SOUND AND VIBRATION DAMPING APPARATUS

Abstract: Device for the damping of vibrations, blows and noise in hydraulic transmissions, at which oil pipes with varying pressure or pulsating flow in the system each are connected to one through a heavy block of cast iron going duct. The duct through the block has a greater diameter than the connecting pipes. Furthermore the duct is angled.

Description: For driving and controlling of working machines of the type loader, digging machines and the like today in an increasing extent different types of hydraulic transmissions are used. This gives considerable advantages regarding wear, controllability etc. Since the machines however become larger and larger even the pumps required for the hydraulic driving get bigger. For instance cog-wheel pumps are used since they in comparison to their capacity can be fabricated at comparatively low costs. These as well as other pumps however have the disadvantage that they do not deliver an absolutely even flow but pulsations, vibrations and even blows occur, the latter in particular when very high pressures are used. These phenomenas give rise to vibrations as well as noise, which are not only disturbing for the driver and the environment but also increase the strains on the machine. A possible way to solve this problem is of course to provide pulsation equalizers. These are however very expensive in particular since the working pressure is high, that is a couple of hundred kp/cm². In this connection it must also be considered that it for each machine not only is a question of one pump but it is frequently a question of two or three pumps that in this way need to be vibration damped. In the past attempts have of course been made to dampen vibrations in hydraulic systems. In for instance MACHINE DESIGN, 14th June 1973, pages 138-143: J.E. MILLER: "Silencing the noisy hydraulic system" * Page 141 "Wall thickness" * it is stated that the pipe wall thickness is important because the noise intensity is proportional to the amplitude of the vibrating pipe surface. Increased wall thickness adds significant impedance to the transmission path, thus reducing noise. This is however an expensive solution. In MACHINE DESIGN, 17 th September 1970, pages 141-145; J.S. NOSS: "Can you hear the hydraulics system?" it is referred to that ressource in tubing can be climinated by adding a man to the resonating length. In this way it is in particular possible to obtain a damping of some frequent ranges, but the blows in present systems have a very broad frequency spectrum and is therefor very difficult to dampen. In AUTOMATION., vol. 22, no 7, July 1975, pages 46-49; S.J. SKAISTIS et al.: "Nine ways to hush your hydraulic system" is also described different ways of dampning sound in and in particular from hydraulic systems. It also known to use air or gas cushions in a hydraulic system to take up blowlike variations and thus of course also the noise. This is however extremely expensive solutions and it is therefor not used-as much as it should. In view of the above problem the object of the invention is to provide a device for damping vibrations, blows and noise generated in hydraulic transmission system in a simple manner. The object of the invention is solved by connecting one more of the hydraulic pipes of the systems to a through duct to a blinde hole provided in a heavy an solid block of several tenths of kilos, e.g. a block of cast iron or the like so that the heavy block is effetive for damping. In a preferable further development of the invention the duct through the block has a larger diameter than the connecting pipes. Instead or additionally the duct can be angled and of course several ducts can be arranged in the same block. As the invention is very suitable for heavy working machines the block can be mounted directly on the frame of a machine that carries the hydraulic transmission. Preferably the block is fabricated of an unyielding material or one with a high density. The block may also be massive. As is apparent this is a comparatively low cost solution even if the block may weigh several tenth of kilos. In any case the cost will only be a fraction of what is the case with conventional pressure and vibrational equalizers. The physical background of why the damping in accordance with the invention works so well is at the moment of writing not known but practical experiments have confirmed the function. The invention is of course not appliable in all cases where hydraulic pumps and engines are used but for the heavy and great working machines as well as stationary hydraulic machines a hundred kilos in addition or not makes no difference and in some cases there is even a desire to increase the weight of the machine. The block used for sound damping can at the same time constitute a counter weight. Further preferable developments of the invention has been submitted in the subclaims and are apparent from the following description of an embodiment of the invention. In the drawing is shown a cast iron block with a weight of about 130 kilos. From two longitudinal sides that are angled relative each other, holes with a diameter of 24 mm have been bored so that they meet each other and constitute in total four right angled ducts. To these have then been connected 3/4 inch connections and the oil pipes to and from driving and controlling means respectively run through these channels or ducts. The shown block was mounted directly in the frame of the digger loader that previously in the driving cabine had a sound level of 90 dB. The sound level was then measured once again and did now turn out to be 71,6 dB, that is a considerable damping. It should in this connection also be mentioned that the driving cabine itself was fastened directly in the frame of the machine. Even with the block lying loosely on the ground but connected to the machinery damping was obtained. The different ducts were connected to different controling and driving means on the machine and the damping seemed to be just as good for respective part of noice or part vibrations in respective pipes independent of if they coincided with each other or not. The block could with other words simultaneously damp several different vibrations that also could have different pressure levels. In other words the block can replace a number of expensive pressure equalizers and it need perhaps not be mentioned that the wear resistance of the block is infinitely superior to that of the pressure equalizers. In the tested case the block was placed in the front end of the machine and it is presumably conceivable that the block in some cases constitutes a swinging unit generating vibrations that in turn can be transmitted to the frame again in such a way that these can be used to annihilate that generated of the machinery. Preferably the block is heavy so that its inertia forces will become great in comparison to the hydraulic forces and vibrations that are to be damped. Furthermore the material of the block is great, high density and preferably itself sound and vibration damping respectively. As have been mentioned above a good function has been achieved with angled ducts. It is possibly also conceivable that the effect may be improved by further angles respectively a longer passage for the duct in the block. If a material with a lower density is used good effects can perhaps be achieved with a larger block. In the shown embodiment only one block has been used for all the pipes or connections that need to be vibrationaly damped. It is of course also conceivable 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. Perhaps however the function is improved if so to say the vibration transfer from the hydraulic pipe to the material of the block is faciliated by disruption in the hydraulic line in one way or the other either by means of angles or throttles. For instance a good damping is also achieved if a hydraulic branched pipe is connected to a blind hole in the material.

Claims: 1. A device for damping vibrations, blows and noise generated in a hydraulic transmission system, characterized in that one or more of the hydraulic pipes of the system are connected to a through duct or a blind hole provided in a heavy and solid block of several tenth of kilos, e.g. a block of cast iron or the like, so that the heavy block is effective for damping. 2. Device according to claim 1, characterized in that the duct through the block has a larger diameter than the connecting pipes. 3. Device according to any of the previous claims characterized in that the duct is angled. 4. Device according to any of the previous claims characterized in that several ducts are arranged in the same block. 5. Device according to any of the previous claims characterized in that the block is mounted directly on the frame of a machine the hydraulic transmission of which is to be sound damped. 6. Device according to any of the previous claims characterized in that the block is fabricated of an unyielding material or one with a high density. 7. Device according to any of the previous claims characterized in that the block is massive.

Inventors: PERSSON, ELERTH
Applicants: EC-MASKIN AB
Application year: 1989
Main classification: F15B21
IPC codes: F15B21