Patent Publication Number: US-2022212647-A1

Title: Electromechanically driveable brake pressure generator for a hydraulic braking system of a vehicle, and vehicle including an electromechanical brake pressure generator

Description:
FIELD 
     The present invention relates to an electromechanically driveable brake pressure generator for a hydraulic braking system of a vehicle and to a vehicle including an electromechanical brake pressure generator. 
     BACKGROUND INFORMATION 
     The electromechanical brake pressure generator includes, in particular, a threaded drive assembly for converting a drive-side rotation into a translation for the hydraulic brake actuation. 
     The foot force of the driver mostly does not suffice for decelerating motor vehicles, and so motor vehicles are usually equipped with a brake booster. Conventional brake boosters generally operate at an underpressure generated by the internal combustion engine. The pressure difference between the engine pressure and the ambient pressure is utilized for applying a boosting force, in addition to the foot force of the driver, onto the piston rod of the piston/cylinder unit. 
     Alternative brake pressure build-up devices are required for future drive concepts of motor vehicles, since the underpressure is no longer available for operating a conventional vacuum brake booster. The electromechanical brake pressure generators of interest here were developed for this purpose. 
     The actuating force at the piston/cylinder unit is generated with the aid of an electric motor. Such electromechanical brake pressure generators may be utilized not only for providing an auxiliary power, but rather, in brake-by-wire systems, also for solely providing the actuating force. For this reason, electromechanical brake pressure generators are advantageous, in particular, with respect to autonomous driving. 
     PCT Patent Application No. WO 2017/045804 A1 describes a conventional electromechanical brake booster, which is represented in  FIG. 1 . In contrast thereto, the present invention is directed to an electromechanical brake pressure generator, which may apply a braking force regardless of an actuation of the brake pedal. The conventional brake booster  1  includes a spindle nut  2  and an electric motor (not outlined), via the operation of which spindle nut  2  is settable into a rotation via a spur gear  3 . 
     Spindle nut  2  is operatively engaged with a spindle  4 , and therefore spindle  4  is settable into a translation along its spindle axis  5  with the aid of the spindle nut  2 , which has been set into rotation. In order to ensure that spindle  4  does not also rotate due to the rotation of spindle nut  2 , brake booster  1  includes a bearing assembly  6 , to which spindle  4  is fixedly connected. 
     Bearing assembly  6  includes a bracket  6   a , at the edges of which two slide bearings  6   b  are situated. Slide bearings  6   b  run at tie rods  7 , which extend essentially in parallel to spindle axis  5 . Due to this bearing assembly  6 , spindle  4  is movable in the axial direction and is secured against rotation. 
     An object of the present invention is to provide an improved electromechanical brake pressure generator, which is more cost-effectively manufacturable. 
     SUMMARY 
     An object of the present invention may be achieved by an electromechanical brake pressure generator for a hydraulic braking system in accordance with an example embodiment of the present invention. Advantageous refinements and embodiments of the present invention are disclosed herein. 
     The present invention provides an electromechanical brake pressure generator for a hydraulic braking system of a vehicle. In accordance with an example embodiment of the present invention, this electromechanical brake pressure generator includes at least one threaded drive assembly for converting a drive-side rotation into a translation in order to generate brake pressure. The threaded drive assembly includes a spindle, which is rotatable via an electric motor, and a spindle nut, which is situated on a thread of the spindle in such a way that the spindle nut and a hydraulic piston formed thereon are axially displaceable upon rotation of the spindle. 
     In addition, the threaded drive assembly includes a housing, which forms a hydraulic cylinder corresponding to the hydraulic piston, in which the spindle and the spindle nut are accommodated, and a rotation lock formed with the housing, via which the spindle nut is secured against rotation upon rotation of the spindle. 
     A threaded drive assembly is understood to be a pure spindle drive, in which the spindle nut is in direct contact with the spindle, as well as a ball screw. A ball screw is a worm gear including balls inserted between the spindle and the spindle nut. Each of the two parts has a helical groove, which, together, form a helical tube filled with balls. The form-fitting connection in the thread transverse to the helix does not take place between the thread groove and dam, as is the case with a pure spindle drive, but rather via the balls. 
     The hydraulic piston rests directly against the brake fluid, so that the brake fluid may be acted upon by pressure via the hydraulic piston. Preferably, the hydraulic piston is designed in the shape of a cup. Preferably, a portion of the spindle engages into the cup-shaped recess. 
     The rotation lock may be formed, for example, by the spindle nut and the housing per se, as well as via an additional part. 
     In accordance with an example embodiment of the present invention, the rotation lock prevents the spindle nut from also rotating when the spindle rotates, so that the spindle nut is axially displaceable on the spindle by rotating the spindle. An advantage of the driven spindle is that the torque introduced into the spindle nut due to the rotation of the spindle may be more easily diverted. As a result, the spindle nut may be guided, for example, by a simple guidance in the housing. As a result, parts for a rotation lock of this type are saved, so that a rotation lock of this type is more economically and, thereby, more cost-effectively manufacturable. As a result, an improved electromechanical brake pressure generator may be provided, which, due to the reduced number of parts, requires less installation space and, thereby, is also more lightweight. 
     In one preferred embodiment of the present invention, the spindle nut and the hydraulic piston are made of different materials and are situated lying coaxially next to one another. Due to the formation from different materials, a material, which is optimal for the different function of the spindle nut and the hydraulic piston, may be selected. In this way, a material may be selected for the hydraulic piston, which has, for example, a greater strength. Correspondingly, a material may be selected for the spindle nut, which has, for example, good tribological properties. 
     In one further preferred embodiment of the present invention, the rotation lock is formed by the housing and the hydraulic piston and/or the spindle nut. The housing and the hydraulic piston and/or the spindle nut preferably interact via structural elements in such a way that a rotation of the spindle nut with respect to the housing is avoided. As a result, a rotation lock may be formed in an easy way. 
     Preferably, the rotation lock is formed via a tongue and groove connection. A tongue and groove connection is characterized, in particular, by a groove and a tongue accommodatable therein, which are exactly matched to each another. The groove and the tongue engage into each other in a form-fitted manner. The tongue and groove connection may be formed as a groove and a tongue, for example, at the components to be secured with respect to one another. It is also possible that an additional part, which is designed as a tongue, engages into grooves of the components to be secured. 
     The tongue and groove connection may be manufactured by stamping, broaching, or a machining operation. As a result, such tongue and groove connections are easily and economically manufacturable and ensure a good rotation lock. 
     In one advantageous refinement of the present invention, the rotation lock of the spindle nut forms two diametrically opposed, radially outwardly extending blades, which engage into corresponding grooves of the housing. The blades have an angle of 180° with respect to one another. Within the scope of the present invention, blades are understood to be elements protruding from the main body of the spindle nut. Due to blades situated in this way, the spindle nut may be sufficiently secured against rotation. Additionally, the spindle nut is centrally retained with little play. 
     Advantageously, at least one portion of the spindle nut is made of plastic. This portion may be attached at a main portion of the spindle nut. As a result, the costs and the weight of a spindle nut manufactured in such a way may be reduced. 
     In one further advantageous embodiment of the present invention, the portion of the spindle nut made of plastic is designed as a plastic injection-molded part. The portion of the spindle nut made of plastic may be injected onto a main portion of the spindle nut. As a result, a simple mounting of the plastic is possible, so that a spindle nut of this type is economically manufacturable. Additionally, as a result, the number of components is reduced. 
     Advantageously, the housing is made of an aluminum or steel alloy. Due to a housing of this type, a sufficient strength against the generated pressures may be ensured. These materials also have a good wear resistance. A good heat dissipation is also ensured. When an aluminum alloy is utilized, in addition, the weight may be reduced as compared to many other metals. In addition, an aluminum alloy has a particularly high heat conductance. 
     According to one further advantageous embodiment of the present invention, at least the rotation lock at the spindle nut and/or the hydraulic piston is made of plastic, in order to improve the slide properties with respect to the housing made of metal. As a result, the side of the rotation lock made of plastic slides on a metal surface of the housing. As a result, a wear-resistant and efficient pair of slide elements is ensured. This pair of slide elements enables an optimized design with respect to NVH (NVH: noise, vibration, harshness). 
     The present invention also relates to a vehicle including an electromechanical brake pressure generator for a hydraulic braking system, in accordance with an example embodiment of the present invention. With a vehicle of this type, the advantages mentioned with respect to the electromechanical brake pressure generator may be achieved. In one preferred embodiment, this vehicle may be an automated or fully autonomous vehicle. 
     Exemplary embodiments of the present invention are represented in the figures and are explained in greater detail in the description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a representation of an electromechanical brake booster from the related art. 
         FIG. 2  shows a schematic representation of a hydraulic braking system for a vehicle including an electromechanical brake pressure generator. 
         FIG. 3  shows a cross-sectional and longitudinal section of an exemplary embodiment of a threaded drive assembly according to the present invention of the electromechanical brake pressure generator, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In  FIG. 2 , a schematic representation of a hydraulic braking system  10  for a vehicle including an electromechanical brake pressure generator  14  is shown. Hydraulic braking system  10  includes electromechanical brake pressure generator  14 . This brake pressure generator  14  includes a piston/cylinder unit  18 , which is supplied with brake fluid via a brake fluid reservoir  22 . 
     Piston/cylinder unit  18  may be activated via a brake pedal  26  actuated by the driver and the resultant brake pedal travel is measured by a pedal travel sensor  30  and forwarded to a control unit  34 . 
     Although  FIG. 2  shows, in principle, a brake booster; here the brake pedal travel is measured via pedal travel sensor  30 . A brake pressure generation without a brake pedal travel is also possible, so that the vehicle is deceleratable also in the autonomous driving condition. 
     Control unit  34  generates, on the basis of the measured brake pedal travel, a control signal for an electric motor  38  of brake pressure generator  14 . Electric motor  38 , which is connected to a transmission (not shown) of brake pressure generator  14 , boosts the braking force introduced by brake pedal  26  according to the control signal. For this purpose, according to the actuation of brake pedal  26 , a threaded drive assembly  40  situated in brake pressure generator  14  is activated by electric motor  38 , so that the rotation of electric motor  38  is converted into a translation. 
     Due to the actuation of brake pedal  26 , the brake fluid present in piston/cylinder unit  18  is pressurized with the aid of brake pressure generator  14 . This brake pressure is forwarded to a brake hydraulics system  46  via brake lines  42 . Brake hydraulics system  46 , which is represented here only as a box, is formed by various valves and further components for forming, for example, an electronic stability program (ESP). Brake hydraulics system  46  is additionally connected to at least one wheel brake unit  50 , so that a braking force is able to be applied at wheel brake unit  50  due to an appropriate switching of valves. 
       FIG. 3  shows a cross-sectional and longitudinal section of one exemplary embodiment of threaded drive assembly  40  according to the present invention of electromechanical brake pressure generator  14 . Threaded drive assembly  40  includes a housing  64 , which forms a cup-shaped hydraulic cylinder  66 . In this exemplary embodiment, housing  64  is made of metal. Additionally, threaded drive assembly  40  includes a spindle  68 , which is drivable via electric motor  38  shown in  FIG. 2 , so that spindle  68  carries out a rotary motion about its longitudinal axis  72 . 
     A spindle nut  80  is situated on a thread  76  of spindle  68  and is engaged with thread  76  of spindle  68 . Spindle nut  80  essentially forms a hollow cylindrical body. Radially outwardly extending blades  84  are located at two diametrically opposed sides of the hollow cylindrical body, which engage into grooves  88  of housing  64  and form the rotation lock of spindle nut  80 . Grooves  88  in housing  64  are formed as longitudinal grooves. 
     A width of blades  84  of spindle nut  80  in the circumferential direction is slightly less than a groove width of housing  64  formed in the circumferential direction. A length of blades  84  in the axial direction is considerably less than a length of grooves  88  of housing  64 . Due to a rotation of spindle  68 , spindle nut  80  is held by rotation lock  84 ,  88 , so that spindle nut  80 , including blades  84 , is movable in the axial direction in housing  64  in the range across the length of grooves  88  of housing  64 . 
     A hydraulic piston  92  is situated at spindle nut  80 , which is connected to spindle nut  80 . In contrast to spindle nut  80 , hydraulic piston  92  is not in engagement with thread  76  of spindle  68 . Hydraulic piston  92  is designed essentially in the shape of a cup. A seal  96  is situated between hydraulic piston  92  and hydraulic cylinder  66  of housing  64 , so that a pressure is generatable in a working chamber  98  of hydraulic cylinder  66 . Due to the rotation of spindle  68 , hydraulic piston  92  may be axially displaced, via spindle nut  80 , in the direction of working chamber  98 , so that a brake fluid present in working chamber  98  may be pressurized.