Abstract:
A controllable coolant pump for a cooling circuit of an internal combustion engine having a pump housing with an inner bore, a shaft drivable via a pulley mounted rotatably via a first bearing and a second bearing, wherein the shaft is configured at least partially as a hollow shaft and has a longitudinal axis, wherein a rotor is fastened to one end of the shaft, which rotor has an idler pulley and vanes which project into a suction chamber to suck water via a suction connector of the pump housing into the suction chamber to an annular channel of the pump housing, wherein the idler pulley can be displaced axially via a push rod connected to an actuator. The fluidic actuator has a first pressure chamber and a second pressure chamber. The weight and the installation space requirement of the controllable coolant pump can be reduced.

Description:
[0001]    The present invention relates to a controllable coolant pump, in particular for an internal combustion engine, having a fluidic actuator. 
       BACKGROUND 
       [0002]    Internal combustion engines are usually water-cooled engines, in which, with the aid of a coolant pump in a closed circuit, cooling water is pumped through cooling channels in the area of the cylinders for cooling the internal combustion engine and subsequently conveyed to an air/water cooler, where the heated water is cooled again with the aid of the air stream. The coolant pump needed for circulating the water is usually connected to a drive pulley of the crankshaft of the internal combustion engine via a driving means. The direct coupling between the coolant pump and the crankshaft establishes a dependency of the rotational speed of the pump on the rotational speed of the internal combustion engine, so that, in modern internal combustion engines, controllable coolant pumps are frequently used whose delivered volume flow may be adapted according to the demand for coolant. 
         [0003]    A controllable coolant pump for a cooling circuit of an internal combustion engine, including a pump housing, is known from DE 10 2008 046 424 A1, in which a hollow shaft, drivable by a belt pulley, is supported, to one end of which a rotor is fastened, which has vanes extending into a suction chamber and which is fixedly connected to a cover disk via axial bars, it being possible, due to the rotation of the rotor together with the cover disk, to suck water into the suction chamber via an intake connection of the pump housing and to deliver it to an annular channel of the pump housing via the vanes, an idler pulley which has a contour corresponding to the rotor being situated between the rotor and the cover disk, the idler pulley being guided via the axial bars and being axially movable with the aid of a piston placed within the hollow shaft, using a final control unit. 
         [0004]    The disadvantage of a configuration of this type is that controlling the coolant flow with the aid of the piston and the final control unit makes for a heavy weight and requires a great deal of installation space. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to provide a controllable coolant pump for a cooling circuit of an internal combustion engine, which has a reduced weight and requires less installation space. 
         [0006]    The present invention provides a controllable coolant pump for a cooling circuit of an internal combustion engine which includes a pump housing having an inner bore, in which a shaft which is drivable by a drive wheel is rotatably supported by a first bearing and a second bearing, the shaft being at least partially designed as a hollow shaft and having a longitudinal axis, a rotor being fastened to the one end of the shaft and having vanes and an idler pulley which extend into a suction chamber, it being possible, due to the rotation of the rotor, to suck water into the suction chamber via an intake connection of the pump housing and to deliver it to an annular chamber of the pump housing via the vanes, the idler pulley being axially movable via a push rod connected to an actuator. According to the present invention, the actuator forms a fluidic actuator, the fluidic actuator having a first pressure chamber to which a pressurized fluid may be applied, and a second pressure chamber to which a pressurized fluid may be applied. 
         [0007]    The controllable coolant pump is drivable via a drive wheel which may be connected to the shaft on an end opposite the drive wheel. The rotor may have vanes extending into a suction chamber, it being possible, due to the rotation of the rotor to suck cooling water into the suction chamber via an intake connection of the pump housing and to deliver it to an annular channel of the pump housing via the vanes. The idler pulley may be axially moved with the aid of a push rod which may be situated coaxially to and partially within the shaft, in particular the hollow shaft, the delivery volume of the suction chamber of the coolant pump being variable. In a first position of the push rod, the delivery volume and the coolant flow of the cooling water pump may reach a maximum, while in a second position of the push rod, the delivery volume and the coolant flow of the cooling water pump may reach a minimum. The pump housing of the coolant pump has an inner bore, in which a first bearing and a second bearing, for example a first ball bearing and a second ball bearing, are situated at an axial distance from each other, the drivable shaft being rotatably supported in the first bearing and in the second bearing. The shaft may be designed, at least in part, in the form of a hollow shaft, the portion of the shaft designed as a hollow shaft being designed in the form of a bore or a blind hole. The shaft may also be designed in the form of a hollow shaft, the hollow shaft being able to have areas having different inner diameters, for example to accommodate a push rod, in particular a push rod having different diameters. The idler pulley is connected to the push rod, via which the idler pulley is movable in the axial direction due to an axial movement of the push rod. The push rod may be situated coaxially to the shaft, it being possible to situate the push rod at least partially within the shaft, in particular the hollow shaft. The push rod is displaceable in the axial direction by a fluidic actuator which is actuatable, for example, by a liquid or a gas. The fluidic actuator has a first pressure chamber and a second pressure chamber, it being possible to apply a pressurized fluid to the first pressure chamber and to the second pressure chamber. 
         [0008]    The pressure may be an underpressure or an overpressure in relation to an ambient pressure. The first pressure chamber and the second pressure chamber may be situated coaxially to the longitudinal axis of the shaft, in particular within the pump housing, in particular within the inner bore of the pump housing. The pressure acting upon the first and the second pressure chambers may be controlled, for example by a four/two-way valve. Due to the fluidic actuator, a continuous, in particular hydraulic or pneumatic, control of the water pump for the cooling circuit of the internal combustion engine is possible. In particular, the control of the coolant pump may take place continuously. Moreover, the weight and the installation space requirements of the controllable coolant pump may be reduced by using a fluidic actuator. The energy demand of the controllable coolant pump may furthermore be reduced. 
         [0009]    In one preferred embodiment, an annular first seal, an annular second seal located at an axial distance therefrom and a movable sealing ring situated between the first seal and the second seal are provided in the inner bore, a first pressure chamber being provided between the first seal and the sealing ring, and a second pressure chamber being provided between the sealing ring and the second seal. The annular first seal may be situated and supported, for example, on the first bearing, and the annual second seal may be situated and supported, for example, on the second bearing opposite the first seal. A sealing ring, which is movably situated and provided in the axial direction between the first seal and the second seal, is situated between the first seal and the second seal. An annular first pressure chamber is provided between the first seal and the sealing ring, the first pressure chamber having a variable volume, and an annular second pressure chamber, which is also variable in its volume size, being provided between the second seal and the sealing ring. The total volume of the first pressure chamber and the second pressure chamber remains essentially constant, an increase in the size of the first pressure chamber being able to essentially correspond to a decrease in the size of the second pressure chamber. The first pressure chamber and the second pressure chamber have an essentially annular shape, it being possible to provide the first and second pressure chambers between the pump housing and the shaft in the radial direction. The first and second pressure chambers essentially have pressure surfaces of essentially the same size, in particular on the sealing ring. The sealing ring is movable in the axial direction by a change in pressure in the first pressure chamber and/or the second pressure chamber, with a corresponding change in volume. The axial movement of the sealing ring is transmittable to the push rod, whereby a change in the position, in particular in the axial direction of the idler pulley, is achievable. The sealing ring may be displaced in the axial direction in the inner bore, in the manner of a piston, whereby a continuous, in particular hydraulic or pneumatic, control of the coolant pump, in particular the idler pulley of the coolant pump, may be facilitated. 
         [0010]    The push rod situated in the shaft preferably has a transmission element, which contacts the sealing ring through at least one opening provided in the shaft. The push rod situated within the shaft may have a transmission element, with the aid of which the push rod may be connected to the sealing ring, the movement of the sealing ring, at least the movement of the sealing ring in an axial direction, being transmittable to the push rod. The transmission element may be designed in the form of a cross pin, which may protrude essentially perpendicularly through the push rod or be situated thereon, and which rests against the sealing ring at least on one side. The transmission element may be fixedly connected to the sealing ring, whereby an axial movement of the sealing ring may be transmittable to the push rod in two axial directions. To feed the transmission element through the shaft, in particular the hollow shaft, the shaft may have at least one opening, for example in the form of an elongated hole. The sealing ring may have an extension in the axial direction, which facilitates a covering of the opening in the shaft, as well as a fluid-tight sealing of the at least one opening with respect to the first and the second pressure chambers. A structurally simple transmission of an axial movement of the sealing ring to the push rod may be ensured with the aid of the transmission element. 
         [0011]    It is preferred that the push rod has a push rod shoulder on a first end situated within the shaft, and a first shaft shoulder is provided within the shaft, through which the push rod protrudes, an annular, variable first pressure chamber being provided between the push rod shoulder, the first shaft shoulder, the push rod and the shaft. The push rod shoulder of the push rod may be provided within the hollow shaft, for example in an annular or disk-shaped manner, the diameter of the push rod being able to be significantly smaller than the diameter of the push rod shoulder, which may essentially correspond to the inner diameter of the hollow shaft. The first shaft shoulder is provided at an axial distance from the push rod shoulder and may have an annular or disk-shaped design, in particular including a push rod lead-through for axial lead- through of the push rod. A first pressure chamber, which is delimited in the radial direction by the inner wall of the hollow shaft and the push rod, is provided between the push rod shoulder and the first shaft shoulder in the axial direction. A second shaft shoulder may be provided within the shaft, in particular the hollow shaft, on a side of the push rod shoulder facing away from the first shaft shoulder. The second shaft shoulder may be designed, for example, in the form of a solid continuation of the shaft or in the form of an insert within the hollow shaft. A second pressure chamber, which is provided in the radial direction by the inner wall of the hollow shaft and the push rod, may be provided between the push rod shoulder and the second shaft shoulder in the axial direction. The second shaft shoulder, in particular in the form of a solid shaft, may have a push rod lead-through for leading through the push rod, for example for contacting the push rod with the aid of the idler pulley. With the aid of the push rod lead-throughs, it may be ensured, in particular, that the pressure surfaces of the first pressure chamber and the second pressure chamber are essentially of the same size, in particular on the push rod shoulder. The push rod shoulder may be situated within the hollow shaft between the first shaft shoulder and the second shaft shoulder in a way which permits movement in the axial direction in the manner of a piston, valve or slide valve. In particular the push rod shoulder may be situated in a hollow shaft which essentially functions like a cylinder in a way which permits movement in the axial direction in a piston-like manner. A first pressure chamber and/or a second pressure chamber may be provided within the hollow shaft for axial displacement of the push rod, in particular the push rod shoulder. An axial movement of the push rod shoulder may be achievable by a change in pressure in the first pressure chamber and/or in the second pressure chamber, it being possible to provide the first pressure chamber and the second pressure chamber within the hollow shaft and to situate them coaxially with respect to each other. 
         [0012]    In one preferred embodiment of the present invention, an actuator housing having a recess and a cover is provided to at least partially accommodate the push rod in the recess, the actuator housing being situated on the side of the drive wheel facing away from the pump housing, a first pressure chamber being provided in the actuator housing with the aid of the push rod and a second pressure chamber being provided with the aid of the push rod and the cover. The recess of the actuator housing may be designed, for example, in the form of a blind bore hole which may be covered by a cover, the cover being able to have a push rod lead-through. The push rod may have a first push rod shoulder, which may be situated within the recess of the actuator housing, the diameter of the push rod shoulder being able to essentially correspond to the inner diameter of the recess of the actuator housing, the diameter of the push rod being able to be significantly smaller than the diameter of the first, for example disk-shaped, push rod shoulder. A first pressure chamber, which is delimited in the radial direction by the push rod and the inner wall and the recess of the actuator housing, is provided between the first push rod shoulder and the actuator housing, a second pressure chamber is delimited between the first push rod shoulder and the cover in the axial direction, which is delimited in the radial direction by the inner wall of the recess of the actuator housing and the push rod. Within the recess of the actuator housing, the push rod, in particular the push rod shoulder, is movably situated and provided in the manner of a piston by a change in pressure in the first pressure chamber and in the second pressure chamber. Due to the axial movement of the push rod shoulder, the movement may be transmitted to the idler pulley via the push rod, whereby the delivery volume, and thus the coolant flow of the coolant pump, is controllable. Due to the provision of the fluidic actuator in the actuator housing, which is situated on the side of the drive wheel facing away from the pump housing, the actuator may be transferred out of the pump housing, whereby the installation space of the pump housing of the coolant pump may be optimized, in particular in the axial direction. 
         [0013]    In particular, at least one first end stop for limiting the axial movement of the push rod is provided on the shaft and/or the actuator housing. The first end stop may be provided on the hollow shaft and/or the actuator housing, the first end stop being able to limit the movement, in particular in the axial direction of the push rod, in particular the push rod shoulder. In addition to the first end stop, a second end stop may be provided, situated at an axial distance from the first end stop. The first end stop and the second end stop may have, for example, an annular or disk-shaped design or be in the form of a shoulder which is provided within the hollow shaft, oriented radially to the inside. An annular first and/or second end stop, for example in the form of a snap ring, may be accommodated in a groove within the inner wall of the hollow shaft. The first and second end stops may be situated in such a way that the push rod, in particular the first and/or the second push rod shoulder(s), is displaceably situated in the axial direction between the first end stop and the second end stop. Due to the design of the first and/or second end stop(s), the movement of the push rod in the axial direction may be limited. It may also be ensured that the first and/or the second pressure chamber(s) has/have a minimum volume. 
         [0014]    The pump housing, the actuator housing and/or the hollow shaft preferably has/have at least one fluid-permeable first bore to the first pressure chamber and a second bore to the second pressure chamber for supplying and/or discharging the fluid. The first bore and/or the second bore facilitate(s) the application of pressure to the first and/or the second pressure chamber(s) by a fluid. The first and/or second pressure bore(s) may extend through the pump housing and the shaft, in particular a wall of the hollow shaft, up to the first and/or the second pressure chamber(s). The pump housing may have a housing shoulder which may be situated within the inner bore, in particular in the axial direction between the first and second bearings, it being possible to provide the housing shoulder radially to the inside and to contact the shaft, in particular the hollow shaft, radially on the outside. Due to the housing shoulder, which extends radially to the inside and contacts the shaft, it is possible to guide the first bore and/or the second bore(s) through the pump housing up to the shaft, in particular the hollow shaft, and to lead the first bore and/or the second bore(s) to the first pressure chamber and/or the second pressure chamber in a fluid-permeable manner. Pressure may thus be applied to the first pressure chamber and the second pressure chamber, due to a simple construction. 
         [0015]    A spring element for actuating the push rod is particularly preferably provided, the spring element being situated between the push rod and the shaft or the actuator housing or the cover. The spring element may be designed in the form of a tension spring or a pressure spring. The spring element may be situated in such a way that an axial displacement of the push rod, in particular the push rod shoulder, for example to reduce the volume flow of the coolant pump, may be directed against the direction of force of the spring element, whereby a return of the push rod, in particular of the push rod shoulder, for example to a first position having a maximum coolant delivery flow, may be ensured if the fluidic actuator fails. If a single first pressure chamber is used, which acts against the force of the spring element, the structural complexity of the fluidic actuator may also be further reduced. 
         [0016]    In one preferred embodiment of the present invention, a sensor element is provided for detecting the position of the push rod. The sensor element may be designed in the form of a mechanical, opto-electronic or electromagnetic sensor. The sensor element may be situated on the sealing ring, the push rod and/or the push rod shoulder, for example in the pump housing and/or the actuator housing. The sensor element may detect an axial displacement and/or position in the axial direction of the sealing ring, the push rod and/or the push rod shoulder. In particular, the sensor element may detect the absolute position in the axial direction of the sealing ring, the push rod and/or the push rod shoulder. Due to the sensor element, the actual position of the sealing ring, the push rod and/or the push rod shoulder may be detected, in particular in the axial direction, whereby the position of the idler pulley is ascertainable. 
         [0017]    Due to the use of a controllable coolant pump according to the present invention in an internal combustion engine, the weight and the necessary installation space of the controllable coolant pump, and in particular the internal combustion engine, may be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention is explained below by way of example on the basis of preferred exemplary embodiments, with reference to the attached drawings. 
           [0019]      FIG. 1  shows a schematic sectional view of a controllable coolant pump according to the present invention; 
           [0020]      FIG. 2  shows a schematic sectional view of a controllable coolant pump according to the present invention, including a first pressure chamber and a second pressure chamber within a hollow shaft; 
           [0021]      FIG. 3  shows a sectional view of a hollow shaft, including a push rod and a first and a second pressure chamber; 
           [0022]      FIG. 4   a  shows a schematic view or a sectional view of a push rod in a first position on a first end stop; 
           [0023]      FIG. 4   b  shows a schematic sectional view of a push rod between a first and a second end stop; 
           [0024]      FIG. 4   c  shows a schematic view of a controllable coolant pump, including a pressurized second pressure chamber; 
           [0025]      FIG. 5  shows a schematic sectional view of an actuator housing, including a sensor element. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a controllable coolant pump  10 , which has a pump housing  12 , including an inner bore  14 . A first bearing  16  is situated within inner bore  14 , and a second bearing  18  is situated at an axial distance therefrom. A shaft  20  is rotatably situated in first bearing  16  and second bearing  18  within inner bore  14  of pump housing  12 . Between first bearing  16  and second bearing  18 , an annular first seal  22  is situated on first bearing  16 , and an annular second seal  24  is situated on second bearing  18 . First seal  22  and second seal  24  form an essentially fluid-impermeable seal in the axial direction. A sealing ring  26 , which is movably supported in the axial direction between first seal  22  and second seal  24 , is situated between first bearing  16  and second bearing  18  and first seal  22  and second seal  24 . A first pressure chamber  28 , which is delimited in the radial direction by shaft  20  and pump housing  12 , is provided between first seal  22  and sealing ring  26  in the axial direction. A second pressure chamber  30 , which is delimited in the radial direction by shaft  20  and pump housing  12 , is provided between second seal  24  and sealing ring  26  in the axial direction. An axial movement of sealing ring  26  is transmittable via a transmission element  32 , which is connected to a push rod  34  situated within shaft  20 . Transmission element  32  is situated essentially perpendicularly to push rod  34  and connected thereto, transmission element  32  protruding through shaft  20  through openings  36  and contacting sealing ring  26  on one side. Transmission element  32  may be fixedly connected to sealing ring  26 . A pressurized fluid may be applied to first pressure chamber  28  via a first bore  38  in pump housing  12 , and a pressurized fluid may be applied to second pressure chamber  30  via a second bore  40  in pump housing  12 . Due to a change in pressure in first pressure chamber  28  and/or second pressure chamber  30 , an axial movement of sealing ring  26  may be implemented, the axial movement of sealing ring  26  being transmittable to push rod  34  via transmission element  32 . Push rod  34  may be connected to an idler pulley (not illustrated) of controllable coolant pump  10 , whereby the volume flow of coolant pump  10  may be controlled. A spring force may be applied to push rod  34  by a spring element  42 , which is situated on the front of push rod  34  and is supported on the inside of shaft  20 . A sensor element  44 , which detects the position of sealing ring  26 , is situated in pump housing  12 . 
         [0027]      FIG. 2  shows a controllable coolant pump  10 , whose pump housing  12  has a housing shoulder  46  between first bearing  16  and second bearing  18 , which extends radially to the inside and contacts shaft  20  on the outside. First bore  38  extends through pump housing  12 , housing shoulder  46  and the wall of shaft  20 , which is at least partially designed as a hollow shaft, whereby a pressurized fluid may be applied to first pressure chamber  28  and second pressure chamber  30 . First pressure chamber  28  is delimited in the axial direction between a push rod shoulder  48  and a first shaft shoulder  50 , which is situated at an axial distance from push rod shoulder  48 . Push rod shoulder  48  is designed in the shape of a disk which is provided on push rod  34 . The diameter of push rod shoulder  48  essentially corresponds to the inner diameter of shaft  20 , which is at least partially designed as a hollow shaft. First shaft shoulder  50  is designed in the form of a disk-shaped insert in the area of shaft  20  designed as a hollow shaft and has a push rod lead-through. Second pressure chamber  30  is provided in the axial direction between push rod shoulder  48  and a second shaft shoulder  52  situated on the side of push rod shoulder  48  facing away from first shaft shoulder  50  and is delimited in the radial direction by shaft  20  and push rod  34 . A spring element  42  is situated within second pressure chamber  30 , with the aid of which push rod  34 , in particular push rod shoulder  48 , may be displaced in the axial direction into a defined position, for example a first position having a maximum delivery volume, in the event of a pressure drop. Sensor element  44  is situated on pump housing  12  in such a way that sensor element  44  is able to contact push rod  34 , whereby the position of push rod  34  may be detected in the axial direction. 
         [0028]      FIG. 3  shows a shaft  20 , which is at least partially designed as a hollow shaft in the form of a blind bore hole, in which push rod  34 , including a first push rod shoulder  48 , is situated, push rod  34  being led through a first shaft shoulder  50  and a second shaft shoulder  52 . First pressure chamber  28 , to which a pressurized fluid may be applied through a first bore  38 , is provided between first shaft shoulder  50  and push rod shoulder  48 . Second pressure chamber  30  is provided between push rod shoulder  48  and second shaft shoulder  52  in the form of the solid shaft continuation, and a pressurized fluid may be applied thereto through second bore  40 . Spring element  42 , which rests against and is situated on push rod shoulder  48  and second shaft shoulder  52 , is situated in second pressure chamber  30 . Shaft  20  has a first end stop  54  and a second end stop  56  on the radial inside, push rod shoulder  48  being displaceable between first end stop  54  and second end stop  56  in the axial direction, the axial movement of push rod shoulder  48 , and thus of the push rod, being limited by first and second end stops  54 ,  56 . 
         [0029]      FIG. 4   a  shows a push rod  34  having a push rod shoulder  48  within a shaft  20 , a pressure being applied to first pressure chamber  28  via first bore  38 , the second opening or bore  40  of second pressure chamber  30  being depressurized, for example connected to a tank. Push rod  34  is shown in a first position, in which controllable coolant pump  10  has its maximum delivery volume. Push rod  34 , in particular push rod section  48 , rests against first end stop  54 . Due to the application of pressure to first pressure chamber  28 , push rod  34  may be displaced to the right in the axial direction in the direction of second end stop  56 , whereby the position of the idler pulley (not illustrated) is variable, whereby the delivery volume of coolant pump  10  is variable.  FIG. 4   b  shows a push rod  34 , whose push rod section  48  is shown in a position approximately between first end stop  54  and second end stop  56 . Spring element  42  is compressed with respect to the illustration in  FIG. 4   a . A fluid is applied to first pressure chamber  28  and second pressure chamber  30  through first bore  38  and second bore  40 , the pressure in first pressure chamber  28  essentially corresponding to the pressure in second pressure chamber  30 . Taking the force of spring element  42  into account, a force equilibrium between first and second pressure chambers  28 ,  30  may be set, whereby push rod  34  may be held in the particular position in a stationary manner. In  FIG. 4   c , first pressure chamber  28  is depressurized via first bore  38 , for example by connecting it to a tank. A pressurized fluid is applied to second pressure chamber  30  through second bore  40 , the pressure being greater than the pressure, for example an ambient pressure, acting in first pressure chamber  28 , whereby push rod  34 , together with push rod shoulder  48 , was moved in the axial direction in the direction of first end stop  54 , starting from the position of push rod  34  illustrated in  FIG. 4   b . The force of spring element  42  may act in the direction or against the direction of the movement of push rod  34 . 
         [0030]      FIGS. 4   a  through  4   c  show, by way of example, a sequence of switching operations for the fluidic actuator according to the present invention, for example using a 4/2-way valve. First and second pressure chambers  28 ,  30  are filled with a fluid. To leave a basic position, for example the first position, of the push rod, a fluid may be supplied to first pressure chamber  28  via first bore  38 , it being possible to connect second bore  40  of second pressure chamber  30  to a tank (not illustrated) or an outlet. The pressurized fluid acts upon push rod shoulder  48  and displaces it against the force of spring element  42  in the manner of a piston. Once the desired position has been reached, both bores, first and second bores  38 ,  40 , may be connected to the pressure line. The fluidic actuator maintains its set position, a control operation being able to only compensate for leaks. If push rod  34  is displaced in the direction of the basic position, first bore  38  may be connected to the tank, pressure continuing to be applied to second bore  40 . If the pressure supply fails, push rod  34  may be returned to the basic position with the aid of spring element  42 . 
         [0031]      FIG. 5  shows a controllable coolant pump  10  having an actuator housing  58 . Actuator housing  58  has a recess, in which push rod  34 , including push rod section  48 , is situated in the manner of a piston. The recess in actuator housing  58  is closed by a cover  60 . Actuator housing  58  and cover  60  have a lead-through for push rod  34 . First pressure chamber  28  is provided between actuator housing  58  and push rod shoulder  48 , and second pressure chamber  30  is provided between push rod shoulder  48  and cover  60 . A spring element  42  is situated in second pressure chamber  30 . A pressurized fluid may be applied to first pressure chamber  28  via first bore  38 , and a pressurized fluid may be applied to second pressure chamber  30  via second bore  40 . Due to a pressure change in first and/or second pressure chamber(s)  28 ,  30 , a displacement of push rod shoulder  48  and push rod  34  may be implemented in the axial direction, whereby push rod  34  connected to the idler pulley may cause a change in the volume flow of coolant pump  10 . A sensor element  44 , which detects the axial position and/or movement of push rod  34 , is situated on actuator housing  58 . 
       List of Reference Numerals 
       [0032]      10  Coolant pump 
         [0033]      12  Pump housing 
         [0034]      14  Inner bore 
         [0035]      16  First bearing 
         [0036]      18  Second bearing 
         [0037]      20  Shaft 
         [0038]      22  First seal 
         [0039]      24  Second seal 
         [0040]      26  Sealing ring 
         [0041]      28  First pressure chamber 
         [0042]      30  Second pressure chamber 
         [0043]      32  Transmission element 
         [0044]      34  Push rod 
         [0045]      36  Opening 
         [0046]      38  First bore 
         [0047]      40  Second bore 
         [0048]      42  Spring element 
         [0049]      44  Sensor element 
         [0050]      46  Housing shoulder 
         [0051]      48  Push rod shoulder 
         [0052]      50  First shaft shoulder 
         [0053]      52  Second shaft shoulder 
         [0054]      54  First end stop 
         [0055]      56  Second end stop 
         [0056]      58  Actuator housing 
         [0057]      60  Cover