Hydraulic timing chain tensioner assembly

#The present invention relates to a hydraulic timing chain tensioner assembly including a spring-controlled oil pressure relief structure configured to vent highly pressurized oil to reduce maximum loads experienced by the timing chain.

#FIG. 1 shows a typical prior art chain-driven dual overhead cam layout, including a timing chain 10 which is driven by a crankshaft 12 to rotate intake and exhaust cam shafts 14, 16, respectively. The chain 10 is guided by guide assemblies 18, 20, and a chain tensioner assembly 22 is provided for properly tensioning the chain 10. The chain tensioner assembly 22 includes a shoe (or lever) 24 which is pivotable about a fixed pivot point 26, and includes a contact feature (or button) 28. The hydraulic tensioner 30 pushes against the contact feature 28 to tension the chain 10 and to cushion loads of the chain 10 which are applied through the shoe 24.

#A typical hydraulic tensioner includes a spring-loaded piston which bears against the contact feature 28 on the pivoting shoe 24. Engine oil pressure is fed through a one-way ball check valve which applies a pressure-dependent load to the piston and shoe. The tensioner also includes a coarse-stepped ratchet device to prevent total collapse of the tensioner in the absence of oil pressure.

#FIG. 1 shows a plan view of a prior art timing chain layout;

#FIG. 2 shows a schematic cross-sectional view of a hydraulic timing chain tensioner in accordance with a first embodiment of the invention, wherein the valve is closed;

#FIG. 3 shows a schematic cross-sectional view of the hydraulic timing chain tensioner of FIG. 2, wherein the valve is open; and

#Referring to FIGS. 2 and 3, a hydraulic chain tensioner is shown schematically in accordance with a first embodiment of the invention. As shown, the hydraulic tensioner 50 includes a tensioner body 52 having a cylindrical opening 54 formed therein to receive a movable plunger 56. The plunger 56 has a distal end 58 configured to contact a shoe, such as the shoe 24 shown in FIG. 1. The distal end 58 receives a force F from the shoe 24 as a result of tension in the timing chain.

#The tensioner body 52 includes an inlet check valve 60, including a check valve ball 62 and spring 64, which allows one-way flow of oil into the cylindrical opening (or chamber) 54 of the tensioner body 52.

#The plunger 56 includes a valve head portion 66 which is positioned within a plunger sleeve 68, and threadedly engaged with a shoe contact end 70 of the plunger via the threads 72. Alternatively, the threads 72 may be replaced by a stepped diameter and press-fit relationship. The plunger 56, including its valve head portion 66, plunger sleeve 68, shoe contact end 70, and internal spring 74, is movable within the cylindrical opening 54 as a result of forces (F) applied against the distal end 58 by the shoe and chain.