Patent Application
20080017152
These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which:
The advantages and benefits afforded to a two-step roller finger follower in accordance with the invention may be better appreciated by first considering a prior art two-step roller finger follower.
Referring to
Mechanism 10 comprises a stepped bore 26, preferably cylindrical, in body 14. Latching mechanism 10 includes a piston 28 defining a locking pin biased outwards in bore 26 by a return spring 30 and extending toward slider member 24 to support a latch member 32 which may slide along a slide surface 34 in body 14. Bore 26 is closed by a plug 36, forming a hydraulic chamber 38 in communication via passage 40 with socket 18. Pressurized oil is supplied to chamber 38 in known fashion from the hydraulic lash adjuster upon command from an engine control module to cause piston 28 to become hydraulically biased toward slider member 24. When such biasing occurs and overcomes the counter-bias of return spring 30, latch member 32 is urged axially into latching and locking engagement with latching surface 42.
When the engine control module determines, in known fashion from various engine operating parameters, that a low-lift condition is desired, oil pressure is no longer supplied to chamber 38, allowing return spring 30 to again bias piston 28 and associated latch member 32 away from slider member 24, and slider member 24 is again free to slide in passage 22. As long as oil pressure is withheld from chamber 38, latching mechanism 10 remains disengaged from slider member 24, and assembly 12 functions as a low-lift rocker.
Referring now to
Latching mechanism 110 includes a stepped lock pin 128 defining a lock pin biased outwards in bore 126 by a return spring 130 and having an inner end 129. Bore 126 is closed by a plug 136, forming a hydraulic chamber 138 in communication via passage 140 with socket 118.
In operation, pressurized oil is supplied to chamber 138 in known fashion from the hydraulic lash adjuster upon command from an engine control module to cause lock pin 128 to become hydraulically biased toward the slider member. When such biasing occurs and overcomes the counter-bias of return spring 130, inner end 129 is urged axially into latching and locking engagement with the slider member.
When the engine control module determines, in known fashion from various engine operating parameters, that a low-lift condition is desired, oil pressure is no longer supplied to chamber 138, allowing return spring 130 to again bias lock pin 128 away from the slider member. As long as oil pressure is withheld from chamber 138, latching mechanism 110 remains disengaged from the slider member, and assembly 112 functions as a low-lift rocker.
Between the outer end 150 of lock pin 128 and the outer end 152 of bore 138, at least one formed indentation such as annular groove 154, and preferably a plurality of grooves, is provided in the wall of bore 126 for receiving material deformed from plug 136 when plug 136 is inserted into bore 126 as described below.
Plug 136 is preferably formed of a relatively soft and malleable metal such as aluminum, lead, tin, or alloys thereof, although various polymers also may be suitable in some applications.
In a preferred method for assembling a lock pin latching mechanism in accordance with the invention, a removable positioning stop 156 is disposed accurately at a predetermined location within bore 126. Spring 130 and lock pin 128 are then loaded into bore 126 through open outer end 152 with inner end 129 of lock pin 128 resting near but not against removable stop 156, being held apart therefrom by the uncompressed length of spring 130. Plug 136, having an outer diameter substantially equal to the diameter of bore 126, is pressed into the open outer end 152 of bore 126. Pressing of plug 136 into bore 126 continues as plug face 158 makes contact with end 150 of lock pin 128 and drives inner end 129 of lock pin 128 against stop 156, thereby fixing lock pin 128 in a desired axial location within bore 126 and setting the compressive load of spring 130. Continued pressing of plug 136 after lock pin 128 is arrested by stop 156 causes radial deformation of plug 136 into grooves 154 which thereby prevents any retreat of plug 136 from its pressed position and also serves to ensure a hydraulic seal of plug 136 within bore 126. Assembly stop 156 is then withdrawn, leaving plug 136 properly positioned axially within bore 126 by being pressed against plug face 158 by spring 130.
Note that when plug face 158 and outer end 150 of lock pin 128 are both planar, as shown in
In an alternative embodiment, the plug face may be curved, for example, hemispherical, shown as plug face 158a in
While the invention has been described as relating to a two-step rocker arm assembly, it is understood that it can relate to a deactivating rocker arm assembly whereby, instead of a lower valve lift, a no valve lift is applied.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
