Abstract:
A device for damping pressure surges in a fluid with a housing ( 10 ) and a piston ( 14 ) that can be longitudinally displaced inside the housing ( 10 ) against the pretensioning force of a spring energy store ( 12 ). The piston ( 14 ) interacts with another piston ( 24 ), which is guided in a connecting piece ( 26 ) of the housing ( 10 ) in a manner that enables it to be longitudinally displaced. During the operation of the device, the piston ( 14 ) exerts a pressure force onto the other piston ( 24 ) when the other piston is in any displacement position. Even pressure surges occurring with a high frequency can be reliably controlled in a functionally reliable manner.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a device for damping pressure surges in a fluid. The device has a housing and a piston displaceable longitudinally against the pretensioning force of a spring-type accumulator. 
   BACKGROUND OF THE INVENTION 
   Devices for damping pressure surges include hydraulic accumulators. One of the main functions of hydraulic accumulators is to receive specified volumes of a pressurized fluid of a hydraulic system and to return them to the system as required. Since the fluid is pressurized, hydraulic accumulators are treated as pressure vessels and must be designed to withstand the maximum operating pressure as determined by the approval standard. For volume equalization in the hydraulic accumulator and as a result the associated storage of energy, the pressurized fluid in the hydraulic accumulator is subjected to the force exerted by a weight, spring, or gas. Equilibrium always prevails between the pressure of the pressurized fluid and the opposing pressure generated by the force of the spring or by the gas. In most hydraulic systems, use is made of hydropneumatic accumulators, that is, ones subjected to the action of a gas and having a separating element. A distinction is made between bladder, piston-type, and diaphragm accumulators. 
   These hydropneumatic accumulators perform a wide variety of functions in a hydraulic system. For example, in addition to performing the energy storage function referred to, they may be called upon to contribute to absorption of mechanical shocks and to surge damping in hydraulic systems. Pulsations occur in the flow volume especially when hydraulic pumps such as positive-displacement pumps are employed. Such pulsations cause vibrations as well as noise, and may result in damage to the hydraulic system as a whole. 
   The hydraulic pumps in question, positive-displacement pumps in particular, are also employed in so-called common-rail technology in the area of diesel engines. Recent third-generation developments add piezo technology for injection systems for diesel fuel. The recently developed piezo inline injectors for the third common-rail generation (cf. VDI-Nachrichten [Association of German Engineers-News], No. 33, Aug. 15, 2003) use piezo actor modules, which act by coupler modules on switching valves. The switching valves in turn act on an injector module of the fuel injection system. The outstanding hydraulic rapidity of the system results from the high degree of integration of the inline injector, that is, from the nearness of the piezo package to the valve needle in the tip of the injector. In comparison to the previous generation, the mass moved was reduced in the new systems from 16 g to 4 g. The mass moved is understood to mean the mass of the valve needle and the fuel with which the control space is filled. The respective technical configuration requires very high system pressures, ones reaching the order of magnitude of 2200 bar. The respective system pressure is to be built up by the hydraulic pump indicated, in particular a positive-displacement pump. The build-up is attended by the disadvantages described of pressure and pulsation surges. If the pressure surges are transmitted to the injector system, this transmission may result in critical states of the system and in failure of the piezo injector system with the injection system. If, as is known in the state of the art (see DE 195 39 885 A1), conventional hydraulic accumulators with separating elements (pistons) are included in the diesel fluid system as outlined in the foregoing. They nevertheless encounter their limits in view of the high system pressures indicated of up to 2200 bar. 
   DE 101 48 220 A1 discloses another device for damping pressure pulsations in a fluid system, especially in a fluid system of an internal combustion engine. The device disclosed comprises a housing in which at least one operating space is present. This space is connected to the fluid system and is limited in area by at least one movable wall element in the form of a metal diaphragm mounted on the edge side in the housing so as to be stationary. This wall element is functionally connected to a first spring unit. To provide the possibility of smoothing out pressure pulsations in the fluid system even with variable pressure present, provision is made such that the device comprises at least a second movable wall element which delimits a second operating space and which has a metal diaphragm fastened on the edge side in the housing. The first spring unit is mounted between the two wall elements in the form of diaphragms and is functionally connected to both. A throttle unit is also provided by which the second operating space is connected to the fluid system. The pressure pulsations in a fluid system may be reliably and efficiently smoothed out with different pressure levels present. However, because of the stationary clamping of the wall elements (diaphragms) their movability is restricted, so that functional safety in operation may be endangered at high pressures and correspondingly large pulsation and pressure surges. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a device for damping pressure surges permitting, even with very high system pressures produced by a hydraulic pump, a diesel fuel pump in particular, ones as high as 2200 bar, damping and/or smoothing out such pressure surges so that there is no harmful introduction of power into a piezo injector system of common-rail technology. 
   This object is attained by a device having one piston that operates in conjunction with another piston that is be guided so as to be displaceable longitudinally in a connecting piece of the housing. In operation of the device, the one piston exerts a compressive force on the other piston in every displaced position of the latter. Very high-frequency pressure surges may be controlled in the diesel fuel system. Yet, operation remains safe, even if due to the hydraulic pump in the form of the diesel fuel pump very high system pressures of up to 2200 bar and higher are produced. As a result of mechanical uncoupling of the two pistons and the constant application of the compressive force by one piston on the other, any pressure surges introduced are reliably intercepted and controlled. In particular, the uncoupling of the pistons ensures that any leakage accompanied by leakage flows, are kept small or controlled so that operational failures are prevented in the system as a whole. Preferably, one piston is of a diameter several times greater than the diameter of the other piston. An unimpeded actuation process may be achieved with such pistons. Processes of canting of the other piston in the connecting piece of the housing in particular are prevented by separate, independent control of this piston. 
   In one preferred embodiment of the device of the present invention, the other piston is configured as a stamp and is controlled by at least one anti-loss device in a through opening in the housing of the connecting piece. Free displaceability of the respective piston between specified displaceability limits in the housing configuration is thereby achieved. 
   In another preferred configuration of the device of the present invention, the other piston is machined to the highest degree on the external circumference side. In particular, the other piston is lapped, so that a metal-sealed gap is obtained at least between parts of the external circumference and the other piston on the inner wall of the opening in the housing. In another configuration of the sealing system, the other piston may be provided with annular or lubrication grooves on the external circumference side. As a result, despite the high pressures of up to 2200 bar and above in the diesel fluid system, reliable sealing of the other piston from the interior of the housing with the first piston is achieved. Especially when annular or lubricating grooves on the external circumference of the other piston are used, a fluid seal may be built up which works against entry of fluid into the gap in the metal. 
   If, in another preferred embodiment of the device of the present invention, a leakage opening configured in the housing communicates with the fluid space between the pistons, diesel medium which succeeds in penetrating the interior of the housing may nevertheless be transferred free of pressure in the block as a sort of return flow for oil leakage in the direction of the tank or leakage side. 
   With respect to the very high pressures indicated, it has been found to be advantageous to provide as a spring-type accumulator at least one helical spring configured as pressure spring and/or a pressure gas. Use of a pure pressure gas may entail the disadvantage that, in view of the very high pressures, a process of liquefaction of the gas will take place in the housing area as a result of compression of the piston first indicated. However, as an alternative or in addition, the system pressures indicated may be reliably controlled by use of a pressure spring as the spring-type accumulator. 
   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 drawing, discloses preferred embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  is a diagrammatic, side elevational view in section of a device for damping pressure surges, according to embodiments of the present invention, not drawn to scale, with two different cover element embodiments. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The illustrated device performs the function of damping pressure surges in a fluid, in particular one in the form of diesel fuel. The device has a cylindrical housing  10  and has a piston  14  which may be displaced longitudinally against the initial pretensioning force of a spring-type accumulator  12 . The respective piston is configured as a cylindrical contact plate and is guided along its external circumference by a slip and/or sealing ring  16  along the cylindrical interior circumference or surface  18  of the housing  10 . The piston  14  accordingly has on its opposite sides two essentially level or planar contact surfaces  20 ,  22 . For the purpose of guiding the spring-type accumulator  12 , the piston  14  is provided on the side facing accumulator  12 , with a cylindrical guide surface  22 . Guide surface  22  also rests against the inner surface  18  of the housing  10  on the guide surface outer circumference side. 
   The first piston  14  operates in conjunction with another or second piston  24 . The other piston  24  may be guided to be longitudinally displaceable in a connecting piece  26  of the housing  10 . As the illustration shows, the piston  14  furthermore operates in the housing by applying the compressive force to the other piston  24 , in every displaced operating position, including its front end contact position as shown, in operation or use of the device. The connecting piece  26  narrows in stages toward the free end of the housing  10  and is provided on the outer circumference side with a connecting thread  28  by means of which the housing  10  in the configuration illustrated may be connected to a fluid system, such as the diesel supply line for an injector system by the common rail technology. The housing  10  is positioned in a connecting line which leads to a hydraulic pump, a positive-displacement pump in particular, for example, one in the form of a diesel fuel pump or the like. The pressure surges occurring in operation of the diesel fuel pump, which may be considerable, with system pressures of up to 2200 bar or higher, are damped and smoothed out by the device of the present invention. Even high-frequency fluid surges are to be evened out. In addition, the damping device of the present invention is independently effective within prescribed limits even in the event of very high pressure amplitudes. 
   The respective connecting piece  26  undergoes transition to a bottom  30  of the housing  10 , which bottom is strengthened lengthwise. The pistons  14 ,  24  and the spring-type accumulator  12  are oriented longitudinally along the longitudinal axis  32  of the housing  10  and connecting piece  26 . In addition, the diameter of the piston  14  is several times greater than the diameter of the other piston  24 , so that very good impact force is introduced between the other piston  24  and first piston  14 , in view of the change in the relative diameters. 
   The other piston  24  is configured as a stamp or push rod and is guided in the through opening in the housing  36  of the connecting piece  26 , and is retained therein by at least one anti-loss device  34  in the form of a retaining ring. The anti-loss device  34  in particular can be a retaining ring, the front of which seals the housing opening  36  from the exterior and the projecting length of which comes in contact with the front end of the other piston  24  when the other piston is in its front limit position. When the other piston  24  is not in operation, its length has been determined so that the piston remains at a short axial distance, with slight clearance, from the anti-loss device  34 . However, as soon as a specified pressure level has been built up by the fuel, the clearance is eliminated. When the device is in the respective state of operation or use, the piston  14  applies a compressive force to the other piston  24  in any displaced position of the latter. In order to obtain good sealing, the other piston  24  undergoes the highest degree of precision machining on the external circumference side, in particular is lapped, so that a metal-sealed gap  38  is obtained at least between parts of the external circumference of the other piston  24  and the interior wall of the housing opening  36 . The other piston  24  has annular or lubricating grooves  40  for the purpose of further improvement in the sealing system. A labyrinth seal is thus obtained, one which makes it difficult for the diesel fuel to penetrate through the housing opening  36  into the clearance space  42  inside the housing  10  between the contact surface  20  and the facing surface  44  of the bottom  30 . 
   The fluid or clearance space  42  between the pistons  14  and  24  communicates with a leakage opening  46  in the form of a bore in the housing  10 . Consequently, an intentionally provided gap or leakage flow may be evacuated by the sealing system in the form of annular or lubricating grooves  40 , the metal gap  38 , and the clearance space  42  by the leakage opening  46  to the pressure-free leakage or tank side of the overall system. A sealing system  48 , such as one in the form of a conventional radial seal ring, is provided as an additional sealing system in the front area of the bottom  30 . When the housing  10  has been screwed into place, sealing, especially in the form of the leakage opening  46 , from the overall hydraulic or fluid system (diesel line network) may accordingly be effected by the connecting piece  26  with its connecting thread  28 . 
   A pressure spring in the form of a helical spring in this instance serves as a spring-type accumulator  12 . Pressure gas, such as gas in the form of nitrogen, may be applied in addition to the interior of the housing. The respective pressure spring  12  extends between the piston  14  and a cover element  50 . The cover element  50  may be in the form of a retaining plate  52 , and is retained in the housing  10  by safety means, a retaining ring  54  in particular. An alternative embodiment is presented in the figure in square framing. In this instance, the cover element  50  is a screw cap  56  screwed onto the housing  10  by external threading  58  on the external circumference side of such housing  10 . 
   The device of the present invention makes certain that any leakage flow which may occur may be reliably controlled and that the separate piston configuration of the pistons  14  and  24  ensures that canting does not occur. Pressure surges of very high frequency, in particular which affect the stamp-like additional piston  24 , may be transmitted at the same frequency as surges to the piston  14 , which then effects pulsation damping or smoothing by reacting on the other piston  24 . The system illustrated may be applied cost-effectively and produced by simple production technology with conventional steel materials, on the housing  10  side in particular. This device may generally be employed where low volumes under high pressure are to have the level damped or are to be displaced. Because of the surface relationships of the pistons, the spring to be employed may be made smaller, since the force required is correspondingly reduced. 
   While various embodiments have 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 appended claims.