Patent Application
20080083382
As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations.
Multiple-cylinder internal combustion engine 10 includes a camshaft 12 disposed within an engine block 14, and may be referred to as a cam-in-block or pushrod engine. Each cylinder 16 (only one of which is shown) includes a reciprocating piston 18 coupled by a connecting rod 20 to a crankshaft (not shown). Cylinder head 22 is secured to engine block 14 and provides conventional intake and exhaust passages (not shown) coupled to corresponding ports (not shown) in cylinder head 22 associated with gas exchange valves 28, which include intake valves 30, 32 and exhaust valves 36, 38. Cylinder head 22 includes conventional hardware such as valve guides, seats, etc. (not shown) associated with operation of gas exchange valves 28. A fuel injector 40 delivers fuel to cylinder 16 in response to a signal provided by an associated engine controller. Although a direct injection engine is illustrated in
Engine 10 includes a valvetrain 50 to control intake of air and/or fuel (for port injected engines) into cylinder 16 and exhaust of combustion gases. Valvetrain 50 includes valves 28, valve springs 52, rocker arms 54, pushrods 56, and lifters 58, sometimes referred to as tappets or cam followers. As best illustrated in
Lifters 82, 84 reciprocate within corresponding bores in engine block 14 driven by lobes 70 of camshaft 12 and include an orientation or anti-rotation feature (not shown), such as a flat or key, to prevent rotation within the bore. Similarly, bucket followers 90, 94 reciprocate within corresponding bores that may be positioned in cylinder head 22, fulcrum 126, and/or a separate carrier (not shown) attached to cylinder head 22 and/or fulcrum 126. Bucket followers 90, 94 also include an anti-rotation feature that allows sliding engagement while preventing rotation within the bore. As described in greater detail with reference to
In operation, lifter 82 contacts lobe 76 of camshaft 12. As camshaft 12 rotates, lobe 76 raises lifter 82 and associated pushrod 88 that exerts corresponding forces on bucket follower 90 and associated rocker arms 100, 102. Each rocker arm 100, 102 pivots in a single plane about an integral ball/socket fulcrum or pivot point 120 with the ball supported by an associated fulcrum 126 secured to cylinder head 22 as known in the art. Rocker arms 100, 102 translate the generally upward motion from pushrod 88 and bucket follower 90 to a generally downward motion to move intake valves 30, 32 against associated springs 52 to open the intake ports. As camshaft 12 continues rotating, lifter 82 follows the profile of lobe 76 and begins a generally downward motion so that the associated springs 52 close intake valves 30, 32. Actuation of exhaust valves 36, 38 proceeds in a similar manner based on the profile of lobe 78, which actuates lifter 84, pushrod 92, bucket follower 94, and rocker arms 106, 108.
As illustrated in
Lifter 58 is a cam follower or tappet that includes a roller 150 mounted for rotation about an axle 152 secured to housing or body 154. A bearing 156 or similar device facilitates rotation of roller 150 about axle 152 when in contact with a corresponding camshaft lobe. Housing 154 reciprocates within a corresponding bore in engine block 14 in response to the camshaft position. Housing 154 includes a cup or socket 158 that engages a corresponding ball or hemispherical surface of pushrod 88. An opposite end of pushrod 88 engages a corresponding socket or recess in bucket follower 90, which includes independently operable hydraulic lash adjustment mechanisms that engage corresponding rocker arms 100, 102.
Bucket follower 90 includes a housing 96 with multiple axial bores having corresponding sleeves 160, 162 fixed therein and each having a closed end and an open end. Each sleeve 160, 162 includes an axially movable plunger 200, 202 disposed therein to define a variable volume high-pressure chamber 170, 172 between the closed end and the plunger. Check valves 174, 176 are disposed within corresponding high pressure chambers 170, 172 to control flow of hydraulic fluid from reservoirs 186, 188 disposed within plungers 166, 168 into chambers 170, 172. Springs 180, 182 act on associated plungers 166, 168 to reduce lash when hydraulic pressure is reduced, such as during the base circle duration, for example.
Bucket follower 90 includes two-part plungers 166, 168 with a lower plunger member or base 200, 202 and an upper plunger member or coupling 204, 206. Upper plunger members 204, 206 may include various geometries to facilitate compliant engagement/coupling with corresponding geometries of rocker arms 100, 102. In the representative embodiment illustrated in
In operation, independent mechanical or hydraulic lash adjusters essentially eliminate any lash or clearance between the valve train components under varying operating and ambient conditions to provide consistent and reliable valve actuations including repeatable valve opening and closing times and peak lift values. As the length of an associated pushrod varies due to temperature variation or wear, hydraulic fluid from a pressurized supply enters bucket follower 90 through a transverse bore 220 in housing 96 and enters reservoirs 186, 188. A small amount of hydraulic fluid passes through check valves 174, 176 into high-pressure chambers 170, 172 moving plungers 166, 168 away from closed end of sleeves 160, 162 to remove any lash or clearance between couplers 204, 206 and corresponding rocker arms 100, 102. As such, the force generated by the cam lobe rotating in contact with roller 150 is transferred through housing 154 and pushrod 88 to housing 96 and sleeves 160, 162, then through the hydraulic fluid within chambers 170, 172 to plungers 166, 168. If pushrod 88 increases in length due to thermal expansion, hydraulic fluid escapes very slowly from chambers 170, 172 between plungers 166, 168 and sleeves 160, 162 to reduce the volume contained within an associated pressure chamber 170 or 172.
The multiple lash adjusters associated with each bucket follower 90 operate independently from one other to more precisely synchronize actuation of multiple valves associated with a single lifter and pushrod as compared to a bridged implementation using a single pushrod and lash adjuster. As such, the individual lash compensation accommodates variations in valve spring force, valve and/or valve seat wear, thermal effects, etc. to provide coupled, synchronous motion for each valve pair. Use of a single pushrod to actuate multiple gas exchange valves for a particular cylinder provides more flexibility in positioning intake/exhaust ports due to the reduced packaging space required. As such, embodiments consistent with the present disclosure provide a pushrod or cam-in-block engine/valvetrain that includes hydraulic lash adjustment at each valve location.
While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
