1. Field of the Invention
The present invention relates to multi-disk synchronizers, particularly of the type used in heavy-duty synchromesh transmissions.
2. Discussion of the Related Art
It is well known to use synchronizers to provide clash-free shifting of gears in a transmission for a motor vehicle, creating a so-called synchromesh transmission. In such a transmission, a gear is rotatably mounted around a shaft. A hub is mounted for rotation with the shaft, and a shift collar is mounted around the hub such that it is axially movable relative to the hub. The inner surface of the shift collar and the outer surfaces of the hub and gear (or an output drum connected to the gear) are splined, so that when the shift collar moves axially towards the gear (or output drum), the splines engage. This provides a positive connection between the shaft and the gear via the hub and shift collar.
Without more, this would be a clash-type transmission, which could be shifted only when the shaft and gear are sitting still, since the splines on the shift collar and the gear would not align if there was any relative rotation therebetween. The function of a synchronizer is to eliminate relative rotation between the gear and hub, without requiring that the two be at rest. The splines of the shift collar and gear then can engage while the vehicle is still moving.
Virtually all synchronizers use friction to eliminate relative rotation between the gear and hub. The simplest and most common synchronizers provide two adjacent conical surfaces, one connected to the gear and one to the shift collar, e.g., as taught in U.S. Pat. Nos. 4,349,090 (Griesser) and 4,566,569 (Eriksson). When the shift collar is axially shifted in the direction of the gear, the two conical surfaces engage, and friction will eliminate any relative rotation therebetween. The splines of the shift collar then can mesh with the splines of the gear.
The size of the friction surfaces needed for the synchronizer to work properly depend on the amount of momentum and energy which must be transferred to bring the gear to the same speed as the hub. The heavier-duty the transmission, the more massive the gears, and therefore the larger the friction surface needed for the synchronizer. In particularly heavy-duty transmissions, e.g., those used on agricultural and construction vehicles, the cone size which would be necessary to obtain the required frictional surface area in a cone-type synchronizer becomes very large, creating an unacceptably large synchronizer. Some such transmissions therefore instead use multiple inter-leaved disks to carry the friction surfaces, much as in a clutch. Such a technique is used in the synchronizers in the Quad-Range transmission used on John Deere Row Crop Tractors and in the transmission used on John Deere 4WD Articulated Tractors, which are extremely large, heavy work vehicles. Alternatively, a synchronizer can use a mix of cone and disk surfaces, e.g., as taught in U.S. Pat. No. 4,413,715 (Michael et al.).
Regardless of the particular type of friction surfaces employed, all synchronizers have a common requirement that the shift collar must be blocked temporarily from moving far enough for its splines to engage the gear splines until the synchronizer has eliminated relative rotation therebetween. A great many different techniques have been developed to provide such blocking. The above-mentioned patents us a variety of different techniques.
Most synchronizers also have some form of neutral detent mechanism which holds the shift collar and the friction surfaces in disengaged positions when no gears are to be engaged. Again, a great many technique have been developed to provide such a netural detent, and several are shown in the above-mentioned patents.
Another problem common to virtually all synchronizers is that manufacturing them takes substantial amounts of machining. This is particularly a problem with the components used to momentarily block axial movement of the shift collar. Naturally, the more machining required, the higher the cost, and as a result, synchronizers tend to be a very expensive part of a transmission.