Abstract:
A power unit bearing, in particular for motor vehicles, is characterized by mechanically integrally joining a conventional bearing, in particular a hydraulic bearing, to a connectable or disengageable hydraulic switching module for the purpose of matching the power unit characteristics to changing operational conditions of this power unit. The switching module is inserted between a chassis-side base plate of the conventional bearing body and a chassis-side adapter of the power unit bearing.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a power unit bearing, in principle for arbitrary purposes, in specific however for motor vehicles. 
     Power unit bearings or so-called “engine mounts” support a motor-vehicle power unit on the chassis. Such bearings are intended to elastically absorb assembly vibrations, to dampen them and in particular to decouple them acoustically and sub-acoustically. Bearings of the most diverse designs meet these tasks in significantly different ways. Rubber-metal bearings of most varied designs with, as well as without, hydraulic damping have been found foremost practical. 
     As hardly any one bearing meets the broad requirements of vehicle comfort, innumerable bearings already have become known with the purpose of controlling or setting or modifying the bearing characteristics. In the field of solid bearings, that is foremost the field of rubber-metal bearings, the elastic rubber body is contoured to hopefully match a particular desired spring constant. As regards hydraulic bearings, that is bearings with a hydraulic damping liquid, foremost those bearings are known in which electrical or magnetic fields control the rheological properties of the damping liquid. 
     The effectiveness of all known bearings is limited in that the known means and procedures to control the bearing characteristics of power unit bearings are able to respond to only comparatively narrow and homogeneous ranges and bands of frequencies and amplitudes. Bearings are not known which for instance are able to both insulate such vibrations illustratively caused by an idling engine at low rpm and to decouple and dampen such vibrations that are generated caused by an engine running at a higher rpm in a moving vehicle, are not known. 
     In the light of this general state of the art, it is the objective of the present invention to create power unit bearings and in particular a motor-vehicle bearing which shall be able both to decouple and dampen low-frequency vibrations of large amplitudes such as are generated typically by an idling engine and vibrations of higher and high frequencies of small amplitudes that are generated by the drive assembly at higher rpms and vehicles moving at significant speeds. 
     SUMMARY OF THE INVENTION 
     Accordingly the basic concept of the invention is not in matching a power unit bearing known per se to its most diverse operating conditions by additionally modifying the bearing itself in complex manner and by acting in increasingly effective manner on the inherent bearing properties, but in that the actual, conventional and well-tested bearing itself is mounted on a switching module and in fact is integrated together with this switching module into one subassembly of which the specific bearing properties can be added to or decoupled from those of the conventional bearing. If the switching module is engaged, the characteristics of the conventional bearing therefore are modified by those of the switching module, whereas when the switching module is disengaged or deactivated, the conventional bearing, ie the bearing body, will be directly and at once transmitted to the chassis adapter of the power unit bearing. In its disengaged state, the switching module&#39;s transmission characteristics are in the ideal case absolutely neutral. 
     However in practice such a completely transmission-neutral behavior can be implemented in general only at great cost and moreover it is frequently less than mandatorily desirable in view of the acoustics. For that reason the overall structure of the power unit bearing with disengaged switching module preferably shall have a transmission behavior which can be considered being “extensively neutrally rubber-damped”. 
     The power unit bearing with switching module of the invention can be used both with conventional solid bearings, in particular rubber metal bearings, and with complex hydraulic bearings. Preferably the switching module shall be integral with the actual, conventional bearing body to form a new, integral power unit bearing. The switching module preferably shall be related to the bearing function by means of, and together with, the bearing housing of the conventional bearing portion. 
     In principle such a switching module can be controlled both mechanically and electrically, electromagnetically or optionally pneumatically and in adjustable manner. Preferably and in particular when used for automotive purposes, the power unit bearing of the invention however shall be switched pneumatically and in the process will behave in its engaged or activated state in the manner of a hydraulic bearing. As a result, and even with simple designs, remarkable effective results are reached, provided that the switching module be fitted with a hydraulic operating chamber in such manner that when the operational fluid in the closed operational chamber is unpressurized, the module shall be disengaged whereas, and also in the closed system, it shall be pressurized in the engaged, activated state of the switching module. In particular hydraulic, axially effective spacing enlargements can be implemented in this manner to separate the previously axially and radially affixed switching module from the conventional bearing body. 
     It is clear per se that the switching module of the power unit bearing is preferably integrated on the bearing&#39;s chassis side but that kinematically reversed solutions are easily implemented as well whereby the switching module is inserted between the support piece of the bearing and the support spring of the conventional bearing body. 
     Moreover the switching module even in its hydraulic mode can be designed in further manner in the spring zone using other support means, for instance using an additional rubber spring or steel spring, in particular a spiral compression spring. However the determinant function of the switching module always shall be that in its disengaged state it will allow the characteristics of the conventional bearing body to be operationally as free as possible of spurious effects and that in its activated state it shall support the conventional bearing body so softly, so floatingly and so three-dimensionally that even low-frequency vibrations of high amplitudes—as are generated by a power unit running in idle—shall be decoupled as fully as possible and shall be extinguished. 
     The invention is elucidated below in relation to an illustrative embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial section of an embodiment of the power unit bearing of the invention in its disengaged state, 
     FIG. 2 shows the bearing of FIG. 2 in the same section but in its activated state, 
     FIG. 3 is a functional diagram of the bearing of FIG. 1; and 
     FIG. 4 is a view similar to FIG. 3 of the bearing shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The power unit bearing shown in axial section in FIGS. 1 and 2 is composed of a conventional hydraulic bearing  3  and a hydraulic switching module  4  inserted between a load adapter  1  and a chassis adapter  2 . The hydraulic bearing  3  consists in conventional manner of a housing  5  containing a hydraulic operational chamber  8  bounded by a support spring  6  and a partition  7  and a compensating chamber  10  bounded by the partition  7  and a compensating membrane  9 . The operational chamber  8  and the compensating chamber  10  hydraulically communicate with each other through a throttling duct  11 . On the chassis side, the conventional hydraulic bearing  3  is sealed by a contoured base plate  12  clamping the compensating membrane  9  in fluid-tight manner against a shoulder  13  of the housing  5 . 
     Essentially the hydraulically switched switching module  4  consists of an expansion spring inset  14 , a module housing  15  and a cover ring  16 . 
     When assembling the power unit bearing, the above parts composing the switching module are sequentially inserted into the housing  5  of the conventional bearing body  3 , this housing being cylindrically open at the chassis side, as shown in FIGS. 1 and 2. In finishing this assembly, the rim segment projecting from this cylindrical bearing-housing segment is flanged in the manner indicated by the arrow  17  of FIG. 1, as a result of which both the bearing  3  and the switching module  4  are sealed in fluid-tight manner and closed as an integral sub-assembly and joined to each other. 
     The expansion-spring inset  14  substantially consists of a fabric-reinforced conical expansion spring  18  and a cylindrical support spring  19  integral with it and resting in a matching recess  20  in the base plate  12  of the bearing  3 , and of an expansion spring flange  21  vulcanized into the expansion-spring material and merging into a cylindrical notch  22  drawn toward the chassis. A radial spring  23  enters this cylindrical ring of the expansion-spring inset  14 , a cylindrical steel reinforcement  24  also being vulcanized into the peripheral zone of this spring  23 . 
     On the support side, the radical spring  23  encloses the annularly flanged and hence reinforced rim of the module housing  15 . The outside diameter of the module-housing flange is substantially smaller than the inside diameter of the cylindrical reinforcement  24 . This reinforcing ring  24  is flexibly connected through the radial spring  23  with the module-housing flange  25 . On the other hand the cylindrical lower notch  26  of the bearing housing  5 , the cylindrical segment  22  of the expansion spring flange  21  and the cylindrical reinforcement  24  of the radial spring  23  form a frictional bond which is enhanced in form-fit locking manner by the flange of the notch  26 . 
     The hydraulic operational chamber  27  of the switching module  4  is defined between the expansion spring  18  and the switching-module housing  15  and hereafter will be called “inner chamber” for brevity. 
     The inner chamber  27  is accessible, ie it can be closed hydraulically by means of a control valve  28  and it can be pressure-loaded by a hydraulic pump  29 . 
     The inner space  30 ,  31 ,  32  between the expansion spring  18  and the compensating membrane  9  is vented in unpressurized manner through the apertures  33 ,  34 , the duct  35  and the outer aperture  36 . 
     Lastly outer chambers  37  are formed in the radial springs  23  and are separated from each other by fixed links  38 . These outer chambers  37  are filled with the same operational fluid that fills the inner chamber  27 . 
     In the state shown in FIG. 1, the operational fluid in the inner chamber  27  is unpressurized, i.e. pressure P (as shown in FIG. 3) is equal or even smaller than zero. Furthermore the operational fluid in the outer chambers  37  also is unpressurized. The control valve  28  is preferably operated electrically and is closed in this instance. Under the static load of the power unit connected to the load adapter  1 —in general, the load to be borne—the surface on the chassis side of the expansion spring flange  21  is pressed in sealing manner against the load-side flange area of the switching-module housing flange, whereby the inner chamber  27  is separated in fluid-tight, hermetic manner from the outer chambers  37 . Sealing is improved further by a peripheral sealing bead  39 . Once the power unit bearing has statically dropped, the control valve  28  is closed and the conventional bearing  3  is fixed in place both axially through the closed outer chambers  37  and radially through the closed inner chamber  27 , and the expansion-rigid, fabric-reinforced expansion spring  18  is fixed in place resp. in geometric or frictional locking manner in the direction of tension or of pressure by the expansion spring flange  21  resting against the switching module housing flange. The switching module  4  is disconnected ie disengaged. Therefore the bearing characteristics of the power unit bearing are determined exclusively by the bearing characteristics of the conventional hydraulic bearing  3 . 
     If on the other hand the control valve  28  is opened while the hydraulic pump  29  is running, pressure P of, for example, 2.5 bar (as shown in FIG.  4 ), will build up in the hydraulic operational chamber  27  on the expansion spring  18  and on the annular spring  19  and ultimately will raise (S) the hydraulic bearing  23  together with the power unit resting on it as shown in FIG. 2, in such manner that the outer chambers  37  communicate hydraulically under pressure compensation with the inner chamber  27 . Whereas the radial spring is now freely operating in the radial direction, that is the x-direction as well as in the y-direction, this same radial spring  23  jointly with the radially inward possible expansion of the expansion spring  18  and its flexibility in the z-direction also ensures additionally axially resilient support of the hydraulic bearing  3  on the switching module  4 . In other words, under these conditions, the hydraulic bearing  3  rests on or in the switching module  4  in softly elastic, gimbaled, uniform, “elastically floating” manner. As a result even large amplitudes (S) such as are introduced in idle operation especially at low rpms from supported power units into the load adapter  1  can be cushioned, decoupled and damped in the presently engaged switching module  4  (FIG.  2 ). 
     By opening the control valve  28  and by opening a return conduit not shown in detail guiding the operational fluid, the power unit bearing can be moved out of the activated state shown in FIG. 2 back into the stiffening, disengaged state shown in FIG.  1 . In this process the control valve  28  closes again as soon as the expansion-spring flange  24  again rests in sealing manner against the switching-module housing flange  25  and pressure compensation is restored in the inner chamber  27  of the switching module  4 .