What is a Variable Valve Timing (VVT) System?
To understand variable valve timing (VVT) solenoids and their associated oil control valves (OCVs), it helps to know the history of this device and how it benefits passenger cars, SUVs, and light trucks today.
Variable valve timing solenoid valves (oil control valves) play a critical role in engine performance and efficiency. VVT solenoid valves improve driving performance and fuel economy by optimizing the opening and closing of the valves. However, they can fail over time. Let’s look at the most common symptoms of a bad oil control valve, what causes it to fail, and how much it costs to replace a VVT solenoid valve.
The valves in your car, SUV, or truck engine control the flow of air, fuel, and exhaust gases through the engine’s combustion chambers. These valves are opened and closed by camshafts.
Depending on the type of engine your vehicle has, there may be up to four camshafts. These camshafts are usually driven by the engine’s crankshaft via a chain or belt. Camshafts in vehicles from previous decades provided a fixed pattern of valve actuation depending on the piston position. This pattern (called valve timing) was predetermined by the manufacturer and built into the engine. The valve timing was adjusted to achieve the best performance with acceptable fuel consumption.
Variable Cam Control
Then variable cam timing (VCT) appeared on the market. This concept introduced cam timing that varied along a predetermined valve actuation pattern. Patents for such systems on early engines date back to the 1920s.
Alfa Romeo was the first manufacturer to offer VCT in a production car, the feature coming as standard on the 2.0-liter fuel-injected engine of the 1980 Spider. The design was very simple, just retarding the intake valves as engine speed increased. This mechanism improved mid-range performance; this one change was a big win for the little Alfa engine.
Variable cam timing gradually gained acceptance. Honda integrated them into their VTEC engines in 1989. Porsche introduced it with VarioCam on their V8-powered 928 models. In the early 2000s, variable cam timing also gained widespread acceptance in motorcycle engines.
Borg Warner recently developed a VCT system for the 2016 Hyundai Lambda II engine series. This system was the first to incorporate the use of a cam center position lock to keep the cam in the center position when advancement or retardation is not required.
Virtually every automaker has now jumped on the VCT bandwagon. And beyond pure performance and fuel economy benefits, VCT has been shown to help reduce vehicle emissions such as nitrogen oxides. What is an Oil Control Valve (and how does it work?)
In most modern automobile engines, valve timing is altered by a cam timing mechanism that changes the position of the cam relative to the engine’s crankshaft. These systems utilize the readily available flow of oil from the engine lubrication system to get their job done. And here’s how it works:
1. You’re at an intersection or just keep driving and accelerating. In response to a signal from the ECU (electronic control unit), the variable valve timing solenoid opens the built-in oil control valve. When this valve opens, oil under pressure flows into the cam timing mechanism, rapidly changing the position of the cam relative to the drive chain or belt.
2. The cam position can be moved forward or backward depending on engine RPM and throttle position (accelerator pedal). When the engine reaches a certain speed, the OCV closes and the cam returns to its original position. This activity occurs almost instantly and is invisible to the driver.