Abstract:
A pump unit with a drive motor mounted onto a pump block which reduces noise problems which stem from clearance fits that are required in order to be able to mount the drive motor onto the pump block. A pump unit set forth eliminates clearance fits required for the perfect assembly of the pump unit by means of plastic introduced into the clearance fits. The pump unit is particularly provided for slip-controlled vehicle brake systems in motor vehicles.

Description:
CROSS REFERENCE TO A RELATED APPLICATION 
     This application is a 371 of PCT/DE98/03806 filed Dec. 29, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention is based on a pump unit. 
     A pump unit, which is comprised of a piston pump and a drive motor that drives the piston pump, has already been disclosed by DE 44 30 909 A1 and U.S. Pat. No. 5,564,909. The pump pistons of the piston pump are disposed in a pump block to which the motor housing of the drive motor is flange mounted. A shaft, which is driven by the drive motor and protrudes from the motor housing into the pump block, is used to drive the pump pistons of the piston pump. The motor housing has a projection which protrudes into a recess provided in the pump block. This projection of the motor housing contains a bearing which is supported on the shaft. 
     In the pump unit disclosed by DE 44 30 909 A1 and U.S. Pat. No. 5,564,909, it is disadvantageous that the bearing forces which arise at the center bearing cannot be optimally absorbed by the motor housing. DE 195 36 794 A1 has disclosed an embodiment which attempts to solve this problem by virtue of the fact that the bearing is built directly into the pump block between the drive motor and the pump pistons. However, this produces considerable technical manufacturing difficulties because with this embodiment, it is not possible to carry out a separate assembly and a possible separate testing of the drive motor before mounting the motor onto the pump block. 
     It has turned out that the connection, which is not optimally play-free, between the drive motor and the pump block contributes to the generation of noise. 
     In DE 44 30 909 A1 and U.S. Pat. No. 5,564,909, a radial clearance fit is disposed between the end of the shaft protruding into the pump block and the inner bearing ring of the bearing, there so that it is possible to assemble the components. With this bearing there is also the problem that this clearance fit also contributes to the generation of noise. 
     Because tolerances and clearance fits cannot be entirely avoided despite extremely high manufacturing precision, unpleasant noise produced by them must be expected. 
     DE 44 30 909 A1 and U.S. Pat. No. 5,564,909 disclosed pump units in which, the shaft is supported by means of an additional bearing in the motor housing, on the end remote from the pump block. However, the cost of manufacturing this bearing and the considerable space requirement for this bearing have up to now been significant disadvantages. 
     ADVANTAGES OF THE INVENTION 
     The pump unit according to the invention has an advantage over the prior art that a considerable reduction of the noise produced by the pump unit and frequently also an improvement in the service life of the pump unit can be achieved at a low manufacturing cost. 
     The clearance fit can advantageously be generous enough so that the drive motor, together with the shaft, can be very simply connected to the pump block. 
     Because the motor housing, the shaft, and the at least one bearing contained by the motor housing constitute a preassembled unit, the advantage of a low manufacturing cost and the advantage that when needed, the drive motor, together with the shaft, can be separately tested before being mounted onto the pump block are retained; and the advantage is also attained that the bearing forces of the at least one bearing can be optimally absorbed by the relatively rigid pump block, which results in a considerable degree of noise reduction. Because of the increase in rigidity, it is advantageously possible without risk to reduce the material thicknesses used, in particular the wall thickness of the motor housing or the thickness of the pump block. 
     Advantageous improvements and updates of the pump unit are possible by means of the measures set forth herein. 
     Injecting plastic into the clearance fit, which can be made fluid for example by means of heating or which hardens for example by means of a chemical reaction only after the passage of time, attains the advantage that the manufacturing cost as a whole is not significantly increased because it is possible to introduce the plastic with ease. 
     The first bearing, which is held by the motor housing between the at least one pump piston and the drive motor, absorbs a considerable part of the forces acting on the shaft. Eliminating the radial play at the projection of the motor housing, which protrudes into the recess of the pump block, by means of the introduced plastic, attains the advantage that the significant part of the bearing forces can be absorbed by the pump block, which is of significant importance for the service life of the pump unit and for an effective noise reduction. 
     Eliminating the clearance fit between the second bearing and the pump block, attains the advantage that the production of unpleasant noise in the vicinity of the second bearing is eliminated or at least sharply reduced. 
     Since the second bearing can be built into the pump block with a radial clearance fit, the second bearing can be connected to the shaft that protrudes from the motor housing before the drive motor is mounted onto the pump block, which significantly decreases the manufacturing cost in an advantageous manner and significantly increases the testability. 
     In the vicinity of the first bearing and in the vicinity of the second bearing, if the radial play between these two bearings and the pump block is eliminated by means of the introduced plastic, then the advantage is attained that the noise generation is eliminated or sharply reduced at both bearings. 
     If the shaft in the motor housing is supported by means of a bearing pin provided on the motor housing, which engages in a bush protruding axially beyond the shaft, then the advantage is attained that the drive motor is made significantly more rigid for a low manufacturing cost and without a noticeable increase in the required installation space. Another advantage is that the shaft does not have to be machined especially for the additional bearing, in particular the end of the shaft oriented toward the additional bearing also does not have to be bored on the end face, which would entail a considerable cost. 
     The engagement of the bearing pin in the bush attains the additional advantage that the diameter of the additional bearing can be selected as relatively large without this resulting in additional cost for manufacturing or material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferably selected, particularly advantageous exemplary embodiments of the invention are shown in a simplified fashion in the drawings and will be explained in detail in the subsequent description. 
     FIG. 1 shows a longitudinal section through a first selected exemplary embodiment; 
     FIG. 2 shows a cross section of a plastic filled radial clearance bit between a projection and a recess for mounting a preassembled unit; 
     FIG. 3 shows a cross section of plastic filled pockets in greater detail; and 
     FIG. 4 shows a longitudinal section through another selected exemplary embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The piston pump of the pump unit embodied according to the invention is provided in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. The abbreviations ABS, TCS, ESP, or EHB are used for such brake systems, depending on the type of brake system. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to supply brake fluid from a storage tank into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS, ESP, or EHB). The pump is required, for example, in a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (ESP) and/or an electrohydraulic brake system (EHB). With wheel slip control (ABS or TCS), for example, a locking of the wheels of the vehicle during a braking event when there is strong pressure on the brake pedal (ABS) and/or a spinning of the driven wheels of the vehicle when there is strong pressure on the gas pedal (TCS) can be prevented. In a brake system that serves as a steering aid (ESP), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump supplies the brake fluid into the wheel brake cylinder or cylinders if an electrical brake pedal sensor detects an actuation of the brake pedal or in which the pump is used to fill a reservoir of the brake system. 
     By way of example, FIG. 1 shows a longitudinal section through a preferably selected pump unit. The pump unit is comprised essentially of an electric drive motor  2  and a pump block  4 . The pump unit functions as a piston pump. A motor housing  6  protects the interior of the drive motor  2  against damaging environmental influences and is used to support permanent magnets  8  of the stator of the drive motor  2 . In the preferably selected exemplary embodiment, the motor housing  6  is composed of a first motor housing part  6   a  and a second motor housing part  6   b.  The second motor housing part  6   b  is embodied as cup-shaped, with its opening in the direction of the pump block  4 . The first motor housing part  6   a  closes the opening of the cup-shaped second motor housing part  6   b  oriented toward the pump block  4 . In contrast to the graphic representation, it is also possible that the first motor housing part  6   a  is embodied as cup-shaped, with its opening in the direction away from the pump block  4 . In this instance, the for example disk-like second motor housing part  6   b  would close the cup-shaped first motor housing part  6   a.    
     The pump block  4  has an end face  4   b  oriented toward the drive motor  2 . Starting from the end face  4   b,  a recess  10  extends in the pump block  4 . The recess  10  begins with a larger diameter  10   a  on the end face  4   b  and then transitions to a smaller diameter  10   c  inside the pump block  4 . 
     The pump block  4  is united with the motor housing  6  and to this end, has at least one threaded opening  12  on the end face  4   b.  This threaded opening  12  is associated with an opening  14  in the motor housing part  6   a  and an opening  16  in the motor housing part  6   b.  A screw, not shown, can be slid through the openings  14  and  16 , by means of which the electric drive motor  2  and the pump block  4  of the piston pump can be clamped together to form the pump unit. 
     A guide bush, not shown, is provided in the pump block  4  and a pump piston  18  is supported so that the pump piston can slide in this guide bush. The pump piston  18  can also be supported directly in the pump block  4  so that the guide bush can be eliminated. In addition to at least one pump piston  18 , other radially disposed pump pistons  18  can be provided. On the whole, the pump unit has for example two or four pump pistons  18 . For the sake of better visibility, only the inwardly directed ends of two pump pistons  18  are shown in the drawing. 
     A shaft  20  is disposed inside the pump unit. The shaft  20  has a shaft end  20   a  that protrudes into the pump block  4  and a shaft end  20   b  that protrudes into the motor housing  6 . The motor housing part  6   a  of the motor housing  6  has an outer region  6   e  extending radial to the shaft  20 , a central region  6   f  extending axial to the shaft  20 , and a narrow inner region  6   g  extending radial to the shaft  20 . A first bearing  21  is provided inside the circumferential central axial region  6   f  of the motor housing  6 . The bearing  21  is supported by the region  6   f  of the motor housing  6 . A rolling bearing, more precisely stated a ball bearing, has been selected for the first bearing  21 . The bearing  21  has an inner bearing ring  21   a  and an outer bearing ring  21   b.  A second bearing  22  is provided on the end  20   a  of the shaft  20  that protrudes into the pump block  4 . The second bearing  22  is a rolling bearing, more precisely stated a ball bearing, with an inner bearing ring  22   a  and an outer bearing ring  22   b.  In the preferably selected exemplary embodiment, another bearing  23  is provided in the vicinity of the shaft end  20   b  remote from the pump block  4 . The additional bearing  23  is preferably a slide bearing. 
     An eccentric bearing  24  is disposed between the first bearing  21  and the second bearing  22 . Between the two bearings  21  and  22 , the shaft  20  has a region that extends eccentrically to the longitudinal axis of the shaft  20 . The eccentric bearing  24  is disposed on this eccentric region of the shaft  20 . The eccentric bearing  24  is a rolling bearing, more precisely stated a roller or needle bearing. The pump pistons  18  are supported against the outer ring of the eccentric bearing  24  and are driven into reciprocating motions when the shaft  20  rotates. The pump pistons  18  give rise to considerable radial forces on the two bearings  21  and  22  by way of the eccentric bearing  24 . 
     The inner ring  21   a  of the first bearing  21  is pressed firmly onto the shaft  20 . The outer ring  21   b  is pressed firmly into the center axial region  6   f  of the motor housing  6  until it comes into contact with the inner radial region  6   g.  The inner ring  22   a  of the second bearing  22  is pressed firmly onto the shaft  20 . Since the bearings  21  and  22  are easily accessible while the bearings  21  and  22  are being pressed onto the shaft  20  and while the bearing  21  is being pressed into the motor housing part  6   a,  the bearings  21  and  22  can be easily pressed in or pressed on with a simple tool, for example with pressing dies, without having to fear a damage to the bearings  21  and  22  or to another component. The bearings  21  and  22  can be pressed in or pressed on spatially separate from and long before the drive motor  2  is mounted onto the pump block  4 . 
     The central axial region  6   f  of the motor housing  6  constitutes a circumferential projection  26 . The projection  26  extends concentric to the shaft  20 . The projection  26  protrudes into the recess  10  of the pump block  4 . 
     In the larger diameter  10   a  of the recess  10 , a circumferential pocket  28  in the form of a circumferential groove is provided in the vicinity of the projection  26 . Another circumferential groove, which constitutes another pocket  30 , is provided on the smaller diameter  10   c  of the recess  10  in the vicinity of the outer bearing ring  22   b  of the bearing  22 . A filling connection  32  feeds into the pocket  28 . A filling connection  34  also feeds into the other pocket  30 . The filling connections  32  and  34  are connected to the surface of the pump block  4  so that a pourable material can be introduced into the pockets  28  and  30  by way of the filling connections  32 ,  34 . Ventilation connections  36  and  38  are provided so that the air can escape from the pockets  28 ,  30  during the introduction of the pourable material into these pockets  28 ,  30 . 
     The drive motor  2 , the motor housing part  6   a  or the motor housing  6   b,  the shaft  20 , and the bearing  21  supported by the motor housing  6  constitute a preassembled unit  40 , which can be assembled and tested as needed, spatially and chronologically independent of the pump block  4 . It is preferable to also mount the second bearing  22  onto the preassembled unit  40  before the preassembled unit  40  is mounted onto the pump block  4 . In this instance, the second bearing  22  can be thought of as another component of the preassembled unit  40 . 
     A radial clearance fit  41  (FIG. 2) is provided between the projection  26  and the recess  10  so that the preassembled unit  40  can be easily mounted onto the pump block  4 . An additional radial clearance fit  42  (FIG. 3) is provided between the outer circumference of the outer bearing ring  22   b  of the bearing  22  and the smaller diameter  10   c  of the recess  10 . Because the radial distance or clearance fit  41 , between the projection  26  and the pump block  4  and also the radial distance or clearance fit  42  between the bearing  22  and the pump block  4  are difficult to see in the scale chosen for FIG. 1, the region with the radial distance between the projection  26  and the pump block  4  is shown once more in a different scale as a detail in FIG. 2, and the region with the radial distance between the bearing  22  and the pump block  4  is shown once more in a different scale as a detail in FIG.  3 . 
     FIGS. 2 and 3 show different details. 
     In all of the Figs., parts that are the same or function in the same manner are provided with same reference numerals. Provided that nothing to the contrary is mentioned or is depicted in the drawings, that which is mentioned and depicted in conjunction with one of the Figs. also applies to the other exemplary embodiments. As long as nothing to the contrary ensues from the explanations, the details of the different exemplary embodiments can be combined with one another. 
     FIG. 1 shows the pockets  28  and  30  before the pourable material is introduced. FIGS. 2 and 3 show the pockets  28  and  30  and the clearance fits  41 ,  42  after a plastic  44  has been introduced. The plastic  44 , which has been pressed as a pourable material into the pocket  28  by means of the filling connection  32 , is distributed inside the pocket  28  essentially over the entire circumference of the projection  26 . From the pocket  28 , the plastic  44  is pressed into the radial clearance fit  41  between the projection  26  and the pump block  4 . Since the plastic  44  has been introduced as a fluid or paste, it hardens, for example, by means of cooling or as a result of a chemical reaction. The projection  26  of the motor housing  6  is therefore embedded firmly and without play in the pump block  4 . It is preferable to fill the pockets  28  and  30  with a plastic  44  which does not shrink during its hardening or better still, undergoes a slight volume increase during its hardening. The plastic  44  can also be produced so that it glues the motor housing  6  or the bearing ring  22   b  to the pump block  4 . 
     As already explained above, because the inner bearing ring  21   a  of the bearing  21  is connected without play to the shaft  20 , and because furthermore, the outer bearing ring  21   b  is connected without play to the axial region  6   f  of the motor housing  6 , and because the motor housing  6  is firmly or at least tightly connected to the pump block  4  in the vicinity of bearing  21  due to the plastic  44  in the pocket  28  and in the clearance fit  41 , a support of the shaft  20  in the vicinity of the bearing  21  is produced that is largely without play in the radial direction, which is evidenced on the whole by the service life and by means of a particularly low noise generation. 
     As has already been suggested further above in the description, because the inner bearing ring  22   a  of the second bearing  22  is connected without play to the shaft  20  and because the outer bearing ring  22   b  is also embedded without play in the pump block  4  due to the plastic  44  in the pocket  30  and in the clearance fit  42 , the shaft  20  is also supported without play in the vicinity of the second bearing  22 , which is also positively evidenced here by means of a service life that is good on the whole and by means of a particularly low noise generation. 
     A rotor of the electric drive motor  2  is disposed on the shaft  20  and inside the motor housing  4 . The rotor is essentially comprised of a coil  45 , which is wound out of insulated copper wire, and a plate stack  46 , which is open toward the outside and is used as an armature. The plate stack  46  is comprised of stamped plates disposed one above the other in layers. As a protection for the coil  45 , a plastic insulation  48  is usually provided between the plate stack  46  and the coil  45 . In the preferably selected exemplary embodiment, the plastic insulation  48  also extends in the axial direction beyond the shaft end  20   b  remote from the pump block  4 . The region of the plastic insulation  48  protruding axially beyond the shaft  20  has the form of a bush  50 . The bush  50  and the remaining region of the plastic insulation  48  are preferably cast or injection molded together in a common mold. The bush  50  and the remaining region of the plastic insulation  48  are therefore a single, coherent component that can be formed in one work cycle. However, the bush  50  and the remaining region of the plastic insulation  48  can also be two separately formed components made of plastic which are joined together. 
     A bearing pin  52  is riveted, screwed, or welded to the bottom center of the cup-shaped motor housing part  6   b.  The outer diameter of the bearing pin  52  is ball-shaped and fits with a small amount of bearing play into the inner diameter of the bush  50 . The ball shape of the bearing pin  52  assures that the shaft  20  can be angularly aligned in relation to the motor housing  4  so that problems, in particular jamming, cannot occur in the vicinity of the additional bearing  23 . 
     FIG. 4 shows another selected, particularly advantageous exemplary embodiment. 
     In the exemplary embodiment shown in FIG. 4, the bearing pin  52  of the additional bearing  23  is formed in such a way that the motor housing part  6   b  of the motor housing  6  has an inwardly directed indentation in the bottom center, concentric to the shaft  20 . As shown in FIG. 4, the bearing pin  52  can be formed directly onto the motor housing  6  by means of a corresponding shaping when stamping or deep drawing the motor housing  6 . It should also be emphasized that the inner diameter of the bush  50  of the bearing  23  can also be greater than the outer diameter of the shaft  20 , which has a positive effect on the stability of the additional bearing  23 , particularly on the stability of the bearing pin  52 . 
     As shown in FIG. 4, the filling connections  32  and  34  can each be separately accessed from the outside so that the two pockets  28  and  30  can be filled with the plastic  44  independently of each other. However, as shown in FIG. 1, it is also possible to connect the two filling connections  32  and  34  to each other inside the pump block  4  so that fewer connections have to be connected in order to fill the pockets  28  and  30 . In the exemplary embodiment shown in FIG. 4, the ventilation connections  36  and  38  according to FIG. 1 have been eliminated, which is possible depending on the dimensions of the pockets  28 ,  30  and the radial clearance fits  41  and  42 . 
     Because of the radial clearance fits  41  and  42  in the vicinity of the bearings  21  and  22 , which are eliminated by means of the introduced plastic  44  after the assembly, an optimal alignment of the shaft  20  is produced without having to fear an increased load on the shaft  20  or even a bending of the shaft  20  due to the three-point support of the shaft  20 . 
     Because the two clearance fits  41  and  42  are eliminated by the plastic  44 , the two clearance fits  41  and  42  can have very large dimensions, which means that significantly less precise measurement tolerances have to be maintained in the manufacture of the parts than was previously the case; and because of the large radial clearance fits  41  and  42  between the preassembled unit  40  and the pump block  4 , the mounting of the preassembled unit  40  onto the pump block  4  can take place with great ease. 
     It is preferable to provide a sufficiently large radial clearance fit  41  and  42 , both in the vicinity of the bearing  21  and in the vicinity of the bearing  22 , which is then eliminated after the preassembled unit  40  is mounted onto the pump block  4  by means of introducing the plastic  44  because then, the best effect with regard to noise reduction and ease of mounting the motor housing  6  onto the pump block  4  is achieved. However, it should be mentioned that even if the radial clearance fit  41 , which is then eliminated with the plastic  44 , is provided only in the vicinity of the first bearing  21  between the projection  26  and the pump block  4 , i.e. that the outer bearing ring  22   b  of the bearing  22  is press-fitted into the pump block  4 , in regard to the desired noise reduction and in regard to the ease of mounting the drive motor onto the pump block  4 , an improvement can likewise be achieved which is, however, hardly as great as when the radial clearance fits  41  and  42 , which are eliminated by means of the plastic  44 , are provided in the vicinity of both bearings  21  and  22 . On the other hand, even if the radial clearance fit  42 , which is eliminated with the plastic  44  after assembly, is provided only in the vicinity of the second bearing  22 , wherein the projection  26  is embodied in the same manner as in previously disclosed pump units, i.e. that in the vicinity of the projection  26  no clearance compensation is carried out by means of introduced plastic, an improvement with regard to service life and/or noise reduction can likewise be achieved, which is, however, hardly as noticeable as when the radial clearance fits  41  and  42 , which are subsequently eliminated with the plastic  44 , are provided in the vicinity of both bearings  21  and  22 . 
     The foregoing relates to a preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.