JP4150348B2 - Hydraulic circuit for construction machinery - Google Patents

Description

The present invention relates to a hydraulic circuit of a construction machine, and more specifically to a technique of a hydraulic circuit for reducing a fuel injection amount when a variable discharge pump by using an inclined plate control or the like is used.

In a hydraulic circuit in a construction machine such as a conventional hydraulic excavator, a discharge amount variable pump using an inclined plate control is used, and when the operation lever is suddenly operated after the work starts or the hardness of the excavation target is increased during the excavation work. When it suddenly changes and becomes hard, there is a disadvantage that the torque of the hydraulic pump increases rapidly and the fuel injection amount of the engine is consumed excessively. However, the reason for this problem has not been analyzed so far and has not been solved. Therefore, this problem is analyzed and a solution method is provided. The present applicant has disclosed similar inventions in Patent Document 1 and Patent Document 2 already submitted. Both are unpublished.
Patent application, Japanese Patent Application No. 2002-329623 Patent application, Japanese Patent Application No. 2003-286572 Therefore, the problem of the prior art will be described below again, although there is a part that overlaps the contents described in the above document.

  FIG. 4A is a hydraulic circuit diagram of a conventional excavator, and FIG. 4B shows the input / output relationship of the solenoid valve. In FIG. 4, a hydraulic pump 51 is a variable discharge amount hydraulic pump by tilt plate control or the like, and is controlled by a regulator 52. The hydraulic pump 51 is driven by the engine 53 and supplies high-pressure working pressure oil to the center oil passage 54. A group of directional control valves 55 and the like for controlling an actuator (not shown) are connected downstream of the center oil passage 54. The direction switching valve 55 is remotely operated by the secondary pilot hydraulic pressure of the remote control valve 56.

  On the other hand, the regulator 52 is provided with two oil chambers 52a and 52b. The oil chamber 52a is negatively fed back from the branch oil passage 59 connected to the center oil passage 54, and the output torque of the hydraulic pump 51 is reduced. Is negatively fed back so that is constant. As a result, constant horsepower control is performed so that the output torque does not exceed the engine torque even if the discharge pressure changes. Further, the secondary pressure Pf of the electromagnetic valve 60 acts on the oil chamber 52b, and the input torque of the hydraulic pump 51 can be set (increase / decrease). Note that the input torque and the output torque of the hydraulic pump do not match in an excessive state but substantially match in a steady state due to a mechanical delay element (a delay in discharge flow rate control by the inclined plate 61 or the like). The solenoid of the solenoid valve 60 is connected to the output side of the controller 57, and the input torque selection switch 58 is connected to the input side of the controller 57.

When the inverse proportional solenoid valve is used as the solenoid valve 60, the relationship between the secondary pressure Pf of the solenoid valve 60 and the pump input torque T is as shown in FIG. Is in an inversely proportional relationship. When the position “H” of the selection switch 58 is selected, a high input torque is obtained. That is, the secondary pressure of the solenoid valve 60 becomes the low pressure Pf1, the regulator 52 increases the discharge amount of the hydraulic pump 51, and the output torque also increases. On the contrary, when the position “L” is selected, the input torque becomes low. That is, the discharge amount of the hydraulic pump 51 is reduced, and the output torque is also reduced.

  Excavators are used for a variety of tasks. For example, there are heavy excavation work, light work, finishing work, and the like. In order to perform these work efficiently, the level of the input torque of the hydraulic pump 51 is switched by the selection switch 58. In the following description, a response when the position “H” is selected by the selection switch 58 and a high input torque is selected will be described. The left side of FIG. 5 shows the characteristics (discharge amount change and input torque change) of the pump 51 when the high input torque is selected. The discharge amount Q is constant (maximum discharge amount Qmax) until the discharge pressure reaches PA, and decreases according to a constant horsepower curve (solid line K) after the discharge pressure reaches PA.

PA is the tilt start pressure (or “discharge amount control start pressure”, hereinafter referred to as “tilt start pressure” for simplicity) at the point where the tilt plate 61 of the pump 51 begins to tilt. If the position {“H”, “S”, “L”} of the selection switch 58 is constant, the tilt start pressure is constant. The input torque T increases linearly until the discharge pressure reaches PA, and becomes constant (Tmax) after the discharge pressure reaches PA. The right side of FIG. 5 shows the relationship between the rotational speed N of the engine 53 and the output torque T.

  Next, for example, a case where the discharge pressure changes during excavation work will be described with reference to FIG. If the idling state is changed to the working state at the time (t1) (excavation operation not operated), the discharge pressure increases from Po to P1. Next, when the excavation work is started at time (t2) and the discharge pressure suddenly increases from P1 to P2, the discharge pressure increases to (P1, P3, PA, P4, P2). At this time, the discharge amount Q is constant (Qmax) until the discharge pressure is PA, but after PA, it does not decrease according to the constant horsepower curve K, and the tilt of the inclined plate 61 is delayed, so the discharge flow rate is Qb (FIG. 5). 2), and settles on a constant horsepower curve K at time (t4). The delay of the inclined plate 61 in this case is the time (t3, t4) in FIG. That is, a delay time of tb = t4−t3 occurs. As a result, the pump 51 requires an input torque Tb (shown) equal to or greater than (Tmax), and the engine speed is reduced from N1 to N2. The engine 63 increases the fuel from qmax to q2 in FIG. 6 in order to return the rotational speed to N1, and as a result, the fuel consumption is excessively consumed by the hatched portion (A).

  The same applies to the case where the excavation operation is continued and the load is increased after the load is lightened. For example, the same applies when the discharge pressure is decreased from P2 to P3 at time (t5) and then rapidly increased from P3 to P4 at time (t6). That is, the inclined plate 61 tilts while being delayed by a delay time (tc = t8−t7), so that the fuel consumption increases by the hatched portion (b) in FIG. The phenomenon described above also occurs when the position of the selection switch 58 is selected as “S” or “L”.

As explained above, in the discharge amount variable pump using the inclined plate control used in construction machines, wasteful fuel is generated if the discharge pressure is frequently increased during the operation, with the discharge pressure sandwiching the tilt start pressure. Consumption increased and was a problem.

The present invention has been made in view of the above-described facts, and an object of the present invention is to provide a hydraulic circuit that does not increase the fuel consumption even when the load suddenly increases with the tilt start pressure interposed therebetween.

The present invention employs the following configuration as means for solving the above-described problems. That is, the invention according to claim 1 is a hydraulic circuit of a construction machine comprising a variable discharge hydraulic pump and input torque setting means capable of changing a discharge control start pressure of the hydraulic pump. A pressure detector that detects pressure, and a controller that connects an output of the pressure detector to an input end, and an output end connected to the input torque setting means,
When the load suddenly increases across the discharge amount control start pressure of the hydraulic pump determined by the load mode, the controller discharges the hydraulic pump by which the measured pressure of the pressure detector is determined by the load mode When the pressure is lower than the control start pressure, the input torque of the input torque setting means is changed so that the discharge amount control start pressure changes. The input torque to be changed is such that the discharge amount control start pressure is slightly lower than the measured pressure. It is characterized by having decided to become high pressure.

According to a second aspect of the present invention, in the first aspect of the present invention, the controller further includes a discharge amount control start pressure of the hydraulic pump in which the measured pressure of the pressure detector is determined by the load mode . The input torque of the input torque setting means is set to a constant predetermined value so that the discharge amount control start pressure matches the discharge amount control start pressure of the hydraulic pump determined by the load mode when It is said.

  According to the present invention, the fuel consumption can be saved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows pump characteristics of a hydraulic circuit according to an embodiment of the present invention. FIG. 2 (A) shows pump output characteristics and FIG. 2 (B) engine characteristics. FIG. 3 shows a hydraulic circuit diagram of the present embodiment. As shown in FIG. 3, the hydraulic circuit of the present embodiment is provided with a pressure sensor (pressure detector) 11 that detects the discharge pressure of the pump 51, and an input torque selection switch 58 and a pressure sensor 11 are connected to the input end of the controller 12. The output is connected and the output (control amount) to the solenoid of the solenoid valve 60 is changed.

In the present invention, since the tilt start pressure ( or the discharge control start pressure of the hydraulic pump ) changes, it becomes confusing. In other words, the distinction between the tilt start pressure of the original control system (the control system of the conventional device) and the tilt start pressure of the new control system (the control system of the present invention) is confused. The tilt start pressure of the control system is called “ tilt start pressure by the load mode ”, and the tilt start pressure of the new control system is simply called “tilt start pressure ”. The output of the controller 12, when the pump discharge pressure P by the pressure detector 11 is lower than the tilting start pressure caused by the load mode, the pump discharge pressure P slightly above pressure (P + [Delta] P) such that the tilting start pressure A control amount (Pf) is determined. On the other hand , when the pump discharge pressure P by the pressure detector 11 is higher than the tilt start pressure in the load mode (including the case of the same value), the tilt start pressure is controlled to be equal to the tilt start pressure in the load mode. Determine the quantity (Pf).

  With reference to FIG. 1, the pump characteristics of the hydraulic circuit of this embodiment will be described. When the discharge pressure P gradually increases, the operation is the same as in the conventional circuit. That is, the wasteful fuel injection amount in the conventional circuit, and the hatched portions (A) and (B) in FIG. The case where the discharge pressure P increases rapidly with the tilt start pressure PA interposed therebetween will be described in comparison with the case of the conventional circuit.

When the working state (excavation operation not operated) is made at time (t1), the discharge pressure rises from Po to P1. Next, when the excavation work is started at time (t2) and the discharge pressure suddenly increases from P1 to P2, the discharge pressure increases to (P1, P3, PA, P4, P2). At this time, the tilt start pressure is set by the controller 12 so as to change according to the discharge pressure P (P1 + ΔP, P3 + ΔP, PA, PA, PA). Curve K1 represents a constant horsepower curve at (P1 + ΔP), and curve K3 represents a constant horsepower curve at (P3 + ΔP). Accordingly, the discharge amount Q decreases in accordance with the two-dot chain line curve Qd due to the delay in tilting of the tilting plate 61 and the rapid increase in tilting start pressure (P + ΔP), and finally converges on the constant horsepower curve K. Is not greatly exceeded. In this case, the input torque increases according to the one-dot chain line curve Td, but does not greatly exceed Tmax.

That is, since the actual discharge flow rate Q with a delay advances the constant horsepower curve Ki (a constant horsepower curve at Pi + ΔP) by a phase corresponding to ΔP, the discharge pressure P is greater than the tilt start pressure PA due to the load mode. Is smaller than the constant horsepower curve K of the original control system. Further, when the discharge pressure P coincides with the tilt start pressure PA in the load mode, the discharge flow rate Q is small, and the gradient is small at a portion where the discharge flow rate Q is small. Therefore, even if the discharge flow rate Q exceeds the constant horsepower curve K, the amount is small, and the loss of the fuel injection amount as in the above-described conventional apparatus can be prevented. Also, if the work is such that the discharge pressure P increases rapidly from the vicinity of the tilt start pressure PA in the load mode , for example, if the heavy work is performed with the light work selection switch “L” selected, select this If the switch is switched to “H”, the tilt start pressure due to the load mode increases, so there is no problem.

  FIG. 2A shows pump output characteristics in this case, and FIG. 2B shows engine characteristics. As shown in FIG. 2, since the input torque of the pump 51 does not exceed the maximum torque Tmax, the engine 53 keeps the rotation speed constant (N1), and the fuel injection amount does not increase beyond qmax, and is wasteful. There is no fuel consumption.

  The same applies to the case where the excavation operation is continued and the load is increased after the load is lightened. For example, the same applies when the discharge pressure is decreased from P2 to P3 at time (t5) and then rapidly increased from P3 to P4 at time (t6). That is, the inclined plate 61 tilts with a delay from the corrected tilt start pressure (P3 + ΔP), but the input torque Te does not greatly exceed Tmax because the corrected tilt start pressure (P + ΔP) rapidly rises earlier. Accordingly, in this case as well, the fuel injection amount does not increase greatly exceeding qmax, and the fuel consumption amount is not wasted.

As described above, according to the present embodiment, there is an effect that it is possible to save wasteful fuel consumption.
Although the embodiment of the present invention has been described in detail with reference to the drawings, the technical scope of the present invention is not limited to this. For example, the variable discharge hydraulic pump is not limited to one using an inclined plate, and can be applied to a hydraulic pump that controls the discharge flow rate with a delay by other methods.

The pump characteristic by the hydraulic circuit of embodiment which employ | adopted this invention is shown. (A) shows the output characteristics of the pump, and (B) shows the characteristics of the engine. The hydraulic circuit diagram of this embodiment is shown. (A) Hydraulic circuit diagram in conventional apparatus, (B) Characteristic of solenoid valve. The pump characteristic by the conventional hydraulic circuit is shown. (A) shows the output characteristics of the pump and (B) shows the characteristics of the engine according to the conventional hydraulic circuit.

Explanation of symbols

11
12 Controller 51 Discharge amount variable hydraulic pump 52 Regulator 53 Engine 60 Electromagnetic inverse proportional valve PA Reference tilt start pressure (discharge control start pressure of original control system)
ΔP Positive slightly higher pressure P + ΔP Corrected tilt start pressure (discharge control start pressure of new control system)

Claims (2)

In a hydraulic circuit of a construction machine having a variable discharge hydraulic pump and input torque setting means capable of changing a discharge amount control start pressure of the hydraulic pump, a pressure detector for detecting the discharge pressure of the hydraulic pump, and the pressure A controller having an output of the detector connected to an input end, and an output end connected to the input torque setting means;
The controller
When the load suddenly increases across the discharge amount control start pressure of the hydraulic pump determined by the load mode, the measured pressure of the pressure detector is greater than the discharge amount control start pressure of the hydraulic pump determined by the load mode . Is lower, the input torque of the input torque setting means is changed so that the discharge amount control start pressure changes, and the input torque to be changed becomes a pressure at which the discharge amount control start pressure is slightly higher than the measured pressure. The hydraulic circuit of the construction machine, characterized in that determined. The controller further includes a discharge amount control start pressure determined by the load mode when a measured pressure of the pressure detector exceeds a discharge amount control start pressure of the hydraulic pump determined by the load mode . 2. The hydraulic circuit for a construction machine according to claim 1, wherein the input torque of the input torque setting means is set to a predetermined value so as to coincide with the discharge amount control start pressure of the hydraulic pump .

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