Abstract:
A hydraulic unit for an electronically controllable brake system of a vehicle includes a housing block with mounting faces for instance for an electric motor and an electronic control unit; a plurality of connections for hydraulically contacting the block; and installation chambers, for pump elements, valves, and damping devices. These damping devices are connected hydraulically downstream to the pump elements, in order to damp operation-caused pressure pulsations and noises. Installation chambers ( 18   i-k ) for the damping devices and the installation chambers ( 18   a-h ) of the valves extend to a common mounting face of the housing block intended for mounting the electronic control unit. The damping devices protrude past this mounting face.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved hydraulic unit for an electronically controllable brake system of a vehicle. 
   2. Description of the Prior Art 
   A housing block of a hydraulic unit of the type with which this invention is concerned is already known, for instance from German Patent Disclosure DE 198 05 843 A1. This housing block has a plurality of mounting faces, to which an electric motor, for instance, for driving pump elements disposed in the housing block, or an electronic control unit for triggering magnet valves provided in the housing block, can be secured. The housing block is furthermore provided with connections for supplying it with pressure fluid and, in addition to the installation chambers for the aforementioned pump drive, the pump elements and the magnet valves, it has still further installation chambers for damping devices. These damping devices are disposed downstream of the pump elements in terms of circuitry, for damping pressure pulsations and the operating noises tripped by them. 
   In the known hydraulic unit, the installation chambers of the damping devices are fully integrated with the housing block and are furthermore disposed perpendicular to the installation chambers of the valves. This limits the possible volume of the damping devices and/or means that the hydraulic unit requires a relatively large installation space. Moreover, the pressure fluid conduits in the hydraulic unit that are required for hydraulically connecting the damping devices can be attained only with great effort in terms of production, and because of their length they further contribute to increasing the structural size of the hydraulic unit. 
   In another hydraulic unit of this generic type, disclosed in DE 199 58 194 A1, the damping devices coaxially adjoin the pump elements and are connected to the pressure buildup valves via pressure fluid conduits that extend radially or tangentially. This mode of construction has the same disadvantages described above. Especially the maximum possible volume of the damping devices is severely restricted, since the pump elements already occupy a substantial proportion of the possible length of the housing block in the direction of the longitudinal axes of the pump elements. 
   OBJECT AND SUMMARY OF THE INVENTION 
   It is accordingly the object of the present invention to improve the known hydraulic units in terms of their operating noise, their structural volume, and the effort and expense of metal-cutting, and thus to improve both their production costs and their adaptability to various types of vehicle. 
   Compared to the hydraulic units known from the prior art cited, a hydraulic unit according to the invention has the advantage that, with unaltered compact dimensions, it includes damping devices for damping the pressure pulsations generated by the pump elements and is especially simple to produce technically. The pressure fluid conduits for hydraulically contacting the damping devices are relatively short and as a result entail little expense for metal-cutting. The idle volume, the hydraulic rigidity, and hence the controllability of the brake system are thus improved. Moreover, the volume of the damping device can be easily adapted to a given specific application, since only a fractional volume is accommodated in the housing block of the hydraulic unit, while a second fractional volume, which is easily varied in size, extends outside the housing block. It is especially advantageous if the damping device protrudes with its second fractional volume into the interior of a mountable control unit, since as a result the emission of sound caused by the pressure pulsations is additionally damped. 
   Further advantages or advantageous refinements of the invention are disclosed. According to one feature the inlet is especially reliably sealed off from the outlet of the damping device, since the sealing point is formed by the outer contour of the pump elements in cooperation with the wall of the installation chamber of the pump elements. The sealing point is created simultaneously with the assembly of the pump elements and does not require any separate sealing elements. Hence the sealing point is not subjected to wear associated with the operating time, and at the same time costs for keeping required parts on hand and for assembly are reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawings, in which: 
       FIG. 1  shows the subject of the invention in a perspective, inverted view of a housing block of an electronic brake system; 
       FIG. 2  is an enlarged detail II of  FIG. 1 ; and 
       FIG. 3  is a longitudinal section through  FIG. 2 , with the pump element installed and with the damping device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The housing block  10  of a hydraulic unit  11 , shown as an example in  FIG. 1 , is intended for use in an anti-lock brake system with VDC (vehicle dynamics control). It comprises a parallelepiped block of nonferrous material, for instance an aluminum alloy, preferably produced by extrusion and then machined by metal-cutting. The housing block  10  has a rectangular upper mounting face  12 , opposite it a lower mounting face  14 , and a total of four circumferential faces  16   a-d , which are oriented perpendicular to the mounting faces  12 ,  14 . The upper mounting face  12  is intended for anchoring an electronic control unit, not shown, while an electric motor can be flanged to the lower mounting face  14 . From the upper mounting face  12 , installation chambers  18  embodied in cup-shaped fashion extend into the housing block  10 . The installation chambers  18  essentially serve to receive magnet valves, but the magnet valves have not been shown in  FIG. 1  for the sake of simplicity. A total of fourteen installation chambers  18   a - 18   o  begin at the upper mounting face  12  and are arranged in a total of four rows A-D parallel to one another. The first row A, located at the outer right in  FIG. 1 , of installation chambers  18   a-d  is located next to four installation chambers  20   a-d  on the circumferential side  16   a  of the housing block  10  and these latter installation chambers form the connections for the brake lines that lead to the various wheel brake cylinders of a vehicle. The installation chambers  18   a-d  for so-called pressure buildup valves are disposed in the first row A, while pressure reduction valves are placed in the adjacent second row B with the installation chambers  18   e-h . The pressure in the wheel brake cylinders can be modulated with the pressure buildup valves and pressure reduction valves. To that end, these valves are embodied as 2/2-way switching valves known per se, which can be switched over electrically by the electronic control unit from an open position to a closed position and vice versa. The triggering is done as a function of measured variables of various sensors, which belong to the brake system and detect for instance the wheel slip at one of the vehicle wheels and/or the brake pressure at one of the wheel brake cylinders and carry it on to the control unit. 
   Damping devices  22 , whose significance will be explained hereinafter, are built into the outermost installation chambers  18   i ,  18   k  of the third row C. Below this third row C, that is, beginning at the lower mounting face  14  of the housing block  10 , the installation chambers  24   a  and  b , among others, for two coaxially facing pump elements  50  (see  FIG. 3 ) extend transversely to the installation chambers  18   i-m  of this third row C. Between the two last-mentioned pump elements, an installation chamber  26  is embodied, beginning at the lower mounting face  14 . This installation chamber  26  serves to receive a rotatably supported eccentric element, which can be set into rotary motion by the mountable electric motor and imposes a reciprocating motion on the pump elements. Because of this reciprocating motion, the pump elements aspirate brake fluid through a pump inlet and pump the pressure fluid to a pump outlet, thereby building up pressure. The pump elements  50  are each single-cylinder piston pumps of a type of construction known per se. In principle, unwanted pressure pulsations, which are perceptible in the surroundings of the hydraulic unit  11  as operating noises, can be created in the pumped flow of pressure fluid. Damping of the operating noises is possible by smoothing the pressure pulsations, for which purpose one damping device  22  each is connected hydraulically downstream to the pump elements. 
   In the exemplary embodiment here, the damping devices  22  shown are oriented axially parallel to the installation chambers  18   a-h  of the magnet valves and extend in the direction of the upper mounting face  12  for the control unit. Each damping device  22  comprises a first part  22   a , which is integrated with the housing block, and a second part  22   b , which is located outside the housing block  10 ; the second part  22   b  protrudes into the interior of the control unit to be mounted. The second part  22   b  is defined by a cup-shaped element  28 , which is inserted by its opening into the installation chamber of the first part  22   a  and thus closes the first part off from the control unit. To that end, the cup-shaped element  28  is preferably anchored by positive engagement to the housing block  10 , for instance by plastic deformation of material comprising the housing block  10  during the process of its being pressed into a circumferential recess provided on the element  28  (a process known as a self-clinching connection). The volume of the damping device  22  can easily be varied for a specific vehicle simply by changing the dimensions of the cup-shaped element  28 . 
   The damping device  22  shown is contacted hydraulically via an inlet  30  and an outlet  32 ; both connections extend from the bottom of the installation chamber  18   i ,  18   k  and each discharges in a straight line into the installation chamber  24  of the pump element. 
   Two so-called high-pressure switching valves can be built in between the two damping devices  22  in the third row C; together with switchover valves in the fourth row D of installation chambers  18   n  and  o , they hydraulically connect a master cylinder, which can be connected to the housing block  10 , to the wheel brake cylinders and control a communication between the inlet side of the pump elements and the master cylinder. For that purpose, both pairs of valves are embodied as triggerable 2/2-way switching valves; in their nontriggered basic position, the switchover valves establish a pressure fluid communication between the master cylinder and the pressure buildup valve, while in the switching position they disconnect it, and conversely the high-pressure switching valves in their basic position block the communication of pressure fluid from the master cylinder to the inlet side of the pump elements and enable it in the triggered state. 
   Opposite the connections of the wheel brake cylinders, the installation chambers  34  of low-pressure reservoirs adjoin the fourth row D of magnet valves. These installation chambers extend transversely to the rows A-D of valves and are open toward the circumferential face  16   c  of the housing block  10  and communicate hydraulically with the inlet of the pump elements via pressure fluid conduits. These low-pressure reservoirs serve to supply the pump elements with brake fluid. 
   With the exception of a single pressure fluid conduit  36 , visible in  FIG. 1 , the courses of the other pressure fluid conduits are of no significance for the present invention, and so a more-detailed explanation of them will be dispensed with. The single pressure fluid conduit  36  mentioned originates at the circumferential face  16   a  of the housing block  10  that has the installation chambers  20   a-d  of the wheel brake cylinder connections, and it connects the installation chamber  18  of one of the pressure buildup valves, disposed in the first row A of magnet valves, with the installation chamber  18   n  and  18   o  of a switchover valve. For that purpose, one short branch conduit  40 , ending in the interior of the housing block  10  and communicating with the pressure fluid conduit  36 , originates at each of the applicable installation chambers  18 ,  18   n  and  18   o . These branch conduits  40  are disposed such that in the installed state of the hydraulic unit  11  in the vehicle, they are each located at the highest points of the respective installation chambers  18 ,  18   n  and  18   o . This makes it possible for the hydraulic unit  11  to be completely vented when it is being serviced. The pressure fluid conduit  36  itself is shown in the form of a continuous, straight blind bore  42 , whose orifice is closed off in pressure fluid-tight fashion by a closure element, for instance in the form of a pressed-in ball (not shown). Moreover, the applicable blind bore  42  has a course in the housing block  10  such that it intersects or penetrates the installation chamber  24  of a pump element in the region of the outer end. In  FIG. 1 , this installation chamber  24  of the pump element is closed from the outside by a pressed-in lid  44 , making the pump element per se not visible in FIG.  1 . 
   For the sake of completeness, the two installation chambers  46   a  and  46   b  will also be noted; they open to the lower mounting face  14  of the housing block  10 . These installation chambers  46   a, b  form connections for a master cylinder of a brake system, on the precondition that this master cylinder is coupled with a brake fluid reservoir and is designed with two circuits. Accordingly, one connection or installation chamber  46   a  or  46   b  is assigned to each brake circuit. The lower mounting face  14  for the electric motor of the hydraulic unit  11  is recessed relative to the face on which the installation chambers  46   a  and  46   b  for the master cylinder are embodied. As a result, the lower mounting face  14  has an offset. 
     FIG. 2 , in an enlarged detail, shows the installation chamber  24 , closed off from the outside, of a pump element, as well as the first part  22   a  of the damping device  22 , which part is integrated with the housing block  10  and has an inlet  30  and an outlet  32 , and portions of the pressure fluid conduit  36  that connects the installation chambers  18  of the pressure buildup valves with the installation chamber  18   n  and  18   o  of a switchover valve and intersects the installation chamber  24  of the pump element. The inlet  30  and outlet  32  of the damping device  22  discharge essentially perpendicular into the installation chamber  24  of the pump element and are axially spaced apart from one another in the direction of the longitudinal axis of this installation chamber  24 . The inlet  30  is embodied as a cylindrical bore and the outlet  32  is embodied as a bore, with a conical widened portion  48  oriented toward the first part  22   a  of the damping device  22 . 
   For the sake of clear illustration of the relationships explained above,  FIG. 3  shows a detail of the housing block  10 , in this case in longitudinal section. In this longitudinal section, the installation chamber  18  of the damping device  22  originating at the upper mounting face  12  and having the inlet  30  and outlet  32  can be seen, along with the outlines of a pump element  50 , inserted into its assigned installation chamber  24 , and the lid  44  that closes off the installation chamber  24  of the pump element  50  from the outside. The element  28  that defines the second part  22   b  of the damping device  22  is shown as well. 
   The pump element  50  comprises a pump cylinder, fixed in the installation chamber  24 , and a piston that is guided movably in the pump cylinder. The internal structure of the pump element  50  is well known from the prior art and moreover is of no significance in comprehending the invention. It can be assumed that the outlet of the pump element  50  discharges into a hollow chamber  52 , which results from a circumferential shoulder  54  on the end of the pump element  50  between the wall of the installation chamber  24 , the pump cylinder, and the lid  44  that closes the installation chamber  24 . This hollow chamber  52  communicates with the first part  22   a  of the damping device  22  via the inlet  30 . The outlet  32  of the damping device  22 , which is axially spaced apart from the inlet  30 , has a conically widened portion  48 , built into it which is a suitably shaped throttle element comprising a throttle baffle and an upstream filter (none of these visible in the drawing). Following the throttle element, the outlet  32  discharges into an annular groove  56  on the circumference of the pump element  50 . The aforementioned pressure fluid conduit  36 , extending between the pressure buildup valve and a switchover valve, discharges into this annular groove  56 . 
   By means of a damping device  22  constructed in this way, hydraulically connected, and disposed on the housing block  10 , system-dictated pressure pulsations of the pump elements can be reliably smoothed out with the least possible structural size and at comparatively little engineering effort and expense. The fundamental prerequisite for this, however, is that there be no hydraulic short circuit, or in other words that the flow through the damping device  22  be assured, between the region at the outlet of the pump element  50  and the region downstream of the throttle element of the damping device  22 . 
   To avoid such a short circuit, the shoulder  54  on the end of the pump cylinder and the annular groove  56  together define an annular rib  58 , which protrudes from the pump cylinder and, when the pump element  50  is installed in final form, is located between the inlet  30  and the outlet  32  of the damping device  22 . Between this annular rib  58  and the wall of the installation chamber  24  there is a press-fit connection, so that the annular rib  58 , with further components, serves as a wear-free sealing point  59  between the two connections. The annular groove  56  that defines the annular rib  58  on one side extends, on its side remote from the annular rib  58 , as far as a circumferential collar  60  of the pump element  50 . This collar  60  rests on a shoulder  62  of the installation chamber  24  and thereby defines the extent to which the pump element  50  is pressed into the housing block  10 . In addition, there is a second press fit between the circumferential face of this formed-on collar  60  and the wall of the installation chamber  24 , and as a result the eccentric chamber  26  (FIG.  1 ), coaxially adjoining the installation chamber  24  of the pump element  50 , is sealed off reliably from the part of the housing block  10  that carries pressure fluid. 
   As already noted, the installation chamber  24  of the pump element is closed off from the outside in pressure fluid-proof fashion by a closure lid  44 . This lid  44  is secured by positive engagement to the housing block  10 , for instance being pressed into it, and rests with its inside on the end face of the pump element  50  and thereby additionally axially braces the pump element  50  toward the outside. 
   It is understood that changes or advantageous refinements may be made in the exemplary embodiment described, without departing from the fundamental concept of the invention. This fundamental concept is based on an arrangement, that is as space-saving as possible and can be produced as simply as possible technically, of a damping device  22  on the housing block  10  of a hydraulic unit  11 ; this arrangement is equally applicable to anti-lock brake systems and brake systems with combined anti-lock and VDC and/or traction control provisions. 
   The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.