WO2018196991A1

WO2018196991A1 - A variable displacement liquid pump

Info

Publication number: WO2018196991A1
Application number: PCT/EP2017/060163
Authority: WO
Inventors: Bernardo Celata; Fabio GUGLIELMO; Andrea MALOTTI; Giuseppe Rossi
Original assignee: Pierburg Pump Technology Gmbh
Priority date: 2017-04-28
Filing date: 2017-04-28
Publication date: 2018-11-01
Also published as: DE112017007483B4; DE112017007483T5

Abstract

The disclosure refers to a variable displacement liquid pump (10) for pumping pressurized liquid, comprising a pump rotor (44) with radially slidable vanes (46) rotating in a shiftable control ring (42), a pressure control system for controlling the discharge pressure of the pressurized liquid. The control system comprises a pressure control chamber (54) for pushing the control ring (42) into high pumping volume direction, and a pressure control valve (78) controlling the pressure in the pressure control chamber (54). The pressure control valve (78) comprises a control plunger (86), which is movable between a first position and a second position, an input pressure plunger (90) being charged with an actual pressure (PA) in an input pressure chamber (88), wherein the input pressure plunger (90) is mechanically connected with the control plunger (86), and a control valve spring (92) preloading the control plunger (86) into the second position against the pressure in the input pressure chamber (88). The control system further comprises a separate damping unit (100), comprising a piston (108), which is moving in a separate damping chamber (112) and which is separating the damping chamber (112) in two chamber parts (112a, 112b), which are fluidically connected to each other by a damping channel (118; 120), wherein the piston (108) is stiffly connected to the control plunger (86).

Description

A variable displacement liquid pump

The present invention refers to a variable displacement liquid pump for pumping pressurized liquid.

The variable displacement liquid pump Is mechanically driven by the engine and comprises a pump rotor with radially slidabie vanes rotating in a shiftable control ring, whereby the control ring is pushed by a pressure control chamber into high pumping volume direction. The pump is provided with a pressure control system for controlling the discharge pressure of the pressurized liquid at the pump outlet port. The pump is provided with a pressure control valve controlling the pressure in the pressure control chamber. The pressure control valve comprises a plunger which is preloaded by a control valve spring.

According to the present invention the term "radially slidabie vanes" also comprises radially slidabie pendulums vanes, wherein the orientation of the vanes has not to be understood as to be precisely radial but can have a constant or variable component in a radial direction.

WO 2014/187503 Al describes a variable lubricant pump, which comprises a pump rotor with radially slidabie vanes, wherein the pump rotor is rotating in a shiftable control ring. The control ring is shiftable between a high pumping volume position and a low pumping volume position. The pump comprises a pressure control system comprising a pressure control chamber for pushing the control ring to a high pumping volume position. The control system further comprises a pressure control valve controlling the pressure In the pressure control chamber. A control piston Is slidably provided in the control valve to open or close a discharge port of the pressure control chamber to thereby control the pressure in the pressure control chamber. The control piston is preloaded by a spring at one axial end.

Advantageously, the lubricant pressure at the engine lubricant outlet is used as the control variable to be controlled by the pressure control circuit. This concept guarantees a sufficient lubricant pressure within the engine. However, as the actual lubricant pressure is picked up at the engine lubricant outlet, considerable time makes the control loop more susceptible to pressure oscillations.

The variable displacement fluid pump according to the state of the art shows oscillations of the lubricant outlet pressure in the range of 5 to 50 Hz. The oscillations of the outlet pressure are around an average pressure value which is at high rotational speed below the adjusted pressure value. As a consequence the average pressure value is lower than expected at high rotational speed.

The object of the present invention is to provide a variable displacement liquid pump with an improved pressure stability.

This object is solved with a variable displacement liquid pump with the features of claim 1.

According to the present invention the variable displacement liquid pump is provided with a separate damping unit. Accordingly, the damping unit is not integrated in the pressure control valve but is provided as a separate unit of the pressure control system. The damping unit comprises a piston, which is moving in a separate damping chamber and which is separating the damping chamber in two chamber parts, which are fluidically connected to each other by a damping channel. A pressure difference between both chamber parts is balanced via the damping channel. The temporal behavior of balancing the pressure difference between the chamber parts depends on the geometry and the design of the damping channel and on the damping fluid. As a consequence the temporal behaviour can be influenced by the geometry and the design of the damping channel and the nature and viscosity of the damping fluid, High frequency movements of the piston in the damping chamber therefore are damped. The piston of the damping unit is stiffly connected to the control plunger so that also the movement of the control plunger is damped. High frequency oscillations of the control plunger, resulting In an oscillating outlet pressure, therefore are damped and reduced. As a consequence the variable displacement liquid pump has a higher pressure stability at high rotational speed of the pump.

According to a preferred embodiment of the present invention the liquid pump is a lubricant pump.

Preferably the control valve spring Is provided within the pressure control valve. With this arrangement, the damping unit can be easily added to an existing pressure control valve.

In an alternative embodiment the control valve spring is provided in the damping chamber. The control valve spring thereby is provided in one chamber part, preferably the chamber part located at a free axial end of the damping chamber. As a consequence an easy access to the control valve spring from the free axial end is possible. The control valve spring therefore can be easily exchanged in order to e.g. adapt the spring constant.

In a preferred embodiment of the present invention a damping fluid in the damping chamber is the pumping liquid. Accordingly, no separate damping fluid Is required.

According to a further preferred embodiment, a damping fluid in the damping chamber is oil. In contrast to gas, oil is not compressible so that no further spring effect is provided by using oil as a damping fluid. Further, oil has a high boiling temperature so that oil has a broad working range.

According to an alternative embodiment a damping fluid in the damping chamber is air. The viscosity of air slightly increases with increasing temperature so that, in contrast to liquids, the damping effect does not decrease with increasing temperature.

In a further alternative embodiment a damping fluid in the damping chamber is grease, Grease is a fluid having a high viscosity so that a high damping effect can be achieved.

Preferably, the piston and the control plunger are mechanically connected to each other by a stiff rod. A rod is a simple structural element for stiffly connecting the control plunger and the piston.

According to a preferred embodiment of the invention, the damping channel is provided as an axial bore in the piston. The piston can be easily provided with a bore so that manufacturing is easy. Further, the bore can be adapted to different viscosities of the damping fluid by providing an adapted geometry of the bore.

In a further preferred embodiment of the present invention the damping channel is provided as radial clearance between the piston and a damping chamber wall. The radial clearance can be provided by choosing an outer radius for the piston, which is significantly smaller than an inner radius of the damping chamber so that a gap between the damping chamber wall and the piston is defined. A sealing provided at the outer circumferential surface of the piston is not necessary. Further, no friction appears.

In a preferred embodiment of the present invention the thermal expansion coefficient of the piston and of the housing of the damping chamber differ from each other so that the radial clearance varies with varying temperature. As the viscosity of the damping fluid like e.g. oil decreases with increasing temperature it is possible to decrease the radial clearance so as to adapt the radial clearance to the viscosity of the damping oil. As a consequence, a substantially stable damping effect over a wide temperature range is realized.

Preferably, the discharge port Is directly connected to a liquid tank.

The control ring Is preferably pretensioned by a spring into the high pumping volume direction. The spring is an antagonist of a pilot chamber and is co-acting with the control chamber.

Preferably, the actual pressure Is the engines lubricant outlet pressure at the engine lubricant outlet. The controlled pressure Is not the pump outlet pressure but the lubricant's engine outlet pressure. It is thereby avoided that the lubricant pressure in the engine falls under a certain value. By using the lubricant pressure at the engine lubricant outlet as the actual pressure a certain dead time in the control circuit is generated. As a consequence the control loop usually is more susceptible to lubricant pressure oscillations. With the present invention these oscillations of the lubricant pressure in the engine are reduced.

Further advantages will become evident by the following detailed description of the embodiments of the present invention in combination with the drawings, which show:

Figure 1 shows a first embodiment of the variable displacement fluid pump in an open state of the pressure control valve,

Figure 2 shows the embodiment according to Figure 1 in a closed state of the pressure control valve,

Figure 3 shows a second embodiment of the variable displacement fluid pump in an open state of the pressure control valve, and Figure 4 shows an enlarged view of the damping unit according to a third embodiment of the variable displacement fluid pump.

Figure 1 shows a schematic representation of a variable fluid pump 10. The variable fluid pump 10 is a displacement lubricant pump 10 for supplying an internal combustion engine 12 with pressurized lubricant. The pump 10 comprises a pumping unit 14, which Is mechanically driven by the engine 12. The pumping unit 14 comprises a housing 40 having a cavity 41 In which a control ring 42 translates, which encircles a pump rotor 44. The pump rotor 44 is provided with numerous radially slidable vanes 46, whereby the vanes 46 are rotating inside the control ring 42. The control ring 42 is radially shiftable so that the eccentricity of the control ring 42 with respect to a rotation axis 47 of the pump rotor 44 can be set to thereby shift the control ring 42 between a low pumping volume position at low eccentricity position and a high pumping volume position at high eccentricity position.

The housing 40 is closed by two side walls 48 of which one is not shown in the drawings. The side walls 48, the vanes 46, the pump rotor 44 and the control ring 42 define five rotating pump chambers 50.

The control ring 42 is provided with a first control ring plunger 52 housed in a pressure control chamber 54 and Is provided with a second control ring plunger 55 housed in a pilot chamber 56. The pilot chamber 56 is provided opposite to the pressure control chamber 54, The control ring 42 and the plungers 52, 55 are one single integral part.

A pretensioned control chamber spring 57 inside the pressure control chamber 54 exerts a pushing force to the first control ring plunger 52. The pressure control chamber 54 is defined by the housing 40. The housing 40 also comprises an inlet port 58 for sucking the lubricant from a lubricant tank 60 and an outlet port 62 for feeding lubricant with a discharge pressure to the engine 12. An engine supply conduit 64 extends from the outlet port 62 to the engine 12 to supply the engine 12 with pressurized lubricant.

An actual pressure PA at an engine lubricant outlet 65 Is transmitted to the pressure control chamber 54 via a conduit 66, 67, 68 and through a pressure throttle valve 70 in which a calibrated pressure drop occurs as the lubricant flows through. The actual pressure PA is also transmitted to the pilot chamber 56 via a pilot chamber conduit 71.

The actual pressure PA is also transmitted via a conduit 66, 72 to an Input pressure port 76 of a pressure control valve 78. The pressure control valve 78 keeps the actual pressure PA at the engine lubricant outlet 65 at a constant nominal pressure value independently of the rotational speed of the engine 12 by regulating the radial position of the control ring 42. The radial position of the control ring 42 is controlled by controlling the pressure in the pressure control chamber 54.

The pressure in the pressure control chamber 54 is regulated by controlling a lubricant discharge of an outlet port 79 of the pressure control chamber 54 via a conduit 81 to a control port 83 provided in a cylinder wall 84 of a pressure control valve housing 85.

Dependent on the axial position of a control plunger 86 in the pressure control valve housing 85, a discharge port 87 is opened or closed. The position of the control plunger 86 is dependent on a pressure in an input pressure chamber 88, which pressure thereby is charged to an input pressure plunger 90 and on a preload applied to the control plunger 86 by a control valve spring 92. The control valve spring 92 acts against the pressure in the input pressure chamber 88. The input pressure plunger 90 is mechanically directly connected with the control plunger 86 so that a high pressure in the input pressure chamber 88 forces the control plunger 86 i an opened position with respect to the discharge port 87. Figure 1 shows a position of the control plunger 86 in which the discharge port 87 is open so that the lubricant is discharged via a discharge conduit 93 to the lubricant tank 60.

In order to damp small pressure variations of the variable displacement lubricant pump 10 the discharge pressure of the pressurized lubricant is further controlled by a damping unit 100, which is arranged on one axial end of the control valve 78. The control valve 78 is fluidically separated from the damping unit 100 by a static separation wall 104. The damping unit 100 comprises a piston 108, which is stiffly connected to the control plunger 86 via a rod 110 and which is moving in a separate damping chamber 112 formed by a housing 113 of the damping unit 100. The damping piston 108 separates the damping chamber 112 filled with lubricant liquid as a damping fluid in two chamber parts 112a, 112b. Both chamber parts 112a, 112b are fluidically connected to each other by a damping channel 118 provided as a bore in the piston 108. When the pressure in the input pressure chamber 88 changes the damping piston 108 is forced in the direction of one of the two chamber parts 112a, 112b, so that the damping fluid is flowing from one chamber part 112a to the other chamber part 112b. As the damping fluid slowly flows through the damping channel 118 from one chamber part 112a to the other chamber part 112b the movement of the piston 108 and therewith of the control plunger 86 is damped. Accordingly, small high frequency pressure variations do not have a strong impact on the movement of the control plunger 86. As a consequence a smoother outlet pressure of the pump is realized, even at high rotational speed of the pump rotor 44.

Figure 2 shows the variable displacement lubricant pump 10 according to Figure 1 in a closed state of the pressure control valve 78. In this state the control valve spring 92 has moved the control plunger 86 in the direction of the input pressure chamber 88. The control plunger 86 thereby closes the discharge port 87 so that no lubricant is discharged from the control chamber 54 to the lubricant tank 60. Figure 3 shows a second embodiment of the variable displacement lubricant pump 10 in an open state of the pressure control valve 78. The control valve spring 92 is provided in the distal chamber part 112b of the damping unit 100, so that the control valve spring 92 preloads the damping piston 108 in a direction to the input pressure chamber 88.

Figure 4 shows an enlarged view of the damping unit 100 according to a third embodiment of the variable displacement lubricant pump 10. The damping channel 120 is provided as a radial clearance between the piston 108 and a chamber wall 124 of the damping chamber 112.

It should be clear that the Invention is not limited to the described embodiment. In particular there are various structural changes and modifications possible falling under the scope of the present invention. For example the actual pressure also can be measured directly at the outlet port of the pump.

Reference signs

10 variable displacement lubricant pump

12 combustion engine

14 pumping unit

5 40 housing

41 cavity

42 control ring

44 pump rotor

46 vanes

10 47 rotation axis

48 side wall

50 pump chambers

52 first control ring plunger

54 pressure control chamber

15 55 second control ring plunger

56 pilot chamber

57 control chamber spring

58 inlet port

60 lubricant tank

20 62 outlet port

64 engine supply conduit

65 engine lubricant outlet

66 conduit

67 conduit

25 68 conduit

70 pressure throttle valve

71 pilot chamber conduit

72 conduit

76 input pressure port

30 78 pressure control valve

79 outlet port 81 conduit

83 control port

84 cylinder wall

85 pressure control valve housing

5 86 control plunger

87 discharge port

88 input pressure chamber

90 Input pressure plunger

92 control valve spring

10 ioo damping unit

104 separation wall

108 piston

110 rod

112 damping chamber

15 112a chamber part

112b chamber part

113 housing

118 damping channel

120 damping channel

20 124 chamber wall

PA actual pressure

Claims

C L A I S

1. A variable displacement liquid pump (10) mechanically driven by an internal combustion engine (12) for pumping pressurized liquid comprising :

- a pump rotor (44) with radially slidable vanes (46) rotating in a shiftable control ring (42) being radially shiftable or pivotable with respect to the rotor axis (47) between a high pumping volume position and a low pumping volume position, and

- a pressure control system for controlling the discharge pressure of the pressurized liquid, the control system comprising :

- a pressure control chamber (54) for pushing the control ring (42) into high pumping volume direction, and

- a pressure control valve (78) controlling the pressure in the pressure control chamber (54), the pressure control valve (78) comprising :

- a control plunger (86), which is movable between a first position, where a control port (83) in a cylinder wall (84) of the pressure control valve (78) is connected to a discharge port (87) in the cylinder wall (84) and a second position where the discharge port

(87) is closed, whereby the control port (83) is connected with an outlet port (79) of the pressure control chamber (54),

- an input pressure plunger (90) being charged with an actual pressure (PA) In an input pressure chamber

(88) , wherein the input pressure plunger (90) is mechanically connected with the control plunger (86), and - a control valve spring (92) preloading the control plunger (86) into the second position against the pressure in the input pressure chamber (88); and

- a separate damping unit (100), comprising a piston (108), which is moving in a separate damping chamber (112) and which is separating the damping chamber (112) In two chamber parts (112a, 112b), which are fluidical!y connected to each other by a damping channel (118; 120), wherein the piston (108) is stiffly connected to the control plunger (86).

2. The variable displacement liquid pump (10) according to claim 1, characterized in that the liquid pump (10) is a lubricant pump,

3. The variable displacement liquid pump (10) according to claim 1 or 2, characterized in that the control valve spring (92) is provided in the pressure control valve (78).

4. The variable displacement liquid pump (10) according to claim 1 or 2, characterized in that the control valve spring (92) is provided in the damping chamber (112).

5. The variable displacement liquid pump (10) of one of the preceding claims, characterized in that a damping fluid In the damping chamber (112) is the pumping liquid.

6. The variable displacement liquid pump (10) of one of the preceding claims, characterized in that a damping fluid in the damping chamber (112) is oil.

7. The variable displacement liquid pump (10) according to one of claims 1 to 5, characterized In that a damping fluid in the damping chamber (112) is air.

8. The variable displacement liquid pump (10) according to one of claims 1 to 5, characterized in that a damping fluid In the damping chamber (112) is grease.

9. The variable displacement liquid pump (10) of one of the preceding claims, characterized in that the piston (108) and the control plunger (86) are mechanically connected to each other by a rod (110).

10. The variable displacement liquid pump (10) of one of the preceding claims, characterized in that the damping channel (118) is provided as a bore in the piston (108).

11. The variable displacement liquid pump (10) according to one of claims 1 to 9, characterized in that the damping channel (120) Is provided as radial clearance between the piston (108) and a damping chamber wall (124).

12. The variable displacement liquid pump (10) according to claim 11, characterized in that the thermal expansion coefficient of the piston (108) and a housing (113) of the damping chamber (112) differ to each other so that the radial clearance (120) varies with varying temperature.

13. The variable displacement liquid pump (10) of one of the preceding claims, characterized in that the discharge port (87) is directly connected to a liquid tank (60). The variable displacement lubricant pump (10) of one of the preceding claims, characterized In that the control ring (42) Is pretensioned by a spring (57) into the high pumping volume direction.

The variable displacement lubricant pump (10) of one of the preceding claims, characterized in that the actual pressure (PA) is the engines (12) lubricant outlet pressure.