Abstract:
An apparatus is proposed for a pump, in particular a water pump of a motor vehicle having a rotating pump wheel which can be driven, and having a switchable clutch arrangement for switchable connection of the pump wheel to a drive side. According to the invention, the pump wheel is mounted such that it can rotate on a rotatable driveshaft.

Description:
[0001]    This application claims the benefit under 35 USC §119(a)-(d) of German Application No. 10 2010 005 936.6 filed Jan. 26, 2010, the entirety of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to an apparatus for a pump, in particular a water pump of a motor vehicle, and a water pump. 
       BACKGROUND OF THE INVENTION 
       [0003]    European Patent Application Publication No. 2 105 624 A1 discloses a clutch, which can be operated electromagnetically, for a water pump in the cooling water circuit of an internal combustion engine having a drive wheel which can be mounted such that it can rotate in the area of or on the water pump, and having an armature disk which interacts with a coil. The clutch is designed to create a so-called “fail safe” arrangement, in which a water pump can be driven via the clutch even when no current is flowing in the coil, for example, if the electrical voltage supply fails. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention is based on the object of providing an apparatus for a pump, in particular a water pump, in a motor vehicle having a clutch arrangement, thus resulting in a switchable pump of compact design. 
         [0005]    The invention is based on an apparatus for a pump in a motor vehicle, in particular a water pump, for example for the cooling water circuit of an internal combustion engine. The pump comprises a rotating pump wheel which can be driven, and a switchable clutch arrangement for switchable connection of the pump wheel to a drive side. The essence of the invention is now that the pump wheel is mounted such that it can rotate on a rotatable driveshaft, such that a relative movement can take place between the pump wheel and the driveshaft. The pump wheel can therefore rotate on the driveshaft. This measure makes it possible to integrate a clutch arrangement at least partially in a simple manner in a pump, in particular within a pump housing. Roller bearings or journal bearings can be used to bear the pump wheel on the driveshaft. A low-cost journal bearing is preferably used, since the operating time in which the pump wheel is at a considerably lower rotation speed than the driveshaft as a result of an appropriately switched clutch is short in comparison to the total usage time. Any increased wear which occurs to a journal bearing, in comparison to a roller bearing, can therefore be coped with. 
         [0006]    When the clutch is engaged, the pump wheel preferably rotates at the same speed as the driveshaft, or at least approximately at the same speed as the driveshaft. However, ideally, there is no slip between the driveshaft and the pump wheel. In the disengaged state, there is at least a relative rotation speed between the pump wheel and a driveshaft which rotates as before. The pump wheel is preferably stationary, or is in a state with a low drag rotation speed, as a result of friction forces which occur as before. 
         [0007]    In order to, produce a disengaged or engaged state of the pump wheel, it is furthermore proposed that the pump wheel be movable axially on the driveshaft. It is therefore feasible for a friction section of the pump wheel to interact with friction means by axial movement, which friction means are arranged on the driveshaft such that they rotate together. 
         [0008]    In order to produce switching states of the clutch arrangement, it is furthermore proposed that an electromagnetic coil be provided, and act on a magnetically permeable armature element when current is flowing. An armature element is advantageously arranged within a pump housing. The electromagnetic coil can likewise be arranged within the pump housing, for a compact and low-cost design. However, an arrangement outside the pump housing is also feasible, and has advantages in terms of an electrical supply to the coil. 
         [0009]    It is also preferable for the armature element to be movable axially by an electromagnetic influence of the coil, wherein the switching state of the pump wheel can be predetermined by a selected axial position of the armature element. By way of example, this allows the pump wheel to move axially or the armature element to move a further element which acts on the pump wheel in order to produce a switching state. 
         [0010]    In order to transmit a torque from the driveshaft to the pump wheel, a further preferred refinement of the invention proposes that contact means, in particular friction means, are arranged on the driveshaft such that they rotate together, and are designed for a force fit and/or an interlock, in particular a force fit, with a friction section on the pump wheel which can rotate on the driveshaft. 
         [0011]    In this context, it is also preferable if the armature element and the friction means are matched to one another such that a friction fit is created between the driveshaft and the pump wheel, as a function of an axial position of the armature element. 
         [0012]    One particularly preferred refinement of the invention proposes a displacement member, by means of which a contact section, for example a friction section of the pump wheel, makes a friction contact with the friction means. The displacement member, for example a spring, and in particular a compression spring, preferably acts in the axial direction on the pump wheel when no current is flowing through the electromagnetic coil, as a result of which a friction section of the pump wheel is displaced against friction means which are connected to the driveshaft such that they rotate together. This results in a “fail safe” arrangement which ensures that the pump wheel rotates even when the voltage supply for the electromagnetic coil fails on a running internal combustion engine with a rotating driveshaft. Particularly when the pump is used in a cooling water circuit of an internal combustion engine, this makes it possible to ensure high operational reliability. 
         [0013]    It is also advantageous if the armature element is arranged on a spring element which is connected to the driveshaft such that they rotate together, wherein the spring element is designed to exert an axial pressure effect on the pump wheel. This likewise makes it possible to create a friction fit between a friction means, which is arranged on the spring element, and a corresponding friction section on the pump wheel when no current is flowing through the electromagnetic coil, and there is therefore no force acting on the armature element, thus creating a “fail safe” arrangement. For example, when current is flowing in the coil, the armature element can be moved axially such that friction means which press in a sprung manner against the pump wheel are lifted off it, thus allowing the pump wheel to rotate freely or essentially freely on the driveshaft. 
         [0014]    In a further preferred embodiment, it is advantageous for the armature element to be arranged on the pump wheel. The armature element can be fitted on the induction side or on the side of the pump wheel remote from the induction side. 
         [0015]    When no current is flowing through the electric coil, a displacement member, in particular a spring element, allows the pump wheel to be displaced to an engaged state. 
         [0016]    Furthermore, for defined positioning of the pump wheel, it is preferable for an axial bearing stop to be formed on the driveshaft for the pump wheel. The bearing stop preferably acts as a rotating bearing, thus allowing to rotate essentially freely in a situation in which the pump wheel is pressing against the bearing stop with an axial pressure force and, furthermore, for example, the friction means are not producing any further friction forces. 
         [0017]    In one preferred embodiment, the friction means on the driveshaft comprise a wedge element which can make a friction fit with a friction section on the pump wheel. This allows the pump wheel to be made to rotate at the same speed as the driveshaft with a comparatively small axial displacement force, by means of a “wedge drive effect” of a friction surface in the form of a wedge, by means of a friction fit. 
         [0018]    The apparatus according to the invention is preferably used for pumps in a motor vehicle, in particular water pumps. In the case of internal combustion engines, the preferred application is the water pump for the water cooling circuit. A switchable cooling water pump allows the engine to be raised to the operating temperature more quickly when it is being started up from the cold state. For this purpose, in this phase of engine operation, the cooling water circuit is switched off by disengaging the pump wheel. As soon as the engine is then at a predetermined operating temperature, the pump wheel is engaged, as a result of which the cooling water circuit starts to run. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    A plurality of exemplary embodiments of the invention are illustrated in the figures and will be explained in more detail in the following text, indicating further advantages and details. 
           [0020]      FIG. 1  shows a schematic illustration of a partially sectioned side view of parts of a cooling water pump with a clutch arrangement, and 
           [0021]      FIGS. 2 and 3  show a corresponding illustration of two further embodiments for comparable parts. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  shows elements of a cooling water pump with a clutch arrangement within a pump housing, which is not illustrated. The cooling water pump comprises a pump shaft  1  on which a pump wheel  2  is borne such that it can rotate via a sliding bush  3  which extends axially and radially. The radial section  3   a  of the sliding bush  3  can rest on a radial bearing stop  4 , for example in the form of a steel disk. A sliding ring seal or a similar seal can also preferably be integrated in the bearing stop. The pump wheel  2  is preferably in the form of an impeller, as is illustrated in  FIG. 1 , which is surrounded by an appropriately shaped housing (not illustrated). 
         [0023]    A compression spring  5  is mounted on the driveshaft such that they rotate together and has an engagement section  6  which can interact in an interlocking and/or force-fitting manner with the pump wheel  2 . In the present case, a groove  2   a  in the form of a V or wedge is incorporated in an annular shape into the pump wheel  2 , and an engagement section  6  enters this groove  2   a  in order to produce a friction fit between the appropriately matched engagement section  6  and the groove  2   a.    
         [0024]    However, it is also feasible for the engagement section  6  to have shaped elements which fit corresponding shaped elements in the V-shaped groove  2   a , thus resulting in an interlock in the engaged state. 
         [0025]    A magnetically permeable armature element  7 , for example an annular element which interacts with an electromagnet  8 , is fitted to the engagement section  6 . The electromagnet  8  may be fitted inside or outside the pump housing. If arranged outside the pump housing, a magnetic circuit must be ensured through the pump housing to the armature element  7 , in order to allow a magnetic force to act on the armature element  7  when current flows through the electromagnet  8 . 
         [0026]    Stop elements, for example in the form of finger-like stop elements, are preferably provided to limit the movement of the compression spring  5  on which the engagement section  6  and the armature element  7  are arranged, which stop elements axially limit axial movement of the armature element  7  when an attraction force is applied by the electromagnet  8 . 
         [0027]    A water pump arrangement as shown in  FIG. 1  operates as follows: 
         [0028]    Because the engagement section is pressed against the pump wheel  2  when no current is flowing through the electromagnet  8 , this results in a “fail safe” arrangement, in which the pump wheel runs at the same rotation speed as the pump shaft  1  when no current is flowing, because of the friction effect of the engagement section  6 . 
         [0029]    In order to “disengage” the pump wheel, a voltage is applied to the electromagnet and can be increased in an initial time interval in order to draw the armature element against the electromagnet  8 . This releases the friction fit between the engagement section  6  and the wedge-shaped groove  2 , and the pump wheel is borne such that it can then rotate freely on the pump shaft  1 . The axial stop fingers, which are not illustrated, in the area of the compression spring  5  limit the axial movement of the armature element  7 , such that it cannot come into contact with the electromagnet  8  when current is flowing through the electromagnet. 
         [0030]      FIG. 2  shows an embodiment in which the wedge-shaped groove  2   a  and the engagement section  6  have been replaced by a wedge element  9 , which interacts with a conical recess  10 , which matches the wedge element  9 , on the pump wheel  2 . A bearing stop  11  which is opposite the radial section  3   a  of the bearing bush  3  can move axially and is pressed by a compression spring in the axial direction against the pump wheel  2 . The pump wheel  2  is therefore moved axially in the direction of the wedge element  9 , thus resulting in a friction fit between the wedge element  9  and the conical recess  10 . In this state, the pump wheel  2  preferably runs at the same rotation speed as the pump shaft  1 . 
         [0031]    The friction torque between the pump wheel  2  and the wedge element  9  drives the pump wheel  2 . When current is passed through the electromagnet  8 , the pump wheel  2  is drawn in the direction of the electromagnet  8  via an armature element  13  which is arranged in or on the pump wheel  2 , thus releasing the force that is transmitted between the wedge element  9  and the conical recess  10 . For example, the armature element  13  can be encapsulated in the pump wheel  2 . The pump wheel is pressed against the bearing stop  11 , for example in the form of a steel disk, with the bearing stop being designed such that no or essentially no drive torque is transmitted to the pump wheel when the pump shaft  1  is rotating. In this case, the pump wheel is disengaged, and no pump effect takes place. 
         [0032]      FIG. 3  shows an embodiment which operates analogously to the embodiment shown in  FIG. 2 , with the difference that the elements  8 ,  11 ,  12 ,  13  have been transferred to the induction side while, in contrast, the wedge element  9  and the conical recess  10  which matches it are arranged on the side  15  remote from the induction side  14 . 
         [0033]    In a corresponding manner to that in the exemplary embodiment shown in  FIG. 2 , when no current is flowing through the electromagnet  8 , the compression spring  12  presses the pump wheel  2  against the wedge element  9 , by means of which the drive torque of the pump shaft  1  can be transmitted to the pump wheel  2  by a friction fit. When current is passed through the electromagnet  8 , the pump wheel  2  can be disengaged, with the pump wheel  2  being pulled away from the wedge element  9  via the armature element  13 , by means of an axial movement of the pump wheel  2  on the pump shaft  1 . This represents the disengaged state. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Pump shaft 
           2  Pump wheel 
           2   a  Groove 
           3  Bearing bush 
           3   a  Radial section 
           4  Bearing stop 
           5  Compression spring 
           6  Engagement section 
           7  Armature element 
           8  Electromagnet 
           9  Wedge element 
           10  Conical recess 
           11  Bearing stop 
           12  Compression spring 
           13  Armature element 
           14  Induction side 
           15  Remote side