Common modes of vehicular transportation may include internal combustion engines that generate drive torque based on a two or four stroke cycle. These internal combustion engines typically have a poppet valve arrangement to facilitate the induction and subsequent exhaust of combusted air and fuel.
For example, engines can operate based on the Otto air-standard thermodynamic cycle with real working fluids. The engine includes a poppet valve system coupled to a slider crank mechanism that forms variable volume in the rotational domain. A piston is stationary at the top of its travel (Top Dead Center—TDC) and begins to travel downward. An intake valve is selectively opened such that air can be inducted into the cylinder by the downwardly moving piston. During the induction process the inducted air mixes with a predetermined amount of fuel to form a combustible mixture. The intake valve closes at the bottom of the piston's cyclical travel (Bottom Dead Center—BDC). The piston reverses direction and then travels upward. The fuel-air mixture is compressed within the cylinders and is combusted when appropriate. Once at TDC, the piston reverses direction. Pressure rise during the quasi-fixed volume combustion process acts over the area of the piston and creates a differential force (this can be described as boundary work). This force is transmitted via the slider to the cranktrain. When coupled to a moment arm, this force forms motive torque. Once at BDC the piston stops and reverses direction. An exhaust valve is selectively opened (specifically the timing and lift) to allow the combustion products to be expelled from the cylinders by the upwardly moving piston. Once at TDC, the exhaust valve closes and the intake valve opens. The piston reverses direction and the mechanical cycle begins anew.
The rotation of a camshaft regulates the opening and closing of the intake and exhaust valves. On a multi-cylinder engine, the camshaft includes a plurality of cam lobes (typically one for each valve) that are affixed to the camshaft. The profiles of the cam lobes determine the profile of the valve lift and are kinematic-ally related by the geometry of the valvetrain. Important parameters associated with valve lift profiles include the period that the valve is open (duration) as well as the magnitude that the valve opens (lift). In the mechanical configuration described herein, these two parameters have significant influence on the gas exchange processes of ICEs.
Manufacturers typically incorporate a fixed valve lift schedule for the engine due to design complexity, cost, and durability constraints. From a gas exchange process perspective, a fixed valve lift schedule may not be optimal for all engine operating conditions encountered. For example, during steady-state highway travel a vehicle may typically require a motive torque that is significantly less than the full capacity of the powertrain. In typical fixed duration and lift valvetrain systems, this demanded load is usually meet via throttling of the engine. When a single (exhaust and intake) valve profile (duration and lift) are chosen for a particular powertrain, compromises are made to provide the best overall (based on load regimes) performance. Performance metrics may include specific torque and or fuel consumption. At these part-load operating conditions a significant amount of work is required to throttle the engine to insure that the proper amount of air into the engine to meet the desired road load.
A variable lift valvetrain can be described as one that has the capability of selecting multiple profiles (with variable duration and lift capability) associated with each intake and or exhaust valve(s). These profiles may be optimized for various load regimes and are specifically chosen to minimize the amount of work required for the gas exchange process and or to support multiple combustion modes.
A discrete variable valve lift (DWL) system enables the engine to operate on more than one intake and or exhaust valve lift schedule. More specifically, a DVVL engine system switches between different valve lift schedules based on the desired load of the engine. This has been shown to minimize pumping losses of the engine and or to support multiple combustion modes.
A malfunction of a DVVL engine system may occur when a component of the DVVL system fails to change to a different valve schedule on command. For example, a malfunction may occur when a switchable roller finger follower (SRFF) of the DVVL system switches from a low-lift (LL) valve schedule to a high-lift (HL) valve schedule thus causing one or more of the valves to fail to switch from the LL schedule to the HL schedule.