The present invention relates to a rolling bearing unit with an encoder, and a manufacturing method thereof, which is used to rotatably support an automobile wheel with respect to a suspension system, and to detect the rotational speed of the wheel by combining with a rotation detecting sensor for detecting rotational speed.
There is a rolling bearing unit with a rotational speed detecting sensor, which is constructed by combining a rolling bearing unit with an encoder, and a rotation detecting sensor for detecting rotational speed installed in a stationary part such as a cover connected to an outer ring.
The rolling bearing unit is used to rotatably support an automobile wheel with respect to a suspension system. Moreover, in order to control an antilock brake system (ABS) or a traction control system (TCS) it is necessary to detect the rotational speed of the wheel. Therefore, a method has been widely used recently where the wheel is rotatably supported with respect to the suspension system, and the rotational speed of the wheel is detected, by using the rolling bearing unit with a rotational speed detector which a rotational speed detector is incorporated into the rolling bearing unit.
As the rolling bearing unit with a rotational speed detector used for such a purpose, for example a construction as shown in
Moreover, the inner ring 6 has a second inner ring raceway 9 on the outer peripheral surface, and is externally fitted to a step portion 10 which is formed on the inside end side of the hub 5 and has a smaller outer diameter than the portion where the first inner ring raceway 8 is provided. Moreover, a first outer ring raceway 11 facing the first inner ring raceway 8 and a second outer ring raceway 12 facing the second inner ring raceway 9 are formed on the inner peripheral surface of the outer ring 4. A second flange 13 for supporting the outer ring 4 on the suspension system is formed on the outer peripheral surface of the outer ring 4. Furthermore, a plurality of rolling elements 14 are provided respectively between the first inner ring raceway 8 and the second inner ring raceway 9, and between the first inner ring raceway 11 and the second outer ring raceway 12, so that the hub 5 and the inner ring 6 are rotatably supported on the inner diameter side of the outer ring 4. In a condition with the inner ring 6 externally fitted to the step portion 10, a nut 15 is screwed onto a male screw portion formed on the inside end of the hub 5, to press against the inner ring 6, so as to keep the inner ring 6 and the hub 5 from being separated.
Moreover, the inside end opening of the outer ring 4 is closed by a cover 16. The cover 16 comprises a bottomed cylindrical main body 17 which is formed from a synthetic resin by injection molding, and a fitting cylinder 18 which is connected to the opening portion of the main body 17. This fitting cylinder 18 is connected to the opening of the main body 17 by molding its base end portion when injection molding the main body 17. The cover 16 constituted in this manner closes up the inside end opening of the outer ring 4, by externally securing the tip half portion of the fitting cylinder 18 (left half in
On the other hand, in order to constitute the rotational speed detector 3, an encoder 19 is externally secured through a slinger 20 to a portion away from the second inner ring raceway 9, at the outer peripheral surface of the inside end of the inner ring 6 which is externally secured to the inside end of the hub 5. The slinger 20 is formed into an overall annular shape of L-shape in cross-section, by bending a magnetic metal plate of a carbon steel plate such as SPCC or the like, and is externally secured to the inside end of the inner ring 6 by interference fit. Moreover, the encoder 19 is made by forming a permanent magnet made from a rubber mixed with ferrite powder, into an annular shape, and is bonded onto the inside surface of the annular portion constituting the slinger 20 by baking or the like. Forming the encoder from such a permanent magnet made from rubber, is heretofore widely known, as described for example in Japanese Unexamined Patent Publication No. Hei 9-203415. The encoder 19 is magnetized for example in the axial direction (left and right direction in
Moreover, an insertion hole 21 is formed in a part of the main body 17 which constitutes the cover 16, in a portion facing the inside surface of the encoder 19, piercing the main body 17 along the axial direction of the outer ring 4. A rotation detecting sensor 22 (including a rotation detecting sensor unit comprising a detecting element or the like embedded in a synthetic resin; this is the same throughout the present description) is inserted into the insertion hole 21. The rotation detecting sensor 22 comprises embedded in a synthetic resin: an IC which incorporates a magnetic detecting element such as a hall element, or a magnetoresistance element (MR element) for which the output changes according to the flow direction of the magnetic flux, and a waveform shaping circuit for shaping the output waveform from the magnetic detecting element; and a pole piece made from a magnetic material for guiding the magnetic flux flowing out from the encoder 19 (or flowing into the encoder 19), to the magnetic detecting element.
Such a rotation detecting sensor 22 comprises: a columnar insertion portion 23 provided towards the tip end (left end in
On the other hand, an engagement cylinder 27 is provided on a part of the outside surface of the cover 16 (on the side face on the opposite side to a space 26 provided with the rolling elements 14, which is to be closed by the cover 16; the right side face in
When using the aforementioned rolling bearing unit with a rotational speed detector 1, the second flange 13 set on the outer peripheral surface on the outer ring 4 is connected and fixed to the suspension system by bolts (not shown), and the wheel is fixed to the first flange 7 set on the outer peripheral surface of the hub 5, by studs 29 provided on this first flange 7, so that the wheel is rotatably supported on the suspension system. When the wheel is rotated in this condition, the north poles and south poles existing on the inside surface of the encoder 19 alternately pass through the vicinity of the end surface, being the detection surface, of the rotation detecting sensor 22. As a result, the direction of the magnetic flux flowing within the rotation detecting sensor 22 is changed, so that the output from the rotation detecting sensor 22 is changed. The frequency of the output from the rotation detecting sensor 22 being changed in this manner, is proportional to the rotational speed of the wheel. Consequently, if the output from this rotation detecting sensor 22 is sent to a controller (not shown), an ABS or TCS can be suitably controlled.
Recently, it is required to control the ABS or TCS more accurately in order to increase the safety of an automobile. For this purpose, it is needed to detect the rotational speed of the wheel with high accuracy. However, if an encoder made from a rubber magnet is used to detect the rotational speed, it is difficult to detect the rotational speed with high accuracy (ensuring sufficient reliability). That is, although the encoder made from a rubber magnet is made into a permanent magnet by magnetizing a substrate in which rubber is mixed with ferrite powder, it is difficult to evenly distribute the ferrite throughout the rubber, so that it is not possible to completely prevent the magnetic properties from being somewhat uneven depending on the position on the rubber magnet. Consequently, an accurate waveform of the magnetic flux variation can not be obtained if an encoder made from a rubber magnet is used. Therefore, it is difficult to detect the rotational speed with high accuracy by an encoder made from a rubber magnet.
The rolling bearing unit with an encoder and the manufacturing method thereof of the present invention take the above problems into consideration, with an object of realizing a structure which enables detection of the rotational speed of a wheel with high accuracy (ensuring sufficient reliability).
A rolling bearing unit with an encoder according to the present invention comprises: an outer ring which has a double-row outer ring raceway on an inner peripheral surface; an inner ring unit which has a double-row inner ring raceway on an outer peripheral surface, and is arranged concentric with the outer ring on the inner diameter side of the outer ring; a plurality of rolling elements which are rotatably provided respectively between the inner ring raceway and the outer ring raceway; and an encoder which is secured to a rotating member, being a bearing ring member of one of the outer ring and the inner ring unit which rotates during use, on which north poles and south poles are arranged alternately around the circumferential direction, and said encoder is formed from a metal magnet.
Preferably the encoder is formed in an annular shape, and a magnetization direction of the encoder is perpendicular to a side face.
Preferably a peripheral rim of the encoder is fitted to a step portion formed on an inside end of the rotating member, and a part on an outside face of the encoder near the peripheral rim on the rotating member side is contacted with a step face which connects between the step portion and a peripheral surface existing axially outside from the step portion, so that the encoder is thereby secured to the rotating member.
Preferably a part of the encoder at the peripheral rim on the rotating member side, in contact with the rotating member is not magnetized.
Preferably the rotating member is the inner ring unit, and there is provided a slinger comprising a cylinder portion, and an annular portion formed by bending the end portion of the cylinder portion radially outward, and the cylinder portion is externally fitted to an outer peripheral surface of the inside end of the inner ring unit, and the encoder is bonded onto an inside surface of the annular portion.
Preferably the slinger has an outer cylinder portion which is bent axially inward from the outer peripheral rim of the annular portion, and an outer peripheral rim of the encoder is contacted with or adjacently opposed to an inner peripheral surface of the outer cylinder portion.
Preferably the whole circumference or a plurality of parts around the circumferential direction of the axial inside end of the outer cylinder portion is crimped radially inwards, so that the outer peripheral rim of the encoder is secured to the slinger.
Preferably the metal magnet is a Fe—Cr—Co magnet.
In the manufacturing method of a rolling bearing unit with an encoder according to the present invention, the encoder is made by: cutting a part of a cylindrical base material of a Fe—Cr—Co alloy which has been formed into a cylindrical shape, into a predetermined length in relation to the axial direction, to thereby make a first intermediate base material; subjecting this first intermediate base material to finishing to thereby make a second intermediate base material; and magnetizing this second intermediate base material with north poles and south poles alternately around the circumferential direction.
A rolling bearing unit with an encoder according to the present invention, similarly to the aforementioned conventionally-known rolling bearing unit with an encoder, comprises; an outer ring, an inner ring unit, a plurality of rolling elements, and an encoder.
The outer ring has a double-row outer ring raceway on an inner peripheral surface.
The inner ring unit has a double-row inner ring raceway on an outer peripheral surface, and is arranged concentric with the outer ring on the inner diameter side of the outer ring.
The plurality of rolling elements are rotatably provided respectively between the inner ring raceway and the outer ring raceway.
The encoder is fixed to a rotating member, being a bearing ring member of one of the outer ring and the inner ring unit which rotates during use, and on the encoder north poles and south poles are arranged alternately around the circumferential direction.
Particularly, in the rolling bearing unit with an encoder of the present invention, the encoder is formed from a Fe—Cr—Co magnet.
In the manufacturing method of a rolling bearing unit with an encoder according to the present invention, the encoder is formed in the following steps.
Firstly, a part of a cylindrical base material of a Fe—Cr—Co alloy which has been formed into a cylindrical shape, is cut into a predetermined length in relation to the axial direction, to thereby make a first intermediate base material.
Next, this first intermediate base material is subject to finishing such as grinding and cutting, to thereby make a second intermediate base material.
Then, this second intermediate base material is magnetized with north poles and south poles alternately around the circumferential direction.
According to the rolling bearing unit with an encoder and the manufacturing method thereof of the present invention constituted as described above, since the encoder is formed from a Fe—Cr—Co magnet, then different from the aforementioned rubber magnet mixed with ferrite powder, the magnetic properties do not become uneven depending on the position on the encoder. Consequently, the rotational speed of the wheel can be detected with higher accuracy (ensuring sufficient reliability).
Hereunder is a description of an embodiment of the present invention, with reference to the drawings.
Differing from the structure of
Moreover, on the outer peripheral surface of the inner ring 6a, axially inward with respect to a cylinder surface 33 where the seal ring 32 is provided, is formed a step portion 34 having a smaller diameter than that of the cylinder surface 33. The step portion 34 is formed concentric with the hub 5a and the inner ring 6a. Furthermore, a step face 35 which connects between the step portion 34 and the cylinder surface 33, is formed perpendicularly with respect to the rotation axis of the hub 5a and the inner ring 6a. The step portion 34 and the step face 35 are accurately processed by turning or the like. That is, the step portion 34 is formed so as to improve the parallelism with respect to the rotation axis of the hub 5a, and the step face 35 is formed so as to improve the perpendicularity with respect to the rotation axis of the hub 5a.
Particularly, in the case of the present example, the encoder 19a is formed from a Fe—Cr—Co magnet. That is, in the case of the present example, the encoder 19a is not made from a rubber magnet such as in the conventional construction shown in
In the case of the present example, of the two side surfaces of the encoder 19a, the surface contacted with the magnetizing member during the magnetizing operation (the magnetized surface and also the surface to be detected) is smoothened. Specifically, the surface roughness of this magnetized surface is made 0.2 μm or less by center line average height roughness Ra. That is, since the Fe—Cr—Co magnet is superior in workability, the dimensional accuracy of the encoder 19a can be improved by applying the finishing described later. If in this manner the magnetized surface of the encoder 19a can be smoothened, corrugations in the micro scales on the magnetized surface can be reduced to a minimum, enabling accurate magnetization of the encoder 19a (reducing the pitch error or the like to an insignificant level).
As described above, the rotation detecting sensor 22a is provided in a position axially facing the inside surface of the encoder 19a which is externally fitted to the step portion 34. The rotation detecting sensor 22a is secured to a part of the suspension system (not shown), and the tip end surface, being the detection surface, is arranged to face the inside surface, being the surface to be detected, of the encoder 19a. Moreover, the rotation detecting sensor 22a is an active type comprising; a magnetic detecting element such as a hall element, or a magnetoresistance element, for which the characteristics change according to changes in the magnetic flux flowing out from a permanent magnet, and a waveform shaping circuit for shaping the waveform (making into a rectangular wave) of the output signals from this magnetic detecting element. Such an active type rotation detecting sensor 22a is used in a condition with a predetermined voltage applied to the magnetic detecting element from a separate power source (for example, a battery in the engine compartment). A passive type may also be used as the rotation detecting sensor 22a. However in order to detect the rotational speed with high accuracy (ensuring sufficient reliability) during low-speed traveling, the active type is preferably used.
In the case of the present example, the encoder 19a is manufactured in the following steps in order to process the encoder 19a with excellent dimensional accuracy as described above. Firstly, as shown in
Next, as shown in
As described above, if the encoder 19a is formed from the cylindrical base material 36, the dimensional accuracy of the encoder 19a can be improved and the yield of the base material can be increased. That is, since the parent material of the encoder 19a is the cylindrical base material 36, the cylindrical base material 36 can be firmly held by the chuck 38 when the end of the cylindrical base material 36 is cut. Therefore, errors caused during this cutting operation can be reduced. On the other hand, if the parent material of the encoder 19a is plate-shape, it is difficult to grip when processing into a predetermined shape, and errors caused during this processing operation are readily increased. Moreover, the yield of the material is decreased. Consequently, as with the present example, by making the parent material for obtaining the encoder 19a the cylindrical base material 36, the encoder 19a can be manufactured with excellent dimensional accuracy at low cost. In the case of the present example also, plate-shaped first and second intermediate base materials are held at the time of finishing. However at this time, the force applied to the intermediate base materials is relatively small, so that errors caused during the processing are almost negligible.
In the aforementioned magnetizing operation of the encoder 19a, if the part at the inner peripheral rim portion of the encoder 19a, which is in contact with the inner ring 6a, is not magnetized, then when the encoder 19a is externally fitted to the step portion 34 which is formed on the outer peripheral surface of the inner ring 6a, it is possible to reduce the degree of effect on the variation of the magnetic flux density of the encoder 19a by the inner ring 6a. That is, since the inner ring 6a is made from steel, if the encoder 19a is magnetized overall, the part of the encoder 19a in contact with the step face 35 of the inner ring 6a has a greater magnetic flux density compared to a part not in contact (a lot of magnetic flux flows through the part in contact). Conversely speaking, in the case where the magnetic flux density of the part not in contact with the step face 35 is reduced, and the detection element of the sensor is arranged to face this part not in contact, it becomes difficult to ensure the detection accuracy (reliability). On the other hand, if as shown in
In the case of the present example constituted as described above, since the encoder 19a is formed from the Fe—Cr—Co magnet, it is possible to reduce the unevenness of the magnetic properties of the encoder 19a, and to detect the rotational speed of the wheel with high accuracy (ensuring sufficient reliability). That is, regarding the Fe—Cr—Co magnet, different to the rubber magnet as mentioned above where a ferrite powder is mixed in the rubber, the magnetic properties do not readily become uneven depending on the position on the encoder 19a. Therefore, the encoder 19a in the present example can obtain an accurate waveform of the magnetic flux variation, and it becomes possible to detect the rotational speed with high accuracy. Moreover, in the present example, as described above, by smoothening the magnetized surface of the encoder 19a, the magnetic accuracy can be improved. Therefore the waveform of the magnetic flux variation of the encoder 19a can be obtained more accurately and the detection accuracy of the rotational speed can be further improved.
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The structure shown in
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In the case of the present example, the encoder 19b is manufactured in the following steps. That is, firstly, a cylindrical base material 36a as shown in
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Moreover, a rotation detecting sensor 22a is inserted into the through hole 51. The rotation detecting sensor 22a is installed at a position radially facing the encoder 19b. The installation direction of the rotation detecting sensor 22a is perpendicular to the tangent of the outer peripheral surface of the encoder 19b. Due to this configuration, even in the case where the hub 2b is tilted with respect to the outer ring 4a due to the moment from the wheel, the effect on the detection of the rotational speed can be reduced. Other structure and operation are similar to in the sixteenth example mentioned above.
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Moreover, in the case of the present example, the encoder 19b made from a Fe—Cr—Co magnet formed in a cylindrical shape, is externally secured to the inside end of the outer ring 4b. Therefore, a cylinder surface 52 with an outer peripheral surface formed in a cylindrical shape, is provided on the inside end of the outer ring 4b. Then the encoder 19b is externally secured to the cylinder surface 52. On the other hand, a rotation detecting sensor 22a is fixed to a part of the suspension system (not shown), and is arranged radially outer side of the encoder 19b. In the present example, the outer ring 4b rotates during use. Therefore, as mentioned above, the encoder 19b is externally fitted to the outer peripheral surface of the inside end of the outer ring 4b, so that the rotational speed of the wheel can be detected.
In the case where the present invention is applied to a rolling bearing unit of an outer ring rotation type as in the case of the eighteenth example, the structure may be such that a step portion is formed on the inner peripheral surface of the inside end of the outer ring, and the annular encoder is internally fitted to the step portion. That is, the encoder is internally fitted to the step portion which is formed on the inner peripheral surface of the inside end of the outer ring, and the outside peripheral rim of the outer surface of the encoder is contacted with a step face which connects between the step portion and a part having a smaller inner diameter than the step portion and existing axially outward from the step portion. Furthermore, if the structure is such that a part at the outside peripheral rim portion of the encoder which contacts with the outer ring, is not magnetized, the rotational speed can be detected with higher accuracy.
Since the present invention is constructed and operated as described above, a rolling bearing unit with an encoder which detects the rotational speed of a wheel with high accuracy (ensuring sufficient reliability) is obtained. Therefore, it is possible to control an ABS or a TCS more accurately, contributing to an increase in the safety of automobiles.
Number | Date | Country | Kind |
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2003-084745 | Mar 2003 | JP | national |
Number | Date | Country | |
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Parent | PCT/JP04/03486 | Mar 2004 | US |
Child | 11135822 | May 2005 | US |