Self-contained hydraulic lash adjuster with pressurizing diaphragm

A hydraulic lash adjuster of the self-contained type including a body defining a cylinder with a closed end, a hollow plunger internally defining a fluid reservoir, the plunger having side walls slidably fitted in the cylinder and an end wall cooperating with the cylinder closed end to define a chamber for fluid in thrust transmitting relation between the cylinder and plunger, said plunger end wall having a one-way passage therethrough for fluid flow from the reservoir to the camber, said plunger side walls having a port extending therethrough intermediate their ends for returning fluid to the reservoir, said fluid having escaped externally of the plunger from the chamber, the plunger side walls being sealed to the cylinder beyond the port relative to the body closed end, said plunger further defining an inner cylinder open toward the reservoir, a piston slidable in the inner cylinder and a spring urging the piston toward the reservoir with a force effective to raise the reservoir pressure substantially above ambient pressure, and the improvement comprising

• a flexible diaphragm extending across the hollow plunger between the piston and the reservoir and sealingly mounted in the side walls to define a sealing wall with a central portion movable to vary the volume of the reservoir, the piston engaging said central portion of the diaphragm and being shaped to partially support the diaphragm against the force of pressure in the reservoir.