JPH04203502A - Automatic engine speed regulator in load sensing system - Google Patents

Abstract

PURPOSE:To make an engine speed certainly return to a normal condition by comparing a detection pressure of a feedback signal circuit in a load sensing system with a neutral pressure in a neutral state of all operating levers so as to switch a pump driving engine to a low speed. CONSTITUTION:A main relief valve 5 and an unload valve 6 are provided in a discharge circuit 3 of a variable capacity pump 1. Direction switching valves 11-17 are operated by hydraulic pressure of operating levers 14a, 15a and operating pressure oil supplying/discharging ports a1-a7, b1-b7, thus driving actuators 21-27. The maximum load pressures of the actuators 21-27 adjacent to each other are selected by shuttle valves 42-46. A detection pressure signal of a feedback signal circuit 7 is input into a controller 52 by a pressure sensor 40, and then, it is compared with a neutral pressure of the feedback signal circuit 7 in a neutral state of the operating levers 14a, 15a so that an engine 75 for driving the variable capacity pump 1 is switched to a low speed. Therefore, an engine speed of the engine 75 can be certainly returned to a normal condition with a simple structure even during an operation at a low load.

Description

[Detailed description of the invention]

[Industrial application field]

The present invention relates to an automatic speed governor for an engine in a load sensing system, particularly in a load sensing system in which multiple actuators can be driven by a single variable displacement pump. The present invention relates to an automatic speed regulating device for an engine in a load sensing system, which automatically regulates the rotational speed of the engine for driving the variable displacement pump to a low speed when the variable displacement pump is in a neutral state.

[Conventional technology]

As a conventional load sensing system in which multiple actuators operated at different operating pressures can be driven by a single variable displacement pump, for example, Japanese Patent Application Laid-Open No. 1-176803
There is something like the one disclosed in the publication. This pump has multiple actuators connected in parallel to the discharge circuit of a single variable displacement pump through nine directional valves with compensator valves, and a directional valve including a compensator valve in the connection circuit to each actuator. The highest load pressure among the load pressures of the plurality of actuators is selected by the shutoff valve 2, and introduced into the pump control device that controls the flow rate of the variable displacement pump via the pilot piping. A discharge pressure is introduced, and the pump control device controls the pressure and flow rate according to the load pressure of each actuator. Additionally, this pump control device is equipped with a flow control valve that controls the introduction and discharge of fluid into and out of the tilting cylinder in order to change the pump capacity. ,
When the differential pressure between the highest load pressure selected by the shuttle valve and the pump discharge pressure exceeds a set value, pressure oil in the discharge circuit is guided to the tilting cylinder to reduce the discharge amount of the pump. [Problems to be Solved by the Invention] In this load sensing system, in order to control the flow rate, the highest pressure among the load pressures of each actuator is selected by a shuttle valve to control the flow rate of the variable displacement pump. Feedback is provided to the flow rate control valve, but when neither directional switching valve nor switching valve is operated, the feedback signal circuit becomes tank pressure. In this state, if the directional control valve is operated to guide pressure oil to the holding side of the actuator, the holding pressure will be transmitted to the feedback circuit. By the way, the pressure when all the operating levers of multiple actuators used in the circuit of a conventional pump that does not employ a load sensing system are in their neutral state is the standard, and any pressure higher than this is determined to be in an operating state. Therefore, even if this method of detecting discharge pressure is adopted in the automatic transmission of the load sensing system,
Accurate operation cannot be expected for the following reasons. In other words, in a normal load sensing system, this is to improve the responsiveness of increasing the discharge volume of a variable displacement pump when the operating lever is changed from a neutral state to an operating state. When the operating lever is in the neutral state, a small amount of pressure oil continues to be discharged from the variable displacement pump, so an underload valve is required. Therefore, the discharge pressure of the variable displacement pump becomes the set pressure of the unload valve that unloads the flow rate at the minimum tilting of the pump to the tank when the pump is in the neutral position. Further, in the load sensing system, when the actuator is operated, that is, when the actuator is in the operating state of one lever, the set pressure of the flow control valve is set to optimize the discharge flow rate of the variable displacement pump. The respective set pressures are the differential pressures between the feedback signal pressure and the pump discharge pressure, but for the following reason, the set pressure of the unload valve needs to be set higher than the set pressure of the flow rate control valve.

【reason】

Here, the set pressure (ΔPu) of the unload valve in the load sensing system will be briefly explained with reference to FIG. Generally, in load sensing systems, the flow rate of the variable displacement pump is controlled by changes in the differential pressure between the discharge pressure of the variable displacement pump and the load sensing pressure, so the pressure when the control lever is in neutral is ΔPu
It is necessary to set the pressure to be higher than the set pressure ΔPf of the flow control valve. This is because (A) When ΔPu<ΔPf If the set pressure of the unload valve 6 is, for example, ΔPu−ΔPu1, then when the operating lever is in the neutral position,
Since the discharge pressure of the pump] is the set pressure of the unload valve 6, pp, =: ΔPu, < ΔPf 6 Also, the feedback signal circuit 7 pressure is the pressure of the tank T.
pressure (=OKg), so the pressure difference applied to both sides of the flow control valve 2 is ΔPu. Therefore, the flow rate control valve 2 is in the state shown in FIG.
The oil in the tilting cylinder IB communicates with the tank T via the flow rate control valve 2, and the tilting plate IA of the variable displacement pump 1 tilts toward the maximum flow rate and cannot maintain the minimum flow rate. (B) If Δ2Pu>ΔPf, unload valve 6
For example, if the set pressure is ΔPu=ΔPu, the discharge pressure of the variable displacement pump 1 is ppo:ΔPu2 when the operating lever is in the neutral position.
:>ΔPf Since the pressure in the feedback signal circuit 7 becomes the pressure in the tank T, the difference in pressure applied to both sides of the flow control valve 2 is
It becomes ΔPu2. Therefore, the flow rate control valve 2 is pushed downward, the tilt cylinder IB and the discharge circuit 3 are communicated, and the variable displacement pump 1 is tilted toward the minimum tilt angle side. This causes the following problems. First, when the operating levers are in the neutral state, the feedback signal circuit 7 is in communication with the tank T, so Ppo: the discharge pressure of the pump when all operating levers are in the neutral state P P x: when the boom is raised The discharge pressure P of pump 1 of
P2: Discharge pressure of pump 1 when the boom is lowered Pb1:
Boom circuit pressure (bottom side) Pb2: Boom circuit pressure (rond side) ΔPIJ: Unload valve setting pressure ΔPf: Bump 1 flow control valve setting pressure. PPo"ΔPu, and the entire discharge I from the variable displacement pump 1 is unloaded to the tank T. Here, during boom work, for example,

[When raising the boom]

Pp1=:Pb1+ΔPf. Since pb, >ΔPu, P P x > P P a
Therefore, it is possible to determine whether the operating lever is in the neutral or operating state, that is, in the 1-working state, based on the discharge pressure.

[When lowering the boom]

Pp, = Pb2 + ΔPf, but this Pb and others are at low pressure, and pb,
There are cases where +ΔPf<ΔPu. Pp2<ΔPυ, therefore p P2<
P p o may occur. In other words, even though the operation lever is operated and the work is actually performed, the discharge pressure of the variable displacement pump 1 is lower than when the operation lever is in the neutral position, so it is possible that only the discharge pressure of the pump 1 is detected. It is not determined that the operating lever has been operated, and therefore, the rotational speed of the engine is maintained at a low (neutral) rotational speed similar to when the operating lever is in the neutral state,
There may be cases where it is not possible to return to the set high rotation speed. As a result, the following disadvantages occur. For example, when a packet is being used for deep digging, when the packet is lowered to a fairly deep and low position, the boom must be lowered quickly to shorten the work time. Similarly to the former case, it is necessary to increase the descending speed of the boom in rock crushing operations that utilize the rapid descent of packets. In any of these cases, the engine speed must be increased. However, in the conventional example, as mentioned above, in any of these working conditions, it is not determined that the engine is still in operation, so the engine remains at low speed (neutral) rotation, and this In this case, it is not possible to lower the boom, packet, etc. rapidly at high speed. The present invention has been made by focusing on such problems in the conventional example, and uses a pressure sensor to detect the pressure in the feedback signal circuit of the rotary sensing system, and uses this detected pressure and the feedback signal when all operating levers are in the neutral state. By making it possible to automatically switch the driving engine of the variable displacement pump to a low speed based on a comparison with the neutral pressure of the signal circuit, the rotation speed of the engine can be returned to its normal state even during low-load work. The present invention aims to provide an automatic speed governor for an engine in a load sensing system that can be used reliably. (Means for Solving the Problems) In order to solve the problems of the conventional example as described above, the present invention uses the differential pressure between the discharge pressure of the variable displacement pump and the highest pressure among the operating pressures of the plurality of actuators. In a load sensing system for controlling a flow rate control valve, an unload valve is provided in the discharge circuit of the variable displacement pump, and a maximum value of the operating pressure of each of the actuators is applied to a feedback signal circuit that applies the same to the flow rate control valve. A pressure sensor is provided to detect the pressure of the signal circuit, and when the detected pressure of the pressure sensor matches the neutral pressure when all operating levers of the drive circuit of the plurality of actuators are in a neutral state, the variable displacement pump is driven. The rotational speed of the engine can be automatically switched to a low speed corresponding to the neutral state of all the operating levers.

[Effect]

Since the present invention has the above-described configuration, the load sensing circuit controls the flow rate control valve based on the differential pressure between the discharge pressure of a single variable displacement pump and the highest pressure among the operating pressures of the plurality of actuators. , when applying the feedback signal circuit pressure to the flow rate control valve of the variable displacement pump to control the discharge flow rate, the detected pressure detected by the pressure sensor provided in the feedback signal circuit and all operating levers of the shoe manufacturer are in the neutral position. When the two pressures match by comparison with the pressure in the feedback circuit at the same time, the rotation speed of the engine for driving the variable displacement pump is automatically switched to a low speed by the switching unit, while the rotation speed of the engine for driving the variable displacement pump is automatically changed to a low speed by operating one of the operating levers. Even if, for example, the boom, packet, etc. are in a rapidly descending state, the operating state is reliably detected and the required action is immediately performed in response to the operation of the operating lever.

【Example】

Embodiments of an automatic speed governor for an engine in a load sensing system according to the present invention are shown in FIGS. 1 to 4 below.
This will be explained with reference to the figures.

[First Embodiment] FIG. 1 is a block diagram of a control circuit according to a first embodiment of the present invention, and FIG. 2 is an explanatory diagram of the control circuit. In Figures 1 and 2, 1 is a variable displacement pump, IA
is the tilting plate of the variable displacement pump 1, IB is its tilting cylinder, 2 is the flow control valve of the variable displacement pump 1, 3 and 4 are the discharge circuit and discharge circuit of the variable displacement pump 1, 5 is the main relief valve, 6 is an unload valve, 7 is a feedback signal circuit, 10 is a directional valve block, 1 to 17 are directional valves, each directional valve], 1 to 17 are pressures discharged from a single variable displacement pump 1 Oil is supplied to the packet cylinder 2 through nine parking circuits 11-E to 17E, respectively.
1. Boom cylinder 23, left and right travel motors 24.25
, the swing motor 26, the arm cylinder 27, and other actuators. Note that 14a and 15a are operating levers for the directional control valves 14 and 15, and a□ to a7, b□ to b7 are oils for supplying and discharging operating pressure oil for the respective operating levers to and from the directional control valves 11 to 17. It is day. 21A, 21B, 23A, 23B, 27A, 27B are
Packet cylinder 2], pressure oil supply and discharge circuits 11E, 13E, 17E to boom cylinder 23 and arm cylinder 27
The boat relief valves 3] to 37 are compensator valves, and the convensator valves 31 to 37 are the directional control valves 51 to 17 (on the variable displacement pump side).
The hydraulic pressure is supplied from the discharge circuit 3 of the variable displacement pump 1, and is supplied to the actuators 21 to 27 via the directional control valves 11 to 17. Reference numerals 42 to 46 and 48 are Schael valves for selecting the highest load pressure of the adjacent actuators 2 to 27. 40 is a pressure sensor provided in the feedback signal circuit 7; 52 is a controller; 53 is a memory section of the controller 52; The pressure in the signal circuit 7 is stored. Reference numeral 54 denotes a comparison section, and the comparison section 54 compares the pressure in the feedback signal circuit 7 detected by the pressure sensor 40 and the pressure in the feedback signal circuit 7 when all operating levers are in the neutral state, which is stored in advance in the storage section 53. When the actual pressure in the feedback signal circuit drops to the pressure stored in the storage section 53, a switching signal is sent from the comparison section 54 to the switching section 57. That is, a deceleration signal is transmitted. 55 is a low rotation speed storage section, and this low rotation speed storage section 55 contains information when all operating levers are in a neutral state (during low speed rotation).
The number of revolutions of the engine 76 at the time is stored. Reference numeral 56 indicates an engine rotation speed setting section for setting the rotation speed of the engine 76, and 57 indicates a switching section. The rotational speed signal from the controller 50 is replaced with the low rotational speed signal stored in the low rotational speed storage section 55, and the accelerator actuator 61 is operated to switch the angle of the governor 62 in accordance with this low rotational speed signal.

[Effect of the first embodiment]

(A) Each direction switching valve] Operating levers 1 to 17 (
For example, when either one of the valves 14a and 1.5a) is operated, the pressure in the feedback signal circuit 7 is the maximum load pressure selected by the shuttle valves 42 to 46.48, and the pressure in the memory section 53 is This is higher than the pressure in the feedback signal circuit when all operating levers are in the neutral position, so
There is no switching signal sent from the comparison section 54, and in this case, the accelerator actuator 61 operates to correspond to the rotation speed set by the rotation speed setting section 56 of the engine E, the governor 62 of the engine 76 is adjusted, and the variable displacement The corresponding discharge amount is discharged from the heavy pump 1, and each part operates normally. (B) When all the operating levers (for example, 14a, 15a, etc.) are set to the neutral state, the pressure of the feedback signal circuit 7 becomes approximately the tank T pressure, and this pressure
This detected pressure matches the pressure of the feedback signal circuit 7 when all operating levers are in neutral, which is stored in advance in the storage section 53. When the two pressures match, a switching signal is sent from the comparing unit 54 to the switching unit 57, and the target engine speed set by the engine speed setting unit 56 changes to the low engine speed stored in the low engine speed storage unit 55. Switched by the switching unit 57, the switching unit 57
The accelerator actuator 61 is operated by the low rotational speed signal transmitted from the engine, and the governor 62 is adjusted to an angle corresponding to the low rotational speed. The engine 76 rotates at a low speed, and the discharge amount of the variable displacement pump 1 becomes small. (C) When any operating lever is operated from the state in which all the operating levers are in the neutral position as in (B) above, one of the directional control valves 11 to 17 corresponding to the operating lever moves to the operating state. The pressure of the drive circuit is selected by the shuttle valves 42 to 46, 48 and applied to the flow rate control valve 2 via the feedback signal circuit 7, while the pressure of the feedback signal circuit 7 in this state and the storage section 53 In this case, the pressure in the feedback signal circuit 7 is compared with the pressure in the feedback signal circuit 7 when all operating levers are in a neutral state, which is stored in advance. The determination is made by the device 54. In this state, the comparator 54 does not transmit a switching signal to low speed rotation, and therefore, the target rotation speed signal corresponding to the operation of the operating lever is continuously transmitted from the engine rotation speed setting section 56 to the switching section. 57 and transmitted from the switching section 57 by the engine speed setting section 56, the accelerator actuator 61
The governor 62 is operated via the. The remaining functions are substantially the same as in (A) above.

[Second example]

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4, which schematically show the main parts of the control circuit. In addition,
The same names and symbols are used for parts common to the first embodiment shown in FIGS. 1 and 2. In Figures 3 and 4, 1 is a variable displacement pump, IA
and IB are a tilting plate and a tilting cylinder of the variable displacement pump 1, 3 is a discharge circuit of the variable displacement pump 1, 7 is a feedback signal circuit, 10 is a directional control valve block, and 70 is a first valve provided in the feedback signal circuit 7. 71 is a second pressure sensor provided in the discharge circuit 3 of the variable displacement pump 1, 72 is a controller, and 73 is a plurality of actuators (
Pressurized oil is supplied and discharged to (see reference numbers 21 to 27 in FIG. The differential pressure between the pressure in the feedback signal circuit 7 of this load sensing system and the discharge pressure of the variable displacement pump 1 when all operating levers of the directional control valves (see reference numerals 11 to 17 in the figure) are in the neutral state, that is, This is a storage unit for the set pressure ΔPu of the unload valve 6. 74 is the variable displacement pump 1 detected by the second pressure sensor 71
a calculation unit 7 that calculates the differential pressure between the discharge pressure of the controller and the pressure of the feedback signal circuit 7 detected by the first pressure sensor 7o;
Reference numeral 5 denotes a comparison unit, and the comparison unit 75 compares the pressure ΔPu stored in the storage unit 73. The differential pressure calculated by the calculation section 74 is compared, and when the two match, a switching signal is sent to the switching section 57, and the rotation speed set by the engine rotation speed setting section 56 is stored in the low rotation speed storage section. 55, the accelerator actuator 61 is driven to correspond to the same rotation speed, the governor 62 is operated to switch the engine 76 rotation speed to a low speed, and the discharge amount of the variable displacement pump 1 is changed. adjust.

[Operation of the second embodiment]

In this second embodiment, the feedback signal circuit 7 has a first
In addition to providing the pressure sensor 70, the discharge circuit 3 of the variable displacement pump 1 is also provided with a second pressure sensor 71 for detecting its discharge force, and the pressure of the discharge pressure circuit 3 detected by the second pressure sensor 71 and feedback are provided. The first circuit provided in the signal circuit 7
The differential pressure between the pressure detected by the pressure sensor 7o, that is,
“Pump discharge pressure” - “feedback signal circuit pressure” is calculated by the calculation unit 74, and this difference pressure and the storage unit 73
The comparison unit 75 compares the pressure ΔPu stored in advance with the pressure ΔPu, and when the two pressures match, the comparison unit 75 transfers
7, and the switching unit 57 switches the engine speed corresponding to the operating state set by the engine speed setting unit 56 to the low engine speed stored in advance in the low engine speed storage unit 55. A signal corresponding to this switched low rotational speed signal is transmitted from the switching unit 57 to the accelerator actuator 61 and operated, thereby switching the lever of the governor 62 of the engine 76 to the low speed side. There is no risk of causing (ζ3) If a method that detects only the pump discharge pressure used in conventional control circuits is adopted for the automatic speed governor of the engine of the load sensing system, the pressure when all operating levers are in the neutral state If a pressure higher than this is detected, it will not be determined that it is in the operating state, and accurate operation cannot be expected. However, according to this invention, when the operating lever is changed from the neutral state to the operating state,
This provides quick responsiveness in increasing the discharge amount of the pump when the pump is in use, which in turn further improves the safety of excavator work, etc. (4) The pressure of the feedback signal circuit when all the operation levers are in the neutral state is stored in the memory device of the controller in advance, and this pressure and the pressure of the feedback signal circuit detected by the pressure sensor are stored in advance. In contrast, the engine speed is switched to a low speed only when both pressures match, so as long as the operating state continues, even if the discharge pressure of the discharge circuit of the variable displacement pump does not change due to the remaining structure and The operation is almost the same as that of the first embodiment. [Effects of the Invention] Since the present invention has the above configuration and operates, the following effects can be obtained. (]) In order to use the feedback signal circuit pressure of the load sensing system 11 to detect the neutral state (work stop state) of all operating levers, a new detection unit is provided to detect the operating state of the load sensing system. Therefore, the structure is simpler and there is a cost advantage compared to, for example, a conventional method that detects the operation of a control lever. (2) Since the pressure in the feedback signal circuit of the load sensing system is detected and used by a pressure sensor, it can be used even during low-load work such as rapidly lowering a power shovel packet to the bottom of a deep hole. In this load sensing system, it is reliably detected that the actuator is in operation. Even if the force that causes a malfunction decreases, the actuator of the engine governor will not be inadvertently switched to the neutral state. Able to actively perform rapid movements.

[Brief explanation of the drawing]

The drawings show an embodiment of an automatic speed governor for an engine in a load sensing system according to the present invention.
Figure 2 is a block diagram of the control circuit of the first embodiment, Figure 2 is an explanatory diagram of the control circuit, Figures 3 and 4 are block diagrams of the main parts of the control circuit of the second embodiment of the present invention, FIG. 5 is an explanatory diagram of the operation of the unload valve. 1...Variable displacement pump, IA...
Tilt plate, ]-B...Tilt cylinder, 2...
...Flow control valve, 3...Discharge circuit,
4...Discharge circuit, 5...Main relief valve, 6...Unload valve, 7...
...Feedback signal circuit, 11 to 17...
・・Directional switching valve, ], 1E～], 7E・・・Komado circuit, 21～27・・
...actuator, 31-37...convencator valve. 40...Pressure sensor, 52.72...Controller, 53.73...Storage section, 54.75...Comparison section, 55...Low rotation speed storage section , 56...Engine speed setting section, 57...
...Switching unit, 61...Accelerator actuator. 62... i banner, 70...-first pressure sensor, 71... second pressure sensor. 74...Arithmetic unit, 76...Engine.

Claims (3)

[Claims] (1) In a load sensing system that controls a flow control valve based on the difference between the discharge pressure of a variable displacement pump and the highest pressure among the operating pressures of multiple actuators, an unload valve is provided in the discharge circuit of the variable displacement pump. In addition, a pressure sensor for detecting the pressure of the signal circuit is provided in a feedback signal circuit that applies the maximum value of the operating pressure of each of the actuators to the flow control valve, and the detected pressure of the pressure sensor and the pressure of the plurality of actuators are connected to each other. By matching the pressure when all operating levers of the drive circuit are in a neutral state, the rotation speed of the engine for driving the variable displacement pump can be automatically switched to a low speed corresponding to the neutral state of all operating levers. An automatic speed governor for an engine in a load sensing system characterized by: (2) A plurality of actuators are connected in parallel to the discharge circuit of the variable displacement pump via a compensator valve and a directional control valve, and the maximum operating pressure of the plurality of actuators is selected by a shuttle valve, and the flow rate of the variable displacement pump is In a load sensing system comprising a feedback signal circuit for applying to a control valve and an unload valve in the discharge circuit of the variable displacement pump, the feedback signal circuit is provided with a pressure sensor for detecting the signal pressure; a comparison unit for comparing the detected pressure of the pressure sensor and the pressure of the feedback signal circuit when all operating levers of the plurality of actuators are in a neutral state, which is stored in a storage unit of the rotation speed controller of the engine for driving the variable displacement pump; and when the two pressures match, a switching signal is sent from the comparison section to the switching section to switch the set rotation speed of the engine rotation speed setting section for driving the variable displacement pump to the bottom rotation speed stored in the low rotation speed storage section. An automatic speed governor for an engine in a load sensing system, characterized in that the accelerator actuator of the engine is controlled by the signal generated by the switching section. (3) A first pressure sensor and a second pressure sensor are provided in the feedback signal circuit and the discharge circuit of the variable displacement pump, and a calculation unit that calculates a differential pressure between the pressures detected by the first and second pressure sensors; , a controller including a storage section that stores a differential pressure between the pressure of the feedback signal circuit and the pump discharge pressure when all operating levers of the plurality of actuators are in a neutral state; A comparison unit is provided for comparing the calculated differential pressure, and when the differential pressure and the differential pressure calculated by the calculation unit match, the comparison unit adjusts the rotation speed of the engine rotation speed setting unit to the low rotation speed. Claim (1) characterized in that a switching signal for switching to a low rotational speed stored in a storage unit is transmitted to a switching unit, and a corresponding operation signal is transmitted from the switching unit to an accelerator actuator of the engine.
) Automatic engine speed governor in the load sensing system described in ).