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.