JP2682663B2 - Variable displacement pump output controller - Google Patents

Description

The present invention relates to an output control device for a dual variable displacement pump.

(Prior Art) Since the horsepower consumption of the pump is proportional to the pressure and the discharge flow rate,
By controlling the pump output so that [pressure x discharge flow rate = constant], the prime mover that drives the pump can be operated most efficiently in rated operation.

Therefore, various pump output control devices have been conventionally proposed (see, for example, JP-A-56-54982).

This is because the pilot piston that responds to the pump discharge pressure displaces the spool for horsepower control against the spring, thereby guiding the pump discharge pressure to the regulator piston that adjusts the pump discharge amount, and the discharge pressure rises. The feedback control is performed so as to reduce the discharge amount in accordance with.

By the way, the control of the pump pressure and the discharge flow rate is based on the relationship between the rated motion output of the prime mover, but in the case where the prime mover drives two pumps at the same time, the total horsepower consumption of both pumps is constant. In order to achieve this, the pump pressure is fed back to control the discharge amount.

FIG. 2 shows this, and the first pump 1 and the second pump 1
The pumps 2 rotate in conjunction with each other by the same drive shaft, and the feed pump 3 is coaxially arranged. Regulator pistons 4 and 5 are provided to control the discharge amounts of the pumps 1 and 2, and the regulator pistons 4 and 5 are provided.
The displacement of the swash plate adjusts the angle of the swash plate to control the discharge amount. The hydraulic pressure supplied to the regulator pistons 4 and 5 is regulated by the regulator valves 6 and 7.

The regulator valves 6 and 7 feedback control the discharge amount based on the discharge pressures of the pumps 1 and 2, and decrease the discharge amount when the discharge pressure (pump load) increases,
Keep the total horsepower generated by both pumps constant.

Therefore, pilot pistons 8 and 9 for driving the regulator valves 6 and 7 are provided, and each pilot piston 8 and 9 has two pressure receiving portions 10A and 10B.
Discharge pressures from the first and second pumps 1 and 2 are introduced into A and 10B through passages 11A and 11B and 12A and 12B, respectively. Therefore, the pilot pistons 8 and 9 are displaced according to the combined pressure of the two pumps to switch the main spools of the regulator valves 6 and 7.

The pressure supplied to the regulator pistons 4 and 5 is adjusted by switching the main spool.

In this case, the areas of the pressure receiving portions on the left and right of the regulator pistons 4 and 5 are different, and when the same pressure is supplied, the pistons are displaced in the direction of decreasing the pump discharge amount Q, and the side with a large pressure receiving area is reduced in pressure. When switching, pump discharge rate Q
The piston displaces in the direction of increasing. The displacement of this piston is transferred to the horsepower control spring 17 via the stays 15 and 16.
Feedback to A and 17B. These springs 17
A and 17B urge the main spools of the regulator valves 6 and 7 to oppose the pilot pistons 8 and 9.

Therefore, the pump discharge pressure rises, the pilot pistons 8 and 9 increase the displacement amount, and the regulator valve 6 and
When 7 is switched to the direction of decreasing the pump discharge amount,
Stays 15 and 16 due to displacement of regulator pistons 4 and 5.
The amount of compression of the springs 17A and 17B is increased via, and the main spool is pushed back to a position where it is balanced with the pilot pistons 8 and 9, and is returned to the neutral position.

At the neutral position of the regulator valves 6 and 7, the regulator pistons 4 and 5 stand still at that position and hold the tilt angle of the pump swash plate at that angle.

Since the pump discharge amount is controlled while detecting the discharge pressures of both pumps, for example, even if the discharge pressure of one does not change, if the discharge pressure of the other increases, the discharge amount of both pumps will decrease. It is controlled so that the total horsepower generated is constant.

Reference numeral 18 is a horsepower control piston, which acts against the pilot pistons 8 and 9 when increasing the generated horsepower. Negative control spool 19 is used to reduce the discharge amount even when the pump discharge pressure is low, such as when the load is extremely low.

(Problems to be solved by the invention) However, this device has a structure in which the discharge pressures of both pumps act on two pilot pistons, and the regulator valves are switched by the pilot pistons.

This complicates the feedback mechanism of the pump discharge pressure, and when the two pumps are separated, the passage for introducing the high pressure becomes long, which not only leads to an increase in cost but also causes a decrease in reliability. There is.

An object of the present invention is to solve such a problem.

(Means for Solving Problems) Therefore, according to the present invention, the first and second pumps that are interlocked with each other, two regulator pistons that control the discharge amounts of these pumps, and the regulator pistons are supplied. Two regulator valves for controlling the hydraulic pressure, and a pilot piston that responds to the combined discharge pressure of both pumps,
A pressure reducing valve that balances the pilot piston to generate a low pressure proportional to the discharge pressure, two pilot spools that drive the regulator valves, and two passages that guide the control pressure generated by the pressure reducing valve to each pilot spool. Equipped with.

(Operation) The pilot piston is displaced by the combined discharge pressure of both pumps, and the pressure reducing valve responsive thereto generates a control pressure by reducing the discharge pressure at a predetermined ratio.

The control pressure acts on the pilot spool of each regulator valve through the two passages to displace the regulator piston and feedback control the pump discharge amount.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In FIG. 1, 20 is a pilot piston having two pressure receiving portions 21A and 21B, and a pressure reducing valve via a horsepower boosting spool 22.
Abut with 23.

In the pressure reducing valve 23, the spool 24 slides in the sleeve 25, and the high pressure port 26 to which the pressure from the feed pump 3 is introduced,
The pressure generated in the control pressure chamber 29 is adjusted by selectively communicating the control groove 28 with the low pressure port 27 connected to the tank.

Two passages 30A and 30B are connected to the control pressure chamber 29, and the control pressure is guided to the pressure chamber 32 of the pilot spool 31 of the regulator valve 6 or 7 via the passages 30A and 30B (however, in the drawing, the passage 30B is provided). Although the other regulator valve 7 is omitted in the drawing for the sake of illustration, since it is configured exactly the same as the regulator valve 6, only one of them will be described below as an example).

The main spool 33 of the regulator valve 6 is a sleeve
It is slidably accommodated in 34, and the pilot spool 31 is in contact with the end surface thereof via the negative control spool 35.
17A and 17B are springs for horsepower control, one end of which is locked to the main spool 33 so as to face the pilot spool 31, and the other end of which is a stay of the regulator piston 4.
Lock to 15.

The displacement of the main spool 33 controls the supply pressure to the left and right pressure chambers 35A and 35B of the regulator piston 4.

 With the above configuration, the following operation will be described.

The discharge pressure P1 of the first pump 1 acts on the pressure receiving portion 21B of the pilot piston 20, and at the same time, the discharge pressure P2 of the second pump 2 is generated.
Acts on the pressure receiving portion 21A.

Due to this pressure, the pilot piston 20 is pressed to the left in the drawing, and the spool of the pressure reducing valve 23 is passed through the horsepower boost spool 22.
Move 24.

By moving the spool 24 to the left, high pressure from the high pressure port 26 is introduced into the control pressure chamber 29, and this pressure is applied to the end surface of the spool 24.

Since the spool 24 is pressed by the pilot piston 20 from the right end, when the pressure in the control pressure chamber 29 is increased until the spool 24 is balanced with this, the spool 24 returns to the neutral state while pushing the pilot piston 20 back.

Here, if each effective area of the pressure receiving portions 21A and 21B of the pilot piston 20 is a, and the effective (pressure receiving) area of the spool 24 of the pressure reducing valve 23 is A ₁ , (A ₁ > 2a), the control pressure chamber 29
The pressure P ₃ generated at is calculated as follows.

From the balance between the spool 24 and the pilot piston 20, a (P ₁ + P ₂ ) = A ₁ · P ₃ (1) Therefore, P ₃ = a / A ₁ · (P ₁ + P ₂ )… (2) Pressure P ₃ is spool 24 and pilot piston
The pump discharge pressure (composite pressure) is reduced according to the area ratio of 20.

The larger the area ratio, the smaller the control pressure P ₃ becomes.

The control pressure P ₃ is introduced into the pressure chamber 32 in which the pilot spool 31 of the regulator valve 6 is accommodated via the passage 30A. This control pressure causes the pilot spool 31 to press the main spool 33 against the springs 17A and 17B.

When the main spool 33 is displaced to the right in this way, the high pressure is also introduced to the pressure chamber 35B on the right side of the regulator piston 4, and becomes the same pressure as the pressure chamber 35A on the left side. But,
The pressure receiving area of the regulator piston 4 is different between the left and right, and the pressure receiving area of the pressure chamber 35B on the right side is large, so the regulator piston 4 is displaced in the direction of reducing the discharge amount of the first pump 1.

This displacement is simultaneously applied to the springs 17A, 1 via the stay 15.
Since it is fed back to 7B, it works to push the main spool 33 back against the pilot spool 31. The main spool 33 stops at a position where the acting forces of the pilot spool 31 and the springs 17A and 17B are balanced, and returns to the neutral state.

In this way, feedback control is performed so that the discharge amount decreases when the pump discharge pressure rises, and conversely, when the pump discharge pressure decreases, the main spool 33 is displaced in the direction in which the discharge amount increases. However, it can be easily understood that the regulator piston 4 adjusts the pump tilt angle to increase the discharge amount.

 This control is analyzed as follows.

Now, considering the balance of the main spool 33, the effective area of the pilot spool 31 is A ₂ , the springs 17A, 17B.
Letting f ₁ and f _{2 be} the acting forces of, A ₂ · P ₃ = f ₁ + f ₂ (3). From (2) and (3) above, aA ₂ / A ₁ · (P ₁ + P ₂ ) = f ₁ + f ₂ (4) Here, the acting force (deflection amount) of the springs 17A and 17B and the regulator piston 4 By setting the relationship with the pump discharge amount Q according to the displacement in advance to (f ₁ + f ₂ ) · Q = K (5), from these (4) and (5), aA ₂ / A ₁ · (P ₁ + P ₂ ) = K / Q (6) Therefore, (P ₁ + P ₂ ) · Q = K · A ₁ / aA ₂ = K ₀ (7), and the product of the discharge pressure and the discharge amount of both pumps becomes a constant value. Constant horsepower control is performed.

Thus, in the present invention, conventionally required,
Only two pilot pistons 20 are required, and the combined value of the discharge pressures of both pumps is reduced by the pressure reducing valve 23 at a predetermined ratio and introduced to each regulator valve 6, 7 to sum the discharge amounts of both pumps. The generated horsepower can be controlled to be constant.

In this embodiment, the operation of the horsepower increase spool 24 and the negative control spool 35 is substantially the same as that of FIG. 2 described above. Also, the regulator valves 6 and 7
The operation of is also the same as the conventional one.

As described above, according to the present invention, a pressure reducing valve that generates a low pressure proportional to the discharge pressures of the first and second pumps is provided, and the regulator valve is feedback-controlled by the reduced control pressure. Therefore, there is only one pilot piston that responds to each pump discharge pressure, and the number of passages that guide high pressure to this pilot piston is reduced from 4 to 2. This simplifies the configuration and reduces the cost, and the operation reliability is high. Is also improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a hydraulic circuit diagram of a conventional example. 1,2 …… Pump, 4,5 …… Regulator piston, 6,7…
… Regulator valve, 20 …… Pilot piston, 23
...... Reducing valve, 29 ...... Control pressure chamber, 30A, 30B ...... Passage, 31
...... Pilot spool, 32 …… Pressure chamber, 33 …… Main spool.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Narita 1805 Asamizodai, Sagamihara-shi, Kanagawa 1 Sagami factory, Kayaba Industry Co., Ltd. (56) Reference JP-A-63-80083 (JP, A) JP-A-62 -91678 (JP, A)

Claims (1)

(57) [Claims] 1. A first pump, a second pump which are interlocked with each other, two regulator pistons which control the discharge amount of each of these pumps, and two regulator valves which control the hydraulic pressure supplied to each regulator piston. By a pilot piston that responds to the combined discharge pressure of the two pumps, a pressure reducing valve that balances the pilot piston to generate a low pressure proportional to the discharge pressure, two pilot spools that drive the regulator valves, and a pressure reducing valve. An output control device for a variable displacement pump, comprising: two passages for guiding the generated control pressure to each pilot spool.