FIELD OF INVENTION:
The present invention relates to an improved hydrostatic parallel series
propulsion system.
Generally the present invention relates 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:
It is well known, that in vehicle such as compactors driven by hydrostatic
transmission having drive on both drum is generally driven by two fixed or
variable motor mostly in parallel configuration or sometime in series. These
machines need to satisfy both gradeabilty and speed requirement. In known
system the motors are simultaneously driven in parallel. The engine is driven in
full speed. The vehicle speed is controlled by changing the displacement of the
pump or motor or both.
The main disadvantage of such system is that a high capacity pump is used to
satisfy speed and gradeability requirement. Another disadvantage is that for the
optimization of system the engine has to run at a high RPM. This decreases the
life of engine as well results in low system efficiency.
The other known system uses motor in series. It reduces the motor size as a
result the speed increases but gradeability decreases. However, this

configuration is rarely used. The objective of the present invention is, to
optimize the efficiency of the hydraulic system, by using parallel series system.
SUMMARY OF THE INVENTION:
Therefore, in view of the disadvantages stated above, the main objective of the
present invention is to describe a parallel series system which satisfy both speed
and gradeability of machine and in turn increase the overall system efficiency.
The present invention relates to, an improved hydraulic system for construction
machines such as compactors having two motors at front and rear drive which
can be witched between parallel and series to attain gradeabilty as well as
speedy mounted control. The proposed system will use half the size of motor
used in purely parallel system.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
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 drawing: The Figure 1 is a block diagram of the new control circuit
system showing an embodiment of the present invention, where (1) is a piston
pump, (2) is a parallel series switch valve (3) is electric control switch (4) and
(5) are propulsion motors.
DETATILED DESCRIPTION OF THE PRESENT INVENTION:

According to the present invention there is provided an improved hydrostatic
parallel series propulsion system is combination of:
(i) parallel flow system used in work mode and attain gradeabilty at low
speed;
(ii) series flow by switching the conversion valve for high speed travel
applications
characterized in that (1) is a piston pump, (2) is a parallel series switch valve (3)
is electric control switch (4) and (5) are propulsion motors.
The oil from engine mounted pump 1 is divided into both front drive motor 4
and rear drive motor 5.
Operation of the switch 3 the direction of the valve 2 shifts and oil travels from
drive motor 1 to drive motor 2.
The combination of above mentioned features make the hydraulic fluid system
highly energy efficient and compact.
The parallel propulsion system makes the machine achieve the working mode
and gradability mode functionalities while the series propulsion system makes
the machine work in transport mode with maximum speed.
There is provided a parallel series drive circuit for hydrostatic propulsion.
As shown Figure 1, the oil from engine mounted pump 1 is divided into both
front drive motor 4 and rear drive motor 5. This mode is referred as parallel

mode and is a low speed high torque mode. This is beneficial in work mode and
climbing steep slope as per specification.
As shown in Figure 2 on operation of the switch 3 the direction of the valve 2
shifts and oil travels from drive motor 1 to drive motor 2. This mode is referred
as series mode. The speed of machine will be double than the parallel mode.
This is beneficial for fast travel of machine.

WE CLAIM:
1. An improved hydrostatic parallel series propulsion system is combination
of:
(i) parallel flow system used in work mode and attain gradeabilty at low
speed;
(iii) series flow by switching the conversion valve for high speed travel
applications
characterized in that (1) is a piston pump, (2) is a parallel series switch valve (3)
is electric control switch (4) and (5) are propulsion motors.
2. An improved hydrostatic parallel series propulsion system as claimed in
claim 1, wherein the oil from engine mounted pump 1 is divided into both front
drive motor 4 and rear drive motor 5.
3. An improved hydrostatic parallel series propulsion system as claimed in
claim 1, wherein operation of the switch 3 the direction of the valve 2 shifts and
oil travels from drive motor 1 to drive motor 2.
4. An improved hydrostatic parallel series propulsion as claimed in of
claims 1 and 3 wherein the combination of above mentioned features make the
hydraulic fluid system highly energy efficient and compact.
5. An improved hydrostatic parallel series propulsion as claimed in of
claims 1 to 4, wherein the parallel propulsion system makes the machine
achieve the working mode and gradability mode functionalities while the series

propulsion system makes the machine work in transport mode with maximum
speed.