Abstract:
The invention relates to a regulatable coolant pump for a cooling circuit of an internal combustion engine, comprising a hollow bearing shaft ( 1 ) carrying a drive wheel ( 2 ) on one end thereof and being secured to an impeller ( 18 ) on the opposite end thereof. The impeller ( 18 ) includes an abutment surface ( 19 ) on the front side, and the space between the impeller ( 18 ) and the abutment surface ( 19 ) is embodied as a conveying cross-section ( 22 ). The drive wheel ( 2 ) can be uncoupled from the bearing shaft ( 1 ) via a draw key ( 3 ).

Description:
[0001]    The present invention relates to a regulatable coolant pump for a cooling circuit of an internal combustion engine, including a hollow bearing shaft carrying a drive wheel on its one end and is fixedly connected to an impeller on its opposite end, the impeller having an abutment surface on its front side, and the space between the impeller and the abutment surface being designed as a conveying cross section. 
         [0002]    In the field of internal combustion engines, water-cooled engines have become widely accepted. 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 pump needed for circulating the water is usually connected to a belt pulley of the crankshaft of the internal combustion engine via a belt. 
         [0003]    The direct coupling between the coolant pump and the crankshaft ensures that the rotational speed of the pump is dependent on the rotational speed of the internal combustion engine. As a result, a corresponding volumetric flow through the pump is provided within the high rotational speed range of the internal combustion engine, which is not needed to this extent for cooling. During a cold start of the internal combustion engine, however, the problem arises that coolant is already circulating through the cooling channels, which hinders the heating of the combustion chambers and thus delays the reaching of an optimal operating temperature. 
       BACKGROUND 
       [0004]    A regulatable coolant pump according to the aforementioned definition of the species is known from the publication DE 10 2008 046 424. In this publication, a guide disk having a contour corresponding to the impeller is situated between the impeller and a cover disk, the guide disk being guided by axial webs, connecting the impeller and the cover disk, and being axially movable via a controlling unit with the aid of a piston placed within the hollow shaft. 
         [0005]    The guide disk has a projection on its outer edge which is oriented in the direction of the impeller and with the aid of which the guide disk covers the annular channel of the pump housing depending on its position between the impeller and the cover disk. This has the advantage that the annular channel may be covered with the aid of simple means. The controlling unit is designed in the manner of an armature which is fixedly connected to the piston and which is axially movable in a targeted manner via a proportional solenoid. Intermediate positions of the guide disk may also be implemented with the aid of a configuration of this type. 
         [0006]    In the water pump illustrated in the prior art, the proportional solenoid would have to apply a force of approximately 200 N. This would result in the solenoid having to be given disproportionately large dimensions in relation to the actual water pump. However, the crucial disadvantage is that the impeller also always rotates when the drive wheel is being driven, since the impeller is connected directly to the crankshaft, even when cooling of the engine is not yet desired. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide a cost-effective, installation space-optimized, regulatable water pump. 
         [0008]    The present invention provides that the drive wheel may be uncoupled from the bearing shaft with the aid of a draw key. Due to the uncoupling, the drive wheel continues to be driven by the rotating crankshaft gear, while the bearing shaft is uncoupled and stands still, as does the impeller. This procedure is required both to reduce unnecessary power output and to warm up the internal combustion engine more rapidly during a cold start, since the pump does not yet pump water through the system. 
         [0009]    In further specifying the present invention, it is proposed that the bearing shaft has a hollow design and the draw key is linearly movably situated therein. This space-saving design is particularly advantageous, since it permits a dual use of the installation space used by the bearing shaft. 
         [0010]    According to another preferred refinement of the present invention, it is proposed that the draw key is linearly adjustable with the aid of an actuator. The actuator may be operated mechanically, hydraulically, pneumatically, electrically, magnetically or in another way. 
         [0011]    According to another preferred refinement of the present invention, a one-sidedly open cylinder on the impeller side is linearly movably situated in the hollow bearing shaft, and one side of the draw key, in turn, is linearly guided in the cylinder. To adapt the quantity of the water throughput within the pump to the cooling requirements of the engine, a guide disk is mounted on the front side of the cylinder base of the one-sidedly open cylinder. The guide disk has a projection on its outer edge which is oriented in the direction of the impeller and with the aid of which the guide disk partially or completely closes the conveying cross section, depending on the axial position of the cylinder. 
         [0012]    Moreover, pressure is axially applied to the draw key by a first spring and a second spring. This safety measure ensures that the drive wheel is nonrotationally connected to the bearing shaft if the actuator fails, and the conveying cross section is reopened by pushing the draw key, to which the spring pressure is applied, into the necessary position. 
         [0013]    In one preferred embodiment of the present invention, it is provided to situate a coupling in the bearing point of the pivot of the drive wheel, the draw key, the bearing shaft, the drive wheel and coupling bodies situated between the draw key and the drive wheel forming the coupling. Placing the coupling in the pivot of the drive wheel is another way to save installation space. Due to the force-fitted connection between the drive wheel and the bearing shaft, the direct transmission of force or torque from the crankshaft gear to the bearing shaft is ensured. 
         [0014]    According to another preferred embodiment of the present invention, it is provided that the bearing point of the pivot of the drive wheel has a shifting geometry, the shifting geometry having radially and axially running grooves with which the coupling bodies engage. In the coupled state, the coupling bodies are clamped in an indentation of one of the axial grooves. The axial grooves, which are spaced a distance apart, are embedded deeper into the bearing point than the radial grooves, which are situated between the axial grooves. The drive wheel is advantageously manufactured in an injection molding or sintering process in such a way that the shifting geometry formed in the pivot of the drive wheel may be easily produced. 
         [0015]    It has proven to be advantageous to design the coupling bodies as rolling elements. In other words, the coupling bodies may be given a spherical, cylindrical or barrel-like shape. 
         [0016]    One particular advantage of the present invention is that both the uncoupling of the drive wheel and the closing of the conveying cross section with the aid of a guide wheel take place by actuating a single component, namely a draw key. Due to this design, the regulatable water pump may be manufactured in a particularly space-saving manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The exemplary embodiment of the present invention is illustrated in  FIGS. 1 through 3 , which are described in detail below. 
           [0018]      FIG. 1   a  shows a schematic representation of a regulatable water pump in the coupled state, having a maximum volumetric flow rate; 
           [0019]      FIG. 1   b  shows a detailed representation of the shifting geometry at the bearing point of the drive wheel; 
           [0020]      FIG. 2  shows a schematic representation of a regulatable water pump in the coupled state, having a zero volumetric flow rate; and 
           [0021]      FIG. 3  shows a schematic representation of a regulatable water pump in the uncoupled state, having a zero volumetric flow rate. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1 through 3  show a regulatable water pump, including a hollow bearing shaft  1  which has a drive wheel  2  on its one end and an impeller  18  on its opposite end. Impeller  18  has an abutment surface  19  on its front side, and the impeller is connected to the abutment surface to form a single piece. The space between impeller  18  and abutment surface  19  is designed as a conveying cross section  22  for the water to be conveyed. Conveying cross section  22  is located, so to speak, between a suction chamber and a pressure chamber. 
         [0023]    A draw key  3  is linearly shifted within hollow bearing shaft  1  with the aid of an actuator  21 . Draw key  3  has different diameters. Draw key end  16  which faces impeller  18  is enclosed by a one-sidedly open cylinder  11  which is also linearly movably situated in bearing shaft  1 . To adapt the quantity of the water throughput within the pump to the cooling requirements, a guide disk  17  is mounted on the front side of cylinder base  14  of one-sidedly open cylinder  11 . Guide disk  17  has a projection on its outer edge which is oriented in the direction of impeller  18  and with the aid of which guide disk  17  may partially or completely close conveying cross section  22 , depending on the axial position of cylinder  11 . The movement of one-sidedly open cylinder  11  is limited, on the one hand, by abutment surface  19  and, on the other hand, by an abutment  20  introduced into hollow bearing shaft  1 , which may be designed as an annular disk. Cylinder  11  has a taper  25  on its open end. A first spring  12  is situated between draw key end  16  situated in cylinder  11  and cylinder base  14 . First spring  12  is supported against cylinder base  14  by its one end and against draw key end  16  by its other end. Due to its different diameters, draw key  3  has a first radial shoulder  23  in the area enclosed by cylinder  11 . The linear movement of draw key  3  within cylinder  11  is limited by the fact that it hits taper  25  of cylinder  11  with its first shoulder  23 . Draw key  3  furthermore has a second spring  9 , which encloses draw key  3  in an area having a smaller diameter. Second spring  9  is supported by its one end on aforementioned annular shoulder  23 , which is situated in bearing shaft  1 . Second spring  9  is supported by its other end on another second shoulder  24  of draw key  3 . 
         [0024]    In the initial position of the draw key ( FIG. 1   a ), both springs  9 ,  12  are relaxed, draw key  3  is in its maximum extended position, and guide disk  17  completely releases conveying cross section  22 . 
         [0025]    A coupling  10  is situated between bearing shaft  1  and drive wheel  2 . The function of the coupling is explained in greater detail below ( FIG. 1   b ). 
         [0026]    A linearly movable draw key  3  is situated in hollow bearing shaft  1 ; draw key  3  having different diameters. Bearing shaft  1  has multiple openings  13  on its circumferential side in the area of coupling  10 , in which coupling bodies  5  are situated. Coupling bodies  5  are rotatably movably mounted in openings  13 . In the radial bearing shaft direction, the mobility of coupling bodies  5  is limited on one side by an adjacent bearing point  4  of drive wheel  2  and on the opposite side by draw key  3 . Draw key  3  is linearly moved within bearing shaft  1  with the aid of an actuator  21 . The subarea of draw key  3  having the larger diameter is guided along the inner circumferential surface of bearing shaft  1 . If the subarea having larger diameter D strikes coupling bodies  5  during the shifting of draw key  3 , coupling bodies  5  are pushed out of their original position in the direction of bearing point  4  of drive wheel  2  and clamped in a form-fitted manner. A shifting geometry  6  is provided within bearing point  4  of drive wheel  2  (see  FIG. 1   b ). Shifting geometry  6  is formed from axially running grooves  7  and from radially running grooves  8 . Axial grooves  7  are spaced an equal distance apart and distributed on the circumference of bearing point  4 , creating flat webs  15  between axial grooves  7  in bearing point  4 . Radial grooves  8  are circumferentially introduced within these flat webs  15  in a type of circular trajectory. Axial grooves  7  are introduced deeper into bearing point  4  than radial grooves  8 . When draw key  3  shifts coupling bodies  5  in the direction of bearing point  4  of drive wheel  2  or in the direction of shifting geometry  6 , coupling bodies  5  engage with deeper situated axial grooves  7  in such a way that flat webs  15  adjoining axial grooves  7  prevent a radial deflection of coupling bodies  5 . A rotatably fixed connection is thereby established between bearing shaft  1  and drive wheel  2 . If drive wheel  2  is driven by a driving means, which is not illustrated herein, e.g., a camshaft gear or belt, bearing shaft  1  rotates as a result of the rotatably fixed connection. 
         [0027]    For the reasons explained above, it may be advantageous in some operating states, e.g., during engine startup, if bearing shaft  1  does not concurrently rotate. However, since the crankshaft gear is constantly directly or indirectly engaged with drive wheel  2 , the drive wheel is always also driven once the crankshaft gear begins to rotate. To enable the rotatably fixed connection between bearing shaft  1  and drive wheel  2  to be released, draw key  3  must be shifted. When draw key  3  is shifted, its subarea having larger diameter D is brought out of the contact area of coupling bodies  5 , so that coupling bodies  5  are able to return to their original position. In their original position, coupling bodies  5  rest against both draw key  3  and bearing point  4 . Since coupling bodies  5  no longer extend so far into bearing point  4 , they slide into radially running grooves  8 . In this uncoupled state, coupling bodies  5  only roll along radial grooves  8  acting as a track. Drive wheel  2  is thus idle. Another advantage of shifting geometry  6  designed according to the present invention is that drive wheel  2  is axially secured by radial grooves  8  which are embedded less deeply into bearing point  4  and with which coupling bodies  5  engage. 
         [0028]      FIG. 2  shows how draw key  3  is moved in the direction of abutment surface  19  under the force influence of actuator  21 . Second shoulder  24  of draw key  3  compresses second spring  9 . To enable the driving force acting upon draw key  3  to be transmitted to one-sidedly open cylinder  11  and to guide disk  17  connected thereto, and to also move these components, it is necessary for first spring  12  to have a greater spring constant than second spring  9 . Draw key  3  continues to be moved until guide disk  17  hits abutment surface  19 , which completely closes conveying cross section  22 , and a so-called zero volumetric flow prevails. 
         [0029]    As the force of the actuator continues to act upon draw key  3 , the latter is moved farther against the spring force of first spring  12 , as shown in  FIG. 3 . If, due to the shifting movement, the area of draw key  3  having larger diameter D is removed from the contact area of coupling bodies  5 , coupling bodies  5  fall back against smaller diameter d of draw key  3 , and drive wheel  2  is uncoupled. Bearing shaft  1  and impeller  18  connected thereto thus stop rotating in closed conveying cross-section  22 . 
         [0030]    If actuator  21  were to fail at the point in time of closed conveying cross-section  22  ( FIG. 2 ), draw key  3  would continue to be pressed back in the direction of drive wheel  2 , due to second spring  9 , so that guide disk  17  again releases conveying cross-section  22 . Drive wheel  2 , which is still connected to bearing shaft  1  at this point in time, ensures that coolant continues to be pumped through the system. 
         [0031]    Were actuator  21  to fail at the point in time of closed conveying cross-section  22  and an uncoupled drive wheel  2  ( FIG. 3 ), first spring  12  would press draw key  3  in the direction of drive wheel  2 , so that coupling bodies  5  slide back into bearing point  4  of drive wheel  2 . Second spring  9  would press draw key  3  farther in the direction of drive wheel  2 , so that guide disk  17  again releases conveying cross-section  22 . 
         [0032]    The two springs  9 ,  12  implement the required failsafe solution, which ensures cooling of the system even if actuator  21  fails. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Bearing shaft 
           2  Drive wheel 
           3  Draw key 
           4  Bearing point 
           5  Coupling bodies 
           6  Shifting geometry 
           7  Axial groove 
           8  Radial groove 
           9  Second spring 
           10  Coupling 
           11  One-sidedly open cylinder 
           12  First spring 
           13  Openings 
           14  Cylinder base 
           15  Flat web 
           16  Draw key end 
           17  Guide disk 
           18  Impeller 
           19  Abutment surface 
           20  Abutment 
           21  Actuator 
           22  Conveying cross-section 
           23  First shoulder on draw key 
           24  Second shoulder on draw key 
           25  Taper