JPH04237875A - Speed controller for piston motor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepless speed control device for a swash plate type piston motor.

0002

2. Description of the Related Art Many self-propelled construction machines are equipped with a hydraulic pump and a motor connected in a closed circuit, and the motor drives the vehicle.

The running speed of a vehicle corresponds to the rotational speed of the motor, and since the motor rotational speed is proportional to the pump discharge amount, the running speed is generally controlled by variably controlling the pump discharge amount. are doing.

In order to further widen the range of control of the running speed, according to the present application and Japanese Patent Application Laid-Open No. 61-49175, the motor rotation speed can be switched between low speed and high speed, and the pump discharge amount and motor speed can be changed. A device has been proposed that allows a wide range of speed (shift) control depending on demand by switching.

FIG. 9 shows this, and 1 is a variable discharge amount type pump, 2 is a motor, these are connected by a closed circuit 3, the motor 2 is rotated by the pump discharge oil, and the discharged oil is sent to the pump 1. It is returned to the suction side.

The pump 1 is equipped with a servo mechanism 5 that controls the pump discharge amount using the discharge oil of the charge pump 4, and controls the horsepower generated by the pump driven by an unillustrated prime mover (engine) to be constant. .

The motor 2 is provided with two speed control pistons 6 for controlling the swash plate angle between two positions, and the pressure of the closed circuit 3 is introduced into the speed control pistons 6 via a speed switching valve 7. Then, the motor 2 is switched to the high speed side with a smaller capacity.

When the solenoid valve 8 is switched and the low pressure in the closed circuit 3 is introduced from the low pressure selection valve 9 as the pilot pressure, the speed switching valve 7 switches from the drain position to the supply position and starts the motor. 2 to the high speed side. Note that the low pressure selection valve 9 switches using the pressure of the closed circuit 3 as a pilot pressure, and always guides the low pressure side to the solenoid valve 8.

On the other hand, when the solenoid valve 8 is not switched, the pilot pressure is cut off, the speed switching valve 8 maintains the drain position, and the pressure applied to the speed control piston 6 is drained, so that the motor 2 is turned on. Keep it on the slow side with more capacity.

Therefore, even if the pump discharge amount is the same, changing the motor capacity changes the motor rotation speed, and by switching the motor capacity in this way as well as increasing or decreasing the pump discharge amount, the relative It is possible to control the speed between low speed and high speed.

[0011]

[Problems to be Solved by the Invention] However, in this device, the pump discharge amount increases and decreases continuously, but the motor capacity can only be switched between two positions: large capacity (low speed) and small capacity (high speed). It is not possible to change the speed steplessly.

[0012] For this reason, there is little room for selection of the control range of the running speed, and if the speed is to be controlled delicately, it must depend on the operation of the operator, and the running feeling is not good.

Therefore, the present invention automatically changes the motor speed steplessly from a small capacity to a large capacity according to the load pressure, and also fixes the motor capacity as necessary. An object of the present invention is to provide a speed control device for a piston motor that can realize speed control.

[0014]

[Means for Solving the Problems] The present invention includes a cylinder block that rotates together with a motor shaft, a plurality of plungers arranged in the cylinder block concentrically with the motor shaft,
A piston motor equipped with a swash plate on which the tip of each plunger slides, a means for regulating the inclination angle of the swash plate within a predetermined range, and a speed for changing the inclination angle of the swash plate against the reaction force of the plunger. The speed control piston includes a control piston, a pressure reducing valve that adjusts a control pressure introduced to the speed control piston according to a motor load, and means for switching the pressure reducing valve so as to forcibly drain the control pressure.

The pressure reducing valve reduces the pump discharge pressure fed to the plunger according to this discharge pressure and guides it to the speed control piston, and when the pump discharge pressure exceeds a first set value, the motor is moved to a low speed position, Below the second set value, which is also lower, the swash plate is held at the high speed position.

Further, the pressure reducing valve reduces the pump discharge pressure in response to the differential pressure between the pump discharge pressure and the control pressure introduced to the speed control piston and the biasing force of the spring, while the switching means of the pressure reducing valve It is comprised of a solenoid valve that applies pressure against the spring to drain the control pressure.

[0017]

[Operation] Therefore, the control pressure adjusted by the pressure reducing valve changes according to the motor load, and the swash plate angle changes continuously accordingly, so the motor capacity also changes between the two positions of low speed and high speed. The motor rotation speed can be changed continuously depending on the load.

Furthermore, by switching the pressure reducing valve, the control pressure of the speed control piston is drained, and the motor is fixed on the large capacity, low speed side.

[0019]

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a sectional view of a motor.

As shown in FIG. 2, the swash plate 12 that controls the rotational speed of the motor 2 is supported by a support shaft 14 that is moved in parallel with an axis perpendicular to the axis of the motor shaft 13, and is mounted on the side of the support shaft 14. The rear surface portion 15a of the motor housing 16 and the rear surface portion 15b of the opposite side freely tilt within a range until they come into contact with the inner wall surface 16a of the motor housing 16, respectively.

The illustrated state in which the back surface 15b of the swash plate 12 is in contact indicates the maximum inclination and the low speed position where the motor capacity is large;
The slope of No. 2 is the minimum, resulting in a high-speed position where the motor capacity is small.

A pair of speed control pistons 6 that press the back surface 15b of the swash plate 12 are provided in parallel with the support shaft 14, and generate a moment in the clockwise direction in the figure in accordance with the control pressure introduced into the pressure chamber 17. Push the swash plate 12 so that it comes out.

On the other hand, the reaction force of a plurality of plungers 19 arranged on the cylinder block 18 at equal intervals on a concentric circle of the motor shaft 13 acts on the swash plate 12 so as to generate a counterclockwise moment. do. Note that the plunger reaction force is proportional to the pump discharge pressure introduced into the plunger chamber.

Therefore, the swash plate 12 is held at an inclination angle that balances these moments, and the motor rotational speed (capacity) is determined according to this inclination angle.

A control pressure obtained by reducing the pump discharge pressure according to the load is introduced into the pressure chamber 17 of the speed control piston 6 by the pressure reducing valve 10 shown in FIG. Change continuously.

Note that a pair of pressure reducing valves 10 are provided in communication with both sides of the closed circuit 3 so that the pump discharge pressure can be taken out at any time regardless of the rotational direction of the motor 2, and one pair is provided from each pressure reducing valve 10. A control pressure is introduced to each of the speed control pistons 6.

The pressure reducing valve 10 creates a control pressure by reducing the pump discharge pressure according to the load, as will be described later.
The control pressure is switched by the pilot pressure introduced when the solenoid valve 11 is switched, and the control pressure is drained. The solenoid valve 11 guides the pilot pressure from the low pressure selection valve 9 to the pressure reducing valve 10,
When pilot pressure is supplied, the control pressure of the pressure reducing valve 10 is drained, and the swash plate 12 is held at a low speed position.

The control pressure applied to the speed control piston 6 in order to continuously change the angle of the swash plate 12 is created as follows based on the pump discharge pressure.

First, FIGS. 3A and 3B show the relationship between the moments acting on the swash plate 12 when the swash plate 12 is at a low speed position (large motor capacity) and a high speed position (small motor capacity), respectively. shows.

The conditions for fixing the swash plate 12 at the low speed position are as follows:
When the moment due to the plunger reaction force of the cylinder block 18 is larger than the moment due to the speed control piston 6,

[0031] f1≦(b'/a)・F...(1)

003
2] Also, the conditions for fixing the swash plate 12 at the high speed position are also based on the relationship of the moment acting on the swash plate 12.

0033
] f2≧(b/a)・F…(2)

Note that in order to prevent the swash plate 12 from lifting due to the moment caused by the speed control piston 6,

[0035] f2≦{(b+L)/(a+L)}・F...(3)

00
It is necessary that the following equations [36] hold true.

However, in the above formulas (1) to (3),
F: plunger reaction force, f1, f2: speed control piston pressing force, a: distance between the center of the speed control piston and the center of the swash plate support shaft, b, b': distance between the center of action of the plunger reaction force and the swash plate support shaft Distance (where b>b'), L: Distance from the center of the swash plate support shaft to the opposite end of the swash plate.

Here, the pump discharge pressure PF applied to the plunger and the control pressure pf1, p applied to the speed control piston are
If f2 is assumed (KF and kf are constants respectively),

[0039]F=KF・PF...(4)

[0040] f1=kf・pf1 (5)

[0041]
f2=kf・pf2...(6)

Therefore, using equations (4) and (5), equation (1) can be expressed as control pressure pf
To summarize about 1,

pf1≦(b'/a)・(KF/kf)・PF…(7)

Similarly, using equations (4) and (6), (2) (
3) If we rearrange the equations for control pressure pf2, we get:

[0045] pf2≧(b/a)・(KF/kf)・PF…(8)

[
pf2≦{(b+L)/(a+L)}・(KF/k
f)・PF…(9)

Therefore, when the condition of formula (7) is satisfied, the swash plate 12 is fixed at the low speed position, and when the condition of formula (8) is satisfied, the swash plate 12 is fixed at the high speed position, and the control pressure is The inclination angle of the swash plate 12 changes continuously between pf1 and pf2.

FIG. 4 is a graph of each of these equations, with the control pressure on the vertical axis and the discharge pressure on the horizontal axis. is also held in a high speed position in the upper region.

Note that in equation (9), {(b+L)/
By setting the dimensions of each part so that (a+L)}・(KF/kf)≧1, the swash plate 12 will not be lifted up due to excessive tilting even if pf2=PF. .

Therefore, from this graph, it can be seen that the pressure reducing valve 1
When the pump discharge pressure PF is reduced by 0 and the piston control pressure pf has the characteristic (10) in the figure, for example, as shown in FIG. 5, when the pump discharge pressure is less than PF1, it is fixed at high speed, At PF2 or higher, the speed is fixed at low speed,
Between PF1 and PF2, the motor capacity changes continuously depending on the PF, and so-called continuously variable speed of the motor 2 becomes possible.

Therefore, in order to make the control pressure pf have the characteristic (10), assuming that the principle configuration of the pressure reducing valve 10 is expressed as shown in FIG. 6, Fs: spring action force, AF: pump discharge pressure. If the pressure receiving area of , Af is the pressure receiving area of the control pressure, then

[0052] pf・Af=PF・AF+F (11)

[
[0053] Therefore, rearranging this equation (11) with respect to pf,

pf=(AF/Af)・PF+(Fs/Af)...(10
)

From now on, if AF, Af, and Fs are determined appropriately, a straight line having characteristics as shown in (10) in FIG. 7 can be obtained. However, when PF is less than or equal to PF0, since it is offset by a spring, PF=pf, and the actual control pressure pf changes as shown by the thick solid line.

Note that the slope of the straight line (10) can be set freely, but this will reduce the pump discharge pressure PF1 when the motor 2 is fixed at low speed and high speed.
Since the range of PF2 is determined, the optimum range can be selected in accordance with the pump discharge pressure characteristics used.

Next, in order to fix the motor 2 at a low speed, it is sufficient to satisfy the condition of equation (7) above, but in this case, regardless of the pump discharge pressure PF, the control pressure pf
If you set it to zero, you can easily and reliably hold it in a fixed position.

To achieve this, as shown in FIG. 6, an external force W may be applied to the pressure reducing valve 10 so as to oppose the spring acting force Fs, thereby draining the control pressure. For this purpose,

[0059] pf・Af+W>PF・AF+Fs…(12)

006
This external force W is determined as the pilot pressure supplied when the solenoid valve 11 is switched, as described above.

In this way, by reducing the control pressure pf acting on the control piston 6 that presses the swash plate 12 from the back side with the pressure reducing valve 10 according to the load, the pressure is reduced between the maximum and minimum positions of the motor capacity. In this case, the inclination angle of the swash plate 12 can be automatically changed in accordance with the load, and as a result, the capacity of the motor 2 is continuously changed, making continuously variable speed possible.

FIG. 8 is a characteristic diagram showing the relationship between driving force and vehicle speed. Each shaded area represents the characteristics when the capacity of the motor 2 is switched between two positions, low speed and high speed. The output characteristics change discontinuously between low speed and low speed, but in the present invention, the motor capacity changes continuously depending on the load between low speed and high speed, so there is no discontinuous area and a wide range of speed change control is possible. realizable.

Furthermore, when the solenoid valve 11 is switched, the low pressure from the low pressure selection valve 9 acts on the pressure reducing valve 10 as pilot pressure, which forcibly drains the pressure reducing valve 10 and brings the control pressure to zero. , the swash plate 12 is pushed to the position where the motor capacity is maximum by the plunger reaction force.

Therefore, the motor 2 is fixed at the low speed position shown in the shaded area in FIG. Note that even at a low speed position, if the pump discharge amount changes according to the constant horsepower curve, the relationship between vehicle speed and driving force will also change accordingly. of course,
Compared to continuously variable speed, the motor side is limited to low speed, so
Its control range is narrow, but it can deliver high output (torque).

[0065]

As described above, according to the present invention, the swash plate angle is continuously changed according to the control pressure obtained by reducing the pump discharge pressure according to the load, and the motor capacity can be adjusted between low speed and high speed. Since it can be changed continuously between positions, the motor rotation speed can be automatically and steplessly changed according to the load, realizing a wide range of speed change control, improving the driving feeling and reducing the operational burden on the operator. Reduced. In addition, when the pressure reducing valve is switched, the control pressure is drained and the motor is fixed on the large-capacity, low-speed side, so it can be used when high speed is not required, such as when working in dangerous places or loading and unloading onto trucks during vehicle transportation. You can safely drive at low speeds in some cases.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of the motor.

FIG. 3 is an explanatory diagram showing the angular position of the swash plate, (A)
indicates a low speed position, and (B) indicates a high speed position.

FIG. 4 is a characteristic explanatory diagram showing the relationship between piston control pressure and pump discharge pressure for controlling the swash plate position.

FIG. 5 is a characteristic explanatory diagram showing motor capacity based on the relationship with pump discharge pressure.

FIG. 6 is a diagram showing the principle configuration of a pressure reducing valve.

FIG. 7 is an explanatory diagram of characteristics of control pressure adjusted by a pressure reducing valve.

FIG. 8 is a characteristic explanatory diagram showing the output characteristics of the motor based on vehicle speed and driving force.

FIG. 9 is a hydraulic circuit diagram of a conventional example.

[Explanation of symbols]

1 Pump 2 Motor 3 Closed circuit 4 Swash plate 6 Control piston 10 Pressure reducing valve 11 Solenoid valve 13 Motor shaft 15a, 15b Back part 16 Motor housing 18 Cylinder block 19 Plunger

Claims (3)

[Claims] 1. A piston motor comprising: a cylinder block that rotates together with a motor shaft; a plurality of plungers arranged in the cylinder block concentrically with the motor shaft; and a swash plate on which the tip of each plunger slides. means for regulating the inclination angle of the swash plate within a predetermined range; a speed control piston for changing the inclination angle of the swash plate against the reaction force of the plunger; and a control pressure that is guided to the speed control piston in accordance with the motor load. A speed control device for a piston motor, comprising: a pressure reducing valve to adjust; and means for switching the pressure reducing valve to forcibly drain the control pressure. 2. The pressure reducing valve reduces the pump discharge pressure fed to the plunger in accordance with this discharge pressure and guides it to the speed control piston, and when the pump discharge pressure exceeds a first set value, the motor is at a low speed position, 2. The piston motor speed control device according to claim 1, wherein the swash plate is held at a high speed position below a second set value lower than this. 3. The pressure reducing valve reduces the pump discharge pressure in response to the differential pressure between the pump discharge pressure and the control pressure guided to the speed control piston and the biasing force of the spring, while the switching means of the pressure reducing valve 3. The speed control device for a piston motor according to claim 2, further comprising an electromagnetic valve that applies exhaust pressure to the spring to drain the control pressure.