Patent Application
20070119397
1. Field of the Invention.
The present invention relates to multiple cylinder internal combustion engines having intake/exhaust valves operated by a camshaft positioned in an engine block with an associated valvetrain.
2. Background Art.
Conventional internal combustion engines use a camshaft-driven valvetrain to operate intake and exhaust valves that control the exchange of gases in the combustion chambers formed between the engine block and cylinder head. Engines are often categorized by the location of the camshaft relative to the valves, with overhead cam valvetrains driven by a camshaft in the cylinder head over the valves, and pushrod valvetrains or “cam-in-block” valvetrains having the camshaft located in the engine block with the valves operated using pushrods and rocker arms.
Current four-valve-per-cylinder pushrod engines include two intake valves and two exhaust valves for each cylinder. Each pair of valves is operated in tandem by a bridged valvetrain that includes a camshaft driven cam follower (also referred to as a tappet or lifter) connected by a single pushrod to a rocker arm that drives a bridge coupled to the pair of valves (intake or exhaust). The bridged valvetrain is a cost-efficient design that achieves acceptable performance for many applications, although operation of the two bridged valves is not precisely synchronized because the force exerted on the bridge can not be perfectly balanced between the valves, the valves may have slightly different spring forces, and the valve components may experience slightly different wear. This may result in one valve opening late and/or at valve closure, one valve may seat first causing the other valve to seat late with a higher than intended velocity. In addition, valve stem tips are edge loaded by the bridge with higher stresses resulting in higher rates of wear and potential noise, vibration, and harshness (NVH) concerns. While single overhead cam (SOHC) and dual overhead cam (DOHC) systems have independently controlled valves to address some of these issues, the SOHC and DOHC systems are significantly more expensive and have large package width relative to a cam-in-block design.
A multiple cylinder internal combustion engine having a camshaft-driven valvetrain with a camshaft disposed within an engine block includes at least two valves operated by a common camshaft lobe and an associated cam follower coupled to at least two pushrods and rocker arms to actuate the at least two valves.
Embodiments of the present invention include a lifter having independent dual hydraulic lash adjusters for driving two valves associated with a single cylinder in tandem. Single plane stamped-steel rocker arms facilitate packaging of two followers and four pushrods per cylinder for four valve per cylinder engine applications.
A method for actuating at least two gas exchange valves associated with a single cylinder in a multiple cylinder internal combustion engine having a camshaft disposed within an engine block according to the present invention includes actuating the at least two gas exchange valves substantially simultaneously using at least two corresponding pushrods and rocker arms coupled to a common cam follower. The common cam follower may independently adjust lash associated with each pushrod and rocker arm.
The present invention provides a number of advantages. For example, the present invention provides embodiments with a dedicated lash adjuster for each valve associated with a particular lifter to compensate for thermal, wear, and tolerance effects and to insure that the valve motion remains very close to the design intent throughout the life of the engine. A common lifter for tandem valve operation with independent lash adjusters according to the present invention should reduce or eliminate noise, vibration, and harshness associated with valve pairs failing to open or close together and/or having different or higher than intended seating velocities. The present invention provides coupled, synchronous motion for each valve pair and allows individual compensation for valve spring force differences, differences in valve/seat wear, and differences due to the rocker arm force not being applied at the mid-point between valve centerlines which is liable to occur using a valve bridge design, for example. In addition, the present invention eliminates wear mechanisms associated with bridged valvetrain implementations, such as pitching and rolling of the bridge resulting in increased stresses on the bridge/rocker arm interface resulting in undesirable contact between the bridge and valve stem tips. Use of single plane stamped steel rocker arms having a ball/socket pivot according to the present invention facilitate packaging while reducing moving mass and increasing valve gear natural frequency. The ball/socket pivot point can be placed so that one rocker arm is significantly longer than the other rocker arm of a valve pair, but the rocker ratios are substantially identical to provide substantially identical valve open, close, and peak lift points.
The above advantages and other advantages and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.
As those of ordinary skill in the art will understand, various features of the present invention as 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 of the present invention 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 the present invention 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 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 in cylinder head 22(not shown) 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
In operation, lifter 82 contacts lobe 76 of camshaft 12. As camshaft 12 rotates, lobe 76 raises lifter 82 and associated pushrods 88, 90 that exert corresponding forces on 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 pushrods 88, 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.
As illustrated in
As best illustrated in the top view of a representative valvetrain 50 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 includes axial bores with 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 166, 168 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 when the engine is shut off, for example.
Lifter 58 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 include a generally concave hemispherical geometry forming a socket for coupling to a corresponding pushrod having a generally convex hemispherical end or ball-shaped end. Lifter 58′ has two-part plungers 166′, 168′ with upper members or couplers 210, 212 having generally convex hemispherical or ball-shaped ends adapted for coupling to corresponding pushrods having concave hemispherical ends forming a socket. As shown 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 lifter 58 through a transverse bore 220 in housing 154 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 pushrods and rocker arms. As such, the force generated by the cam lobe rotating in contact with roller 150 is transferred through housing 154 to sleeves 160, 162 and through the hydraulic fluid within chambers 170, 172 to plungers 166, 168. If the pushrod 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 lash adjusters associated with each lifter operate independently from one other so that the present invention can more precisely synchronize actuation of valves associated with the lifter 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.
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.
