Abstract:
An actuator which, by a movement of a component which is generated by means of an electric current, can effect control of another component in a mechanical environment having rotating parts which are housed in a very small space. A rotating element, for example a clutch shaft ( 1; 21 ), is hollow, and an electromagnetic coil arrangement ( 7; 24 ) is housed in this cavity in such a way that the excitation of the coil is converted into a mechanical displacement of a component arranged outside the clutch shaft, for example of a sleeve sliding axially on the clutch shaft. For this purpose, parts of the clutch shaft are made ferromagnetic and are integrated in the magnetic loop of the coil ( 7; 24 ). The actuator according to the invention can be used, for example, in a viscous clutch for controlling the throughput of shear medium.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to actuators for viscous clutches and more particularly to viscous clutches with actuators with oil circulation valves.  
       BACKGROUND OF THE INVENTION  
       [0002]     In viscous clutches, the torque of a rotation source is transmitted via discs enclosing a shear region, a small distance apart and substantially parallel to one another, from the rotation source to an element to be driven. The amount of shear fluid which is introduced between the rotating discs into the shear region controls the degree of torque transmission between a lower threshold value, for example 10%, to virtually completely.  
         [0003]     The control of the amount of shear fluid, for example silicone oil, which is introduced into the shear region is effected by a valve which can be opened and closed by means of an actuator. European Patent Application 1 248 007 describes such an actuator, which is arranged outside the clutch shaft and around the latter. Since the actuator is stationary and the clutch shaft rotates, it is necessary to use a correspondingly dimensioned ball bearing whose internal diameter according to the EP Patent Application corresponds to the external diameter of the shaft. For each shaft size, it is therefore necessary to use and especially to stock an appropriate ball bearing. Furthermore, the solution according to the EP Patent Application requires the use of insulating material.  
         [0004]     It is an object of the present invention to provide an improved viscous clutch. It is also an object of the present invention to provide a viscous clutch which is smaller in size and is less complex than known viscous clutches.  
         [0005]     It is an additional object of the present invention to provide a viscous clutch with an actuator which minimizes or eliminates the use of insulating material.  
         [0006]     It is a still further object of the present invention to provide an actuator for the shear fluid circulation, for example of a viscous clutch, in which the size of the actuator components are substantially reduced which in turn reduces the size of the entire viscous clutch.  
       SUMMARY OF THE INVENTION  
       [0007]     These and other objects are achieved by the present invention as described, depicted, and claimed herein. In general, the present invention relates to an actuator for actuating, for example, a valve for controlling the oil throughput of a viscous clutch. The actuator cooperates functionally with a rotating part of the viscous clutch, such as, for example, the clutch shaft. The actuator also has a primary actuator which is mounted by means of a bearing permitting a rotation of the actuator relative to the clutch shaft or the like on the clutch shaft or the like. The clutch shaft or the like preferably has a hollow cylindrical region, and the primary actuator is arranged inside the hollow cylindrical region. The actuator and clutch shaft or the like have means for communicating the control activity of the primary actuator from inside the hollow cylindrical region to the outside.  
         [0008]     The arrangement of the primary actuator inside the clutch shaft makes it possible to design the actuator substantially smaller than if it were arranged around the clutch shaft. It is also possible to use a standard actuator side since the internal bore of the clutch shaft can be kept constant, depending on its external diameter. The ball bearings or roller bearings for relative positioning between coil axle and clutch shaft can be made much smaller than the ball bearing of the EP Patent Application, in which a ball bearing is arranged outside the clutch shaft.  
         [0009]     According to an embodiment of the invention, the primary actuator comprises a solenoid coil. By means of this solenoid coil, it is possible to produce a magnetic field with the aid of which a mechanical component can be brought into different positions. These different positions can be transmitted to a valve, which is controllable thereby between open and closed.  
         [0010]     With the use of the actuator according to the invention in a viscous clutch, the valve controlled by the actuator can be used for controlling the flow rate of shear fluid, such as silicone oil.  
         [0011]     According to an embodiment of the invention, the moveable component may be a sleeve. The sleeve is mounted on the clutch shaft, closely but to permit sliding, outside the clutch shaft. The sleeve can be moved by the primary actuator between two end positions defined by corresponding stops.  
         [0012]     For this purpose, it is advantageous if regions of the clutch shaft and the moveable sleeve are part of the magnetic loop of a solenoid coil.  
         [0013]     According to an embodiment of the invention, the solenoid coil may be mounted on a stationary coil axle. The outer contour of the coil axle carries the inner contour of a ball bearing which rests with its own outer contour on the inner surface of the hollow cylindrical clutch shaft. This allows relative rotation between the coil axle and clutch shaft.  
         [0014]     In one embodiment, the wall of the hollow cylindrical region of the clutch shaft consists of a hollow cylindrical main shaft of ferromagnetic material, a pot like shaft front part of ferromagnetic material and nonmagnetic intermediate part which is arranged axially between main part and shaft front part. This results in a hollow cylinder of ferromagnetic material with a nonmagnetic sector more or less in the middle of its axial length, said sleeve being arranged outside this hollow cylinder in such a way that it extends over the nonmagnetic part, and, in one end position, it has a considerable overlap with one of the two ferromagnetic parts and little or no overlap with the other of the two ferromagnetic parts whereas, in the other end position, it has substantially equal overlaps with both ferromagnetic parts of the clutch shaft.  
         [0015]     Main shaft, intermediate part and shaft front part can be screwed, welded, or otherwise fixedly secured to one another.  
         [0016]     According to another embodiment of the invention, the actuator can be designed such that the moveable component is formed from a pot-like shaft front part enclosing, with its sleeve-like region, the cylindrical part of the clutch shaft.  
         [0017]     The pot-like front part of the clutch shaft may be moved in a telescopic-type manner on the clutch shaft, and this displacement can be utilized as a control movement, for example of the oil flow valve of a viscous clutch.  
         [0018]     In the embodiments of the invention which have been described, the moveable components or the sleeves can also be pretensioned by means of a resilient member, such as a spring in one of their two end positions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The invention will now be explained in more detail with reference to the drawings, in which:  
         [0020]      FIG. 1  shows a first embodiment of the present invention,  
         [0021]      FIG. 2  shows another embodiment of the present invention, and  
         [0022]      FIG. 3  shows a viscous clutch having an actuator according to an embodiment of the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]      FIG. 1  shows a lower unit of a viscous clutch. The input shaft I of the viscous clutch is mounted by means of a ball bearing or roller bearing  14  in a clutch housing, which is not shown, and can rotate freely in the clutch housing (if it is caused to rotate by a clutch disc rotationally connected to it and not shown).  
         [0024]     As shown in  FIG. 3 , the input shaft of the clutch is nonrotatably connected to a primary disc  42  which has, in its radially outer region, a labyrinth formation which, together with an opposite similar formation, forms the so-called shear zone of the viscous clutch. Shear fluid is introduced into the shear zone in order to transmit the rotation from the driven primary disc to the clutch disc  45  (in  FIG. 3 , this is the clutch cover), the amount of shear fluid being decisive for the ratio of the speed of the driven primary disc to the driven clutch disc carried along. This ratio may vary between a preselectable minimum value, e.g. 10°s, to virtually 100%, the variation being controllable by means of the amount of the oil introduced between the clutch disc and the primary disc.  
         [0025]     The clutch shaft  1  of  FIG. 1  has a main shaft  1   a,  an intermediate part  2  and a front part  3 . Main shaft  1  and front part  3  are produced from a ferromagnetic material, whereas the intermediate part  2  is nonmagnetic. The reason for this will be explained further below.  
         [0026]     Arranged outside the clutch shaft is a sleeve  4 , which is axially displaceable on the clutch shaft between a stop  6  and a ferromagnetic ring  5 . The stop can be of any conventional type, such as a snap ring.  
         [0027]     Arranged inside the hollow cylindrical clutch shaft is a coil axle  8  which has, approximately in its axial middle, a radially enlarged region  8   a  whose external diameter is slightly smaller than the internal diameter of the hollow cylindrical clutch shaft. In this manner, the coil axle, which is kept in its position and prevented from rotating by means not shown, permits a rotation of the clutch shaft. To enable this rotation to take place virtually without friction, a ball bearing  13  or the like whose inner contour rests on the outer surface of the coil axle  8  and whose outer contour rests on the inner surface of the hollow cylindrical clutch shaft is provided adjacent to the radially enlarged region  8   a.    
         [0028]     A coil  7  which surrounds the coil axle is arranged on that side of the radially enlarged region  8   a  of the coil axle  8  which is opposite the ball bearing  13 .  
         [0029]     The coil axle is slightly longer than the coil on the side of the coil and carries a likewise stationary magnetic flux ring  9 , so that the coil  7  is completely enclosed in section, in particular starting from radially inside and extending in a clockwise direction, by the coil axle  8 , the radially extended region  8   a  of the coil axle  8 , the intermediate part  2  of the clutch shaft  1  and the flux ring  9 . All these parts, with the exception of the intermediate part  2 , are ferromagnetic, and only the intermediate part  2  is nonmagnetic.  
         [0030]     Excitation of the coil  7  generates a magnetic field which, starting from the coil axle  8 , penetrates on the one hand via the radially enlarged region  8   a  of the coil axle into the main shaft  1   a  and the ring  5  and, on the other hand, via the flux ring  9  into the front part  3  of the clutch shaft.  
         [0031]     This creates an axial magnetic gap between the ring  5  and the sleeve  4 , the force generated by the magnetic field attempting to move the sleeve  4  in the direction of the ring  5 .  
         [0032]     A restoring means which is not shown and, for example, is in the form of a spiral spring, pretensions the sleeve in the position shown. From this position, the sleeve can be moved against the force of the restoring device into another position adjacent the ring  5  on application of an electric current of a certain strength through the turns of the coil  7 .  
         [0033]     A bolt  10  is screwed into the hollow coil axle in such a way that it clamps the coil  7  axially between the radially enlarged region  8   a  of the coil axle  8  and the magnetic flux ring  9 .  
         [0034]     In order to ensure an exact tolerance, constant over the circumference of the flux ring  9 , between the circumferential surface of the flux ring and the inner surface of the front part  3  of the clutch shaft, a second ball bearing  15  may be used, as shown.  
         [0035]     In order to avoid any vibrations, a Belleville ring  11  can be inserted between the flux ring  9  and the coil  7 , as shown.  
         [0036]     The description so far of  FIG. 1  shows that the clutch shaft  1  carries a sleeve  4  which can be axially displaced by applying an electric current.  
         [0037]     This axial displacement can now be used in a manner not shown to control a valve, with the aid of which the amount of shear fluid between the above-mentioned primary disc and the coupling disc can be adjusted in order to control the degree of torque transmission between these two discs.  
         [0038]      FIG. 2  shows another embodiment of the invention, which is illustrated laterally inverted in comparison with the view in  FIG. 1 .  
         [0039]     A hollow cylindrical clutch shaft  21  is mounted by means of a twin ball bearing  10   a  in a housing which is not shown, for example of a viscous clutch.  
         [0040]     In contrast to  FIG. 1 , the clutch shaft  21  consists only of two parts, namely the main shaft  21   a  and the front part  21   b.    
         [0041]     Both parts of the clutch shaft are produced from ferromagnetic material, the front part  21   b  having a pot-like design, the cylindrical part  22  of which is mounted telescopically on the main shaft  21   a  and can be moved axially thereon.  
         [0042]     Similarly to the first embodiment, the clutch shaft is hollow and holds a coil axle  25  mounted rotatably relative to the clutch shaft by a twin ball bearing  29  inside the clutch shaft.  
         [0043]     The coil axle carries a coil  24  which is held firmly in its position by a Belleville spring  27  and which can produce a magnetic loop described further below.  
         [0044]     The front part  21   b  of the clutch shaft or, on the basis of the first embodiment, the sleeve  22  is clamped by means of a spiral spring  31  in an end position which most greatly lengthens the main shaft  21 , the front part  21   b  thereby being prevented from falling off the shaft by a stop which is not shown.  
         [0045]     In contrast to the embodiment shown in  FIG. 1 , the magnetic gap is formed not axially between the sleeve  22  and the ring  23 , since both elements rest on the likewise ferromagnetic shaft  21   a,  but between a stationary magnetic pole  26 , which encloses the coil axle in an annular manner, and a central sleeve  22   b  which is in the form of an annular cone and is shaped from one piece together with the base part  22   a  of the front part  21   b  or is at least welded thereto, and extends axially towards the stationary magnetic pole.  
         [0046]     The magnetic loop of the coil  24  thus extends, starting from the coil axle  25  and continuing in the clockwise direction, through a radially enlarged region  25   a  of the coil axle  25 , the clutch shaft, the sleeve  22 , the base part  22   a,  the central sleeve  22   b  in the form of an annular cone, the stationary magnetic pole  26 , back to the coil axle.  
         [0047]     The magnetic gap is formed between the stationary magnetic pole  26  and the central sleeve  22   b,  the thin edge of the central sleeve  22   b  being only a small radial distance (e.g. 0.3 mm) away from the stationary magnetic pole when the gap is opened to a maximum extent and, on application of an electric current, a force occurring which attracts the front part  21   b  in a direction, against the force of the spring  31 , which increases the magnetic cross-section of the gap when the central sleeve is pushed telescopically onto the stationary magnetic pole, owing to the conical shape of the central sleeve.  
         [0048]     Moreover, the base part  22   a  of the front part  21   b  is attracted by the stationary magnetic pole  26 .  
         [0049]     Here, as in the case of the movement of the sleeve  4  in the first embodiment, the movement of the sleeve  22  or of the front part  21   b  can be used for controlling a valve for throughput control of the shear liquid of a viscous clutch.  
         [0050]     Common to both embodiments of the invention which have been described is that the coils  7  and  24  can be operated by means of electric cables which are led, in a manner not shown, from the coil directly into the central bore of the coil axle and follow said axle axially and emerge from the coil axle centrally at the end of the coil axle at  12  (in  FIG. 1 ) or at  28  (in  FIG. 2 ) and are therefore very easy to mount and to handle.  
         [0051]     The coil axles  8  and  25  are fixed in their position by means which prevent rotation and are not shown.  
         [0052]      FIG. 3  shows an actuator according to the invention in a viscous clutch for controlling a cooling fan of a truck.  
         [0053]     Here, the actuator is identical to that of  FIG. 2 , and the reference numerals  21  to  31  are identical to those of  FIG. 2 .  
         [0054]     The clutch shaft  21  is rotatably connected via the ball bearing or roller bearing  10   a  to the housing  41  of the viscous clutch. Furthermore, the clutch shaft  21  is rigidly connected to a primary disc  42 , also referred to as the rotor. In its radially outer region on both sides, the rotor  42  has a labyrinth-like formation which engages, closely but without contact, a corresponding similar labyrinth-like formation on the one hand in the clutch cover  45  and in the housing  41 . By introducing shear fluid, for example viscous silicone oil, into this labyrinth region, the rotation of the rotor  42  is transmitted simultaneously on one side to the clutch cover  45  as well as on the other side to the housing  41 , the amount of oil being critical for the efficiency of the transmission of rotation.  
         [0055]     A fan for the radiator of a vehicle is mounted, in a manner not shown, on the housing  41  which is caused to rotate.  
         [0056]     Corresponding to  FIG. 2 ,  FIG. 3  shows the front part  21   b  of the clutch shaft  21 , whose sleeve  22  axially displaceable by the actuator according to the invention is connected to one end of a valve arm  43 , this valve arm having, at its other end, an extension ( 53 ) with the aid of which, on movement of the valve arm, an oil outlet hole  52  can be opened to a greater or lesser extent in order thereby to influence the amount of oil in the shear region.  
         [0057]     The viscous clutch of  FIG. 3  furthermore has a stop  51  for driving the primary disc  42  by the clutch shaft  21 , a stop sleeve  40  for the front part  21   b  and hence for the valve lever  43  and a cover for the oil reservoir, the functions of which are self-evident and need not be explained in more detail here.  
         [0058]     The invention was explained with reference to two nonlimiting embodiments. It is possible to make numerous changes without deviating from the spirit of the present invention.  
         [0059]     Thus, for example, the entire arrangement could rotate inside the hollow cylindrical part together with the clutch shaft, and it would be necessary to provide a corresponding rotational contact for the electric current supply of the coil. This would have the advantage that no ball bearings would have to be used inside the clutch shaft.