Machine element or mechanism – Gearing – Interchangeably locked
Patent
1990-04-17
1991-03-12
Wright, Dirk
Machine element or mechanism
Gearing
Interchangeably locked
74356, B60K 2010, F16H 308
Patent
active
049984438
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a system for controlling the gear-changing process in a mechanical, automatic gearbox of the kind having concentrically journalled and alternately driven input shafts, and two intermediate shafts which carry gears which engage with gears on the input shafts, and in which at least one gear in each pair of mutually engaging gears can be disengaged from its respective shaft, including pressure-medium activated piston-cylinder devices for disengaging and engaging said disengageable gear, and a control circuit which includes valve means for regulating the flow of medium to and from the piston-cylinder devices.
Double input shafts and double intermediate shafts are used in gear boxes of the so-called "power shift" type, in which the gear change is effected through pre-selection, wherein two gear pairs, each driven by a respective input shaft, are engaged simultaneously. Prior to changing form, for instance, first gear to second gear, the gears of the second gear transmission are engaged, whereafter the actual gear change takes place by disengagement of the input shaft of the first gear and engagement of the input shaft of the second gear.
One feature characteristic of this type of gearbox is that they are well suited to automation. For example, the process of gear changing can be controlled by a microcomputer-controlled electro-hydraulic control system, in which electromagnetic valves regulate the supply of working medium to hydraulic cylinders whose pistons are connected to the shift rods in the gearbox. It is necessary to construct such control systems with the aim of minimizing the risk of error in the microcomputer or in the remainder of the electric system, e.g. such errors are those which will result in two gears on and the same shaft, e.g. the disengageable gears of the first and third gear, being engaged simultsaneously. The result of wrongly engaging two gears in this way can have extremely serious consequences, not only in total destruction of the gearbox but also in a direct driving hazard, as a result of braking or locking of the driven vehicle wheels.
The object of the present invention is to provide a control system of the aforedescribed kind which will totally eliminate the risk of simultaneously engaging two disengageable gears on one and the same shaft, irrespective of erroneous control signals from a microcomputer incorporated in the system or of any other fault in the electric system.
This object is achieved generally in accordance with the invention, in that the control circuit includes valve means which are constructed and interconnected such that the supply of pressure medium for engaging a second gear on a shaft which already has a first gear engaged will result in the disengagement of the first engaged gear through a pressure medium control facility.
For instance, in the case of a gearbox having five gears, in which the gear pairs or sets of the first, third and fifth gear, and the reverse gear are each driven by one and the same input shaft, whereas the gear pairs or sets of the second and fourth gear are each driven by the second input shaft, a pair of electromagnetic valves, each of which controls the supply of pressure medium for engagement of the gears of the first and second gear, may be connected to one another and also with further pressure-medium control valve means, in a manner such that activation of the third gear valve while the valve of the first gear is still activated will result in disengagement of the gear wheel of the first gear and engagement of the gear wheel of the fifth gear. By allowing, in this way, two valves of mutually different functions to function jointly to provide an additional function, the risk of simultaneous engagement of two gear wheels on one and the same shaft is totally eliminated.
The invention will now be described in more detail with reference to an exemplifying embodiment illustrated in the accompanying drawing, in which
FIG. 1 is a schematic illustration of an inventive gearbox, and
FIG. 2 is a circuit diagram
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patent: 4637269 (1987-01-01), Hasegawa et al.
patent: 4660441 (1987-04-01), Young
patent: 4674345 (1987-06-01), Furukawa et al.
patent: 4756213 (1988-07-01), Mainquist et al.
patent: 4843902 (1989-07-01), Patton et al.
AB Volvo
Wright Dirk
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