What is sought at present In modern machines and industrial vehicles transmission is a durable filling with machine oil or transmission oil, a typical mileage using this transmission being on the order of 1 million kilometers.
For adjusting the oil amount or oil level in automatic transmissions, a great precision is required due to the small differences between the admissible minimum and maximum amounts of oil. In addition, the difference between the minimum and maximum to be adjusted must be as small as possible for reasons of weight.
When falling below the minimum, especially under coil, vehicle inclination (lengthwise or transverse) or acceleration (cornering, starting or braking), suction noises appear to happen in the simplest cases. In serious cases, due to insufficient pressure supply, operation interferences or also great damages to the clutch lining are possible which result in failure of the transmission.
When the maximum is exceeded, in turn, the danger consists in that at high temperatures and high rotational speeds of the transmission, the oil level rises to the point that the rotating parts sink in the oil. The direct consequence is a great coating with high oil discharge from the exhauster, the oil discharge possibly leading later to falling below the minimum with the resulting consequences. When the maximum is exceeded with the resulting oil escape, there is the added danger of overheating, since the exiting oil can ignite on hot parts such as the exhaust system. An oil level that is too high with the oil discharge resulting therefrom can also lead to pollution of the environment and to formation of a slippery road surface.
Therefore, an exacting adjustment of the oil amount or of the oil level proves itself to be indispensably necessary. To be taken into consideration here is the clear dependence on temperature of the automatic transmission fluid.
A simple method for adjustment of the oil level results in taking the temperature into account by means of an oil dipstick. By this method, the oil level can be adjusted only with reduced precision. An oil level adjustment, both in a cold and in a hot transmission, is fundamentally possible since a full level range for cold and also for hot is normally marked in the dipstick. It is problematic here that the oil temperature has to be either measured or evaluated. In addition, the accuracy of the filling amount depends on how accurately the oil level can be read on the dipstick. Up to the definitive adjustment, intermediate readings can be needed under certain circumstances.
Another method for oil level adjustment consists in carrying out the filling operation by means of fixed overflow edges at a precisely defined temperature. During the filling, the precision of the filling amount depends here on how precisely the temperature hits the temperature for which the overflow edge has been defined. Only relatively narrow temperature range is normally allowed here for the adjustment in order not to let the filling tolerances become too great. The consequence of this is that an oil level control is not always possible. Thus, for example, a hot running vehicle has to stand some time until the oil temperature has sunk to a level within the narrow temperature tolerances for the adjustment.
A method for electrically determining the oil level with thermal device has been described in EP 0 133 069. Also in EP 0 589 507 is disclosed another method for electric level measurement with the aid of a sensor and a calculation of the needed oil level correction for adjustments.
DE 196 44 738 A1, in addition, discloses a device for adjusting a liquid level, particularly the oil level in an automatic transmission, by means of an adjustable overflow edge or overflow aperture according to the temperature. The use of a thermostatic valve for adjusting the oil level has been disclosed in U.S. Pat. No. 4,921,165.
There are known besides fillings with fixed amounts according to the different weighting methods or by means of suction by immersion of lances, but these methods work with great tolerance.
The problem on which this invention is based is to outline a method for oil filling of transmission, particularly automatic transmissions, which makes an exact filling possible, taking into account constructional tolerances and different parts. In addition, a filling device is proposed which makes an exact dosing possible. The method must also be applicable to adjustment of the liquid level for other parts.