Patent Publication Number: US-4548170-A

Title: Longitudinal housing wall of an internal combustion engine

Description:
FIELD OF THE INVENTION 
     This invention relates to a longitudinal wall of a crankcase or an outer pan of an internal combustion engine, which wall can be provided with at least two parallel ribs. 
     BACKGROUND OF THE INVENTION 
     Vibration is often induced in such crankcase or pan wall, particularly by the crankshaft mechanism, and causes the wall to radiate sound, which is often rather loud. 
     It is known from Austrian Patent Specification No. 325,897 to reduce the radiation of sound from housings or housing parts of internal combustion engines in that the housings or housing parts are provided with crossing ribs, which protrude from a wall surface and increase the geometrical moment of inertia and the stiffness of the wall and also increase the natural frequencies of vibration. The ribs however contribute greatly to the mass and the natural frequencies cannot be increased unless the ribs are relatively large so that structural problems arise. 
     From VDI-Zeitschrift No. 121-1979, No. 6, pages 253-261, it is known to provide vibration absorbers in order to reduce the noise emitted by the engine. If such absorbers are to effect an adequate attenuation, they must have dimensions which are so large that they cannot be used in conventional internal combustion engines. Such absorbers have been used only in stationary engines or in order to preclude the generation of a squealing noise by a tramcar. 
     German Patent Publication No. 1,405,857 discloses resonant vibration absorbers comprising a mass-spring system that is coupled to the component that is to be damped and tuned to a frequency of vibration of said component. Such absorbers attenuate vibration by absorbing vibration energy at a predetermined frequency from the component that is to be damped. Said energy is dissipated in most cases by a damping element that is connected in parallel to the absorber spring. A resonant absorber of this type has the disadvantage that it is effective only in a narrow frequency band so that it can be used only where vibration at a constant frequency is to be expected, e.g., to attenuate noise in transformer housings. 
     OBJECT OF THE INVENTION 
     It is an object of the invention to avoid these disadvantages and to provide a longitudinal housing wall which is of the kind described first hereinbefore and is substantially damped by the use of simple, inexpensive means, which occupy only a small space. 
     SUMMARY OF THE INVENTION 
     This object is accomplished in accordance with the invention in that a rod is disposed between two ribs or in a groove of the wall and extends over at least two-thirds of the length of the ribs or of the groove and is either under initial stress and in direct contact with or coupled to the wall or is embedded in a viscoplastic material or in a plastic material having a high mechanical loss factor and is adapted to act as a resonant absorber for absorbing flexural vibration of said longitudinal wall. 
     It is known that the sound radiation from a platelike member, which is constituted by such longitudinal wall, is mainly due to flexural vibration. A large part of the radiated sound is due in most cases to the first or second mode of flexural vibration of the plate. To ensure an attenuation particularly at the corresponding frequencies, the rod provided in accordance with the invention is tuned to the wall that is to be damped. That tuning is effected by the selection of the material, mass and natural frequency of the rod. The vibrational energy is dissipated as a result of the relative motion taking place between the rod and the ribs or between the rod and the sides of the groove. If the rod is embedded in a viscoplastic material or in a plastic material, this material greatly contributes to the dissipation. The rod is so tuned to the predominating mode of flexural vibration of the longitudinal wall that the rod is capable of acting as a resonant absorber for flexural vibration at the corresponding frequency. Because it is not possible in most cases to design the rod as a resonant absorber for a vibration of the longitudinal wall in a different mode or at a different frequency, an absorption in a broad band can be achieved by the relative motion which arises. 
     The viscoplastic material or plastic material can be bonded to the ribs or to the groove sides by adhesive or vulcanized joints, which ensure that the rods will be properly tuned even if the longitudinal walls are mass-produced. 
     To reduce the natural frequency of the rod and to tune it to a low frequency of the longitudinal wall, the rod may be rigidly connected to the longitudinal wall at least at two points. The frequency can be even more exactly matched if additional weights are carried by and secured to the rod. 
     The rod may be biased by the provision of at least one spring, which is held under initial stress between the rod and each rib or between the rod and each side of the groove and which exerts approximately normal forces on the confronting surfaces of the rod and of the ribs or of the groove. In a simple alternative design the rod is prestressed and resiliently flexible in a direction that is transverse to its longitudinal direction and parallel to the wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is illustrated by way of example in the accompanying drawing, in which 
     FIG. 1 is a vertical sectional view on a plane that is transverse to the crankshaft and shows the lower part of an internal combustion engine comprising an engine block surrounded by an outer pan, 
     FIG. 2 is a similar view showing the lower part of an internal combustion engine of more conventional type. 
     FIG. 3 is an enlarged transverse sectional view showing a housing wall portion provided with ribs, 
     FIG. 4 is a transverse sectional view showing a modified wall formed with a groove, 
     FIG. 5 is a side elevation showing a wall portion provided with a different rod, and 
     FIG. 6 is a side elevation showing another embodiment. 
    
    
     SPECIFIC DESCRIPTION 
     As can be seen from FIG. 1 the engine block of an internal combustion engine is surrounded by an outer pan, which has a longitudinal wall 1a. In accordance with FIG. 2 an internal combustion engine comprises a crankcase having a longitudinal wall 1b. Each of the longitudinal walls 1a and 1b comprises two parallel ribs 2, which extend in the longitudinal direction of the wall and have spaced parallel confronting surfaces defining an elongate channel. An absorption of vibration is ensured in that a rod 3 is disposed between the ribs 2 and is capable of acting as a resonant absorber for flexural vibration of the longitudinal wall 1a of the pan or of the longitudinal wall 1b of the crankcase. The rod 3 extends over at least two-thirds of the length of the channel defined by the ribs 2 and is so embedded in a plastic material 4 having a high mechanical loss factor that the plastic material 4 is under initial stress. The plastic material 4 is bonded to the ribs 2 by an adhesive or vulcanized joint. 
     As is apparent from FIG. 4, the rod 3 that is embedded in plastic material may be provided between the confronting side faces of an elongate channel, which consists of a groove 5, which is formed in the longitudinal wall 1a of the pan. In accordance wth FIG. 5 the rod 3a is channel-shaped and inherently resiliently flexible and is held under initial stress in direct contact with the confronting surfaces of the ribs 2 so that the rod 3a is resiliently flexible in a direction that is transverse to the longitudinal direction of the rod and parallel to the longitudinal wall. Additional weights 6 may be carried by and secured to the rod 3a. 
     The embedding plastic material 4 may be replaced by springs 7, which are disposed between the rod 3 and respective ribs 2 (FIG. 6) and which bias the rod 3 by exerting approximately normal forces on the confronting surfaces of the rod 3 and ribs 2.