JP4804499B2 - Engine speed control circuit for construction machinery - Google Patents

Description

  The present invention relates to an engine speed control circuit for a construction machine, and in particular, in a construction machine such as a hydraulic excavator that uses an engine for a drive system, the fuel consumption is suppressed while suppressing a decrease in working speed when working at a high load pressure. The present invention relates to an engine speed control circuit for a construction machine capable of reducing the above.

  In an engine speed control circuit in a construction machine such as a conventional excavator, the engine speed decreases when the operation lever is suddenly operated at the start of excavation and when the symmetric hardness of excavation changes suddenly during excavation operation. In order to return the engine speed to the original value, the combustion injection amount was rapidly increased. For this reason, there was an inconvenience that fuel consumption deteriorated.

  This point will be described with reference to FIGS. FIG. 3 shows an example of an electrohydraulic circuit of a hydraulic excavator. The discharge amount of a variable displacement hydraulic pump 2 driven by the engine 1 is controlled by a regulator 3 as discharge amount control means, and the controlled pressure oil is centered. The oil is supplied to the oil passage 4. A group of directional control valves 5 for controlling an actuator (not shown) are connected downstream of the center oil passage 4. The direction switching valve 5 is switched by the secondary pilot pressure of the remote control valve 6.

  The regulator 3 is provided with two oil chambers 3a and 3b. One oil chamber 3a is connected to the center oil passage 4 through an oil passage 7, and discharges in accordance with an increase in discharge pressure of the hydraulic pump 2. The amount is decreased, and the pump output torque is maintained substantially constant. Thus, constant horsepower control is performed so that the pump output torque does not exceed the engine torque even if the discharge pressure changes. The secondary pressure Pf of the electromagnetic valve 8 as torque control means acts on the other oil chamber 3b, so that the pump output torque can be increased or decreased.

The solenoid 8a of the electromagnetic valve 8 is connected to the output side of the controller 9, and a mode changeover switch 10 for selecting a work mode such as heavy excavation, standard excavation and light excavation is connected to the input side of the controller 9. Here, since an inverse proportional solenoid valve is used as the solenoid valve 8, the control signal (current value) input to the inverse proportional solenoid valve 8 and the secondary pressure Pf of the inverse proportional solenoid valve 8 are inversely proportional. When the mode changeover switch 10 is set to the heavy excavation mode “H”, a high current value is input to the solenoid 8 a of the inverse proportional solenoid valve 8, and the secondary pressure of the inverse proportional solenoid valve 8 becomes the low pressure Pf ₁ . The discharge amount of the variable displacement hydraulic pump 2 increases, and the pump output torque also increases. To the contrary, when the mode changeover switch 10 to the light excavation mode "L" low current value is inputted to the solenoid 8a of the reverse proportional solenoid valve 8, secondary pressure of the reverse proportional solenoid valve 8 pressure Pf ₂ next The discharge amount of the variable displacement hydraulic pump 2 is reduced and the pump output torque is also reduced.

  The mode changeover switch 10 allows selection of a work mode such as a heavy excavation mode “H” that emphasizes speed and power, a standard excavation mode “S” that prioritizes fuel consumption, and a light excavation mode “L” that is suitable for fine operation. In the following description, a response when the heavy excavation mode “H” is selected by the mode changeover switch 10 will be described. In FIG. 4, the constant horsepower curve when the high output torque is selected is the H mode, and the constant horsepower curve when the low output torque is selected is the L mode, and the pump output torques in that case are “Tmax” and “Tmax”, respectively. Tmin ".

4 shows the hydraulic pump characteristics indicating the relationship between the discharge amount Q and the discharge pressure P of the variable displacement hydraulic pump 2, and the right figure shows the torque characteristics of the engine 1. 5 and 6 are graphs showing changes in response over time, the horizontal axis indicates time t, and the vertical axis indicates the discharge amount Q of the variable displacement hydraulic pump 2,
The discharge pressure P, the pump output torque T, the engine speed N, the fuel injection amount q, and the secondary pressure Pf of the inverse proportional solenoid valve 8 are shown. Hereinafter, a case where the excavation work is started and a case where the hardness of the excavation object suddenly changes in the middle will be described as an example with reference to FIGS. 4 to 6.

5, when suddenly the operation lever 6a of the remote control valve 6 from the drilling start time t _1, the discharge pressure P of the variable capacity hydraulic pump 2 rises suddenly from P ₀ to P _1. On the other hand, the discharge amount Q of the variable displacement hydraulic pump 2 is changed from the point C ₀ (Qmax) in FIG. 4 to the point C ₁ (Q ₁ ) along the two-dot chain line curve C over time (t _{1 to} t ₂ ). Decrease. That is, when the discharge pressure P is P _{0 to} P ₅ , the discharge amount Q is Qmax, and during P _{5 to} P ₁ , it moves along the curve C instead of the H-mode curve with constant horsepower. This is because a delay occurs because the discharge amount control of the regulator 3 is mechanically configured. As a result, the pump output torque T exceeds Tmax as shown by the curve D.

Therefore, as shown in FIG. 6, the engine speed N decreases from N ₀ to N ₁ so as to be balanced with this. Further, in order to secure the output, the engine 1 increases the fuel injection amount q from q ₀ to over q ₁ to q ₂ in order to return the rotational speed to N ₀ , and then settles to the state of q ₁ . That is, the portion (a) indicated by the oblique lines in FIG. 6 indicates the amount of fuel wasted.

Next, times t _{3 to} t ₄ indicate a case where the operation is slowly performed after the start of excavation. In this case, the discharge pressure P of the variable capacity hydraulic pump 2 also rises slowly from P ₁ to P _2. Therefore, in this case, since the pump discharge amount Q can also follow, the pump discharge amount Q slowly decreases from the point C ₁ (Q ₁ ) to the point C ₂ (Q ₂ ), and the H mode curve (solid line) ) Move up.

Further, the discharge pressure P of the operating amount even hardness of the excavation suddenly changes at a constant (if the hydraulic excavator is bumped to a large rock underground, etc.) hydraulic pump 2 operating lever 6a of the remote control valve 6 at the time t ₅ as shown in FIG. 5, to jump from _{P 2} to _{P 3.} Also in this case, since the response of the control of the regulator 3 is delayed as in the case of the sudden operation, the pump discharge amount Q moves on the two-dot chain line curve E in FIG. It moves up and temporarily exceeds Tmax. As a result, the engine rotational speed N as shown in FIG. 6 is sharply from N _0, the fuel injection amount q is increasing rapidly. Accordingly, the fuel is consumed as much as the amount indicated by the shaded portion (b) in FIG.

Further, for example, a construction shown in Patent Document 1 is an example in which the pump output torque is controlled during sudden operation of the operation lever or when the hardness of the excavation target is changed to reduce fluctuations in the engine speed to improve fuel consumption. Machine engine control devices are known. This prior art includes a main pump driven by an engine, an electromagnetic proportional valve that controls the torque of the main pump, a control valve that is operated by a remote control valve to control the supply and distribution of pressure oil to a hydraulic actuator, and the control valve And a controller connected to each of the pressure switch, the electromagnetic proportional valve, and the engine control actuator. The engine control device described in Patent Document 1 sets the main pump to a predetermined low torque when not operated, and sets the set torque of the main pump for a predetermined time when the start of operation of the hydraulic actuator is detected by the pressure switch. By switching from low torque to high torque, the rapid decrease in engine speed at the start of operation of the hydraulic actuator is prevented, and fuel consumption and exhaust gas deterioration are prevented.
JP 2001-271777 A.

In the prior art shown in FIGS. 3 to 6, when the abrupt operation of the operation lever 6a, as shown by curve D in FIG. 4, the pump output torque T between the pump discharge pressure P is P ₅ to P ₁ is temporarily will exceed significantly high torque (Tmax), also when the hardness of the excavation is suddenly changed, the pump output torque between the pump discharge pressure as shown by curve F in FIG. 4 is P ₂ to P ₃ T temporarily exceeds the high torque (Tmax) temporarily, and as a result, the engine speed N decreases in proportion to this. In order to ensure engine output, it is necessary to increase the fuel injection amount and restore the reduced engine speed, which inevitably increases fuel consumption.

In the prior art described in Patent Document 1, the pump output torque is controlled to prevent a rapid decrease in the engine speed at the start of operation and prevent deterioration of fuel consumption and exhaust gas. As shown in FIG. 3 and the like, when the hydraulic actuator is not operated, a predetermined small current i ₁ is input to the electromagnetic proportional valve to set the main pump to a predetermined low torque t ₁ , and the hydraulic actuator is operated by the pressure switch. When the start of operation is detected, the electromagnetic proportional valve is raised from a predetermined small current i ₁ to a predetermined large current i ₂ at a predetermined time T from that point, whereby the torque of the main pump is increased at a predetermined time T at a predetermined time T. since changing from a low torque t ₁ to a predetermined high torque t _2, without the engine rotational speed is lowered, without need for a large supply of transient fuel, never fuel economy deteriorates Although those say, if the signal changes at the predetermined time T from a predetermined small current i ₁ from the controller to the predetermined large current i ₂ is input to the solenoid proportional valve, from the signal is inputted to the electromagnetic proportional valve Since a response delay occurs until the discharge amount and torque are increased or decreased by changing the tilt angle of the main pump, the pump output torque may not become the high torque t ₂ at the predetermined time T. There is a problem in that optimal control cannot be performed because the value is only proportionally changed from the predetermined small current i ₁ to the predetermined large current i ₂ .

  Thus, a technical problem to be solved in order to reduce fuel consumption to a minimum while suppressing a decrease in work speed during high-load work occurs, and the present invention aims to solve this problem.

The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is a variable displacement hydraulic pump driven by an engine, and discharge according to an increase in discharge pressure in the variable displacement hydraulic pump. In the engine speed control circuit of the construction machine, comprising a discharge amount control means for reducing the amount and controlling the pump output torque substantially constant,
The pressure detecting means for detecting the discharge pressure, and the variable displacement hydraulic pressure by changing the engine speed in the pump output torque constant control by the discharge amount control means by inputting the discharge pressure detected by the pressure detecting means. The engine speed starts to decrease from a point when a predetermined high pressure is reached at which the amount of change in the discharge amount from the pump becomes small , and the engine speed decreases to an arbitrary speed as the discharge pressure increases. An engine speed control circuit for a construction machine having a control means is provided.

  According to this configuration, the variable displacement hydraulic pump is subjected to constant horsepower control in which the pump output torque is controlled to be substantially constant by the discharge amount control means. In this operating condition of constant horsepower control, the amount of change in the discharge amount from the variable displacement hydraulic pump due to the change in the engine speed decreases as the discharge pressure increases. That is, as the discharge pressure (load pressure) is higher in the actual work of the construction machine, the work speed does not decrease much even if the engine speed is lowered. Therefore, by reducing the engine rotational speed to an arbitrary rotational speed as the discharge pressure increases during work at high load pressure, it is possible to reduce engine fuel consumption while suppressing a reduction in working speed. Also, if the engine speed is reduced to an arbitrary rotational speed at once, the pump output torque that is being controlled to a constant level will temporarily overrun, and the engine rotational speed will be temporarily adjusted to balance this. Decreases below rotation speed. The engine suddenly increases the fuel injection amount in an attempt to return the reduced engine speed to the arbitrary speed, thereby deteriorating fuel consumption. On the other hand, when the engine speed is reduced, the pump output torque is prevented from over-torque by starting to decrease when the discharge pressure reaches an arbitrary high pressure without reducing it at once. In this case, the fuel consumption of the engine can be reduced.

According to the first aspect of the present invention, the pressure detection means for detecting the discharge pressure of the variable displacement hydraulic pump, and the discharge pressure detected by the pressure detection means are inputted, and the discharge pressure is constant in the pump output torque by the discharge amount control means. In control, when the engine reaches the predetermined high pressure at which the amount of change in the discharge amount from the variable displacement hydraulic pump becomes small due to the change in the engine speed, the engine speed starts to decrease and the engine speed increases to the discharge pressure. Accordingly, the rotation speed control means for reducing the rotation speed to an arbitrary rotation speed is provided, so that the change amount of the discharge amount from the variable displacement hydraulic pump due to the change in the engine rotation speed becomes smaller as the discharge pressure increases. As a result, the fuel consumption of the engine can be reduced while suppressing a decrease in working speed. Further, since only the pressure detecting means and the rotation speed control means are additionally provided with respect to the prior art and no major modification or improvement is involved, there is an advantage that fuel consumption can be reduced at a low cost.

  The purpose of reducing fuel consumption to a minimum while suppressing a reduction in work speed during high-load work is the variable displacement hydraulic pump driven by the engine and the discharge amount according to the increase in the discharge pressure in the variable displacement hydraulic pump. In an engine speed control circuit of a construction machine having a discharge amount control means for reducing and controlling the pump output torque substantially constant, a pressure detection means for detecting the discharge pressure, and a discharge pressure detected by the pressure detection means And a rotation speed control means for starting to decrease the engine rotation speed from the time when the discharge pressure reaches an arbitrary high pressure and reducing the engine rotation speed to an arbitrary rotation speed as the discharge pressure increases. Realized by having.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an electrohydraulic circuit diagram of an engine speed control circuit of a construction machine, and FIG. 2 is a characteristic diagram showing a constant horsepower control by pump discharge pressure and pump discharge amount, which are pump characteristics. In FIG. 1, the same or equivalent components as those in FIG. 3 are denoted by the same reference numerals as those in FIG.

  First, the configuration of the engine speed control circuit of the construction machine according to the present embodiment will be described. In the present embodiment, only the discharge pressure (load pressure) of the variable displacement hydraulic pump 2 is introduced as a control signal into the regulator 11 as the discharge amount control means, and the discharge amount is decreased by the regulator 11 as the discharge pressure increases. The constant horsepower control for controlling the pump output torque to be almost constant is performed. In addition, a pressure sensor 12 is provided as pressure detection means for detecting the discharge pressure of the variable displacement hydraulic pump 2, and the discharge pressure detected by the pressure sensor 12 is input to the main controller 9.

The main controller 9 outputs a control signal that starts to gradually decrease the engine speed from the time when the discharge pressure of the variable displacement hydraulic pump 2 reaches an arbitrary high pressure. Is input to an engine controller 13 for controlling the engine. The engine controller 13 and the main controller 9 start to gradually decrease the engine speed from the time when the discharge pressure of the variable displacement hydraulic pump 2 reaches an arbitrary high pressure, and the engine speed. Rotational speed control means is configured to reduce the pressure to an arbitrary rotational speed as the discharge pressure increases.

Next, the operation of the engine speed control circuit of the construction machine configured as described above will be described with reference to FIG. Now, the operation state of horsepower constant control indicated horsepower constant curve PS _1, horsepower constant curve PS ₁ Dropping the engine speed by an arbitrary rotational speed, a horsepower constant curve PS ₂ and as it shifts downward. Oil horsepower variable displacement hydraulic pump 2 is expressed by P × Q / 450, for example, the discharge amount difference Delta] Q ₁ by the engine speed changes when the discharge pressure (load pressure) P is P _1, the
ΔQ ₁ = 450 (PS ₁ -PS ₂ ) / P ₁ (1)
When the discharge pressure P is P ₂ higher than P ₁ , the discharge amount difference ΔQ ₂ is
ΔQ ₂ = 450 (PS ₁ -PS ₂ ) / P ₂ (2)
It becomes.

  As apparent from the equations (1) and (2), the change width ΔQ of the discharge amount Q from the variable displacement hydraulic pump 2 due to the change of the engine speed becomes smaller as the discharge pressure P becomes higher. That is, as the discharge pressure (load pressure) P is higher in actual work of the construction machine, the work speed does not decrease much even if the rotation speed of the engine 1 is decreased.

  Therefore, the pressure sensor 2 detects the discharge pressure P of the variable displacement hydraulic pump 2, and a control signal for gradually decreasing the engine speed from the main controller 9 from the time when the discharge pressure P reaches an arbitrary high pressure. By outputting to the engine controller 13 and reducing the rotational speed of the engine 1 to an arbitrary rotational speed as the discharge pressure P increases, the fuel consumption of the engine 1 is suppressed while suppressing a decrease in working speed during high-load work. Can be reduced.

Further, when the engine speed is reduced to an arbitrary speed at a stretch, as shown by a constant horsepower curve PS ₁ or the like, the pump output torque that is constantly controlled temporarily torques over, and the engine speed is In order to balance this, it temporarily falls below the arbitrary rotational speed. The engine 1 suddenly increases the fuel injection amount in an attempt to return the reduced engine speed to the above-mentioned arbitrary speed, thereby deteriorating fuel consumption.

  On the other hand, when lowering the engine speed, the pump output torque can be reduced by gradually reducing the discharge pressure P from the point of time when the discharge pressure P reaches an arbitrary high pressure without reducing it at once. In this respect, the fuel consumption of the engine 1 can be reduced.

  As described above, in the engine speed control circuit of the construction machine according to the present embodiment, the change width ΔQ of the discharge amount Q from the variable displacement hydraulic pump 2 due to the change in the engine speed is a region where the discharge pressure P increases. Since the engine speed is reduced as much as the discharge pressure P increases, the engine fuel consumption can be reduced while suppressing a decrease in working speed.

  When the engine speed is reduced, the pump output torque is prevented from over-torque by starting to gradually decrease from the point when the discharge pressure P reaches an arbitrary high pressure without reducing it at once. In this case, the fuel consumption of the engine 1 can be reduced.

  Since only the pressure sensor 12 and the engine controller 13 are additionally provided with respect to the prior art and no major modification or improvement is involved, the fuel consumption can be reduced at a low cost.

  The present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

1 is an electrohydraulic circuit diagram of an engine speed control circuit of a construction machine according to an embodiment of the present invention. The characteristic view which shows the horsepower constant control by the pump discharge pressure and pump discharge amount which are the pump characteristics in the said Example. The electrohydraulic circuit diagram of the hydraulic pump drive system control apparatus of the conventional construction machine. The characteristic view which shows the pump characteristic and engine torque characteristic in the said prior art example. The figure which shows the response curve with respect to various time passage in the said prior art example. The figure which shows the response curve with respect to various time passage in the said prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Variable displacement hydraulic pump 3 Regulator 4 Center oil path 5 Directional switching valve 6 Remote control valve 7 Oil path 8 Inverse proportional solenoid valve 9 Controller 10 Mode change switch 11 Regulator (discharge amount control means)
12 Pressure sensor (pressure detection means)
13 Engine controller which constitutes the rotational speed control means together with the controller

Claims (1)

An engine of a construction machine comprising: a variable displacement hydraulic pump driven by an engine; and a discharge amount control means for controlling a pump output torque to be substantially constant by decreasing a discharge amount according to an increase in discharge pressure in the variable displacement hydraulic pump. In the rotation speed control circuit,
The pressure detecting means for detecting the discharge pressure, and the variable displacement hydraulic pressure by changing the engine speed in the pump output torque constant control by the discharge amount control means by inputting the discharge pressure detected by the pressure detecting means. The engine speed starts to decrease from a point when a predetermined high pressure is reached at which the amount of change in the discharge amount from the pump becomes small , and the engine speed decreases to an arbitrary speed as the discharge pressure increases. And an engine speed control circuit for a construction machine.

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