GB2292781A

GB2292781A - Cold forged pulsar ring

Info

Publication number: GB2292781A
Application number: GB9517285A
Authority: GB
Inventors: Eiji Tajima
Original assignee: NTN Corp; NTN Toyo Bearing Co Ltd
Current assignee: NTN Corp
Priority date: 1994-08-30
Filing date: 1995-08-23
Publication date: 1996-03-06
Anticipated expiration: 2015-08-23
Also published as: GB9517285D0; GB2292781B; JPH0868804A; DE19531992A1

Description

- 1 Cold Forged Pulsar Ring 2292781 The present invention relates to a

cold forged pulsar ring adapted to be used in a rotation detecting device for detecting revolving speed of a wheel in an automobile anti-lock brake system (ABS).

The pulsar ring of the kind referred to above is in the form of a ring gear having a plurality of gear teeth adapted to be detected by an electromagnetic induction sensor during the rotation of such ring gear so that the electromagnetic induction sensor can provide a pulse output indicative of the speed of rotation of the ring gear. The prior art pulsar ring is generally formed by sintering or milling and, as shown M Fig. 5A, the gear teeth of the prior art pulsar ring is of a shape having a pair of steeply inclined opposite tooth faces protruding radially outwardly from the ring body.

Since the use of either the sintering technique or the milling technique to manufacture the prior art pulsar ring involves an increased manufacturing cost, an inexpensive method has been longed for. As one of the inexpensive methods for the manufacture of the pulsar ring, a cold forging technique can be envisaged. In this cold forging technique, material for the pulsar ring is pressed into dies to facilitate formation of gear teeth.

Where the gear teeth are formed by the use of such a cold forging technique, generally it has been difficult to form each gear tooth to have such a steeply inclined shape as shown in Fig. 5A and each gear tooth is likely to be shaped to 2.5 have a pair of moderately inclined opposite tooth faces such as shown in Fig. 5B.

It has, however, been found that, when the gear teeth of the pulsar ring are of such a shape as shown in Fig. 5B, the pulsar ring would no longer be used -9,5 2 in practice because the electromagnetic induction sensor tends to output a decreased voltage to such an extent that no stable detection of wheel rotation is possible. By way of example, the output voltage from the sensor is of such a waveform as shown by a curve a or a curve b in Fig. 6A depending on the number of revolutions of the pulsar ring. The output voltage is low when the number of revolutions of the pulsar ring is small.

This output voltage from the sensor is processed by a predetermined threshold level SL to eliminate any possible influence brought about by noise and is then shaped as to be converted into a rectangular waveform as shown in Fig. 6B.

Accordingly, when the pulsar ring is rotated at a low speed, no detection of the rotational speed is possible because of the threshold level SL. Therefore, if the gear teeth of the pulsar ring are made to be of a profile having moderately inclined tooth faces, and where the output voltage from the sensor is lowered consequent upon the gear teeth of the pulsar ring having so shaped, a minimum possible speed of rotation of the pulsar ring at which detection of the rotational speed can be accomplished satisfactorfly tends to be increased.

Accordingly, the present invention has been devised to provide a pulsar ring which can be cold forged and which effectively provides a sufficiently required output voltage.

To this end, the improved cold forged pulsar ring according to the present invention comprises a ring body having inner and outer peripheral surfaces, a plurality of circumferentially spaced gear teeth - integrally formed by the use of a cold forging process at one of the inner and outer peripheral surfaces of the ring bsdy so as tT-) FrotruJe =dially of the=ig bcdy, each of + e gdar teedl Ideam g w prof.,lfBJ as to have a substantially trapezoidal shape having a tooth angle not smaller than ', but not greater than 15'.

3 In general, the pulsar ring is such that a relatively high output voltage can be obtained from the sensor as the tooth angle 6 decreases. However, if the tooth angle () is smaller than 5', the cold forging would be almost Impossible to accomplish. Also, if the tooth angle e exceeds 15', the output voltage firom the sensor would be lowered considerably.

Therefore, in the practice of the present invention, the tooth angle of each gear teeth of the cold forged pulsar ring is chosen to be within the range of 5 to 15% it is possible not only to accomplish the manufacture of the pulsar ring by the use of the cold forging process, but also to secure the required output voltage from the sensor.

Preferably, the tooth angle referred to above is not smaller than 7', but not greater than 15' and, more preferably, not smaller than C, but not greater than 14'.

Also, each of the gear teeth has a tooth height which is preferably not smaller than 1 mm, but not greater than 3 mm.

In addition, each of the gear teeth has a tooth thickness which is preferably not smaller than 1 mm, but not greater than 2 mm.

With this design according to the present invention, not only can a cold forging process be employed to manufacture the pulsar ring, but also a required output voltage can be secured ftorn a sensor.

In any event, the present invention will become more clearly under stood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying 4 drawings, like reference numerals are used to denote like parts throughout the several views, and:

Fig. 1 is a fragmentary front elevational View of a pulsar ring according to a first preferred embodiment of the present invention; Fig. 2 is a diagram schematically showing arotation detecting device comprised of the pulsar ring of the present invention and a sensor; Figs. 3A and 3B are schematic side sectional views showing the sequence of manufacture of the pulsar ring with a punch held in different operating conditions, respectively; Fig. 4 is a fragmentary front elevational view of the pulsar ring according to a second preferred embodiment of the present invention; Fig. 5A is fragmentary front elevational views of pulsar rings, showing the shape of a gear tooth in one conventional pulsar ring; Fig. 5B is a view similar to Fig. 5A, showing the shape of a gear tooth in another conventional form of the pulsar ring of Fig. 5A; Fig. 6A is a graph showing an output voltage generated from an electromagnetic induction sensor of the rotation detecting device utilizing the pulsar ring; and Fig. 6B is a graph showing the output voltage from the sensor which has been processed to have a rectangular waveform; A first preferred embodiment of the present invention will now be described with particular reference to Figs. I to 3. A pulsar ring I according to the present invention comprises a ring body la having its outer peripheral surface formed with a plurality of gear teeth 2 protruding radially outwardly therefrom and spaced equally from each other at a predetermined pitch in a circumferential direction thereof These gear teeth 2 integral with the ring body I are formed by cold forging a material for the pulsar ring I so that each gear tooth 2 can present a generafly trapezoidal shape of particular dimensions which will now be described.

Specifically, each tooth 2 has a base 2a integral with the ring body I a, opposing gear faces 2b protruding an equal length radially outwardly from the outer peripheral surface of the ring body I a, and a substantially flat crest 2c and is so profiled and so dimensioned in the illustrated embodiment that the respective gear tooth 2 may have a tooth angle 6 not smaller than 5', but not greater than 15'; a tooth height h not smaller than I mm, but not greater than 3 mm; and a tooth thickness B not smaller than I mm and not greater than 2 mm.

The tooth angle 8 referred to above is defined as the angle of inclination of each tooth face 2b as measured in a direction radially inwardly of the ring body I relative to the imaginary line drawn so as to pass the center of the ring body 2 (the axis of rotation of the pulsar ring 1) and also a point intermediate of the tooth thickness B. The tooth thickness B of each gear tooth 2 referred to above is measured in a direction circumferentiaUy of the pulsar ring I along an imaginary circle passing through a point C intermediate of the tooth height h. According to the present invention, the ratio H/h of the tooth height h relative to the ring width H of the ring body 2 as measured between the outer and inner peripheral surfaces of the ring body 2 in the radial direction is chosen to be within a specific range to which the cold forging can be exercised, that is, not smaHer than 1.0, but not greater than 5.0. Material for the pulsar ring I may be either soft steel or stainless steel.

Where the soft steel is chosen as material for the pulsar ring 1, a surface treatment or a surface plating is carried out for rust prevention.

r The tooth angle 8 is preferably not smaller than 7', but not greater than 15'and, more preferably, not smal-ler than 8', but not greater than 14'. The tooth height h is preferably not smaller than 2 mm, but not greater than 3 mm. The tooth thickness B is preferably not smaller than 1.0 mm, but not greater than 1. 5 mm.

A preferred combination of the tooth angle E), the tooth height h and the tooth thickness B is such that the tooth angle E) is within the range of 7 to 15', the tooth 6 height h is within die range of 2 to 3 mm and the tooth thickness B is within the range of 1.0 to 1.5 mm.

As shown in Fig. 2, the pulsar ring 1 of the present uivention is in practice used to form a rotation detecting device 4 in combinationwith an electro magnetic induction sensor 3 for detectMg the gear teeth 2.

Fig. 3 comphsed of Figs. 3A and 3B fflustrates the sequence of manufacture of the pulsar ring 1 by means of a cold forging process proposed by the applicant of the present invention (See the German Laid-open Patent Apphcation No. 4,411,4 10, published March 2, 1995, or British Laid-open Patent Specification

No. 2,281,527, published March 8, 1995). According to this cold forging process, a rulg-shaped die 11 and a generally shaft-like, stepped punch 12 are employed and cooperate with each other to forge a ring-shaped material W for the pulsar ring 1, which has been placed inside a shaped cavity in the die 11, by means of an annular step 12c of the punch 12. The ring-shaped material W for the pulsar ring 1 may be a slice of a tubular or pipe-like metallic member or the like. By so forging, the rLng-shaped material W is plasticized with an outer peripheral portion of the material W consequently recessed inwardly by a plurality of tooth defining protru sions 13, formed on an ulner peripheral surface of the die 11 in a gearlike pattem, and is subsequently discharged, as shown in Fig. 3B, out from the die 11 to thereby complete the pulsar ring having the gear teeth 2 which are a replica of the pattern of the tooth defining protrusions 13. It is to be noted that an upper end portion 13a of each of radially inwardly tooth defining protrusions 13 in the die 11 is inclined to converge radially inwardly so as to facilitate guidance of the ringshaped material W as the latter is forged into the shaped cavity in the die 11 by means of the punch 12.

After the ring-shaped matenal W has been forged in the manner described above, the punch 12 is lifted to depart from the die 11, permitting, the C) 7 resultant pulsar ring 1 to be separated from the punch 12 while caught by a stopper pawl 15 mounted on a die holder 14.

With this pulsar ring 1 so formed, the gear teeth 2 are shaped to have the required profile and, accordingly, not only can the electromagnetic induction sensor of the rotation detecting device utilizing this pulsar ring 1 provide a required output voltage, but also the cold forging process to make this pulsar ring 1 can be accomplished with no difficulty. In other words, although a relatively high output voltage can be obtained from the sensor as the tooth angle E) decreases, the cold forging would be almost impossible to accomplish if the tooth angle e is smaller than 5 '. Also, if the tooth angle E) exceeds 15 ', the output voltage from the sensor would be lowered considerably. Accordingly, the selection of the range of 5 to IS' for the tooth angle 0 makes it possible to accomplish the cold forging process and also to secure the required output voltage from the sensor.

With respect to the tooth height h, a high output voltage can be obtained from the sensor as the tooth height h increases. However, if the tooth height h is greater than 3 mm, no cold forging is possible with no difficulty, but if the tooth height h is smaller than 1 mm, the required output voltage cannot be obtamed from the sensor. Accordingly, the selection of the range of 1 to 3 inni for the tooth height h makes it possible to accomplish the cold forging process and also to secure the required output voltage from the sensor.

Also, with respect to the tooth thickness B, if it is smaller than 1 mm, no cold forging is possible with no difficulty and this is true even when the tooth thickness B exceeds 2 min. Also, if the tooth thickness B exceeds 2 min, the output voltage from the sensor would be lowered.

For the reason discussed above, the selection of the tooth angle within the range of 5 to 15', tile tooth height h within the range of 1 to 3 mm and the tooth thickness within the range of 1 to 2 min results in the gear teeth 2 each having an optimum proftle sufficient to make it possible to secure the required 8 output voltage from the sensor without accompanying an undue reduction thereof and also to accomplish manufacture of the inexpensive pulsar ring 1 by the use of the cold forgmg process. 'I'lle optimum ranges of the tooth anglee, the tooth height h and the tooth thickness B for the purpose of the invention have been ascertained as a result of experiments conducted by the inventors of the. present invention.

It is pointed out that although the tooth height h and the tooth thickness B discussed above may be related to the ring width H, the inner diameter d of the ring body I a and the pitch angle p subtended by the pitch between the neighboring gear teeth 2, not only can the required output voltage be secured from the sensor, but also the cold forging of the pulsar ring la having the above dis cussed tooth parameters within the above discussed specific ranges is possible, provided that the ring width H is not smaller than 5 mm, but not greater than 20 min, the inner diameter d of the ring body I a is not smaller than 50 mm, but not greater than 90 nim and the pitch angle p is not smaller than 2', but not greater than C.

Although the present invention has been fully described m connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. For example, although in describing the preferred embodiment of the present invention reference has been made to the externally tooth-formed pulsar ring 1, the present invention equally applied to an internally tooth-formed pulsar ring 1 such as sho,..vn in Fig. 4.

-)5 9

Claims

1. A cold forged pulsar ring which comprises: a ring body having inner and outer peripheral surfaces; and a plurality of circumferentially spaced gear teeth integrally formed by the use of a cold forging process at one of the inner and outer peripheral surfaces of the ring body so as to protrude radially of said ring body, each of said gear teeth having a base integral with the ring body, opposing tooth faces and a crest opposite to the base; each of said gear teeth being so profiled as to have a substantially trapezoidal shape having a tooth angle not smaller than 50, but not greater than 150, said tooth angle is being an angle of inclination of each tooth face.

2. The cold forged pulsar ring as claimed in claim wherein each of said tooth angles is not smaller than 70.

3. The cold forged pulsar ring as claimed in claim 2, wherein each of said tooth angles is not smaller than 80.

4. A pulsar ring according to any of claims 1 to 3, wherein each of said tooth angles is not greater than 140.

5. The cold forged pulsar ring as claimed in any of the preceding claims, wherein each of said gear teeth has a tooth height not smaller than Imm.

6. A pulsar ring according to any of the preceding claimsf wherein each of said gear teeth has a tooth height not greater than 3mm.

7. The cold forged pulsar ring as claimed in any of the preceding claims, wherein each of said gear teeth has a tooth thickness not smaller than lmm.

8. A pulsar ring according to any of the preceding claims, wherein each of said gear teeth has a tooth thickness not greater than 2mm.

9. A cold forged pulsar ring substantially as hereinbefore described with reference to any of the examples shown in Figures 1 to 4 of the accompanying drawings.