AU2010233048A1

AU2010233048A1 - Cushioned hydraulic piston

Info

Publication number: AU2010233048A1
Application number: AU2010233048A
Authority: AU
Inventors: Michael Burke
Original assignee: STERLING HYDRAULICS Pty Ltd
Current assignee: STERLING HYDRAULICS Pty Ltd
Priority date: 2009-10-16
Filing date: 2010-10-14
Publication date: 2011-05-12

Description

1 CUSHIONED HYDRAULIC PISTON FIELD OF THE INVENTION 5 This invention relates to the cushioning of pistons in hydraulic cylinders to reduce clunking impact at the limit of their travel. BACKGROUND OF THE INVENTION 10 Hydraulic cylinders are used to lift garbage bins in order to empty the garbage into collection vehicles for transport to dump sites. The bins are picked up by arms connected to the cylinders and the latter lift and tilt the bin so that the rubbish falls out of the bin into the vehicle. 15 However at the top of the lifting cycle the bin tilts over the center of gravity of the combined system and the pistons accelerate under the inverted load and impact the end of the cylinders. This causes a loud clunking which is a noise nuisance and places stress on the whole lifting mechanism. 20 There are a number of possible approaches to cushioning this impact and thereby reducing noise and stress. One approach is to use valves which regulate the input to and output from the cylinder of hydraulic fluid. A valve controller is programmed to provide maximum hydraulic pressure during the initial lift but then to reverse the pressure during the emptying phase to cushion the final travel and 25 to return the bin to the ground. However such electronic control is sophisticated and costly and requires precise adjustment to achieve the desired result. OBJECT OF THE INVENTION 30 It is therefore an object of the present invention to provide a simple mechanism for cushioning the pistons of hydraulic cylinders at the limit of their travel.

2 STATEMENT OF THE INVENTION According to the present invention a hydraulic piston cushioning mechanism comprises a mechanical compression device inserted between the two segments 5 of the piston in a hydraulic cylinder which which absorbs the forces when the piston reaches the end of the stroke of the cylinder. Preferably the mechanism consists of one or more helical springs. 10 Alternatively the mechanism consists of one or more split spring washers. Alternatively the mechanism consists of one or more disc spring washers. Preferably two or more adjoining disc spring washers are series mounted so that 15 they nest in a compact stack. Alternatively two or more pair of spring disc washers are parallel to maximize compressive resistance. 20 BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention is now described by way of example only with reference to the accompanying drawings in which: 25 Fig 1 is an external elevation of an hydraulic cylinder Fig 2 is a vertical cross section through the mid line of the cylinder of Fig 1 Fig 3 is an elevation of a spring disc washer and Fig 4 is a cross section through the mid line of the washer of Fig 3. 30 3 DETAILED DESCRIPTION OF THE INVENTION Fig 1 is an external view of a double acting hydraulic cylinder 1, that is one in which the piston can be driven in either direction. Outer cylinder 1 has an integral 5 end 2 with a hole 3 for coupling to a mount and internal piston rod 4 has an integral ring end 5 for coupling to the device to be driven. The internal construction of the cylinder revealed in Fig 2 shows piston rod 4 with attached piston sliding within annular seals 6 located in internal grooves at the 10 open end of cylinder 1. Accordingly when hydraulic fluid (not shown) is pumped into cylinder 1 via inlet 7, the piston attached to rod 4 is driven towards end 2. In the absence of any cushioning mechanism end 8 of piston rod 4 impacts end 2 of cylinder 1. Reversal of piston rod 4 is achieved by pumping hydraulic fluid (not shown) in the opposite direction through inlet 9. 15 When a standard hydraulic cylinder without any cushioning mechanism is used for lifting garbage bins as discussed above, the impact of the piston attached to rod 4 against end 2 of cylinder 1 causes a clunking noise and stressing of the whole mechanism. But according to the present invention cushioning mechanism 20 10 is provided at the internal end of piston rod 4 to cushion impact thereby reducing noise and acting as a shock absorber. Mechanism 10 can be, for example, a helical or coil spring fitting between a reduced section of piston rod 4 and outer cylinder 1 or a stack of split spring 25 washers in the same space. Accordingly when the piston approaches end 2 of cylinder 1 the helical spring or split spring washers start to absorb the driving force of the hydraulic fluid thereby cushioning the limit of travel of the piston attached to rod 4. 30 However both spring washers and helical springs of the dimensions allowed by the restricted space between the piston segments and cylinder 1 have relatively low compression resistance to provide impact cushioning. In particular, when a 4 heavily loaded garbage bin passes over dead centre during the lifting cycle the force on the piston is high and a corresponding high compression resistance is required to prevent severe impact. 5 The present inventor has found that the most efficient cushioning mechanism is provided by a stack of disc spring washers, one of which is shown in Figs 3 and 4. Disc spring washer 11 has a slightly concave (or convex from the opposite side) face and is made of high tensile spring steel. Accordingly a stack of washers 11 provides a highly effective cushioning mechanism 10 for hydraulic 10 cylinders in applications where severe impact occurs at the limit of travel of the piston. Further the compressive resistance of mechanism 10 can be adjusted by varying the number and size of the disc spring washers used in the stack and also by 15 varying their orientation to each other. That is, two adjoining washers 11 can nest with their concave faces in the same orientation (series mounting) or they can oppose with their concave or convex faces in opposite orientation (parallel mounting). Accordingly a highly variable resistive force can be achieved from a minimum where all washers are in series to a maximum where adjacent washers 20 are in parallel. ADVANTAGES It will be obvious that the spring disc washer stack provides a highly variable 25 cushioning mechanism which is easily adjusted for a wide range of impact loadings from very high to quite low. It is cheaper than an electronically controlled hydraulic cushioning system and does not require sophisticated adjustment as in the case of the latter. The latter also suffers from over heating and break down of hydraulic fluid under high impact pressures such as are experienced in the 30 garbage truck application.

5 VARIATIONS It will be realized that the foregoing has been given by way of illustrative example only and that all other modifications and variations as would be apparent to 5 persons skilled in the art including mechanical equivalents are deemed to fall within the broad scope and ambit of the invention as herein set forth. Throughout the description and claims of this specification the words "comprise" and variations of that word such as "comprises" and "comprising" are not 10 intended to exclude other additives components integers or steps. 15 20 25 30

Claims

1. A hydraulic piston cushioning mechanism comprises a mechanical compression device inserted between the piston and the cylinder which limits the 5 travel of the piston.

2. The mechanism of claim 1 which consists of one or more helical springs.

3. The mechanism of claim 1 which consists of one or more split spring washers. 10

4. The mechanism of claim 1 which consists of one or more disc spring washers.

5. The mechanism of claim 4 in which the two or more adjoining washers are series mounted so that they nest in a compact stack. 15

6. The mechanism of claim 4 in which two or more pair of washers are parallel mounted to maximize compressive resistance. 20 25 30