The present invention relates to high pressure linear hydraulic cylinders, and-more particularly, to such cylinders having an improved main piston seal and wear ring assembly.
Many hydraulic cylinders of the type to which the present invention relates are used on agricultural vehicles. One particular use is in connection with implement depth control systems wherein there are typically two hydraulic cylinders, connected hydraulically in series, to control the depth (relative to the ground) of the particular element, such as a plow or disc.
The hydraulic cylinders used in implement depth control systems are typically of the single rod type, such that the fluid displacement of the cylinder is different when the cylinder is being extended than when the cylinder is being retracted. As a result, if there is internal leakage in one of the cylinders, past the piston, the result is that one cylinder retracts slightly, while the other cylinder extends an approximately equal amount. This causes erratic and inconsistent depth control across the width of the implement.
In reviewing a number of the cylinders from systems in which erratic and inconsistent depth control occurred, what was observed was a pattern of scratches or scuffing on the cylindrical, internal surface of the cylinder barrel, with most of the scratch pattern coinciding with the piston wear ring. As one step in the development of the present invention, it was hypothesized that the scratch pattern was the result of contamination particles lodging between the wear ring and the cylinder barrel, and traveling with the wear ring (actually embedded in the wear ring), and thus causing the scratch pattern, and resulting in leakage.