Abstract:
A hydraulic vehicle brake has a piston which acts upon a friction element and is displaceable by a rotationally drivable spindle/nut arrangement into an actuating position. A spindle of the spindle/nut arrangement is secured against rotation and movable by the spindle nut either into abutment against the piston or away from the piston. The spindle nut comprises a first part, which at least close to one end thereof is configured for screw-type engagement with the spindle, and a second part, configured for rotationally driving the first part and connected to the first part by a rotationally fixed connection. The first part at an other end thereof is provided with a support surface for the rotatable, axial mounting of the spindle/nut arrangement and the second part at the other end extends into the first part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage of International Application No. PCT/EP2011/000883 filed Feb. 23, 2011, the disclosures of which are incorporated herein by reference in entirety, and which claimed priority to German Patent Application No. DE 10 2010 008 927.3 filed Feb. 23, 2010, the disclosures of which are incorporated herein by reference in entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a vehicle brake, having a housing and a brake piston arranged therein, which piston acts upon a friction element and is displaceable by means of a rotationally drivable spindle/nut arrangement arranged coaxially with the central axis of the brake piston into an actuating position, in which the brake piston presses the friction element against a rotor of the vehicle brake, wherein the spindle is secured against rotation and is moved by means of a rotation of the spindle nut in a translatory manner along the central axis either into abutment against the brake piston or away from the brake piston in dependence upon the direction of rotation. A similar, also hydraulically actuable vehicle brake is known from European Patent EP 0 996 560 B1. 
         [0003]    Vehicle brakes of the described type may be used as a service brake and also as a hand brake—also known as a parking brake—because by means of the spindle/nut arrangement the brake piston may be displaced mechanically into a position, in which it presses a friction lining of the brake against a brake disk or brake drum. The rotary driving of the spindle/nut arrangement that is required for this purpose is effected as a rule in a motorized manner, for example by means of an electric motor. If the vehicle brake is additionally also hydraulically actuable, then service braking operations are implemented conventionally by applying hydraulic pressure, which is supplied to the vehicle brake from an associated hydraulic vehicle brake system. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    The underlying feature of the invention is to achieve an even more compact design of such a vehicle brake and moreover improve the force path within the vehicle brake. The improved vehicle brake is moreover to be adaptable as easily as possible to various types of rotary drive of the spindle/nut arrangement. 
         [0005]    Proceeding from the initially described, generic vehicle brake this feature is achieved according to the invention in that the spindle nut comprises a first part, which at least close to its one end is configured for screw-type engagement with the spindle, and a second part, which is configured for rotationally driving the first part and is connected to the first part by a rotationally fixed connection, wherein the first part at its other end remote from the one end is provided with a support surface for the rotatable, axial mounting of the spindle/nut arrangement and the second part at the other end extends into the first part. 
         [0006]    According to the invention the spindle nut accordingly comprises two parts, which are manufactured separately and then connected in a rotationally fixed manner to one another. For example, these two parts may be manufactured economically by forming as cold extruded parts, because machining of the spindle nut is necessary only at the support surface used for mounting and at the thread that interacts with the spindle. Because the second part extends into the first part of the spindle nut, the overall length of the spindle nut may be kept short. By means of the support surface on the first part of the spindle nut an immobilizing force is transmitted from the brake piston, without major changes in diameter, to the spindle and the spindle nut and is introduced by the latter, again without any significant change in diameter, into the housing of the vehicle brake. Finally, by virtue of the two-part construction of the spindle nut it is possible to adapt the entire mechanism to different rotary drives by modifying only the second part. 
         [0007]    In preferred embodiments of the vehicle brake according to the invention the rotationally fixed connection is a polygonal connection, a compression connection or a toothed connection. It is also possible to use a combination of a polygonal connection or toothed connection and a compression connection. Further types of rotationally fixed connection are possible. 
         [0008]    In order to keep the overall length of the spindle/nut arrangement as short as possible, in preferred embodiments the second part of the spindle nut at its side facing the first part is of a hollow-cylindrical configuration so that the spindle may extend, depending on the actuating position, into the hollow space thus formed. At its side remote from the first part the second part is preferably provided with a connection for an external rotary drive. This connection may for example take the form of a hexagon socket or a multi-grooved profile. 
         [0009]    In order to be able to accommodate the spindle/nut arrangement in a space-saving manner, the brake piston of the vehicle brake is preferably open at one end and of a hollow-cylindrical configuration. In order to secure the spindle against torsion, in preferred embodiments of the vehicle brake according to the invention the spindle has a mushroom-shaped spindle head that is guided axially in a twistproof manner in the brake piston. A twistproof guidance of the spindle head in the hollow-cylindrical brake piston is achievable in various ways. In one embodiment the spindle head at its circumference is provided with a plurality of radial projections, which engage into axial grooves that are formed in an inner circumferential surface of the hollow-cylindrical brake piston. A single radial projection on the spindle head that engages into a corresponding axial groove of the brake piston is however also adequate as an anti-rotation device. Equally the brake piston may be provided with an inwardly protruding axial projection that engages into a groove on the spindle head. An anti-rotation device for the spindle is moreover achievable also by means of a spindle head, the circumference of which is not circular and which is guided in a correspondingly shaped hollow-cylindrical recess of the brake piston. Further possibilities are conceivable. 
         [0010]    If the spindle/nut arrangement has a spindle head with a diameter that is greater than the diameter of the spindle nut, then in preferred embodiments the spindle head at its underside facing the spindle is provided with an indentation extending in a circumferential direction, which has a front end face serving as a stop for a projection that is formed at the front end of the spindle nut facing the spindle head. In such embodiments the front stop face on the one hand serves as a reference position, in which the spindle is fully retracted, and on the other hand prevents a “driving home” of the spindle head on the spindle nut, with the undesirable consequence of extremely high release forces. Preferably the indentation in the underside of the spindle head is fashioned in such a way that its depth increases continuously in the direction of and up to its front end face. In a corresponding manner the projection at the front end of the spindle nut is preferably of a complementary design to the shape of the indentation, i.e. has for example the shape of a continuously ascending ramp with for example a semicircular cross section, which ramp terminates in a stop face that corresponds to the cross-sectional shape of the ramp and is intended to interact with the front end face of the indentation. 
         [0011]    For space-saving and low-friction mounting of the spindle/nut arrangement, in preferred embodiments the support surface is supported on an annular plain- or needle bearing, which is in turn supported against the housing of the vehicle brake and through which the second part of the spindle nut projects. In such embodiments the support surface accordingly surrounds the second part of the spindle nut in an annular manner, thereby on the one hand creating a broad support base and on the other hand achieving a very advantageous—because substantially deflection-free—course of the support force from the spindle head through the first part of the spindle nut into the brake housing. 
         [0012]    The vehicle brake according to the invention may be actuable exclusively by means of the spindle/nut arrangement, i.e. service braking operations and/or a parking brake function are achieved by a change of length of the spindle/nut arrangement, but the brake piston or a corresponding component of the brake may be displaced into the actuating position also by means of hydraulic pressure, which may be introduced into a hydraulic chamber that interacts with the brake piston or the corresponding component. If hydraulic actuation is provided, this is used as a rule for the service braking operations, while the spindle/nut arrangement is used only in a stationary state of the vehicle to realize a parking brake function. In an emergency situation, say in the event of failure of the hydraulic actuation, the spindle/nut arrangement may be used also for service braking operations. The vehicle brake according to the invention may take the form of a disk brake or a drum brake. 
         [0013]    In all embodiments of the vehicle brake according to the invention the spindle/nut arrangement may be of a self-locking design, usually by virtue of suitable selection of the lead of a thread that connects the nut to the spindle. A self-locking spindle/nut arrangement makes it possible to dispense with a separate arresting device once the vehicle brake, in order to realize the parking brake function, has been locked by rotation of the spindle nut. 
         [0014]    Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates a vehicle brake according to the invention in the form of a disk brake, which is also hydraulically actuable, in cross section, 
           [0016]      FIG. 2  illustrates a brake piston of the brake of  FIG. 1  with a spindle/nut arrangement accommodated therein, in longitudinal section and in an enlarged view, 
           [0017]      FIG. 3  illustrates the spindle/nut arrangement of  FIG. 2  in an exploded, three-dimensional view, 
           [0018]      FIG. 4  illustrates the spindle/nut arrangement of  FIG. 3  together with the brake piston and an axial bearing in an exploded, three-dimensional view, 
           [0019]      FIG. 5  illustrates the arrangement of  FIG. 4  in an assembled state, and 
           [0020]      FIG. 6  illustrates a spindle/nut arrangement according to a modified embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The vehicle brake reproduced in  FIG. 1  and generally denoted by  10  is configured here as a floating-caliper disk brake, which in a known manner comprises a housing  12 , on which is displaceably mounted a floating caliper  14  that straddles a brake disk, which is not represented here. 
         [0022]    Situated in the housing  12  is a hydraulic chamber  16 , in which a brake piston  17  is accommodated sealingly and displaceably along its longitudinal central axis A. For supplying the hydraulic chamber  16  with hydraulic fluid there is provided on the outside of the vehicle brake  10  a connection  20 , which is in communication with a brake pressure generating unit that is not represented here, for example a brake-booster/master-cylinder unit that is actuable via a brake pedal. Upon actuation of the brake pressure generating unit the hydraulic fluid in the hydraulic chamber  16  is pressurized, so that the brake piston  17  is displaced to the left along the axis A in order to move friction linings  18 ,  19  into frictional engagement with the non-represented brake disk. When actuation of the brake pressure generating unit is terminated, hydraulic fluid may flow out of the hydraulic chamber  16  back in the direction of the brake pressure generating unit, so that the brake piston  17  is displaced back along the axis A in order to move the friction linings  18 ,  19  out of engagement with the brake disk. A radially circumferential sealing element denoted by  22 , which seals off the brake piston  17  in the hydraulic chamber  16 , assists the resetting of the brake piston  17  in that in accordance with the “rollback” principle it exerts a resilient resetting force on the brake piston  17 . The operation of the disk brake  10  just described and occasioned by a hydraulic actuation, as well as the further mechanical construction of the disk brake  10  is well-known to experts in this field and therefore requires no further explanation. 
         [0023]    So that the illustrated vehicle brake  10  may not only fulfill the previously described function of a hydraulic service brake but may also be used as a parking- or hand brake, a spindle/nut arrangement generally denoted by  24  is provided, which comprises a spindle  26  arranged coaxially with the axis A and having an external thread  28  as well as a substantially sleeve-shaped spindle nut  30 , which is provided with an internal thread  32  that matches the external thread  28  (see also  FIG. 2 ). 
         [0024]    The construction of the spindle/nut arrangement  24  emerges more clearly from  FIG. 3 . As is evident from this figure, the spindle nut  30  is of a two-part construction and comprises a sleeve-shaped, first part  34 , of which the, in the figures left, end portion  36  is provided with the internal thread  32 . The outside diameter of the first part  34 , viewed from the left end portion  36 , increases slightly in the illustrated manner in the direction of an, in the figures right, end portion  38 , wherein there is formed on the right end, i.e. on the end remote from the end portion  36 , a radial support surface  40 , by which the spindle/nut arrangement  24  is supported via an axial bearing configured here as needle bearing  42  rotatably against the housing  12  of the vehicle brake  10  (see  FIG. 1 ). Extending from the support surface  40  into the right end portion  38  of the first part  34  is a recess  44 , the cross section of which in the present case is polygonal. The recess  44  serves to form-fittingly receive, in a circumferential direction, a second part  46  of the spindle nut  30  that for this purpose is provided with a polygonal, internally hollow stud  48  formed in a complementary manner to the recess  44 . In the state of connection to the first part  34 , the longitudinal central axis A of the brake piston  17  is also the longitudinal central axis of the spindle  26  and of the first part  34  and the second part  46  of the spindle nut  30 . Integrally connected to the polygonal stud  48  is a further stud  50  with a circular cross section. A connection  52  for an external rotary drive is formed in this stud  50  and in the present case takes the form of an internal multi-grooved profile. By means of the rotary connection  52  a rotary drive, which is not represented here, may rotate the spindle nut  30  in both directions of rotation in order to screw the spindle  26  out of and back into the spindle nut  30  and hence change the effective length of the spindle/nut arrangement  24 . This only works however if the spindle  26  is secured against co-rotation. In the illustrated embodiment this is achieved by the spindle  26  having a mushroom-shaped spindle head  54 , which at its outer circumference is provided with a plurality of radial projections  56  that engage into axial grooves  58  provided in an inner circumferential surface of the hollow-cylindrical brake piston  17 . As is evident in particular from  FIG. 2  and  FIG. 4 , as a result of the interaction of the radial projections  56  with the axial grooves  58  the spindle head  54  is guided axially in a twistproof manner in the brake piston  17 . 
         [0025]    The spindle/nut arrangement  24  is accordingly used to convert a rotary motion of the spindle nut  30  to a translatory movement of the spindle  26  in order in this manner to move the brake piston  17  towards the non-illustrated brake disk and press the friction linings  18 ,  19  against the brake disk (parking brake function). As may be seen in particular from  FIG. 2  and  FIG. 5 , which both reproduce the fully retracted state of the spindle/nut arrangement  24 , i.e. the state of a released parking brake, the entire arrangement owing to its accommodation in the hollow part of the brake piston  17  and owing to the internally hollow construction of the first part  34  and the second part  46  of the spindle nut  30  is extremely compact and in this state projects only slightly from the brake piston  17 . 
         [0026]    For rotationally driving the spindle nut  30  it is possible to use for example an electric motor (not represented), which is capable of transmitting its rotary motion to the spindle nut  30  by means of an output shaft formed in a complementary manner to the rotary connection  52 . The spindle/nut arrangement  24  is of a self-locking design so that its change of length achieved by means of rotation of the spindle nut  30  is maintained in each case after the rotary drive has stopped. A separate arresting device is therefore not required. 
         [0027]    When the spindle  26  is screwed out of the spindle nut  30  as a result of rotation thereof, the upper side of the spindle head  54  comes into contact with the underside of a head  60  of the brake piston  17 . To achieve the best possible abutment the upper side of the spindle head  54  and the underside of the piston head  60  are formed in a complementary manner in terms of their shape, so that the spindle head  54  is applied over a large area and hence in a material-sparing manner against the brake piston  17 , thereby allowing good transmission of high locking forces. 
         [0028]    In order to release a vehicle brake  10  that is locked as a result of increasing the length of the spindle/nut arrangement  24 , the spindle nut  30  has to be rotated in the opposite direction. The spindle  34  is then screwed back into the spindle nut  30  and the spindle head  54  detaches from the underside of the piston head  60 , with the result that there is no longer any locking force transmitted to the brake piston  17 . In order during this release operation to prevent the spindle head  54  from being driven home too powerfully on the spindle nut  30 , a situation which might occur in the fully retracted state of the spindle  26 , and in order moreover to create a reference position corresponding to a fully retracted state of the spindle/nut arrangement  24 , the spindle head  54  at its underside  62  facing the spindle nut  30  is provided with an indentation  64  extending in circumferential direction, which may be seen clearly in  FIG. 3 . The indentation  64  begins quite flat and increases in depth continuously in circumferential direction up to a front end face  66 , which forms the end of the indentation  64  and serves as a stop, as will be explained below. 
         [0029]    For interacting with the indentation  64  in the underside  62  of the spindle head  54  there is formed on the front end of the spindle nut  30  facing the spindle head  54  a projection  68 , which is formed in a complementary manner to the indentation  64 . The projection  68  is accordingly ramp-shaped with a semicircular cross section, the height of which increases continuously from its start to its end. The projection  68  terminates in a stop face  70  (see  FIG. 3 ), which upon reaching the described reference position abuts against the front end face  66  of the indentation  64  and prevents further retraction of the spindle  26 , without the spindle  26  being able to be driven home in the spindle nut  30 . 
         [0030]    In an advantageous manner a portion  72  of the first stud  48  that is adjacent to the further stud  50  of the second part  46  is designed with a circular cross section and serves as a centering surface for the needle bearing  42 . 
         [0031]    As already described, during operation of the vehicle brake  10  the hydraulic chamber  16  is filled with hydraulic fluid, the pressure of which ensures that the brake piston  17  is displaced in order to press the friction linings  18 ,  19  against the non-illustrated brake disk. To enable the entire cross-sectional area of the brake piston  17  to be loaded with hydraulic pressure, in the previously described embodiment of the spindle/nut arrangement  24  there is provided in the first part  34  of the spindle nut  30  a plurality of radial bores  74  (see  FIG. 1  and  FIG. 3 ), through which the interior of the spindle/nut arrangement  24  may be vented and filled with hydraulic fluid. 
         [0032]      FIG. 6  shows a longitudinal section through a modified embodiment of a spindle/nut arrangement  24 ′, in which the first part  34  of the spindle nut  30  has no such bores  74 . Instead, the second part  46  of the spindle nut  30  at its outer circumferential surface is provided with a substantially axially running channel  76 , which extends over the entire length of the polygonal stud  48  and hence reaches from an internal hollow space  78  of the spindle/nut arrangement  24 ′ to a point axially under the radially inner circumferential surface of the needle bearing  42 . In this manner by means of the axial bearing in the form of needle bearing  42  a fluid-conveying connection is created between the inner hollow space  78  and the hydraulic chamber  16 . Such an axial channel  76  is more economical to manufacture than the radial bores  74 . 
         [0033]    If the rotationally fixed connection between the first part  34  and the second part  46  of the spindle nut  30  is designed, not as described above as a polygonal connection, but for example as a toothed connection, say in the form of a multi-grooved profile, then the axial channel  76  may also be easily formed by a tooth gap of the toothed connection. 
         [0034]    The axial support of the spindle/nut arrangement  24 ′ is designed exactly the same as in the spindle/nut arrangement  24 , i.e. via the support surface  40  of the first part  34  and via a further support surface  80  disposed radially inside of and flush with the surface  40  against the second part  46  of the spindle nut  30 . 
         [0035]    In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.