JP2009198427A - Rotational speed detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotational speed detector capable of compensating a change with time of an error of each pole in an encoder and always obtaining correct signal accuracy. <P>SOLUTION: The rotational speed detector includes the encoder, a rotation detecting sensor, and a computing unit 102 for processing an output signal from the rotation detecting sensor and detecting a rotational speed of a rotary member. The computing unit 102 has a function of obtaining a size of a pitch between each s pole and each n pole while the encoder turns one rotation, a function of obtaining a phase related to a rotation direction of other parts of the s and n poles using a part having a pitch largely different from that of other parts as a reference, a function of correcting a pitch error between the s and n poles to obtain the rotational speed of the rotary member, and a correcting function of periodically calculating to compensate the time with change of the encoder to correct the stored encoder error. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rotation speed detection device for detecting, for example, the rotation speed of wheels of various vehicles (automobiles, railway vehicles) or for detecting the rotation speed of a rotation shaft of various industrial machines.

  In order to control the anti-lock brake system (ABS) and the traction control system (TCS), it is necessary to detect the rotational speed of the wheel supported by the suspension device by the rolling bearing unit. Moreover, in order to drive various industrial machines appropriately, it is necessary to detect the rotational speed of the rotating shaft of the industrial machine. For this reason, various rotational speed detection devices have been proposed and used in practice. For example, Patent Document 1 describes a rotational speed detection device as shown in FIGS. 6 and 7.

  This rotational speed detection device rotatably supports a rotating shaft 2, which is a rotating member that rotates during use, on the inner diameter side of a housing 1 that is a stationary member that does not rotate during use. Further, the end opening of the space 4 between the outer peripheral surface of the rotating shaft 2 and the inner peripheral surface of the housing 1 is closed by the combination seal ring 5. An annular encoder 7 is attached to the outer surface of the slinger 6 constituting the combination seal ring 5. The encoder 7 is a permanent magnet such as a rubber magnet and is magnetized in the axial direction. The magnetization direction is changed alternately and at equal intervals in the circumferential direction. Accordingly, N poles and S poles are alternately arranged at equal intervals on the outer surface of the encoder 7. The number of combinations of these N poles and S poles is 20 to 60 on the entire circumference. Accordingly, there are 40 to 120 boundaries between the N pole and the S pole with respect to the entire circumference of the encoder 7.

  On the other hand, a rotation speed detection sensor 8 is supported on the housing 1, and a detection portion of the rotation speed detection sensor 8 is made to face and face an outer surface that is a detection surface of the encoder 7. The rotational speed detection sensor 8 includes a magnetic detection element whose characteristics change according to the direction and strength of the magnetic flux, such as a Hall element, a magnetoresistive element (MR element), etc., and outputs in response to the change in the characteristics of the magnetic detection element. Change the signal. When the rotating shaft 2 rotates, the S pole and the N pole arranged on the outer surface of the encoder 7 alternately pass through the vicinity of the end face of the detection portion of the rotation speed detection sensor 8. For this reason, the characteristics of the magnetic detection element incorporated in the rotational speed detection sensor 8 change, and the output of the rotational speed detection sensor 8 changes. The frequency at which the output of the rotational speed detection sensor 8 changes in this way is proportional to the rotational speed of the rotary shaft 2.

  Therefore, if the output of the rotational speed detection sensor 8 is sent to a processing circuit (not shown), the rotational speed of the rotating shaft 2 can be obtained (or a signal commensurate with the rotational speed can be obtained). In this processing circuit, in order to obtain the rotational speed of the rotating shaft 2 based on the output signal of the rotational speed detection sensor 8, a method of obtaining from the change cycle of the output signal and the number of changes (frequency) per unit time. There is a method to ask from. The rotational speed is inversely proportional to the period and proportional to the frequency. Although not shown, Patent Document 2 describes a rotational speed detection device having a similar structure that is used to detect the rotational speed of a vehicle wheel.

  However, in order to obtain the rotation speed of the rotation member such as the rotation shaft 2 in real time, it is preferable to obtain this rotation speed from the cycle of change of the output signal of the rotation speed detection sensor 8. By calculating from the frequency of this change, the rotational speed can be determined only every predetermined time (unit time) that is several times to several tens of times the period. For this reason, a difference is likely to occur between the obtained rotational speed and the instantaneous rotational speed, and the ABS and TCS cannot be appropriately controlled by the obtained rotational speed. On the other hand, if the rotational speed is obtained from the period of change of the output signal, the difference between the obtained rotational speed and the instantaneous rotational speed can be almost eliminated, and the ABS or TCS can be determined depending on the obtained rotational speed. Can be controlled appropriately.

  However, in order to accurately obtain the rotation speed from the change cycle of the output signal, it is necessary to accurately regulate the pitch at which the characteristic of the detected portion of the encoder 7 changes in the circumferential direction. Even if the rotational speed is the same, if the pitch is longer than the design value, the period of change of the output signal becomes longer, and if the pitch is shorter, the period becomes shorter. For this reason, the pitch at which the characteristics of the detected portion of the encoder 7 changes is equal over the entire circumference in the portion facing the detection portion of the rotational speed detection sensor 8, so that the rotational speed can be accurately determined from the cycle of the change in the output signal. Necessary for seeking.

On the other hand, the pitch may be unequal with respect to the circumferential direction for the following two reasons (1) and (2).
(1) Manufacturing error of encoder 7 (2) Assembly error of encoder 7 Here, (1) occurs because the pitch for changing the magnetization direction of the encoder 7 becomes nonuniform in the circumferential direction. For example, FIG. 8 schematically shows an example of the pitch error between the S pole and the N pole existing on the magnetized surface of the encoder 7. As shown in FIG. 8, the pitch between these S poles and N poles may deviate by about 2% at the maximum compared to the standard value.

  Further, (2) occurs when the geometric center and the rotation center of the detected portion of the encoder 7 are shifted. Since the magnetization width of the detected portion becomes wider toward the outer side in the radial direction, the pitch at which the S pole and the N pole change becomes nonuniform in the circumferential direction when both the centers are shifted. In any case, if the change pitch becomes non-uniform in the circumferential direction, the rotation speed cannot be accurately obtained from the change cycle of the output signal of the rotation speed detection sensor 8.

  Of course, if the processing accuracy and assembly accuracy of the encoder are improved, the pitch of the change can be made uniform in the circumferential direction, and the rotation speed can be accurately obtained from the change period of the output signal of the rotation speed detection sensor. . However, it is necessary to sufficiently improve both the accuracy of processing and assembly, and it is inevitable that the cost increases.

  Therefore, in Patent Document 3, a specific region having a pitch error that is not so large as to be generated by a magnetization error is provided in a part of the permanent magnet encoder so that the rotation speed of the rotating member can be accurately obtained in real time. Using the specific area, the pitches of the S pole and N pole in the non-specific area and the phase in the rotation direction are associated with each other and stored in the memory. When the rotational speed is detected, the rotational speed is calculated based on the actual pitch and the period of the output signal of the rotational speed detection sensor.

JP-A-8-338435 JP 2002-155962 A JP 2004-354101 A

  Patent Document 3 shows the effectiveness of using a encoder to create a rotation detection device capable of detecting the origin, storing the error of each pole, and correcting the speed signal. However, errors in encoders may change over time due to surface wear and scratches, and deterioration of rubber and adhesives. Therefore, even if only the initial error is stored and the signal is corrected, the corrected signal accuracy may deteriorate with time.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rotational speed detection device that always compensates for changes in errors of each pole in an encoder and can always obtain accurate signal accuracy. .

  In order to achieve the above object, the rotational speed detection device of the present invention includes a permanent magnet encoder supported on a rotating member concentrically with the rotation center of the rotating member, and a detection unit on a detection surface of the permanent magnet encoder. And a calculator for processing the output signal of the rotation detection sensor to detect the rotation speed of the rotating member, and the permanent magnet encoder is formed into an annular shape by a permanent magnet. S poles and N poles are alternately arranged at a predetermined pitch on a single arc centered on the center of rotation, and at least one pitch in the circumferential direction is set to the pitch of other portions. The arithmetic unit is configured to obtain a pitch size between each S pole and N pole during one rotation of the permanent magnet encoder, and each of these functions. A function for obtaining the phase in the rotation direction of the other parts of the pole and the N pole on the basis of a part having a pitch that is significantly different from the other parts, and correcting the pitch error between each S pole and the N pole, and It is characterized by having a function for obtaining the rotation speed of the member and a correction function for performing a calculation periodically to compensate for the change over time of the encoder and correcting the stored encoder error.

  According to the present invention, it is possible to correct a pitch error between the S pole and the N pole arranged on the detection surface of the encoder. That is, every time the boundary between the S pole and the N pole of the detected surface of the encoder passes through the detection section of the rotational speed detection sensor, the rotational speed of the encoder is calculated or a signal corresponding to the rotational speed is calculated. Even if the rotation speed is output and obtained in almost real time, a signal in which this pitch error is corrected can be obtained regardless of the pitch error between the S pole and the N pole existing on the detected surface of the encoder. For this reason, the said rotational speed can be calculated | required correctly irrespective of the manufacture error and assembly | attachment error of an encoder. In addition to this, computation is performed periodically to compensate for changes in the encoder over time, and errors in the stored encoder are corrected, so that accurate signal accuracy is always obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a pitch error between an S pole and an N pole existing on the magnetized surface of an encoder 7a as an embodiment of a permanent magnet encoder constituting the rotational speed detection device of the present invention. . In the case of the present embodiment, the pitch of the specific region 9 (oblique lattice portion) that is one portion with respect to the circumferential direction is a standard value (a pitch when it is assumed that the pitches of the S pole and the N pole are all equal). Is about 5% larger. On the other hand, the pitch in the non-specific region 10 which is another part is magnetized so as to be as equal as possible within a range where the manufacturing cost does not increase. However, an error between each S pole and N pole pitch in the non-specific region 10 and the standard value is about 0.2 to 2.0%. Further, the error direction (whether it is + or-) in this non-specific area 10 is various. However, the magnitude of the error in the non-specific area 10 portion does not become larger than the error in the specific area 9 portion. Therefore, the position of the specific region 9 can be reliably specified with respect to the rotation direction of the encoder 7a. The pitch error of the specific area 9 is preferably small as long as it can be reliably distinguished from the non-specific area 10. Therefore, it is realistic to suppress the pitch error of the specific region 9 to about 10% at the maximum. However, if there is a possibility that the pitch error of the non-specific region 10 becomes large, the pitch error of the specific region 9 is also increased further.

  If the permanent magnet encoder 7a of the present embodiment configured as described above is used, an S pole disposed on the detected surface is detected from a rotational speed detection sensor having a detection portion opposed to the detected surface of the encoder 7a. A signal in which the pitch error between the N pole and the N pole is corrected can be obtained. In other words, the rotation speed obtained based on the signal from the rotation speed detection sensor is present even though there is an error in the magnetization pitch of the surface to be detected as shown in FIG. The measured value can be corrected to the same value as when no error exists as shown in FIG. Therefore, the rotational speed of the rotary member that supports the encoder 7a can be measured almost accurately in real time.

  That is, if the encoder 7a is rotated together with the rotating member while the detection surface of the rotation speed detection sensor is opposed to the detection surface of the encoder 7a, the output signal of the rotation speed detection sensor is applied to the detection surface. It changes according to the pitch of the existing S pole and N pole. The period of this change varies depending on the pitch. On the other hand, the phase relating to the rotation direction of the S pole or N pole existing in the non-specific area 10 with reference to the specific area 9 portion can also be known by the above operation. Therefore, when the output signal of the rotational speed detection sensor changes k times from the specific region 9 part, how much the pitch of the part of the rotational speed detection sensor facing the detection part is deviated from the standard value. , All can be specified. The rotation speed of the rotating member can be calculated in consideration of the pitch error between the S pole and the N pole for all the parts (specific area 9 and non-specific area 10).

  As described above, according to the present embodiment, every time the boundary between the S pole and the N pole passes through the detection portion of the rotation speed detection sensor in the detected surface of the encoder 7a (every pitch of the magnetized region). Even if the rotation speed of the rotating member that supports the encoder 7a is calculated or a signal corresponding to this rotation speed is output and the rotation speed is obtained in almost real time, the S pole and N present on the detected surface of the encoder 7a Regardless of the pitch error with the pole, a signal with this pitch error corrected can be obtained. For this reason, the rotational speed can be accurately obtained regardless of the manufacturing error of the encoder 7a and the assembly error of the encoder 7a with respect to the rotating member. Note that it is sufficient that only one specific region 9 is provided in the circumferential direction, but two or more specific regions 9 may be provided. However, in this case, the specific areas can be identified by arranging the specific areas at unequal intervals in the circumferential direction.

The storage operation of the central angle pitch and phase for all the S poles and N poles was supported with the encoder 7a supported with the detection portion of the rotation speed detection sensor facing the detection surface of the encoder 7a. This is done by rotating the rotating member at a constant speed one or more times. In this way, the memory (storage device...) Associates the central angle pitch between a large number of S poles and N poles (each 20 to 60) arranged on the detection surface of the encoder 7a with the phase in the rotation direction. (See FIG. 5). More specifically, this operation is performed as shown in FIG. That is, the period t _{k at} which the output signal of the rotational speed detection sensor changes and the time t ₀ required for the encoder 7a to make one rotation while rotating the rotating member that supports the encoder 7a one or more times at a constant speed are set. Observe. The number of boundaries between the S pole and the N pole, and the central angle of these S or N poles corresponding to the S pole or N pole starting from the k (= 1 to n) th boundary counted from the specific region 9 The pitch θ _k is represented by θ _k = 2π · t _k / t ₀ . Therefore, information about the central angle pitch theta _k of S-pole or N-pole, respectively n / 2 pieces each, in all the sum of n S and N poles, the phase associated with the direction of rotation relative to the specific region 9 The information is stored in the memory 100 together with the (k-th) information.

When detecting the rotation speed of the rotating member that supports the encoder 7a, the period of change in the output signal of the rotation speed detection sensor is observed, with the detection unit facing the detection surface of the encoder 7a. The output signal of this rotational speed detection sensor changes as shown in FIG. 3, for example. In this case, the number of boundaries between the S pole and the N pole, and the period corresponding to the S pole or the N pole starting from the kth (= 1 to n) th boundary counted from the specific region 9 is T _k.
When the central angular pitch of the S pole or N pole is θ _k , the rotational speed S of the rotating member is expressed as “S∝θ _k / T _k ”. As described above, since the center angle pitch θ _k is all known for each S pole and N pole, the rotational speed can be accurately obtained. Further, since the period T _k can be measured 40 to 120 times during one rotation of the encoder 7a, the rotation speed can be obtained almost in real time.

  Next, an example of a rolling bearing unit in which the permanent magnet encoder is installed will be described with reference to FIG. In this example, the present invention is applied to a rolling bearing unit for a wheel of an automobile so that the rotational speed of the wheel can be detected. This rolling bearing unit is formed on the outer peripheral surface of a hub 11 that is a rotation side raceway, and the inner peripheral surfaces of double row inner ring races 12 and 12 that are rotation side raceways and the outer ring 13 that is a stationary side raceway. A plurality of balls 15, 15 each of which is a rolling element are provided so as to be freely rollable between the double-row outer ring raceways 14, 14 each formed as a stationary side track. The hub 11 is formed by fitting and fixing an inner ring 17 to an end portion of the hub body 16. Since the illustrated example is a rolling bearing unit for driving wheels, a spline shaft 20 attached to a constant velocity joint 19 is inserted into a spline hole 18 provided at the center of the hub body 16.

  In order to apply the present invention to the rolling bearing unit as described above, a case 21 that is externally fitted and fixed to the slinger 6 that supports the encoder 7 a on the outer peripheral surface of the end of the inner ring 17 and is fixed to the end of the outer ring 13. The rotation speed detection sensor 22 is held. The case 21 is formed in an annular shape by bending a metal plate, and only the portion that holds the rotational speed detection sensor 22 is inflated in the axial direction, and the portion serves as the holding portion 23. The structure and operation of the rotational speed detection sensor 22 and the encoder 7a are as described with reference to FIGS.

  Further, in the present embodiment, in order to compensate for the change over time in the error of each pole in the encoder 7a and always obtain accurate signal accuracy, the arithmetic unit (CPU... See FIG. 5) 102 In order to compensate for the change over time of the encoder 7a, a calculation function is periodically performed to correct the stored error of the encoder 7a. The computing unit 102 has the functions described above, that is, a function for obtaining the magnitude of the pitch between each S pole and N pole during one rotation of the permanent magnet encoder, and other functions of each S pole and N pole. There is also a function for obtaining a phase related to the rotation direction of a part with reference to a part having a pitch that is significantly different from other parts, and a function for obtaining a rotational speed of the rotating member by correcting a pitch error between each of the S and N poles. is doing.

  Specifically, the correction function of the arithmetic unit 102 is to periodically perform correction calculation to correct an encoder error. Here, the period may be time or mileage. It is also possible to combine the two methods. As a correction method, it is detected from the G sensor 104 and the steering angle of the steering (steering angle sensor 106) that the vehicle travels straight and is at a substantially constant speed. Signal) is compared with the rotational speed of the other three wheels or the rotational speed of the drive shaft (the rotational speed signal from the other wheel rotation sensor 112 and the signal from the other speed sensor 108), and a correction calculation is performed. Possible (see FIG. 5).

More specifically, when the speed control for each pitch of the encoder is considered as in this proposal and the calibration is performed by the in-vehicle control, it is necessary to consider the following four error factors.
(1) The calibration of the error for each pitch of the encoder needs to be performed in a straight traveling state. Even in the straight traveling state, the G sensor and the rudder angle sensor are mainly used for the determination of the straight traveling due to the difference in tire radius due to the wear state of each tire and the difference in air pressure. By measuring the rotational speed difference of each wheel in a straight-running state, first, the error of each wheel is grasped.
(2) Next, the speed increase / decrease factor that occurs every revolution of the engine also occurs in the drive shaft rotation sensor and other wheel speed sensors in the same way. Averaging correction of the target wheel speed signal is performed. Using the signal that has been subjected to the averaging correction (by creating a virtual signal when the wheel rotates at a constant rate), the encoder itself is deteriorated and each pitch error when magnetic powder adheres is obtained and stored in the storage device. . At this time, instead of rewriting data at once, an interpolation value with the old data may be stored.
(3) When actually performing vehicle control, the wear state of each tire determined in (1) above is calculated using a virtual signal in which the increase / decrease in speed generated every engine revolution is corrected by the method (2) above. The actual rotational speed is evaluated by correcting the error between tires due to the difference in air pressure, and subtracting the pitch error due to the deterioration of the encoder itself and the adhesion of magnetic powder stored in the storage device.
(4) The increase / decrease in speed that occurs every lap due to tire mounting eccentricity occurs with one round of the tire as a period, so it may be considered by taking into account the pitch error of the encoder without forcibly correcting it, Since correction is relatively easy as compared with others, it is more preferable to perform correction.

  As described above, according to the rotational speed detection device of the present embodiment, the calculation is periodically performed to compensate for the change over time of the encoder, and the stored encoder error is corrected. , Always accurate signal accuracy can be obtained.

It is a schematic diagram of the to-be-detected surface which shows one Embodiment of the encoder made from a permanent magnet which comprises the rotational speed detection apparatus of this invention. It is a diagram for explaining a method of storing the central angle pitch between the S pole and the N pole of the encoder in a memory in association with the phase relating to the rotation direction. It is a diagram which shows the period when the output signal of a rotational speed detection sensor changes. It is sectional drawing which shows an example of the roller bearing unit with an encoder made from a permanent magnet. It is the schematic which shows an example of the means which correct | amends periodically in order to compensate the change with time of an encoder, and correct | amends the error of the memorize | stored encoder. It is a fragmentary sectional view showing an example of conventional structure. It is the figure which looked at FIG. 6 from the right side. It is a schematic diagram which shows an example of the pitch error of the S pole and N pole which exist in the magnetized surface of the encoder made from a permanent magnet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing 2 Rotating shaft 7, 7a Encoder 8 Rotational speed detection sensor 9 Specific area | region 10 Non-specific area | region 11, 11a Hub 12 Inner ring track 13 Outer ring 14 Outer ring track 16, 16a Hub main body 17 Inner ring 22 Rotational speed sensor 100 Memory (storage device)
102 CPU (calculator)

Claims (2)

A permanent magnet encoder supported on the rotating member concentrically with the rotation center of the rotating member;
A rotation detection sensor having a detection unit opposed to a detection surface of the permanent magnet encoder;
An arithmetic unit for processing the output signal of the rotation detection sensor to detect the rotation speed of the rotating member;
With
The encoder made of permanent magnets is made of a permanent magnet in an annular shape, and S poles and N poles are alternately arranged at a predetermined pitch on a single arc centered on the center of rotation. The pitch of at least one point with respect to the direction is different from the pitch of the other part to be greater than the possible difference based on the error,
The arithmetic unit has a function of obtaining the pitch size of each S pole and N pole during one rotation of the permanent magnet encoder, and a phase relating to the rotation direction of the other part of each S pole and N pole. For obtaining a rotation speed of the rotating member by correcting a pitch error between each of the S poles and the N poles, and a change with time of the encoder. And a correction function for correcting an error of the stored encoder, which is periodically calculated to compensate for the error.   The rotational speed detection device according to claim 1, wherein the permanent magnet encoder has a pitch at least one greater than a pitch of other portions in the circumferential direction.

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