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Side loading is the most-common damage observed on master-cylinder field returns and can lead to premature product failure. In an effort to improve master-cylinder performance, several samples of existing and new designs were tested.
Under ideal conditions, particularly linear loading, it was shown that existing master-cylinder design is sufficient. However, subsequent testing under side loading showed that the current design is susceptible to damage. We found that the major cause of damage from side loading is the steel rod wearing against the aluminum cylinder bore. The wear patterns created in testing are quite similar to those observed on field returns. The design and testing of a nylon cap on the rod end showed that side-loading damage can be virtually eliminated. Implementing this solution will result in a product with a longer life.
Master cylinders are a common hydraulic component used in brake and clutch systems to generate hydraulic pressure from a nonhydraulic pressure source. The master cylinders tested in this experiment are generally used in a fail-safe brake system on forklift trucks. In such a system, brakes are spring applied and released by depressing the brake pedal.
A master cylinder for this application typically is comprised of a cast-aluminum body with a machined cylindrical bore and various ports, Figure 1. A piston assembly is inserted into the body and is actuated by applying compressive force to a steel push rod. Push-rod diameter, cylinder bore, and surface finish are critical for the piston to generate pressure without leaking. The master cylinder push rod is attached to the body via a washer and snap ring. The push rod is designed to allow deflection of +-5 degrees from the main axis of the part. This allows for linkages and mounting configurations that are not colinear with the cylinder. When the push rod is not colinear with the cylinder bore, side loading , Figure 2, is generated.
The problem of side loading
Although most master cylinders are designed to permit some side loading, any side loading is...