JPH10184906A - Overload prevention device in hydrostatic power transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent overload condition in a hydrostatic power transmission, and enable effective use of power by letting a hydraulic pump itself prevent such overload condition. SOLUTION: In a hydrostatic power transmission in which a hydraulic motor is connected through piping to a variable displacement hydraulic pump 1 driven and rotated by an engine or the like and the displacement of the variable displacement hydraulic pump 1 is varied by manually operating a control member 15 connected to a tilting shaft 8 for a swash plate 9 and thereby rotating the tilting shaft 8, the tilting shaft 8 and the control member 15 are fixed each other through an elastic piece 15. As the discharge pressure of the variable displacement hydraulic pump 1 increases, a tilting moment is caused at the swash plate 9 in such a direction as to decrease its tilting angle, and the pump displacement is decreased irrespective of the operating position of the control member 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overload prevention device for a hydraulic power transmission used in a construction vehicle such as a working vehicle or an agricultural machine.

[0002]

2. Description of the Related Art Conventionally, for example, a hydraulic transmission for driving an agricultural machine or a truck is connected to a swash plate type variable displacement hydraulic pump b and a traveling wheel c driven by an engine a as shown in FIG. A hydraulic transmission (HST) in which a hydraulic motor d and a hydraulic circuit d are connected by a closed circuit e is used. In such a circuit, the hydraulic motor d is controlled by operating the tilt angle of the swash plate f of the variable displacement hydraulic pump b in the forward / reverse or neutral state.
Is rotated forward / reversely or stopped to perform a predetermined operation. As a method of operating the swash plate f, a manual operation (JIS) in which the tilt axis g of the swash plate f is directly operated by a human hand or foot via a link, a rod, a wire, or the like, and the tilt angle is changed. B01
42-1994) is often used.

On the other hand, the relationship between the engine horsepower (H), the HST pressure (P) and the flow rate (Q) in such a device is shown in FIG. And the engine speed (N)
Is constant, it can be expressed as the relationship between pressure and pump displacement as shown in FIG. The hydraulic power is engine horsepower = P (kgf / cm ² ) · Q (l / min) / 450
2 and 3, the region B indicates that the product of the pressure and the flow rate exceeds the engine horsepower (H). For simplicity, when the constants are omitted and displayed, area A:
P × Q <H, B area: P × Q> H, where Q = D · N
Holds.

[0004]

When working with, for example, a work vehicle equipped with this hydraulic transmission, it is conceivable to load as much luggage as possible and climb a steep slope in order to increase the amount of work. At this time, the position of the human-powered operation means such as the operation lever for changing the tilt angle of the swash plate f remains on a flat road, that is, Q
If P remains constant, P rises and enters the B region. When the vehicle enters the region B from the region A, the engine is overloaded, the engine is stalled (stalled), and the engine speed decreases.

[0005] This state is similar to a state in which the vehicle stops due to insufficient driving power of the vehicle, and the driver of the work vehicle thinks that he or she will depress the accelerator pedal in the vehicle, and reduces the power of the work vehicle. An operation to increase the tilt angle of the swash plate f in order to increase the pump displacement D
Operation to increase. This operation increases Q, and more and more enters the region B in FIG. 3, and eventually the engine stops and the vehicle stops. If such a state occurs on a steep hill while carrying a heavy object, the work vehicle is undesirably self-propelled down the hill.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent an overload state in a hydraulic power transmission and to provide a device capable of effectively using horsepower by preventing the overload state by a hydraulic pump itself. is there.

[0007]

According to the present invention, a hydraulic motor is connected to a swash plate type variable displacement hydraulic pump rotatably driven by an engine or an electric motor, and the displacement of the variable displacement hydraulic pump is reduced by the swash plate. In a hydraulic transmission device in which an operating member connected to a tilting shaft is manually operated to change the rotation of the tilting shaft, the tilting shaft and the operating member are connected to each other via an elastic body, and the tilting shaft is connected to the tilting shaft. By increasing the discharge pressure of the variable displacement hydraulic pump on the plate to generate a tilting moment in the direction of decreasing the tilt angle of the swash plate, thereby reducing the displacement of the pump regardless of the operating position of the operating member. The above objectives are achieved. A tilting moment in the direction of decreasing the tilting angle of the swash plate is generated by changing the processing shape of the valve plate of the variable displacement hydraulic pump or adjusting the advancement angle, and turning the valve plate to advance the tilting angle. The adjustment pin to be adjusted is configured to be engaged, and further, a notch is formed around the valve plate, and the tip of the adjustment pin, whose tip is eccentric, is fitted into the notch, and the adjustment pin is turned. It is preferable to adjust the advance angle of the valve plate.

Further, the end of the tilt shaft is constituted by a square axis, a square through hole is formed in the operating member, and the square cylindrical member is inserted into the square through hole through elastic bodies filled at four corners thereof. The elastic body is compressed and deformed, and the durability is improved by fitting the rectangular cylinder member into the tilt shaft and engaging the operation member.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In FIGS. 4 and 5, reference numeral 1 denotes a swash plate type variable displacement hydraulic pump which is rotationally driven by a motor 2 of an engine or an electric motor. Reference numeral 3 denotes a hydraulic motor connected to the hydraulic pump 1 by a closed circuit via a closed circuit, and the hydraulic motor 3 is connected to an operating body 13 such as a wheel of a transport work vehicle. The variable displacement hydraulic pump 1 has a cylinder block 7 having a plurality of pistons 6 which can be moved in and out integrally with a drive shaft 5 rotated by an engine, and the head of the piston 6 is tilted by a tilt shaft 8. The end surface of the cylinder block 7 is slidably contacted with the casing of the hydraulic pump 1 via the valve plate 10 in sliding contact with the surface of the swash plate 9 whose turning angle is changed. When the drive shaft 5 was rotated, hydraulic oil was discharged from one of the flow holes 11 and 12 according to the tilt direction and the tilt angle of the swash plate 9 as in the conventional case, and the hydraulic motor 3 was rotated. Thereafter, the hydraulic fluid is circulated from the other port to the hydraulic pump 1, and the operating body 13 is operated by the rotation of the hydraulic motor 3.

The hydraulic motor 3 is shifted by the hydraulic pump 1
The tilt angle of the swash plate 9 is changed, and a manual operating member 15 such as a manual operating lever is connected to the tilt shaft 8 integrated with the swash plate 9 for changing the tilt angle. . When the manual operation member 15 is tilted in the direction of the arrow, the swash plate 9 is tilted to the normal and reverse angles and the neutral angle. In addition, the valve plate 10
As shown in FIG. 6, a set of three ports 16 and 17 is formed on both sides of the axis XX of the tilt shaft 8. Ports at both ends of each set of ports are provided with discharge pressure In order to prevent pulsation and improve suction efficiency, V-shaped notched grooves 16a, 17
a was formed respectively.

Although such a configuration is conventionally known, this configuration does not prevent overload. Therefore, in the present invention, an elastic body 18 such as synthetic rubber is interposed between the operating member 15 and the tilting shaft 8 as shown in FIG. A tilting moment is generated in the swash plate 9 in a direction to reduce the tilting angle, and the swash plate 9 is tilted in a direction to reduce the displacement of the pump irrespective of the operating position of the operating member, thereby preventing an overload state. I did it.

More specifically, a square through hole 16 is formed in the operation member 15 and an extension 14a of the square shaft is formed at the end of the tilt shaft 8, so that the inside 19 of the square through hole 16 is formed. The square tube member 23 was fitted and fixed via the substantially triangular elastic members 18 fixed to the four corners, and the extension portion 14a was fitted to the square tube member 23 to connect the operation member 15 to the tilt shaft 8. . As the elastic body 18, for example, one having a moment (M _T ) required for torsion as shown in FIG. 7 is used. In general, in a swash plate type hydraulic pump, as shown in FIG. 8, a tilting moment (Mp = M _B − M _A ) occurs. However, this moment is not necessarily the M _B> M _A, even operating conditions are the same, V-shaped cutout groove 16a of the valve plate 10 in FIG. 6, from the port by machining shape such as the shape of 17a Although the pressure changes depending on the state of the pressure waveform of the fluid to be discharged or the advance angle で は, in the present invention, when the discharge pressure of the hydraulic pump 1 increases, the tilting moment Mp is generated in a direction to surely reduce the pump displacement. Regardless of the operating position of the operating member 15, the swash plate 9 is tilted to reduce the displacement of the pump, thereby preventing the engine 2 from being overloaded.

Now, the torsional moment MT of the elastic body 18
Is assumed to be as shown in FIG. 7. For convenience of explanation, the tilt angle (pump capacity) of the swash plate 9 is maximum (D _MAX ), the pump discharge pressure is maximum (P _MAX ), and the horsepower of the HST is Figures 2 and 3
Considering that the corner horsepower is at this time,
The operation angle of the operation member 15 and the tilt angle of the swash plate 9 of the hydraulic pump 1 (rotation angle αp of the tilt shaft 8) match as shown in FIG. 9, and the torsion angle α _T of the elastic body 18 is zero. 2 and FIG. 3 and FIG.

In this state, when a tilting moment Mp acts on the swash plate 9 in a direction to reduce the tilt angle, the elastic body 18 is deformed by α _T1 as shown in FIG. 10 without moving the operation member 15. The tilt angle of the swash plate 9 is reduced, whereby the tilt axis 8 becomes α _P1 , and the area A in FIGS.
Therefore, the overload state of the prime mover 2 can be prevented. In this case the tilting shaft 8 and acts moment corresponding to M _T1 in FIG. 7, a relationship of Mp = M _T1. Further, if the tilting moment Mp exceeds the torsional moment of the elastic body 18, the tilting angle becomes zero as shown in FIG. Stop.

The above relationships are summarized in Table 1 below. When the discharge pressure changes, D at a point along the engine horsepower (H) diagram of FIGS. 2 and 3 is obtained, and αP1, αT1, and MT1, Mp for maintaining this D are obtained.
By repeating this operation, D that does not cause the engine to stall at each pressure can be obtained.
It was shown to. As described above, such a tilting moment Mp is caused by changing the machining shape of the notched concave grooves 16a and 17a of the valve plate 10 and changing the eccentric tip 21 of the adjusting pin 20 having the advance angle ψ shown in FIG. The adjustment plate 20 is rotated by turning the adjustment pin 20 into the notch 22 around the valve plate 10 so that the valve plate 1
By turning 0 and changing the advance angle １３, Mp can be obtained as shown in FIG.

[0016]

As described above, according to the present invention, the tilting shaft of the swash plate of the variable displacement hydraulic pump is connected to the operating member via an elastic material, and the machining shape and the advance angle of the valve plate of the pump are changed. When the discharge pressure is increased, the tilting angle of the swash plate is increased by twisting the elastic body when the discharge pressure is increased. Smaller,
As a result, the displacement of the pump is reduced, and the hydraulic power matches the engine horsepower of the engine, etc., eliminating the inconvenience of stopping the engine. This has the effect of improving the operability and the like, and has the effect of easily generating a tilting moment corresponding to the discharge pressure by turning the valve plate with the adjustment pin.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a conventional example.

FIG. 2 is a diagram of a relationship between a flow rate and a pressure.

FIG. 3 is a diagram of the relationship between pump displacement and pressure.

FIG. 4 is a cut-away plan view of the embodiment of the present invention.

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is a side view of the valve plate and the adjustment pin of FIG. 4;

FIG. 7 is a diagram of a moment required for torsion of an elastic body.

FIG. 8 is an explanatory view of a tilting moment generated in a swash plate.

FIG. 9 is an explanatory diagram of a relationship between a tilt axis and an operation member.

FIG. 10 is an explanatory diagram of a relationship between a tilt axis and an operation member.

FIG. 11 is an explanatory diagram of a relationship between a tilt axis and an operation member.

FIG. 12 is a diagram showing a relationship between pressure and tilting moment.

FIG. 13 is a diagram showing the relationship between pressure and tilting moment.

[Explanation of symbols]

1 variable displacement pump, 2 motors, 3 hydraulic motors, 8
Tilt axis, 9 swash plate, 10 valve plate, 15 operating member, 1
8 elastic body, 20 adjustment pin, 22 notch,

Claims (4)

[Claims] An operating member in which a hydraulic motor is connected to a swash plate type variable displacement hydraulic pump rotatably driven by an engine or an electric motor, and a displacement of the variable displacement hydraulic pump is connected to a tilt shaft of the swash plate. Is manually operated to change the rotation of the tilting shaft, the tilting shaft and the operating member are connected to each other via an elastic body, and the variable displacement hydraulic pump is mounted on the swash plate. A hydraulic transmission device characterized in that a displacement of the pump is reduced regardless of the operating position of the operating member by generating a tilting moment in a direction to decrease the tilting angle of the swash plate with an increase in the discharge pressure. Overload protection device. 2. A tilting moment in the direction of decreasing the tilting angle of the swash plate is generated by adjusting the advancement of the valve plate of the variable displacement hydraulic pump, and the valve plate is turned to increase the advancement angle. The overload prevention device in the hydraulic transmission according to claim 1, wherein an adjustment pin to be adjusted is engaged. 3. A notch is formed around the valve plate, the tip of the adjustment pin having an eccentric tip is fitted into the notch, and the advancement of the valve plate is adjusted by turning the adjustment pin. The overload prevention device in the hydraulic transmission according to claim 2, characterized in that: 4. An end portion of said tilting shaft is constituted by a square axis, a square through hole is formed in said operating member, and a square tube member is formed in said square through hole through elastic bodies filled at four corners thereof. 2. The overload prevention device in the hydraulic transmission according to claim 1, wherein the operating member is engaged by fitting the square tube member to the tilt shaft.