Power plants – Pressure fluid source and motor – With means purging – cleaning or separating undesirables from...
Patent
1996-03-21
1998-07-07
Nguyen, Hoang
Power plants
Pressure fluid source and motor
With means purging, cleaning or separating undesirables from...
60454, 60488, F16D 3102
Patent
active
057751030
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/SE94/0078, filed Apr. 27, 1994.
BACKGROUND OF THE DISCLOSURE
This invention relates to a method and an apparatus for a fluid operated system where the condition of the fluid has a great importance for the reliability and the life length of the system. The system preferably comprises a hydraulic system in a mobile machine.
Hydraulic technique is common in different types of mobile working machines and is utilized for the propulsion of the machine as well as for the control and the working functions of the machine.
The propulsion is made by a so called hydrostatic transmission which is an advanced hydraulic system with a separate feeding circuit. The remaining functions of mobile machine are almost without exception driven by a hydraulic system in which force-transmitting pumps suck hydraulic medium directly from a hydraulic tank. The different hydraulic systems of a vehicle normally have the same hydraulic medium and a common hydraulic tank.
Oils are utilized as a hydraulic medium. Most common are mineral oils but for environmental reasons vegetable oils are utilized to an increasing extent. The oils are in a varying degree an article of consumption which has to be periodically exchanged.
The hydraulic tank is normally open towards the outer atmosphere so that the hydraulic oil gets a direct contact with the air. Due to that fact the oil of the tank will be more or less saturated with different air gases. In addition to that the water will be concentrated in the tank by the fact that during temperature reductions the water steam of the atmospheric air becomes supersaturated and condensates to water drops on internal tank surfaces. Moreover, solid particles accompany the incoming air in spite of the fact that this air is filtrated. Due to the direct air contact, the oil becomes polluted in different ways which contributes to the fact that the operation conditions of the hydraulic systems are deteriorated.
Oxygen, which is one of the air gases dissolved into the oil, contributes to the chemical breaking down of minerally and vegetably based hydraulic oils as well as of different rubber products. This process is accelerated during increases temperature. A high oxygen content of the oil also contributes to an increased corrosion and gives an increased wear of internal surfaces.
Air as well as free bubbles in the oil causes an efficiency reduction, a high oil temperature, a high sound level and erosion damages in pumps. Pumps sucking oil directly from the tank are especially exposed for this risk.
Water is a severe pollution which contributes to a quick stop-up of filters and hurries up the breaking down of hydraulic oils. The water is supplied to the oil from the outside but is also created as a rest product during the chemical breaking down of the oil.
Great efforts are made for keeping the hydraulic oil in the best condition and to prevent the oil from being polluted. This is made by a powerful filtration, by frequent oil and filter exchanges and by different constructive measures. In spite of these measures, the oil of the hydraulic tank is normally saturated with both air and water which, as has been stated previously, gives a shorter life length and to a worse reliability of the functions of the hydraulic system.
By way of introduction, the main features of the conventional technique shall be described here.
FIG. 1 is a diagram with ISO symbols describing an hydraulic system with a hydrostatic transmission comprising a pump 51 which has a variable deplacement and is connected with a motor 52 to a closed circuit which can have a high pressure and where the flow direction can be reversed. The two transmission units, below called the hydraulic machines, can work in all four operation quadrants, i.e. the rotational as well as the torque direction of the hydraulic motor can be reversed.
A feeding circuit of the transmission comprises a feeding pump 53 which sucks oil from the tank 54 and puts the closed circuit under pressure via the non-return
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patent: 4348864 (1982-09-01), Ichimura et al.
patent: 4432775 (1984-02-01), Won
patent: 5020324 (1991-06-01), MacDonald et al.
patent: 5317872 (1994-06-01), Ingvast
patent: 5493860 (1996-02-01), Bjerke et al.
patent: 5600953 (1997-02-01), Oshita et al.
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