Abstract:
A hydraulically drive train mount ( 1 ), in particular for a motor vehicle, includes a mount housing ( 2 ) in which an elastic mount body ( 3 ) is arranged in a partially movable manner. The elastic mount body at least partially encloses a first fluid chamber ( 4 ) and has a fluid-filled equalization chamber ( 6 ) sealed by a sealing element ( 5 ) that can be moved in the mount housing ( 2 ). A membrane ( 7 ) arranged in the mount housing ( 2 ) separates the first fluid chamber ( 4 ) from the equalization chamber ( 6 ). The pressure in the equalization chamber ( 6 ) can be adjusted by the sealing element ( 5 ) that is formed as an axially movable piston ( 8 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a hydraulically damped drive train mount, in particular for a motor vehicle, having a mount housing, in which an elastic mount body is disposed to be displaceable. The elastic mount body at least partially encloses a first fluid chamber and has a fluid-filled equalization chamber sealed by a sealing element that can be displaced in the mount housing. A membrane disposed in the mount housing separates the first fluid chamber from the equalization chamber. 
     BACKGROUND OF THE INVENTION 
     DE 40 21 039 C2 describes a hydraulically damping drive train mount having a working chamber or first fluid chamber disposed on top, and an equalization chamber or second fluid chamber disposed below. The working chamber is enclosed by a suspension spring that receives the weight of the drive unit. The two chambers are separated from one another by a wall having an annular channel. The hydraulic fluid can overflow from the working chamber into the equalization chamber by the annular channel when the drive train mount is pressurized. Conversely, the hydraulic fluid can flow back when the load is removed from the drive train mount. In addition to the internal friction of the suspension spring, a hydraulic damping of the drive train mount is also achieved in this manner. In particular, the annular channel can be designed in such a way that a vibration of the fluid column in the annular channel develops, which vibration is specifically adjusted to a specific low-frequency vibration of the drive unit. In this range of maximum damping, the fluid column moving back and forth in the annular channel behaves like a hydraulic absorber. The vertical vibrations of the drive unit generated by the roadway are to be counteracted by the natural frequency of the drive unit. 
     The hydraulic damping of a drive train mount of this kind cannot be modified and cannot deal with all dynamic driving conditions and accelerations of the drive train to be mounted resulting therefrom. 
     DE 41 21 939 A1 shows and describes a drive train mount, in which an annular mount body made of an elastomer material assumes the static load-bearing function of the drive train mount. A second rubber-elastic mount body is integrated in the annular mount body, which mount body in turn works together with a mount core. The drive train mount thereby has a hydraulic damping function and a switchable, hydraulic absorber system. 
     EP 1 580 452 A1 describes a hydraulically damped drive train mount for motor vehicles having at least one first fluid chamber filled with hydraulic fluid and having at least one gas-filled equalization chamber. The drive train mount has a mount core that can be connected to the drive train that is to be mounted, such as an internal combustion engine. The mount core is housed in a body-mounted, cup-shaped mount housing. The drive train mount additionally has two functionally separated rubber-elastic mount bodies, to which the first fluid chamber and the equalization chamber are connected and divided by a nozzle body. The first fluid chamber faces away from the mount bodies or is separated by the nozzle body, respectively, and is pressurized with pressure from a pressurizing medium source or an unpressurized return line in defined frequencies. 
     The drive train mount has numerous components that possess predetermined elastic properties and due to the structure thereof, in particular when using a throttle in the form of the nozzle body functioning as a damping element, that drive train mount is relatively slow in its response behavior, which response behavior may lead to deviations in the control response. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved hydraulically damped drive train mount having low deviation in its control behavior with a large variance in the spring stiffness. 
     This object is basically achieved by a hydraulically damped drive train mount where the pressure in the equalization chamber can be adjusted by the sealing element formed as an axially displaceable piston. A very direct acting control element that can create fine pressure differences is provided in the drive train mount on the one hand, and on the other hand a possibility is created for the membrane that delimits the first fluid chamber from the equalization chamber to be able to bend and roll accordingly to temporarily allow a high degree of spring stiffness in the entire drive train mount. Due to this structural feature, higher loads can be temporarily absorbed than in known drive train mounts. The installation space of the drive train mount is not increased thereby, and the production cost for the drive train mount is low. Unlike the prior art, an increase in the control accuracy and an improvement in the response sensitivity can be achieved by displacing the piston in the equalization chamber as a control element for the pressure control. Depending on the fill level in the equalization chamber, the piston crown of the piston can serve as a supporting surface for the membrane or for an annular bead of the membrane, so that in addition, the static properties of the drive train mount are improved. 
     The piston itself is preferably not moved mechanically, but rather hydraulically. A second fluid chamber is disposed on the rear side of the piston crown, which can be pressurized by a pressurized fluid (liquid) or gaseous fluid. 
     The first fluid chamber is preferably filled with a mixture of water and glycol. The equalization chamber is filled with a low-viscosity hydraulic oil, which oil is available on the market under the brand name Pentosin®. The mixture of water and glycol can, for example, be composed in the manner of a frost-protecting coolant and may have an ethylene-glycol component comprising 30 to 50% of the total quantity of fluid such that it is readily possible to operate the drive train mount at temperatures as low as −35° C. The elastomer materials used in the drive train mount are not affected thereby. The rubber swelling, as well, falls in a range similar to that when water is used. 
     Preferably, the fluid that places a load on the piston to the equalization chamber is preloaded or pressurized in the second fluid chamber by a pressure transmitter. A pressure transmitter or pressure transformer is used especially in the case that supply or control pressures are to be reduced proportionally. In so doing, the pressure generated by the pressure transmitter is regulated at a fixed, constant ratio to the supplied pressure. For this purpose, the differential piston of the pressure transmitter is disposed in such a way, relative to the second fluid chamber, that the larger surface of the piston is directed towards the second fluid chamber. The fluid pressure for pressurizing the second fluid chamber and for moving the piston is provided by a pressurizing medium source, which comprises a pump and a pressure accumulator. 
     A pressure-control valve controls the pressurization of the second fluid chamber with pressure or the outflow of fluid in an unpressurized return line in definable frequencies. It can be actuated electrically and is preferably controlled by digital circuitry. Here, the smoothing low-pass action of an inductor such as a solenoid coil known from control engineering can be used. By controlling the solenoid coil of a pressure-control valve of this kind can result in a pre-definable, very finely adjustable force on the armature of the valve and on the control piston. Thus, by applying this principle, the position of the control piston in the pressure-control valve, which is directly related to the armature position, can be finely controlled. The solenoid coil of the pressure-control valve can be controlled with digital circuitry, such as a microcomputer, which in turn may be part of an electronic control unit ECU of a motor vehicle. The control unit can measure the accelerations at the drive train mounted by the drive train mount and at the body of the motor vehicle by sensors, and actively counteract the movement and vibration in the drive train through appropriate pressure control by the pressure-control valve with a very fine resolution. This arrangement can reduce vibration in the body of a motor vehicle and increase driving comfort. 
     To control the solenoid coil of the pressure-control valve, the control unit or the microcomputer generates a pulse-width modulated digital signal. The pulse-width modulation, abbreviated as PWM, is also referred to as pulse-duration modulation (PDM). 
     According to the invention, a stop valve is provided between the drive train mount and in particular between the pressure transmitter and the pressure-control valve. In the event of any malfunction in the pressure control of the second fluid chamber or in the event of a failure of the power supply to the pressure-control valve, the current fill level in the second fluid chamber can then be retained. The pressure of the pressurizing medium source can be adjusted by a pressure control valve. 
     To achieve a modular, simple structure of the drive train mount, advantageously the mount housing of the drive train mount is divided into multiple, individual segments, in particular in an annular shape. Advantageously a first segment can be rigidly connected with the elastic mount body. A second segment can preferably serve, on the one hand, to secure a membrane between the first and the second segment forming a seal, and on the other hand, to create an annular casing for the equalization chamber. The piston for the pressurization of the equalization chamber can be disposed in a third segment such that it is axially displaceable. The third segment can directly form a cylinder for the piston. 
     In a fourth segment of the mount housing, the pressure transmitter or a piston that pressurizes the second fluid chamber can be housed, which piston, together with the piston that pressurizes the equalization chamber, forms the actual pressure transmitter. 
     Similarly, the pressure-control valve can be disposed in the fourth segment. The segments of the mount housing can be assembled in a positive locking and releasable manner. Thus, threaded fasteners can be screwed through the respective casing of the first and third segments and can hold the segments disposed therebetween together in the manner of stud bolts. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure: 
         FIG. 1  is a schematic side view in section of a hydraulically damped drive train mount according to an exemplary embodiment the invention; 
         FIG. 2  is a circuit diagram of a control system for the hydraulically damped drive train mount according to  FIG. 1 ; and 
         FIG. 3  is a perspective view of the hydraulically damped drive train mount according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic longitudinal section, not to scale, of a hydraulically damped drive train mount  1  for the active mounting of a drive train  17  as an internal combustion engine, not shown in greater detail, in a chassis of a motor vehicle. The drive train mount  1  has a cupular mount housing  2  with an annular cross section. A mount body  3  made of an elastomer material is disposed on the upper surface of mount housing shown in  FIG. 1  from the perspective of the viewer, wherein the mount body  3  forms a ring having a double-T-shaped cross section. The mount body  3  is connected to a first annular segment  22  of the mount housing  2  by vulcanization in a manner that forms a seal and projects over the first segment  22  at the upper edge thereof with a protruding ridge. A sleeve-shaped mount core  25  is vulcanized centrally in the mount body  2 , from which a stud bolt  26  extends axially from the mount housing  2  upward. 
     The stud bolt  26  serves, among other things, to connect the drive train mount  1  to the drive train  17  being mounted, for example in the form of an internal combustion engine of a motor vehicle, which is shown only schematically in  FIG. 1 . The radial edge of a membrane  7  is inserted into a circumferential groove  27  on a side of the segment  22  of the mount housing  2  that faces the ridge of the mount body  3 . The membrane  7  and the cross-sectional shape of the mount body  3  form a first fluid chamber  4 , which first fluid chamber is filled with an incompressible mixture of water and glycol. The membrane  7  itself has an annular bead  9  in the region of the annular mount body  3 , which bead protrudes axially away from the first fluid chamber  4 . The membrane  7  is disposed in the axial region of a second annular segment  22 ′ of the mount housing  2 , wherein the second segment  22 ′ encompasses approximately half of the outside of the lower half of the first segment  22  from below, so that the first segment  22  can be inserted into the second segment  22 ′ from above. A thickening of the wall, which is radially directed towards the inside of the mount housing  2 , is provided on the second segment  22 ′ in the region of the radial edge of the membrane  7  as a stop for the first segment  22 . 
     A radial edge on the second segment  22 ′, in turn, protrudes in part over a third segment  22 ″ of the mount housing  2 , which is also annular. An O-Ring  28  as well as additional sealants, if necessary, are inserted in an annular groove on the outer circumference of the third segment  22 ″ in the area of overlap of the two segments to create a seal. The third segment  22 ″ of the mount housing  2  is formed as a cylinder for a piston  8  that is displaceable therein. The piston  8  has approximately the same cross sectional area as the mount body  3 . The piston  8  forms a sealing element  5 , which seals an equalization chamber  6  that lies between the membrane  7  and the piston  8  in the axial direction of the drive train mount  1 . When viewed in terms of its inner pressure, the equalization chamber  6  can thus be modified by the displacement of the piston  8 . The equalization chamber  6  is preferably filled with a low-viscosity hydraulic oil, in particular with Pentosin®. The annular bead  9  of the membrane  7  can move in the direction of the piston  8  in the case of any load peaks in the form of pressure applied to the mount body  3 . Thus, higher loads and vibration amplitudes that emanate from the drive train  17  to be mounted, as is known in the prior art, can thereby be absorbed by the drive train mount  1 . 
     A fourth segment  22 ′″ of the mount housing  2  is formed as the base of the drive train mount  1  and has a cylindrical mating component  29  that protrudes axially downward to fix the drive train mount  1  to parts of a motor vehicle chassis, not shown in greater detail here. A cylindrical bore  30  is introduced in the center of the fourth segment  22 ′″ that serves as a guide for an additional pressure piston, in particular in the form of a high-pressure piston  13 . The high-pressure piston  13  can be displaced in the same direction as the piston  8  and is coupled with the piston  8  by a positive locking releasable, sealing connection. A pin  31  extends from the piston crown of the piston  8 . A lock washer  32  is inserted into a circumferential groove  33  of the pin  31  for the positive releasable, sealing connection. Diametrically opposed to the lock washer  32 , a sealing element formed as an O-ring  34  is inserted in an annular groove on an axial face  35  of the piston  13  and thereby seals the equalization chamber  6 . An additional seal  34 ′ is disposed on the high-pressure side of the arrangement between the chamber  11  and the chamber  45  on the outer circumference of the piston  13 . 
     Pressure can be applied to the high-pressure piston  13  on the rear side thereof in the fourth segment  22 ′″ by a fluid  10 , in particular in the form of a hydraulic oil, by a pressurizing medium source  14 . Thus, the piston  8 , together with the high-pressure piston  13 , forms a kind of pressure transmitter  12 . A second fluid chamber  11  on the rear side of the high-pressure piston  13  can be connected to the pressurizing medium source  14  by a line  36  that passes radially through the fourth segment  22 ′″ of the mount housing  2 . All four segments  22 ,  22 ′,  22 ″ and  22 ′″ of the mount housing  2  are connected to one another by a positive locking releasable connection using three threaded fasteners  24  (c.f. also  FIG. 3 ). 
     As the circuit diagram according to  FIG. 2  shows, the pressurizing medium source  14  comprises in particular a pressurizing medium pump  19  that conveys pressurizing medium from a pressurizing medium container  37  (tank) to a pressure-control valve  15  for the respective drive train mount  1 , and to an accumulator block  38  together with a pressure accumulator  20 . A pressure-control valve  15  is allocated to each drive train mount  1 . The accumulator block  38  can be disconnected from the pressurizing medium pump  19  by a check valve  39  and has an electric drive for the filling of the pressure accumulator  20  and the pressurization of the drive train mounts  1 . A stop valve  18  is provided between each pressure-control valve  15  and the respective high-pressure piston  13 . The stop valve  18  is formed in particular as an electrically controlled 2/2-way valve and serves to block the fluid-conducting connection from the pressurizing medium pump  19  to the high-pressure piston  13  of each drive train mount  1 , for example in the event of a power failure or in the event that the drive train  17  being mounted is taken out of operation. An unpressurized return-flow line  40  is directed from each pressure-control valve  15  to the pressurizing medium container  37 . Thus, during operation, each pressure-control valve  15  alternatively connects a pressurized flow line  36  or the respective return-flow line  40  to the rear side of the high-pressure piston  13  and in this respect, to the second fluid chamber  11 . The delivery pressure of the pressurizing medium pump  19  can be adjusted in a conventional manner by a pressure control valve  21 . 
     Each pressure-control valve  15  of each drive train mount  1 , shown  FIG. 2  and supplied by a common pressurizing medium source  14 , is preferably formed as a pulse-width modulated, electrically controlled 3/2-way valve or pressure-reducing valve. Digital circuitry  16 , which can be part of a microcomputer of the motor vehicle, thereby provides a pulse-width modulated digital signal, which generates a very finely adjustable force on a magnetic armature (not shown) of the respective pressure-control valve  15 . The Position of a control piston of the pressure-control valve  15  is thus directly dependent on the respective position of the armature. The fact that a pressure transmitter  12  is formed in the drive train mount  1 , which controls the pressure on the equalization chamber  6  and the pressure that is thereby propagated in the first fluid chamber  4  permits controlling the drive train mount  1  very directly and in this way, applying very high thrust and/or pressure forces to the mount body  3  and the drive train  17 . 
     Operating data from the internal combustion engine, such as the engine speed, accelerations in all axes of the drive train  17  and accelerations by the motor vehicle frame are supplied to the digital circuitry  16 . The respective pressure-control valve  15  can be individually controlled by an amplifier stage. The digital circuitry  16  may contain a control strategy to the extent that the pressure control in the second fluid chamber  11  is effected in such a way that a vibration reduction of the body of the motor vehicle and therefore a significantly increased driving comfort of the motor vehicle is achieved. 
       FIG. 3  shows a perspective view of the drive train mount  1  in a compact design, in particular made possible by the fact that the pressure-control valve  15  as well as the stop valve  18  are integrated as part of the drive train mount  1 . The valves  15 ,  18  of that sort are screwed into the fourth segment  22 ′″ of the mount housing  2  in the manner of a cartridge solution. Various filling ports can be seen on the outside of the mount housing  2 . Thus, a filling port  42  is provided for the Pentosin® in the equalization chamber  6 , as well as a filling port  43  that flows into the wall of the second segment  22 ′ for the mixed solution of water and glycol, which solution is received from the first fluid chamber  4 . In addition, an air vent  44  for the rear piston chamber  45  of the piston  8  can be seen. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.