FIELD OF THE INVENTION

The present invention relates to an off-road vehicle and/or construction, earthmoving equipment and particularly to a downstream flow type hydraulic control system used in off-road vehicle and/or construction, earthmoving equipment to regulate and control a discharge flow of a variable displacement hydraulic pump.
BACKGROUND OF THE INVENTION
Due to the huge size and weight of off-road or construction machine and functions need to perform while in the field and hence all off-road or construction machine generally well equipped with hydraulics system to control various operation of machine.
Hydraulic system further utilized in earthmoving or construction machine to convenience to operator to control various functions and also to provide better safety to operator and people working around the machine.

Various operations such as digging, excavation, loading, hammer, compaction etc. including an additional equipment used in such machine, requires a source of hydraulic fluid to perform these abovementioned operations. Hydraulic fluid is generally circulated by a pump driven by the machine engine.
Yet in another known system, to meet and optimize the flow demand of the hydraulic system, fixed displacement or variable displacement hydraulic pumps are used as power source with known pressure compensation methods. Such hydraulic systems requires high degree of complexity and very precise contamination control is required, again which is relatively difficult to maintain for many off-road machines working in extreme conditions of environment and put a significant cost impact and complexion in the whole system.
The hydraulic pump is used to supply flow against resistance given by application across various fluid circulation lines to perform various mentioned operations. The standard corresponding fluid pressure is required throughout these lines to perform such operation. However, if there has been least little pressure drop or more across the pressure line causes operation get stop or stall. There has been high probability that the hydraulic pump become disabled or is not operating.
In order to overcome a stalling effect which might result if hydraulic pumping system is disabled or not operating because of overloading, there is need to have an automatic hydraulic fluid pressure detection system to measure pressure across the hydraulic line and further gives instructions to regulate or manipulate the discharge rate of hydraulic fluid through the hydraulic pump.
In a conventional hydraulic system, the fixed or variable displacement hydraulic pumps are used as a power source for the hydraulic actuators. The fixed displacement hydraulic pump delivers a constant flow at particular pump shaft speed irrespective of the energy demand of the system whereas the variable displacement hydraulic pump delivers a variable flow with respect to the energy demand of the system. There is substantial loss of energy in such systems due to non-demanded energy supply.
A typical earthmoving or construction equipment whenever ran in neutral position, the whole hydraulic fluid pumped by the hydraulic pump circulated through neutral channel and again delivered it to hydraulic reservoir. During this position, the hydraulic pump is used to run into maximum shaft speed although no actuator was working hence there was zero utilization of energy. It causes substantial loss of energy.
To solve above mentioned problem mechanically controlled hydraulic pump system introduced in the conventional earthmoving or construction equipment. In such system, the discharge rate of hydraulic fluid by the hydraulic pump is controlled through the mechanical signals received from the orifice and relief valve installed on the hydraulic fluid lines.
However, the conventional mechanically controlled hydraulic pump system is very complex in construction and also less effective and observed as inefficient.
To overcome abovementioned shortcoming and problems associated with conventional system, it is more desirable to achieve a control method that is more simple, fast and energy-efficient than previously known methods and solves or at least relieves some of the problems discussed above.
It is therefore an object of the present invention is to overcome one or more problems associated with the prior art.
The main objective of the present invention is to develop electronically controlled hydraulic pump management system which is simple in construction. The advantage of the present system over conventional mechanical system is that, it does not require any mechanical component to control the hydraulic torque. The present system does not require any types of hoses for sensing hydraulic pressure across the hydraulic lines. In electronic pump according to the present invention, the power demand of hydraulics can be easily varied with engine rpm whereas in the conventional mechanical pump only maximum power limit can be set by using springs.
One another object of the present invention is to develop simple and electronically controlled hydraulic pump management system.
Yet another object of the present invention is to develop mechanically and automatically controlled a downstream flow hydraulic control system.
One more object of present invention is to develop a a downstream flow hydraulic control system which is user friendly and cost effective.
Yet another object of present invention is to supply required hydraulic fluid according to requirement and at pre-determined pressure.
A method according to an aspect of the present invention is also disclosed.
Further advantageous embodiments and further advantages of the invention emerge from the detailed description below.

SUMMARY OF THE INVENTION
The present invention is directed to a downstream flow type hydraulic control system for an earthmoving or construction machine to regulate and control a discharge of a variable displacement hydraulic pump.
An embodiment of the present invention is relates to downstream flow type hydraulic control system which is simple in construction, efficient, effective and robust in nature.
In a preferred embodiment of the present invention includes a variable displacement hydraulic pump unit mounted on a hydraulic fluid reservoir , an electronic control unit , a hydraulic pressure sensors to measure upstream and downstream hydraulic fluid pressure across the hydraulic pressure line, multiple control valves, multiple relief valves, multiple hydraulic actuators, multiple orifices, hydraulic fluid lines etc.
When the control valves are in neutral position, the whole hydraulic fluid pumped by the hydraulic pump mounted on hydraulic reservoir circulated through the hydraulic fluid line 15 and delivered again to hydraulic reservoir. The main actuator/s installed on the hydraulic system are remain in inactive condition during this case. The downstream hydraulic pressure across the hydraulic fluid line 15 is measured by the downstream hydraulic pressure sensor and pressure sensor sends signal to ECU in voltage, further signal to pump given in terms of PWM signal.
During neutral position, whole hydraulic fluid gets transferred to reservoir through hydraulic fluid line 15 hence downstream hydraulic pressure sensor observes high pressure across the hydraulic fluid line due to high resistance of hydraulic fluid passing through the orifice then such output signal may be provided to ECU which further regulates the hydraulic pump. During high pressure phase ECU reduces the displacements of the hydraulic pump which further reduce the hydraulic fluid discharge rate.
When the control valves are start switching due to movement of spool in the control valve, during this case the main actuator/s installed on the hydraulic system are get into active condition. The downstream pressure sensor is mounted on the hydraulic fluid line 15 observe less pressure since spool in control valve switches which further partially and/or fully blocks the hydraulic fluid line 15 that results less flow to the orifice and relief valve. The downstream pressure sensor measure such less pressure and sends output signals in terms of PWM to the said ECU. In this case ECU actually increases the displacements of the hydraulic pump which further increase the hydraulic fluid discharge rate.
An another embodiment of the present invention includes the upstream pressure sensor installed in between hydraulic pump and the control valve on the hydraulic fluid line 15 to measure upstream hydraulic pressure across the hydraulic fluid line 15.
When any of the control valves of the hydraulic system are switched due to partial or full movement of spool, the hydraulic fluid get supplied to the main actuator/s. The said upstream pressure sensor measure pressure across the hydraulic fluid line 15 and sends output signals to ECU. If the power demand of hydraulic pump is more than the power supplied by the engine then the displacement of hydraulic pump needs to be decreased to match with the engine power to avoid stalling and/or abnormality observed in the hydraulic system. The displacement of the hydraulic pump may be regulated by ECU. If upstream pressure sensor observe high pressure across the hydraulic fluid line 15 then displacement of the pump reduces accordingly on the basis of output signal received through upstream pressure sensor and with the help of ECU.

BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention explained with reference to the following drawings. A more detailed description of different exemplary embodiments of the invention will follow below.
In the drawings:
Figure 1 Illustrates side view of a construction or earthmoving machine incorporating a hydraulic control system according to the present invention;
Figure 2 Illustrates a schematic representation showing a downstream flow hydraulic control system during hydraulic fluid line 15 is active according to the present invention;
Figure 3 Illustrates a schematic representation showing a downstream flow hydraulic control system during hydraulic fluid line 16 is active according to the present invention;
Figure 4 Illustrates a schematic representation showing a downstream flow hydraulic control system during hydraulic fluid line 17 is active according to the present invention;
Figure 5 Illustrates a graph explaining relationship between hydraulic pump displacement and the pressure measured by downstream sensor according to the present invention;
Figure 6 Illustrates a graph explaining relationship between hydraulic fluid flow and the torque required according to the present invention; and
Figure 7 Illustrates a graph explaining relationship between engine rpm and the hydraulic pump displacement according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The matters defined in the description, such as the detailed construction and elements, are nothing but specific details provided to assist those of ordinary skill in the art in a comprehensive understanding of the invention, and thus the present invention is not limited to thereto.
A downstream flow type hydraulic control system for an earthmoving or construction machine to regulate and control a discharge flow of a variable displacement hydraulic pump according to an embodiment of the present invention will be described hereinunder with reference to FIGS. 1 to 6.
As shown in FIG. 1, a construction or earthmoving machine 10.
The construction or earthmoving machine 10 may be machine incorporating an improved hydraulic control system; however embodiments of present invention are not restricted to machine depicted in FIG.1. The concept and other embodiments of the present invention may be used in other types of machine and machine illustrated in FIG.1 is merely shown as example.
The construction or earthmoving machine 10 consisting of a main body 12, cab structure 14, actuating means 24, wheels 18, working element or working implement 22, arm or boom structure 20, and an engine 16.
The said cab structure 14 is mounted on said wheels 18. There may be multiple numbers of wheels mounted on single or multiple axles. The said wheels 18 are driven by said engine 16. The said working element or working implement 22 is attached to arm or boom structure 20 through pivot joint. The said actuating means 24 are working on hydraulic mechanism and there may be multiple actuating means located at multiple locations. The said actuating means 24 are critical part of machine and it may be used for performing various hydraulic operations through the construction or earthmoving machine 10. There may be multiple said working elements or working implement 22 attached to the construction or earthmoving machine 10.
As shown in FIG. 2, the downstream flow type hydraulic control system 100 for an earthmoving or construction machine to regulate and control a discharge flow of a variable displacement hydraulic pump according to the first embodiment of the present invention is provided, which includes a variable displacement hydraulic pump unit 2 (hereinafter referred as hydraulic pump) mounted on a hydraulic fluid reservoir 1, an electronic control unit 3 (hereinafter referred as ECU), a hydraulic pressure sensors 4 & 12 to measure upstream and downstream hydraulic fluid pressure across the hydraulic pressure line 15, multiple control valves 7 & 8, multiple relief valves 6 & 14, multiple hydraulic actuators 9 & 10, and check valves 5,11 & orifice 13, hydraulic fluid lines 15,16 17 & 18 etc.
The hydraulic pump unit 2 for pumping hydraulic fluid from hydraulic reservoir driven by either machine engine, external engine, battery, external or internal power source, combination of either mentioned sources or any other means (which is not shown in fig.). The said hydraulic pump unit 2 pumps hydraulic fluid from the hydraulic reservoir 1 and supply it to hydraulic fluid line 15 as shown in FIG. 2.
The hydraulic pump unit 2 is connected to ECU 3 whereby the operation and manipulation of the hydraulic pump unit 2 is controlled by ECU 3 depending upon input signals received through upstream and downstream pressure sensors 4 & 12 respectively. The upstream pressure sensor 4 measures the hydraulic pressure across the hydraulic fluid lines 15, 16 & 17 before the hydraulic fluid passes through the control valve 7 whereas the downstream pressure sensor 12 measures the hydraulic pressure across the hydraulic fluid lines 15 after the hydraulic fluid passes through control valve 8. One or more hydraulic actuator may be installed on the said hydraulic fluid lines 15, 16 & 17. The check valves 5, 11 & orifice 13 may be installed on the said pressure lines 15, 16, 17 & 18 before or after the control valves. The multiple relief valves 6 & 14 may be installed on the said pressure lines 15, 16, 17 & 18 as shown in FIG. 2
The construction and functioning of hydraulic pump unit 2 may be same or different depending upon the requirements. The hydraulic fluid lines deliver hydraulic fluid to main actuator/s to perform various functions such as digging, excavating, loading, hammering, compaction etc.
The upstream and downstream pressure sensors provide output singles in terms of pulse width modulation (hereinafter referred as PWM) to ECU 3 which further control the hydraulic pump unit 2 and according manipulate the discharge flow of hydraulic fluid.
Referring to FIG. 2, the control valves 7 & 8 are in neutral position and hydraulic fluid supplied through the hydraulic fluid line 15 may be called as neutral channel.
The hydraulic fluid is pumped from hydraulic fluid reservoir 1 by the hydraulic pump unit 2 and supplied to the said hydraulic fluid line 15. The flow direction and channel of hydraulic fluid is highlighted by dark dotted lines as shown in FIG. 2.
The upstream pressure sensor 4 is placed between hydraulic pump unit 2 and the control valve 7 and it is mounted on the hydraulic fluid line 15 to measure upstream pressure across the hydraulic fluid line 15. When control valves are in neutral position (as shown in FIG.2), whole hydraulic fluid passed to the hydraulic reservoir 1 via orifice 13 and/or the relief valve 14. The downstream pressure sensor 12 is placed after the control valve 8 and it is mounted on the hydraulic fluid line 15 to measure downstream pressure across the hydraulic fluid line 15.
In the neutral position, whole hydraulic fluid gets transferred to reservoir through neutral channel or hydraulic fluid line 15. During this case, large amount of hydraulic fluid passes through the orifice 13 and/or relief valve 14. The downstream pressure sensor 12 observes high pressure across the hydraulic fluid line 15 due to high resistance of hydraulic fluid passing through the orifice 13. In such case, the downstream pressure sensor 12 sends output signals to the said ECU 3 in voltage, further signal to pump given in terms of PWM signal which further manipulate or control the discharge rate of the hydraulic fluid. In this case ECU 3 actually reduces the displacements of the hydraulic pump 2 which turns reduce the hydraulic fluid discharge rate.
The downstream pressure sensor 12 sends output signals in terms of PWM and frequency of the signals may be pre-determined. Hence real time pressure detection across the hydraulic fluid line 15 and real time control of the discharge rate of the hydraulic fluid through the hydraulic pump may be performed.
As illustrated in FIG.3, the downstream flow type hydraulic control system 200 for an earthmoving or construction machine to regulate and control a discharge flow of a variable displacement hydraulic pump according to the first embodiment of the present invention is provided, the control valves 7 & 8 start switching when spool in the control valves move in anyone direction. The hydraulic fluid is pumped from hydraulic fluid reservoir 1 by the hydraulic pump unit 2 and supplied to the said hydraulic fluid line 16. The flow direction and channel of hydraulic fluid is highlighted by dark dotted lines as shown in FIG. 3.
The downstream pressure sensor 12 is mounted on the hydraulic fluid line 15 observe less pressure on the hydraulic fluid line 15 since spool in control valve switches which further partially and/or fully blocks the hydraulic fluid line 15 that results less flow to the orifice 13 and relief valve 14.
During this case, the hydraulic fluid lines deliver hydraulic fluid to main actuator/s to perform various functions such as digging, excavating, loading, hammering, compaction etc. In the FIG.3, the main actuator as hydraulic cylinder is in expanding position. The application of main actuator as hydraulic cylinder is merely shown as an example and application of actuator is not limited to thereto.
The downstream pressure sensor 12 measure such less pressure and sends output signals in terms of PWM to the said ECU 3. In this case ECU 3 actually increases the displacements of the hydraulic pump 2 which turns increase the hydraulic fluid discharge rate.
The output signals generated through upstream and downstream pressure sensors 4 & 12 transferred to the ECU 3. The output signal path is highlighted by thin dotted lines as shown in FIG. 3.
As illustrated in FIG.4, the downstream flow type hydraulic control system 300 for an earthmoving or construction machine to regulate and control a discharge flow of a variable displacement hydraulic pump according to the first embodiment of the present invention is provided, the control valves 7 & 8 start switching in opposite direction when spool in the control valves move in other direction. The hydraulic fluid is pumped from hydraulic fluid reservoir 1 by the hydraulic pump unit 2 and supplied to the said hydraulic fluid line 17. The flow direction and channel of hydraulic fluid is highlighted by dark dotted lines as shown in FIG. 4.
The downstream pressure sensor 12 is mounted on the hydraulic fluid line 15 observe less pressure on the hydraulic fluid line 15 since spool in control valve switches which further partially and/or fully blocks the hydraulic fluid line 15 that results less flow to the orifice 13 and relief valve 14.
During this case, the hydraulic fluid lines deliver hydraulic fluid to main actuator/s to perform various functions such as digging, excavating, loading, hammering, compaction etc. In the FIG.3, the main actuator as hydraulic cylinder is in retracting position. The application of main actuator as hydraulic cylinder is merely shown as an example and application of actuator is not limited to thereto.
The downstream pressure sensor 12 measure such less pressure across the hydraulic fluid line 15 and sends output signals in terms of PWM to the said ECU 3. In this case ECU 3 actually increases the displacements of the hydraulic pump 2 which turns to increase the hydraulic fluid discharge rate.
The upstream pressure sensor 4 installed in between hydraulic pump 2 and the control valve 7 on the hydraulic fluid line 15 to measure upstream hydraulic pressure across the hydraulic fluid line 15.
When any of the control valves 7 & 8 of the hydraulic system are switched due to partial or full movement of spool as shown in FIG. 3 & 4, the hydraulic fluid get supplied to the main actuator/s 9 & 10. The said upstream pressure sensor 4 measure pressure across the hydraulic fluid line 15 and sends output signals to ECU 2 in terms of PWM. If the power demand of hydraulic pump is more than the power supplied by the engine 2 then the displacement of hydraulic pump needs to be decreased to match with the hydraulic pump power to avoid stalling and/or abnormality observed in the hydraulic system. The displacement of the hydraulic pump 2 may be regulated based on the formula as below,
Power (kW) = Pressure (bar) x Displacement (cc) x RPM / 1000 x 600
So when, power of hydraulic pump is constant or pre-determined and hydraulic pressure measured by upstream pressure sensor 4 is increasing then to maintain constant load on the hydraulic pump, the displacement of the hydraulic pump needs to be decrease with respect to increase in hydraulic pressure measured by upstream pressure sensor 4.
The upstream pressure sensor 4 sends output signals in terms of PWM and frequency of the signals may be pre-determined. Hence real time pressure detection across the hydraulic fluid line 15 and real time control of the discharge rate of the hydraulic fluid through the hydraulic pump may be performed.
The output signals generated through upstream and downstream pressure sensors 4 & 12 transferred to the ECU 3. The output signal path is highlighted by thin dotted lines as shown in FIGS. 2, 3 & 4.
The continuous dark lines in all FIGS.2, 3 & 4 represent that those lines are filled with hydraulic fluid and there is no movement of hydraulic fluid across the lines.
The relief valves 6 & 14 are fixed in the system to protect the system from the excess pressure and thermal expansion. The hydraulic pressure across the hydraulic pressure line 15 get increased due to excessive pressure then the relief valve 14 get opened and hydraulic fluid delivered to reservoir 1 via relief valve 14. The second relief valve 6 is installed on the hydraulic fluid line 18 which protect the hydraulic pump and hydraulic system from excessive pressure. Whenever hydraulic system observe any abnormality due to the hydraulic pump and/or actuator stalling or overloading then to protect the hydraulic system, the relief valve 6 get opened and hydraulic fluid delivered to reservoir 1 via relief valve 6.
As illustrated in FIG.5, the graphical representations of relation between the hydraulic pump displacement and the pressure measured by downstream sensor 12. When pressure across the pressure line 15 get heightened the downstream pressure sensor 12 sends output signals to ECU 3 which further reduce the hydraulic pump displacement as shown in graph (FIG.5). Whereas when downstream pressure sensor 12 observe less hydraulic pressure across the hydraulic fluid line 15, the downstream pressure sensor 12 sends signals to ECU 3 which further increase the hydraulic pump displacement as shown in the graph (FIG.5). Basically there is inverse relationship between the hydraulic pressure observed by downstream pressure sensor 12 and hydraulic pump displacement.
As illustrated in FIG.6, the graphical representation of hydraulic fluid flow based on the hydraulic pump displacement and the torque required to meet the power demand required by the actuator/s. When system pressure starts increasing at max flow of pump, then due to limit in power, the displacement of pump decreased to decrease torque load required by pump and to prevent engine from going to stall condition.
As illustrated in FIG.7, the graphical representation of relationship between engine rpm and the hydraulic pump displacement is shown. The least stroke of pump is adjusted in such a way that pump always gives a certain pre-determined amount of hydraulic flow through neutral channel and this hydraulic flow is independent of engine speed. For maintaining the pre-determined certain amount of hydraulic flow, an inverse proportional logic given to ECU which has a relation between engine speed and displacement of pump. If this logic is not present then due to change in engine speed flow increase or decrease which will effect downstream flow characteristics curve and then there is need multiple curves for different neutral channel flow
This kind of hydraulic schematic gives significant energy saving in the system without affecting much on the performance. The energy saved by using above explained system can be used in other hydraulic power requirements. If saved energy is not used in other hydraulic power requirement then also it may help in reducing the energy load on the hydraulic pump.

Claims:

1. A downstream flow hydraulic control system to control discharge flow of a variable displacement pump in an earthmoving or construction equipment comprising:
? at least one hydraulic fluid reservoir through which hydraulic fluid may be circulated to a hydraulic fluid line;
? at least one hydraulic fluid line to circulate the hydraulic fluid;
? at least one variable displacement pump for pumping the hydraulic fluid from the hydraulic reservoir and supply it to the hydraulic fluid line ;
? at least one hydraulic fluid pressure relief valve and control valve for controlling fluid circulation across the hydraulic fluid line;
? at least one upstream hydraulic fluid pressure sensing unit mounted on hydraulic fluid line and placed between the variable displacement pump and the control valve;
? at least one downstream hydraulic fluid pressure sensing unit mounted on hydraulic fluid line and placed after the control valve;
? at least one orifice unit and at least one check valve mounted on the hydraulic fluid line; and
? at least one electronic control unit for processing input data received through said the hydraulic fluid sensing unit and for control functioning of the variable displacement pump.
2. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the variable displacement pump for pumping hydraulic fluid from the hydraulic reservoir driven by either machine engine, external engine, battery, external or internal power source, combination of thereof or any other means.
3. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the upstream and downstream hydraulic pressure sensing unit measure hydraulic fluid pressure across the hydraulic fluid line and further output signals send to electronic control unit.
4. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the electronic control unit process the signals received through the upstream or downstream hydraulic fluid pressure sensing unit or both and give further control signals to the variable displacement pump to regulate the discharge rate of the hydraulic fluid.
5. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the upstream and downstream hydraulic pressure sensing unit provide signals mechanically, electronically, hydraulically or by any other means in terms of pulse width modulation or continuous signals.
6. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the downstream hydraulic fluid pressure sensing unit observe equal or high pressure than the pre-determined pressure value then the electronic control unit provide signals to the variable displacement pump to reduce displacement of the variable displacement pump to reduce the discharge rate of the hydraulic fluid.
7. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the downstream hydraulic fluid pressure sensing unit observe equal or less pressure than the pre-determined pressure value then the electronic control unit provide signals to the variable displacement pump to increase displacement of the variable displacement pump to increase the discharge rate of the hydraulic fluid.
8. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the control valves are controlled either mechanically, hydraulically , electrically or combination of thereof.
9. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the upstream hydraulic fluid pressure sensing unit observe equal or high pressure than the pre-determined pressure value then the electronic control unit provide signals to the variable displacement pump to reduce displacement of the variable displacement pump to reduce the discharge rate of the hydraulic fluid.
10. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the upstream hydraulic fluid pressure sensing unit detect stalling or functional abnormality or both of hydraulically controlled operation due to overloading.
11. The downstream flow hydraulic control system to control discharge flow of a variable displacement pump claimed in claim 1, wherein the said ECU working in neural position on a logic which allow the constant hydraulic fluid flow irrespective of the engine speed.