JP7051294B2 - Electronic torque and pressure control for load sensing pumps - Google Patents

Description

Cross-reference to related applications This application claims priority to US Provisional Patent Application No. 61 / 884,318, filed September 30, 2013.

An object of the present invention is control for a load detection pump. The use of mechanical torque control is known in the art. In known systems, the swash plate angle is mechanically connected to a relief valve whose relief set point changes with the swash plate angle. One problem with the system is that the torque setting points cannot be changed quickly to cope with, for example, a secondary load on the engine or a decrease in torque at low engine speeds. Another problem with known systems is that the maximum pressure setting point cannot be changed on the fly.

For example, FIG. 1 shows a conventional load detection system. Conventional load detection circuits use variable displacement open circuit pumps with integrated controls to maintain a given pressure drop across variable openings in the system using feedback pressure. The given pressure drop is specified by setting the control unit of the pump and is set to 20 bar in the example of FIG. The pump attempts to maintain a 20 bar pressure drop across the variable opening to provide the required flow rate to maximum capacity. The pressure drop of 20 bar is called a load detection limit pressure (LS pressure).

The output pressure of the pump is equal to the pressure required to lift the load plus a drop at both ends of the variable opening. If the pressure required to lift a load is equal to 180 bar, the resulting pump output pressure will be equal to 200 bar in this example.

The input torque to the pump to be provided by the engine is calculated by calculating the product of the output pressure of the pump and the capacity required to maintain the LS pressure drop at both ends of the opening. A sample of the calculation is shown in Example 1 below.

As either the pressure or capacity (flow rate) of the pump increases, the required input torque increases as a result. Often, when high flow rates and pressures are required for the pump, the torque requirements on the prime mover exceed capacity, resulting in engine stall. In addition to stalls in which the input torque to the pump exceeds the torque output capacity of the operating engine, it results in operator frustration and / or poor performance. Systems with dual setting points are known, but are extremely complex and expensive. Therefore, there is a need for a system that overcomes these shortcomings in the field.

An object of the present invention is to provide a control function of a load detection pump capable of rapidly changing a torque setting.

Another object of the present invention is to provide a control function of a load detection pump that can change the maximum pressure setting point on the fly.

A further object of the present invention is to provide a control function of a load detection pump that reduces the possibility of engine stall.

The above and other purposes will be apparent to those skilled in the art by means of the following description, drawings, and claims.

The electric torque and pressure control unit for the load detection pump includes a pump with a swash plate angle sensor. The pump is in-line connected to a pressure compensating load detection controller with electrically variable pressure relief valves and openings. An engine speed sensor and a microcontroller are connected to the circuit. The microcontroller has software that controls the pressure relief setting of the electrically variable pressure relief valve in the pressure detection control unit based on the signals from the swash plate sensor and the engine speed sensor.

It is a schematic diagram of the load detection system of the prior art. It is a schematic diagram of an electronic torque / pressure control circuit. The streamline 20 includes a flow path from the tank 16 to the pressure limit compensation valve 26 and the load detection compensation valve 28 via the control valve 18, the pressure relief valve 22, and the flow path from the tank 16 to the cylinder 19. The streamline 24 is a flow path from the pressure relief valve 22 to the pressure limit compensation valve 26. The pump discharge line 30 is a flow path whose one end is connected to the pressure limit compensation valve 26 and the load detection compensation valve 28 and the other end is connected to the torque control valve (pump control unit or cylinder) 32. It is the figure which compared the pump capacity with the maximum torque pressure. The wire 100 is the maximum pressure ( without ETL), the wire 101 is the usable engine torque, and the wire 102 is the required torque (without ETL). It is the figure which compared the pump capacity with the current to a valve. Line 104 is the maximum system pressure ( ETL effective) and 105 is the current to the valve. It is the figure which compared the pump capacity with the pressure. The wire 106 is the required torque (ETL valid), the wire 107 is the maximum system pressure (ETL valid), and the wire 108 is the usable engine torque. It is the figure which compared the pump capacity with the system capacity. Line 109 is the maximum system pressure . It is a schematic diagram of an electronic torque / pressure control circuit. It is a schematic diagram of the torque control circuit which has a load holding valve. It is a schematic diagram of the torque control circuit which has a pressure compensation pump. It is a figure which shows the allocation of the margin in torque control by comparing capacity with pressure. The line 110 is a Pctrl line, the line 111 is a PLS line, and the line 112 is a Ppump line. It is a figure which shows the allocation of the margin in torque control by comparing capacity with pressure.

With reference to the drawings, an example of a pump control system 10 includes a motor 12 configured to drive a pump 14. In one embodiment, the motor 12 is a gearbox transmission from engine power takeoff and the pump 14 is a variable shaft piston pump. The pump 14 discharges and pressurizes the fluid from the tank 16 to the control valve 18 and the cylinder 19 at the system pressure through the streamline 20.

A pressure relief valve 22 is connected to the streamline 20 downstream of the control valve 18. A pressure limiting compensating valve 28 is also connected to the streamline 20 by a streamline 24, and is connected to the pressure limiting compensating valve 26 to supply air. The load detection compensation valve 28 is also connected to the streamline 20, and the pump discharge line 30 is connected to the swash plate 34 of the pump 14 and is connected to the torque control valve 32 that controls the capacity thereof. A swash plate angle sensor 36 is connected to the swash plate 34, and an engine speed sensor 38 is connected to the motor 12. Both the angle 36 and velocity 38 sensors are connected to a computer 40 with software 42. The computer 40 is connected to and controls the pressure relief valve 22.

During operation, the swash plate sensor 36 provides information about the angle of the swash plate 34 if it increases the force exerted on the cylinder 19 in the circuit and thus receives a resistance that creates pressure in the circuit of the pump 14. To the computer 40. Software 42 calculates the maximum pressure that results in the torque level that the engine can produce at a given capacity. The computer then sends a signal to the pressure relief valve 22 to pass an accurate current through the pressure relief valve 22 to achieve maximum pressure. The pressure relief valve 22 is adjusted to release the LS pressure.

The high pressure on the pump side of the torque control valve 32 destrokes the pump 14. As the pump destrokes, software 42 increases the LS pressure by relaxing the current command to the pressure relief valve 22. The pump 14 continues to destroke and the LS pressure continues to increase based on the swashplate 34 angle until the desired difference is reached between the pump output and the LS pressure. This allows the system 10 to apply maximum pressure to a given capacity without causing an engine stall.

Basic ETL circuit operation As an example, in a load detection open circuit system, the torque required for the engine often exceeds the capacity of the engine. If this happens, the operator is required to relax his command, which may slow down the machine and make it difficult to operate efficiently. Alternatively, the engine simply stalls and the operator needs to restart the machine.

Start with the calculation of the engine torque in Example 1.

It is assumed that the operator of the machine is commanding the operation and has received some resistance to the circuit that increases the force exerted on the cylinder and as a result raises the pressure in the circuit to 300 bar (320 bar in the pump). .. If there is no change in command to the valve, the pump will try to maintain the same output flow at the new higher pressure. The resulting new torque requirement for the engine is shown in Example 2.

If the engine mounted on the machine produces only 150 Nm of output torque, the engine will not be able to respond to the new load and maintained flow command described above, resulting in a stall if the operator continues to command. You will fall into a state. The system 10 uses the basic ETL to adjust the LS pressure in the pressure relief valve 22 to keep the torque level below the maximum torque that the engine can generate to prevent the engine from stalling. Stroke can be controlled.

As shown in FIG. 3, as an example, there is a large area in which the pump 14 can operate, and as a result, an engine stall state may occur. Line 101 indicates the maximum torque level that the engine can transmit to pump 12. Line 100 indicates a steady maximum pressure limit commonly used by conventional load detection systems.

During the operation of the machine, software 42 continuously monitors the swash plate angle of the pump 14. The software 42 uses the swash plate angle to calculate the maximum pressure resulting from the torque level that the engine can generate at a given capacity and to the proportional pressure relief valve 22 in the pump control to achieve that maximum pressure. Send accurate current. As shown in FIG. 4, as the swash plate angle increases, the current to the pressure relief valve 22 increases (while lowering its own setting), limiting the amount of torque that the pump 14 can absorb.

Using this control logic, the hydraulic system 10 can instead cause engine stall at a given capacity, excluding region 103 of FIG. 3, where electronic torque limitation results in engine stall. The maximum pressure can be applied at all times.

To refer to this example again, since ETL is valid this time,
1) The operator commands the same flow rate and capacity as in the first example, ie 45 cc and 200 bar.
2) The machine is loaded to raise the system pressure to 320 bar.
3) The ETL is always in effect and the pump 14 quickly destrokes to an angle where the load can be increased without stalling the engine.

ETL operation from a mechanical point of view 1) The operator commands the same flow rate and capacity as in the first example, ie 45 cc and 200 bar.
2) The machine receives a load that raises the load pressure to 300 bar (320 bar received by the pump).
3) The operator maintains the same command. A load pressure of 300 bar is electronically transmitted down the LS line 20 to the proportional pressure relief valve 22. A pressure of 320 bar is transmitted to the pump 14 and the pump control unit 32 through the variable opening.
4) The LS pressure is released by the microcontroller 40 with a setting calculated based on the angle of the swash plate 34. As a result, the pressure applied to the LS side of the pump control unit 32 is reduced.
5) The high pressure applied to the pump side of the pump control unit 32 switches the control unit so as to send oil to the servo piston while destroke the pump 14.
6) As the pump 14 destrokes, the software 42 can relax the current command to the LS variable relief valve 22 to increase the LS pressure on the pump control unit 32.
7) The pump 14 continues to destroke and the LS pressure continues to increase based on the swash plate angle until the difference between the pump output and the LS pressure reaches 20 bar delta.

Torque Control with Load-Retaining Valves Systems that include a traditional mechanical torque control with multiple functions and a load-retaining or load-reducing check valve have pump outlet pressures below the pressure at which the "returned" load can be lifted. If the function is restricted and the function is effective, there is a risk of falling into an immovable situation. Electronic torque controls can be used with electronically controlled valves, pressure transducers, and software solutions to alleviate this problem.

In FIG. 8, for example, the valve 22 for function 1 opens, requiring a pressure of 150 bar and a flow rate exceeding the current torque limit setting of the ETL software 42 to lift the load. In this scenario, the ETL will adjust the capacity of the pump 14. If the function 2 valve 22 opens, it requires 250 bar of pressure to lift the load, so the check valve 50 continues to maintain the load and the ETL needs to function properly and lift the load. Pressure will not be returned to the pump control unit 32. To solve this problem, a pressure transducer (pressure switch or shuttle valve) 52 is added to monitor the pressure required to raise function 2 when commanded by the operator. If a command has been issued for function 2 but the load cannot be lifted at the current torque setting point of pump 14, software 42 will pump capacity to the point where the pressure is high enough to lift the load on function 2. Withdraw the command of function 1 (or other functions) until is reduced. In considering this feature, the ETL software 42 continuously monitors the swash plate angle and increases the pressure limit of the pump 14 as the pump capacity decreases to maintain the torque level acceptable to the engine. I want to be recalled.

Torque Control for Pressure Compensation Pumps In backhoe systems, it is common to use a pressure compensation pump with a torque limiting pump control and a manually operated open center stacking valve. All of the above advantages in load sensing circuits still apply to pressure compensation systems. Also, as shown in FIG. 9, it is common to have a special dump valve 54 that lowers the set point of the PC pump 14 while the engine is cranking (mainly under cold conditions). The problem is that when the oil is cold, it requires fairly strong pressure to push the oil through the open center valve. The torque limiting system can reduce the load on the engine starter by lowering the pressure setting point of the PC during crank operation to reduce outlet pressure and capacity, without any additional components.

Margin reduction at the torque control unit and both ends of the valve In a set of proportional valves, especially multiple compensating valves, the valve design is usually designed so that the valve operates properly and the load sensing pressure is properly transmitted to the pump 14. Requires a minimum pressure drop (or margin) at both ends of the valve. As described above, the torque control unit functions by shifting the margins at both ends of the valve to the openings arranged in the pump control unit 32. As the torque control unit further reduces the torque, the margins at both ends of the valve 22 may drop to a level at which the valve does not function properly. This is particularly noticeable when the level of torque reduction is extremely high and the engine speed RPM is low.

FIG. 10 shows the pump outlet pressure (Pump), the actual load pressure (PLS) which is the pressure actually applied to the load, and the load detection control unit of the pump 14 (Pctrl) arranged after the relief valve 22 and the opening. The outline of the pressure is shown.

The starting condition indicated by the X at the tip of the arrow requires a capacity of 147 cc to maintain the margin at both ends of the valve 22 and a pressure of 75 bar to lift the load. Under the conditions, the position is not under the influence of the torque control unit, and the entire margin is filled by the reduction at both ends of the proportional control valve 22. If the command to the valve does not change as the load pressure increases, the valve initially moves upwards until the PLS line turns to the left. This is the position where the torque control unit is activated and the pressure in the control unit starts to be released. As the pressure continues to increase (along the PLS line), the pump 14 continues to destroke, reducing the flow rate through the control valve 22. As described above, since the valve 22 still receives the same command, the decrease in flow rate alleviates the pressure drop at both ends of the valve 22. Since the total pressure drop between the pump outlet (Pump) and (Pctrl) is still satisfied by the increasing pressure drop at both ends of the opening of the LS control unit 32, the pump 14 strokes. It meets the necessary margin to prevent it from entering. It can be seen that as the pressure continues to rise, the pressure drop that satisfies the margin requirement of the pump 14 moves away from the control valve 22 and continues to approach the opening of the LS control unit 32 of the pump 12. The position where the pressure drop reaches the vertical line is the position where the margins at both ends of the control valve 22 drop to a position where the valve no longer functions properly. At that position, the performance of the machine begins to be impaired, and further reductions in pump angle can result in further deterioration of valve performance.

To solve this problem, a method of controlling the total valve flow rate requirement has been used. The algorithm used is to limit the valve opening so that the torque limiter is not affected by reduced margins, while avoiding unnecessarily limiting the valve output when the torque limiter is not actively tuned. Is. By using an electronically controlled valve in conjunction with the pump angle sensor 36 and the microcontroller 40, the movement of the margin from the control valve 22 to the opening is manipulated and the pump 14 to meet load and output torque requirements accordingly. Can be further destroked.

With reference to FIG. 10 again, the vertical lines of the graph representing the minimum margin requirement for proper control valve function (assumed to be 7 bar in this example) can be examined in more detail. This means that the difference between the intermediate curve (PLS) and the upper curve (Ppup) at the intersection of the vertical lines is 7 bar. If the load pressure continues under the stable valve command in this example, the pump 14 will continue to be destroked to the left of the line as standard torque control and the control valve performance will begin to deteriorate. The generation of these performance lines is based on the initial conditions of the valve 22, load, and pump 14. When changing the opening (flow rate requirement) of the control valve 22, the properties of these curves can be changed to allow the pump 14 to make further destrokes without further margin reduction.

Continuing to refer to this example, if the requirement from the pump 14 is reduced from the maximum value of 147 cc to 115 cc, the characteristics of the PLS curve are reshaped and then the above-mentioned margin movement changes. This slightly tightened valve opening increases the relative margins at both ends of the valve, allowing further pump destrokes to meet the increased load requirements. As seen in FIG. 11, reducing the valve requirement in this example from 147 cc to 115 cc allows the total system pressure to be reached before margin reduction at both ends of the valve becomes a problem.

Claims (3)

A motor or engine (12) configured to drive the pump (14), and
A pressure relief valve (22) that communicates fluid with the output side of the pump (14) and the tank (16) connected to the pump (14) .
A pump control unit or cylinder (32) connected to the swash plate (34) of the pump (14) and communicating with the pressure relief valve (22) in fluid communication.
The swash plate angle sensor (36) connected to the swash plate (34) and
The computer (40) and the pressure relief valve (22), which are connected to the swash plate angle sensor (36) and control the pressure relief setting of the pressure relief valve (22), press the pressure at both ends of the pressure relief valve. It includes a torque control unit that adjusts the angle of the swash plate (34) to reduce the capacity of the pump (14) so that the pressure drop does not drop to a level where the drop does not function properly.
As the system pressure applied to the pressure relief valve (22) from the pump (14) increases according to the load, the torque control unit reduces the angle of the swash plate (34) to the capacity of the pump (14). Change to
The current that the computer (40) flows through the pressure relief valve (22) as the pressure relief setting in order to achieve the maximum system pressure at a given capacity of the pump (14) by the swash plate (34). To increase the flow rate through the pressure relief valve (22) to increase the pump side pressure of the pump control unit or the cylinder (32), and the torque control unit of the swash plate (34). The angle is changed to reduce the capacity of the pump (14) so that the system can operate even if the capacity of the motor or engine (12) is insufficient .
The computer (40) calculates the torque that the motor or engine (12) can generate and the required torque for the motor or engine (12) at a given pump capacity of the pump (14). When the required torque exceeds the generateable torque, the torque control unit controls the pressure relief setting of the pressure relief valve (22) to operate the system below the generateable torque. A pump control system that changes the angle of the swash plate (34) so as to reduce the capacity of the pump (14). A first load for the first function and a second load for the second function are connected to the system so that they can be applied to the pump (14), and further, the first and second loads. The system of claim 1, further comprising a pressure switch or shuttle valve (52) that switches between the first load and the second load between the load and the system. To reduce the capacity of the pump (14) during crank operation under cold conditions for starting the motor or engine (12), which is connected to the system so that a load can be applied to the pump (14). The system according to claim 1, wherein a dump valve (54) for reducing a load applied to the pump (14) is further provided between the system and the load.

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