Electronic load sense control with electronic variable load sense relief, variable working margin, and electronic torque limiting

Abstract

An electrical pressure control load sense system having a pump connected inline to an operator control spool valve and a compensation circuit. The system also has a plurality of sensors, at least one pressure transducer, a micro-processor, a fixed orifice, a proportional pressure relief valve, and a swashplate angle sensor.

Claims

1. An electronic load sense control system, comprising; a pump connected in line to an operator control spool valve, a pressure compensation spool valve, and a load sense spool valve; a first sensor connected between the pump and the operator control spool valve for measuring pump outlet pressure; a second sensor connected between an actuator and the operator control spool valve for measuring pressure at load; a load sense port of the pump is routed through a fixed orifice to a proportional pressure relief valve; and a micro-processor connected to the first sensor, the second sensor and the proportional pressure relief valve.

2. The system of claim 1 wherein the micro-processor is configured to turn a sensed load pressure into a corresponding current sent to the proportional pressure relief valve, which is configured to relieve pressure so that pressure between the fixed orifice and the proportional pressure relief valve are equal to the sensed load pressure.

3. The system of claim 2 wherein the current is adjusted based upon temperature sensed at the proportional pressure relief valve.

4. The system of claim 1 wherein the micro-processor includes software logic is configured to calculate an offset of a resolved load sense pressure to create a variable working margin.

5. The system of claim 4 wherein the software logic adds to the resolved load sense pressure.

6. The system of claim 4 wherein the software logic subtracts from the resolved load sense pressure.

7. The system of claim 1 further comprising a first and a second pressure transducer.

8. The system of claim 1 further comprising a swashplate angle sensor.

9. The system of claim 8 wherein the micro-processor is configured to calculate input torque based upon sensed pressure at pump outlet and displacement required to maintain load sense drop at the fixed orifice.

10. The system of claim 8 wherein the micro-processor is configured to calculate maximum pressure between the fixed orifice and the proportional pressure relief valve based upon constant monitoring of the swashplate angle.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic view of a prior art pressure control load sense system;

(2) FIG. 2 is a schematic view of a pressure control load sense system;

(3) FIG. 3 is a schematic view of a pressure control load sense system;

(4) FIG. 4 is a schematic view of a pressure control load sense system;

(5) FIG. 5 is a schematic view of a pressure control load sense system;

(6) FIG. 6 is a chart showing pressure compared to resolved load sense pressure;

(7) FIG. 7 is a schematic view of a pressure control load sense system;

(8) FIG. 8 is a chart showing pump displacement compared to torque required; and

(9) FIG. 9 is a chart showing pump displacement compared to torque required.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(10) FIG. 1 shows a traditional pressure control load sense system (PCLS) 10. By way of example only, the system 10 includes a pump 12 connected inline to a pressure compensation spool valve 14, a load sense spool valve 18. The pump 12 is of any type and preferably is a variable displacement pump. The pump provides pressurized fluid to the operator control spool valve 18 through flow line 13 associated with flow line 13 between pump 12 and valve 18 is a sensor (PA) for measuring pump outlet pressure.

(11) From valve 18, fluid flows to cylinder or actuator 15 and pressure compensator spool valve 14 via flow line 17. Associated with flow line 17, between cylinder 15 and valve 14, is a sensor (PB) for measuring pressure at load. Fluid then flows from valves 14 and 16, depending on operating conditions, to a torque control valve 19 via flow lines 21 and 23. The torque control valve 19 controls displacement of swashplate 25.

(12) When the pump outlet pressure (PA) exceeds the valve 14, fluid is routed by valve 14 via flow line 21 to destroke valve 25 and pump 12. For example, as shown in FIG. 1, valve 14 has a spring setting of 250 bar. When pump outlet pressure (PA) exceeds 250 bar, pressure compensator spool valve 14 is activated allowing fluid to flow to valve 25 and destroke the pump 12 until pump outlet pressure (PA) is equal to or lower than 250 bar.

(13) The load sense spool 16 compares pump outlet pressure (PA) to pressure at the load pressure (PB) which is sensed after the operator control spool 18. The load sense spool 16 uses a spring to keep a constant difference between the pump outlet pressure (PA) and pressure at load (PB). The spring setting is added to pressure at load (PB) and the sum is kept equal to the pump outlet pressure (PA) by varying pump displacement. Hence, pump displacement varies to keep a constant pressure drop across the operator control spool 18. As an example only where the load pressure (PB) is equal to 200 bar, and the load sense spool spring setting is 20 bar, the load sense spool 16 ports oil to stroke the pump until the pump outlet pressure (PA) is 20 bar higher than the pressure at load (PB) so that (PA) is equal to 220 bar.

(14) In this basic electronic load sense system 10 the resolved (highest) load pressure in the system 10 is measured and the resolved pressure is replicated at the load sense port of the pump 12. The maximum pump pressure is controlled by the pressure compensating spool 14 in the control, and the pump margin is controlled by the load sensing spool 16 spring setting. Both spools 14 and 16 remain in control of pump displacement through a traditional method of porting oil to a servo piston based on a pressure balance and spring setting.

(15) To add benefits to this system, as shown in FIG. 2, a pressure transducer 20, a proportional pressure relief valve 22, a fixed orifice 24, and an angle sensor 26 are added. The proportional pressure relief valve 22 is added to the control of the pump 12 while the load sense port of the pump 12 is routed through the orifice 24 instead of routing to the resolved load sense pressure port in the valve 22, which is usually located at load pressure (PB), directly to the pump outlet either outside the pump 12, at the pump outlet pressure (PA) or internally in the control spool of the pump 12. The pressure at load (PB) is communicated to a micro-processor 28 that turns the load pressure (PB) into a corresponding current which is sent to the proportional pressure relief valve 22. The proportional pressure relief valve 22 then relieves the pressure so that pressure PC in flow line 27 is equal to the load pressure (PB). The pump margin pressure as set by the load sense spool 16 in the pump control is satisfied across the fixed orifice (margin orifice) 24. The micro-processor 28 constantly makes current adjustments so that pressure PC is always equal to load pressure (PB). Simultaneously, the margin setting is concurrently satisfied across the margin orifice 24 and the operator control spool 18. Additionally, by measuring temperature at the proportional pressure relief valve 22 and adjusting current in relation to pressure a more consistent performance over a broad temperature range is maintained.

(16) The pressure in the system is created by the resistance of the load with the flow provided by the pump 12. As an example only, and shown in FIG. 3, the load pressure (PB) is 200 bar, which is replicated by the micro-processor 28 and proportional pressure relief valve 22 so that the pressure at PC is also equal to 200 bar. The 20 bar spring setting in the load sense spool 16 strokes the pump 12 to maintain the pump outlet pressure (PA) at 20 bar higher pressure so that pump outlet pressure (PA) is equal to 220 bar. If the load encounters a different pressure, the different pressure is communicated to the micro-processor 28, which adjusts the pressure at PC, and the pump displacement adjusts to maintain the load sense spool 16 setting. When an operator changes the operator control spool 18, pressure at the load (PB) changes, and the system adjusts as it would with a normal PCLS (Power Control Load System) system.

(17) As shown, the electronic load sense system 10 replicates the pressure in the load sense port of the pump 12 that is seen at the resolved load sense port, and normally communicated to by a hydraulic load sense line. By replicating the pressure in the load sense port, the margin across the operator control spool 18 is equal to the margin across the margin orifice 24 which is the same as the margin spring setting in the pump 12.

(18) Utilizing software logic 30 an electronically variable working margin can be realized by a slight change or offset of the resolved load sense pressure instead of replicating the resolved load sense pressure. As an example only, and shown in FIG. 4, the load pressure (PB) is 200 bar. Instead of replicating pressure in PC to be exactly equal to the 200 bar load, the software logic 30 adds 5 bar to the setting so that the pressure in PC is now equal to 205 bar. The load sense spool 16 will maintain a 20 bar margin between the pressure at pump outlet (PA) and PC, such that the pump 12 will be stroked until the outlet pressure is equal to 225 bar. The load sense spool 16 maintains a spring setting of 20 bar at the margin orifice 24 ((PA)-PC), while the real working margin across the operator control spool 18 is 25 (PA)-(PB). As a result, an operator will experience more flow through the valve at a given flow command and experience additional flow above what was originally available when the spool is at maximum displacement.

(19) In another example, as shown in FIG. 5, the pressure at load (PB) is at 200 bar. The software logic 30 subtracts 5 bar from the setting so that pressure in PC is equal to 195 bar. Here, the load sense spool 16 will maintain a 20 bar margin between pressure at pump outlet (PA) and PC such that the pump will be stroked until the outlet pressure is equal to 215 bar. The margin across the operator control spool 18 is now 15 bar (PA)-(PB) compared to the margin across margin orifice 24 which is 20 bar ((PA)-PC). For any spool setting that is decreased, an operator will experience less flow through the valve for a given flow command. This mode of operation saves energy due to the reduced pressure drop across the operator control spool 18. Proportionally, more of the pump outlet pressure (PA) is available to do work by lifting the 200 bar load with 215 bar of pump outlet pressure (PA) versus a pump outlet pressure of 220 bar as previously required.

(20) To have an operating envelope larger than a traditional system, one need only take advantage of both high and low margin settings or rely on margin settings that continuously vary between high and low. With low operator spool commands, a lower working margin could be maintained which would save energy. As the operator control spool demand increases, the working margin pressure would increase, offering more flow for a given spool setting. In one embodiment, this is done automatically with software algorithms or with operator interactive controls.

(21) To increase the stability of the system, and improve overall system performance, some level of flow dependency is placed on the pressure of the working function to dampen the system. This improves upon the state of the art where PCLS system controls are very rigid against changes in load systems, which can be the prime driver of system instabilities.

(22) To accomplish this, the micro-processor 28 slightly modifies the pressure that is replicated at PC in relation to what is being measured at (PB) as shown by example in FIG. 6. As resolved load sense pressure is increased, the margin across the operator control spool 18 is reduced such that PC would be lowered in relation to (PB) as the absolute value of (PB) increased. Thus, for a given constant operator command, as the load pressure (PB) increased the effective working margin at the operator control orifice would decrease leading to a decrease in flow for a given function. The slight reduction in flow would act as a dampening function for the system 10. For the reduction in flow to not interfere with machine productivity or cause a negative perception by machine operators, the system would need to be tuned.

(23) Where slight variation occurs between pressure measured at (PB) and pressure generated at PC due to changes in temperature, a second pressure transducer 32 is used near the margin orifice 24 associated with flow line 27 as shown by example in FIG. 7. By measuring the pressure at PC, a closed loop algorithm is used to ensure that the pressure relationship required by the control algorithm is accurately reproduced.

(24) Often, with load sensing open circuit systems, the torque requested to be supplied by the engine exceeds the engine's capabilities. When this happens, the operator reduces his command which slows the machine and makes the machine difficult to operate efficiently, or the engine simply stalls requiring restarting of the machine. Also, when high flows and pressures are commanded of the pump 12, the torque requirement placed on the prime mover exceeds capabilities resulting in a stalled engine. To avoid these situations an electronic variable torque control is used such that output pressure of the pump 12 is equal to the required pressure to lift the load plus the drop across the operator control spool 18.

(25) To accomplish this, first the input torque to the pump 12 that must be supplied by the engine is calculated by the micro-computer 28 by taking the product of the output pressure (PA) of the pump 12 and the displacement required to maintain the LS pressure drop across the orifice 24. A sample of the calculation is shown below:

(26) Pump Torque=200 bar×45 cc/rev/62.8×100=143.31 Nm where the pressure required to lift a load is equal to 180 bar and the resultant output pressure (PB) of the pump 12 is equal to 200 bar. When resistance to the circuit is encountered that raises the force on a cylinder 15 the resultant pressure in the circuit will increase. With no change in the valve command, the pump 12 will attempt to maintain the same output flow at the higher pressure. For example, where load pressure required is equal to 300 bar and output pressure at the pump is 320 bar:
Pump Torque=320 bar×45 cc/rev/62.8×100%=229.30 Nm
If the engine on the machine is only capable of 150 Nm of output torque, this new load and sustained flow command would overwhelm the engine and result in a stalled condition if the operator continued the command. Using the electronic torque control the system can control the stroke of the pump 12 by regulating the LS pressure PC in the control while maintaining a torque level at or below the maximum torque that the engine can provide keeping the engine from stalling.

(27) As shown in FIG. 8, based on the previous example, there is a large area in which the pump 12 is capable of operating that would result in an engine stall condition. Line 34 shows the maximum torque level that the engine is capable of delivering to the pump. Line 36 shows the constant maximum pressure limit usually employed with a traditional load sense system. During operation, the software 30 is continually monitoring the angle of the swash plate using the swashplate angle sensor 26 in the pump 12. Swash plate angle is used to calculate a maximum pressure that would result in a torque level that the engine could produce at a given displacement and the correct current is sent to the proportional pressure reliving valve 22 in the pump control to achieve the maximum pressure at PC. Using control logic 30, electronic torque limiting is able to prevent operation in area 38 that results in engine stall, and instead allows the hydraulic system to always deliver maximum possible pressure for a given displacement without engine stalling.

(28) The system also provides an electronic load sense relief. Since the proportional pressure relief valve 22 is limiting the pressure seen by the pump control, it can also take the place of other load sense relief valves in the system. Even if load pressure (PB) spikes to an undesirable level, the micro-controller 28 can maintain the pressure relief setting being sent to the relief valve to a limited pressure and the pump 12 will de-stroke until the pump outlet pressure (PA) reaches a desirable level.

(29) Thus an electronic sense control has been disclosed that at the very least meets all the stated objectives.