Energy Efficient Two Sections/Two Differently Mounted Positive Displacement Pump And Hydraulic System

FIELD OF INVENTION; The present invention relates generally to a hydraulic fluid system, and more particularly, to a method and apparatus for controlling a hydraulic fluid system in a construction industry vehicle. BACKGROUND OF INVENTION: The present invention relates to, a energy efficient two section positive displacement pump and hydraulic system for construction industry vehicle, for example a Back Hoe Loader, having a control system which dumps the oil at low pressure in neutral circuit, which also by-passes the remotely mounted control valves from each other, thereby reducing the accumulated pressure drops and thus limits the peak power requirement by dumping the oil from one of the section at pre-specified lower pressure. As is known well, the fixed displacement pumps produce a certain volume of fluid for each revolution of the drive shaft. In other words, when pump is driven at a fixed speed, the pump flow rate will remain constant. In the known fixed displacement hydraulic systems, in its neutral circuit, oil flows from the pump to control valve bank in series and then to the tank. In this process, the pressure drops across each valve gets added up at every step in the process. The main disadvantage of the present hydraulic system as outlined above is, that the accumulated pressure drops results in high-energy wastage as heat, which results in increased fuel consumption. Another disadvantage of the present system is, while working with second valve block in series, the pressure losses of first valve block gets added up. This results in high setting of system relief valve than actually required which results in considerable wastage of energy.

In another known fixed displacement hydraulic system, a load sensing gear pump system is used with close center valve system. The load sensing system is generally built up on the gear pump. In neutral circuit the oil is dumped to the tank at low pressure. In working mode, the oil is supplied as per the demand from the valve section. The disadvantage of the above mentioned system is that it is normally a single pump system and peak energy requirement is defined by the setting of main relief valve. A further disadvantage is that in this system, the operator does not get the feel of the control. Yet another disadvantage is that the closed center valve is generally costly, as it requires a parallel rail or a shuttle arrangement for load sensing. Another prevailing design available is having a low pressure dumping arrangement on valve, which primarily is used with a single pump system. The disadvantage of this system is that it limits only the neutral circuit losses. Therefore, in view of the disadvantages stated above, the main objective of the present invention is to describe an energy efficient open center hydraulic system using a fixed displacement pump. Another objective of the present invention is, to increase the efficiency of the hydraulic system, by dumping the oil at low pressure in neutral. We shall now describe the invention with reference to accompanying drawings which are given for the sake of illustration, but do not restrict the scope of present invention. Referring to drawings:- Fig. 1 shows the hydraulic fluid system of the present invention.

According to present invention there is provided the conceptual design involved in the present improved energy efficient hydraulic fluid system is shown in accompanied Figure 1. As shown Figure 1, the oil from each section of tandem pump 1, combines at the junction 9 after the check valve 2. In the neutral circuit, the combined oil passes through an orifice 4. There is a definite pressure drop across the orifice. The compensator 6 senses the pressure drop across the orifice. At a particular flow, the pressure drop across the orifice signals the compensator 6 to dump the balance flow at a low-pressure drop to tank 11. This value is substantially low than the over all pressure drop, in neutral circuit. In normal working condition this is the majority flow. The balance neutral flow passes through the power beyond circuit at low- pressure drop. In working mode, if we operate valve 7, the oil at junction 10 will only flow to external application and will remain blocked at valve 8. Similarly, if we operate valve 8, the oil through junction 10 will be available for valve 8, as it will remain blocked at valve 7. Therefore, it becomes a parallel system and remains independent of the other. The system also consists of an unloading mechanism. The unloading relief valve 6 is set at a lower pressure than the main relief valve 12. Whenever the pressure reaches the value of preset unloading pressure, ths unloading relief valves open and the pressure drop allows the lift of poppet of valve 3, resulting in the first section of pump 1 getting unloaded. Then the second section pressure reaches the relief valve setting and this function ultimately restricts the peak energy requirement. The combination of above mentioned features make the hydraulic fluid system highly energy efficient in both neutral as well as in the working mode.

In actual working mode another unique feature allows the oil to by pass the valve-block, which is not in use, there by restricting the accumulated pressure losses. Further more the feel of control to operator remains intact. Another objective is to combine a two-pump combination system, which unloads one pump at certain preset pressure. This helps in reducing peak energy requirement. Therefore uniqueness of the present invention is that it is energy efficient in both in neutral as well as in the working mode.