Abstract:
A pressure generator for a hydraulic vehicle brake system includes a piston-cylinder unit, a piston, a ball screw drive configured to move the piston, an electric hollow-shaft motor that surrounds and is configured to drive the ball screw drive, and a planetary gear set configured to transmit a rotational movement of the hollow-shaft motor to the ball screw drive. The generator also includes a flange part, a sleeve, and an axial needle-roller bearing. The flange part has a tubular collar configured to axially guide the piston in a movable fashion therein. The sleeve has a flange configured as a counterbearing which is attached to an interior of the tubular collar, and is further configured to support the bearing. The bearing is configured to rotatably mount and axially support the ball screw drive.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2014 212 417.4, filed on Jun. 27, 2014 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
         [0002]    The disclosure relates to a pressure generator for a hydraulic vehicle brake system. The pressure generator is provided in particular for a hydraulic power brake system, and can also be used for slip regulation in hydraulic power brake systems, servo brake systems and manual brake systems. 
       BACKGROUND 
       [0003]    The Japanese patent application JP H04 22767 A has disclosed a pressure generator, referred to as a hydraulic plunger pump, with a ball screw drive and a piston-cylinder unit. The ball screw drive has a spindle nut which can be driven in rotation by means of an electric motor and which thus axially moves a spindle, which in turn moves a piston in a cylinder of the piston-cylinder unit. A housing of the ball screw drive is connected by way of tie rods to a cylinder head which holds the cylinder on the housing of the ball screw drive. 
       SUMMARY 
       [0004]    The pressure generator according to the disclosure has a piston-cylinder unit with a cylinder and with a piston which is movable in the cylinder, and has a helical gearing for moving the piston. The helical gearing has a rotatable, axially fixed component which has a thread, and an axially movable, rotationally fixed component which has a counterpart thread, the counterpart thread of which engages directly or indirectly, for example via rolling bodies, with the thread of the rotatable component of the helical gearing. The act of the rotatable component of the helical gearing being driven in rotation causes the axially movable component of the helical gearing to be moved axially. The axially movable component of the helical gearing is axially fixed and radially fixed to the piston of the piston-cylinder unit, such that a movement of the axially movable component of the helical gearing moves the piston in the cylinder of the piston-cylinder unit. 
         [0005]    For the connection of the piston-cylinder unit to the helical gearing, the pressure generator according to the disclosure has a flange part with a flange and with a tubular collar. The flange is rigidly connected to the cylinder of the piston-cylinder unit and the collar guides the piston of the piston-cylinder unit coaxially with respect to the cylinder and in axially movable fashion. With the piston, the tubular collar of the flange part according to the disclosure guides the axially movable component of the helical gearing, said axially movable component being radially fixed to the piston of the piston-cylinder unit. 
         [0006]    Furthermore, the pressure generator according to the disclosure has an axial bearing which serves for axially supporting and rotatably mounting the rotatable component of the helical gearing. The axial bearing is supported axially on a counterbearing, which is connected axially fixedly to the collar of the flange part. 
         [0007]    The disclosure makes it possible to realize a compact pressure generator in which axial tensile and compressive forces which arise during the generation of pressure are conducted as internal forces on short paths from the piston of the piston-cylinder unit to the axially movable component of the helical gearing, to which the piston is axially fixed, from the axially movable component via the counterpart thread and the thread to the rotatable component of the helical gearing, from the latter via the axial bearing and the counterbearing thereof to the flange part, and from the flange part to the cylinder, to which the flange of the flange part is rigidly connected. There is no need for external forces to be supported. A further advantage of the disclosure is the axially movable guidance of the piston, and of that component of the helical gearing which is radially fixed thereto, in the tubular collar of the flange part. 
         [0008]    The claims relate to advantageous embodiments and refinements of the disclosure. 
         [0009]    In one embodiment, the pressure generator has an electric hollow-shaft motor for driving the rotatable component of the helical gearing in rotation and which surrounds the helical gearing, which permits a compact construction of the pressure generator. A rotary bearing for a hollow shaft of the hollow-shaft motor is preferably arranged on the outside of the tubular collar of the flange part and/or close to the flange of the flange part. 
         [0010]    In another embodiment, the generator includes a radial bearing for the rotatable component of the helical gearing on the flange part, which radial bearing is preferably arranged in the tubular collar of the flange part so as to be remote from the flange and thus from the rotary bearing for the hollow shaft of the hollow-shaft motor. 
         [0011]    A refinement according to another embodiment provides a planetary gear set for rotational speed reduction and for driving the rotatable component of the helical gearing in rotation. 
         [0012]    In a further embodiment, the generator includes a second rotary bearing, arranged remote from the flange, for the hollow shaft of the hollow-shaft motor, which second rotary bearing is arranged remote from the flange and thus preferably remote from the first rotary bearing of the hollow shaft, such that the hollow shaft is rotatably mounted at spaced-apart positions. The second rotary bearing does not need to be arranged on the flange part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The disclosure will be discussed in more detail below on the basis of an embodiment of the disclosure which is illustrated in the drawing. The single FIGURE shows an axial section through a pressure generator according to the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The pressure generator  1  according to the disclosure as illustrated in the drawing serves for generating pressure in a hydraulic power brake system. Said pressure generator may also be used for slip regulation. The pressure generator  1  has a piston-cylinder unit  2  with a piston  3  and with a cylinder  4  which is in the form of a cylindrical countersunk recess in a hydraulic block  5  of the vehicle brake system, which is not otherwise illustrated. The hydraulic block  5  serves for the mechanical mounting and hydraulic interconnection of hydraulic components of a slip regulation system of the vehicle brake system, such as solenoid valves, check valves, hydraulic accumulators and the piston-cylinder unit  2 . Hydraulic blocks  5  of said type for vehicle brake systems with slip regulation are known and will not be discussed in any more detail here. In a power brake system, the piston-cylinder unit  2  serves for building up a pressure instead of a foot-operated or hand-operated master brake cylinder, the latter serving as a brake force setpoint value encoder for a power braking operation and being capable of generating a brake pressure for a servo braking operation in the event of failure of the power brake. 
         [0015]    The piston  3  of the piston-cylinder unit  2  is in the form of a hollow piston and has a spindle  6  arranged coaxially, and rigidly connected, therein. The spindle  6  is thus axially fixed and radially fixed to the piston  3 . The spindle  6  is arranged coaxially in a spindle nut  7  which projects into the piston  3  of hollow form. The act of the rotatable and axially fixed spindle nut  7  being driven in rotation causes the spindle  6 , and with it the piston  3 , to be moved axially, such that the piston  3  generates a hydraulic pressure in the cylinder  4 . Together, the spindle  6  and the spindle nut  7  form a helical gearing  8 . In the illustrated embodiment, the helical gearing is in the form of a ball screw drive with a ball return channel  36  and with balls  9  as rolling bodies which roll in helical grooves formed as a thread and counterpart thread on the spindle  6  and in the spindle nut  7 . In general, the spindle  6  and the spindle nut  7  may be regarded as being components of the helical gearing  8 , wherein the spindle nut  7  forms a rotatable, axially fixed component, which has a thread, of the helical gearing  8 , and the spindle  6  forms an axially displaceable, rotationally conjoint component, which has a counterpart thread, of the helical gearing  8 . In the embodiment as a ball screw, the thread of the spindle nut  7  and the counterpart thread of the spindle  6  are in indirect engagement by way of the balls  9 , such that as already described, the act of the spindle nut  7  being driven in rotation causes the spindle  6  together with the piston  3  to be moved axially. In embodiments of the disclosure, a reversed situation is also conceivable, that is to say a rotatable and axially fixed spindle and a rotationally fixed and axially movable spindle nut (not illustrated), wherein in this case, the spindle nut is connected to, and is for example also integral with, the piston  3  and moves the latter when the spindle is driven in rotation. For rotational fixing, the piston  3  and the spindle  6  have an axial blind bore  34  with a hexagonal cross section, into which there projects a hexagonal bar  35  which is screwed rotationally fixedly into the hydraulic block  5  at the base of the cylinder  4 . 
         [0016]    The spindle nut  7  is rotatably mounted by way of a radial bearing  10  in a tubular collar  14  of a flange part  15 , and is supported axially and rotatably by way of an axial bearing  11 , which in the embodiment is in the form of a needle-roller bearing, on a flange, which in this case is referred to as counterbearing  12  and which is arranged in a sleeve  13 . Instead of a needle-roller bearing, it is for example also possible for a ball bearing, even a four-point bearing, or a plain bearing to be used as an axial bearing (not illustrated). This list is exemplary and not exhaustive. In the embodiment, the radial bearing  10  and the axial bearing  11  are arranged at an end of the spindle nut  7  which is remote from the piston  3 . The sleeve  13  has a thread  37  by means of which it is screwed onto a counterpart thread of the tubular collar  14  of the flange part  15 , that is to say fixedly connected to the collar  14 . 
         [0017]    The flange part  15  has a flange  16  which is fastened in a countersunk recess of the hydraulic block  5 . The flange part  15  is coaxial with the cylinder  4 , the piston  3 , the spindle  6  and the spindle nut  7 . The collar  14  of the flange part  15  guides the piston  3  coaxially with respect to the cylinder  4  and in axially displaceable fashion. Via the piston  3 , the collar  14  of the flange part  15  guides the spindle  6 , which is rigidly and thus radially fixedly connected to the piston  3 , of the helical gearing  8  coaxially with respect to the cylinder  4  and with respect to the spindle nut  7  and in axially displaceable fashion. If the piston  3  is moved into the cylinder  4  for the purposes of generating pressure, a compressive force acts on the spindle  6  and on the spindle nut  7 , which compressive force is supported axially, via the axial bearing  11 , on the counterbearing  12  in the sleeve  13 . The sleeve  13 , which is screwed to the collar  14  of the flange part  15 , conducts a tensile force, which arises as a reaction force to the compressive forces in the spindle  6  and the spindle nut  7 , into the hydraulic block  5 , which has the cylinder  4  of the piston-cylinder unit  2 , via the flange part  15  which is fastened to the hydraulic block  5 . The compressive and tensile forces that arise during the generation of pressure are thus conducted on a short path as internal forces in a closed loop, such that there are no outwardly acting forces that must be supported. 
         [0018]    The spindle nut  7  has, on its end remote from the piston  3 , three planet gears  17  which are arranged rotatably on the spindle nut  7  by means of pins  18 . In this way, the spindle nut  7  forms a planet carrier for the planet gears  17 . The planet gears  17  mesh with a coaxially arranged sun gear  20  and with a likewise coaxial internal gear  21 , which surrounds the planet gears  17 . The internal gear  21  is, at an end remote from the flange  16  of the flange part  15  and from the hydraulic block  5  with the cylinder  4 , pressed into the sleeve  13 , that is to say the internal gear  21  is rotationally conjoint. The planet gears  17 , the sun gear  20  and the internal gear  21  form a planetary gear set  22  of the pressure generator  1  according to the disclosure, which planetary gear set serves for driving the spindle nut  7  in rotation. 
         [0019]    The sun gear  20  is rotationally conjoint with a shaft  23  which is pressed rotationally conjointly into a collar  24  in a face wall  25  of a cup-shaped hollow shaft  26  of an electric hollow-shaft motor  27 . The hollow shaft  26  has poles or permanent magnets  28  at the outside, and may also be regarded as the rotor of the electric hollow-shaft motor  27 . The hollow shaft  26  concentrically surrounds the planetary gear set  22 , the helical gearing  8 , the sleeve  13  and the collar  14  of the flange part  15 . Said hollow shaft is rotatably mounted, close to the flange  16 , by way of a ball bearing as rotary bearing  29 . The rotary bearing  29 , which is close to the flange, of the hollow shaft  26  is pressed onto a bearing seat  19  on the outside of the flange part  15  close to the flange  16 . 
         [0020]    The electric hollow-shaft motor  27  has a motor housing  30 , which is likewise cup-shaped and of stepped diameter and the open end of which is fastened to the flange  16  of the flange part  15 . At an inner side, the housing  30  has electromagnets as stator magnets  31 . The motor housing  30  with the stator magnets  31  can also be regarded as the stator of the electric hollow-shaft motor  27 . At a closed end remote from the flange  16 , there is formed on the motor housing  30  a hollow cylindrical bearing receptacle  32  in which there is arranged a ball bearing as rotary bearing  33 . The rotary bearing  33  serves for rotatably mounting the shaft  23 , with which the sun gear  20  of the planetary gear set  22  is rotationally conjoint and which is rotationally conjoint with the hollow shaft  26  by being pressed into the collar  24  of the hollow shaft  26 . The rotary bearing  23  thus serves for rotatably mounting both the hollow shaft  26  of the electric hollow-shaft motor  27  at the end remote from the flange  16 , and at the same time also for rotatably mounting the sun gear  20  of the planetary gear set  22 . When the hollow shaft  26  of the electric hollow-shaft motor  27  is driven in rotation, the sun gear  20 , which is rotationally conjoint with the hollow shaft  26 , of the planetary gear set  22  is driven in rotation and drives the planet gears  17  such that they perform a revolving movement, which causes the spindle nut  7 , which as described simultaneously forms the planet carrier of the planetary gear set  22 , to be driven in rotation.