Patent Application
20130146008
The present disclosure relates to a rocker arm for an internal combustion engine and, more particularly, to a type two rocker arm that facilitates cylinder deactivation or two-step valve lift.
Cylinder deactivation and variable valve lift techniques are used to vary the power characteristics of internal combustion engines. Engines with cylinder deactivation capabilities are fuel efficient while still providing additional power when necessary. Improved fuel economy is achieved by deactivating a number of cylinders when the engine is under lower loads, effectively decreasing the displacement of the engine during these times. For example, four cylinders of an eight cylinder engine can be deactivated to halve the engine displacement and realize the improved fuel economy of a smaller displacement four cylinder engine. When larger loads are present, such as during periods of acceleration or traveling up hill, all eight cylinders are used to provide ample power until the higher load conditions subside.
Rather than entirely deactivating cylinders, variable valve lift systems allow the power characteristics of an engine to be changed during driving while continuing to utilize all of the cylinders. These systems can also provide improved fuel economy and may be used to provide other benefits in situations where it would be beneficial to dynamically change engine power characteristics. It would be beneficial to improve current cylinder deactivation and variable valve lift techniques.
The present disclosure provides a new rocker arm which facilitates either cylinder deactivation or two-step valve actuation.
In one form, the present disclosure provides a rocker arm apparatus comprising at least one inner arm portion and at least one outer arm portion. The at least one inner arm portion is pivotally connected to the at least one outer arm portion by a shaft located near a valve end of the rocker arm such that the at least one inner arm portion can rotate relative to the at least one outer arm portion.
In another form, the present disclosure provides a rocker arm apparatus comprising at least one generally U-shaped outer arm portion including a first outer arm segment and a second outer arm segment. The rocker arm apparatus further comprises at least one inner arm portion pivotally attached to the first and second outer arm segments near a valve end of the rocker arm apparatus, the at least one inner arm portion positioned between the first and second outer arm segments. Additionally the rocker arm apparatus comprises a first bearing attached to the at least one inner arm portion to provide rolling contact with a lobe of a cam shaft, a second bearing attached to the first outer arm segment, a third bearing attached to the second outer arm segment, and a lost motion spring positioned between the at least one inner arm portion and the at least one outer arm portion near a hydraulic lash adjuster end of the rocker arm apparatus. The lost motion spring resists rotation of the at least one inner arm portion relative to the at least one outer arm portion.
Further areas of applicability of the present disclosure will become apparent from the detailed description and claims provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the invention, its application or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention.
The present disclosure provides a new rocker arm, which provides either cylinder deactivation or two-step valve actuation. The disclosed rocker arm actuates two valves simultaneously and uses rollers in contact with the cam rather than sliding surfaces. Additionally, the disclosed rocker arm utilizes a hydraulic system to activate and deactivate valves in a cylinder deactivation system or to switch between valve actuation profiles in a variable valve lift system.
Referring now to the drawings,
As seen in
Outer arm section 200 includes two holes 202 in which shaft 500 is situated, pivotally connecting outer arm section 200 to inner arm section 100. Outer arm section 200 also includes two bearing mounting sections 212, each containing holes 204 in which outer arm bearings 404 are mounted. Outer arm section 200 further includes blind holes 206 near the HLA end. Holes 206 are positioned such that when inner arm section 100 is rotated relative to outer arm section 200 holes 206 can be aligned with holes 106.
Outer arm section 200 also includes outer arm spring engagement element 230 at the HLA end. Outer arm spring engagement element 230 includes a central cylindrical pin 232 extending upward from a bottom portion to engage lost motion spring 400. Outer arm section 200 also includes two valve abutment sections 214 at the valve end. The valve abutment sections 214 have a curved profile, as seen in
The rocker arm assembly 10 includes a hydraulic latch-up system for connecting and disconnecting the inner arm portion 100 to and from the outer arm portion 200 near the HLA end. As discussed above, each hole 106 in the inner arm portion 100 can be aligned to a corresponding hole 206 in the outer arm portion 200. Pistons 302 and biasing springs 304 are situated in the space formed by corresponding holes 106 and 206. Hydraulic fluid passages 218 (best seen in
As seen in
The operation of the rocker arm assembly 10 is now discussed. In a first state, biasing springs 304 bias pistons 302 such that they are located partially in holes 206 and partially in holes 106, effectively locking the inner arm portion 100 to the outer arm portion 200 near the HLA end. In this first state, the inner arm portion 100 cannot rotate relative to the outer arm portion 200 and the rocker arm assembly 10 acts as a unitary structure. In this first state, the rocker arm assembly 10 provides regular valve lift similar to a conventional rocker arm. When the elongated portion of cam lobe 32 contacts inner arm bearing 402, the rocker arm assembly 10 is rotated and valves 20 are forced open. During the valve lift event, base circles 34, which generally interact with outer arm bearings 404, lose contact with the outer arm bearings 404. As the elongated portion of cam lobe 32 rotates past inner arm bearing 402, valve springs (not shown) close the valves 20 and rotate the rocker arm assembly 10. As the rocker arm assembly 10 is rotated back into the closed valve position, base circles 34 regain contact with outer arm bearings 404.
In order to deactivate a cylinder or to provide alternative valve lift, hydraulic pressure is provided via pass-through HLAs 40 to hydraulic fluid passages 218. This exerts a force on pistons 302, compressing biasing springs 304. Sufficient pressure is applied to move pistons 302 such that they are located entirely within holes 106. In this second state, inner arm portion 100 is able to rotate relative to outer arm portion 200. In the second state, as the elongated portion of cam lobe 32 rotates past inner arm bearing 402 the valves 20 are not opened. Rather, inner arm portion 100 is rotated relative to outer arm portion 200 about shaft 500 compressing lost motion spring 400. As the elongated portion of cam lobe 32 rotates past inner arm bearing 402, inner arm portion 100 is rotated back to its original position by lost motion spring 400. To achieve such relative rotation, lost motion spring 400 has a lower spring constant than the combined spring constant of the valve springs (not shown) associated with valves 20. Unlike the first state discussed above, when the cylinder is deactivated, base circles 34 stay in contact with outer arm bearing 404 throughout the entire cam rotation.
Although cylinder deactivation is described above, it is also possible to achieve reduced valve lift with the disclosed rocker arm assembly 10. In order to produce a reduced valve lift, as opposed to full cylinder deactivation, base circles 34 are replaced with reduced lift lobes (not shown). Similar to base circles 34, the reduced lift lobes ride on outer arm bearings 404. In the second state, as discussed above, the elongated portion of cam lobe 32 causes the inner arm portion 100 to rotate relative to the outer arm portion 200 compressing lost motion spring 400. During reduced valve lift, rather than staying stationary due to base circles 34, outer arm portion 200 is rotated due to the interaction between the reduced lift lobes and outer arm bearings 404 thus opening valves 20. Lost motion spring 400 and the valve springs (not shown) act together as the elongated portion of the cam lobe 32 and the reduced lift lobes rotate past the inner and outer arm bearing 402, 404 to rotate the inner and outer rocker arm portions 100, 200 back into their closed valve position.
Disengaging inner arm portion 100 from outer arm portion 200, by applying hydraulic pressure to pistons 302 as discussed above, effectively allows outer arm portion 200 to operate independently of inner arm portion 100. This negates any valve event normally caused by cam lobes 32 and allows for either full cylinder deactivation by use of base circles 34 or reduced valve lift by including reduced lift lobes in place of base circles 34.
Various techniques are available to control the transition between traditional valve lift and cylinder deactivation or reduced valve lift. Generally the transition will be automatically actuated by the engine control unit based on current operating conditions. It is also possible to change valve lift states based on direct input, such as a push button or switch, from a vehicle operator.
