Patent Publication Number: US-2004045431-A1

Title: Roller bearing, piston pump and pump unit

Description:
PRIOR ART  
       [0001] The invention relates to a roller bearing that is particularly provided for rotatably supporting a cam of a piston pump, and also relates to a piston pump and pump unit, as generically defined by the preamble to claims 1, 8, and 10. The piston pump and the pump unit are particularly provided for use in slip-controlled hydraulic vehicle brake systems.  
       [0002] A pump unit of this kind with an electric motor as the pump motor for driving a piston pump is known from DE 44 30 909 A1. The piston pump has a pump housing, in which a cam is rotatably supported. A rotary drive of the cam drives a pump piston, which is contained so that it can move in the pump housing to execute a stroke motion. In a manner that is intrinsically known from piston pumps, the stroke motion of the pump piston produces a delivery of fluid.  
       [0003] In the known piston pump, the cam is supported so that it can rotate in the pump housing by means of a ball bearing, wherein an outer bearing ring of the ball bearing is pressed into a bearing seat in the pump housing. Due to cost and space considerations, the ball bearing should be replaced by a needle bearing. The compression of the bearing ring in the bearing seat of the pump housing produces a reduction of a diameter of the bearing ring. Since the compression can vary from piston pump to piston pump due to tolerances not only of the bearing seat in the pump housing, but also of the bearing ring, this changes a bearing play of the bearing. A diameter tolerance of a shaft of the cam also influences the bearing play. The greatest possible play due to the tolerances leads to a distinctly noticeable and unacceptable running noise of the bearing. With the least possible bearing play, the needles of the bearing can become jammed between the bearing ring and the shaft of the cam, which causes the bearing to wear prematurely.  
       ADVANTAGES OF THE INVENTION  
       [0004] In the roller bearing according to the invention, with the characterizing features of claim 1, the bearing ring has a lateral extension with which the bearing can be pressed into a bearing seat. The compression of the bearing ring in the bearing seat occurs outside the region in which rolling elements of the roller bearing are disposed and revolve. There is no compression of the bearing ring by the bearing seat in the vicinity of the rolling elements; the bearing seat into which the roller bearing is pressed does not compress a rolling region of the roller bearing. This has the advantage that a bearing play of the roller bearing is not influenced by the compression of the bearing seat into which the roller bearing is pressed, which permits a more closely toleranced bearing play. This has the advantage of a reduced running noise of the roller bearing, a more precise support of a shaft of the cam of the piston pump, and a reduced wear and consequently a longer service life of the roller bearing.  
       [0005] Advantageous embodiments and modifications of the invention disclosed in the main claim are the subject of the dependent claims.  
       [0006] The invention can in principle be used in all types of roller bearings, i.e. even in ball bearings, which is why claim 1 is directed toward roller bearings in general. Since ball bearings, in comparison to roller bearings or needle bearings, have a relatively solid and stable outer bearing ring, the bearing play in them is less influenced by the compression of the bearing seat. In addition, ball bearings have an inner bearing ring that is not usually present in roller bearings, especially not in needle bearings. The inner bearing ring of ball bearings reduces the influence of the diameter tolerance of a shaft on the bearing play. The influence of the compression on the bearing by the bearing seat is therefore lower in ball bearings than in roller bearings and needle bearings; the invention is therefore particularly advantageous in roller bearings and needle bearings (claim 2).  
       [0007] According to claim 3, the extension of the bearing ring is disposed coaxial to the roller bearing. As a result, the bearing seat in the pump housing is also disposed coaxial to the shaft of the cam, to a possible additional bearing seat, and/or to the motor shaft of the pump motor, which simplifies the manufacture of the bearing seat and the insertion and press-fitting of the roller bearing into the bearing seat.  
       [0008] According to claim 4, the end face of the bearing ring is closed on the side of its extension, i.e. the roller bearing is closed on one side and consequently is protected from the penetration of dirt. This has the advantage that the roller bearing can be inserted into a stepped through bore in the pump housing and that the bore is closed at the end oriented away from the pump motor by the bearing ring that is closed at the end face, and the pump is therefore protected against the penetration of dirt. This is advantageous since it is easier to produce a through bore than it is to produce a blind bore.  
       [0009] According to claim 5, the extension is of one piece with the bearing ring. This has the advantage of permitting the roller bearing to be inexpensively produced since an additional part is not needed. According to claim 6, the roller bearing according to the invention has a bearing bracket into which the roller bearing is inserted and which has the lateral extension of the roller bearing. This embodiment of the invention has the advantage that a commercially available standard bearing can be used. In fact, in this embodiment of the invention, the bearing bracket exerts a compression on the bearing ring of the roller bearing inserted into the bearing bracket, in the vicinity of the rolling elements, but a wall thickness of the rolling elements can be slight or the bearing bracket can be embodied as elastic in the radial direction by being slit in the vicinity of the roller bearing so that the influence of the compression of the bearing bracket on the bearing play of the roller bearing is less than when the roller bearing is pressed directly into the bearing seat of the pump housing.  
       [0010] Claim 7 provides a noise-damping material, which is applied to the bearing ring in the vicinity of the rolling bodies. The noise-damping material prevents the transmission of structure-borne noise from the bearing ring to the pump housing and thus reduces perceptible running noise of the roller bearing. In addition, the noise-damping material damps oscillations of the bearing ring and therefore counteracts noise production. Since the noise-damping material is not disposed on the extension of the roller bearing and is therefore not disposed in the bearing seat, the seat of the roller bearing in the bearing seat is not influenced by noise damping material.  
       [0011] The roller bearing according to the invention is particularly provided for rotatably supporting a cam of a piston pump in its housing, but is not limited to this application since the roller bearing according to the invention can also be used other supports. The collateral claims 8 and 10 are directed toward a piston pump or a pump unit with a pump motor and a piston pump, wherein a cam, which serves to drive a pump piston to execute a stroke motion, is rotatably supported in a pump housing by means of the roller bearing according to the invention.  
       [0012] The piston pump according to the invention is particularly provided as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, these brake systems are referred to by the abbreviations ABS, TCS, ESP, or EHB. In the brake system, the pump is used, for example, to return brake fluid from one or more of wheel brake cylinders to a master cylinder (ABS) and/or for supplying brake fluid from a reservoir into one or more of wheel brake cylinders (TCS, ESP, or EHB). The pump is required, for example, in a brake system with a wheel slip regulation (ABS or TCS) and/or in a brake system used as a steering aid (ESP) and/or in an electrohydraulic brake system (EHB). Wheel slip regulation (ABS or TCS) can, for example, prevent the wheels of the vehicle from locking when powerful pressure is exerted on the brake pedal during a braking maneuver (ABS) and/or can prevent the driven wheels of a vehicle from spinning when powerful pressure is exerted on the accelerator pedal. In a brake system used as a steering aid (ESP), a brake pressure is built up in one or more wheel brake cylinders, independent of an actuation of the brake pedal or accelerator pedal, in order, for example, to prevent the vehicle from swerving out from the path desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump supplies brake fluid to the wheel brake cylinder(s) when an electric 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. 
     
    
    
     DRAWINGS  
     [0013] The invention will be explained in detail below in conjunction with preferably selected exemplary embodiments shown in the drawings.  
     [0014]FIG. 1 shows an axial section through a pump unit with a piston pump and a roller bearing according to the invention; and  
     [0015] FIGS.  2  to  4  show show modified embodiments of the pump unit from FIG. 1. 
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
     [0016] The pump unit  10  according to the invention shown in FIG. 1 has an electric motor as a pump motor  12 , which is flange-mounted to a pump housing  14  of a piston pump  16 . For the sake of clarity, only a small fraction of the housing of the pump motor  12  is shown; the pump motor  12  has a diameter many times greater than the bearing depicted in the drawing. The pump motor  12  has a centering collar  18  with which it is inserted in a precisely fitting manner into a countersink  20  at the mouth of a stepped bore  22 , which is let into the pump housing  14 .  
     [0017] The pump housing  14  is part of a hydraulic block  14  of an otherwise not shown slip-control device of a hydraulic vehicle brake system. The hydraulic block  14  is comprised, for example, of an aluminum diecasting alloy. Only a fraction of the hydraulic block  14  in the vicinity of the piston pump  16  is shown in the drawing, i.e. the part that forms the pump housing  14 . The stepped bore  22  in the pump housing  14  is embodied as a blind bore; it ends closed on a side oriented away from the pump motor  12 . For example, the pump motor  12  is screwed to the pump housing  14  by means of screws that are not shown in the drawing.  
     [0018] A motor shaft  24  of the pump motor  12  protrudes into the stepped bore  22  in the pump housing  14 . A cam  26  is non-rotatably pressed onto the motor shaft  24  close to the motor. The cam  26  is embodied as a cylindrical sleeve with a cylindrical through bore, wherein the bore is disposed axially parallel and eccentric to an outer circumference of the cam  26 . The motor shaft  24  onto which the cam  26  is non-rotatably pressed thus simultaneously constitutes a shaft of the cam  26 .  
     [0019] A first needle bearing  28  with needles  30  and a bearing ring  32  is placed onto the cam  26 , wherein the needles  30  roll along the cam  26  when the motor shaft  24  rotates. Due to the eccentricity of the cam  26 , the bearing ring  32  moves along a circular path.  
     [0020] Radial to the motor shaft  24 , a pump piston  34  of the piston pump  16  is inserted into a bore  36  in the pump housing  14 . The pump piston  34  is guided so that it can move axially in the bore  36 , wherein the axial direction and thus the movement direction of the pump piston  34  are disposed radial to the motor shaft  24 . A piston return spring that is not visible in the drawing pushes the pump piston  34  from the outside against the bearing ring  32  of the first needle bearing  28 . When the motor shaft  24  rotates, the cam  26  drives the piston  34  to execute a stroke motion, which causes the piston pump  16  to deliver brake fluid in an intrinsically known fashion. The piston return spring that is not visible in the drawing is disposed at an end oriented away from the cam  26  and is embodied as a helical compression spring, which presses against an end face of the pump piston  34  oriented away from the cam  26 .  
     [0021] On an end oriented away from the pump motor  12 , the motor shaft  24  protrudes beyond the cam  26 ; on a side of the cam  26  oriented away from the pump motor  12 , the motor shaft  24  is supported by means of a second needle bearing  38  according to the invention so that it can rotate in the pump housing  14 . The second needle bearing  38  has needles  40 , which roll along the motor shaft  24  when it rotates, and a bearing ring  42 , which encompasses the needles  40  and in which the needles  40  roll when the motor shaft  24  rotates. The bearing ring  42  is a sleeve-shaped part, which, at an end oriented away from the pump motor  12  and the cam  26 , tapers by means of an annular step  44  down to a smaller diameter extension  46  with which the bearing ring  42  is pressed into a bearing seat  48  in the pump housing  14 . The bearing seat  48  is constituted by a section of the stepped bore  22  in the pump housing  14 . In the vicinity of the needles  40  of the second needle bearing  38 , there is an annular gap  50  between the pump housing  14  and the bearing ring  42  so that the bearing ring  42  is not compressed in the vicinity of the needles  40 . The bearing ring  42  of the second needle bearing  38  is only compressed in the vicinity of the extension  46 , which is pressed into the bearing seat  48 . A bearing play of the second needle bearing  38  is therefore not influenced by the compression of the bearing ring  42  in the bearing seat  48 .  
     [0022] The annular gap  50  encompassing the bearing ring  42  of the second needle bearing  38  in the vicinity of the needles  40  can be empty. In the exemplary embodiment shown, the annular gap  50  is filled with an elastomer  52  that serves as a noise-damping material. The elastomer  52  is vulcanized onto the outside of the bearing ring  42  in the vicinity of the needles  40 . There is an axial gap  54  between the annular step  44  of the bearing ring  42  and the pump housing  14 .  
     [0023] In the description of FIGS.  2  to  4  below, the discussion will essentially center solely on the differences from FIG. 1 and otherwise, reference is made to the corresponding descriptions in conjunction with FIG. 1 in order to avoid repetition. Parts that are the same are labeled with the same reference numerals. By contrast to FIG. 1, the second needle bearing  38  of the pump unit  10  according to the invention shown in FIG. 2 is embodied as closed on one side, i.e. on the side oriented away from the pump motor  12 . On the side oriented away from the pump motor  12 , the extension  46  of the sleeve-shaped bearing ring  42  is closed by an end wall  56 , which is of one piece with the extension  46 . As a result, the stepped bore  22  in the pump housing  14  can be produced as a through bore. After the second needle bearing  38  is pressed with the extension  46  into the bearing seat  48 , the end wall  56  of the extension  46  closes the stepped bore  22  in the pump housing  14  and thus prevents the penetration of dirt and possibly the escape of lubricants or hydraulic fluid.  
     [0024] In addition, the noise-damping material has been eliminated from the annular gap  50  between the bearing ring  42  and the pump housing  14 . The annular gap  50  is empty.  
     [0025] In the embodiment of the invention shown in FIG. 3, the second needle bearing  38  is inserted into a bearing bracket  58 . The second needle bearing  38  can be fixed in the bearing bracket  58  by means of a compression between the bearing bracket  58  and the bearing ring  42 . Another possibility is to fix the bearing ring  42  in the bearing bracket  58 , for example by means of an adhesive or a so-called screw retention lacquer. The bearing bracket  58  is a sleeve-shaped deep-drawn part that tapers by means of an annular step  44  down to a coaxial extension  46 . The extension  46  of the bearing bracket  58  is pressed into the bearing seat  48  in the pump housing  14 . The extension  46  of the bearing bracket  58  also constitutes the extension  46  of the second needle bearing  38  according to the invention. In this embodiment of the invention, too, the compression between the needle bearing  38  and the bearing seat  48  in the pump housing  14  occurs laterally outside the region in which the needles  40  of the second needle bearing  38  are disposed and revolve.  
     [0026] In the exemplary embodiment of the invention shown in FIG. 3, a compression also occurs between the bearing bracket  58  and the bearing ring  42  of the needle bearing  38 , but due to the slight wall thickness of the bearing bracket  58 , the influence of this compression on the bearing play of the needle bearing  38  is less than in the vicinity of its needles  40  in a conventional pressing of the needle bearing  38  into a bearing seat. The advantage of this embodiment of the invention is the ability to use a conventional standard needle bearing. In the vicinity of the needles  40 , there is an annular gap  50  between the bearing bracket  58  and the pump housing  14  so that the pump housing  14  does not exert any compression on the needle bearing  38  in the vicinity of the needles  40 .  
     [0027] In the exemplary embodiment of the invention shown in FIG. 4, the second needle bearing  38  has a bearing bracket  58  like the one in FIG. 3, into which the needle bearing  38  is inserted. The bearing bracket  58  in FIG. 4, however, is not embodied as a deep-drawn part, but as a shaped part, for example produced by means of cold forming. It is also possible to produce the bearing bracket  58  by means of cutting machining. The bearing bracket  58  in FIG. 4 has a cup-like, thin-walled section  60  into which the needle bearing  38  is inserted. The section  60  has an end wall  62  that is of one piece with it, from which a pin extends coaxially outward, which constitutes the extension  46  of the second needle bearing  38  according to the invention. The pin  46  of the bearing bracket  58  of the second needle bearing  38  is inserted into the bearing seat  48  in the pump housing  14 .  
     [0028] In the exemplary embodiment of the invention shown in FIG. 4, as in FIG. 1, an elastomer  52  serving as a noise-damping material, is vulcanized onto the outer circumference of the cup-shaped section  60  of the bearing bracket  58 . The elastomer  52  fills the annular gap  50  between the bearing bracket  58  and the pump housing  14 .  
     [0029] In order to reduce a possible compression between the bearing bracket  58  and the bearing ring  42  of the second needle bearing  38  inserted into the bearing bracket  58  in FIGS. 3 and 4, the section  60  of the bearing bracket  58  into which the needle bearing  38  is inserted can be provided with longitudinal or oblique slits (not shown).