JP2521582B2 - Constant horsepower control type variable displacement piston pump - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant horsepower control type variable displacement pump, and more specifically, to a swash plate element for changing the stroke volume of a piston pump, and to direct the swash plate element to a maximum discharge amount position. Means for biasing the swash plate element toward the minimum discharge amount position against the spring means, and discharge and supply of discharge pressure to and from the operation piston means. Control valve means for controlling in proportion to the mechanical input amount according to the pressure, and the product of the discharge pressure and the discharge flow rate of the pump according to the tilted position of the swash plate element, that is, the stroke volume. The present invention relates to a constant horsepower control type variable displacement pump provided with a lever mechanism for changing so as to be held constant.

[0002]

2. Description of the Related Art A constant horsepower control type variable displacement pump equipped with a lever mechanism of this type is used as a pressure oil supply source for a vehicle-mounted hydraulic system such as a construction machine in order to operate with a substantially constant shaft input torque. It is known from JP-A-49-37927. In a constant horsepower control type variable displacement pump based on a conventional lever mechanism such as this prior patent, a tilt angle of a swash plate is taken out by a rod or a lever and a rotary joint and converted into a linear displacement. The constant horsepower characteristic is realized by changing the length of one lever arm to give a negative feedback to the mechanical input amount to the control valve and controlling the product of the discharge pressure and the discharge flow rate to be constant.

However, in these conventional constant horsepower control type variable displacement piston pumps, the play (play) of the connecting portion between the rod or the lever and the rotary joint causes the control characteristics to become unstable, and the lever or the like is not used. The mechanical feedback mechanism is complicated, and it may be necessary to attach an external relief valve separately. In this case, the pump body must be equipped with large and complicated mounting parts.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned drawbacks, and a mechanical feedback mechanism is provided to a tilting support of a swash plate without causing an unstable phenomenon of control characteristics. The purpose of the present invention is to provide a constant horsepower control type variable displacement piston pump having a simple and compact structure which is almost built in the shaft element portion.

[0005]

In order to solve the above-mentioned problems, in the constant horsepower control type variable displacement piston pump according to the present invention, a swash plate element for changing the stroke volume of the piston pump is provided. Spring means for biasing the swash plate element toward the maximum discharge amount position, and operating piston means for pressing the swash plate element toward the minimum discharge amount position against the spring means, Control valve means for controlling the supply / discharge of the discharge pressure to / from the operating piston means in proportion to the mechanical input amount according to the discharge pressure, and the mechanical input amount of the pump according to the tilted position of the swash plate element. In a constant horsepower control type variable displacement pump including a lever mechanism that changes a product of a discharge pressure and a discharge flow rate so as to be held constant, the lever mechanism is a tilt support shaft integrated with the swash plate element. The tilt axis and A small piston element arranged in parallel with a predetermined eccentric amount, an oil passage means for introducing the discharge pressure to the tail end of the small piston so as to axially displace the small piston by the discharge pressure, and a force point side. And a pivoting lever member for applying a mechanical input to the control valve means against the spring force of the control valve means at the point of action by rotating about the fulcrum axis in response to axial displacement of the small piston. And the tip of the small piston element is rotated around the tilt axis of the tilt support shaft element by tilting the discharge amount variable element, whereby the lever arm length of the pivot lever member on the force point side is changed. Thus, the pivot lever member is brought into contact with the pivot lever member so as to be displaceable in the direction intersecting the fulcrum axis.

Further, in the constant horsepower control type variable displacement piston pump according to the invention as defined in claim 2, when the tilt support shaft element is supported by a bearing fixed to the pump housing side, a part of the oil passage means is provided. As a result, a passage is provided to allow the discharge pressure to act on the tail end side of the small piston element via the bearing, and discharge pressure oil is introduced from the passage to the bearing surface of the tilt support shaft element to respond to the discharge pressure. The hydrostatic bearing mechanism is configured.

[0007]

In the constant horsepower control type variable displacement piston pump according to the first aspect of the present invention, the small piston opposes the spring force of the control valve means with the pivot lever member interposed therebetween.

The small piston is arranged in parallel with the tilt axis in a tilt support shaft element integrated with the swash plate element with a predetermined eccentricity, and its tip is a fulcrum of the pivot lever member. Since the pivotal lever member is abutted against the force point side of the pivotable lever member so as to be displaceable in the direction intersecting the axis, the small piston element is caused by the rotation of the tilt support shaft element around the tilt axis center due to the tilt of the discharge amount variable element. Of the lever changes the contact position with the pivot lever member, whereby the lever arm length on the force point side of the pivot lever member changes.

The discharge pressure is introduced into the tail end of the small piston by the oil passage means, and when the small piston is displaced in the axial direction by the discharge pressure, the pivot lever member moves toward the force point side. In response to the axial displacement of the small piston, the small piston rotates about a fulcrum axis, whereby the pivot lever member provides a mechanical input to the control valve means at the point of action.

Now, the discharge pressure is P, the pressure receiving area of the small piston is A, the arm length on the force point side of the pivot lever member is X, the arm length on the action point side is L, and the spring of the control valve means is When the force is F, the equilibrium formula of the control valve means including the small piston and the pivot lever member is F × L = P × A × X, and when this is deformed, F × L / A = P × It becomes X. Here, F × L / A on the left side is a constant, and X is proportional to the tilted position of the swash plate element, that is, the discharge flow rate Q corresponding to the stroke volume. Therefore, P × X = P · Q = constant It is possible to obtain constant horsepower characteristics.

In the constant horsepower control type variable displacement piston pump according to the second aspect of the present invention, the tilt support shaft element is supported by a bearing fixed to the pump housing side, and the bearing is the tilt support shaft element. To form a hydrostatic bearing. Therefore, the oil passage means has a passage through which the discharge pressure acts on the tail end side of the small piston element through the bearing, and the discharge pressure oil is also introduced from this passage to the bearing surface of the tilt support shaft element. As a result, the bearing surface functions as a hydrostatic bearing according to the discharge pressure.

A preferred embodiment of the present invention will be described below with reference to the drawings.

[0013]

1 to 4, a pump element 1 of a variable displacement pump according to this embodiment is a basket type piston / cylinder assembly which is rotationally driven by a shaft 7 connected to a prime mover (not shown). In the pump housing 8, the pump element 1 is rotated by the shaft 7 so that the sliding ring 13 connected to the tip of the piston 11 through the universal joint 12 is brought into sliding contact with the swash plate 2 so that the swash plate tilts. Pressure oil from a suction port (not shown) is discharged to the delivery port with a stroke volume (push-away volume) according to the corner.

In this pump discharge amount control mechanism, the tilt angle of the swash plate 2 is changed in opposition to the spring load of the return spring 3 to rotate the shaft 7 around the piston 11.
This is accomplished by changing the piston stroke volume during one full revolution of.

The tilting angle of the swash plate 2 is displacement-controlled by the hydraulic pressure acting on the pressure chamber 4a at its tail end.
This is achieved by the balance of forces between the return spring 3 and the return spring 3, and the return spring 3 always urges the swash plate 2 toward its maximum discharge amount position, and in opposition thereto, the operating piston 4 moves the swash plate 2 It is pressed toward the minimum discharge amount position.

As shown in FIG. 2, the swash plate 2 integrally has a support shaft portion 21 having a semicircular cross-sectional shape protruding to the left and right sides, and a front surface portion of the support shaft has a cylindrical surface shape. Bearing surface 2
It is 2. In order to support this bearing surface 22, the housing 8 is provided with a cylindrical bearing portion 81, whereby the swash plate 2 opposes the force of the return spring 3 and the operating piston 4 by the bearing portion 81. The bearing is supported so as to be tiltable about the tilt axis O.

Pump discharge pressure oil is guided to the bearing portion 81 from a delivery port side (not shown) through a passage 82 in the housing 8, and a discharge pressure is applied to the bearing surface 22 to form a static pressure bearing. It has become so.

A control valve 5 having a substantially three-way valve structure is provided outside the housing 8 in the vicinity of the support shaft portion 21, and a safety valve 6 is provided outside the housing at an appropriate position (not shown).

As shown in FIG. 4, the control valve 5 and the safety valve 6 are connected in parallel to the operating piston 4 in a circuit manner, and a part of the discharge pressure is supplied to the pressure chamber 4a of the operating piston 4. To push the operating piston 4 against the return spring 3 to tilt the swash plate 2 to the maximum discharge amount position (maximum tilt angle), or to transfer the pressure oil in the pressure chamber 4a to the drain. A three-way flow control operation for returning the swash plate 2 to the minimum discharge amount, that is, the cut-off position (minimum tilt angle) is performed by dropping the operation piston 4 and retracting the operation piston 4 by the return spring 3.

The control valve 5 controls the supply and discharge of the hydraulic pressure in the pressure chamber 4a of the operating piston 4 in proportion to the mechanical input amount based on the discharge pressure, and this mechanical input amount is used for constant horsepower control. A lever mechanism 9 for changing the position is provided between the support shaft portion 21 and the control valve 5 (FIG. 1).

That is, a small piston 91 is slidably arranged in the support shaft portion 21 in parallel with the tilt axis O with a predetermined eccentric amount, and the static piston is provided in the pressure chamber 92 on the tail end side thereof. The discharge pressure is guided from the passage 82 via the bearing surface 22 of the pressure bearing.

The small piston 91 is displaced in the sliding axis direction of the spool 51 of the control valve 5 within the range of the maximum displacement amount X (FIG. 1) determined by the eccentric amount according to the tilt of the swash plate 2. . Strictly speaking, the locus of this displacement is a circular arc, but it can be approximated to a straight line by appropriately selecting the amount of eccentricity.

A pivot lever member pivotally supported by a pivot shaft 95 between the tip of the small piston 91 and the tip of the spool 51 of the control valve 5 so as to be pivotable by the axial displacement of both. 94 are arranged.

The tip end of the small piston 91 abuts on the opposite surface of the pivot lever member 94 through a ball 93 which is rotatable by the discharge pressure acting on the tail end, and the tip end of the spool 51 of the control valve 5. Also the valve spring 52 acting on the tail end
Adjustable spring force abuts the opposing surface of pivot lever 94 via a similar ball 53. FIG.
As shown in FIG. 6, the lever arm of the lever member 94 is a distance (maximum value X) from the axis of the pivot shaft 95 as a fulcrum to the tip contact point of the small piston 91 in the axial direction of the spool 51 on the force point side. The action point side is the distance L to the tip contact point of the control valve spool 51 in the axial direction of the small piston 91.

The lever arm length on the side of the force point is shown in FIG.
Alternatively, as shown by the solid line in FIG. 2, the minimum value is set at the full cut-off position where the discharge amount is substantially zero (this gives a slight offset from zero so that the pivot lever 94 does not rotate in the reverse direction). The amount of change is such that it increases as the swash plate 2 tilts and reaches the maximum value X at the maximum tilt angle. On the other hand, the lever length on the side of the action point is a fixed value which is always L.

The control valve 5 is, in order from the top in FIG. 1, a T port communicating with the drain through the housing 8, a pilot port P _P communicating with the pressure chamber 4a of the operating piston 4 through the housing 8 and the safety valve 6, and a housing. 8
And a P port communicating with the delivery port together with the passage 82 of the bearing portion 81, and the pilot port P _P is opened to a P port or a T port at a controlled opening degree.

The safety valve 6 acts on the operating piston 4 in parallel with the control valve 5 as shown in FIG. In the illustrated embodiment, the safety valve 6 introduces the discharge pressure into the pressure chamber 4a of the operating piston 4 when the pump discharge pressure reaches a preset full cut-off pressure to make the tilt angle of the swash plate 2 substantially zero. Of the pump is fully tilted to the full cut-off position, so that the full cut-off control of the pump can be stably performed when the swash plate 2 is near the cut-off position.

The discharge pressure is introduced into the hydraulic chamber 92 at the tail end of the small piston 91 by the oil passage 82, and when the small piston 91 is displaced in the axial direction by the discharge pressure, the pivot pressure is increased. The dynamic lever member 94 receives the axial displacement of the small piston 91 toward the force point side and rotates around the fulcrum shaft 95, whereby the pivot lever member 94 is attached to the spool 51 of the control valve 5 at the action point side. Give mechanical input.

Here, the discharge pressure is P, the pressure receiving area of the small piston 91 is A, the arm length of the pivot lever member 94 on the force point side is X, the arm length of the action point side is L, and the control valve is When the spring force of the valve spring 52 of No. 5 is F, the balance equation of the control valve 5 including the small piston 91 and the pivot lever 94 is F × L / A = P × X. Here, F × L / A on the left side is a constant, and X is proportional to the tilted position of the swash plate 2, that is, the discharge flow rate Q corresponding to the stroke volume of the pump element 1. Therefore, P × X = P・ The constant horsepower characteristic of Q = constant can be obtained.

[0030]

As described above, according to the present invention,
When the pump is in operation, the opposing forces are always acting on both sides of the fulcrum of the pivoting lever member, so that there is no rattling due to play and an unstable phenomenon of control characteristics does not occur. In addition, a mechanical feedback mechanism for obtaining constant horsepower characteristics is built in the spindle of the swash plate and returned to the control valve as a position change due to the rotation of the spindle around this spindle, so it is simple and compact. A constant horsepower type variable displacement pump having a different structure can be obtained.

[Brief description of drawings]

FIG. 1 is a half-section partial cross-sectional view perpendicular to a pump rotation axis showing an example of the structure of a main part of a constant horsepower control type piston pump according to an embodiment of the present invention.

FIG. 2 is a partial vertical cross-sectional view of an essential part of the constant horsepower control type piston pump according to the embodiment.

FIG. 3 is a partial side view of the constant horsepower control type piston pump according to the embodiment, in which a part of the structure of the control valve is also shown in cross section.

FIG. 4 is a hydraulic circuit diagram of the constant horsepower control type piston pump according to the embodiment.

[Explanation of symbols]

 1: Pump element (piston / cylinder assembly) 2: Swash plate 3: Return spring 4: Operating piston 4a: Pressure chamber 5: Control valve 6: Safety valve 7: Shaft 8: Housing 9: Lever mechanism 11: Piston 12: Universal joint 13: Sliding ring 21: Spindle part 22: Bearing surface 51: Spool 52: Valve spring 53: Ball 81: Bearing part 82: Passage 91: Small piston 92: Hydraulic chamber 93: Ball 94: Pivoting lever member 95: Pivot axis

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Go Kitamura 203-5 Koda-cho, Sakae-ku, Yokohama-shi, Kanagawa (56) Bibliography 1-1141374 (JP, U)

Claims (2)

(57) [Claims] 1. A swash plate element for changing a stroke volume of a piston pump, a spring means for biasing the swash plate element toward a maximum discharge amount position, and a swash plate element opposed to the spring means. Operating piston means for pushing the discharge piston toward the minimum discharge amount position, control valve means for controlling supply / discharge of discharge pressure to / from the operating piston means in proportion to a mechanical input amount according to discharge pressure, and the machine. In a constant horsepower control type variable displacement pump having a lever mechanism for changing the static input amount according to the tilted position of the swash plate element so that the product of the discharge pressure and the discharge flow rate of the pump is held constant, The lever mechanism includes a small piston element arranged in parallel with a tilt axis in a tilt support shaft element integrated with the swash plate element with a predetermined eccentric amount, and the small piston is axially moved by the discharge pressure. To be displaced An oil passage means for introducing the discharge pressure to the tail end of the small piston, and an axial displacement of the small piston on the force point side to rotate around a fulcrum axis to oppose the spring force of the control valve means on the action point side. And a pivoting lever member for giving a mechanical input to the control valve means, wherein the tip of the small piston element is rotated about the tilt axis of the tilt support shaft element by tilting of the discharge amount variable element. A constant horsepower control type variable capacitor, which is displaceably contacted with the pivot lever member in a direction intersecting the fulcrum axis so as to change a lever arm length on the force point side of the pivot lever member. Piston pump. 2. The tilt support shaft element is supported by a bearing fixed to the pump housing side, and the oil passage means has a passage for allowing the discharge pressure to act on the tail end side of the small piston element via the bearing. 2. The constant horsepower according to claim 1, wherein the discharge pressure oil is introduced from the passage to the bearing surface of the tilt support shaft element to form a static pressure bearing mechanism corresponding to the discharge pressure. Controlled variable displacement piston pump.