Camless Variable Valve Timing Andrew Butler Dr. M. K. ...

Camless Variable Valve Timing
Andrew Butler
Dr. M. K. Ramasubramanian

Various engine systems have been developed in the effort to improve the engine
performance and fuel economy of an automobile. The Variable Valve Timing and Lift Electronic
Control (VTEC) engine is the latest development designed by Honda to enhance the efficiency of
an engine. This system changes cam profiles from the use of synchronized pins controlled and
powered by electro-hydraulic devices. Depending on the speed of the engine, one of the three
different cam profiles are actuated and used to provide the engine with the appropriate amount of
air to achieve a better engine performance and fuel efficiency at that particular range of engine
speeds. As a result, the VTEC provides a degree of fuel economy but the design only offers
optimum engine performance at three different engine speeds. Even though the Honda VTEC has
made substantial efforts toward engine optimization, there is still room to improve on the theory.
The theory behind engine efficiency is to increase the amount of air that is supplied to the engine
as the speed of the engine is increased. From this basic rule of thermodynamics, the idea of
camless variable valve timing (VVT) was conceived.
Camless VVT allows an engine to experience maximum engine performance and fuel
efficiency at each and every engine speed while following the same principles of the VTEC.
Instead of using multiple cam profiles with synchronizing pins, camless VVT is electronically
operated by a microcontroller which will control electro-mechanical rotary solenoid actuators.
Due to the required amount of force and speed needed from a solenoid in order for this system to
be effective, linear actuators are ignored since rotary solenoids meet the specifications needed for
this system. Moreover, each of these solenoids will be connected to the intake and exhaust valves
relieving the engine of the load of a cam system. The camshaft alone decreases the mechanical
efficiency of an engine since the friction of the cams and the load of a timing belt increase the

irreversibility’s of an engine. Furthermore, with implementing this design, the flow of air
through the engine’s cylinder can be directly controlled to supply the engine with precise
amounts of air at designated engine speeds while eliminating the old technology of resistive
timing belts and extensive camshafts. Depending on the load and engine speed, the
microcontroller will process the information given and use pulse width modulation (PWM) to
actuate the solenoid valves. These PWMs will generate square waves that are identical to the
timing profile for the most efficient engine at that particular speed and load combination.
Solenoid
Rocker Arm
Solenoid
Actuation
Valve
Spring
Valve
Motion
Intake
Port
Valve
Air
Flow
Figure 1: Camless VVT Models
As shown above in Figure 1, these PWMs will be sent to the solenoids to actuate the
timing of these devices. Once the solenoid is actuated, the rocker arm pivots and compresses the
valve and valve spring which in turn releases the flow of air into the engine’s cylinder.

Revisiting the idea of engine optimization, theses generated PWMs are predetermined square
waves that will be hard coded and referenced by the microcontroller depending on the load and
speed of the engine for maximum engine efficiency. In order to implement this hypothesis,
engine simulation tools were used to compare the advantages of this design (camless VVT)
versus the Honda VTEC. Through these simulations, the timing events of the exhaust and intake
valves are manipulated to determine the best engine performance that can occur at the desired
engine speed and loading. In addition, the valve lift was also controlled to further analyze the
performance of the engine. Shown below is a screenshot of the program used to simulate the
engine performance of an Acura Integra 1.8L with timing profiles that were tailored for each
engine speed from 1000 rpm to 5500 rpm in 500 rpm increments.
Computer Simulation
Figure 2: Screenshot of Engine Analyzer Pro v3.5

Based on the simulation results, a timing diagram was generated to represent the
maximum engine performance for each designated range of engine speeds. From implementing
this technique, the research found that the valve lift and timing events of the valve train each
independently affect the efficiency of this engine. As a result, these factors were experimentally
balanced to gain the largest amount of engine performance while limiting fuel consumption.
Figure 2 displays the timing profiles of exhaust and intake valves at 1000 rpm, 2500 rpm and
5500 rpm. Neglecting the other 500 rpm increments between 1000 and 5500 rpm, these plots
were organized in this manner in order to illustrate how the timing profiles change as the engine
speed increases.
@ 5500rpm
@ 2500rpm
Exhaust
Intake
@ 1000rpm
Figure 3: Timing Diagram using Computer Simulation

After implementing these timing profiles into the engine performance simulator, the
Acura Integra 1.8L engine is compared with the implementation of the “small cam” VTEC
versus the camless VVT system while keeping all other factors constant. From the observed data,
the brake torque of the crankshaft was plotted against the volumetric flow rate of consumed fuel
within the each system. As shown below in Figure 4, overall, the camless VVT system produces
more crankshaft torque while consuming the same amount of fuel for each engine speed.
Figure 4: Engine Performance between the VTEC and Camless VVT Systems
From the implementation of computer based simulation for camless variable valve
timing, the results show that this design would improve the fuel economy of an engine by
2.3% overall compared with the Honda VTEC, ranging from a high 6.5% at engine idle to a low

0.3% at mid range speeds. Even though the fuel efficiency would only increase by a small
amount overall if this design was constructed, due to the inability to simulate the gain of not
having the loading effects of a camshaft on the engine, the fuel economy of this design is
underrepresented. However, the research was able to determine that varying the lifts of the intake
and exhaust valves contributes to having the greatest effect on an engine’s performance. More
experiments with this theory will be conducted and a basic model of this design will be
constructed in the near future. Starting with a simple approach, a small lawnmower engine will
be purchased in order to implement this design on a small scale. Removing the camshaft of this
engine and applying the camless VVT system, the actual efficiency of an engine can then be
analyzed with this design and compared with the engine’s original performance.