GB2128689A

GB2128689A - Piston pump

Info

Publication number: GB2128689A
Application number: GB08327918A
Authority: GB
Inventors: Anton Bader
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1982-10-20
Filing date: 1983-10-19
Publication date: 1984-05-02
Also published as: DE3334697A1; DE8229382U1; GB8327918D0; FR2534979A1; BR8305771A

Abstract

A piston pump, intended to act as a secondary pump driven from the secondary side of a drive transmission, for supplying the transmission with oil when the primary pump driven by a driving unit of the transmission is inoperative, has an arrangement for lifting the plunger (2) off its lifting element (4) under the influence of a control pressure produced by the primary pump. This arrangement consists in a piston chamber (14) disposed on the side of the plunger (2) opposite the suction/pressure chamber (10). This piston chamber (14) is connectible, via a check valve (16) which opens in the direction towards the piston chamber (14), with a pressure port (8) connectible both with the suction/pressure chambers (10) and with the oil circuit of the primary pump. <IMAGE>

Description

SPECIFICATION Piston pump The invention relates to piston pumps, particularly piston pumps of the kind having at least one spring-loaded plunger actuatable by means of a lifting element, a suction port, a pressure port, a common suction/pressure chamber, a check valve interposed between the suction/pressure chamber and the delivery port, and an inlet control member interposed between the suction/pressure chamber and the suction port.

Such piston pumps are used, for example, as secondary pumps for the lubrication and cooling of gearboxes or engines, in which case such pumps are driven, not from their primary side, but from their secondary side. In such an arrangement the secondary pump is driven from the gearbox output, as compared with the primary pump drive which is taken directly from the engine or drive unit. Secondary pumps are also used to produce an oil pressure for the engagement of a hydraulic coupling, in order, for example, to start an engine from a starter motor. Such operating conditions are encountered in motor vehicles with automatic transmissions, rail vehicles and ships.

Such operational conditions occur, for example, in a ship in which a propeller is driven by twin or multiple engines through a transmission unit. When the engines are shut down and the propeller is rotated by the slipstream, secondary units connected to the transmission are also driven.

Should these operational conditions prevail over a lengthly period of time the transmission must be supplied with lubricating oil and, sometimes, this lubricating oil must also be cooled.

A further instance of such operating conditions arises in a marine propulsion system where, for example, a ship is lying in waters with strong currents, so that the propeller is driven, imparting drive to secondary units connected to the propeller transmission. This could be prevented by means of a locking brake acting upon the propeller shaft. The technical complexity of such a brake is, however, considerable, necessitating a special control for the brake so that unintentional engagement thereof can be avoided when the transmission clutch is engaged.Moreover, if the ship is under tow the locking brake must not be actuated since the immobilized propeller would produce too great a resistance: in this case the propeller transmission, and secondary units connected thereto, must be lubricated and cooled by a secondary pump driven from the transmission, the primary engine-driven pump being inoperative.

In the known arrangements the primary pump and the secondary pump are always in operation when the primary and the secondary sides of the unit to be supplied are coupled together. In order to reduce the power input of the secondary pump under the aforementioned operating conditions provision is made in, for example, a marine propulsion system, for a change-over valve through which, when the primary pump is delivering, the oil delivered by the secondary pump flows back into the sump at virtually no pressure.

Such a pump will nevertheless be subject to wear through continuous use, even when no pressure is produced. The secondary pump must accordingly be designed to function for the entire life of the transmission, although it is operative only for a fraction of the entire period of use.

The object of the present invention is to provide a piston pump which can be used as a secondary pump, avoiding the drawbacks of known pumps, and ensuring a reliable supply of oil for the lubricating and cooling circuits of transmissions or other units, without undue performance losses in terms of the output required, and without unnecessary power consumption. On using two such piston pumps as primary and secondary pumps respectively it can be ensured that when the delivery pressure of the pumps fails, the other pump takes over delivery automatically.

Accordingly the present invention provides a piston pump of the kind specified, which further comprises an arrangement for lifting the plunger off the lifting element in dependence upon the presence of a control pressure produced outside the piston pump so that, when the control pressure is present the plunger is lifted off the lifting element.

When the piston pump according to the invention is used as a secondary pump, the plunger is lifted off the lifting element by the delivery pressure of the primary pump, so that the secondary pump ceases to be operated when the primary pump is operating. When the delivery -pressure of the primary pump fails, the plunger is forced by its spring into engagement with the lifting element and the secondary pump then operates to deliver oil through its pressure control member into the oil circuit of the unit to be supplied. In this connection it is clearly advantageous that sticking of the plunger or of the control members should not occur as a result of hardening of the oil after a lengthy period of operation. Thus after every shut-down of the main engine the plunger returns to its starting position.

Such an arrangement may appropriately be constructed by the provision of a pressure chamber which adjoins directly the front face of the plunger, adjacent the lifting element, and which can be primed through a check valve with oil under pressure from the primary pump.

A particular advantage of the piston pump according to the invention when used as a secondary pump is the cost-effective lightweight construction possible for the pump, since it has to work for only a fraction of the life of the unit to be supplied.

The invention will be further described, by way of example, with reference to the accompanying drawing, which is a diagrammatic longitudinai section through a pump according to one embodiment of the invention.

The pump has a housing 1 in which a plunger 2 slides to effect suction and delivery. The plunger 2 has on its front face a stem 3 which cooperates with a lifting element 4. The lifting element is, in this example, in the form of an eccentric or cam on the secondary side of a drive transmission. The plunger 2 is acted upon by a compression spring 5 which presses the stem 3 against the lifting element 4. The compression spring 5 bears at its end opposite the stem 3 against a stop ring 6 fixed in the pump housing 1.

The pump housing 1 has a suction port 7 and a pressure port 8. The suction port 7 communicates through an inlet plate valve 9 with a chamber 10 which contains the compression spring 5 and acts both as a suction and as a pressure chamber.

Between this suction/pressure chamber 10 and the pressure port 8 there is interposed a check valve 11 which opens in the direction towards the pressure port 8. The check valve 11 is contructed as a piston valve the control piston 12 of which is biased towards its closed position by a compression spring 1 3.

Adjacent the front face of the plunger 2, opposite the suction/pressure chamber 10, there is disposed a piston chamber 14 which can be connected with the pressure port 8 through connecting passages 1 so, 1 SB disposed in the pump housing 1. A check valve 1 6 controls the flow from the piston chamber 14 through the passages 1 5A, 1 5B. The check valve 1 6 is biased towards its closed position by a compression spring 1 7. In the illustrated embodiment the check valve 16 comprises a piston valve which closes off the connecting passage 1 SB when in its rest position. The check valve 1 6 may alternatively be constructed as a plate valve or as a ball valve.

In a typical example the delivery pressures of the secondary pump and of the primary pump (not shown) would be substantially in the ratio of 1:10.

The compression springs 1 3 and 1 7 of the two check valves 11 and 1 6 must therefore be tuned relatively to each other. The compression spring 13 must be able to move the control piston 12 into its closed position when the pump delivery stroke has ended and when the secondary pump is stationary. The force of the compression spring 1 7 must exceed the force exerted on the check valve 1 6 as a result of the delivery pressure of the secondary pump.

An accumulator chamber, not shown, is connected to the suction port 7, while an oil circuit (not shown) is connected to the pressure port 8 for supplying oil for the lubrication, cooling and switching of the unit to be supplied by the necessary secondary piston pump. Oil is supplied to this oil circuit by a primary pump - also not shown -- which is driven directly by an engine or motor acting as the primary drive unit.

In the rest condition the stem 3 is urged by the compression spring 5 into engagement with the lifting element 4. Upon starting the drive unit oil under pressure delivered by the primary pump is supplied to the pressure port 8. The check valve 1 6 is opened against the force of its compression spring 13 and the oil pressure of the primary pump acts in the piston chamber 14 on the plunger 2. The plunger 2, with the stem 3, is therefore moved against the force of its compression spring 5, so that the stem 3 rises off the lifting element, rendering the piston pump inoperative.

If subsequently the drive unit is shut down, the primary pump no longer delivers oil under pressure and the plunger 2 will be moved by its compression spring 5 to return the stem 3 into engagement with the lifting element 4, rendering the piston pump operative. For the rapid emptying of the piston chamber 14 there is interposed between the latter and the transmission housing adjacent the pump housing 1 a bleeding bore or vent 18. The bleeding bore 18 also prevents the formation of an oil or air cushion in the piston chamber 14 when the secondary pump is delivering; such a cushion could be lifted by the plunger 2. The oil loss occurring through the bleeding bore 18 when the primary pump is delivering is of no importance when the considerable delivery volume of the primary pump is taken into account.

If the transmission and thereby the lifting element 4 are driven from the secondary side, the plunger 2 draws oil from the suction port 7 through the plate valve 9. On the compression stroke of the plunger 2 the pressure in the suction/pressure chamber 10 builds up to the desired working pressure, whereupon the control piston 12 is moved against the force of the spring 1 3. This brings the suction/pressure chamber 10 into communication with the pressure port 8. The connection from the pressure port 8 to the piston chamber 14 is interrupted under these conditions of operation by the closed check valve 1 6. The piston pump, therefore, under these operation conditions, draws oil from the suction port 7 and delivers it under pressure through the pressure port 8 into the oil circuit of the unit to be supplied.

Claims

1. A piston pump, particularly a piston pump, having at least one spring-loaded plunger actuatable by means of a lifting element, a suction port, a pressure port, a common suction/pressure chamber, a check valve interposed between the suction/pressure chamber and the delivery port, and an inlet control member interposed between the suction/pressure chamber and the suction port, and further comprising an arrangement for lifting the plunger off the lifting element in dependence upon the presence of a control pressure produced outside the piston pump so that, when the control pressure is present the plunger is lifted off the lifting element.

2. A piston pump according to Claim 1, in which a piston chamber is disposed on the side of the plunger opposite the suction/pressure chamber, the piston chamber being connected with the pressure port through a check valve which opens in the direction towards the piston chamber.

3. A piston pump according to Claim 2, in which respective check valves are interposed between the suction/pressure chamber and the pressure port and between the pressure port and the pressure chamber, each check valve being biased towards the closed position by a respective spring.

4. A piston pump according to Claim 2 or 3, in which.the check valve interposed between the suction/pressure chamber and the pressure port is a piston valve.

5. A piston pump according to Claim 4, in which the force of the spring acting on the check valve interposed between the pressure port and the piston chamber is greater than the force on the said check valve resulting from the delivery pressure of the piston pump.

6. A piston pump substantially as herein described with reference to and as shown in the accompanying drawing.