Back in the early sixties, a car’s intake valve would open for a specific duration during a predetermined time in the engine’s four-stroke cycle. It was not an especially flexible system, but in the early days of motor vehicles, this wasn’t a big problem. In the engines of those days, idle and operating RPMs were often quite similar. However, as vehicles advanced in complexity, the range of potential RPMs widened, leading to greater compromises in systems with static valve timing. The need for a better solution lead to the rise of variable valve timing (VVT).
With VVT, modern engines can alter not only valve timing, but also overlap, duration, and lift throughout the four-stroke cycle. With these parameters no longer set in stone, it is possible to achieve a whole host of operational improvements as compared to engines with static valve timing systems. VVT can lead not only to more engine power, but also to increased efficiency and decreased emissions.
This blog post will examine how automotive manufacturers across the industry approach VVT differently, and how LHP Technology Solutions (LHPTS), along with National Instruments (NI) works together to assist in those solutions.
If VVT is not implemented in an engine, the valve timing across all engine conditions are held constant, whether the vehicle is idling at a stoplight or accelerating to merge on the interstate. Clearly, if the engine is unable to shift its operational characteristics based on the situation, certain compromises are necessary. These compromises often lead to reduced engine efficiency and performance, while also causing more environmentally damaging emissions.
When implemented correctly, a VVT system brings with it a host of improvements. Across the RPM spectrum, the engine can perform much better, as a VVT system is able to bring great fuel economy and power at low RPMs while providing much higher performance when demanded by a high RPM situation.
VVT is typically achieved by a switching mechanism in the vehicle’s computer that is activated by hydraulic oil pressure in the engine. This switching mechanism allows the engine to move between different camshaft profiles and to provide the best available option under the given engine conditions. This camshaft profile switching supports not only improved engine power, but also torque output, and fuel economy.
Moreover, VVT also assists in reducing the emissions of a vehicle by allowing for more internal recirculation of exhaust gas. This is achieved by increasing valve overlap in the engine, which in turn suppresses peak combustions temperatures. Many modern vehicles are equipped with a dedicated Exhaust Gas Recirculation (EGR) system to achieve this same result, but with a well-implemented VVT system, it is sometimes possible to eliminate the need for such EGR systems.
At an even more advanced level, some vehicles are equipped with so-called “continuous” VVT systems. Instead of a discrete mechanism of switching between camshaft profiles, a continuous VVT system can adjust the valve timing along a continuous range, adding even more control and capacity for performance improvements to the system.
For a more robust description of how VVT is implemented in practice, below is a discussion of a few tier one OEM solutions to VVT systems from Honda, Nissan, and Ford. Though they are far from the only manufacturers implementing such systems these days, their systems are instructive in gaining a greater understanding of the power of VVT in practice.
Honda tackles this by using the Variable Valve Timing and Lift Electronic Control (VTEC), a system developed by Honda engineer Ikuo Kajitani. By hydraulically switching between two to three profiles for the camshaft, which enables a great deal of improvement in the efficiency of the engine at high RPM. VTEC is set apart from a standard VVT system by way of its ability to change not only the valve timing, but also the camshaft profile and the lift on the valves.
Nissan uses the Continuous Variable Valve Timing Control (CVTC or CVTCS) system. Together with their Variable Valve Event and Lift (VVEL) technology, CVTC controls the valve phases and events, allowing complete continuous adjustments of the engine’s valve timing and lift throughout the four-stroke cycle.
VVEL adds a rocker arm to the engine’s construction, which creates two types of links to open the intake valves. The output cam’s motion is altered by rotation of the control shaft. This rotation is achieved with a DC stepper motor that is capable of modifying the fulcrums of the links within the device, which results in a much more responsive and powerful engine design across a wide range of RPM conditions.
Ford uses four VVT strategies to manage engine efficiency and high torque output. On newer Ford vehicles, such as those with the 5.4L three valve engines, variable cam timing (VCT) can eliminate the need for an EGR system in the vehicle. A phaser in the system enables the camshaft to move independent of the timing sprocket, which enables VCT to advance or retard the timing in the camshaft as needed.
The first strategy used in some Ford vehicles is intake phase shifting (IPS). In this strategy, VCT only impacts the intake camshaft. Alternatively, exhaust phase shifting (EPS) uses VCT to manage the exhaust camshaft. Dual independent phase shifting (DIPS) allows VCT to control intake and exhaust camshafts independently while dual equal phase shifting (DEPS) has VCT control intake and exhaust equally and together.
Different strokes require a different approach. As seen above, there are many ways to take on the theory and application of VVT. Whether it is applied to a small engine or a large one, to a bike or to a truck, the basic approach must be adapted. However, with gas prices always fluctuating, VVT is crucial as it is capable of increasing fuel efficiency by nearly 6%.
Along with fuel efficiency, because of its ability to help limit emissions, the growth of VVT implementation has been rapid due to strict federal and state standards. In an automotive industry increasingly reliant on VVT, motorists can find comfort in knowing that companies such as LHP and National Instruments have engineers who are well versed in VVT research and development and who can implement solutions on a wide range of engine types.
LHPTS are experts in automotive control and test systems. We can help organizations prioritize and manage the wide variety of new tests necessary for emerging hybrid and PEV propulsion system technology. While automotive organizations focus on advancing their vehicles, LHPTS is concentrating on staying ahead of the industry’s propulsion system testing needs. From performing diesel-to electric vehicle conversions to building high-voltage propulsion battery packs, power inverter test systems, and electric vehicle supply equipment solutions, LHPTS can help automotive R&D centers, manufacturers, suppliers, and national labs prepare for whatever the future may bring to the industry.
Contact LHPTS for more information on how we can help your organization prepare for the future of the automotive industry:
ABOUT LHP TECHNOLOGY SOLUTIONS:
The LHP Technology Solutions Powertrain Controls Group (LHP PCG), builds on a 17-year history of providing powertrain controls for OEMs, Tier 1 suppliers and engine research labs around the world. In addition, LHP PCG creates HIL solutions to test and prove functional safety for tomorrow’s vehicles. With experience in evolving regulations like ISO 26262 a proven understanding of interconnected and networked vehicle systems, and the ability to provide test solutions as an ongoing service, we partner with companies for accurate and trusted HIL systems that will advacne hybrid and.
With a targeted focus on automotive powertrain applications, deep internal combustion expertise, and a history integrating NI technology, our solutions are custom designed and use open architecture hardware, allowing precision and flexibility to refine engine technology, validate safe and reliable components, and succeed in the market.
The Advantages of Variable Valve Timing, www.oards.com, 05-JUL-18
Variable Valve Timing: The Next Big Thing, www.bennetts.co.uk,