Abstract:
A pressure generator for a hydraulic vehicle brake system includes a piston cylinder unit with a cylinder and a piston, a ball screw drive, an electric hollow-shaft motor which 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 planetary gear set includes a planetary carrier and an internal gear which are respectfully connected via pint-type positive locking connections to a spindle nut of the ball screw drive and a static tubular force transmitter. The locking connections are configured to enable connections between parts via the respective parts being brought together axially in a hollow shaft of the hollow-shaft motor.

Description:
This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2014 212 413.1, filed on Jun. 27, 2014 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
     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. The disclosure also relates to an installation tool for the pressure generator, and to a method for assembling the pressure generator. 
     BACKGROUND 
     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. In one embodiment, the spindle nut is driven in rotation directly by way of a coaxially arranged electric hollow-shaft motor which surrounds the ball screw drive, and in another embodiment, by way of an electric motor, which is arranged axially parallel and adjacent to the helical gearing, via a spur gear mechanism. 
     SUMMARY 
     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 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. 
     According to the disclosure, the pressure generator has a hollow, for example tubular, force transmitter by means of which an axial force imparted by exertion of pressure by way of the piston-cylinder unit is transmitted between the piston-cylinder unit and the rotatable component of the helical gearing. The force transmitter can transmit the axial force directly or indirectly via one or more further components. In particular, the rotatable component of the helical gearing is rotatably supported axially on the force transmitter, and the force transmitter is connected directly or indirectly to the cylinder of the piston-cylinder unit. At least a part of a length of the helical gearing is accommodated in the hollow force transmitter, permitting a compact construction of the pressure generator. 
     The pressure generator according to the disclosure has a planetary gear set for driving the rotatable component of the helical gearing in rotation, which planetary gear set is arranged coaxially with respect to the helical gearing at an end of the helical gearing remote from the piston-cylinder unit. A planet carrier of the planetary gear set is connected rotationally conjointly to the rotatable component of the helical gearing by way of a positively locking connection, such that the act of the planet carrier of the planetary gear set being driven in rotation causes the rotatable component of the helical gearing to be driven in rotation. For assembly, the planet carrier can be mounted axially onto the rotatable component of the helical gearing, that is to say the positively locking connection is designed so as to engage, that is to say to connect the planet carrier rotationally conjointly to the rotatable component of the helical gearing by positive locking, by way of an axial movement of the planet carrier relative to the rotatable component of the helical gearing. 
     Furthermore, an internal gear of the planetary gear set of the pressure generator according to the disclosure is likewise connected rotationally conjointly to the force transmitter by way of a positively locking connection. Said positively locking connection, too, is engaged by way of an axial movement of the force transmitter relative to the internal gear. 
     The claims relate to advantageous embodiments and refinements of the disclosure. 
     Rotationally conjoint positively locking connections that can be made by way of an axial movement are for example a tongue-and-groove connection, a polygonal connection or a spline connection. An embodiment of the disclosure provides a pin-type connection with an eccentrically arranged, axially parallel pin which engages into a hole. A pin is basically sufficient which is suitable for example for the rotationally conjoint positively locking connection of the internal gear of the planetary gear set to the hollow force transmitter. A refinement provides a pin-type connection with multiple pins as a positively locking connection, the pins of which are arranged so as to be distributed uniformly or non-uniformly over a circumference. 
     A preferred refinement of the disclosure which permits a compact construction of the pressure generator provides an electric hollow-shaft motor for the rotational drive of the planetary gear set. The hollow-shaft motor has a cup-shaped rotor which surrounds the planetary gear set and at least a part of a length of the helical gearing. A face wall of the rotor situated at the planetary gear set side has installation openings through which the planet gears together with the planet carrier and the internal gear of the planetary gear set can be held in the rotor while being assembled together with the rotatable component of the helical gearing and the hollow force transmitter. 
     Another embodiment relates to an installation tool with holders for the planet gears and the internal gear of the planetary gear set, wherein the planet gears can also be held by way of the planet carrier. The installation tool holds the planet gears and the internal gear in the correct position through the installation openings in the face wall of the rotor of the hollow-shaft motor. “In the correct position” means that the positively locking connections of the internal gear to the force transmitter and of the planet carrier to the rotatable component of the helical gearing are made by way of an axial movement, and in particular do not strike one another as a result of their being rotationally misaligned. After assembly, the installation tool or the holder thereof is pulled out axially through the installation openings in the face wall of the rotor of the hollow-shaft motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be discussed in more detail below on the basis of an embodiment of the disclosure which is illustrated in the drawing, in which: 
         FIG. 1  shows an axial section through a pressure generator according to the disclosure; and 
         FIG. 2  shows parts of the pressure generator and an installation tool according to the disclosure during the assembly process. 
     
    
    
     DETAILED DESCRIPTION 
     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 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. 
     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 of the disclosure, the helical gearing  8  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  respectively. 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 drive, 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 . 
     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 one 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 tubular force transmitter  13 . 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 force transmitter  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 . 
     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 force transmitter  13 . The force transmitter  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 force 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. 
     At an end of the spindle nut  7  remote from the piston  3 , there is arranged a planetary gear set  22  with a sun gear  20 , planet gears  17 , a planet carrier  38  and an internal gear  21 . The planet gears  17  are arranged rotatably on pins which are inserted as planet gear shafts  39  into the planet carrier  38 . In the embodiment illustrated, the planetary gear set  22  has three planet gears  17 , though this is not imperatively necessary for the disclosure. 
     The planet carrier  38  is a circular disk which, by way of a positively locking connection  40 , is attached rotationally conjointly to a face end, which is remote from the piston  3 , of the spindle nut  7 . In the illustrated embodiment of the disclosure, the positively locking connection  40  of the planet carrier  39  to the spindle nut  7  is in the form of a pin-type connection with a number of axially parallel pins  41  arranged eccentrically and uniformly or non-uniformly over a circumference. The positively locking connection  40  can be assembled by way of axial movement of the planet carrier  38  relative to the spindle nut  7 , which may also be referred to as the positively locking connection  40  being made. Other positively locking connections  40  that can be made axially are possible for the purposes of the rotationally conjoint connection of the planet carrier  38  to the spindle nut  7 , such as for example a tongue-and-groove connection, a spline profile or a polygon. This list is not exhaustive but merely exemplary. 
     The internal gear  21  of the planetary gear set  22  is inserted into an end of the tubular force transmitter  13  remote from the piston  3 ; said internal gear bears axially against an annular step in the force transmitter  13 . The internal gear  21  is connected rotationally conjointly, by way of a positively locking connection  42 , to the force transmitter  13 . In the illustrated embodiment of the disclosure, said positively locking connection  42  is also a pin-type connection with pins  43  projecting axially in parallel from the internal gear  21 , which pins engage into holes in the force transmitter  13 . The positively locking connection  42  of the internal gear  21  to the force transmitter  13  is also made by way of an axial movement of the internal gear  21  relative to the force transmitter  13 , and in this case, too, other positively locking connections  42  that can be made axially are possible for the purposes of the rotationally conjoint connection of the internal gear  21  to the force transmitter  13 , such as for example a tongue-and-groove connection, a spline profile or a polygon. This list is not exhaustive but merely exemplary. 
     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 force transmitter  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 . 
     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 seat  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 planet carrier  38  and the spindle nut  7  to be driven in rotation. 
     For the assembly of the pressure generator  1  or for the installation of the planetary gear set  22  and the spindle nut  7  of the helical gearing  8  into the hollow shaft  26  of the hollow-shaft motor  27 , the shaft  23 , which is rotationally conjoint with the sun gear  20 , is pressed from the inside into the collar  24  of the face wall  25  of the hollow shaft  26 , such that the sun gear  20  is arranged rotationally conjointly and coaxially with the hollow shaft  26  on an inner side of the face wall  25  of said hollow shaft. The rotary bearing  33  may be pressed from the outside onto a protruding end of the shaft  23  at the same time or later. From the outside, an installation tool  44  is mounted onto the face wall  25  of the rotor  26 , which installation tool has axially parallel pins as holders  45 ,  46  for the planet carrier  38  and the internal gear  21  ( FIG. 2 ). Pins as holders  45 ,  46  are not imperative for the disclosure. The holders  45 ,  46  extend through installation openings  47  in the face wall  25  of the hollow shaft  26 . The planet carrier  38  and the internal gear  21  have holes corresponding to the holders  45 ,  46  associated therewith. The planet carrier  38 , with the planet gears  17  arranged rotatably thereon, is mounted from the inside, in the hollow shaft  26 , onto the holder  45  of the installation tool  44 , and the internal gear  21  is likewise mounted from the inside, in the hollow shaft  26 , onto that holder  46  of the installation tool  44  which is associated therewith. The installation tool  44  has a hollow cylindrical hub  48 , by way of which it is mounted onto the rotary bearing  33  which is pressed onto the shaft  23 . In this way, the installation tool  44  is centered on the hollow shaft  26 . If the rotary bearing  23  is pressed on at a later point in time, the installation tool  44  may be centered on the shaft  23  or in some other way on the hollow shaft  26  (not illustrated). The installation tool  44  holds the planet carrier  38  and the internal gear  21  in a specified angular position, such that the force transmitter  13  and the spindle nut  7  can be inserted into the hollow shaft  26  from an inner side of the rotor  26 , wherein the positively locking connections  40 ,  42  between the spindle nut  7  and the planet carrier  38  and between the force transmitter  13  and the internal gear  21  are made, and the planet carrier  38  is connected rotationally conjointly to the spindle  7  and the internal gear  21  is connected rotationally conjointly to the force transmitter  13 . The force transmitter  13  may be screwed to the flange part  15  before insertion into the hollow shaft  26 , or the flange part  15  may be screwed to the force transmitter  13  after the insertion of the latter. By means of the installation tool  44 , the force transmitter  13  can be held rotationally fixed for the process of being screwed to the flange part  15 . After the installation of the planetary gear set  22 , the spindle nut  7  and the force transmitter  13  into the hollow shaft  26 , the installation tool  44  is pulled out axially.