Valvetronic - An Answer to Variable Valve Lift

Introduction: As euro standards were becoming more and more environment friendly it was needed at that time (in the 70’s to the 90s) to gain more and more control over the engine to optimize power, torque, and fuel consumption. So, to gain this different car brands developed different mechanisms of variable valve timing or variable valve lift. Also, engines are getting more and more electrification over time.

Valvetronic Technology is an answer to BMW’s Variable Valve Lift. By this, the use of a throttle body is minimized, reducing the pumping losses in the engine intake. As the engine will have near atmospheric pressure to the intake valves. To further understand Valvetronic Technology we must know why this technology is better than other ones, why this technology is needed, or why this was developed and when this technology was designed and launched. By these questions, we will have a reason to acknowledge this technology. Furthermore, I will discuss how this technology works.

History

To reduce fuel consumption and emissions BMW developed Valvetronic technology and first used it in 316ti in 2001. BMW engineers invented this technology in 2000 and first utilized it in 2001.

The first turbocharged engine used Valvetronic technology was the BMW N55(straight-6) engine in 2009. It was the first engine technology that no longer require a throttle butterfly which is the major cause of pumping losses in an engine.

The idea behind this is that the human body also applies Valvetronic when we have to do some kind of work with great effort we take a deep-long breath.

What are these Pumping Losses?

Pumping losses in an engine occurs during the suction and exhaust stroke of an engine. As the engine sucks air for intake it losses power when the piston moves downward to suck air during the intake stroke the energy is lost when the air passes from the intake manifold to intake valves and ports another example of this is the engine has to open the throttle valve to suck air that also causes power losses. These losses also occur when the engine injects air and fuel mixture into the combustion chamber. During exhaust, when it pumps exhaust gases out of the engine as exiting exhaust gases, it offers backpressure because it has to work against atmospheric pressure.

These losses may vary depending on factors like engine design or operating conditions. Normally engine loses 10% to 15% of its energy due to pumping at higher loads while at lower loads this may increase up to 20% to 30% because at higher speeds and loads, the engine is working more efficiently.

For pumping losses we can use this equation:

P_red = (m_rate/ ρ) x ΔP

Here P_red refers to a reduction in power during the suction of air. Mass flow rate is represented by m_rate and ΔP refers to a change in pressure and ρ refers to density. So, if the pressure drop in air intake is greater it will cause more power losses. So, it’s clear that by having more pressure over the intake valve we’ll improve fuel efficiency by reducing pumping losses.

To overcome these losses engine manufacturers design different technologies such as variable valve timing and lift, turbochargers and superchargers, and direct and high-precision injection.

How Valvetronic contributes to the reduction of pumping losses?

Valvetronic eliminates the role of the throttle body which is the main cause of pumping losses. The valves are closed and opened by a valvetronic motor. So, we have near atmospheric pressure at the valves which reduces the pumping losses in an engine. With this technology, under practical driving conditions, BMW claims to reduce 10% of fuel consumption.

Construction of Valvetronic Mechanism:

To understand the basic function of the valvetronic mechanism first keep in mind that this mechanism doesn’t use a throttle body for controlling air intake. This thing is also clear from the following diagram that shows the construction of the Valvetronic mechanism. Its components are:

1. Servo Motor: Servo motors are used where precise motion is required. So, here in Valvetronic, it is used and it is an important component here. It is attached to the worm shaft and rotates from the command of DME(the Control unit used in BMW Valvetronic is Digital Motor Electronics and is responsible for this variable valve lift mechanism). It is also known as an eccentric shaft motor. This motor is a Brushless Direct Current Motor which makes it maintenance-free.
2. Eccentric Shaft: This shaft is attached to the worm gear which takes command(in the form of motion) from the worm shaft and rotates the intermediate lever to adjust the follower for a particular valve lift. This could rotate up to 225 degrees.
3. Intermediate Lever/Arm: This lever is attached to an eccentric shaft and from its movement it modifies roller cam follower to control cam stroke.
4. Roller Cam Follower: This component has controls intake valve from action of intermediate lever.

Other components can be seen in following figure.

Working: First of all, the image above shows minmum valve lift which is about 0.18mm. During minimum lift condition the eccentric shaft turn intermediate arm away from camshaft so that the valve lift is minimum because lower tip of intermediate arm does not touch this.

For Maximum Lift: For maximum lift you can see following image where eccentric shaft moves intermediate arm close to camshaft and lower tip of intermediate shaft touches the roller cam follower’s bearing so that the valve lift is larger this could be up to 9.9mm.

Sensors used for Valvetronic:

Folloing Sensors play an important role in bmw valvetronic:

Throttle Position Sensor: This sensor takes input from accelerator position sensor and give it that to DME for amount of air to be entered.

Mass Air Flow Sensor: This sensor measures amount of air entering the engine and gives a signal to DME to optimize valve lift. Such as if mass air flow sensor measures that air intake is less it would signal DME to increase valve lift for more air.

Oxygen Sensor: This sensor measures the amount of oxygen in exhaust gases and signals this information to DME. The amount of oxygen in exhaust gasses gives the information that is the air/fuel mixture rich or lean. So, rich air/fuel mixture enters the engine which means more air intake is needed so DME will increase the valve lift.

Crankshaft Position Sensor: Rotational Speed and position of the crankshaft is measured by crankshaft position sensor. So, if it is noted that speed of crankshaft is increased DME will increase valve lift for more air intake.

Camshaft Position Sensor: Camshaft position and speed is determined by this sensor. This sensor tells the engine which cylinder’s piston is at Top Dead Center.

Coolant Temperature Sensor: Coolant Temperature sensor tells DME about the temperature of engine coolant. If for example, it detects that engine coolant is not at optimum temperature DME can increase valve lift to input more air to warm up the engine.

Eccentric Shaft Sensor: This sensor tells the engine about the position of eccentric shaft. This sensor is located on the cylinder head cover near eccentric shaft.

Conclusion: Valvetronic is really a great technology developed by BMW. This helps in lowering emissions, increasing fuel economy and optimizing performance.