JPS6149518B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a constant horsepower control device for a hydraulic pump, and a variable displacement hydraulic pump (hereinafter simply referred to as a variable pump) driven by an engine mainly installed in construction machinery, etc. This invention relates to a constant horsepower control device.

BACKGROUND ART Conventionally, this type of constant horsepower device is as shown in FIG. 6, for example, in which the angle of the swash plate a' of the variable pump a is changed by a servo control mechanism g to adjust the discharge flow rate per revolution of the variable pump a. At the same time, the servo control mechanism g is supplied with oil discharged from the fixed pump e via the constant horsepower control mechanism d and the guide valve f, and the variable pump a
The hydraulic pressure supplied to load circuit b is transferred to shuttle valve c.
The discharge pressure is taken out as the discharge pressure of the variable pump, and the discharge pressure is supplied to the constant horsepower control mechanism d, and the discharge oil supplied from the fixed pump e to the servo control mechanism g is controlled to increase or decrease according to the discharge pressure. When the discharge pressure of variable pump a is high, the swash plate angle is controlled so that the discharge flow rate per revolution decreases, and when the discharge pressure of variable pump a is low, the swash plate angle is controlled so that the discharge flow rate per revolution increases. The product of the discharge pressure of pump a and the discharge flow rate per revolution is always constant, so that the output of variable pump a, that is, the product of the discharge pressure, the discharge flow rate per revolution, and the rotation speed is always constant. is controlled.

In other words, the discharge flow rate per rotation of the variable pump is directly proportional to the swash plate angle of the variable pump a, and by operating the constant horsepower control mechanism d based on the discharge pressure of the variable pump a, the flow rate is lower than that of the fixed pump e. By controlling the pressure oil sent to the servo control mechanism g and changing the angle of the swash plate of the variable pump a to increase or decrease the discharge flow rate per rotation, the pump output does not change even if the discharge pressure changes and a constant horsepower is maintained. I try not to exceed it. In other words, the swash plate angle is changed according to the discharge pressure so that the product of the discharge pressure and the discharge flow rate per revolution is always constant.

In the constant horsepower control device for a variable pump as described above, the maximum output of variable pump a is
The variable pump a is set to be equal to the maximum output of the engine h, and is controlled so that the maximum output of the variable pump a does not exceed the maximum output of the engine. This prevents the engine from stalling even when a load is applied.

Problems to be Solved by the Invention Therefore, the maximum output of the variable pump a is set to be the same as the engine maximum output _L1 as shown in Fig. 3A, specifically, the maximum engine output
The product of the rotational speed N ₁ at L ₁ , the discharge pressure, and the discharge flow rate per revolution is set to be the same as the engine maximum output L ₁ , and as mentioned above, the product of the discharge pressure and the discharge flow rate per revolution is set. If controlled to be constant, the discharge pressure and 1 will be constant regardless of engine speed.
Since the product of the discharge flow rate per rotation is always constant, the output of the variable pump decreases in proportion to the decrease in engine rotation speed, and when the engine rotation speed is zero, the output becomes zero, so the output of variable pump a is the third
It will change along the straight line X in the figure.

For example, when the engine output decreases to L ₂ , the engine rotation speed decreases from N ₁ to N ₂ , so the rotation speed of the variable pump also decreases from N ₁ to N ₂ , and the output of the variable pump decreases by the rotation of the straight line Point RO corresponds to speed N ₂ and variable pump output L′ ₂ is obtained.

In other words, since the rotational speed is reduced from N ₁ to N ₂ , the pump output is lower than the maximum engine output L ₁ by the rotational speed ratio N ₂ /N ₁ , and the output of variable pump a is reduced as shown in FIG. decreases from L ₁ to L′ ₂ . L′ ₂
=N ₂ /N ₁ L ₁ On the other hand, since the relationship between engine speed and output is as shown by curve Y in Figure 3, the maximum output L ₁ of the variable pump and the maximum output L ₁ of the engine match. , As mentioned above, when the engine output becomes L ₂ , the output of the variable pump becomes L′ ₂ , and the output of only L ₂ −L′ ₂ is no longer used as the pump output.

In other words, the engine output in the shaded area between the straight line X and the curve Y in FIG. 3 is not used at all as pump output and is wasted, and the variable pump cannot effectively utilize the engine output at any rotational speed.

Therefore, it is an object of the present invention to enable a variable pump to effectively utilize engine output at any engine rotational speed.

Means and action for solving the problem The pressure on the high pressure side of the pipes 5 and 6 is installed in the middle of the pipes 5 and 6 that supply the discharge force of the variable pump 2 driven by the engine 1 to the load circuit 7. A shuttle valve 10 is provided to take out the pressure, and the pressure taken out by the shuttle valve 10 is introduced into one end of a spool 15 provided in the constant horsepower control mechanism 12, and the spool 15 is switched. The fixed pump 3 is connected to the variable pump 2 via the constant horsepower control mechanism 12 and the guide valve 36.
In the constant horsepower control device for a variable pump, which controls the control pressure supplied to the servo control mechanism 32 of In addition to introducing pressure, the configuration introduces a differential pressure across the throttle 21 provided in the discharge circuit of the fixed pump 3, so that the engine output at any rotational speed of the engine 1 can be effectively converted into pump output. It is made to be removable.

Embodiment An embodiment of the present invention will be described in detail with reference to the drawings. In the figure, 1 is an engine mounted on a construction machine (not shown), 2 is a variable displacement hydraulic pump (hereinafter simply referred to as variable pump) driven by the engine,
Reference numeral 3 denotes a fixed capacity hydraulic pump (hereinafter simply referred to as a fixed pump) which also serves to charge the circuit of the variable pump 2, and is linked to the engine 1 via a gear train 4, respectively. Further, the variable pump 2 is connected to a load circuit 7 via pipes 5 and 6, and check valves 8 and 9 are connected in series between the pipes 5 and 6. Hydraulic pressure insufficient from the fixed pump 3 is charged to the low pressure side of each conduit 5 and 6 via valves 8 and 9.

Further, a shuttle valve 10 is interposed between each of the pipes 5 and 6, and the pressure on the high pressure side of each of the pipes 5 and 6 is introduced to a constant horsepower control mechanism 12 via a pipe 11. As shown in FIG. 2, the constant horsepower control mechanism 12 includes a sleeve 14 contained within a valve body 13, and a spool 15 slidably contained within this sleeve 14. The sleeve 14 is biased to the left by a compression spring 17 housed in a spring chamber 16, and its left end is in contact with a cam surface 18a of a cam link 18. Through holes 14 ₁ and 14 ₂ are opened at positions that coincide with the ports 13 ₁ and 13 _{2 of} . Further, one end side of the spool 15 housed in the sleeve 14 is provided protruding from one end side of a piston 19 that is operated by a differential pressure detected from a flow rate that changes in proportion to the discharge pressure of the variable pump 2 and the engine rotation speed. It is in contact with the tip of the rod portion 19a. The piston 19 is housed in a cylinder 20 formed at one end of the valve body 13, and the inside of the cylinder 20 is divided into chambers 20a and 20b.
The pressure before and after the throttle 21 interposed in the discharge side circuit of the fixed pump 3 is introduced into a and 20b via pipes 22 and 23, and a rod portion protruding from the other end of the piston 19. 19b is the cylinder 20
The piston 19 is housed in a small cylinder 24 connected to the small cylinder 24, and the piston 19 is pushed leftward by the pressure on the high pressure side of the pipes 5 and 6 introduced into the small cylinder 24. .

The other end of the spool 15 is pressed to the right by a compression spring 26 housed in the left spring chamber 25 of the valve body 13, and the set pressure of the compression spring 26 is applied to the end surface of the valve body 13 by a screw thread. The horsepower can be arbitrarily adjusted using a set screw 27 for setting the horsepower.

On the other hand, the cam link 18, which is in sliding contact with the end surface of the sleeve 14, is rotatably supported by the valve body 13 by a pivot shaft 28, and the cam surface 1 of the cam ring 18
8a is formed so that the output is constant.
Further, one end of the cam ring 18 is pivotally connected to the lower end of a lifting link 30 via a link 29, and the upper end of the lifting link 30 is connected to a control piston 33 of a servo control valve mechanism 32 via another link 31. . The servo control valve mechanism 32 is for varying the swash plate angle of the variable pump 2 to arbitrarily control the discharge amount within a preset control horsepower, and has a control piston 33 that interlocks with the swash plate 2a. , the control piston 33 is housed in the control cylinder 34 and is biased toward the neutral direction by a compression spring 35, and the position of the control piston 33 is such that it is interposed between the constant horsepower control mechanism 12 and the control cylinder 34. Feedback is provided to the guide valve 36 via a link 37.

Now, when the engine 1 is near the maximum output point L ₁ (rotational speed N ₁ at this time) shown in FIG. 3, the pump 2,
3, the set output of the variable pump 2 becomes the curve _L1 shown in FIG. Conduit 3
8 to the control cylinder 3 via the constant horsepower control mechanism 12
4 into one of the pressure chambers 34 ₁ and presses the control piston 33 to the right. As a result, guide valve 3
The swash plate 2a of the variable pump 2 is tilted by an amount corresponding to the displacement of the operating lever 36a that operates the pipe line 6.
Hydraulic oil is discharged at a pressure corresponding to the load. This corresponds to, for example, the state at point A in FIG. Further, the tilt angle of the swash plate 2a is fed back to the sleeve 36b of the guide valve 36 via the link 37, and the sleeve 36b is moved to the left.
The hydraulic pressure supplied from the guide valve 36 to the pressure chamber ₃₄₁ is restricted by the sleeve 36b, and the control piston 33 stops when the pressure within the pressure chamber ₃₄₁ and the spring force pushing the control piston 33 to the left are balanced. The swash plate 2a is positioned at that position, and the movement of the control piston 33 is controlled by the links 31, 3.
0 and 29 to the cam link 18, thereby rotating the cam link 18 and deflecting the sleeve 14 of the constant horsepower control mechanism 12 to the right.

On the other hand, the pressure on the high pressure side of pipes 5 and 6, for example 6, is
The pressure is introduced into the small cylinder 24 of the constant horsepower control mechanism 12 via the shuttle valve 10, and the pressure before and after the throttle 21 provided in the discharge circuit of the fixed pump 3 is introduced into each chamber 20a, 20b of the cylinder 20, respectively. The spool 15 is then displaced to the left via the piston 19 to a position where it is in balance with the compression spring 26. When the load on the load circuit 7 increases and the pressure in the pipe line 6 rises, the spool 15 is further pushed to the left, cutting off the ports ₁₃₁ and ₁₃₂ .
Port 13 ₁ communicates with drain port 13 ₃ . As a result, the pressure chamber 34 of the control cylinder 34
₁ communicates with the tank 39 through the guide valve 36 and the ports 13 ₁ , 13 ₃ of the constant horsepower control mechanism 12 , so the pressure in the pressure chamber 34 ₁ is drained and the piston 33 is returned to the neutral direction by the compression spring 35 . Ru. At the same time, the movement of the piston 33 is
0,29 and the sleeve 1 via the cam link 18
4, the sleeve 14 is again displaced to the left by the compression spring 17 to a position where the ports 13 ₁ and 13 ₃ are in slight communication, and the swash plate angle of the variable pump 2 is reduced. This corresponds to the state at point B shown in FIG. As a result, even if the load pressure increases, the discharge flow rate of the variable pump 2 decreases, and the product of the discharge pressure, the discharge flow rate per rotation, and the rotational speed, that is, the pump output, is operated without exceeding the output of the engine 1. It becomes like this. In other words, the product of the discharge pressure, the sum of the differential pressure before and after the throttle 21, and the discharge flow rate per revolution is controlled to be always constant, and the product of the above product and the rotational speed is the same as the engine output L ₁ It's like this.

Next, when engine 1 is driving pumps 2 and 3 near the output L ₂ (corresponding rotational speed is N ₂ ) shown in FIG. Since it is directly proportional, when the rotational speed of the engine 1 decreases from N ₁ to N ₂ , the discharge flow rate of the fixed pump 3 also decreases proportionally.
The flow rate flowing through the throttle 21 also decreases proportionally, the differential pressure across the throttle 21 decreases, and the differential pressure applied across the piston 19 of the constant horsepower control mechanism 12 also decreases. The operating pressure required to switch the spool 15 against the compression spring 26 in the constant horsepower control mechanism 12, that is, the constant horsepower control mechanism operating pressure, is constant regardless of the rotational speed of the engine 1, as shown in FIG. Constant and variable pump discharge pressure P ₁ and throttle 21
Since it is the sum of the differential pressure P ₂ before and after the spool 15
When switching, the discharge pressure of the variable pump increases by a decrease in the differential pressure across the throttle 21 among the pressure applied to the piston 19.

In other words, even if the discharge pressure increases by the amount by which the differential pressure decreases before and after the throttle 21, the swash plate angle does not decrease, and the product of the discharge pressure and the discharge flow rate per revolution increases, and the output of the variable pump increases accordingly.

For example, when the engine speed is N ₁ , the differential pressure P ₂ before and after the throttle becomes P′ ₂ , and the discharge pressure of the variable pump
P ₁ is P′ ₁ (P′ ₁ = P ₃ −P′ ₂ ). However, P ₃ is the constant horsepower control mechanism operating pressure.

Furthermore, when the engine speed decreases to N ₂ , the differential pressure P ₂ before and after the throttle decreases to P″ ₂ (P″ ₂ < P′ ₂ ),
The discharge pressure P ₁ of the variable pump becomes P″ ₁ (P″ ₁ = P ₃ − P″ ₂ ), and the discharge pressure P ₁ of the variable pump that shares the constant horsepower control mechanism working pressure changes as the engine speed changes from N ₁ to N ₂
When it decreases to , it increases by (P′ ₂ −P″ ₂ ), so
Even if the discharge pressure of the variable pump increases by that pressure (P′ ₂ −P″ ₂ ), the swash plate angle of the variable pump, that is, the discharge flow rate per revolution, will not decrease, and the discharge pressure and discharge per revolution will increase accordingly. Since the product of flow rates increases, the output of the variable pump can be changed from L′ ₂ in Figure 4.
Can be increased to L ₂ .

Moreover, since the differential pressure before and after the throttle 21 is proportional to the flow rate, that is, the square of the rotational speed of the engine 1,
The discharge pressure of the variable pump 2 for switching the spool 15 with respect to the rotational speed of the engine 1 is as shown in curve Z in FIG. The output of the variable pump 2 increases in a curved manner relative to the straight line
All of the output can be effectively taken out as pump output.

Effects of the Invention As described in detail above, this invention applies differential pressure taken from before and after a throttle provided on the discharge side of a fixed pump to a spool operated by the discharge pressure of a variable pump, and thereby Since the switching actuation force of the spool is obtained at , the share of the discharge pressure of the variable pump has a characteristic similar to the engine output curve. This makes it possible to extract it as output, allowing efficient use of the engine's output.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a hydraulic circuit diagram, Fig. 2 is a detailed diagram of a constant horsepower control mechanism, and Fig. 3 is a diagram showing the relationship between engine output and pump output with respect to engine rotation speed. , Fig. 4 is a diagram showing the relationship between pump output characteristics and changes in engine rotational speed, Fig. 5 is a diagram showing the relationship between engine rotational speed and differential pressure characteristics before and after the throttle, and Fig. 6 is a conventional explanatory diagram. It is. 1 is the engine, 2 is the variable pump, 2a is the swash plate,
3 is a fixed pump, 12 is a constant horsepower control mechanism, 14 is a sleeve, 15 is a spool, 21 is a throttle, 26 is a compression spring, 32 is a servo control valve mechanism, and 33 is a control piston.

Claims (1)

[Claims] 1 A shuttle valve 10 is provided in the middle of the pipes 5 and 6 that supplies the discharge pressure of the variable pump 2 driven by the engine 1 to the load circuit 7, and a shuttle valve 10 is provided to take out the pressure on the high pressure side of the pipes 5 and 6. By introducing the pressure taken out by the valve 10 into one end of a spool 15 provided in the constant horsepower control mechanism 12 and switching the spool 15, the constant horsepower is controlled by the fixed pump 3 driven by the engine 1. The variable pump 2 via the control mechanism 12 and the guide valve 36
In the constant horsepower control device for a variable pump, which controls the control pressure supplied to the servo control mechanism 32 of 2. A constant horsepower control device for a variable pump, characterized in that, in addition to introducing the above-mentioned pressure, a differential pressure across a throttle 21 provided in the discharge circuit of the fixed pump 3 is introduced.