The present invention refers to a mechanical variable displacement lubricant pump for providing pressurized lubricant for an internal combustion engine.

The mechanical pump is directly driven by the engine and comprises a pump rotor with radially siidable vanes rotating within a radially shiftable control ring, whereby the control ring is pushed by a plunger pushing the control ring to a high eccentricity direction and thereby to high pumping volume direction. The plunger is shiftably arranged within a control chamber. The pump comprises a pressure control system for controlling the discharge pressure of the pressurized lubricant leaving the pump. The pump's discharge pressure is controlled by controlling the position of the shiftable control ring which is controlled by the pressure in the hydraulic control chamber. By moving the control ring plunger the eccentricity of the control ring is decreased or increased, so that the discharge pressure can be controlled.

WO 2005/068838 Al discloses a variable displacement lubricant pump with an opening in the lateral control chamber wall. The opening is connected to atmospheric pressure whereby an electric valve is provided to open or close the connection of the iateral wall opening to the atmospheric pressure. The valve is controlled by an electronic temperature sensor, so that the eccentricity of the control ring can be limited to a maximum eccentricity if the lubricant temperature is below or above a temperature limit. WO 2010/146087 A2 discloses a mechanical variable displacement pump with an opening in the lateral control chamber wall. The opening is provided in a slider which is shiftable in a radial direction so that the radial 5 position of the opening can be varied within a particular range to vary the maximum eccentricity of the control ring. The radial position of the opening is controlled by a temperature sensitive mechanical actuator.

It is an object of the invention to provide a variable displacement lubricant o pump with a variable maximum eccentricity of the control ring with a simple construction.

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

The variable displacement lubricant pump of claim 1 is provided with a first and a second eccentricity limiting opening in the lateral control chamber wall. The eccentricity limiting openings can be - referring to the radial direction which is the direction of the plunger movement path - being arranged overlapping or can be arranged with a radial distance to each other so that the eccentricity limiting openings do not overlap in lateral projection. Additionally, an eccentricity limiting control system is provided to connect or disconnect the eccentricity limiting openings to atmospheric pressure dependent on the lubricant temperature T. The eccentricity limiting control system is provided with a valve arrangement downstream of the eccentricity limiting openings and allows to selectively control the connection of the eccentricity limiting openings to atmospheric pressure. With this simple arrangement two different maximum eccentricities of the control ring can be chosen to adapt the maximum pump rate to the lubricant temperature T. According to a preferred embodiment, a third eccentricity limiting opening is provided In the side wall of the control chamber to allow a finer adaptation of the maximum eccentricity and the maximum pump rate to the lubricant temperature T, Providing two or more eccentricity limiting openings which are individually switchable allows an individual programming of the maximum eccentricity limit which is not necessarily linear with the lubricant temperature T.

According to a preferred embodiment, the eccentricity limiting control system is provided with at least one bimetal element causing opening or closing of the eccentricity limiting openings. A bimetal element is a simple, reliable and cost effective temperature-sensitive actuator. The bimetal element does not necessarily cause a direct closing of the eccentricity limiting openings but can be provided downstream of the eccentricity limiting openings to block or unblock any flow through the respective eccentricity limiting opening.

Preferably, every eccentricity limiting opening is provided with a separate bimetal element which directly can close the respective conduit between the eccentricity limiting opening and the atmospheric pressure in the closed position of the bimetal element. The bimetal element serves as a valve body which directly closes a valve channel. The respective bimetal valve elements have different switching temperatures TS so that the maximum eccentricity can be adapted dependent on the lubricant temperature T in relation to the different switching temperatures. This arrangement allows with simple means a non-linear programming of the maximum eccentricity dependent on the lubricant temperature T.

According to a preferred embodiment of the invention, the eccentricity limiting control system can be provided with a separate valve plunger which is directly actuated by the bimetal element. The plunger opens and closes the connection between the respective eccentricity limiting openings and the atmospheric pressure. Even if the bimetal element has a more or less linear temperature/way-characteristics, the use of a valve 5 plunger actuated by the bimetal element allows to individually define and program a non-linear control of the maximum eccentricity limit dependent on the lubricant temperature T.

Preferably, the valve plunger is preloaded by a preload element into its o closed position wherein all eccentricity limiting openings are closed. This arrangement makes the eccentricity limiting control system fail-safe if the bimetal element should not work properly or break.

Preferably, the switching temperatures TS of the eccentricity limiting ; control system are between 0°C and 100°C. The switching temperatures TS can be, for example, 0°C, 20°C and/or 90°C.

The following is a detailed description of an embodiment of the invention with reference to the drawings, wherein:

figure 1 shows a schematic representation of a variable displacement lubricant pump including an eccentricity limiting control system, the pump being arranged in a lubricant circuit including an internal combustion engine,

figure 2 shows a first embodiment of an eccentricity limiting control system,

figure 3 shows a second embodiment of an eccentricity limiting control system, and

fig , 4 shows another embodiment of an alternative arrangement of three overlapping eccentricity limiting openings. Figure 1 shows a variable displacement lubricant pump 10 as a part of a pumping system 100 for supplying an internal combustion engine 70 with pressurized lubricant. From the engine 70 the lubricant flows back via a 5 flow-back conduit 86 to a lubricant tank 50 with more or less atmospheric pressure.

The pump 10 comprises a pump housing 11 having a cavity 16 in which a radially shiftable control ring 12 translates. The control ring 12 encircles a o pump rotor 13 which is provided with numerous radially slidable vanes 14, whereby the vanes 14 are rotating inside the shiftable control ring 12. The pump housing 11 comprises two pump side walls 15 of which one is not shown in fig. 1 to allow to see the inside of the pump 10. The pump side walls 15, the vanes 14, the pump rotor 13 and the control ring 12 define five rotating pump chambers 17. One of the side walls 15 is provided with a pump chamber inlet opening 18 and with a separate pump chamber outlet opening 19.

The control ring 12 is provided with a first plunger 24 housed in part in a first hydraulic control chamber 25 and with a second plunger 22 housed in part in a second hydraulic control chamber 23 opposite to the first control chamber 25.

A pretensioned spring 28 inside the first control chamber 25 exerts a pushing force to the first plunger 24. Both control chambers 25, 23 are formed inside and by the pump housing 11. The pump housing 11 also comprises a pump intake port 20 for sucking the lubricant from a lubricant tank 50 and a pump outlet port 21 for feeding lubricant with a discharge pressure to the engine 70. A conduit 80 extends from the pump outlet port 21 to supply the engine 70. The lubricant, which is supplied to the engine 70, is conducted to the second control chamber 23 via a pressure conduit 81, and the lubricant is fed to the first pressure control chamber 25 via pressure conduits 82, 87, 5 More specifically, the lubricant in pressure conduit 82 is finally fed to the first pressure control chamber 25 via a conduit 87 through a pressure throttle valve 67 in which a calibrated pressure drop occurs as the lubricant flows through.

l o The pressure conduits 82, 88 are connected to a control port 61 of a first pressure control valve 60 by a conduit 88. The first pressure control valve 60 comprises a cylinder 65 housing a piston 61. More specifically, the piston 61 comprises a first portion 62 and a second portion 64 connected to each other by a rod 63. The piston portions 62 and 64 are in cross5 section equal to cross section of the cylinder 65, whereas the rod 63 is smaller in cross section than the cylinder 65. The cylinder 65 is provided with an inlet port 66 connected hydraulicaily to the first pressure control chamber 25 by a conduit 83 and is provided with an outlet port which is hydraulicaily connected to the lubricant tank 50 by a conduit 84. Another0 conduit 88 transfers the discharge pressure in conduit 82 to the front surface of the first portion 62 of piston 61. The dashed line in figure 1 shows the situation when the inlet port 66 of the first pressure control valve 60 is closed by the second portion 64 of the piston 61. 5 In figure 2, the first embodiment of the eccentricity limiting control system 30 is shown in more detail. The lateral control chamber wall 27 is provided with the first eccentricity limiting opening 26, the second eccentricity limiting opening 31 and the third eccentricity limiting opening 32. The three eccentricity limiting openings 26, 31, 32 are arranged with a radial distance to each other and do not overlap. The radial direction is the direction in which the control ring plunger 24 is moving. The eccentricity limiting control system 30 is provided with three independent bimetal elements 34,35,36 which define separate valve bodies connecting or disconnecting the eccentricity limiting openings 26, 31, 32 with the atmospheric pressure in the lubricant tank 50 via a lubricant channel 89. The bimetal elements 34,35,36 are bimetal strip bodies which are in two dimensions dished so that they have a sharp switching characteristic and a relatively low hysteresis. The switching temperature TS1 of the first bimetal element 34 is about 90°C, the switching temperature TS2 of the second bimetal element 35 is about 20°C and the switching temperature TS3 of the third bimetal element 36 is about 0°C. As soon as the lubricant temperature T is below the respective switching temperature TS, the respective bimetal element 34, 35, 36 switches into its open position as shown in figure 2. As a consequence, the maximum eccentricity is the lowest at a lubricant temperature T below 0°C.

In figure 3, a second embodiment of an eccentricity limiting control system 30' is shown in more detail. In this embodiment, a single bimetal actuator element 42 is provided to directly shift a valve plunger 44 more or less linear with the lubricant temperature T in radial direction. The valve plunger 44 is radially moving inside a valve cylinder 46. The valve plunger 44 is provided with a circular ring passage 45 which allows the lubricant to flow from one of the eccentricity limiting openings 26,31,32 through corresponding lubricant inlet openings 37, 38, 39 at the inner wall of the valve cylinder 46 to an outlet recess 49 of the valve cylinder, if the circular ring passage 45 is aligned with one of the lubricant inlet openings 37, 38, 39. The form and the axial extension of the three lubricant inlet openings 37, 38, 39 can be different from each other to define different control characteristics. The outlet recess 49 Is connected to the atmospheric pressure of the lubricant tank 50. The valve plunger 44 is pretensioned by a preload element 48 into an axial closing position in which none of the eccentricity limiting openings 26, 31,

32 is connected to the lubricant tank 50. The preload element 48 can be realized as a coil spring.

In figure 4 an alternative arrangement of eccentricity openings 26', 31', 32' is shown, which are arranged overlapping with reference to the radial movement path of the control ring 12.