Every aspect of an engine is a compromise: torque for horsepower, efficiency for emissions, performance for fuel economy, compression for octane tolerance. During the evolution of the internal combustion engine, we have learned to limit this give-and-take with variable-runner-length intake manifolds, high-flow multivalve cylinder heads, electronic engine controllers, and variable valve timing. While this technology has effectively removed many of the limitations that were thought of as inherent to the internal combustion engine, valve timing still remains a problem.
Without question, the current crop of engine-management-controlled valve event strategies have improved matters, but they are still flawed by the physical limitations of the camshaft as the mechanism to operate the poppet valve. Even with separate intake and exhaust cams, the amount of influence imparted on the opening ramp has the same impact on the closing side, forcing camshaft designers to contend with only one-half of the benefit of early opening or closing. Current layouts situate the camshafts in relation to the lobe center, while others include variable lift by employing a dual-lobed cam and controlling oil pressure to the follower to engage the higher-lift strategy, like Honda's VTEC system. This leads to complication and cost, and the phasing mechanism alone requires a sophisticated transmission to accomplish the task.
With the quest for increased performance unabated, a totally new approach is necessary if the valvetrain is to enter the 21st century. Methods have included rotary valves in lieu of camshafts and poppet valves, electronic and pneumatic actuators, as well as the reassessment of the reed valves indigenous to two-stroke technology. In light of the criteria for cost, manufacturing ease, longevity, and overall efficiency, all these theories fall short.
IVC Systems of Renfrew, Pennsylvania, believed there was a better way. The company has developed an ingenious valve-timing mechanism (U.S. Patent 5,463,987) that replaces the rocker arm or cam follower with a simple four-part device that employs linear motion to operate the valves. The IVC system works on the rudimentary principle of an inclined plane and offers infinitely variable valve events that are adjustable and independent of one another.
Before exploring the virtues of the IVC system, we must first acknowledge the effect that valve events have on the internal combustion engine. It is common practice to degree-in the camshaft to determine the valve events in crank-angle degrees which can be referenced from the center of the intake lobe. Decreasing the number of crank-angle degrees to reach the intake centerline is considered advancing the camshaft; a longer rotation to arrive at the same point is identified as retarding the camshaft. When the camshaft is installed at the intake center-line, it is considered straight up. Advancing the cam increases low-speed power at the expense of high-speed performance; conversely, retarded positioning undermines low-rpm torque but increases efficiency at high rpm. Duration is the amount of time the valves are open from a specified lift point and back down to that same value, allowing the cylinders to fill with the air/fuel charge. The fill rate is then measured in terms of volumetric efficiency (VE).
Additional design criteria includes valve lift and overlap (the period of time both valves are open), along with opening and closing rates. Camshafts ground with different valve events are used to increase power but foster power losses at a certain rpm level. Witness the large camshaft that produces impressive power at high rpm but has virtually no torque down low. The rough idle, high hydrocarbon emissions from overlap, and ancillary changes to the vehicle, such as a loose torque converter and steep final drive ratio, make such an engine marginally appealing.
Changes in rocker-arm ratios are also used to multiply the camshaft valve event and increase the lift of the valve while accelerating its opening rate. By changing the mechanical advantage imparted by rocker ratios (numerically higher), the valve is lifted further at the same number of crankangle degrees. Obviously, this is extremely important on the OE level: The power issue is always countermanded by concerns for emissions and fuel economy. The camshaft designer must take all of the above factors into consideration when developing a profile, trying to limit the compromises to the engine while serving many masters.
To understand the technology behind the IVC system, we need to review the effects of valve timing. The following theories are based on engineering facts and are not specific to any particular engine. Additional areas, such as intake-manifold design, compression ratio, flame-expansion (burn) rates, combustion-chamber shape, and so on, all impact valve events and are used to either complement or diminish performance.
To avoid a dip in cylinder pressure early in the intake stroke, intake-valve opening (IVO) typically occurs 10-25 degrees before TDC. Intake-valve closing (IVC) usually occurs 40-60 degrees after BDC to provide more time for the bore to fill when cylinder pressure is less than intake-manifold pressure. IVC is one of the dominant factors responsible for moving the powerband down (advanced) or to a higher speed (retarded) when changing cam phasing.
Exhaust-valve opening (EVO) occurs at 50-60 degrees before BDC, well before the completion of the expansion (power) stroke, so that blowdown can help to evacuate residual gases. The intention is to reduce cylinder pressure as close to exhaust-manifold pressure as soon as possible, and over the full range of engine speed. Since it determines the effectiveness of the expansion ratio, the timing of the EVO also affects cycle efficiency. Exhaust-valve closing (EVC) terminates the exhaust stroke and encompasses the pumping action of the piston as it sweeps up toward TDC to remove residual gases that were not purged during blowdown.
The EVC also determines overlap. It is typical for EVC to occur 8-20 degrees after TDC. At idle and light load, it regulates the amount of exhaust gases that flow back into the combustion chamber through the exhaust valve and influences the area that remains to be filled with combustible mixture, as well as the amount of vacuum in the intake manifold. At high engine speed, EVC regulates the amount of burned gases that are evacuated. Ideally, EVC timing should occur sufficiently past TDC so that cylinder pressure does not rise near the end of the exhaust stroke. Late EVC favors high power production at the expense of low-speed torque and idle quality.
When defining the lift curve of a lobe, it is desirable to open a valve as quickly as possible. The maximum lift of the valve is usually determined by the flow capacity of the cylinder head, the design of the valve, and properties of the valvespring. On a production engine, it is desirable to have maximum valve lift at approximately 12 percent of the cylinder-bore diameter. Since a valve spends more time traversing its lift range than at maximum lift, cylinder-head flow capabilities at low- to midlift influence VE more than maximum lift flow.
A problem arises when trying to increase velocity, which requires greater valvespring pressure and advanced roller-tappet profiles to keep the lifter in contact with the steep angle of the ramp. In theory, if we could open the valve quicker, we would not have to open it as far to achieve the same amount of airflow. It is a common design practice to work with an averaging method and open the valve beyond the airflow stall point of the head to increase the average time that the valve stays open.
Most current cylinder-head designs incorporate mixture motion as a method to increase octane tolerance and speed up the burn rate. Many methods are employed to achieve swirl motion, and it is usually easiest to create at low valve lifts due to valve shrouding. A control system that varies valve lift could then be employed to limit valve travel at low engine speeds, keeping the valve in a region where it will increase swirl. The higher swirl rates will then burn quicker and allow for leaner air/fuel ratios during light load.
Overlap becomes a major concern due to its positive and negative influence on engine performance, all of which are dependent on rpm. Used as an aid to evacuate the cylinder at high rpm, overlap creates inefficient combustion at low speeds due to reversion that acts similar to an internal EGR. Ideally, overlap would be absent at low speeds but present as a function of the rise in rpm.
Steady-state applications such as industrial or lawn-mower engines, are engineered to work efficiently in a very narrow rpm window. The design of the camshaft, intake manifold, and fuel system is much simpler due to the controlled speed in which they will function. An automobile engine, of course, is a completely different story. The need for varying intake and exhaust events to deal with transient acceleration and deceleration, idle, and maximum power and rpm, is painfully apparent.
Obviously, we can't change cam grinds for every driving situation, but if we could, let's identify the most desirable features. We would want to advance the cam for better cranking vacuum, and we would also like to decrease lift, eliminate overlap, and possibly even create a separation from overlap. Separation from overlap occurs when the exhaust valve is closed, the crank turns, and the intake valve is then beginning to open. The IVC system has run a single-cylinder engine with as much as 35 crank degrees of separation to lower idle emissions and rpm. This could be defined as negative overlap. Idle-speed and low-speed engine loads could use low lift advantageously with a very rapid valve open-and-close rate to increase mixture motion and octane tolerance and employ leaner air/fuel ratios. Duration would be limited, and overlap would be zero. As load is applied and leading-edge flame-front temperatures and cylinder pressures increase, small amounts of overlap would be added to introduce enough inert end gas to keep leading-edge flame-front temperatures below 2,500 degrees F (the point where NOx emissions production is amplified). If the engine were equipped with a variable-runner intake manifold, the lift, duration, opening, and closing could be used to extend the range of the intake-manifold tuning. It is customarily accepted that during resonance, the second harmonic is both the strongest and longest, so it is desirable to have the intake valve open to coincide with the arrival of this inertial supercharging effect. Wide-open-throttle cam phasing could easily map the tuning points of the intake manifold while adding duration and overlap to help fill and evacuate the cylinder. Blowdown could be optimized at all rpms and be effective in limiting the pumping losses of the fourth stroke of the Otto cycle process. Rapid valve deployment for opening and closing could lead to lower valve lifts, less spring pressures, and smaller squish regions due to limited piston-to-valve clearance issues. Smaller TDC volumes would promote quick-burn rates, reduce spark advance, and create higher thermal efficiency.
Traditional rocker designs only impact opening and closing positions simultaneously while working under fixed duration. Only the most complex designs offer varying valve lift. Another obstacle is the limitations for the valve-opening rate that using a camshaft creates. Mark and Steve Cukovich and George Koszarsky (see "American Ingenuity" below) are the pioneers of applying linear motion to open a poppet valve. The basis of their design incorporates four mechanical pieces that replaces either the rocker arm or cam follower/finger for each valve. By using a drive ram, valve activator, and separate open and close stops, they can control all aspects of the valve events independently of one another. Today's current valve-event systems employ a maximum of 6 degrees of freedom, whereas the IVC employs 9 defined degrees of freedom, with infinitely variable steps. The term "degree of freedom" defines the number of ways a mechanical system can be changed.
The IVC system still uses the camshaft and pushrod assembly (or lobe follower on OHC designs) but only as a signal to the drive ram and to supply a mechanical advantage to overcome valvespring pressure. The cam grind becomes moot since, in essence, it is used only to operate the drive ram, and all factors of the valve event are controlled by the positioning of the stops. Actually, the camshaft could now resemble that of the distributor cam in an old points ignition and be used to move just the pushrod, thus saving manufacturing costs. A drive ram activated by the pushrod with an angled drive surface traveling in a linear direction makes contact with the angled surface of the valve activator. The drive ram forces the valve activator against an adjustable valve-opening stop. When the valve activator contacts the adjustable opening stop, the valve activator is prevented from traveling in a linear direction with the ram. But the ram continues its linear travel, and the angled surfaces cause the valve activator to travel perpendicular from the ram, forcing the valve open. Once the ram reaches its farthest point of linear travel, it reverses direction and moves in the opposite direction. As it travels, the perpendicular motion of the valve activator also reverses direction, permitting the valve to close.
IVC Systems has been working on this revolution for more than 11 years; all the original development work was done on an 8hp Wisconsin engine. The original design was refined and simplified, and the complexity has been reduced to where the complete mechanism can be retrofitted to almost any internal combustion engine. The final version incorporates a drive ram and valve activator, along with the opening and closing stops made from DuPont Zytel 6/6 nylon. This plastic-like material offers reduced manufacturing costs, a light weight, and virtually no noise or wear. Oiled by the splash method, the linear action of either material produces unquantifiable friction for years of trouble-free service.
Thus, the IVC Systems' design allows all aspects of the valve events to be controlled separately. Duration, independent opening and closing events overlap and lift can all be varied continuously with the integration of a duty-cycle controller to move the stop positioner, along with a simple linear encoder for position confirmation. Beyond the infinite valve-event control, the IVC also has the ability to open a valve in less degrees of crankshaft rotation than any current conventional design while retaining OE levels of component and valvetrain reliability.
Referencing a standard GM L79 camshaft and benchmarking it against Comp Cams' excellent new Xtreme Energy XE 262, the IVC system, in high-performance form, requires only 60 rotational degrees of crank movement to reach full lift, while the L79 and XE 262 require approximately 150 and 135 degrees, respectively. That represents a valve-opening rate almost 65-percent quicker than a well-defined performance camshaft. IVC systems for a production engine would be slightly less aggressive, completing the same open cycle in 90 degrees of crank rotation. Valve-closing events can occur even faster with the IVC system, and tests have shown that if desired, closing could occur approximately 15 degrees of crank rotation quicker than opening. All of this could be accomplished with only 0.150-inch linear travel of the drive ram on the high-performance version and 0.260-inch linear travel for the less-aggressive production style.
The integration of this system on a production V-8 would require a total of eight duty-cycles or linear controllers and the ratio of travel for the position stop would equate to just 0.003 inch for every degree of valvetiming control! The design would delete the rocker-arm assembly and would fit neatly under most valve covers without any changes other than the wire to the controller.
Though prototype engines used manual control of the positioner stops, we were impressed by the results. The later compact version of the IVC system was installed on a new 5.5hp Briggs & Stratton Europa-series OHV engine. This test module, without the manipulation of the spark-advance curve and air/fuel ratio to enhance the changes in cylinder pressure, produced 30 percent more torque and lower idle speeds and cleaner emissions, as documented by the graphs and charts shown elsewhere.
Emissions test results from a stock- and IVC Systems-equipped one-cylinder engine are indicative of the improvement on a multi-cylinder engine and are realized strictly from valve-event changes. Once spark timing and the fuel curve are readjusted, the decrease in emissions will be even better.
At first, the theory behind rapid and infinitely variable valve events may seem to hold no real purpose, but as one studies the process of filling and emptying a cylinder, the deficiencies of current technology become very apparent. Integration of the IVC system into a production engine will attain levels of torque, horsepower, and efficiency that were once considered impossible. The theory can be expanded to offer enhanced fuel economy during part-throttle/light-load conditions by keeping the intake valve closed on certain cylinders.
But the true beauty of this design lies in its simplicity. It is easy to manufacture, minimally intrusive (so it is cost effective to integrate with current production engines), easy to control, and reliable. If a failure should occur, the engine would not stop running because the valve event on that cylinder would become fixed. The influence of this design is of historic proportions and may well be remembered as one of the last great breakthroughs for the internal combustion engine. With the development work completed and the system refined, IVC Systems' next big step is to implement an aggressive marketing campaign to get this technology out to the industry. With the promise it holds, we wouldn't be surprised if it is commonplace in the next few years.
The spirit that makes this country the greatest in the world still lives on and is represented by the troika at IVC Systems. Its mind-set seems without limitation, and it views obstacles and challenges as merely stepping stones to discovery. When I contacted IVC. I was impressed by what it had developed, but as I got to know these individuals at IVC better. I was flat amazed. The theory, design, and actual execution of the IVC system would be impressive if they came from an OE or even a research center such as MIT, but IVC's idea was developed by a retired machinist, an electrician, and a heavy-equipment operator in the garage of a split-level house in the woods north of Pittsburgh.
The brainchild belongs to Mark Cukovich, an electrician and tinkerer. along with his father Steve, who suffered a heart attack 12 years ago and was forced to retire from his 47-year career at Economy Tooling Company in Ambridge, Pennsylvania. Steve told us, "If it wasn't for my forced retirement, IVC Systems would probably not exist." Mark and he would work on drawings, and Steve's former employer allowed him night visits to the shop to complete the prototype machining. "Without the folks over at Economy Tooling, we would have never been able to prove our theories on linear motion," Steve was quick to add. With early prototypes in hand, they needed a means of testing the valve events on an engine, and that's when George Koszarsky became involved. With an educational background from the Pittsburgh Institute of Aeronautics in powerplant technology and his love for engines, he was a natural. George spends his days with the Department of Defense as a heavy-equipment operator, but over the last few years, he's been designing and building a dyno for IVC. George brought more to the table than just his design skills; his intimacy with engines provided IVC Systems with the missing link.
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