Variable Valve Timing (VVT): A Comprehensive Guide

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Variable Valve Timing (VVT) is a critical technology in engine design that can significantly impact engine output, whether it be power or torque. This advanced system works by utilizing two sets of cams with different shapes, one for normal speed (below 4,500 rpm) and another for higher speed, allowing for improved peak power and top-end performance.

Understanding the Mechanics of VVT

The core of VVT lies in the ability to vary the lift of the valve, which is a crucial aspect of this technology. Cam-changing systems, such as Honda’s VTEC, Mitsubishi’s MIVEC, and Nissan’s Neo VVL, offer the most significant change in valve lift by using a mechanical linkage to switch between different cam profiles. This allows for a more substantial change in valve lift compared to other continuously variable systems.

Quantifying the Impact of VVT

Numerous studies have been conducted to understand the influence factors of power performance in VVT engines. One such study found that the intake valve timing can significantly impact the power performance of gasoline engines. By using Formula (16), the influence of intake valve timing on gasoline engine power performance can be quantified.

Additionally, the in-cylinder indicated thermal efficiency of a gasoline engine is dependent on various factors, but a strong correlation has been revealed between the indicated thermal efficiency and operational parameters such as engine speed, load, and excess air coefficient.

Advancements in VVT Technology

variable valve timing vvt

The Automotive Variable Valve Timing (VVT) & Start-Stop System market is projected to grow at a CAGR of 5.8% from 2022 to 2028, driven by the increasing demand for higher fuel efficiency. Key players in this market include Denso Corporation, Schaeffler AG, Delphi Technologies, Hitachi Automotive, Valeo, Eaton Corporation, Borgwarner Inc., Aisin Seiki Co. Ltd, and Robert Bosch GmbH.

Continuous Valve Timing Adjustment

While the traditional VVT systems with two sets of cams offer improved peak power and top-end performance, they do not allow for continuous change of timing. To address this limitation, some manufacturers have developed continuously variable valve timing (CVVT) systems, which can adjust the valve timing continuously throughout the engine’s operating range.

One example of a CVVT system is Hyundai’s Dual Continuously Variable Valve Timing (D-CVVT), which can adjust the intake and exhaust valve timing independently, providing better control over the engine’s breathing and improving both power and fuel efficiency.

Integrated Starter-Generator (ISG) Systems

Another advancement in VVT technology is the integration of Integrated Starter-Generator (ISG) systems, which combine the VVT system with a start-stop function. This integration allows for seamless engine restarts and improved fuel efficiency by shutting off the engine during idling or deceleration.

The ISG system works by using the VVT system to precisely control the valve timing, ensuring a smooth and efficient engine restart when the driver resumes acceleration. This technology is becoming increasingly popular in modern vehicles, contributing to the growth of the Automotive Variable Valve Timing (VVT) & Start-Stop System market.

Conclusion

Variable Valve Timing (VVT) is a highly advanced technology that plays a crucial role in engine design, offering significant improvements in power, torque, and fuel efficiency. By understanding the mechanics, quantifiable impacts, and the latest advancements in VVT technology, engineers and enthusiasts can better appreciate the importance of this innovative system in the automotive industry.

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