System for preventing gear hopout in a tooth clutch in a vehicle transmission

Abstract

A system is provided for preventing gear hopout in a tooth clutch in a vehicle transmission, the tooth clutch including an engaging sleeve having sleeve clutch teeth. The tangent function for at least one of driving back-taper angle and braking back-taper angle is larger than the average value of clutch coefficient of friction and spline coefficient of friction multiplied by the sum of unity and the ratio of clutch teeth pitch diameter and spline teeth pitch diameter.

Description

BACKGROUND AND SUMMARY[0001]The present invention relates to vehicle transmissions, and more particularly to a system for preventing gear hopout in tooth clutches that are subjected to misalignment due to forces acting on rotating parts they connect.BACKGROUND OF THE INVENTION[0002]Tooth clutches are frequently used in stepped vehicle transmissions to engage and disengage the gears. A tooth clutch can rotatably connect a main part with a substantially coaxial connectable part. Normally, an engaging sleeve is used as an interconnecting member between these two parts. This engaging sleeve is often rotatably fixed but axially moveable with respect to said main part by means of, for instance, splines. On the engaging sleeve there are clutch teeth at the end that faces the connectable part. These clutch teeth need to be compatible with corresponding clutch teeth on the connectable part. These two sets of clutch teeth can be brought into mesh with each other by moving the engaging sleeve ...

AI Technical Summary

Benefits of technology

[0012]There are some applications where conventionally made back-tapered clutch teeth have been shown to have insufficient self-retaining action. One example is shown in FIG. 2, where, in comparison with FIG. 1a, a retarder unit 230 has been added to the range section 201. The retarder unit 230 is an auxiliary brake that can be used in long down-hill slopes in order to reduce wear and prevent over-heating of the ordinary wheel brakes of the vehicle. The retarder unit is driven by a retarder shaft 231 that is rotatably connected to a retarder driven gearwheel 232. In turn, the retarder driven gearwheel 232 meshes with a retarder driver gearwheel 233 that is rotationally connected to the output shaft 214 of the range section 201.

[0013]When the retarder unit 230 is in operation, gear mesh forces 240 will act on the retarder driver gearwheel 233. These forces will tend to misalign the output shaft 214. Normally, engine braking is used simultaneously with retarder operation. Thereby, torque will be transferred by the range section, and there will be contact forces in the gear meshes and between the clutch teeth of the range section. These contact forces will urge the parts of the range section towards a substantially coaxial state, as was described earlier. Hence, the contact forces will counteract the tendency of the gear mesh forces on the retarder driver gearwheel 233 to misalign the output shaft 214.

[0026]There are some known methods to prevent gear hopouts of the type described above. In general, radial support devices, such as bearings, have been introduced or improved in order to limit the possible misalignment of the supported shaft. In U.S. Pat. No. 5,839,319 a splitter unit similar to the one in FIG. 3 is shown. However, a headset / fourth gear 74 (corresponding to the second gearwheel 354 in FIG. 3) is not supported by a main shaft (corresponding to 355 in FIG. 3) but by a spindle 62 that is rigidly secured to an input shaft 42 (corresponding to 352 in FIG. 3). Thereby, a gear mesh force acting on the headset / fourth gear 74 will not cause any significant urge to misalign the main shaft. Hence, the tendency for gear hopout has been eliminated. However, the additional spindle will imply increased production cost.

[0027]U.S. Pat. No. 5,083,993 presents a planetary gear 1 that is similar to the planetary range section 101 in FIG. 1a. In order to reduce possible misalignment, a roller bearing has been included between a planet wheel carrier 9 (corresponding to the planet carrier 113 in FIG. 1a) that is integral with an output shaft 3 (corresponding to 114 in FIG. 1a) and a sun wheel 5 (corresponding to the sun gearwheel 108 in FIG. 1a) that is arranged in a rotationally fixed manner on an input shaft 2 (corresponding to the main shaft 102 in FIG. 1a). Thus, the roller bearing acts as a radial support device for a supported shaft, the output shaft 3, on a supporting shaft, the input shaft 2. However, the roller bearing will imply increased cost.

[0028]EP-239555B1 discloses a similar planetary gear 2. Therein, with the aid of a ball bearing 18 a clutch ring 16 supports a planet wheel keeper 10 that is fastened to a planet wheel carrier 11 which, in turn, is integrated with an output shaft 4. The clutch ring 16 is non-rotatably mounted on a sun wheel 7 that is non-rotatably mounted on an input shaft 3. In FIG. 1a the equivalence would be an additional ball bearing between the engaging ring 120 and the part of the planet carrier 113 that is to the left of the planet gearwheel 111. The additional ball bearing 18 will provide a radial support of the output shaft 4 and thereby reducing the possible misalignment. However, the ball bearing 18 will imply increased cost.

Problems solved by technology

Unfortunately, the material volume that can be plastically deformed in a rolling operation is small.

There are some applications where conventionally made back-tapered clutch teeth have been shown to have insufficient self-retaining action.

Some retarder operating conditions have shown to cause problems in a planetary range section as in FIG. 2.

This urge for relative motion may turn into an unstable state if the friction between the contacting clutch teeth is large and the self-retaining action from for instance back taper is insufficient.

Thereby, no torque can be transferred by the range section 201, and, consequently, no engine braking is possible.

A proper conventional radial support device between those shafts, such as a radial bearing (358), is either missing or insufficient under some conditions.

These contact forces tend to misalign the engaging sleeve.

Under certain conditions this misalignment might lead to gear hopout, that is, unwanted and uncontrolled disengagement of the tooth clutch.

However, the additional spindle will imply increased production cost.

However, the roller bearing will imply increased cost.

However, the ball bearing 18 will imply increased cost.

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