Abstract:
A vibration damper comprising a body part via which the damper can be fastened to the object to be dampened, an oscillating piece movably arranged in the space of the body part and fastened by at least one spring to the body part, the oscillating piece consisting of more than one part, removably fastened to each other. The invention also relates to a method of producing a vibration damper and an arrangement of reducing the vibration in a piston engine.

Description:
This is a national stage application filed under 35 USC 371 based on International Application No. PCT/FI2004/050147 filed Oct. 12, 2004, and claims priority under 35 USC 119 of Finnish Patent Application No. 20031531 filed Oct. 20, 2003. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a vibration damper the damper comprising a body part, by means of which the damper can be fastened to the object to be dampened, an oscillating piece movably arranged in the space of the body part, the oscillating piece being connected to the body part by at least one spring. 
   The invention also relates to a method for producing a vibration damper. 
   The invention further relates to a vibration dampening arrangement of an engine. 
   The vibration of a piston engine is known as such, and in order to reduce it, there are a number of various solutions, such as balancing solutions. In engines there can be noted vibration forms of which both the engine and the auxiliaries attached in connection therewith, such as a compressor or compressors, are part of. In this case it is a matter of a global vibration form, i.e. the engine and its subconstruction/s together form a vibration system. The engine can also include local vibration of a certain auxiliary, whereby the dynamic properties of the auxiliary are determining as far as the vibration is concerned. 
   Control of local vibrations is usually easier than control of global vibrations of the whole construction. In local vibration the rigidity, fastening, mass etc. can be modified more easily. In the control of the global vibration of the engine, however, the need for modification can be directed at the engine itself, whereby it may be required to increase the rigidity of the cylinder block etc. This is, naturally, impossible, in case there is a desire to use standard engine components. The viewpoint of costs must also be considered when looking for new solutions. 
   In all types of vibration, the mass and gas forces of the engine act as the stimuli of the engine. A special difficulty in vibration dampening of engines is that the vibration properties of engines of different sizes (number of cylinders, cylinder diameter etc.) differ from each other. Further, the engine running speed also has an effect on the vibration. 
   In order to dampen the vibrations, U.S. Pat. No. 5,816,373, for example, discloses a solution, in which an oscillating piece is arranged between springs in a space containing compressible gas. Because the operation of the damper depends on, among others, the mass of the oscillating piece and its dimensions (throttling), the properties of the gas and the properties of the springs, such a solution will always have to be dimensioned and produced individually for dampening a vibration of a certain frequency. 
   The aim of the present invention is to produce a vibration damper minimizing the problems associated with prior art. Another aim of the invention is to produce a vibration damper the dampening properties of which can easily be changed even after the manufacture. 
   SUMMARY OF THE INVENTION 
   The basic idea of the invention is that the oscillating piece consists of more than one part, removably fastened to each other. Thus, the oscillating piece can be assembled so as to have a desired mass by using certain components having a standard shape. 
   Preferably the oscillating piece comprises two end pieces and a number of intermediate pieces arranged between the end pieces. In various applications the end pieces are preferably always similar and the final total mass of the oscillating piece is determined by the choice of the intermediate pieces. Preferably the intermediate pieces comprise adjustment discs and/or support sleeves, the length of which in each case depends on the amount of adjustment discs. The oscillating piece is essentially cylindrical in shape and it comprises a through-hole parallel with the longitudinal axis thereof for supporting it to the housing construction. The outer circumference of the oscillating piece is located a small distance away from the body part. 
   The oscillating piece is essentially cylindrical in shape and it comprises a through hole parallel with the longitudinal axis thereof for supporting the oscillating piece to the body part. Additionally, bearing means for the oscillating piece have been arranged in connection with the end pieces. 
   The body part of the oscillating piece comprises a cylindrical space limited by the first and second end walls. The guide shaft of the oscillating piece is located on the place of the center axis of the cylindrical space, the guide shaft extending from the first end wall to the second end wall. The guide shaft comprises a space extending essentially the whole length of the guide shaft. Adjacent the opposite ends of the space are openings forming a flow connection between the space of the guide shaft and the space of the body part on different sides of the oscillating piece. This kind of construction enables the movement of the oscillating piece to cause a flow of dampening medium via the space of the guide shaft into the space of the body part on different sides of the oscillating piece according to its movement and position. 
   The flow of the dampening medium can be effected on, because in connection with the space of the guide shaft there are means for adjusting the flow connection between the space of the guide shaft and the space of the body part. 
   The oscillating piece is arranged to be supported to the first and second end walls by springs. 
   In a method according to the invention for producing a vibration damper, in which method an oscillating piece is arranged in the space of the body part by means of at least one spring, the oscillating piece is formed by joining a number of pieces to each other. 
   In an arrangement according to the invention for dampening the vibration of an engine comprising at least one auxiliary, in which arrangement the said at least one auxiliary is rigidly attached to the said engine, a vibration damper has been arranged in connection with the said at least one auxiliary. Preferably the dampening arrangement comprises means for controlling the temperature, the means being connected to the medium circulation of the engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the invention is described by way of example and with reference to the appended schematic drawings, of which 
       FIG. 1  is an illustration of a vibration damper in connection with an engine, 
       FIG. 2  illustrates an embodiment of the vibration damper according to the invention, 
       FIG. 3  illustrates section A-A of  FIG. 1 , and 
       FIG. 4  illustrates another embodiment according to the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic illustration of a piston engine  1  comprising a turbocharger  2 . According to the invention a vibration damper  3  has been arranged in connection with the turbocharger of the engine  1 . It is rigidly attached to the turbocharger  2  or its support structure. This means that no essentially flexible special spacer is used in connection with the attachment. The vibration levels of both the engine and the turbocharger can be reduced on the desired frequency range by means of the vibration damper. In order to keep the operation of the vibration damper stable as far as temperature is concerned, it is provided with temperature control means  4 ,  5 ,  6 . The temperature control means can be implemented by providing the actual damper  3  with a shell construction  6  being in connection to the medium circulation, such as lubrication and cooling system, of the engine via channels  4 . In some cases the damper can also be provided with a fan  5 , by means of which the cooling can be accomplished. 
     FIGS. 2 and 3  show the vibration damper  3  of  FIG. 1  in more detail. The damper comprises a body part, into which a closed space  19  has been arranged by means of first  11  and second  12  end walls. The cross-section of the space  19  and the body part is preferably round. The end walls are fastened to the body part in a suitable way, such as bolting (not shown in figures) and so that the mating surface is tight. A guide shaft  13  is arranged in the space  19  inside the damper  3 , on the center axis thereof, the guide shaft extending essentially from the first end wall  11  to the second end wall. An oscillating piece  20 , i.e. a piston, has been arranged on the guide shaft movably along its longitudinal axis, the oscillating piece comprising a through hole  20 . 1  parallel with its longitudinal axis, by means of which the oscillating piece is fitted on the guide shaft. The guide shaft is arranged on the center line of the body part of the damper. A fastening flange  14  supporting the guide shaft to the end wall is arranged in the end of the guide shaft  13  adjacent the second end wall. The guide shaft and the fastening flange  14  are arranged in a recess provided in the end wall. 
   A space  15  has been arranged in the guide shaft, the space extending from one end of the guide shaft almost through it. Preferably the space is made by boring. Additionally, openings  16 ,  17  have been arranged in the wall  13  of the guide shaft, by means of which a flow connection is formed between the space  15  of the guide shaft and both sides of the oscillating piece of the space  19  of the body part. Thus, as the oscillating piece moves, dampening medium can flow from one side of the oscillating piece to other side thereof. The other end of the guide shaft is provided with an adjustment screw or needle  18 , which is arranged together with the flow opening  17  so that the flow opening  17  can be blocked, i.e. throttled, by means of the adjustment screw or needle  18 . By means of this arrangement it is possible to effect the flow of dampening medium in the space  19  as the oscillating piece moves and thereby to effect the dampening properties of the vibration. The dampening medium is chosen according to the dampening effect needed in each case, it can be a suitable gas or liquid, such as oil. 
   In the shell construction  6  a second outer shell  10 . 1  has been arranged in connection with the outer surface of the body part  10 , the shell  10 . 1 . forming a space for the cooling medium in the body part  10 . There are also connection conduits  10 . 2 ,  10 , 3  provided in connection with the outer shell for directing cooling medium into the space and away from there. These allow the use of cooling medium for controlling the temperature of the body part and the whole of the damper and maintaining it at the desired level. The temperature has an effect on the operation of the apparatus by having an effect on the viscosity of the dampening means. 
   The oscillating piece  20  is supported by a spring system comprising at least one spring  29  to the first and second end walls either directly or via the collar part  13 . 1  of the guide shaft and the fastening flange  14 , as shown in  FIG. 2 . Here, the spring system comprises a number of separate springs on both sides of the oscillating piece. According to the invention the oscillating piece is formed by a number of parts, improving the possibilities of tuning the vibration damper. 
   The oscillating piece  20  comprises a body part  21  and a cover part  22 . A bearing arrangement  23 ,  24  between the oscillating piece and the guide shaft  13  has been provided in connection with the above-mentioned parts so that both the body part  21  and the cover part comprise the bearing arrangement  23 ,  24 . A number of intermediate parts  25 , i.e adjustment discs  25 . 1 - 25 . 3  are provided between the body part and the cover part, by means of which the mass of the oscillating piece can be influenced. The intermediate parts are located between the body part  21  and the cover part  22  and in the embodiment shown in  FIG. 2  they are all fastened by means of threaded bars  26  and nuts  27  to form an assembly. Here, a certain space, i.e. a longitudinal distance, remains between the body part  21  and the cover part  22 , and if the desired total mass does not necessitate the use of intermediate pieces in such an amount that the whole available space is filled, a support sleeve  25 . 4  is used in connection with the threaded bar. This accomplishes, among others, the advantage that a mass necessary for tuning of the damper in each case can be arranged in the space between the body and cover parts produced in standard sizes. The mass of the oscillating piece can be varied by arranging a different number of intermediate pieces. It is also possible to produce the intermediate pieces from materials having different densities. Thus the mass of the oscillating piece can be varied without changing its external dimensions, whereby it is possible to standardize the physical dimensioning. It is, however, important that all parts of the oscillating piece are immovable in relation to each other. The shape of the body part  21 , cover part  22  and the intermediate parts  25  can differ from those shown in the figures; it is however, essential that they are rotationally symmetrical in shape and their center of mass in on the center shaft. 
   Flow paths  28  can be arranged in the oscillating piece for the dampening medium filling the space  19 , whereby the movement of the oscillating piece can cause it to flow along the flow path. The dampening medium can correspondingly flow via the flow openings  16  and  17  and the space  19 . The flow via this path, along with the dampening effect of the oscillating piece, can be adjusted by changing the position of the adjustment screw or needle  18 . 
     FIG. 4  shows another embodiment of the vibration damper according to the invention. It corresponds in structure to that shown in  FIG. 2 , and in the following, reference is generally made only to the features differing from those of  FIG. 2 . Here, the body part  10  is provided with an area  10 . 4  having a smaller diameter, the area forming an upper and a lower (in the figure) shoulder  10 . 5 ,  10 . 6 . Here, two superimposed rings  30 ,  31  are arranged against the shoulders, the fastening of the rings being secured by sleeves  32 . The rings extend in the space  19  towards the centre so that there&#39;s only a small clearance between them and the oscillating piece  20 . The clearance acts as a flow path and a throttling point for the dampening medium. On the other hand, a clearance defined by about the rings  30 ,  31  remains between the oscillating piece and the body part  10 . A projection ring  21 . 2  is arranged on the outer circumference of the oscillating piece, extending around it, in the area in the direction of the longitudinal axis between the rings, the projection ring being formed to a shell  21 . 1  separate from the body part  21  of the oscillating piece. The shell and the body part can be an integral piece as well, as shown in  FIG. 2 . The projection ring  21 . 2  on its part functions as a throttling point of the dampening medium and has an effect on the tuning of the vibration dampening of the apparatus. 
   In order to dampen the movement of the oscillating piece the rings  30 ,  31  are provided with through-holes  33  along the circumference thereof, the size and location which can be used to influence the flow, i.e. throttling, of the medium. The openings of the superimposed rings can be of different sizes and partly overlapping, which improves the adjustability of the throttling. The position of the openings  33  can be moved by rotating the rings in relation to the center axis to a suitable position in relation to each other. 
   During operation, the oscillating piece of the damper produces a reaction force as it oscillates back and forth on the guide shaft in the space  19 . The magnitude, frequency and phase angle of the reaction force can be effected on by changing the mass of the oscillating piece, by changing the spring constant of the spring system and by the dampening medium filling the space  19  and the flow thereof. The vibration damper transforms vibration energy into heat, formed as the dampening medium flows in narrow throttling points from one space to another forced by the vibrating piston. 
   The invention is not limited to the embodiments described here, but a number of modifications thereof can be conceived of within the scope of the appended claims.