Patent Publication Number: US-2022234560-A1

Title: Power brake-pressure generator for a hydraulic vehicle brake system

Description:
FIELD 
     The present invention relates to a power brake pressure generator for a hydraulic vehicle brake system. 
     BACKGROUND INFORMATION 
     The power brake pressure generator is provided for a brake pressure buildup and/or for the conveying of brake fluid for a slip controlling and/or for a brake pressure buildup for a power braking. Slip control systems are anti-locking, drive slippage, and/or driving dynamics regulating/electronic stability programs, for which the abbreviations ABS, ASR, and/or FDR/ESP are standardly used. Driving dynamics regulation systems/electronic stability programs are also commonly referred to as slip and slide protection. Anti-slip control systems are conventional and are not explained here. 
     German Patent Application No. DE 10 2017 214 563 A1 describes a hydraulic assembly having a cuboidal hydraulic block that has a cylinder hole into which a cylinder sleeve is pressed in which a piston is accommodated in axially displaceable fashion. The cylinder hole, or the cylinder sleeve and the piston, form a piston-cylinder unit. For a displacement of the piston, the conventional hydraulic assembly has an electric motor that displaces the piston in the cylinder sleeve via a planetary gear as a reduction gear mechanism and a ball screw gear. The ball screw gear is situated in coaxial fashion in the piston, fashioned as a hollow piston. The electric motor is configured, coaxially to the cylinder sleeve, externally on the hydraulic block, and the planetary gear is also configured coaxially to the cylinder sleeve, between the electric motor and the cylinder sleeve or the ball screw gear. 
     SUMMARY 
     A power brake pressure generator according to an example embodiment of the present invention has a piston-cylinder unit, a screw gear, a mechanical reduction gear mechanism, and a drive motor, the drive motor being in particular an electric motor. The reduction gear, which is effectively situated between the drive motor and the screw gear, reduces a rotational drive movement of the drive motor and transmits it to the screw gear. The screw gear converts the rotational drive movement into a translational movement in order to displace a piston in a cylinder of the piston-cylinder unit, and, conversely, the cylinder can also be displaced on the piston. “Effectively” here means that the reduction gear transmits the rotational drive movement of the drive motor, with a lower rotational speed, to the screw gear. 
     According to an example embodiment of the present invention, the reduction gear is a cycloidal gear. A cycloidal gear has the advantage that it has small dimensions, in particular axially, and that its driveshaft and its output shaft lie along the same axis. In addition, a cycloidal gear is a rolling gear, and is therefore low-wear, and has a large reduction ratio. A large reduction ratio enables a high drive rotational speed, a small drive torque, and thus a small and light drive motor. 
     Developments and advantageous embodiments of the present invention are disclosed herein. 
     In accordance with an example embodiment of the present invention, as a screw gear, a sliding screw gear is provided, meaning a screw gear whose threads slide on one another. In comparison with, for example, a ball screw gear, which when axially loaded has a high degree of mechanical tension between its balls and its threads, a sliding screw gear has force-transmitting surfaces that are many times larger, which reduce mechanical tensions to a fraction of what a smaller screw gear enables. Due to the high load-bearing capacity, the sliding screw gear has, in particular, trapezoidal threads. 
     All the features disclosed in the description herein and in the figures may be realized individually or, in principle, in any combination in specific embodiments of the present invention. Embodiments of the present invention that do not have all, but have only one or some features of a specific embodiment of the present invention are possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the present invention is explained in more detail based on a specific embodiment shown in the figures. 
         FIG. 1  shows a section of a hydraulic assembly having a power brake pressure producer according to the present invention. 
         FIG. 2  shows individual parts of a cycloidal gear of the power brake pressure producer of  FIG. 1 , in a perspective exploded view. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1  shows a hydraulic assembly  1  that is provided in order to produce pressure in a hydraulic vehicle power brake system, and/or to produce pressure and to convey brake fluid in a slip-controlled hydraulic vehicle brake system during a slip controlling. Such slip controlling systems are for example anti-lock systems, drive slippage controlling and/or driving dynamics regulation/electronic stability programs, for which the abbreviations ABS, ASR, and/or FDR/ESP are standardly used. 
     Hydraulic assembly  1  has a hydraulic block  2  that is used for mechanical fastening and hydraulic switching of hydraulic and other components of the slip controlling, such as magnetic valves, check valves, hydrostorage devices, and damping chambers. The components are situated on and in hydraulic block  1 , and are hydraulically connected to one another by a boring (not shown) of hydraulic block  2  corresponding to a hydraulic circuit plan of the vehicle power brake system and the slip controlling. 
     In the depicted and described specific embodiment of the present invention, hydraulic block  2  is a cuboidal flat metal block made of, for example, an aluminum alloy, provided with borings in order to accommodate the components, and bored corresponding to the hydraulic circuit plan of the vehicle brake system and the slip controlling system. 
     Hydraulic block  2  has a power brake pressure producer  7  that is explained below; hydraulic block  2  can also be regarded as a component of power brake pressure producer  7  according to the present invention. 
     Hydraulic block  2  has a cylinder hole  3  that is made perpendicular to two large sides, situated opposite one another, of hydraulic block  2  in hydraulic block  2 . Cylinder hole  3  is open at one of the two large sides of hydraulic block  2 , here referred to as engine side  4 . The oppositely situated large side of hydraulic block  2  is here referred to as valve side  5 . At this side, hydraulic block  2  has, in the exemplary embodiment, a bowl-shaped prolongation  6  of cylinder hole  3 , protruding axially to cylinder hole  3 , so that as a result cylinder hole  3  is axially longer than the thickness of hydraulic block  2 . 
     In cylinder hole  3 , a piston  8  is accommodated so as to be axially displaceable, which in the exemplary embodiment is a cylindrical tube-shaped hollow piston having an open end and a closed end. Piston  8  and cylinder hole  3  form a piston-cylinder unit  9  that is a component of power brake pressure producer  7  according to the present invention. Cylinder hole  3  forms a cylinder  10  of piston-cylinder unit  9 . 
     For the displacement of piston  8  in cylinder hole  3 , power brake pressure producer  7  has an electric motor as drive motor  11 , a screw gear  12 , and a cycloidal gear  13  as mechanical reduction gear. 
     The electric motor forming drive motor  11  is configured coaxially to cylinder  10  or to cylinder hole  3 , externally at the engine side  4  of hydraulic block  2 . 
     In the depicted and described specific embodiment of the present invention, screw gear  12  is a sliding screw gear  14  having a rotationally drivable spindle nut  15  and an axially displaceable spindle  16  whose threads slide on one another when there is a rotation of spindle nut  15 . Screw gear  12  does not have any balls or similar roller elements. Spindle nut  15  can in general also be understood as a rotationally drivable drive element  17 , and spindle  16  can be understood as a displaceable output element  18  of screw gear  12 . Constructions are also possible in which spindle  16  is rotationally driven and spindle nut  15  is displaced (not shown). In this case, the spindle would form the rotationally drivable drive element, and the spindle nut would form the displaceable output element of the screw drive. Screw gear  12 /sliding screw gear  14  has a trapezoidal thread in the exemplary embodiment. 
     Screw gear  12  is configured coaxially in piston  8 , fashioned as a hollow piston, and is also configured coaxially in cylinder hole  3 , forming cylinder  10 , of hydraulic block  2 . Piston  8  fashion as a hollow piston has a head pin  19  on an inner side of a piston floor  20  onto which spindle  16  of screw gear  12  is snapped, which spindle has for this purpose a corresponding blind hole having a circumferential radial groove on its base, into which a head of head pin  19  is snapped. 
     Piston  8  is displaced axially in cylinder hole  3  of hydraulic block  2 , i.e., in cylinder  10  of piston-cylinder unit  9  of power brake pressure producer  7  according to the present invention, by a rotational drive of spindle nut  15 , or in general of the rotational drive element  17  of screw gear  12 . Through the displacement of piston  8  in cylinder hole  3 , or in cylinder  10 , a brake pressure is produced for an actuation of hydraulic wheel brakes (not shown) that are connected to wheel connections  24  of hydraulic block  2  via brake lines (not shown). During a slip controlling, brake fluid is conveyed by displacing piston  8  in cylinder hole  3 , or in cylinder  10 . 
     Spindle nut  15  is rotatably mounted outside piston  8  in a ball bearing as rotational bearing  21 . Rotational bearing  21  is situated in an annular bearing mount  22  that is pressed into an annular step at the opening of cylinder hole  3  in hydraulic block  2 , and is fastened to a spring ring  23  that engages in a circumferential groove externally in bearing mount  22  and in a circumferential groove internally in a circumferential wall of the annular step at the opening of cylinder hole  3 . Bearing mount  22  has a parallel knurling  50  having axially parallel grooves (see  FIG. 2 ) that, when pressed into a circumferential wall of the annular step, conforms to the opening of cylinder hole  3  and holds bearing mount  22  on hydraulic block  2  in rotationally fixed fashion. 
     Cycloidal gear  13 , whose individual parts are shown in  FIG. 2 , forms a mechanical reduction gear that is situated coaxially between the electric motor forming drive motor  11  and screw gear  10 . A hollow gear  25  of cycloidal gear  13  is fastened on bearing mount  22  of rotational bearing  21  of spindle nut  15  of screw gear  12 , and stands out from the annular step at the opening of cylinder hole  3  in hydraulic block  2 . 
     Hollow gear  25  has an internal toothing  26  having wave-shaped rounded teeth with which an external toothing of a curved plate  28  of cycloidal gear  13  meshes, which has complementarily wave-shaped rounded teeth. Curved plate  28  has a diameter that is smaller by at least the height of a tooth than the internal toothing  26  of hollow gear  25 , and curved plate  28  is configured in axially parallel fashion and eccentrically in hollow gear  25  in such a way that its external toothing  27  meshes, at a point on the circumference, with internal toothing  26  of hollow gear  25 . In a rotational drive, curved plate  28  runs on a circular path in hollow gear  25 , so that the circumferential point at which the toothings  26 ,  27  mesh runs around in hollow gear  25 . Here, curved plate  28  rotates about its axis. 
     Hollow gear  25  has, internally, axially parallel ribs  51  that engage in axially parallel grooves in the outer circumference of bearing mount  22 , whereby hollow gear  25  is situated in rotationally fixed fashion on bearing mount  22 . Axially, ribs  51  extend up to an end face of internal toothing  27 , and hollow gear  25  is set onto bearing mount  22  until its inner toothing comes to be seated on bearing mount  22 . For example, hollow gear  25  is pressed onto bearing mount  22 , or is shrink-fitted thereon, or is welded therewith. 
     A motor shaft  29  of the electric motor forming drive motor  11  has an axially parallel, eccentric pin, made in one piece therewith, as eccentric  30  that extends through a center hole  31  of curved plate  28  of cycloidal gear  13 . On eccentric  30  of motor shaft  29  there is situated a ball bearing as rotational bearing  32  on which center hole  31  of curved plate  28  of cycloidal gear  13  is situated. When drive motor  11  is rotationally driven, motor shaft  29  rotates, causing rotary bearing  32  to execute a circular movement on eccentric  30  that moves curved plate  28  on the circular path in hollow gear  25  of cycloidal year  13 . Through the engagement of toothings  26 ,  27  of hollow gear  25  and curved plate  28 , curved plate  28  carries out a rotation about its axis, in additional to its circular movement. Instead of a ball bearing, for example a roller bearing or needle bearing, or also a sliding bearing, can be provided as rotational bearing  32 , or curved plate  28  is immediately mounted in sliding fashion on eccentric  30  (not shown). 
     In order to compensate an imbalance of eccentric  30  and rotational bearing  32  situated thereon, motor shaft  29  of the electric motor forming drive motor  11  has a balancing weight  33 . 
     Axially, hollow gear  25  of cycloidal gear  13  is supported on a bearing shield  39  of drive motor  11 . Via hollow gear  25 , rotational bearing  21  of screw gear  12  is supported axially on bearing shield  39  of the electric motor forming drive motor  11 , and via rotational bearing  21  spindle nut  15  of screw gear  12 , which forms drive element  17  of screw gear  12 , is also supported axially on bearing shield  39  of the electric motor forming drive motor  11 . Drive motor  11 , or its bearing shield  39 , forms a kind of axial counter-support that axially supports cycloidal gear  13  and screw gear  12 . 
     On an end face oriented towards drive motor  11 , hollow gear  25  of cycloidal gear  13  has a coaxial collar  52  in the shape of a cylindrical tube that axially overlaps a motor bearing  53  that stands out a short distance axially from bearing shield  39 . In this way, drive motor  11  is centered on hollow gear  25  of cycloidal gear  13 . 
     In order to communicate its rotation to screw gear  12 , curved plate  28  of cycloidal gear  13  has circular through-holes  34  that are situated around its center hole  31  and are distributed around a circumference. Drive pins  35  of a perforated plate that forms a output element  36  of cycloidal gear  13  engage in through-holes  34 . Due to the eccentricity of curved plate  28 , drive pins  35  have a smaller diameter than do the through-holes  34  in which they engage. 
     For a rotationally fixed connection of output element  36  of cycloidal gear  13  with spindle nut  15 , which forms drive element  17  of screw gear  12 , pins  37  stand out from an end face of spindle nut  15  oriented towards cycloidal gear  13 , which pins engage in holes  38  that are made between drive pins  35  in output element  36  of cycloidal gear  13 . 
     In the depicted and described specific embodiment of the present invention, hydraulic block  2  has a master brake cylinder bore  40  in which a master brake cylinder piston (not shown) can be situated that is mechanically displaceable in master brake cylinder bore  41  via a piston rod, by a foot brake pedal (not shown) or a hand brake lever. 
     In valve side  5  of hydraulic block  2 , diametrally stepped blind holes are made as receptacles  41  for magnetic valves (not shown). The magnetic valves are components of the slip controlling and of a brake pressure controlling that provide a regulation or controlling of the brake pressure or of wheel brake pressures in the wheel brakes. Equipped with the components of the slip controlling system, hydraulic block  2  forms hydraulic assembly  1 .