The invention refers to a mechanical switchable automotive coolant pump for providing a liquid coolant for an automotive engine.

A mechanical automotive coolant pump is mechanically driven by an automotive internal combustion engine so that the coolant pump generally rotates with a rotational speed which is proportional to the rotational speed of the engine. In some situations, and in particular after starting a cold engine, no coolant flow is needed. A switchable automotive coolant pump is provided with a friction clutch so that the rotational connection between the pulley wheel of the pump and the pump wheel can be engaged and disengaged as needed. The friction clutch can generally be provided in a dry zone or in the wet zone of the pump. In a wet friction clutch, the disengaged clutch disk is still rotating and thereby rotating the coolant liquid which rotates the pump wheel. In practice, a significant drag moment is transferred by a wet friction clutch in the disengaged clutch state so that a considerable pump performance is generated even if no pump performance is needed. The friction clutch can be actuated by an electromagnet which attracts at least one clutch element when the electromagnet is electrically energized.

It is an object of the invention to provide a mechanical switchable automotive coolant pump with a reduced pump performance when the wet clutch of the pump is disengaged.

This object is achieved with a switchable mechanical automotive coolant pump with the features of claim 1. The mechanical switchable automotive coolant pump according to the invention Is provided with a static pump frame which is provided with some kind of fixation means for fixing the coolant pump to an automotive engine or to an automotive frame. The pump frame can also be provided with a pump wheel housing comprising a coolant inlet and a coolant outlet.

The coolant pump is provided with a rotatable rotor shaft which is rotatably supported at the pump frame. The rotor shaft is not necessarily directly supported at the pump frame but can be directly supported at another rotatable part which itself is directly rotatably supported at the static pump frame.

A pulley wheel is co- rotatably and axially fixed at the rotor shaft and is suitable to be mechanically driven by the engine. Generally, the pulley wheel can be driven by any kind of mechanical transfer elements such as a gear wheel, a transmission belt, a friction wheel etc. The term 'pulley wheel' in the present application is not limited to a be It- driven wheel. But preferably, the pulley wheel can be and is driven by the engine via a transmission belt. The pulley wheel is fixed to the rotor shaft and is not rotatable and not axially shiftable with respect to the rotor shaft.

The coolant pump is provided with a rotatable and axially shiftable pump wheel which is rotatably supported and is axially shiftable with respect to the rotor shaft and with respect to the pump frame. The pump wheel can be axially moved and can rotate independently of the dynamic state of the rotor shaft. The pump wheel is provided with a ferromagnetic means so that an energized electromagnet magnetically attracts and axially pulls the ferromagnetic pump wheel.

The coolant pump is provided with an electromagnetic wet friction clutch arrangement of which the frictional clutch means are arranged in the wet zone of the coolant pump. The clutch arrangement is provided with a static electromagnet in the dry zone and with a clutch disc which is co- rotatably supported by the rotor shaft. The clutch disk always rotates with the rotational speed of the rotor shaft. The clutch disk is provided with a clutch friction surface and the pump wheel is provided with a corresponding clutch friction surface, both in the wet zone. In the engaged clutch state, both clutch friction surfaces are in full frictional contact with each other so that the pump wheel and the clutch disk rotate with the same rotational speed.

The pump wheel is provided with a separate stop friction surface and the pump frame is provided with a corresponding static stop friction surface. When the stop friction surfaces of the pump wheel and of the pump frame are in frictional contact with each other, a sufficient braking torque is generated which completely stops the rotation of the pump wheel when the wet friction clutch is in the fully disengaged state.

If the electromagnet is not excited at all, the friction clutch is in the engaged state so that the pump wheel rotates with the same rotational speed as the rotor shaft. The stop friction surfaces are not in contact.

When the electromagnet is electrically excited, the pump wheel is axially attracted by the and in the direction of the electromagnet so that the stop friction surfaces of the pump frame and the pump wheel are axially engaged with the result that the rotation of the pump wheel is completely stopped. The clutch friction surfaces are not in contact.

The coolant pump according to the invention is provided with a frictional brake arrangement defined by the stop friction surfaces which, in the disengaged state, completely stops any rotation of the pump wheel when the electromagnet is fully energized. In the fully disengaged clutch state, a zero-flow of the coolant is realized. As a consequence, the internal combustion engine is not cooled by any flowing coolant anymore, if no cooling performance is needed or wanted.

Preferably, the clutch disk is provided with a ferromagnetic means and Is supported axially shiftable at the rotor shaft. The rotor shaft supports the pump wheel as well as the clutch disk. Since the clutch disk is provided with a ferromagnetic means, the clutch disk is axially attracted by the energized electromagnet. Both, the clutch disk as well as the pump wheel are axially attracted by the energized electromagnet. When the electromagnet is energized, the clutch disk is axially pulled from an engaged position in which the clutch friction surfaces are in frictional engagement with each other into a disengaged position in which the clutch friction surfaces are not in any frictional contact with each other. However, since the clutch disk is co-rotating with the rotor shaft, the rotating clutch disk rotates the liquid coolant which thereby generates a significant drag torque to the pump wheel. The energized electromagnet also axially attracts the pump wheel so that the stop friction surfaces come and remain in frictional contact with each other so that the pump wheel stops and does not at all rotate anymore.

According to a preferred embodiment, the clutch disk Is axially preloaded by a preload spring into an engaged clutch position. If the electromagnet is not energized at all, the preload spring pushes all elements of the clutch disk axially into the engaged clutch position so that the clutch friction surfaces get in frictional contact with each other with the consequence that the pump wheel is co- rotating with the rotor shaft. If the clutch actuation fails, the pump wheel always co-rotates with the rotor shaft. As a consequence, the clutch arrangement is fail safe.

Preferably, the pump wheel is provided with a non-ferromagnetic pump wheel body comprising pump blades and with a separate ferromagnetic clutch ring which is fixed to the pump wheel body, for example by bolts or by g!uing. The pump wheel body can be made of plastic which allows to realize a complex form with good fluidic properties and low weight, whereas the ferromagnetic clutch ring can be provided with good electromagnetic properties and/or with good frictional properties.

According to a preferred embodiment, the wheel-sided clutch friction surface and the wheel-sided stop friction surface are provided at the ferromagnetic clutch ring. Both pump-wheel-sided friction surfaces are provided at the ferromagnetic clutch ring which is part of the pump wheel. Preferably, an axial stop surface is provided to axialiy stop the clutch disk in the disengaged position. The stop surface is preferably provided co- rotatably with the rotor shaft but is axialiy fixed. The rotor-shaft-sided axial stop surface defines the axial disengagement position of the clutch disk in the disengaged state, namely when the electromagnet is energized and thereby attracts the clutch disk into the disengaged clutch disk position. The axial clutch disk stop limits the axial movement path of the clutch disk to an extent so that the clutch disk is not in frictional contact with the pump wheel even if the pump wheel is also axialiy attracted and pulled by the energized electromagnet into its axial disengagement position.

The clutch arrangement must not get jammed in the disengaged state. Preferably, the stop surface is lying in a transversal plane with respect to the longitudinal rotational axis of the rotor shaft and the pump wheel. The stop surface does not generate any frictional force in axial direction so that the clutch arrangement always reliably returns into the preloaded engaged position if the electromagnet is not energized.

According to a preferred embodiment, the axial electromagnetic gap between the ferromagnetic clutch ring and the ferromagnetic clutch disk is, in any clutch state, at least two times larger than the axial electromagnetic gap between the clutch ring and the electromagnet and between the clutch disk and the electromagnet. In other words, no relevant axial electromagnetic force is generated between the ferromagnetic clutch ring and the ferromagnetic clutch disk. Relevant magnetic forces in axial direction are only directly generated between the electromagnet and the ferromagnetic clutch ring, and between the electromagnet and the ferromagnetic clutch disk. As a another result of this arrangement, no relevant eddy currents can appear between the ferromagnetic clutch disk and the ferromagnetic clutch ring so that there is no relevant electromagnetic drag torque. Preferably, the axial electromagnetic gap between the ferromagnetic clutch ring and the ferromagnetic clutch disk is at least 1,0 mm, and preferably is at least 2,0 mm.

According to a preferred embodiment, the pump wheel is provided with a separate non-ferromagnetic friction ring arranged in the axial electromagnetic gap between the ferromagnetic clutch ring and the ferromagnetic clutch disk. The friction ring has a double-function, namely providing good friction quality as the antagonist of the friction disc and also defining a sufficiently large axial electromagnetic gap between the ferromagnetic clutch ring and the ferromagnetic clutch disk. The friction ring ensures that the axial electromagnetic gap between the ferromagnetic clutch ring and the ferromagnetic clutch disk always remains above a minimum value even in the engaged clutch state, so that no relevant magnetic field and eddy currents appear in this area.

According to a preferred embodiment, an electronic clutch control is provided to energize the electromagnet in a full-disengagement state. The clutch control is provided with an intermediate-engagement-state in which the clutch control provides the electromagnet with less electric energy than in the full-disengagement state. In the intermediate clutch- engagement-state, the electric energy can be on a level which puts the clutch wheel into a disengaged position but does not pull the pump wheel completely into its disengagement position so that the stop friction surfaces of the pump wheel and the pump frame do not come into full frictional contact. As a consequence, the pump wheel still can rotate and is rotated by the fluidic drag moment generated by the rotating clutch disk. With the third switching state of the clutch arrangement, a third rotational speed of the pump wheel can be realized, namely an immediate pump wheel speed which can be, for example in the range of 20% to 50% of the rotational speed of the rotating clutch disk. The intermediate clutch state thereby allows to adapt the pump performance of the coolant pump more accurately to the cooling performance requirement. One embodiment of the invention is explained with reference to the enclosed drawings, wherein

figure 1 shows a longitudinal section of a mechanical switchable automotive coolant pump in the with a clutch arrangement in the engaged state,

figure 2 shows the enlarged clutch arrangement of figure 1,

figure 3 shows the clutch arrangement of figure 2 in a disengaged state, and

figure 4 shows the clutch arrangement of figure 2 in an intermediate state.

The figures show a mechanical switchable automotive coolant pump 10 for providing a liquid coolant for an automotive engine 12. The coolant pump 10 is mechanically driven by a rotating driving means of the engine 12 which drives a transmission belt 13. The transmission belt 13 drives a pulley wheel 22 of the coolant pump 10. The coolant pump 10 of this embodiment is not provided with its own pump wheel housing but is adapted to be mounted directly to an engine body 11 of the engine 12. The engine body 11 defines an axial pump inlet channel 17 and an outlet volute 18 radially surrounding a pump wheel 60.

The coolant pump 10 is provided with a static pump frame 30 which is fixed to the engine body 11 by suitable fixation means, namely by screws and/or bolts. The static pump frame 30 rotatably supports a rota table rotor shaft 20 which is supported at the pump frame 30 by a shaft bearing 26, which is a roller bearing in this embodiment. The pump frame 30 also supports a static electromagnet 32 which is provided as a ring-shaped electromagnetic coil which, if energized with electric energy, generates a toroidal electromagnetic field.

The pump frame 30 also fixedly supports a shaft sealing 34 which surrounds and seals the rotor shaft 20 and thereby fluidically separates the wet zone of the pump 10 from the dry zone. The electromagnet 32, the shaft bearing 26, the pulley wheel 22 and a part of the rotor shaft 20 are provided in the dry zone. The other rotating elements of the pump are provided and located in the wet zone.

The rotor shaft 20 co-rotatably supports a ferromagnetic clutch disk 51 which is axially shiftable with respect to the rotor shaft 20 but is co- rotating with the rotor shaft. The rotor shaft 20 is provided with an axial transmission groove 27 and the clutch disk 51 is provided with a corresponding transmission nose 52 protruding radially into the transmission groove 27.

The rotor shaft 20 is also provided with a support structure 40 which is fixed to the rotor shaft 20 and axially supports an axial preload spring 28 which pushes the clutch disk 51 in axial distal direction away from the support structure 40. The support structure 40 is provided with an axial stop surface 56 to axially stop the clutch disk 51 in the disengaged position as shown in figure 3.

The rotor shaft 20 rotatably supports a pump wheel 60 which is rotatabie as well as axially shiftable with respect to the rotor shaft 20. The pump wheel 60 is provided with a plastic pump wheel body 67 which is not ferromagnetic, with a ferromagnetic clutch ring 66 and with a separate non-ferromagnetic friction ring 70. The pump wheel body 67 is rotatably and axially shiftable supported by a sliding bearing at the rotor shaft 20. The sliding bearing is defined by a separate sliding bearing sleeve 24 which is axially fixed by a fixation ring 22 at the rotor shaft 20.

The pump wheel body 67 comprises numerous pump blades 65 axially protruding from the distal side of a base disk 74 of the pump wheel body 67, The ferromagnetic clutch ring 66 is fixed to the pump wheel body 67 at the proximal side of the pump wheel body base disk 74 at the outer circumference thereof. The clutch ring 66 is provided with an axial leg and with a radial leg, seen in cross-section. At the proximal end of the axial clutch ring leg a stop friction surface 64 is provided which is in frictional contact with a corresponding stop friction surface 36 of the pump frame 30 in the disengaged state of the friction clutch arrangement, as shown in figure 3. Both stop friction surfaces 62, 64 are lying in a transversal plane being rectangular to the rotational axis 21 of the rotor shaft 20.

The pump wheel 60 is also provided with a separate non-ferromagnetic friction ring 70 at the proximal surface of the radial leg of the clutch ring 66. The proximal side of the friction ring 70 serves as a clutch friction surface 62 of the pump wheel 60. The clutch disk 51 is provided with a ring-like clutch friction surface 54 which corresponds with the clutch friction surface 62 at the pump wheel 60. If the clutch friction surfaces 54, 62 are in full frictional contact with each other, the pump wheel 60 co- rotates with the clutch disk 51 and the rotor shaft 20.

The electromagnet 32, the clutch disk 51 and the clutch ring 66 together define an electromagnetic wet friction clutch arrangement 50.

An electronic clutch control 14 is provided which controls and energizes the electromagnet 32. In the engaged clutch state of the clutch arrangement 50, as shown in figures 1 and 2, the clutch control 14 does not at all energize the electromagnet 32 so that the preload spring 28 axially pushes the clutch disk 51 into its engaged position so that the clutch friction surfaces 54, 62 are in full frictional contact with each other. The pump wheel 60 rotates with the rotational speed of the rotor shaft 20. In the fully disengaged clutch state as shown in figure 3, the clutch control 14 fully energizes the electromagnet 32 so that the ferromagnetic clutch disk 51 is axially attracted with a relatively high axial attraction force and the ferromagnetic clutch ring 66 of the pump wheel 60 is axially attracted with a relatively low axial attraction force. As a result, the clutch disk 51 first axially contacts the axial stop surface 56 and after that the stop friction surface 64 of the pump wheel 60 contact the corresponding stop friction surface 36 of the pump frame 30.

In the intermediate clutch state as shown in figure 4, the electromagnet 52 is moderately energized by the control 14 so that the clutch disk 51 is fully retracted into its disengaged position but the pump wheel 60 is not substantially attracted. As a result, the stop friction surfaces 64, 36 do not get into relevant frictional contact. As a result, the pump wheel 60 is rotated with about 20% of the rotational speed of the clutch disk 51 because of the fluldic drag torque transmitted by the liquid coolant which fills the wet zone.

In the engaged state of the clutch as shown in figures 1 and 2, the electromagnetic gap E between the stop friction surfaces 64, 36 is about 0,2 mm, the electromagnetic gap F between the clutch disk 51 and the axial stop surface 56 is about 0,4 mm. In the disengaged state of the clutch arrangement 50 as shown in fig. 3, the electromagnetic gap D between the ferromagnetic clutch ring 66 and the wheel-sided clutch friction surface 62 is about 1,5 mm. The axial thickness of the separate non-ferromagnetic friction ring 70 is at least 1,0 mm, preferably much more than 1,0 mm. The relatively large axial electromagnetic gap D ensures that no relevant axial magnetic forces are present in this gap D and that not relevant eddycurrents appear in this area.