How Does BMW’s Valvetronic Works?

Valvetronic Unit in BMW N52 Engine

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. In this article, we’ll discuss one of the legendary technology designed and developed by BMW.

BMW’s variable valve lift or Valvetronic is designed to reduce pumping losses as its mechanism controls the amount of air intake which could be higher or lower depending upon needs. That, BMW minimized the use of the throttle body such as the throttle body remains fully open and is just for vacuum.

By Valvetronic, the pressure equivalent to atmospheric pressure is right above the intake valve so the engine puts less effort to pump in the air. To understand this we first need to know what are pumping losses.

Pumping Losses: An automobile engine has to pump in air for the intake of air/fuel mixture. This requires energy from an engine. Normally the air travels from the throttle body to the intake manifold and from there, it reaches the intake port. During this phase pressure is reduced which leads to more fuel consumption, power losses, and bad performance. 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.

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 veValvetronicstathe nds for 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.

This Figure shows basic Construction of Valvetronic Mechanism

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.

This figure shows maximum valve lift.

Sensors used for Valvetronic: Folloing Sensors play an important role in bmw valvetronic:

1. Throttle Position Sensor: This sensor takes input from accelerator position sensor and give it that to DME for amount of air to be entered.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.

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