Machine element or mechanism – Gearing – Interchangeably locked
Patent
1998-09-02
1999-11-02
Wright, Dirk
Machine element or mechanism
Gearing
Interchangeably locked
74339, F16H 312
Patent
active
059749059
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a motor vehicle gearbox, comprising two concentrically arranged alternately driveable first and second input shafts, first and second layshafts, pringary gears carried by the first input shaft and the first layshaft, said pringary gears engaging each other for transmitting torque from the first input shaft to the first layshaft, pringary gears carried by the second input shaft and the second layshaft, said pringary gears engaging each other for transmitting torque from the second input shaft to the second layshaft, an output shaft, gears carried by the layshafts and the output shaft, said gears engaged in each other in pairs for transmitting torque from either layshaft to the output shaft and of which at least one gear in each pair is a releasable idler gear, and synchronizing means comprising firstly, a pair of synchronizing gears rotatably mounted on one of the layshafts, said gears being in driving engagement with gear rings on one input shaft, and secondly friction means, by means of which a driving connection between one synchronizing gear and the shaft can be established to adapt the rotational speed of the layshaft which is driveably coupled to the momentarily undriven input shaft, to a rotational speed determined by the selected gear speed.
A gearbox of the above stated construction is known by SE-A-8700583. It is a so called power shift gearbox with a two-position central synchronization, whereby six synchronizing functions are obtained in a seven speed gearbox with only two synchronizing gears and a synchronizing clutch on only one of the layshafts. This provides a basic construction which is compact and easily achieved with very short shafts. The latter is advantageous with respect to torque capacity and gear and bearing life.
The purpose of the present invention is, in a gearbox of the type described by way of introduction, to increase the number of gear speeds in the most economical manner as regards design and cost.
This is achieved according to the invention by virtue of the fact that that at least one of the synchronizing gears is co-ordinated with engaging means which permit transmission of higher torque to its layshaft than what is required for said rotational speed adaptation.
The invention is based on the idea of reinforcing the engaging force and the torque transmission capacity of at least one synchronizing gear so that the gear is not only used to accelerate an essentially unloaded layshaft during the synchronizing phase but also can be used to transmit driving torque. In practise this is achieved in the known gearbox described by way of introduction which has very narrow synchronizing gears only dimensioned for the synchronizing torque, by broadening the gear and for example providing it with engaging means with a positive connection instead of merely a frictional engagement. In this manner it is possible to provide an extra gear speed, for example a so called crawl gear with a higher gear ratio than the lowest gear speed in the known gearbox, or an overdrive with a lower gear ratio than the highest gear of the known gearbox.
The invention will be described in more detail with reference to examples shown in the accompanying drawings, where
FIG. 1 shows a longitudinal section through a gearbox with seven ordinary speeds forward as well as a crawl gear and reverse.
FIG. 2 is a longitudinal section through a gearbox with seven ordinary forward gear speeds as well as overdrive and reverse.
1 in the figures designates an engine fly wheel, which via a multi-disk wet disk clutch, generally designated 2, drives a gearbox 3 according to the invention. The clutch 2 is a double clutch of a type known per se and therefore it does not need to be described in more detail here. The left hand clutch unit 4 seen in the figure is coupled via a sleeve element 5 to a first input shaft 6 in the gearbox, while the right hand clutch unit 7 is coupled via a sleeve element 8 to a second input shaft 9 in the form of a hollow shaft mounted concentrically with the first shaft 6
REFERENCES:
patent: Re33551 (1991-03-01), Andersson et al.
patent: 2612787 (1952-10-01), Youngren et al.
patent: 4727764 (1988-03-01), Klaue
patent: 4876907 (1989-10-01), Andersson et al.
patent: 5150628 (1992-09-01), Alfredsson
AB Volvo
Wright Dirk
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