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

An automotive variable mechanical lubricant pump is mechanically driven by the internal combustion engine. The mechanical lubricant pump is designed as a positive displacement pump and is provided with a pump rotor with numerous slidable rotor vanes rotating within a shiftable control ring which is slidable between a maximum eccentricity position and a minimum eccentricity position. The rotor vanes separate the pumping chamber into numerous pumping compartments. The compartment stroke is varied by increasing or decreasing the eccentricity of the control ring with respect to the pump rotor. Since the compartment stroke is variable, the pump outlet pressure can be controlled and kept more or less constant independently of the rotational speed of the lubricant pump.

In practice, it is advantageous to control the so-called lubricant gallery pressure at the engine because the lubricant gallery pressure is the parameter which is decisive for a sufficient lubrication of the engine.

In a relative simple and cost-effective construction, the mechanical lubricant pump is provided with one control ring preload spring for pushing the control ring into the maximum eccentricity position in which the compartment stroke is the most and is provided with one single counter-acting hydraulic pilot chamber for pushing the control ring into the minimum eccentricity position. The pilot control chamber is directly charged with the pump outlet pressure or with the gallery pressure. The hydraulic pressure in the pilot chamber can be controlled by a separate hydraulic control valve which regulates the hydraulic control chamber pressure. The separate hydraulic control valve can be regulated in dependency on the engine's gallery pressure to keep the gallery pressure constant.

In general practice it is not a significant problem that the actual pressure value is picked up remote from the pump outlet. But when the engine is started after having stood still, the engines and the pumps hydraulic system is empty and is only successively filled with the pressurized lubricant. As a result, the detected gallery pressure is very low at the beginning of the starting procedure so that the control ring stays in the maximum eccentricity position until the lubricant has arrived at the engine's gallery and until the separate hydraulic control valve is charged with the real lubricants gallery pressure. As a consequence, the mechanical lubricant pump runs with a maximum eccentricity as long as the lubricant has not arrived at the pickup location of the gallery pressure. As long as the hydraulic pressure control circuit is not filled and is not working properly, and if the lubricant is cold and/or the rotational speed of the pump rotor is relatively high, a hydraulic overpressure can occur in the pumping compartments which could damage or destroy the rotor vanes and the engine components like filter or cooler.

It is an object of the invention to provide an automotive variable mechanical lubricant pump with a relatively simple control circuit and with means for avoiding overpressure during the engine's starting procedure.

This object is solved with an automotive variable mechanical lubricant pump with the features of claim 1.

The lubricant pump is provided with a pump rotor with numerous slidable vanes rotating in a shiftable control ring which is shiftable between a maximum eccentricity position and a minimum eccentricity position. The control ring encloses a pumping chamber where the pumping action takes place. The pumping chamber is divided by the slidable vanes into numerous pumping compartments.

The control ring can be provided linearly shiftable or, alternatively, pivotable. The term 'eccentricity' refers to the distance between the rotation axis of the pump rotor and the middle of the inner circumference of the control ring. The inner circumference of the control ring can be precisely circular or can have a non-circular form. However, the middle of the control ring is the geometric middle. At low control ring eccentricity, the compartment stroke is low, at high control ring eccentricity, the compartment stroke is high.

The lubricant pump is provided with a control ring preload spring for pushing the control ring into the maximum eccentricity direction and with a hydraulic pilot chamber pushing the control ring into the minimum eccentricity direction against the force of the preload spring. The hydraulic pilot chamber is charged directly with the pump outlet pressure or the gallery pressure, and the hydraulic pressure in the pilot chamber is adjusted and regulated by a hydraulic control circuit which is charged with a remote gallery pressure of the engine via an actual-pressure inlet. In other words, the actual-pressure in the control chamber is controlled at least temporarely by the control circuit in dependency on the remote gallery pressure.

A part of the outer circumference of the control ring is surrounded by a hydraulic outlet chamber which is directly filled with pressurized lubricant coming from the pumping compartments through a pumping chamber outlet opening. The pumping chamber outlet opening can be provided in the control ring and/or in a pumping chamber side wall lying in a cross- section of the lubricant pump. The pressurized lubricant flows from the outlet chamber directly to the pump outlet for the pressurized lubricant, from where the pressurized lubricant flows to the engine's gallery. In other words, the hydraulic outlet chamber is an intermediate room through which the pressurized lubricant coming from the pumping chamber flows through on its way to the engine, so that the outlet chamber is filled with pressurized lubricant right after the start of the engine.

According to the invention, the effective anti-spring hydraulic surface of the control ring circumference in the hydraulic outlet chamber is larger than the counter-acting pro-spring hydraulic surface. The effective hydraulic surface is the control ring area within the outlet chamber and seen in the control ring's shifting direction. In state of the art pumps, the anti-spring hydraulic surface and the pro-spring hydraulic surface are equal so that the hydraulic pressure in the outlet chamber has no influence on the pump pressure control circuit.

According to the invention, the two effective hydraulic outlet chamber surfaces are not equal. Since the anti-spring hydraulic surface is larger than the pro-spring hydraulic surface within the outlet chamber, a resulting anti-spring force pushes the control ring into the low eccentricity direction against the spring force if a lubricant overpressure is present, namely a pressure higher than atmospheric pressure. The higher the hydraulic overpressure in the outlet chamber is, the higher is the total force directed into the low eccentricity direction. As a result, the control ring is pushed and moved into the low eccentricity direction if the hydraulic pressure in the outlet chamber is very high so that damaging of the vanes or engine components is avoided. This mechanism is effective and active right after the start of the engine because, after the pumping chamber has been filled with lubricant, the first room hydraulically downstream of the pumping chamber is the outlet chamber which is filled with the pressurized lubricant right after the engine's start. The dissymmetric outlet chamber thereby protects the lubricant pump against too high overpressure of the pressurized lubricant in the pumping chamber so that in particular the vanes are protected against damage caused by overpressure in the puping compartments.

Preferably, no other additional hydraulic control chamber is provided or has a relevant direct effect on the position and movement of the control ring, except the pilot chamber and the outlet chamber. No additional overpressure valve is necessary anymore to avoid overpressure.

Preferably, the hydraulic pressure control circuit is provided with a separate hydraulic control valve which is charged with the remote gallery pressure. The hydraulic control valve is provided with a valve plunger which valve position is defined by the charged gallery pressure.

According to a preferred embodiment of the invention, the projected height of the hydraulic anti-spring surface, seen in a plane perpendicular to the control ring's shifting direction, is larger than the corresponding pro-spring hydraulic surface height. The respective height value results from the projection of the outer circumference of the control ring within the hydraulic outlet chamber to a plane perpendicular to the shifting direction. Since the axial extent of the control ring is equal all over its complete circumference, only the projected heights of the control ring cause the difference of the hydraulic surface of the control ring circumference.

Preferably, the effective anti-spring hydraulic surface is at least 10% larger, preferably at least 20% larger, than the pro-spring hydraulic surface. More preferably, the difference is less than 100% because the total force generated in the hydraulic outlet chamber should not become too strong. According to a preferred embodiment of the invention, the hydraulic control valve is provided with a plunger comprising a valve body for opening and closing a valve opening, with a valve preload spring pushing the valve body into the open valve position, and with a first active plunger surface which is charged with the gallery pressure of the pump's actual- pressure inlet. The hydraulic control valve is a pure hydraulic control valve which is not directly electrically actuated. The valve preload spring pushes the valve body into the open valve position. The gallery pressure of the engine which is charged to the first active plunger surface causes the plunger to be pushed into the closed valve position against the valve preload spring.

If the gallery pressure at the first active plunger surface is high, the valve opening is small or closed, and if the gallery pressure is relatively low, the valve opening is relatively wide open or is completely open. When the engine is started, the hydraulic control circuit is normally empty and only filled with air at atmospheric pressure. As a result, the valve opening is completely open, when the engine is started, so that no relevant pressure is present in the hydraulic pilot chamber.

Preferably, the hydraulic control valve is provided downstream of the hydraulic pilot chamber so that the pressure in the hydraulic pilot chamber is low if the control valve is open and the pressure in the pilot chamber is high, when the control valve is closed. In this embodiment it is preferred, that a hydraulic throttle is provided upstream of the pilot chamber and downstream of the source of the pump outlet pressure which is normally the hydraulic outlet chamber.

However, it is generally possible that, alternatively, the hydraulic control valve is provided upstream of the pilot chamber and the throttle is provided downstream of the pilot chamber. According to a preferred embodiment of the invention, the control valve plunger comprises a second active plunger surface which is charged with the gallery pressure of the pressure inlet via a separate hydraulic switch which is electrically actuated. The second active plunger surface is connected to atmospheric pressure or to the gallery pressure, dependent on the switching status of the hydraulic switch. As a result, two different set-pressures can be chosen. The electrically actuated hydraulic switch is controlled by an electronic pump control which can be a part of an engine control. The electronic pump control selects the set pressure in dependency on numerous conditions, for example the lubricant temperature, the atmospheric air temperature, engine's rotational speed etc.

Three embodiments of the invention are described with reference to the enclosed drawings, wherein: figure 1 shows schematically a first embodiment of a control circuit with an automotive variable mechanical lubricant pump, an engine which is supplied with pressurized lubricant coming from the lubricant pump, a pump control chamber being directly charged with the pump outlet pressure, and a hydraulic control valve, in a low set-pressure condition, figure 2 shows the lubricant pump of figure 1 in a high set-pressure condition,

figure 3 shows a second embodiment of the control circuit with the pump control chamber being charged with the gallery pressure via the hydraulic control valve, and figure 4 shows a third embodiment of the control circuit without a hydraulic control valve. The figures show an arrangement 10 of an automotive variable mechanical lubricant pump 20, an internal combustion engine 12 and a lubricant tank 14 with a liquid lubricant 15, namely engine oil. The lubricant 15 in the lubricant tank 14 is sucked by the lubricant pump 20 and is delivered as pressurized lubricant to the engine 12 for lubrication and cooling of the engine 12.

The lubricant pump 20 of the first embodiment comprises a pumping unit 22, a hydraulic control valve 50 and a hydraulic switch 60 which all together can be integrated in one single lubricant pump device. The pumping unit 22 is provided with a rotatable pump rotor 26 with five radially slidable vanes 28 which are rotating in a linearly shiftable control ring 27. The pump rotor 26 is directly mechanically driven by the engine 12. The control ring 27 is linearly shiftable in a linear shifting direction 82. The control ring 27 encloses a pumping chamber which is divided into five pumping compartments by the rotor vanes 28. The pump rotor 26 rotates in the present embodiment in clockwise direction.

The control ring 27 is shiftable between a maximum eccentricity position as shown in figures 1 and 2 providing a maximum compartment stroke, and a minimum eccentricity position providing a minimum compartment stroke. In the maximum eccentricity position of the control ring 27, the pumping performance is maximized, whereas in the minimum eccentricity position of the control ring 27, the pumping performance is minimized. The control ring 27 is arranged shiftable within a pumping unit housing 24 which supports the control ring 27 linearly shiftable. The control ring 27 is pushed by a control ring preload spring 34 into the maximum eccentricity position, as shown in the figures. The preload spring 34 is provided in a spring chamber 33 which is hydraulically connected to the lubricant tank 14 and which is generally under atmospheric pressure. A pilot chamber 31 is provided opposite to the spring chamber 33. The pilot chamber 31 is defined by the pumping unit housing 24 and by a pilot chamber piston 30 which is a part of the body of the control ring 27. If the hydraulic pilot chamber 31 is charged with the pressurized lubricant, the control ring 27 is pushed into the minimum eccentricity position against the preload spring 34.

The lubricant which is pumped and pressurized in the pumping chamber and in the pumping compartments is directly discharged from the pumping chamber to a hydraulic outlet chamber 36 which is defined by a sector of the circular outside circumference 29 of the control ring 27 and by the pumping unit housing 24. The pressure of the lubricant in the hydraulic outlet chamber 36 is the outlet pressure PO of the lubricant pump 20 which is the lubricant pressure at a pump outlet port 90.

The hydraulic outlet chamber 36 is designed dissymmetric so that the effective anti-spring hydraulic surface 291 of the control ring circumference 29 in the hydraulic outlet chamber 36 is about 20% larger than the counter acting pro-spring hydraulic surface 292. The hydraulic surface 291, 292 is the projection of the control ring circumference surface within the outlet chamber 36 seen exactly in the control ring shifting direction 82. As can be seen in figure 1, the anti-spring hydraulic surface height H I perpendicular to the control ring shifting direction 82 is larger than the pro-spring hydraulic surface height H2.

As a result, an anti-spring force is generated if the lubricant in the outlet chamber 36 is pressurized. The anti-spring force is the result of the hydraulic surface difference dA multiplied by the overpressure PO-PA with respect to atmospheric pressure. If the overpressure PO-PA is high enough, the control ring 27 is shifted into minimum eccentricity direction against the force of the control ring preload spring 34. The hydraulic pilot chamber 31 is directly charged with lubricant having the pump's outlet-pressure PO via a hydraulic throttle 38. The hydraulic pilot chamber 31 is discharged via a valve inlet opening 57 and a valve outlet opening 58 of the hydraulic control valve 50 to atmospheric pressure. The hydraulic control valve 50 is provided with a valve housing

52 which is generally cylindrical inside. A complex valve plunger 59 comprising a cylindrical valve body 56 is provided axially shiftable within the valve housing 52. The valve plunger 59 is mechanically preloaded by a valve preload spring 51 pushing the valve plunger 59 into the open valve position in which the hydraulic pilot chamber 31 is connected without restriction or fluidic resistance to the lubricant tank 14 being under atmospheric pressure PA.

The valve plunger 59 is provided with a valve body 56 which steplessly completely covers, covers in part or leaves completely open the valve inlet opening 57 which is fluidically directly connected to the pilot chamber 31. The valve outlet opening 58 is fluidically directly connected to the lubricant tank under atmospheric pressure PA.

The valve plunger 59 is provided with a first circular active plunger surface

53 and a second ring-like active plunger surface 54. The first active plunger surface 53 is directly charged with the gallery pressure PG which is transferred from the engine 12 to the lubricant pump 20 through a pump gallery pressure inlet 80 and via an internal gallery pressure line 70. The second active plunger surface 54 is charged with the gallery pressure via a separate hydraulic switch 60 which is a 2/3 valve and via a hydraulic line 72 between the hydraulic switch 60 and the control valve 50. The second active plunger surface 54 is charged with the gallery pressure PG or, alternatively, with atmospheric pressure PA via a hydraulic line 71, depending on the switching status of the hydraulic switch 60. The hydraulic switch 60 is electronically controlled by an electronic pump control 92 which controls the switching state of the hydraulic switch 60 dependent on the lubricant temperature and the rotational pump speed. The hydraulic switch 60 hydraulically connects the second active plunger surface 54 to gallery pressure PG if the set-value of the gallery pressure PG should be low, as shown in figure 1. If the set-value of the gallery pressure PG should be relatively high, the hydraulic switch 60 is switched into the low pressure position to connect the second active plunger surface 54 to the atmospheric pressure PA of the lubricant tank 14, as shown in figure 2.

The position of the control ring 27 is the equilibrium position in which the spring force of the control ring preload spring 34 is more or less equal to the hydraulic force generated by the pilot chamber pressure PP in the pilot chamber 31 plus the hydraulic force in shifting direction 82 caused by the lubricant outlet pressure PO in the outlet chamber 36.

When the engine 12 is started after having stood still, the liquid lubricant 15 is sucked from the lubricant tank 14 into the pumping chamber where the lubricant is pumped by the pumping compartments to the hydraulic outlet chamber 36. If the lubricant is cold and has a relatively low viscosity, the lubricant's outlet pressure PO in the outlet chamber 36 can be relatively high. In that case, the total lubricant pressure outlet pressure PO generates a force at the control ring 26 which is directed against the spring force of the control ring preload spring 34 and thereby moves the control ring 27 into the low eccentricity direction so that the compartment stroke of the pump 20 is reduced, with the result, that the outlet pressure PO is reduced accordingly. As soon as the lubricant has arrived at the pilot chamber 31 and at the hydraulic control valve 50, the pump pressure control works properly. The arrangement 10 according to the second embodiment as shown in figure 3 is similar to the first embodiment. But the control chamber 31 is charged with the gallery pressure (PG) via the control valve 50. The gallery pressure (PG) is directed by a hydraulic line 72 ^' to a valve inlet of the control valve 50 depending on the position of the valve plunger 59. The control chamber 31 is charged with the gallery pressure (PG) or with the atmospheric pressure (PA). The hydraulic switch 60 ^' has a similar function as in the arrangement according to the first embodiment. The hydraulic switch 60 ^' charges the first circular active plungers surface 53 with the gallery pressure (PG) or alternatively with atmospheric pressure (PA) to thereby define a second set outlet pressure (PO).

The arrangement 10 according to the third embodiment shown in figure 4 is not provided with any hydraulic control valve anymore. The control chamber 31 is directly charged with the gallery pressure (PG) or with atmospheric pressure (PA) depending on the switching position of the hydraulic switch 60 ^{' '} .

In all embodiments 10 no additional overpressure valve is provided.