WO2004085105A1

WO2004085105A1 - Method to produce spline teeth on a ring- or disc-shaped coupling element

Info

Publication number: WO2004085105A1
Application number: PCT/SE2004/000343
Authority: WO
Inventors: Dag Nilsson
Original assignee: Scania Cv Ab (Publ)
Priority date: 2003-03-28
Filing date: 2004-03-10
Publication date: 2004-10-07
Also published as: DE112004000526T5; SE525011C2; SE0300889D0; SE0300889L

Abstract

Spline teeth on clutch rings (e.g. for range gearboxes in vehicle transmissions) have previously had shapes constituting locking steps imparted to them by pressure rolling. However, the pressure rolling technique entails a large amount of material for the clutch ring blank (24), involving more material and greater weight than is required for purely strength reasons. The method of the invention obviates pressure rolling and replaces it by profiling (form milling) of the spline teeth (30). During the profiling the milling tool moves initially relative to the clutch ring blank, parallel with the centreline (CL) of the clutch ring blank, but this straight basic movement (41') is interrupted before the milling tool has completed a milled groove with continuous straight bottom, thereby imparting to the lateral surfaces (42') of the spline teeth a slightly concave curve (R) constituting a locking step.

Description

Method to produce spline teeth on a ring- or disc-shaped coupling element

The present invention relates to a procedure for forming spline teeth to serve as coupling teeth on an outside of an annular or disc-shaped clutch element, according to the preamble of claim 1.

State of the art

A modern truck gearbox often incorporates a range gear, usually in the form of a planetary gear, mounted on the output side of a multi-speed main gear. EP 0 239 555 A2 may be quoted as an example of this kind of planetary gear. Such a planetary gear has a low-speed section and a high-speed section. This invention has quite generally to do with the forming of spline teeth to serve as coupling teeth on an annular or discshaped clutch element for a gear section belonging to a gearbox, and especially for a low-speed or high-speed section of a planetary gear.

Forming such an annular/disc-shaped clutch element starts with a clutch element blank which in a manner known per se is advantageously first provided with a conical outside (external contact surface) intended to constitute a friction surface for cooperation with a corresponding internal contact surface of a synchronising ring (latch cone).

A planetary gear of the abovementioned kind comprises an input gear with a sun wheel mounted on, and for joint rotation with, the shaft, and a clutch disc (on the high-speed side of the planetary gear) which is likewise connected to, and for joint rotation with, the shaft and is provided with an external conical friction surface for cooperation with a corresponding internal friction surface on a relating synchronising ring (latch cone) on the high-speed side. The planetary gear further incorporates a planet wheel carrier which supports the gear's planet wheels (which are in driving engagement with the sun wheel) and is connected firmly to an output shaft from the planetary gear. The planet wheels are further in driving engagement with a surrounding ring gear which in a usual way is movable axially for connection either to the clutch disc on the high-speed side of the planetary gear or to an annular clutch element which is fixed to, and for joint rotation with, the housing of the planetary gear and is situated on the low-speed side of the planetary gear. This annular clutch element has an annular portion with a conical external friction surface for cooperation with a corresponding internal friction surface on a relating synchronising ring (latch cone) on the low-speed side. One of the two synchronising rings (latch cones) is fitted between the inside of the ring gear and the external friction surface of the clutch disc (on the high-speed side), and the other between the inside of the ring gear and the external conical friction surface on the annular clutch element on the low-gear side.

However, connecting the ring gear either to the clutch disc (on the high-speed side) mounted on the planetary gear input shaft or to the annular clutch element (on the low- speed side) requires that the spline teeth be provided with a so-called locking step to prevent "gear disconnection" ("gear jump-out") during torqueless driving connection between, on the one hand, the ring gear and the clutch disc and, on the other hand, the annular clutch element. Such a locking step effect may be obtained by the side surfaces of the spline teeth being made with a slight rearward slope, e.g. 3°, relative to the axial longitudinal extent of the spline teeth.

Locking steps on spline teeth are currently formed by so-called pressure rolling. This pressure rolling technique is used both in forming the internal splines of the ring gear and in forming the external splines on the clutch ring on the low-speed side (or the splines on the clutch disc on the high-speed side).

However, ensuring that the pressure rolling technique can be used with satisfactory spline formation results (so that satisfactory counterforce can be exerted on the blank during pressure rolling) requires a great deal of material in the clutch ring blank (or clutch disc blank), leading to more conversion of material and greater weight than is inherently justified from the strength point of view as regards the finished clutch ring or clutch disc. Pressure rolling also causes protrusion of material pressed out, thereby entailing further subsequent processing, particularly for removal of burrs of protruding material. Objects of the invention

The primary object of the invention is to provide a new and more effective procedure intended for the forming and shaping of spline teeth to serve as coupling teeth on the outside of the clutch ring blank or clutch disc blank.

The new procedure has more precisely to be such that forming the surfaces which constitute locking steps on spline teeth can be carried out without use of pressure rolling.

The new method has to be based on machining of material by removal of cuttings and also make it possible for the machining operation to be shorter than would be required in a procedure whereby each spline was formed by creating a complete groove with an entirely linear groove bottom on each longitudinal side of the respective splines.

As regards in particular the forming of splines on the clutch ring for the low-speed side, a further object is to achieve a spline shape which makes the finished clutch ring easier to press firmly onto the straight splines on the inner circumference (inside diameter) of the "low disc" used for fixing the clutch ring relative to the planetary gear housing.

Summary of the invention

The abovementioned objects are achieved according to the invention by the procedure indicated in the introduction being distinguished by adoption of the measures indicated in the characterising part of claim 1.

A primary distinguishing feature of the invention is thus that on an annular or discshaped clutch element blank (which comprises an annular first portion with conical outside, and an associated annular second portion) a circle of spline teeth extending substantially axially is formed by profiling (form milling) within a clutch engagement region of the second portion of the coupling element blank, which region is heightened radially relative to the conical outside of the first portion. Each spline tooth is formed by profiling during progressive mutual linear movement between a milling tool and the clutch element blank, parallel with the centreline of the clutch element blank. However, the straight linear basic movement of the milling tool parallel with the centreline is interrupted before the milling tool has completed a milled groove with continuous straight bottom, thereby imparting to the lateral surfaces of the spline teeth what in horizontal section is seen as a slightly concave curve constituting a locking step.

In practice, the profiling may for example be done by the clutch element blank being moved relative to the rotating milling tool, or alternatively by the rotating milling tool being moved relative to a stationary clutch element blank.

Particularly in cases where the clutch element in which spline teeth are to be formed by profiling is a clutch ring for the low-speed section of a planetary gear, the spline teeth are provided with an axial length which is sufficient not only to provide space for mutual connection (by spline engagement) with internal splines of a ring gear of the gear but also to provide space for locking engagement with a so-called low disc used as an intermediate part for the firm connection of the clutch ring to the gear housing.

The spline teeth lateral surface curvature forming a locking step is created by the straight linear basic movement of the milling tool parallel with the centreline being interrupted before a complete milled groove with continuous straight bottom has been formed. The interruption of the linear basic movement of the tool may be by the tool being guided radially outwards, with or without continuing axial movement of the tool, as indicated by claims 3 and 4 respectively.

In cases where the clutch element in which spline teeth are being formed is a clutch disc for a high-speed section of the planetary gear, it is sufficient for the teeth to be long enough to provide space for the splines to engage with the internal splines of the ring gear. In this kind of clutch element, the movement of the milling tool after completing the straight linear basic movement may be as per claim 7. If the axial movement of the tool is interrupted entirely immediately after the completion of the linear basic movement, there is no need thereafter for any real guidance of the tool, which can then quite easily be moved away in the simplest possible manner from the clutch disc blank.

Brief description of the drawings

The invention will now be illustrated with reference to a number of diagrams depicting both a general view of a planetary gear used as range gear and views of a clutch ring (low clutch cone) which forms part of the planetary gear and has spline teeth formed by a procedure according to the invention. The diagrams are as follows:

Fig. 1 depicts an axial longitudinal section through a planetary gear provided with a clutch element with spline teeth formed by conventional pressure rolling, Figs. 2 and 3 depict (on a smaller scale) axial sections respectively through an end view of a clutch element in the form of a clutch ring (low clutch cone) corresponding to the clutch element depicted on the right in Fig. 1 , but in this case the clutch ring has spline teeth formed by the procedure according to the invention, Fig. 4 depicts on a larger scale a detail (within the circle S) of the clutch element in Fig. 2, Fig. 5 depicts a horizontal section along the line B-B in Fig. 4, Fig. 6 depicts (in a sectional view similar to that in Fig. 4) a clutch ring which is fixed firmly to a surrounding planetary gear housing and has splines formed by conventional pressure rolling,

Fig. 7 depicts (on a larger scale than Fig. 6) a horizontal section along the line C-C in Fig. 6, Fig. 8 depicts in the same kind of view as in Fig. 6 a clutch ring (low clutch cone) with splines formed by interrupted milling according to the invention, and Fig. 9 shows finally in the same kind of view as in Fig. 7 a horizontal section along the line D-D in Fig. 8. Description of an embodiment

As the invention relates to a method for the forming of spline teeth to serve as coupling teeth on a clutch element blank which is to constitute a clutch ring or clutch disc intended to form part of a gearbox, preferably a vehicle gearbox, this description refers initially to a planetary gear depicted in Fig. 1.

The planetary gear depicted in Fig. 1 comprises in a conventional manner an input shaft 2 (e.g. from an undepicted main gear) on which are mounted a sun wheel 4 and a clutch disc 6 (also called high clutch disc or high clutch cone) which is arranged on the high-speed side of the gear and has a circle of spline coupling teeth 8 on its outer circumference. The clutch disc 6 also has a conical friction surface 10 facing radially outwards and intended to cooperate with a corresponding conical friction surface 12 facing inwards on a relating synchronising ring (latch cone) 16 provided with splines 14. The planetary gear further comprises a planet wheel carrier 18 for here undepicted planet wheels which are in driving engagement with a surrounding ring gear 20 with internal splines 22. The planet wheel carrier 18 is integral with an output shaft from the planetary gear.

The ring gear 20 is movable axially in a conventional manner for mutual engagement either with the clutch disc 6 on the high-speed side of the planetary gear or with an annular clutch element in the form of a clutch ring 24 (low clutch ring/low clutch cone) arranged on the low-speed side of the planetary gear and fixed to, and for joint rotation with, the undepicted housing surrounding the planetary gear. The connection of the clutch ring 24 to, and for joint rotation with, the planetary gear housing is via an annular so-called low disc 26 which has its outer circumference firmly connected to the gear housing and which has its inner circumference provided with spline teeth 28 in firm engagement with a circle of axially external spline teeth 30 on the outside of an engagement region of the heightened clutch portion 32 of the clutch ring 24. The clutch ring 24 also has a conical friction surface 34 facing outwards on a recessed portion 36. The friction surface 34 of the clutch ring 24 is intended to cooperate with a corresponding conical friction surface 37 facing inwards on a relating synchronising ring (latch cone) 40 provided with splines 38 which are in engagement with the splines 22 of the ring gear 20.

The clutch ring 24 depicted in Fig. 1 and Fig. 6 is provided with spline teeth 30 formed by a pressure rolling technique which, as indicated above in the general part of the description, entails disadvantages both from the weight point of view and with regard to time-consuming and expensive subsequent treatment inter alia to remove burrs along protruding material. The grooves on either side of each spline tooth 30 have, as may be seen, a continuous straight bottom 41, and the lateral surfaces 42 of the spline teeth have, as may be seen (Fig. 7), a shape narrowing rearwards (rearward slope) required to prevent gear disengagement ("gear jump-out") when no torque is being transmitted. This oblique configuration of the lateral surfaces 42 (surfaces constituting locking steps) created by pressure rolling is often formed with an oblique angle α of approximately 3°.

As indicated above, the invention aims at forming these surfaces constituting locking steps by a method other than pressure rolling. According to invention they are formed instead by profiling (form milling) whereby each spline tooth is formed during progressive movement of the milling tool parallel with the centreline C_L of the clutch element (i.e. the clutch ring 24 or the clutch disc 6). A distinguishing feature of the procedure of the invention in this respect is that the straight linear basic movement of the milling tool (parallel with the centreline) is interrupted (see Fig. 8) before the milling tool has completed a continuous straight-bottomed milled groove all the way from the rear side 44 of the clutch portion 32 to the latter's front side 46.

The linear basic movement of the tool, parallel with the centreline, from the rear side towards the front side of the portion 32 is interrupted advantageously one or a few millimetres before the straight groove bottom 41 ' has reached the transverse plane in which the front side 48 of the low disc 26 is designed to be after the assembly of the clutch ring 24 and the low disc 26. The bottom of the milled groove will thus have, owing to the circular shape of the milling tool, a contour (shown by the radius of curvature R in Fig. 8) which curves slightly upwards in a forward direction (towards the left in Fig. 8). The length of the straight groove bottom 41 ' may for example amount to at least 30% of the total length, parallel with the centreline, of the clutch engagement region 32.

The result of this "prematurely" interruption of the tool movement will be that the lateral surfaces 42' of the spline teeth exhibit what in horizontal section is seen as a slightly concave curve (see Fig. 9) which is practice will substantially perform the same purpose of constituting a locking step as the obliqueness of the lateral surfaces 42 formed by pressure rolling (compare with Fig. 7).

As soon as the linear basic movement of the milling tool is interrupted, the tool is moved radially away, possibly (but not necessarily) during continuing axial movement. Assuming that when the basic movement of the milling tool is interrupted the tool has already travelled so far that it has already "broken through" the front side 46 clutch ring blank, the tool can be moved radially straight outwards away from the clutch ring blank.

Figs. 2-3 depict a complete finished clutch ring 24 with spline teeth 30 which have been formed by profiling according to the invention. As may be seen in the detail view in Fig. 4, the teeth 30 are bounded rearwards by transverse recesses 50 which form part of a circumferential retaining ring groove on the outside of the clutch ring 24. A retaining ring 52 (see Figs. 1 and 8) is inserted in this retaining ring groove for axial locking of the clutch ring relative to the low disc 26. There is also a spacing washer 54 on the front side 48 of the low disc 26.

In cases where the clutch element blank subjected to profiling in accordance with the forming method of the invention takes the form of a clutch disc blank for forming a clutch disc 6 with the location depicted in Fig. 1 in the planetary gear, the spline coupling teeth 8 of the clutch disc may in principle be formed by the same profiling technique as used for forming the spline teeth 30 of the clutch ring 24. However, the coupling teeth 8 need only have an axial length such as is required for mutual coupling with the splines 22 of the ring gear 20.

Claims

1. A method of forming coupling teeth (spline teeth) on a radial outside of a clutch element (6;24) for a gear section belonging to a gearbox, characterised in that on an annular (24) or disc-shaped (6) clutch element blank which comprises an annular first portion (36) with conical outside (34;10) and an associated annular second portion (32), a circle of spline teeth (8;30) extending substantially axially is formed within a clutch engagement region of the second portion of the clutch element blank (which region is heightened radially relative to the conical outside of the first portion) by profiling (form milling) whereby the respective spline teeth are formed by progressive relative movement between a milling tool and the clutch element blank, parallel with the centreline (C_L) of the clutch element blank, but the straight linear basic movement (41 ') of the milling tool, parallel with the centreline, is interrupted before the milling tool has completed a milled groove with continuous straight bottom, thereby imparting to the lateral surfaces (42') of the spline teeth (8;30) what is seen in horizontal section as a slight concave curve (R) constituting a locking step.

2. A method according to claim 1, characterised in that the selected clutch element blank subjected to profiling is a clutch ring blank (24) for a low-speed section of a planetary gear, and the spline teeth (30) which are formed on the clutch ring blank are provided with an axial extent such as to enable them to be used both for mutual coupling with a ring gear (20) of the planetary gear and for connecting the finished clutch ring (24) to the housing of the planetary gear.

3. A method according to claim 2, characterised in that when the milling tool has completed its straight linear basic movement parallel with the centreline, the tool is guided, during continuing axial movement, successively radially outwards in a slightly curved movement path.

4. A method according to claim 2, characterised in that when the milling tool has performed its straight linear basic movement parallel with the centreline, its continuing axial movement is halted, after which the tool is instead moved in a direction radially straight outwards away from the clutch ring blank (24).

5. A method according to claim 3 or 4, characterised in that the straight linear basic movement of the milling tool is pursued at least until the length of the straight milled groove created by it amounts to at least 30% of the total length, parallel with the centreline, of the heightened clutch engagement region (32) of the clutch ring blank (24).

6. A method according to claim 1 , characterised in that the selected clutch element blank subjected to profiling is a clutch disc blank (6) for a high-speed section of a planetary gear, and the spline teeth (8) which are formed on the clutch disc blank are only provided with an axial extent which is sufficient to provide space for mutual coupling with a ring gear (20) of the planetary gear.

7. A method according to claim 6, characterised in that when the milling tool has performed its straight linear basic movement parallel with the centreline, the tool is guided radially outwards away from the clutch disc blank (6), with or without continuing axial movement.