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

A mechanical lubricant vane pump, as known from WO 2011/107156 Al, is generally a volumetric pump which is mechanically driven by the engine so that the pump rotates with the rotational speed proportional to the engine's rotational speed. The lubricant vane pump is provided with a pump rotor body holding radially slidable vanes rotating inside a shiftable control ring. The slidable vanes, the rotor body and the control ring wall define a plurality of rotating pump compartments, rotating within a pump chamber thereby pumping the lubricant from an inlet cavity to an outlet cavity of the pump.

The control ring is shiftable with respect to the rotor axis between a high pumping volume position with high eccentricity and a low pumping volume position with low eccentricity, so that the lubricant volume per rotation pumped by the pump can be adapted to keep the discharge pressure of the pump on a constant level. The eccentricity position of the control ring with respect to the rotational axis of the pump rotor is determined by two counter acting hydraulic chambers, i.e. the pressure control chamber for pushing the control ring into a high pumping volume direction and the pilot chamber for pushing the control ring into a low pumping volume direction against the pressure control chamber. Both chambers are fluidically connected to the outlet cavity by the respective fluidic channels. The pilot chamber is connected to the outlet cavity by a pilot chamber channel with a large cross-section so that the fluidic resistance is low. The control chamber is connected to the outlet cavity by a relatively long control chamber channel with a pressure throttle valve in the course of the control chamber channel. The fluidic pressure in the control chamber is controlled by a control valve which allows to connect or disconnect the pressure control chamber to a lubricant tank being under atmospheric pressure. The control valve itself is controlled by the discharge pressure of the pump or by the effective lubricant pressure in or at the engine.

After a cold start of the engine the pilot chamber of the pump is filled relatively quickly with the cold and viscous lubricant because the fluidic resistance between the outlet cavity and the pilot chamber is relatively low. As a consequence, the control ring is pushed into the low pumping volume direction right after the engine's cold start. In contrast to the pilot chamber, it takes a while until the control chamber is filled with lubricant and is pressurized with the fluidic pressure of the outlet cavity because the fluidic resistance between the outlet cavity and the control chamber is relatively high due to the long control chamber channel and the throttle provided in the course of the control chamber channel. As a consequence, it can take 5, 10 or even more than 60 seconds after an engine cold start until pressurized lubricant is generated by the pump and until the engine is sufficiently lubricated after a cold start of the engine.

Beside of the fact that the engine runs at high mechanical resistance without sufficient lubrication, the wear of the engine and the danger of jamming are high with non-sufficient lubrication. It is an object of the present invention to provide a mechanical variable lubricant vane pump with immediate functionality right after a cold start of the engine.

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

According to the invention, the control chamber channel directly connects the outlet cavity with the pressure control chamber so that the fluidic length of the control chamber channel is very short. The control chamber channel has a relatively large cross-section which is larger than 1/10 of the smallest cross-section of the pilot chamber channel providing the pilot chamber with lubricant from the outlet cavity. Therefore, it can be assured that the control chamber is filled with lubricant and is pressurized with the fluidic pressure of the outlet cavity shortly after a cold start of the engine. As a consequence, the control ring is pushed by the control chamber into the high pumping volume direction or into the highest pumping volume position shortly after a cold start of the engine. This guarantees that a high discharge pressure of the lubricant leaving the pump is realized a few seconds after the cold start of the engine so that even at very low lubricant temperatures the lubrication of the engine starts the latest only a few seconds after the cold start of the engine.

Preferably, the smallest flow cross-section of the control chamber channel is larger than 1/4, more preferably larger than 1/3 and even more preferably larger than 1/2 of the smallest flow cross- section of the pilot chamber channel. The closer the cross-sectional values of the control chamber channel and of the pilot chamber channel are, the more it can be guaranteed that both chambers are filled simultaneously after a cold start of the engine. This guarantees that the control of a stable and sufficient discharge pressure of the lubricant leaving the pump is realized only a few seconds after a cold start of the engine. A throttle valve is not provided in the course of the control chamber channel.

According to a preferred embodiment of the invention the control chamber channel is provided as a groove in the control ring. This concept of the control chamber channel is easy in manufacturing, and therefore is very cost-effective. Providing the control chamber channel in the body of the control ring allows to realize a control chamber channel with a very short fluidic length so that the fluidic resistance of the control chamber channel is low.

As an alternative, the control chamber channel can be provided as a groove in a wall of the pump housing. Preferably, the control chamber channel can be provided in the wall separating the outlet chamber from the control chamber. This concept of the control chamber channel can be easy to manufacture, and can also be a cost-effective alternative.

The following is a detailed description of embodiments of the invention with reference to the drawings, in which :

Fig.l : shows a transversal cross section of a first embodiment of a lubricant vane pump with a control chamber channel provided in the control ring , and

Fig.2: shows a transversal cross section of a second embodiment of a lubricant vane pump with a control chamber channel provided in a housing wall. The figures show a variable lubricant vane pump 10 being a part of a pumping system for supplying an internal combustion engine (not shown) with pressurized lubricant. The lubricant vane pump 10 pumps the lubricant to the combustion engine with a discharge pressure pd and is mechanically driven by the engine so that the rotational speed of the lubricant pump 10 is proportional to the rotational speed of the engine.

The pump 10 comprises a pump housing 12 defining a pumping cavity 18, an inlet cavity 16 and an outlet cavity 14. In the pumping cavity 18 a pump rotor 30 with seven radially slidable vanes 32 is rotating within a shiftable control ring 28. The vanes 32 are supported and hold in vane slits 36 of the pump rotor hub 34. The pump housing 12, the pump rotor 30 and the slidable vanes 32 define seven rotating pump compartments 19i - 19 ₇ . In the center of the rotor hub 34 a shiftable support ring 38 is provided which supports the radially inward ends of the slidable vanes 32. The pump rotor 30 rotates around a static rotor axis 33 in anticlockwise direction.

The seven rotating pump chambers 19 have a pump chamber angle of about 51°. Each pump chamber 19 continuously rotates from a charge zone 22 over the intermediate zone 26 to the discharge zone 24 and back to the charge zone 22. The lubricant is sucked by the rotating pump compartment 19 from the inlet cavity 16 and is delivered to the outlet cavity 14 where the lubricant is pressurized to discharge pressure pd.

The radial position of the control ring 28 is determined by the fluid pressure in a pressure control chamber 40, the fluid pressure in a pilot chamber 54 and by the force generated by a pretension element 42, The pretension element 42 is provided as a spring arranged inside the control chamber 40. In the present embodiment, the control ring 28 is linearly shiftable between a high pumping volume position as shown in figures 1 and 2 and a low pumping volume position. In the high pumping volume position, the control ring 28 has a high eccentricity with respect to the rotor axis 33, whereas in the low pumping volume position the eccentricity of the control ring 28 with respect to the rotor axis 33 is small or zero. The pilot chamber 54 as well as the control chamber 40 both are fluidically connected to the outlet cavity 14 via a pilot chamber channel 48 and a control chamber channel 60; 60'. The pilot chamber 54 is not provided with another fluid connection so that the fluidic pressure in the pilot chamber 54 is always a more or less equal to the discharge pressure PD of the outlet cavity 14.

The control ring 28 is provided with a control chamber plunger 44 shiftable within the pressure control chamber 40 and with a pilot chamber plunger 56 shiftable within the pilot chamber 54. The effective hydraulic surface of the control chamber plunger 44 is higher than the effective hydraulic surface of the pilot chamber plunger 56.

The pressure control chamber 40 is fluidically connected to the atmospheric pressure pa of a lubricant tank 52 via a pressure control valve 50 which is pressure controlled by the discharge pressure PD of the outlet cavity 14. If the pressure control valve 50 is open, the hydraulic pressure in the pressure control chamber 40 depends on the degree of opening of the control valve 50. If the control valve 50 is closed, the hydraulic pressure in the control chamber 40 is equal to the discharge pressure pd of the outlet cavity 14. If the control valve 50 is open, the hydraulic pressure in the control chamber 40 is between the discharge pressure PD and the atmospheric pressure pa.

In the first embodiment shown in figure 1, the fluidic connection of the control chamber 40 with the outlet cavity 14 is provided by a short control chamber channel 60 which is provided as a groove 62 in body of the control ring 28 and of the connected control chamber plunger 44. The control chamber channel 60 therefore is moving together with the control ring 28. At one end of the control chamber channel an opening orientated to the outlet cavity 14 is provided and at the other end of the control chamber channel 60 an opening orientated to the control chamber 40 is provided. The cross section of the control chamber channel 60 is more or less constant over its entire length.

The pilot chamber 54 is connected to the discharge pressure PD in the outlet cavity 14 by the pilot chamber channel 48 which is provided in a part of the housing wall 15 of the pump housing 12. The pilot chamber channel 48 as a more or less constant cross - section over its entire length . The cross section of the control chamber channel 60 is about 1/2 of the cross section of the pilot chamber channel 48.

In the second embodiment shown in figure 2, the fluidic connection of the control chamber 40 with the outlet cavity 14 is provided by a short control chamber channel 60' which is provided as a groove 62' in the wall 13 of the pump housing 12. The fluidic length of the control chamber channel 60' is short because only the side wall of the control chamber 40 separates the control chamber 40 from the outlet cavity 14. The cross section of the control chamber channel ' is about 1/2 of the cross section of the pilot chamber channel.