Variable exhaust valve closing is advantageous because it allows the exhaust valve timing to be adjusted according to engine load and operating conditions.

Advantages include:

• Improves fuel efficiency at part load operation.
• Optimizes scavenging efficiency by controlling the exhaust gas flow.
• Reduces pumping losses and improves overall engine performance.
• Helps maintain correct cylinder pressure and temperature.
• Reduces thermal and mechanical stresses on engine components.
• Improves combustion efficiency and reduces exhaust emissions.

Variable exhaust valve closing is usually achieved hydraulically by using an electronically controlled exhaust valve actuator arrangement.

Working Principle

• The exhaust valve is opened hydraulically by high-pressure oil supplied through a cam-operated pump or electronically controlled hydraulic system.
• During valve closing, the hydraulic oil is released through a control valve.
• By controlling the release of hydraulic oil, the closing timing of the exhaust valve can be advanced or delayed.
• Electronic control systems adjust the timing according to engine load, speed, and operating conditions.

High impact during exhaust valve closing is avoided by cushioning arrangements in the hydraulic system.

Methods include:

• Hydraulic damping is provided near the end of valve travel.
• The oil outlet passage becomes restricted during final closing movement.
• This restriction slows down the valve just before seating.
• Soft landing of the valve reduces hammering, wear, and mechanical stress on the valve seat and spindle.