder 13 is supported and fixed to one end of the torque transmission shaft 1a in the axial direction. Therefore, the first encoder 13 is rotatable (in synchronization) with the one axial end of the torque transmission shaft 1a. On the other hand, the second encoder 14 is externally fitted and fixed to the other end of the torque transmission shaft 1a in the axial direction. Therefore, the second encoder 14 is rotatable (in synchronization) with the other end of the torque transmission shaft 1a in the axial direction.

The first encoder 13 includes an annular threaded ring 20 such as a nut that is screwed and fixed to one end of the torque transmission shaft 1a in the axial direction, and a rubber or synthetic resin fixed to the outer peripheral surface of the threaded ring 20. The encoder body 21 is made of a permanent magnet such as a rubber magnet or a plastic magnet, and the encoder body 21 is made entirely of a cylindrical shape by dispersing magnetic powder in a polymeric material such as a rubber magnet or a plastic magnet. On the other hand, the second encoder 14 includes a threaded ring 22 such as a nut screwed onto the other end of the torque transmission shaft 1a in the axial direction, and a permanent magnet fixed to the outer peripheral surface of the threaded ring 22. It is composed of an encoder main body 23.

Examples of the magnetic powder contained in the encoder bodies 21 and 23 include ferrite magnetic powder such as strontium ferrite and barium ferrite, and rare earth element magnetic powder such as samarium-iron, samarium-cobalt, and neodymium-iron-boron. can be adopted. The outer peripheral surfaces of the encoder bodies 21 and 23, each of which is a surface to be detected, have the same diameter and are arranged coaxially with each other. Further, on the outer circumferential surfaces of the encoder bodies 21 and 23, S poles and N poles are arranged alternately and at equal pitches in the circumferential direction, and the magnetic properties are arranged alternately and at equal pitches in the circumferential direction. It's changing. The total number of magnetic poles (S poles, N poles) on the outer peripheral surfaces of the encoder bodies 21 and 23 are the same.

The sensor unit 15a is supported and fixed to an outer ring 17a that constitutes a rolling bearing 12a, and includes a first sensor 24, a sensor block 25 made of synthetic resin that supports the first sensor 24, and a sensor block 25 with the sensor block 25 inside. A metal sensor cap 26 is also provided. On the other hand, the sensor unit 15b is supported and fixed to an outer ring 17b constituting the rolling bearing 12b, and includes a second sensor 27, a sensor block 28 made of synthetic resin that supports the second sensor 27, and the sensor block The sensor cap 29 is made of metal and has a sensor cap 28 held inside.

As shown in FIG. 2, the first sensor 24 includes a magnetic detection element 30a such as a Hall element, a Hall IC, an MR element (including a GMR element, a TMR element, and an AMR element), and converts the output signal of the magnetic detection element 30a into a digital signal. It includes a controller 31a and an oscillator (oscillation circuit) 32a for converting into signals. The magnetic detection element 30a is arranged at the detection part of the first sensor 24, and outputs a sinusoidal analog signal according to the magnetic flux density passing through itself. The analog signal of the magnetic detection element 30a is converted by the controller 31a into a pulse signal expressed in binary values of Hi and Low. The controller 31a determines the magnitude relationship between the analog signal of the magnetic detection element 30a and the threshold value at the time interval of the clock frequency of the clock signal output by the oscillator 32a. Although there are individual differences in the clock frequency _f1 of the oscillator 32a, it is determined depending on the resolution, shaft rigidity of the torque transmission shaft 1a, rotation speed, etc., as described later.

As shown in FIG. 2, the second sensor 27 includes a magnetic detection element 30b of the same type as the first sensor 24, a controller 31b for converting the output signal of the magnetic detection element 30b into a digital signal, and an oscillator (oscillation circuit) 32b. It is equipped with such things as The magnetic detection element 30b is arranged in the detection section of the second sensor 27, and outputs a sinusoidal analog signal according to the magnetic flux density passing through itself. The analog signal of the magnetic detection element 30b is converted by the controller 31b into a pulse signal expressed in binary values of Hi and Low. The controller 31b determines the magnitude relationship between the analog signal of the magnetic detection element 30b and the threshold value at the time interval of the clock frequency of the clock signal output by the oscillator 32b. Note that although there are individual differences in the clock frequency _f2 of the oscillator 32b, it is determined depending on the resolution, shaft rigidity of the torque transmission shaft 1a, rotation speed, etc., as described later.

With the sensor units 15a and 15b supported by the outer rings 17a and 17b, respectively, the detection part (magnetic detection element 30a) of the first sensor 24 is placed on the detection surface of the first encoder 13 (the outer peripheral surface of the encoder body 21). In addition, the detection portion (magnetic detection element 30b) of the second sensor 27 is made to closely oppose the detection surface of the second encoder 14 (the outer peripheral surface of the encoder main body 23). As a result, the first sensor 24 changes its output signal according to the magnetic flux density passing through its detection section (magnetic flux passing through its detection surface/area of its detection surface), and the second sensor 27 The output signal is changed according to the magnetic flux density passing through the detection section. In this example, the output signals of the first sensor 24 and the second sensor 27 can be transmitted to the computing unit 16 through harnesses 33a and 33b, respectively.

The computing unit 16 has the function of determining the rotational speed of the torque transmission shaft 1a using the output signals of the first sensor 24 and the second sensor 27, and also determining the torque transmitted by the torque transmission shaft 1a.

The output signal of the first sensor 24 and the output signal of the second sensor 27 change periodically as the first encoder 13 and the second encoder 14 rotate together with the torque transmission shaft 1a. Here, since the frequency (and period) of change is the product of the rotational speed of the torque transmission shaft 1a and the number of poles of the encoder, it is necessary to check the number of poles of the first encoder 13 and the second encoder 14 in advance. , the rotational speed of the torque transmission shaft 1a is determined based on the frequency (or period).

Further, when transmitting torque by the torque transmission shaft 1a, a portion of the torque transmission shaft 1a between the input gear 10 and the output gear 11 is elastically torsionally deformed. As a result, the ends of the torque transmission shaft 1a on both sides in the axial direction are displaced relative to each other in the rotational direction. As a result, the first encoder 13 and the second encoder 14 are displaced relative to each other in the rotational direction, so that the position between the output signals of the first sensor 24 and the second sensor 27, which corresponds to the torsion angle of the torque transmission shaft 1a, is The phase difference (and phase difference ratio) changes. The phase difference has a correlation with the amount of elastic deformation of the torque transmission shaft 1a in the torsional direction. Therefore, the computing unit 16 uses data such as a table or map showing the relationship between torque and phase difference determined in advance based on the torsional rigidity of the torque transmission shaft 1a, and calculates the torque transmitted by the torque transmission shaft 1a. Torque can be determined.

However, if the first sensor 24 and the second sensor 27 are randomly selected from a plurality of sensors that are candidates for use as the first sensor 24 and the second sensor 27, the clock frequency of the first sensor 24 The clock frequency difference (absolute value), which is the difference between the clock frequency of There is sex. As a result, the torque output value calculated by the computing unit 16 will include a large drift error (details will be described later), and the torque measurement accuracy may deteriorate.

Hereinafter, while explaining the process of determining the torque transmitted by the torque transmission shaft 1a from the phase difference between the output signals of the first sensor 24 and the second sensor 27, The relationship between the clock frequency difference (Δf _clock = f ₁ - f ₂ ) and the drift error will be explained. Note that the clock frequency difference (Δf _clock = f ₁ − f ₂ ) between the first sensor 24 and the second sensor 27 is constant unless the combination of sensors is changed.

Torque is applied to the torque transmission shaft 1a, and elastic torsional deformation occurs in the torque transmission shaft 1a, so that the output signal A of the first sensor 24 and the output signal B of the second sensor 27 change to the state before torque input. Consider a case in which the state changes from (A) in FIG. 3, which shows the state, to (B) in FIG. 3, which shows the state after torque input. Here, the phase difference (measured value) between the output signal A of the first sensor 24 and the output signal B of the second sensor 27 after torque input is t [s], and the first sensor 24 and the second sensor 27 Let T[s] be the period (measured value) of the output signals A and B. Further, the phase difference (initial phase difference) between the output signal A of the first sensor 24 and the output signal B of the second sensor 27 before torque input is tx[s].

Since the phase difference t changes according to the rotational speed (rotational speed) of the torque transmission shaft 1a, unless the rotational speed of the torque transmission shaft 1a is a known constant value, the torque cannot be calculated only from the phase difference t. I can't. Therefore, in order to remove the influence of the rotational speed of the torque transmission shaft 1a, the phase difference ratio r is obtained by dividing the phase difference t by the period T. The phase difference ratio r can be expressed by the following equation (1).

As described above, the output signal A of the first sensor 24 has a delay time corresponding to the clock frequency _f1 of the first sensor 24, whereas the output signal B of the second sensor 27 has a delay time corresponding to the clock frequency f1 of the first sensor 24. A delay time is generated depending on the clock frequency _f2 . Therefore, if the clock frequency _f1 of the first sensor 24 and the clock frequency _f2 of the second sensor 27 are different, there is a delay between the output signal A of the first sensor 24 and the output signal B of the second sensor 27. This causes a time difference. Therefore, the phase difference t in the above formula (1) is the original (correct) phase difference t ₀ [s] reflecting the torsion angle of the torque transmission shaft 1a, the output signal A of the first sensor 24, and the second sensor The difference in delay time between the output signal B and the output signal B of 27 can be divided into Δt[s]. Therefore, the above equation (1) can be expressed as the following equation (2). A term including the delay time difference Δt[s] becomes an error component in torque calculation. Note that the phase difference t ₀ includes the initial phase difference tx.

また、ホールＩＣなどの磁気検出素子３０ａ、３０ｂは、固有の駆動周期及びクロック周波数を有するため、遅延時間（τ）は固有の値になる。なお、応答クロック数（ｃ）は、第一センサ２４と第二センサ２７とでプログラムが共通であるため一定になる。このため、磁気検出素子３０ａ、３０ｂの駆動周期差を△τとし、駆動周期をそれぞれτ_０、τ_０＋△τと置くと、応答には、次の式（４）で表される遅延時間の差（△ｔ）を生じる。

Here, the delay time (τ), which is the time required for the magnetic detection elements 30a and 30b such as Hall ICs to respond, is determined by the following (3) using the response clock number (c) and the drive period (τ ₀ ). ) can be expressed by the formula.

Furthermore, since the magnetic sensing elements 30a and 30b such as Hall ICs have a unique drive cycle and clock frequency, the delay time (τ) has a unique value. Note that the number of response clocks (c) is constant because the first sensor 24 and the second sensor 27 have a common program. Therefore, if the drive period difference between the magnetic sensing elements 30a and 30b is △τ, and the drive periods are set as τ ₀ and τ ₀ +△τ, respectively, the response will have a delay time expressed by the following equation (4). A difference (Δt) is generated.

On the other hand, the right side of the above equation (2) can be divided into the first term expressed by t ₀ /T and the second term expressed by Δt/T, of which the first term ( t ₀ /T) is a true phase difference ratio that does not depend on the rotational speed (rotational speed) of the torque transmission shaft 1a and does not include an error caused by the difference in delay time of the magnetic detection elements, and is expressed as By substituting _r0 , the following equation (5) is obtained.

As mentioned above, the right side of the above equation (5) is the true phase difference ratio r ₀ (first term) that does not depend on the rotation speed of the torque transmission shaft 1a and does not include an error component, and the torque transmission shaft 1a The phase difference ratio Δt/T (second term) is caused by the difference in delay time depending on the rotation speed. Therefore, this second term becomes a component of the drift error of the phase difference ratio r.

In addition, the above equation (5) can be expressed as a relational equation (torque calculation formula ) can be transformed into Note that in formula (6), M [Nm] represents the torque output value calculated by the calculator 16, and M ₀ [Nm] represents the magnitude of the true torque transmitted by the torque transmission shaft 1a. where _k1 represents a coefficient, and N [rpm] represents the rotational speed of the torque transmission shaft 1a.

Therefore, if there is a clock frequency difference between the first sensor 24 and the second sensor 27, the torque output value M calculated by the calculator 16 will include the second term ( It can be seen that a drift error (ΔM) represented by k ₁ ΔtN) is included.

Further, it can be seen that the drift error (ΔM) included in the torque output value M is proportional to the difference in delay time Δt and the rotational speed N of the torque transmission shaft 1a. Therefore, the drift error (ΔM) included in the torque output value M increases as the delay time difference Δt increases, and increases as the rotational speed N of the torque transmission shaft 1a increases. It should be noted that the torque output value M calculated by the calculator 16 is proportional to the phase difference ratio r (M∝r), and the period T is given by the number of pole pairs of the first encoder 13 and the second encoder 14 as P. , T=60/PN. Therefore, the drift error (ΔM) can also be expressed by the following equation (7). Note that in formula (7), k ₂ represents a coefficient, and when the torsional rigidity of the torque transmission shaft 1a is G [Nm/rad], k ₂ =2πG/P.

Therefore, in this example, not only sensors with the same product number are used as the first sensor 24 and the second sensor 27, but also the clock frequency _f1 of the first sensor 24 and the clock frequency f1 of the second sensor 27 are changed when assembling the torque transmission device. The first sensor 24 and the second sensor 27 are selected so that the absolute value of the difference (|Δf _clock |) from the frequency f ₂ is small. Specifically, the clock frequencies of a plurality of sensors that are candidates for use as the first sensor 24 and the second sensor 27 are measured in advance, and the absolute value of the clock frequency difference among the plurality of sensors is less than or equal to a predetermined threshold. Two sensors are selected and used as the first sensor 24 and second sensor 27.

Theoretically, the smaller the clock frequency difference (absolute value) between the first sensor 24 and the second sensor 27 is (preferably zero), the more it will be included in the torque calculated by the calculator 16. This is preferable because drift errors can be suppressed. However, it may be practically difficult to make the clock frequency difference between the first sensor 24 and the second sensor 27 zero, and it may not meet the torque measurement accuracy required of the torque measurement device. There is also the possibility of over-quality in the relationship. Therefore, it is important to keep the clock frequency difference within a range that satisfies the torque measurement accuracy required of the torque measurement device. Hereinafter, a method of setting a threshold value (upper limit value) of the clock frequency difference necessary to satisfy the torque measurement accuracy required of the torque measuring device will be described.

Equation (6) obtained as described above is expressed in the graph shown in FIG. 4, when the horizontal axis represents the rotational speed of the torque transmission shaft 1a and the vertical axis represents the torque output value calculated by the calculator 16. The slope is k ₁ Δt [Nm/rpm]. In this example, this slope is called a speed characteristic and is represented by the symbol S. Since the speed characteristic S is correlated with the difference in delay time Δt, if the clock frequency difference between the first sensor 24 and the second sensor 27 changes, as shown in FIG. Its value changes proportionally. Therefore, using the clock frequency difference Δf _clock , the speed characteristic S can be expressed by the following equation (8).

In the above formula (8), h corresponds to the slope of the graph in FIG. 5, and is a coefficient that changes depending on the magnitude of the torsional rigidity of the torque transmission shaft 1a. Therefore, it can be seen that the speed characteristic S has a proportional relationship with the coefficient h determined by the torsional rigidity of the torque transmission shaft 1a used. Furthermore, it can be seen that by setting the clock frequency difference Δf _clock small, it is possible to suppress the difference in delay time, and it is possible to suppress the drift error of the speed characteristic S and, by extension, the torque. Furthermore, by transforming the above equation (8), the following equation (9) can be obtained.

Using the above equation (9), by setting the value of the speed characteristic S to an allowable limit value that satisfies the torque measurement accuracy, it is possible to obtain the clock frequency difference Δf _clock required therefor. In other words, by setting the degree to which the drift error needs to be suppressed, the necessary clock frequency difference Δf _clock can be found. Next, a specific method of calculating the above equations (8) and (9) will be explained.

First, a plurality of sensors (at least three or more) having the same product number are prepared as candidates for use as the first sensor 24 and the second sensor 27. Then, from among the plurality of sensors, a plurality of sensor sets consisting of two sensors arbitrarily combined are prepared. Then, a torque transmission device is temporarily assembled using a pair of sensors constituting each sensor group.

Thereafter, the rotation speed of the torque transmission shaft 1a is changed while applying a known constant torque to the torque transmission shaft 1a. As a result, the above-mentioned equation (6) (second relational equation), which is a relational equation representing the relationship between the rotational speed of the torque transmission shaft 1a and the magnitude of the torque calculated by the calculator 16, is calculated for each sensor group. demand. Then, a speed characteristic S corresponding to the slope (k ₁ Δt) of this relational expression is determined.

Then, using the clock frequency difference and speed characteristic of each of the plurality of sensor sets, the above equation (8) (first relational expression), which is a relational expression expressing the relationship between the clock frequency difference and the speed characteristic, is determined. That is, the value of the coefficient h determined by the torsional rigidity of the torque transmission shaft 1a is specified.

Specifically, for example, when the clock frequency difference (△f ₁ , △f ₂ ... △f ₉ ) and speed characteristic (S ₁ , S ₂ ... S ₉ ) are calculated for each of nine sensor sets. , when these clock frequency differences and speed characteristics are plotted on coordinates, it becomes as shown in FIG. Therefore, by linearly approximating the relationship between the clock frequency difference and the speed characteristic, for example, the relational expression S=0.0085△f _clock corresponding to equation (8) and △ f _clock = corresponding to equation (9) are obtained. A relational expression of S/0.0085 can be obtained. Therefore, if these relational expressions are determined in advance, if the allowable limit value of the speed characteristic S that satisfies torque measurement accuracy is set to, for example, 2.0×10 ^-3 [Nm/rpm], this It can be calculated that the clock frequency difference that satisfies the following is 235 kHz. In this way, in this example, the speed characteristic S can be set to an arbitrary allowable limit value according to the torque measurement accuracy required of the torque transmission device, and the threshold value that is the upper limit value of the clock frequency difference can be determined. .

ここで、ｋ_２を２πＧ／Ｐに置き換えるとともに、Ｔ_０を６０／Ｎ_０Ｐに置き換えると、次の式（１１）が得られる。

この式（１１）からは、たとえば、トルク伝達軸の軸剛性Ｇが１．０×１０^４Ｎｍ／ｒａｄであり、回転数Ｎ_０が６０００ｒｐｍである場合に、分解能ｍ_０を１Ｎｍとしたい場合には、センサのクロック周波数ｆ_０を６．３ＭＨｚとすればよいことが求められる。 Next, a method for determining the clock frequency and clock frequency difference of the sensors (first sensor 24 and second sensor 27) will be explained.
In a pulse phase difference type torque measuring device such as the present example, it is impossible to detect torque that causes a time change that is shorter than the drive cycle of the magnetic detection element used. Therefore, if you want the resolution to be m ₀ [Nm] when the rotational speed of the torque transmission shaft is N ₀ [rpm] (the period is T ₀ [s]), the resolution m ₀ is m ₀ = k ₂ × Since it is expressed by τ ₀ /T ₀ , the sensor clock frequency f ₀ (1/τ ₀ ) [Hz] can be expressed by the following equation (10).

Here, by replacing k ₂ with 2πG/P and replacing T ₀ with 60/N ₀ P, the following equation (11) is obtained.

From this equation (11), for example, when the axial rigidity G of the torque transmission shaft is 1.0×10 ⁴ Nm/rad and the rotational speed N ₀ is 6000 rpm, if you want the resolution m ₀ to be 1 Nm, It is required that the clock frequency f ₀ of the sensor should be 6.3 MHz.

Note that the time resolution of the output of the sensor is the delay time τ [s] required for the response of the magnetic detection element. Also, the delay time τ is the product of the number of response clocks c and the driving period τ ₀ , so if the response frequency is f (=1/τ) [Hz], the following ( 12) Equation is obtained.

Furthermore, if the respective clock frequencies of the two sensors are set as f ₀ , f ₀ +△f _clock [Hz], the drive cycle difference (△τ) between the two magnetic detection elements is expressed by the following equation (13). can be expressed.

また、式（１４）は、次の式（１５）に変形することができる。

さらに、式（１５）より、クロック周波数差△ｆ_{ｃｌｏｃｋ}［Ｈｚ］とクロック周波数ｆ_０との比は、次の式（１６）で表すことができる。

この式（１６）からは、たとえば、応答クロック数（ｃ）が１００の磁気検出素子を使用し、最高回転数で速度依存誤差を分解能と同程度にしたい場合には、クロック周波数差△ｆ_{ｃｌｏｃｋ}を、クロック周波数ｆ_０の１％以内に抑えれば良いことが求められる。つまり、クロック周波数差△ｆ_{ｃｌｏｃｋ}の絶対値を、上記式（１６）から求められる値以下になるように設定すれば良い。 Furthermore, if the rotation speed of the torque transmission shaft is N ₁ [rpm] and you want the speed-dependent error (measurement error) to be m ₁ [Nm], then the rotation speed of the torque transmission shaft is N ₁ [rpm]. If the pulse period in this case is T ₁ [s], the measurement error m ₁ [Nm] can be expressed by the following equation (14).

Further, equation (14) can be transformed into the following equation (15).

Furthermore, from equation (15), the ratio between the clock frequency difference Δf _clock [Hz] and the clock frequency f ₀ can be expressed by the following equation (16).

From this equation (16), for example, if you use a magnetic detection element with a response clock number (c) of 100 and want to make the speed-dependent error at the maximum rotation speed the same as the resolution, the clock frequency difference △f _clock It is required that the clock frequency f0 be suppressed to within 1% of the clock frequency _f0 . In other words, the absolute value of the clock frequency difference Δf _clock may be set to be equal to or less than the value obtained from the above equation (16).

According to the torque transmission device of this example assembled by carrying out the method for selecting the first sensor 24 and the second sensor 27 as described above, the clock frequency difference between the first sensor 24 and the second sensor 27 is determined by torque measurement. The torque measurement accuracy required for the device can be kept within a satisfactory range. Therefore, the difference in delay time between the output signal A of the first sensor 24 and the output signal B of the second sensor 27 is made sufficiently smaller than when using a pair of randomly selected sensors. Therefore, it is possible to suppress a drift error occurring in the torque output value calculated by the calculator 16. As a result, it is possible to improve torque measurement accuracy.

The torque transmission shaft constituting the torque measuring device of the present invention is not limited to the rotary shaft constituting the power train of an automobile, but includes, for example, the rotary shaft of a wind turbine (the main shaft, the rotary shaft of a speed increaser), the roll neck of a rolling mill, Various mechanical devices, such as rolling shafts of railway vehicles (axles, reducer shafts), machine tool shafts (main shafts, feeding system shafts), construction machinery, agricultural machinery, household appliances, motor shafts, etc. The axis of rotation can be targeted. Further, when configuring a power train of an automobile, for example, an input shaft (turbine shaft) into which torque is input from a torque converter or a countershaft can be targeted.

Furthermore, when the torque measuring device of the present invention is incorporated to configure a transmission, the type of the transmission is not particularly limited, and may be an automatic transmission (AT), various continuously variable transmissions (CVT) such as a belt type or a toroidal type. , automated manual transmission (AMT), dual clutch transmission (DCT), transfer, and other transmissions that change gears under vehicle control can be used. Furthermore, the relationship between the installation position of the transmission and the drive wheels is not particularly limited; front-engine front-wheel drive vehicles (FF vehicles), front-engine rear-wheel drive vehicles (FR vehicles), four-wheel drive vehicles, etc. Targeted.

Further, the measured rotational speed and torque may be used to perform vehicle control other than gear change control and engine output control. Further, the power source placed upstream of the transmission does not necessarily have to be an internal combustion engine such as a gasoline engine or a diesel engine, but may be an electric motor used in a hybrid vehicle or an electric vehicle, for example.

Furthermore, in the embodiment, the first encoder and the second encoder are each made of a permanent magnet, and N poles and S poles are arranged alternately in the circumferential direction on the detection surfaces of both the first and second encoders. An example in which a configuration is adopted has been explained. However, when implementing the present invention, both the first and second encoders are simply made of magnetic material, and the detection surfaces of the first and second encoders are provided with a convex portion, a tongue piece, a pillar portion, etc. It is possible to adopt a configuration in which portions and thinned portions such as recesses, cutouts, or through holes are arranged alternately in the circumferential direction. When adopting such a configuration, permanent magnets are incorporated on both the first and second sensor sides.

1, 1a Torque transmission shaft 2a, 2b Encoder 3a, 3b Sensor 4a, 4b Sensing surface 5a, 5b Detection section 6 Magnetic detection element 7 Controller 8 Oscillator 9 Housing 10 Input gear 11 Output gear 12a, 12b Rolling bearing 13 First encoder 14 Second encoder 15a, 15b Sensor unit 16 Arithmetic unit 17a, 17b Outer ring 18a, 18b Inner ring 19 Rolling element 20 Threaded ring 21 Encoder main body 22 Threaded ring 23 Encoder main body 24 First sensor 25 Sensor block 26 Sensor cap 27 Second sensor 28 Sensor block 29 Sensor cap 30a, 30b Magnetic detection element 31a, 31b Controller 32a, 32b Oscillator 33a, 33b Harness

Claims (4)

A torque transmission shaft that transmits torque during use,
a pair of encoders having detection surfaces whose magnetic properties are alternately changed in the circumferential direction and supported by a member that rotates directly on the torque transmission shaft or in synchronization with the torque transmission shaft during use;
A pair of encoders supported by a portion that does not rotate during use, the detection unit being opposed to each detection surface of the pair of encoders, and changing the output signal in response to changes in the magnetic characteristics of the detection surface. sensor and
a computing unit having a function of determining the torque transmitted by the torque transmission shaft based on the phase difference between the output signals of the pair of sensors;
A method for assembling a torque measuring device comprising:
A method for assembling a torque measuring device, comprising the step of selecting two sensors whose absolute value of clock frequency difference is less than or equal to a predetermined threshold value from among a plurality of sensors that are candidates for use of the pair of sensors. The torque measuring device is temporarily assembled using a plurality of sensor sets consisting of two sensors arbitrarily combined from among the plurality of sensors, and the torque is transmitted while applying a known constant torque to the torque transmission shaft. When changing the rotation speed of the shaft, the speed corresponds to the slope of the graph obtained when the horizontal axis is the rotation speed of the torque transmission shaft and the vertical axis is the torque output value calculated by the arithmetic unit. The characteristics are determined for each sensor group, a first relational expression representing the relationship between the clock frequency difference and the speed characteristic is determined in advance, and the speed characteristic is set to an allowable limit based on the first relational expression. 2. The method of assembling a torque measuring device according to claim 1, wherein the clock frequency difference is determined when the clock frequency difference is set as a value, and the clock frequency difference is used as the threshold value. The torque measuring device according to claim 2, wherein the first relational expression is obtained by determining a clock frequency difference and a speed characteristic for each sensor group and linearly approximating the relationship between the clock frequency difference and the speed characteristic. Assembly method. A torque transmission shaft that transmits torque during use,
a pair of encoders having detection surfaces whose magnetic properties are alternately changed in the circumferential direction and supported by a member that rotates directly on the torque transmission shaft or in synchronization with the torque transmission shaft during use;
a pair of sensors supported by a portion that does not rotate even during use, with a detection unit facing each detection surface of the pair of encoders, and changing an output signal in response to a change in the characteristics of the detection surface; ,
a computing unit having a function of determining the torque transmitted by the torque transmission shaft based on the phase difference between the output signals of the pair of sensors;
Let the clock frequencies of each of the pair of sensors be f ₀ , f ₀ +△f _clock [Hz],
The number of response clocks of each of the pair of sensors is c,
When the rotation speed of the torque transmission shaft is N ₀ [rpm], the resolution is m ₀ [Nm],
When the speed dependent error is m ₁ [Nm] when the rotational speed of the torque transmission shaft is N ₁ [rpm],
A torque measuring device in which the absolute value of the clock frequency difference Δf _clock is set to be less than or equal to a value that satisfies the following relational expression.

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