HYDRAULIC PUMP WITH DOUBLE DIRECTION OF ROTATION

Abstract

A hydraulic pump with two rotation directions has axial pistons bearing against a swashplate, the pump with a head having two chambers to be connected to a high-pressure circuit and to a low-pressure circuit. A port plate in the form of a flat plate is arranged between a rotary barrel and the head and has two identical ports passing through the thickness of the flat plate. The port plate pivots about an axis to be able to occupy two angular positions according to the direction of rotation of the pump. The pump has a hydraulic-control device for controlling the angular position of the port plate and is able automatically to bring about a change in angular position of the port plate when the direction of rotation of the pump is reversed, under the effect of a pressure differential between the two chambers of the head.

Description

The present invention relates to a hydraulic pump with axial pistons bearing against a swashplate and with porting by means of a port plate, said pump being able to rotate in both directions of rotation, and in particular to a device for automatically controlling the port plate.

As is known, pumps with axial pistons and port plates comprise, behind the pistons, a planar surface referred to as the port plate, into which are engraved two curved ports intended to perform the porting, one of the ports being used for intake and the other for delivery.

Because the construction of a pump ported by a planar port plate, with two directions of rotation, requires ports that are identical so that they can alternately become an intake port or a delivery port, depending on the direction of rotation chosen by the user, it is necessary, in order not to detract from the performance of the pump, to adjust the angular position of said port plate by an angle X so as to optimize the angular position thereof, this entailing means that allow an offset X in both directions about the axis of rotation thereof.

In known pumps of this kind, the change in angular position of the port plate is performed manually by the user.

Such a mechanism for manually changing the angular position of the port plate is described, for example, in French patent application FR-A1-2965311.

U.S. Pat. No. 3,227,095 discloses, in FIG. 16, a reversible pump. An internal ring 286 and an external ring 296 slide rotationally in two mutually opposite directions under the effect of the overpressure present on the delivery side, so as to reduce the intake cavity I and enlarge the delivery cavity E. The delivery cavity E and the intake cavity I are defined between the two rings 286 and 296 and between the crossover segments 288 and 298 borne respectively by these two rings.

FR 2 119 108 describes a pump with axial pistons bearing against a swashplate. This pump is not reversible. The port plate 5 is fixed to the cover 12 of the pump in an angular position that cannot be altered.

It is an object of the present invention to provide a pump equipped with an automatic device for changing the angular position of the port plate.

To do that, the invention proposes a hydraulic pump with two directions of rotation, comprising axial pistons bearing against a swashplate, the pump comprising a rotary barrel rotated by a shaft and bearing cylinders in which the pistons slide, the pump comprising a head comprising two chambers which are intended respectively to be connected to a high-pressure circuit and to a low-pressure circuit, the pump porting being performed by a a port plate having two identical ports arranged facing two chambers of the head and able to constitute an intake port and a delivery port in each direction of rotation of the pump, each cylinder being equipped at its base with an orifice which passes in succession past the intake port and the delivery port as the barrel rotates, said port plate being able to pivot about an axis so as to be able to occupy two angular positions according to the direction of rotation of the pump, characterized in that the pump comprises a hydraulic-control device for controlling the angular position of the port plate and able automatically to bring about a change in angular position of the port plate when the direction of rotation of the pump is reversed, under the effect of the pressure differential between the two chambers of the head; and the hydraulic control device comprises a free piston mounted in a cylinder which is connected at each of its ends to one of the two chambers of the head.

Such a piston may be coupled to the port plate by any suitable means for driving it about its axis. According to one embodiment, the free piston is provided with a finger the end of which is engaged in a housing formed at the periphery of the port plate.

The invention will be better understood, and further objects, details, features and advantages thereof will become more clearly apparent during the course of the following description of one particular embodiment of the invention, given solely by way of nonlimiting illustration with reference to the attached drawings. In these drawings:

FIG. 1 is a view in longitudinal section of a pump with two directions of rotation and axial pistons borne by a rotary barrel and the rear end of which rests against a port plate.

FIG. 2 is an overall perspective view of the pump of FIG. 1 set up for rotating in the clockwise direction, viewed from the head end.

FIG. 3 is a view similar to FIG. 2, the pump being set up for rotating in the counterclockwise direction.

FIG. 4 is a perspective view in section on IV-IV of FIG. 1, showing a piston for the angular control of the port plate, said piston being in a first position corresponding to a rotation in counterclockwise direction.

FIG. 5 is a view similar to FIG. 4, the control piston being in its second position corresponding to rotation in the clockwise direction.

FIG. 6 is an enlarged perspective view in section on VI-VI of FIG. 4 of the pump head, illustrating the position of the components when the pump is rotating in the counterclockwise direction.

FIG. 7 is an enlarged perspective view in section on VII-VII of FIG. 5 of the pump head, illustrating the position of the components when the pump is rotating in the clockwise direction.

With reference to FIG. 1, which is a schematic axial section through the body of a variable-capacity pump, it may be seen that the pistons 1 of the pump bear against a swashplate 2 of which the information with respect to the axis of the pump is variable and controlled by two actuators 5 and 6 working in opposition. Because the pistons 1 of the pump bear against the swashplate 2, the inclination of the latter determines the stroke of the pistons and therefore the capacity of the pump. This type 20 of pump is referred to as a variable-displacement pump or a variable-capacity pump.

Each piston 1 slides in a cylinder la which bears against the port plate 3. The port plate 3 is a planar metal plate positioned between the rotary barrel 20 and the head 40 and pierced in the thickness direction with two kidney bean ports 22 and 23 (FIG. 7). The cylinders 1 a are borne by a rotary barrel 20, rotated by a shaft 21. Each cylinder is provided at its base with an orifice 4 which, when the barrel rotates, passes successively past the ports 22 and 23 (FIG. 7) of the port plate 3.

With reference to FIGS. 2 and 3, the head 40 of the pump is pierced with two similar ducts used alternately, one of them as a delivery duct 41 and the other as an intake duct. An intake flange 43 is mounted on the head 40 at the intake duct in FIGS. 2 and 3. The roles of two ducts are swapped over when the direction of rotation of the pump is reversed.

Automatic control of the angular position of the port plate will now be described. This is illustrated in FIGS. 4 to 7.

The port plate 3, the overall shape of which is that of a ring pierced with a central hole for the passage of the shaft 21 and having an essentially circular exterior contour, is mounted with freedom to rotate about the axis of the shaft 21 of the pump. The port plate 3, provided with its two identical ports 22 and 23 and mounted to rotate on the shaft 21 has, at its periphery 35, a U-shaped housing 36. Positioned in this housing 36 is the end of a finger 37 which is borne by a piston 38 which slides freely in its cylinder 39.

When liquid under pressure is introduced on one side of the cylinder 39, the piston 38 is driven until it comes into abutment against the opposite end of the cylinder 39 and is held there by the pressure. This movement of the piston 38 sets the port plate 3 in a rotational movement. The two opposite positions of abutment of the piston 38 define the two extreme angular positions of the port plate 3 (X and −X), which correspond, one of them to rotation in the clockwise direction (FIGS. 2, 5 and 7) and the other to the rotation in the counterclockwise direction (FIGS. 3, 4 and 6).

FIGS. 4 and 5 depict the pump head without the port plate 3 but with the intake orifice 48 and delivery orifice 41, which are alternately the right-hand orifice and the left-hand orifice of the pump head 40 according to the connections made in accordance with FIGS. 2 and 3. The cylinder 39 accommodating the free piston 38 is formed in the head 40, above two symmetric chambers 49 situated respectively facing the orifices 48 and 41.

Each of the two chambers 49 communicates via a passage 42 with a respective end of the cylinder 49. Thus, under the effect of the hydraulic pressure, the piston 38 is always kept in abutment at the end of the cylinder 39 that communicates with the chamber 49 situated at the low pressure, namely the intake side 48, and held away from that end of the cylinder 39 that communicates with the chamber 49 situated at the high pressure, namely the delivery side 41.

In FIG. 5, which corresponds to rotation of the pump in the clockwise direction, the orifice 48 is the intake orifice, the orifice 41 being the delivery one. The pressure arrives via the passage 42 on the left-hand side of the cylinder 39 and the piston 38 is pushed to the right until it comes into abutment against the right-hand end of the cylinder 39 where it is held by the pressure. This movement of the piston 38 causes the port plate 3 to pivot into the position depicted in FIG. 7 (angle X).

In FIG. 4, which corresponds to the rotation of the pump in the counterclockwise direction, the orifice 41 is the delivery orifice, the orifice 48 being the intake orifice. The pressure arrives via the passage 42 on the right-hand side of the cylinder 39 and the piston 38 is pushed to the left until it comes into abutment with the left-hand end of the cylinder 39 where it is held by the pressure. This movement of the piston 38 causes the port plate 3 to pivot into the position depicted in FIG. 6 (angle −X)

Thus, the change in the angular adjustment (X or −X) of the port plate 3 is performed with no intervention by the user other than connecting up the inlet and outlet orifices of the pump head 40.

Each end of the piston 38 is equipped with an elbowed internal passageway 50 connecting the end face of the piston 38 to the lateral face of the piston 38 in line with the passageway 42, so that the hydraulic pressure from the passageway 42 can be transmitted to the corresponding end of the cylinder 39 when the pump direction is reversed, thus causing the piston 38 to begin its axial movement.

As visible in FIGS. 4 and 5, supply ducts 51 and 52 formed in the head 40 lead from the cylinder 39 in the opposite direction to the passageways 42 toward the pump control unit (not depicted) to supply this control unit with hydraulic pressure. Each of the ducts 51 and 52 is fitted with a ball valve 53 which opens only on the side of the pump delivery pressure.

Although the invention has been described in conjunction with one particular embodiment it is quite clear that it is not in any way restricted thereto and that it comprises all technical equivalents of the means described and combinations thereof where these fall within the scope of the claimed invention.

The use of the verbs “comprise”, “have” or “include” and conjugated forms thereof does not exclude the presence of elements or steps other than those listed in a claim. The use of the indefinite article “a” or “an” for an element does not, unless mentioned otherwise, preclude there being a plurality of such elements.

In the claims, any reference sign between parentheses must not be interpreted as limiting the claim.

Claims

1. A hydraulic pump with two directions of rotation, comprising axial pistons (1) bearing against a swashplate (2), the pump comprising a rotary barrel (20) rotated by a shaft (21) and bearing cylinders (1a) in which the pistons (1) slide, the pump comprising a head (40) comprising two chambers (49) which are intended respectively to be connected to a high-pressure circuit and to a low-pressure circuit, the pump porting being performed by a port plate (3) defining an intake port and a delivery port, each cylinder (1a) being equipped at its base with an orifice (4) which passes in succession past the intake port and the delivery port as the barrel (20) rotates, the pump comprising a hydraulic-control device (38, 39, 42) for controlling the angular position of the port plate (3) and able automatically to bring about a change in angular position of the port plate when the direction of rotation of the pump is reversed, under the effect of the pressure differential between the two chambers (49) of the head (40),characterized in that the port plate (3) is produced in the form of a flat plate arranged between the rotary barrel (20) and the head (40), the port plate (3) having two identical ports (22, 23) passing through the thickness of the flat plate and arranged facing two chambers (49) of the head and able to constitute the intake port and the delivery port in each direction of rotation of the pump, said port plate (3) being able to pivot about an axis (21) so as to be able to occupy two angular positions according to the direction of rotation of the pump,the hydraulic control device comprising a free piston (38) mounted in a cylinder (39) which is connected at each of its ends to one of the two chambers (49) of the head (40).

2. The hydraulic pump as claimed in claim 1, in which the free piston (38) is provided with a finger (37) the end of which is engaged in a housing (36) formed at the periphery (35) of the port plate (3).

3. (canceled)