The Evolution of Engine Valve Mechanisms

📖 By Mark Snow | JDM Car Enthusiast Magazine | November 7, 2022

🔗 Original source: WeChat Public Account - Mark Snow

Many Honda enthusiasts like to boast about VTEC, but whether it’s Honda’s VTEC, Toyota’s VVTL, or other variable valve timing systems, they are all part of the valvetrain mechanism. So how has valve technology evolved throughout the history of internal combustion engines? This article will enhance your automotive knowledge and provide valuable insights.

In vehicle specification sheets, you often see the terms SOHC or DOHC under the engine type. Some manufacturers emphasize additional technologies like VVT (Variable Valve Timing) or VVL (Variable Valve Lift), while most car buyers tend to skip over them. Instead, they focus on maximum horsepower, peak torque, or fuel consumption figures. But what do SOHC and DOHC me

📸 Illustration: The fundamental structure of a valvetrain, one of the core components required for an engine to function properly. Without the "mini explosions" from air and fuel mixtures pushing the piston, there is no internal combustion engine.

The valvetrain is responsible for controlling when the intake and exhaust valves open and close in a four-stroke engine.

• Intake valves allow fresh air or air-fuel mixture into the cylinder.
• Exhaust valves direct burnt gases out into the exhaust system or turbine.

Key components of a valvetrain include:

🔹 Camshaft (凸轮轴)
🔹 Pushrod (推杆) – Also known as "chopsticks" 🥢 in the car community!
🔹 Tappet (顶杆)
🔹 Rocker Arm (摇臂) – Think of it as a mini lever! ⚙️
🔹 Valve Spring (气门弹簧) – Keeps valves in position 🌀
🔹 Valves (气门) – The gateways for air and exhaust 🚪

Modern VVT, VVL, and VTEC systems are just enhancements built onto the camshaft to improve efficiency and power output! 🔥

The Evolution of Engine Valvetrain Systems

📌 Early Development: The Birth of Camshafts
Camshafts have been responsible for valve operation since the birth of internal combustion engines. Early engines featured IOE (Inlet Over Exhaust) configurations, with only exhaust valves actively controlled, while intake relied on atmospheric pressure.

📸 Illustration: The camshaft and its supporting components. In four-stroke engines, the camshaft rotates at half the speed of the crankshaft.

🚗 OHV ("Pushrod") Engines

• Pushrod (推杆), nicknamed "chopsticks", is commonly found in OHV engines.
• In OHV engines, the camshaft is located inside the engine block, pushing the rods to open or close the valves.

📸 Illustration: Pushrods, commonly seen in OHV engines, push against rocker arms to operate intake and exhaust valves.

Development of Overhead Camshaft (OHC) Systems

In 1919, Swiss inventor Ernest Henry developed the first-ever DOHC (Dual Overhead Camshaft) four-valve engine. This breakthrough allowed for higher RPM performance and increased airflow.

📸 Illustration: Ernest Henry’s first DOHC four-valve engine, originally designed for Peugeot’s L76 racing car.

In 1930, the United States introduced hydraulic tappets, which automatically adjusted valve clearance and remain widely used today.

📸 Illustration: Bucket tappets for overhead camshaft engines, allowing precise valve clearance adjustments.

Valve Spring Evolution & Alternative Designs

Most modern OHV, SOHC, and DOHC engines use coiled valve springs to return valves to their closed positions.

However, high-performance engines—such as Formula 1 race cars—have moved towards pneumatic or hydraulic valve springs since the 1990s.

📸 Illustration: Traditional coiled valve springs and the evolution of valve return mechanisms.

Some exotic solutions, like Desmodromic Valve Systems, eliminate valve springs altogether. This system, first introduced in 1896, was used in Mercedes’ Formula 1 W196, Ducati motorcycles, and Maserati’s four-cylinder engines.

📸 Illustration: The Desmodromic Valve System, which uses mechanical linkages instead of springs to control valve movement.

Major Milestones in Engine Valvetrain Evolution

🚘 Phase 1: Side-Valve Engines (SV / Flathead Engines) [1890s-1970s]
✔️ Simple design, easy maintenance 🛠️
❌ Low efficiency, overheating issues 🥵

🏁 Phase 2: Overhead Valve (OHV) Engines [Post-WWII]
✔️ Improved combustion efficiency 🔥
❌ More complex than SV engines

⚙️ Phase 3: Overhead Camshaft (OHC) Engines [Modern Era]
✔️ Higher RPM potential ⏫
✔️ Used in today’s performance vehicles 🚗💨

📸 Illustration: Comparison of Side-Valve, OHV, and OHC configurations.

🔍 Did You Know? The first DOHC engine was introduced in 1912 for the Peugeot L76 racing car, producing 148 horsepower at 2,200 RPM, with a top speed of 190 km/h! 🏎️💨

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The Future of Engine Valves: Camless Technology 🚀

The next generation of engines eliminates camshafts entirely! Instead, electromagnetic actuators precisely control each valve.

Brands like Koenigsegg, Lotus, Ford, and Qoros are pioneering this technology. Expect better fuel efficiency, increased power, and lower emissions in the coming years! ⚡

📸 Illustration: FreeValve’s electromagnetic valve system, removing the need for traditional camshafts.

Final Thoughts 💭

Engine valvetrain technology has evolved for over a century. However, with the rise of electric vehicles, many new car buyers today are unaware of the importance of valvetrain systems.

🚗 What do you think? Will internal combustion engines continue evolving, or will EVs take over completely? Let’s discuss in the comments! 💬👇