Patent Publication Number: US-5020766-A

Title: Sound and vibration damper

Description:
FIELD OF THE INVENTION 
     This invention relates to a damper for reducing sound and vibration in hydraulic lines. In particular, this invention relates to damping and sound and vibration in the hydraulic lines of heavy machinery. 
     BACKGROUND OF THE INVENTION 
     Increasingly at present, hydraulic power is being used to drive and control heavy machinery such as loaders and digging machines. The use of hydraulic power has considerable advantages in wear, controllability et cetera. 
     Because heavy machinery is becoming large, larger and larger hydraulic drive pumps are now required. For example, cog-wheel pumps are used because they are fabricated at low cost relative to their large capacity. Cog-wheel pumps and other pumps unfortunately, however, do not deliver an absolutely even flow. Pulsations, vibrations, shocks and even blows occur. Blows are particularly prevalent when very high pressures are used. The resulting vibration and noise are disturbing for the driver, disturbing for the environment, and increase strain on the machine. 
     A possible way to solve this problem is to provide pulsation equalizers. Pulsation equalizers which can handle very high hydraulic pressures are, however, very expensive. The working pressures encountered in heavy machinery can be as high as 200 kp/cm 2 . In addition, a single piece of heavy machinery may require damping the vibration of two or three pumps. Multiple expensive pulsation equalizers would then be required. 
     SUMMARY OF THE INVENTION 
     In view of the above problem, it is an object of this invention to provide a simple apparatus for eliminating vibrations and blows in a hydraulic system. 
     The present invention solves the problem by connecting one or more hydraulic pipes the vibrations in which are to be damped, to a duct in a heavy mass. The mass may involve a large cast iron block in which a number of holes or ducts have been bored. As is apparent, this is a comparatively low cost solution even if the block weighs several tens of kilograms. The cost will be a mere fraction of the cost of using multiple conventional pressure and vibrational equalizers. 
     In operation, the present invention damps vibration and sound surprisingly well. Although the actual mechanism by which this improved damping occurs is not well understood at the time of this writing, the improved damping has been confirmed practical experiments. 
     The invention is, of course, not appliable in all cases where hydraulic pumps and engine are used. This invention is to be used in connection with heavy machinery and as stationary hydraulic equipment. The invention should be used with machinery to which a hundred kilograms can be added or removed without affecting the performance of the machine. In some cases, the additional weight of the invention can simultaneously be used as a counter weight on a piece of machinery. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows one embodiment of the present invention. 
     FIG. 2 shows the embodiment of FIG. 1 mounted on a piece of heavy machinery. 
    
    
     Additional desirable features of the invention are apparent from the following description of the preferred embodiment. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a cast iron block weighing about 130 kilos. Two adjacent longitudinal sides of the block which are angled relative each other each contain holes of a diameter of 24 mm. The holes in each of these two sides are bored so that they meet each other inside the block, thereby forming the shown four right-angled ducts. 3/4 inch connections and hydraulic oil lines are then connected to the ducts. The hydraulic lines lead both to and from the driving and controlling means so that both types of lines lead pass through the ducts. 
     The block such as the one depicted in FIG. 1 was mounted directly in the frame of the digger loader. This loader previously had had a sound level of 90 db in the operator&#39;s cab. After the block was installed, the sound level was measured to be 17.6 db. Considerable damping was therefore achieved. For this test, the operator&#39;s cab was fastened directly to the frame of the loader. 
     Damping was also observed with the block lying loosely on the ground. When different ducts were connected to different controlling and driving means, the amount of residual noise and vibration in individual hydraulic lines seemed to be independent of the particular duct to which the lines were connected. The block therefore simultaneously damps out several different vibrations at several different pressure levels. This test demonstrates this block can be used to replace a number of expensive pressure equalizers. Furthermore, the wear resistance of this block is vastly superior to that of pressure equalizers. 
     In this test, the block was placed in the front end of the loader. FIG. 2 shows the damping block 22 mounted in a non-specific way onto a piece of heavy machinery 21. Hydraulic lines 23, 24, 25 and 26 are shown connected to ducts inside the block. The block may, however, comprise a swinging unit which generates vibrations. These vibrations may that in turn be transmitted to the frame of the machinery in such a way that they annhilate undesirable vibrations generated by the machinery itself. 
     Preferably, the block is heavy so that its inertia is great in comparison to the hydraulic forces and vibrations to be damped. Furthermore, the material of the block is preferably an unyielding, high density, sound and mentioned function well. It is possible that damping may be further improved by ducts with other angles as well as ducts with greater length. If a material with a lower density is used, good effects may be achieved with larger blocks. 
     In the embodiment of FIG. 1, only one block is used for all the lines and connections that need to be vocationally damped. It is of course also possible to arrange different blocks at different places on the machine if this is practical. Presumably one is then forced to have comparatively heavy masses for the damping at all places. 
     The angled ducts in the embodiment are presumably not necessary. Damping is presumably improved, however, when the transfer of vibration from the hydraulic lines to the block is facilitated by means of angles, throttles or expansions. For example, good damping is achieved if a hydraulic branched line is connected to a blind hole in the material. Note in the embodiment of FIG. 1 that the ducts are wider than the connected pipes.