Patent Publication Number: US-2023137126-A1

Title: Hydraulic control unit and hydraulic motor vehicle braking system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Priority Application No. 102021128767.7, filed Nov. 4, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The disclosure relates to a hydraulic control unit for a vehicle. Moreover, the disclosure relates to a hydraulic motor vehicle braking system. 
     BACKGROUND 
     Hydraulic control units usually include liquid reservoirs, which can make brake fluid available if necessary. In order to ensure an approximately uniform delivery rate, ventilation is necessary behind a piston unit of the liquid reservoir, otherwise an underpressure can arise, which prevents a complete emptying of the liquid reservoir. In order to achieve this pressure compensation, a direct connection to the surroundings conditions or to the atmosphere is usually established as the piston advances. As a result thereof, however, not only does the required ventilation take place, but an entry of, for example, dirt particles, such as water or salt water, also takes place. A utilisation of the hydraulic control unit in or under water is also not enabled as a result. Additionally, in the case of a temperature change (for example, temperature shock), a vacuum can arise between the piston unit and the end cap, which prevents the piston from moving and, thus, can prevent a braking function. 
     For example, U.S. Pat. No. 6,634,386 B1 describes a liquid reservoir for use in a vehicle anti-lock braking system. The hydraulic control unit includes a main body and the liquid reservoir mounted in the main body, wherein a sealing buffer is used for mounting the main body at a vehicle body. The sealing buffer establishes a venting path for the liquid reservoir toward the outside to the surroundings of the vehicle. 
     SUMMARY 
     What is needed is structurally and/or functionally improving an aforementioned hydraulic control unit, as well as structurally and/or functionally improving an aforementioned hydraulic motor vehicle braking system. 
     Disclosed herein is a hydraulic control unit (HCU) for a braking system. The hydraulic control unit and/or the braking system can be utilised or intended for a vehicle, such as a motor vehicle. The motor vehicle can be a passenger car or a truck. The braking system can be a vehicle braking system and/or a motor vehicle braking system, such as a hydraulic motor vehicle braking system. The hydraulic control unit can be an electrohydraulic control unit (ENCU). The hydraulic control unit can be an assembly, such as a hydraulic assembly. 
     The hydraulic control unit can include a hydraulic fluid reservoir. The hydraulic fluid reservoir can be a reservoir, such as an intermediate reservoir, for a hydraulic fluid, such as brake fluid. The hydraulic fluid reservoir can be an accumulator and/or a brake fluid reservoir. 
     The hydraulic fluid reservoir can include a hydraulic fluid reservoir space. The hydraulic fluid reservoir space can be a chamber, such as a fluid chamber or a hydraulic fluid reservoir space. The hydraulic fluid reservoir and/or the hydraulic fluid reservoir space can be designed in such a way that a hydraulic pressure generator is able to suction hydraulic fluid out of the hydraulic fluid reservoir space. The hydraulic control unit and/or the braking system can include the hydraulic pressure generator. The hydraulic pressure generator can be an electrical hydraulic pressure generator. The hydraulic pressure generator can be a, for example, electrical, brake pressure generator for example, a second brake pressure generator of a second functional unit. The hydraulic pressure generator can be a fluid supply device. The hydraulic pressure generator can be or include an, electrical pump, such as a hydraulic pump and/or a piston pump and/or a radial piston pump and/or a gear pump and/or a multi-piston pump. 
     The hydraulic fluid reservoir can include an air space. The air space can be a chamber, such as an air chamber, a ventilation chamber, or an aeration chamber. The hydraulic fluid reservoir space and the air space can be separated from each other. The air space can be connectable and/or connected to an interior space of the hydraulic control unit. The hydraulic control unit can include and/or define the interior space. The interior space can be separated from the surroundings, for example, from the outer surroundings of the hydraulic control unit, such as the atmosphere, and/or dosed off from, such as hermetically sealed with respect to, the surroundings. The volume of the interior space can be greater than the volume of the air space. 
     The hydraulic fluid reservoir can include a piston. The piston can be an accumulator piston. The piston can be movably, for example, slidingly, accommodated in the hydraulic fluid reservoir. The piston can be, for example, slidingly, accommodated in the hydraulic fluid reservoir. The piston can be designed in such a way that the piston separates the hydraulic fluid reservoir space and the air space from each other. The piston can be cylindrical. The piston can be cup-shaped. The piston can have a first piston surface. The piston can have a second piston surface. The first piston surface can delimit the hydraulic fluid reservoir space at least in some areas The second piston surface can delimit the air space at least in some areas. The piston can be designed in such a way that a displacement of the piston in a first direction enlarges the hydraulic fluid reservoir space and reduces the hydraulic fluid reservoir space in an opposite, second direction. The piston can be designed in such a way that a displacement of the piston in the first direction reduces the air space and enlarges the air chamber in the opposite, second direction. Due to the displacement of the piston in the first direction, hydraulic fluid can flow into the hydraulic fluid reservoir space, and so the hydraulic fluid reservoir space is filled with the hydraulic fluid. Due to the displacement of the piston in the second direction, hydraulic fluid can flow out of the hydraulic fluid reservoir space and/or air can flow and/or be suctioned into the air space from the interior space. 
     The hydraulic fluid reservoir can include at least one hydraulic fluid outlet. The at least one hydraulic fluid outlet can be assigned to and/or open into the hydraulic fluid reservoir space. Via the hydraulic fluid outlet, the hydraulic pressure generator can suction hydraulic fluid out of the hydraulic fluid reservoir space. The hydraulic pressure generator can be designed to provide the hydraulic fluid present in the hydraulic fluid reservoir space of the hydraulic fluid reservoir to the braking system or at least to a brake circuit, for example to generate a brake pressure at, at least one wheel brake. The hydraulic pressure generator can be designed to suction in the hydraulic fluid present in the hydraulic fluid reservoir space of the hydraulic fluid reservoir and feed the hydraulic fluid to at least one brake circuit in order to generator a brake pressure at, at least one wheel brake. 
     The hydraulic fluid reservoir can include a cap, such as an end cap. The air space can be delimited by the cap at least in some areas. The cap can be arranged at the side opposite the second piston face. The cap can be sealingly mounted. The cap can be plate-shaped. The hydraulic fluid reservoir can have an open side. The open side can be closed, for example tightly, by the cap. 
     The hydraulic fluid reservoir can include at least one ventilation inlet for ventilating the air space. The ventilation inlet can be assigned to the air space and/or open into the air chamber. The at least one ventilation inlet can be connectable and/or connected to the interior space of the hydraulic control unit, example, via a venting path and/or venting duct. The hydraulic control unit and/or the hydraulic fluid reservoir can be designed in such a way that air can flow out of the interior space of the hydraulic control unit into the air space of the hydraulic fluid reservoir. Due to a displacement of the piston of the hydraulic fluid reservoir, for example in the second direction, air can flow and/or be suctioned out of the interior space of the hydraulic control unit into the air space of the hydraulic fluid reservoir. The hydraulic fluid reservoir and/or the hydraulic control unit can be designed in such a way that air can flow, such as subsequently flow, out of the interior space into the air space. 
     The air space can be connectable and/or connected to the interior space of a housing of the hydraulic control unit, for example, via the at least one ventilation outlet. The air space can be connectable and/or connected to the interior space of a housing of an electric control unit of the hydraulic control unit, for example, via the at least one ventilation outlet. The hydraulic control unit can include the electric control unit. The electric control unit can be a control unit and/or an electronic controller. The electric control unit can be an electronic control unit (ECU). Additionally or alternatively, the air space can be connectable and/or connected to the interior space of a housing of a motor of the hydraulic control unit, for example, via the at least one ventilation outlet. The hydraulic control unit can include the motor. The motor can be an electric motor. The electric motor can be a DC motor. The motor can be a drive motor of the hydraulic pressure generator. 
     The hydraulic control unit can be a bore, such as an axial bore. The hydraulic control unit can include a body, such as a main body. The bore can be formed in the body of the hydraulic control unit. The piston of the hydraulic fluid reservoir can be movably, for example, slidingly, accommodated and/or mounted in the bore. The bore can delimit the hydraulic fluid reservoir space at least in some areas. The bore can delimit the air space at least in some areas. 
     The hydraulic control unit and/or the hydraulic fluid reservoir can include a cylinder. The cylinder can be mounted and/or arranged in the body, such as the main body, of the hydraulic control unit. The cylinder can be designed to accommodate hydraulic fluid. The piston of the hydraulic fluid reservoir can be movably, for example, slidingly, accommodated and/or mounted in the cylinder. The cylinder can delimit the hydraulic fluid reservoir space at least in some areas. The cylinder can delimit the air space at least in some areas. 
     The hydraulic fluid reservoir can include a sealing element. The piston of the hydraulic fluid reservoir can be sealed with respect to the bore and/or the cylinder via or by the sealing element. The sealing element can be designed to seal the hydraulic fluid reservoir space and the air space with respect to each other. The sealing element can be designed to seal in a fluid-tight manner. The sealing element can be ring-shaped. The sealing element can be designed as an annular seal. The sealing element can include a circumferential sealing lip. The piston of the hydraulic fluid reservoir can include a groove, such as a circumferential groove. The sealing element can be effectively arranged in the groove of the piston, at least in some areas. The sealing lip of the sealing element can protrude over the circumference/circumferential surface of the piston, at least in some areas. 
     The piston can be designed to separate the air space from the interior space of the hydraulic control unit, for example, to close the at least one ventilation outlet, in a position of the piston, for example, the rearward position of the piston, such as the hydraulic fluid reservoir position and/or end position. This position can be the end position in the direction of the first direction. The hydraulic fluid reservoir can be in a condition in which the hydraulic fluid reservoir is filled and/or charged with hydraulic fluid. In the filled and/or charged condition, the hydraulic fluid reservoir space can be filled with hydraulic fluid and/or hydraulic fluid can be stored, such as reserved, in the hydraulic fluid reservoir space. In the filled and/or charged condition, the piston can rest against the cap and/or against a support element, such as a support ring. The hydraulic fluid reservoir can include the support element. In the filled and/or charged condition, the piston can be positioned and/or designed in such a way that the at least one ventilation outlet is closed. 
     The piston can be designed to connect the air space to the interior space of the hydraulic control unit by means of an axial movement of the piston, for example, a movement to empty and/or discharge the hydraulic fluid present in the hydraulic fluid reservoir space. The movement to empty and/or discharge the hydraulic fluid present in the hydraulic fluid reservoir space can take place in the direction of the second direction. Due to the movement, the piston can be or will be positioned in such a way that the at least one ventilation outlet is opened. 
     The hydraulic fluid reservoir can be or will be acted upon, for example, by suctioning in the hydraulic fluid by the hydraulic pressure generator. The hydraulic fluid reservoir can be designed in such a way that the piston is or will be, for example, exclusively, acted upon by suctioning in the hydraulic fluid by the hydraulic pressure generator. The hydraulic fluid reservoir can be or will be acted upon exclusively by atmospheric pressure. The hydraulic fluid reservoir can be designed in such a way that the piston is or will be, for example, exclusively, acted upon by atmospheric pressure. The hydraulic fluid reservoir can be designed as a fluid reservoir, such as a low-pressure reservoir, that is not acted upon by spring force. The hydraulic fluid reservoir can be designed in such a way that the hydraulic fluid reservoir and/or the piston are/is pressureless in the filled and/or charged condition. The piston of the hydraulic fluid reservoir can be a pressureless piston and/or can be designed in this way. 
     The hydraulic control unit can include a venting path. The venting path can be connectable and/or connected, on the one hand, to the air space, for example, to the at least one ventilation outlet of the air chamber. The venting path can open into the air space. The venting path can be connectable and/or connected, on the other hand, to the interior space, for example, to the interior space of the housing of the electric control unit and/or to the interior space of the housing of the motor. The venting path can open into the interior space of the housing of the hydraulic control unit. The venting path can open into the interior space of the housing of the electric control unit and/or into the interior space of the housing of the motor. The air space can be connected to the interior space via the venting path. 
     The interior space, for example the interior space of the housing of the electric control unit and/or the interior space of the housing of the motor, can be separated from the surroundings, for example, from the atmosphere surrounding the hydraulic control unit, and/or closed off from, such as hermetically sealed with respect to, the surroundings, Additionally, or alternatively, the electric control unit and/or the housing of the electric control unit can include an air-permeable diaphragm. 
     The hydraulic control unit can include at least one duct, such as a duct bore. The at least one duct can open, on the one hand, into the air space. The at least one duct can open, on the other hand, into a supply path, such as a supply duct. The supply path can extend between the interior space of the housing of the electric control unit and the interior space of the housing of the motor and connect these to each other. The supply path can open, on the one hand, into the interior space of the electric control unit and, on the other hand, into the interior space of the housing of the motor. The supply path can be utilised for the electrical supply and/or control of the motor. The supply path can be designed in such a way that supply lines, such as power lines and/or control lines, can extend from the electric control unit to the motor. A gap, such as an annular gap, can be formed between the supply lines and the supply path/duct. The at least one duct can open into the gap. 
     At least one sealing element can be effectively arranged in the supply path. The at least one sealing element can be designed to seal in a fluid-tight manner. The at least one sealing element can be ring-shaped. The at least one sealing element can be an annular seal and/or an O-ring. For example, a sealing element can be effectively arranged in a first path section of the supply path. The first path section can be provided and extend between the mouth of the at least one duct and the interior space of the housing of the electric control unit. The sealing element can be designed to seal the air space and the interior space of the housing of the electric control unit with respect to each other. Additionally or alternatively, a sealing element can be effectively arranged in a second path section of the supply path. The second path section can be provided and extend between the mouth of the at least one duct and the interior space of the housing of the electric control unit. The sealing element can be designed to seal the air space and the interior space of the housing of the motor with respect to each other, 
     A hydraulic motor vehicle braking system can be for a vehicle, such as a motor vehicle. The motor vehicle can be a passenger car or a truck. The vehicle and/or the motor vehicle braking system can include wheel brakes, such as front wheel brakes and/or rear wheel brakes. The motor vehicle braking system can include a hydraulic control unit. The hydraulic control unit can be designed as described above and/or in the following. 
     The hydraulic motor vehicle braking system can be for and/or include and/or be designed for a redundant brake pressure control. 
     The motor vehicle braking system can include a first functional unit, The first functional unit can include a first, for example, electric, brake pressure generator. The first brake pressure generator of the first functional unit can be designed to generate a brake pressure at each of a plurality of wheel brakes, for example, at each of all wheel brakes. The first functional unit can include a brake cylinder that is couplable or coupled to a brake pedal. 
     The motor vehicle braking system can include a second functional unit. The second functional unit can be designed to lead through a brake pressure at each wheel brake of the plurality of wheel brakes redundantly with respect to the first functional unit. The second functional unit can include the hydraulic control unit, which is described above and/or in the following. 
     The two functional units can be logically and/or physically separated from each other. Functional units that are physically separated from one another can be accommodated in different housings or housing parts at least with respect to some of their components. The different housings or housing parts can be attached to one another directly, i.e., at least approximately without spacing, and, thus, can be considered as two housing parts of a higher-order overall housing. 
     With the disclosure, the inner area can be separated from the surroundings conditions also during the piston travel. An entry of, for example, water or salt water, is avoided. Simultaneously, it can be ensured that the hydraulic pressure generator, such as a pump, can be able to access the volume, such as the hydraulic volume or hydraulic fluid, also after a temperature shock; for example when a sufficiently large connecting volume has been selected. It can be achieved that the pressure drop behind the piston has no significant effect on the delivery rate of the hydraulic pressure generator. The delivery rate of the hydraulic pressure generator can be improved. Pressure differences, also with respect to the surroundings and/or due to temperature changes or altitude changes, can be compensated for. The hydraulic control unit can be actuated and used in and/or under water, for example due to the separation into an inner area and an outer area. Fewer parts are required. The assembly effort can be reduced. The costs can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Exemplary arrangements of the disclosure are described in greater detail in the following with reference to figures. Schematically and by way of example: 
         FIG.  1    shows a hydraulic fluid reservoir in a filled/charged condition; 
         FIG.  2    shows the hydraulic fluid reservoir according to  FIG.  1    in the emptied/discharged condition; 
         FIG.  3    shows a variant of a hydraulic control unit; 
         FIG.  4    shows another variant of a hydraulic control unit; 
         FIG.  5    shows another variant of a hydraulic control unit; 
         FIG.  6    shows another variant of a hydraulic control unit; and 
         FIG.  7    shows another variant of a hydraulic control unit. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    schematically shows a hydraulic fluid reservoir  1  in a filled/charged condition. The hydraulic fluid reservoir  1  is formed by a cylindrical bore  2  in a body  3  of a hydraulic control unit  4 . A piston  5  is movably and slidingly accommodated in the bore  2 . The bore is closed toward one side and open toward the opposite side. An end cap  6  is sealingly mounted at the open side. 
     The hydraulic fluid reservoir  1  includes a hydraulic fluid reservoir space  7  and an air space  8 , The hydraulic fluid reservoir space  7  and the air space  8  are separated from each other by the piston  5 . The piston  5  has a first piston surface  9  and a second piston surface  10 . The first piston surface  9  delimits the hydraulic fluid reservoir space  7  at least in some areas. The second piston surface  10  delimits the air space  8  at least in some areas. The hydraulic fluid reservoir space  7  is delimited by the first piston surface  9  of the piston  7  and the bore  2 . The air space  8  is delimited by the second piston surface  9  of the piston  7 , the bore  2 , and the end cap  6 . Moreover, the piston  5  is designed in such a way that a displacement of the piston  5  in a first direction  11  enlarges the hydraulic fluid reservoir space  7  and reduces the air space  8  and a displacement of the piston  5  in a second direction  12  reduces the hydraulic fluid reservoir space  7  and enlarges the air chamber  8 . 
     The hydraulic fluid reservoir  1  can include at least one hydraulic fluid outlet  13  see  FIG.  2   ). The at least one hydraulic fluid outlet  13  is assigned to the hydraulic fluid reservoir space and opens into the hydraulic fluid reservoir space. Via the hydraulic fluid outlet  13 , a hydraulic pressure generator (not represented) can suction hydraulic fluid out of the hydraulic fluid reservoir space  7 , as the result of which the piston  5  moves, for example is displaced in the second direction  12 . 
     The hydraulic fluid reservoir  1  can include at least one ventilation inlet  14 , in particular for ventilating the air space  8 . The ventilation inlet  14  is assigned to the air space  8  and opens into the air space  8 . The ventilation inlet  14  is connectable and/or connected via the venting duct  15  to an interior space of the hydraulic control unit  4 . The hydraulic fluid reservoir  1  is designed in such a way that air can flow out of the interior space of the hydraulic control unit  4  into the air space  8  of the hydraulic fluid reservoir  1 . Due to a displacement of the piston  5  of the hydraulic fluid reservoir  1  in the second direction  12 , air can flow and/or be suctioned out of the interior space of the hydraulic control unit  4  via the venting duct  15  into the air space  8  of the hydraulic fluid reservoir  1 . The interior space of the hydraulic control unit  4  can be an interior space of a housing of an electric control unit of the hydraulic control unit  4  and/or an interior space of a housing of a motor of the hydraulic control unit  4 . 
     The hydraulic fluid reservoir  1  also includes a sealing element  16 , via which the piston  5  of the hydraulic fluid reservoir  1  is sealed with respect to the bore  2 . The sealing element  16  is designed for the purpose of fluidically sealing the hydraulic fluid reservoir space  7  and the air space  8  with respect to each other. The piston  5  has a circumferential groove, in which the sealing element  16  is effectively arranged. The sealing element  16  includes a circumferential sealing lip  18 , which protrudes over the circumferential surface of the piston, at least in some areas, and sealingly rests against the inner wall of the bore  2 . 
     In  FIG.  1   , the piston  5  is in its rearward position, such as the hydraulic fluid reservoir position and/or end position, and so the hydraulic fluid reservoir space  7  is filled with hydraulic fluid. The hydraulic fluid reservoir  1  is in a condition in which the hydraulic fluid reservoir  1  is filled and/or charged with hydraulic fluid. In the filled and/or charged condition, the piston  5  rests against the end cap  6  and closes the ventilation outlet  14 , as the result of which the air space  8  is separated from the interior space of the hydraulic control unit. 
       FIG.  2    schematically shows the hydraulic fluid reservoir  1  according to  FIG.  1    in an emptied/discharged condition. 
     The piston  5  is designed in such a way that the piston  5  connects the air space  8  to the interior space of the hydraulic control unit due to an axial movement of the piston  5  in the second direction  12  to empty and/or discharge the hydraulic fluid present in the hydraulic fluid reservoir space  7 . Due to the movement of the piston  5  in the second direction  12 , the piston  5  is positioned in such a way that the ventilation outlet  14  is opened and air can flow out of the interior space of the hydraulic control unit  4  into the air space  8 . As a result, the underpressure in the air space  8  caused by the piston movement can be compensated for, but at least reduced. 
     Due to the increase in volume achieved as a result, the underpressure in the air space  8  does not become so great upon actuation of the piston  5  that the hydraulic pressure generator could no longer approximately completely convey the hydraulic fluid out of the hydraulic fluid reservoir space  7 . 
     For the rest, reference is also made to  FIG.  1    and the associated description. 
       FIG.  3    schematically shows an exemplary variant of a hydraulic control unit  19  that includes an electric control unit  20  and an electric motor  21 . 
     The electric control unit  20  includes a housing  22 , which defines an interior space  23 . The electric motor  21  is located in a motor housing  24 , which defines an interior space  25 . Both the interior space  23  of the housing  22  of the electric control unit  20  and the interior space  25  of the motor housing  24  are separated from the surroundings, from the atmosphere surrounding the hydraulic control unit  19 , and are dosed off from, such as hermetically sealed with respect to, the surroundings. 
     The hydraulic control unit  19  includes a supply duct  26  for the electrical supply and/or control of the electric motor  21 . The supply duct  26  connects the interior space  23  of the housing  22  of the electric control unit  20  to the interior space  25  of the motor housing  24 . Supply lines  27 , such as power lines and/or control lines, extend through the supply duct  26 . A gap  28 , such as an annular gap, is formed between the supply lines  27  and the supply duct. 
     The hydraulic control unit  19  also includes the hydraulic fluid reservoir  1  according to  FIGS.  1  and  2   , wherein the venting duct  15 , on the one hand, opens into the air space  8  and, on the other hand, opens into the supply duct  26  and the gap  28 . As a result, the air space  8  can be connected to the interior space  23  of the housing  22  of the electric control unit  20  and to the interior space  25  of the motor housing  24 . Consequently, a direct path is established into the housing  22  of the electric control unit  20  and into the motor housing  24 . The arrows represented in  FIG.  3    illustrate a possible air flow between the air space  8  of the hydraulic fluid reservoir  1  and the interior space  23  of the housing  22  of the electric control unit  20  and the interior space  25  of the motor housing  24 . 
     For the rest, reference is also made to  FIGS.  1  and  2    and the associated description. 
       FIG.  4    schematically shows another exemplary variant of a hydraulic control unit  29 . The hydraulic control unit  29  corresponds to the hydraulic control unit  19  according to  FIG.  3   . 
     In contrast, the hydraulic control unit  29  of the present exemplary arrangement includes a sealing element  30 , which is effectively arranged in a first path section  31  of the supply duct  26 . The first path section  31  extends between the mouth  41  of the venting duct  15  and the interior space  23  of the housing  22  of the electric control unit  20 . The sealing element  31  is designed to seal the air space  8  and the interior space  23  of the housing  22  of the electric control unit  20  with respect to each other. Therefore, air can flow only between the air space  8  of the hydraulic fluid reservoir  1  and the interior space  25  of the motor housing  24 . 
     The arrows represented in  FIG.  4    illustrate a possible air flow between the air space  8  of the hydraulic fluid reservoir  1  and the interior space  25  of the motor housing  24 . 
     For the rest, reference is also made, in particular, to  FIGS.  1  through  3    and the associated description. 
       FIG.  5    schematically shows another variant of a hydraulic control unit  32 . The hydraulic control unit  32  essentially corresponds to the hydraulic control unit  19  according to  FIG.  3   . 
     In contrast, the hydraulic control unit  32  of the present exemplary arrangement includes a sealing element  33 , which is effectively arranged in a second path section  34  of the supply duct  26 . The second path section  34  extends between the mouth  41  of the venting duct  15  and the interior space  25  of the housing  24  of the electric motor  21 . The sealing element  33  is designed to seal the air space  8  and the interior space  25  of the housing  24  of the electric control unit  21  with respect to each other. Therefore, air can flow only between the air space  8  of the hydraulic fluid reservoir  1  and the interior space  23  of the electric control unit  20 . 
     The arrows represented in  FIG.  5    illustrate a possible air flow between the air space  8  of the hydraulic fluid reservoir  1  and the interior space  23  of the housing  22  of the electric control unit  20 . 
     For the rest, reference is also made to  FIGS.  1  through  4    and the associated description. 
       FIG.  6    schematically shows another variant of a hydraulic control unit  36  that includes a first variant of an approach to a bore hole. The hydraulic control unit  36  can be designed essentially similar to one of the hydraulic control units described with respect to  FIGS.  1  through  5   . 
     The hydraulic control unit  36  includes two hydraulic fluid reservoirs  1  according to  FIGS.  1  and  2   . The two hydraulic fluid reservoirs  1  are connected to the venting duct  15  via their ventilation inlets  14 . The venting duct  15  is designed to be essentially T-shaped and opens into the gap  28  of the supply duct  26 . Moreover, the venting duct  15  connects the air ducts  8  of the two hydraulic fluid reservoirs  1  to each other. 
     Certain sections of the venting duct  15  for example sections that do not open directly into the gap  28  of the supply duct  26  or establish an opening to the outer surroundings, are closed with blocking elements  37 , such as balls  37 . As a result, it can be ensured that an access to the outer surroundings of the hydraulic control unit  36  is not present. 
     The arrows represented in  FIG.  6    illustrate a possible air flow between the air chambers  8  of the two hydraulic fluid reservoirs  1  and the interior space  23  of the housing  22  of the electric control unit  20  and/or the interior space  25  of the motor housing  24  of the electric motor  21 . 
     For the rest, reference is also made to  FIGS.  1  through  5    and the associated description. 
       FIG.  7    schematically shows another exemplary variant of a hydraulic control unit  38  that includes a second variant of an approach to a bore hole. The hydraulic control unit  38  can be designed similar to one of the hydraulic control units described with respect to  FIGS.  1  through  6   . For example, the hydraulic control unit  38  corresponds to the hydraulic control unit  36  according to  FIG.  6   , but has one other bore hole. 
     As shown in  FIG.  7   , the hydraulic control unit  38  includes two oblique, duct bores, such as venting ducts  15 . The two duct bores  15  meet at an LPA bore chamfer  39  and/or open into the LPA bore chamfer  39 . The two duct bores  15  are connected to another duct bore  40 , which opens into the gap  28  of the supply duct  26 . 
     The arrows represented in  FIG.  7    illustrate a possible air flow between the air chambers  8  of the two hydraulic fluid reservoirs  1  and the interior space  23  of the housing  22  of the electric control unit  20  and/or the interior space  25  of the motor housing  24  of the electric motor  21 . 
     For the rest, reference is also made to  FIGS.  1  through  6    and the associated description. 
     Optional features of the disclosure are designated with “can.” Consequently, there are also refinements and/or exemplary arrangements of the disclosure that additionally or alternatively have the particular feature or the particular features. 
     Isolated features can also be extracted from the combinations of features disclosed in the present case as necessary, and, while resolving a structural and/or functional correlation possibly existing between the features, used in combination with other features to demarcate the subject matter of the claim,