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The invention refers to a mechanical fluid pump which is driven by an internal combustion engine and is providing a liquid, pressurized gas or vacuum to an automotive unit.

o The fluid pump can be a lubricant pump, a coolant pump, a vacuum pump or a pump providing pressurized liquid or gas, for example pressurized air. The mechanical fluid pump is not driven by an electric motor but is directly connected to the combustion engine. As a consequence, the rotational speed of the fluid pump is proportional to the rotational speed of the combustion engine so that the fluid pump is always rotating even if there is no need for fluid supply or for a suction activity to create a vacuum.

In US 7 422 093 B2 a fluid pump for providing a pressurized liquid for a hydraulic power steering is described. The fluid pump is provided with a magneto-rheological clutch so that the pump performance can be controlled depending on the fluid demand and pressure demand of the power steering.

A risk of failure is not acceptable for vital fluid pumps, such as a lubricant pump, a coolant pump or a vacuum pump for a pneumatic brake assistance unit. The fluid pump including the clutch should be as compact as possible. In many applications a relatively high torque has to be coupled by the clutch. It is an object of the invention to provide a mechanical combustion- engine-driven fluid pump with a compact magneto-rheological clutch.

This object is solved with a mechanical combustion-engine-driven fluid pump with the features of claim 1.

The fluid pump according to the invention is provided with an input shaft which is directly driven by the combustion engine and with a pumping unit with a pump rotor for pumping the fluid which can be a liquid or a gas. The term "directly driven" is to be understood as that there is no disengagable clutch between the rotational element of the engine and the input shaft of the pump. The input shaft of the pump can be driven by the engine via a belt, gear wheels or by a direct coupling with the camshaft or the crankshaft of the engine.

The clutch is realized as a magneto-rheological clutch in the form of a multi-disc clutch. The clutch is provided with at least two radial input clutch disks and at least two radial output clutch disks, whereby the clutch disks define numerous radial clutch liquid gaps between them. The multi-disk configuration of the magneto-rheological clutch allows a compact diameter of the clutch and to transfer high torques from the clutch input to the clutch output.

The radial clutch liquid gaps arranged axially between the input clutch disks and the output clutch disks are filled with a magneto-rheological clutch liquid which has a relatively high viscosity when a magnetic field is present and which has a relatively low viscosity when no magnetic field is present. The term liquid in context with the magneto-rheological liquid is not to be taken literally but is to be understood as a kind of a magneto- rheological fluid which can also be somehow solid when activated by a magnetic field. The magnetic field for increasing the viscosity of the magneto-rheological clutch liquid is not generated by an electromagnetic means but is generated by a permanent magnet element which is shiftable between a disengaged position in which the permanent magnet element's magnetic field penetration flux in the clutch liquid gaps is low and an engaged position in which the magnetic field flux penetration in the clutch liquid gaps is high . In its engaged position, the permanent magnet is positioned close to the clutch liquid gaps, and in the disengaged position, the permanent magnet is more distant and remote from the clutch liquid gaps. The permanent magnet element can be provided co-rotating with the input clutch disks so that the permanent magnet element is always rotating with the rotational speed of the input shaft.

The permanent magnet element is moved between the engaged and the disengaged position by a separate magnet element actuator.

Since the magnetic field for penetrating the clutch liquid gaps and the magneto-rheological clutch liquid therein is not generated by an electromagnet, the magneto-rheological clutch can generally also be engaged if the control means of the pump and for the clutch actuation fails.

Generally, the magneto-rheological eddy-current clutch can also be combined with other automotive devices around or not around the engine, or even outside automotive applications. Preferably, the permanent magnet element is provided shiftable in axial direction. Preferably, the permanent magnet element is magnetized in circumferential direction.

The permanent magnet element can preferably be pretensioned by a passive pretension element into its engaged position. If the actuator fails, the pretension element pushes the permanent magnet element into the engaged position. This arrangement makes the clutch concept totally failsafe. The passive pretension element can be, for example, a spring or another permanent magnet. However, the passive pretension element does not need any external energy to provide the pretension force.

According to a preferred embodiment, the magnet chamber is provided radially inwardly of the clutch disks. The permanent magnet element is provided shiftable in the magnet chamber between the engaged and the disengaged position. The clutch disks are arranged radially outwardly and radially adjacent to the magnet chamber. Preferably, the radial planes of the clutch liquid gaps intersect with the permanent magnet element in its engaged position. In other words, the magnetic field of the engaged permanent magnet element generally radially penetrates the fluid liquid gaps. This arrangement allows a homogenous penetration of the radial fluid liquid gaps when the permanent magnet element is in its engaged position.

The magnet chamber is the chamber wherein the permanent magnet element is arranged shiftable between its engaged and disengaged position. Preferably, a longitudinal engagement section of the magnet chamber wall intersecting with the planes of the clutch liquid gaps is made out of a non-ferromagnetic material. As a consequence, the magnetic field of the permanent magnet element is radially not shielded in the engagement section of the magnet chamber wall so that the magnetic field of the permanent magnet element penetrates the clutch liquid gaps without any relevant weakening. The radial thickness of the magnet chamber wall in the engagement section should be as small as 5 possible to minimize the magnetic gap between the permanent magnet element and the clutch liquid gaps.

According to a preferred embodiment, the longitudinal disengagement section of the magnet chamber wall is made of a ferromagnetic material o to shield the magnetic field of the permanent magnet element with respect to the clutch liquid gaps in the disengaged position of the permanent magnet element. The better the magnetic shielding of the permanent magnet in its disengaged position is, the less torque is transferred between the input clutch disks and the output clutch disks in the disengaged position of the permanent magnet element.

Preferably, the actuator can be provided as a vacuum actuator. The vacuum actuator is magnetically neutral and does not generate any electromagnetic field which could penetrate the clutch liquid gap filled with the magneto-rheological clutch liquid.

One embodiment of the invention is described with reference to the enclosed drawings, wherein

figure 1 shows a mechanical combustion-engine-driven fluid pump with a magneto-rheological multi-disc clutch in longitudinal cross-section in the engaged state, and

figure 2 shows the fluid pump of figure 1 in the disengaged state. The figures 1 and 2 show a typical automotive arrangement consisting of an internal combustion engine 12 and a mechanical fluid pump 10 directly driven by the combustion engine 12. The fluid pump 10 can be designed as a vacuum pump 10, but also can be provided as a lubricant pump, coolant pump etc. The combustion engine 12 is mechanically directly connected to an input shaft 20 of a clutch 16 of the vacuum pump 10 so that the input shaft 20 is always co-rotating with a rotational speed being directly proportional to the rotational speed of the combustion engine 12.

The clutch 16 is arranged between the input shaft 20 and an output shaft

21 and is designed as a magneto-rheological multi-disc clutch 16. The clutch 16 connects the input shaft 20 with the output shaft 21 in the engaged clutch state, as shown in figure 1, and disconnects the output shaft 21 from the input shaft 20 in the disengaged state, as shown in figure 2. The output shaft 21 of the clutch 16 is directly coupled to a vacuum pumping unit 18 with a pump rotor 19. The clutch 16 is provided with four radially input clutch disks 62 and with five radial output clutch disks 64. All clutch disks 62, 64 lie in a radial plane, respectively. Between the clutch disks 62, 64 eight radial clutch liquid gaps 66 are defined which are filled with a magneto-rheological clutch liquid 28. The magneto- rheological clutch liquid 28 can not disappear because the clutch liquid gaps 66 are hermetically closed.

A permanent magnet element 32 is positioned radially inside and in the center of the clutch disks 62, 64. The permanent magnet element 32 can be provided as a cylindrical magnet body 30 being provided axially shiftable within a cylindrical magnet chamber 22. The magnet chamber

22 is provided and defined by cylindrical chamber walls 25, 27 defining a engagement section 24 intersecting with the radial planes of the clutch disks 62, 64 and the clutch liquid gaps 66 and a disengagement section 26 not intersecting with the radial planes of the clutch disks 62, 64 and the clutch liquid gaps 66. The magnet chamber wall 25 of the engagement section 24 is made out of a non-ferromagnetic material, such as for example aluminium or plastic. The magnet chamber wall 27 of the disengagement section 26 is made out of a ferromagnetic material to shield the magnetic field of the permanent magnet element 30 with respect to the clutch liquid gaps 66 in the disengaged position of the permanent magnet element 32, as shown in figure 2.

In engaged position, the permanent magnet element 32 is close to the radial clutch liquid gaps containing the magneto-rheological clutch liquid 28 therein so that the magnetic field generated by the permanent magnet element 32 penetrates the magneto-rheological clutch liquid 28 inside the clutch liquid gaps 66 with a maximum magnetic flux.

The axially shiftable permanent magnet element 32 is pretensioned by a pretension element 44 into its engaged position, as shown in figure 1. This arrangement makes the clutch 16 failsafe because the permanent magnet element 32 is always pushed into its engaged position if the pneumatic actuator 42 should fail.

As long as the clutch 16 remains disengaged by activation of the pneumatic actuator 42, the shiftable permanent magnet element 32 is pulled into and hold in its disengaged position, as shown in figure 2. In the disengaged position of the permanent magnet element 32 the magnetic field is remote and shielded with respect to the clutch liquid gaps 66 so that the magnetic flux in the clutch liquid gaps 66 is relatively low with the result that the viscosity of the magneto-rheological clutch liquid is relatively low. The clutch is disengaged. As soon as the clutch 16 is switched into the engaged state by deactivating the actuator 42, the shiftab!e magnet element 32 is pushed into its engaged position by the pretension element 44, as shown in figure 1. In this state the magnetic field flux penetrating the clutch liquid gap 66 is relatively high so that the viscosity of the magneto-rheological clutch liquid is relatively high. In this engaged state, the output shaft 21 rotates with the same rotational speed as the input shaft 20. The output shaft 21 drives the pump rotor 19 of the pumping unit 18 so that the pumping unit 18 is pumping the fluid.