Variable displacement lubricant pump

A variable displacement lubricant pump providing a pressurized lubricant for an engine includes a control ring. A pump housing comprises a pump rotor with radially slidable vanes which rotate in the control ring. A pressure control chamber pushes the control ring into a low pumping volume direction against a force of a flexible pretensioning element. The pressure control chamber is connected with a pump outlet port via a first pressure conduit. A pretension control unit adjusts discharge pressures of the pressurized lubricant. The pretension control unit comprises a pretension cylinder with a plunger and an outlet opening arranged in a cylinder wall. The plunger is axially moveable and supports the flexible pretensioning element to push the control ring into a high pumping volume direction. The pretension cylinder is connected with the pump outlet port via a second pressure conduit. The outlet opening is connectable to a low-pressure via an electrical pretension control valve.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2010/068128, filed on Nov. 24, 2010. The International Application was published in English on May 31, 2012 as WO 2012/069083 A1 under PCT Article 21(2).

FIELD

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

BACKGROUND

Variable displacement pumps have previously been described. These pumps usually comprise a pump housing with a pump rotor, whereby the pump rotor is provided with radially slidable vanes rotating in a shiftable control ring. The control ring is pushed into a low or a high pumping volume direction depending on the rotational speed of the engine. If the rotational speed increases, the control ring is pushed into a low pumping volume direction; if the rotational speed decreases, the control ring is pushed into a high pumping volume direction so that the lubricant can be pressurized at a more or less constant level, independent of the rotational speed of the pump rotor or engine.

The lubricant pressure requirement is, however, dependent on the working conditions of the engine. The lubricant pressure requirement is lower at low rotational speeds and higher at high rotational speeds of the engine. A device with a control system which provides one level of pressure of the pressurized lubricant is described in WO 2005/026553 A1.

SUMMARY

An aspect of the present invention is to provide a compact variable displacement lubricant pump with more than one lubricant pressure level.

In an embodiment, the present invention provides a variable displacement lubricant pump for providing a pressurized lubricant for an internal combustion engine which includes a control ring configured to be shiftable. A pump housing comprises a pump rotor. The pump rotor comprises radially slidable vanes which are configured to rotate in the control ring. A first pressure conduit. A second pressure conduit. A pump outlet port. A pressure control chamber is configured to push the control ring into a low pumping volume direction against a force of a flexible pretensioning element. The pressure control chamber is connected with the pump outlet port via the first pressure conduit. A pretension control unit is configured to adjust at least one discharge pressure of the pressurized lubricant. The pretension control unit comprises a pretension cylinder comprising a plunger and an outlet opening arranged in a cylinder wall. The plunger is arranged so as to be axially moveable and to support the flexible pretensioning element so as to push the control ring into a high pumping volume direction. The pretension cylinder is connected with the pump outlet port via the second pressure conduit. An electrical pretension control valve. The outlet opening is connectable to a low-pressure via the electrical pretension control valve.

DETAILED DESCRIPTION

The variable displacement lubricant pump for providing a pressurized lubricant for an internal combustion engine comprises a pump housing with a pump rotor, whereby the pump rotor is provided with numerous radially slidable vanes rotating in a shiftable control ring, a pressure control chamber which pushes the control ring into a low pumping volume direction against the force of a flexible pretensioning element. The pressure control chamber is connected with a pump outlet port via a first pressure conduit. The pump further comprises a pretension cylinder, wherein a plunger is provided to be axially moveable. The pretension cylinder is integrated into the pump housing or can alternatively be a separate part which is fixed to the pump housing. The plunger supports the pretensioning element so that the control ring is pushed into a high pumping volume direction. The pretension cylinder is connected with the pump outlet port via a second pressure conduit. The pretension cylinder is provided with an outlet opening in a cylinder wall, whereby the outlet opening is connectable to a low-pressure by an electrical pretension control valve. Both the second pressure conduit inlet of the pretension cylinder and the outlet opening are arranged axially distally of the plunger in its low pressure position so that the plunger never covers the second pressure conduit inlet of the pretension cylinder and/or the outlet opening.

The plunger is switchable between two different positions. If the electrical pretension control valve opens the outlet opening, the pretension cylinder is connected to the low-pressure, for example, to atmospheric pressure. The plunger is in the low pressure position. The pump provides the pressurized lubricant, for example, with a pressure of approximately 2.5 bar. If the electrical pretension control valve closes the outlet opening, the pressure increases in the pretension cylinder so that the plunger is moved into the high pressure position. As a result, the equilibrium position of the control ring is moved into the high pressure position so that the pump provides the pressurized lubricant, for example, with a pressure of approximately 4.5 bar. In both pressure positions, the control ring can be pushed into a low or a high pumping volume direction so that both pressure levels are more or less constant, independent of the rotational speed of the pump rotor or the engine driving the pump.

The pump therefore provides two different lubricant pressure levels with a simple mechanical system, namely, with a pretension cylinder with an axially moveable plunger supporting a pretension element which pushes the control ring into high pressure direction. This allows a compact pump to be designed.

In an embodiment of the present invention, the pretension cylinder can, for example, be provided with a stopping element at each axial end of the pretension cylinder so that the plunger is exactly positioned at its two different preset positions.

In an embodiment of the present invention, the pretension control valve can, for example, be controlled by a pump control unit. The pump control unit is provided with set-values for the pretension control valve and determines the pressure set-value and thereby the plunger position dependent on engine conditions and parameters, such as lubricant temperature etc.

In an embodiment of the present invention, the second pressure conduit can, for example, be provided with a throttle valve and the pretension control valve is provided downstream of the pressure control chamber. The throttle valve limits the maximum lubricant consumption of the pretension cylinder.

One embodiment of the invention is hereinafter described with reference to the drawing.

FIG. 1shows a variable displacement lubricant pump10as a part of a pumping system100for supplying an internal combustion engine70with a lubricant. The pump10comprises a pump housing12having a cavity13in which a radially shiftable control ring18can radially translate.

The control ring18encircles a pump rotor14which is provided with numerous radially slidable vanes16, whereby the vanes16are rotating inside the control ring18. The pump housing12is closed by two pump side walls15of which one is not shown in the drawing. The pump side walls15, the vanes16, the pump rotor14and the control ring18define five pump chambers17. One of the side walls15is provided with a pump chamber inlet opening19and with a pump chamber outlet opening21.

The pump10is provided with a pressure control chamber20, whereby the pressure in the pressure control chamber20can push the control ring18into the low pumping volume direction against the force of a flexible pretensioning element22. Opposite to the pressure control chamber20, the pump10is provided with a pretension control unit28for adjusting different discharge pressures of the pressurized lubricant.

The pretension control unit28comprises a pretension cylinder30wherein an axially moveable plunger32is provided. The pretension cylinder30is provided with stopping elements33,35at both axial ends of the pretension cylinder30. The plunger32supports the pretensioning element22so that the control ring18is pushed into a high pumping volume direction. The plunger32is switchable into two different positions, namely, the low pressure position and the high pressure position, so that the pump10can pressurize the lubricant with two different pressures. In the low pressure position, the plunger32is stopped by and touches the stopping face43of the stopping element33; in the high pressure position, the plunger32is stopped by and touches the stopping face45of the stopping element35.

The pump housing12also comprises an intake port37for sucking the lubricant from a lubricant tank50and a pump outlet port24for feeding lubricant with a discharge pressure to the internal combustion engine70. A conduit71extends from the pump outlet port24to supply the internal combustion engine70.

The lubricant, which is supplied to the internal combustion engine70, is also conducted to the pressure control chamber20via a first pressure conduit26, and the lubricant is also conducted to the pretension cylinder30via a second pressure conduit34. More specifically, the lubricant of second pressure conduit34is finally fed to the pretension cylinder30via the second pressure conduit34through a pressure throttle valve46in which a calibrated pressure drop occurs as the lubricant flows through. The second pressure conduit34is connected with an inlet39of the pretension cylinder30.

The pretension cylinder30is provided with an outlet opening36in a cylinder wall38, the outlet opening36being connected hydraulically to an electrical pretension control valve40. The pretension control valve40is controlled by a pump control unit44. The pump control unit44is provided with set-values for the pretension control valve40and determines the pressure set-value, and thereby the position, of the plunger32, dependent on engine conditions and parameters, such as lubricant temperature etc.

If the electrical pretension control valve40opens the outlet opening36, the pretension cylinder30is connected to the low-pressure, for example, to atmospheric pressure. The plunger32is in the low pressure position, and the equilibrium position of the control ring18is moved into the low pressure position. The pump10provides the pressurized lubricant, for example, with a pressure of approximately 2.5 bar. If the pretension control valve40closes the outlet opening36, the pressure in the pretension cylinder30increases so that the plunger32switches into the high pressure position. As a result, the equilibrium position of the control ring18is shifted into the high pressure position so that the pump10provides the pressurized lubricant, for example, with a higher set pressure of approximately 4.5 bar.