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

The mechanical pump comprises a pump rotor with radially slidable vanes rotating within a shiftable control ring, whereby the control ring is pushed by a plunger pushing the control ring into high pumping volume direction.

The plunger is shiftably arranged in 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 by controlling the pressure in the hydraulic control chamber thereby moving the plunger.

Variable displacement vane pumps of the state of the art are known from WO 2005/026553 Al. The pump is provided with a pressure control system for controlling the discharge pressure of the lubricant. The pressure control system comprises a first pressure control chamber wherein a first plunger is provided being axially movable. The first pressure control chamber is connected via a pressure conduit with the pump outlet port. The pressure control system also comprises a separate control element which is realized as a cylinder-piston-element which keeps the pressure of the pressurized lubricant provided by the pump at a more or less constant level, independent of the rotational speed of the pump rotor. This is realized by opening and closing a control outlet of the first pressure control chamber, thereby moving the control ring into a low volume direction or pushing the control ring into a high pumping volume direction.

However, the lubricant pressure demand of the engine and the mechanic stress of the pump is dependent on the working conditions, such as the engines and the lubricants temperature.

It is an object of the invention to provide a simple and reliable variable displacement lubricant vane pump with different lubricant pressures levels dependent on the lubricant temperature.

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

The variable displacement lubricant vane pump according to the invention is provided with a temperature control opening in a wall of the control chamber. Downstream of the temperature control opening, a temperature control valve is provided which connects or disconnects the temperature control opening to atmospheric pressure, dependent on the lubricant temperature T. The temperature control valve is provided with a switching strip with a switching temperature, whereby the switching strip is in the open position if the lubricant temperature T is below a switching temperature T _s and is in the closed position if the lubricant temperature T is above of the switching temperature T _s of the switching strip.

The switching strip preferably is provided as a bimetal strip. A bimetal switching strip it is a very simple, cost-effective and reliable valve concept which allows to define two different lubricant discharge pressure levels dependent on the lubricant temperature. According to a preferred embodiment of the invention, the temperature control valve is provided with a separate closing body strip. The closing body strip is actuated by the switching strip. The valve bore is directly closed and left open by the closing body strip, not directly by the switching strip.

Preferably, the closing body strip is preloaded in its closing position so that the closing body strip defines a non-return reed valve. The closing body strip can be, for example, realized as a flexible tongue body. In the open position of the switching strip, the temperature control valve is a unidirectional non-return reed valve. In the closed position of the switching strip, the closing body strip is forced and kept in its closing position so that the temperature control valve is closed in both flow directions.

Preferably, a stop strip is provided for limiting the opening angle of the switching strip. The stop strip is stiff and remains in the same position and angle independently of the lubricant temperature, and limits the maximum opening movement of the switching strip.

Preferably, the strips are provided as a strip packet which is, according to a preferred embodiment, held together by one single screw. The strips defining the strip packet have, more or less, the same contour so that they define a rectangular strip packet.

According to a preferred embodiment of the invention, the switching temperature T _s of the switching strip is between 60°C and 100°C, and is preferably between 70°C and 90°C. According to a preferred embodiment of the invention, the temperature control opening is provided at a side wall of the control chamber and a plunger element of the control ring is shifting along the side wall thereby covering or not covering the control opening.

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 a temperature control valve, the pump being arranged in a lubricant circuit including an internal combustion engine, figure 2 shows a cross section of a first embodiment of a temperature control valve in the closed position,

figure 3 shows the temperature control valve of figure 2 in the open position,

figure 4 shows a second embodiment of a more simple temperature control valve in the open position, and

figure 5 shows the temperature control valve of figure 4 in the closed position.

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 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 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 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, 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. 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 cross 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 hydraulically to the first pressure control chamber 25 by a conduit 83 and is provided with an outlet port which is hydraulically connected to the lubricant tank 50 by a conduit 84. Another 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.

The first pressure control chamber 25 is provided with a temperature control opening 26 connected hydraulically to a temperature control valve 30. The temperature control opening 26 is provided in a side wall 27 of the first control chamber 25 so that the first plunger 24, sliding along the side wall 27, thereby covers and closes the temperature control opening 26 or leaves the opening 26 open, dependent on the plunger position inside the control chamber 25. If on the temperature control valve 30 is open, the first control chamber 25 is connected to the lubricant tank 50 having atmospheric pressure.

The first embodiment of the temperature control valve 30 is shown in figures 2 and 3. The temperature control valve 30 is arranged downstream of the temperature control opening 26 and connects or disconnects, dependent on the lubricant temperature T, the temperature control opening 26 to the atmospheric pressure of the lubricant tank 50 via a lubricant conduit 89. The temperature control valve 30 is provided with a switching strip 31 with a switching temperature T _s , whereby the switching strip 31 is in the open position if the lubricant temperature T is below the switching temperature T _s and is in the closed position if the lubricant temperature T is above of the switching temperature T _s of the switching strip 31, The switching temperature T _s of the switching strip is around 80°C. The switching strip is provided as a bimetal strip consisting of two different metal strips 34, 35 of different thermal expansion coefficients.

The switching strip side orientated to a valve bore 40 could be provided with a rubber layer 36, in order to improve the sealing when the switching strip 31 closes the valve bore 40. The rubber layer 36 could be co- moulded or assembled, as separate part, with the switching strip 31.

The temperature control valve 30 is provided with a separate closing body strip 32 consisting of a single metal strip body 39 of which the side orientated to a valve bore 40 is provided with a rubber layer 36. The rubber layer 36 is co-moulded or assembled, as a separate part, with the metal strip body 39 of the closing body strip 32. The valve bore 40 is directly covered by the closing body strip 32, and is not directly covered by the switching strip 31. The closing body strip 32 is preloaded into its closing position so that the closing body strip 32 defines a non-return reed valve. In the open position of the switching strip 31, as shown in figure 3, the temperature control valve 30 is working as a unidirectional non-return reed valve so that the lubricant from control chamber 25 can flow to the lubricant tank 50. In the closed position of the switching strip 31, as shown in figure 2, the temperature control valve 30 is totally closed in both flow directions.

Opposite to the closing body strip 32, with respect to the switching strip 31, a stop strip 33 is provided for limiting the maximum opening angle of the switching strip 31. The stop strip 33 is made out of a metal strip body 38, and is stiff at every lubricant temperature. The stop strip 33 limits the opening movement of the switching strip 31 to a maximum opening angle.

The three strips 32, 31, 33 are provided as a strip packet 42 which is held together and mounted to the pump housing 11 by one single assembling screw 37. The three strips 32, 31, 33 defining the strip packet 42 have the same contour so that they define a rectangular strip packet 42.

A second embodiment of a temperature control valve 30' is shown in figures 4 and 5. This temperature control valve 30' is simpler than the temperature control valve 30 of the first embodiment, and is provided with the switching strip 31, only, of which the side orientated to the valve bore 44 is provided with the rubber layer 36.