Lubrication – Systems – Gearing
Patent
1986-02-28
1988-04-12
Croyle, Carlton R.
Lubrication
Systems
Gearing
184 131, 184 39, 123196AB, 74467, F01M 906, F16N 726, F16N 728, F16N 1110
Patent
active
047368195
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a splash lubrication system for motor vehicle transmissions comprising a case forming an oil sump in its bottom portion, and a transmission shaft provided with gears which are immersed in the oil at least partly when the said oil sump is filled completely.
Splash lubrication systems of this type are generally known in modern transmissions, in particular motor vehicle transmissions. Due to the rotation of the gear immersed in the oil of the oil sump, the oil is whirled upwardly and the transmission case is filled with an oil mist which ensures proper lubrication of all points required to be lubricated.
However, experience has shown that under extreme operating conditions, in particular in the presence of extremely low temperatures, such a splash lubrication system is connected with certain disadvantages because under extremely low temperatures the transmission oil assumes a relatively high viscosity and the splashing and/or the drag moment demanded from the transmission due to the very viscous oil tends in particular to brake the synchronizing mechanisms of the transmission so heavily that unsynchronized shifting operations may occur. The latter may, however, cause considerable damage to the transmission because, generally, modern motor vehicle transmissions are not designed to stand unsynchronized faulty shifting without damage as the synchronizing mechanisms of modern transmissions normally ensure smooth gear changes.
Now, it is the object of the present invention to improve a splash lubrication system of the type described above in such a manner that unsynchronized faulty gear shifting is prevented even under extremely low temperatures, without any disadvantageous consequences for the shifting behavior under normal operating temperatures.
This object is achieved according to the invention by an arrangement in which the oil sump is connected with a cavity to which oil is transferred from the oil sump when the transmission operates at a low operating temperature.
This measure ensures that the lubricating effect of the splash lubrication system is reduced under low temperature conditions and that, in particular, the very viscous oil which is the result of low temperatures, can no longer enter the synchronizing mechanisms and, thus, prevent the synchronization of the transmission parts to be brought into engagement with each other during the gear shift operation, while under normal operating temperature conditions the full oil quantity is again available so that any rattling and shattering of the transmission is avoided safely.
The oil may be transferred to the oil sump from the cavity and vice versa by means of a pump or the like. However, in a particularly preferred embodiment of the invention, the oil is transferred by suction because this method does not require any separate motor-driven elements.
In a particularly preferred embodiment of the invention, the filling level is reduced by suction far enough to ensure that the gears do not get immersed in the oil at a predetermined lower operating temperature limit.
This measure offers the advantage that once the temperature drops below the said limit temperature, no oil mist is produced at all in the transmission case. This condition can be accepted for the gear flanks that normally have to be lubricated because the lower temperature limit will be exceeded again after a very short period of time, typically one minute or a few minutes, and sufficient lubrication will then be re-established. The synchronizing mechanisms, however, are not wetted during this short interval with whirled-up oil and are, therefore, permitted to operate in a perfect manner.
According to a further improvement of the invention, the cavity is filled partly with a material exhibiting a high expansion temperature coefficient.
This measure provides the advantage that no separate oil pumps or the like are required and that the material to be firmly arranged in the cavity may be one requiring no further maintenance.
A particularly favorable effect is achieve
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Croyle Carlton R.
Obee Jane E.
ZWN Zahnradwerk Neuenstein GmbH & Co.
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