What is a VVT engine
see also | Variable timing | Performance increase | Filling | Performance | Multi-valve | Supercharging | Comparison P / M |
|Time and again, nature serves as a model for the development of innovative technologies. The comparison with the breathing technique of humans makes, for example, the functioning of VALVETRONIC clear:|
When exerting a lot of effort, the person breathes deeply and long. If he needs less air, then he does not cut back the air supply by covering his nose and mouth a little, but rather he breathes shorter and shallower. In conventional gasoline engines, the throttle valve corresponds to the locked nose or mouth. VALVETRONIC with large valve lift (= deep, long breathing) or small valve lift (= shallow, short breathing) enables you to breathe like nature - without throttling and always efficiently.
|BMW 316ti cylinder head|
VALVETRONIC enables a fully variable valve lift of 0.0 to 9.7 millimeters. It is achieved by an intermediate lever that can be adjusted by an electric motor, which is placed between the camshaft and the rocker arm that actuates the valve. The VALVETRONIC not only works precisely, but also extremely quickly. The adjustment from minimum to maximum stroke can be done in just 300 milliseconds. In order to be able to use these setting options, very powerful controls are necessary. The VALVETRONIC therefore has its own 32-bit computer networked with the engine control.
Inlet valve with Valvetronic
The mixture supply is controlled via a variable valve lift without a throttle valve.
For the BMW driver, the new 316ti four-cylinder with VALVETRONIC means lower consumption, reduced exhaust emissions and, at the same time, better responsiveness and smoother running.
According to the EU, the 85 kW / 115 PS strong and 201 km / h fast 316ti compact consumes 6.9 liters of Super per 100 kilometers - 0.7 liters less than the previous model with 77 kW / 105 PS and well over a liter less than all of them Competitors in this class. The 316ti compact fulfills the EU4 pollutant standard.
Although all vehicle manufacturers like to speak of a "new engine" even with minor modifications, little has changed in the past decades with regard to the crucial components. So also with the mixture preparation. Nowadays, ignition is carried out using an electronic map and injection systems have replaced the carburettor, but the most important component still works as it did in the childhood days of engine construction: The throttle, installed somewhere in the intake tract, determines the volume of air or ignitable mixture that gets into the cylinder with its opening. The driver controls the position of the throttle valve with the accelerator pedal. What is unsatisfactory about this solution are the losses caused by undesired turbulence on the throttle valve.
fully variable valve lift
Valvetronic has now abolished the throttle valve. In future, their function will be taken over by the inlet valve (1). The inlet valve is not rigidly driven by the camshaft (2), but by means of an eccentric shaft (3) and intermediate lever (4). If the driver steps on the gas, an electric motor turns this eccentric shaft. The intermediate lever transmits the rotation of the cams, depending on the position of this shaft, to the valve.As a result, the stroke is variable. When the throttle is low, the valve has only a small stroke; when the throttle is full, the valve opens further.
What does the effort actually bring?
In engines with a throttle valve, when the intake valves open, the volume of the intake manifold between the valve and the throttle valve must be overcome before the air starts moving in the direction of the cylinders. The intake manifold volume thus forms a damper that reduces the response behavior. If it is possible to switch off the throttle valve and move the inlet valve to load control, then you can expect lower consumption, increasing power and a drastically better response of the engine to the command of the accelerator pedal. However, the Valvetronic motor is not dethrottled because the throttle valve is no longer used. There is still a throttle point - namely at the valve gap. However, dethrottling was made possible by the fact that, as a result of the better mixture preparation, a higher (internal) EGR rate can be used.
The reason for this is a significantly better atomization of the gasoline injected into the intake manifold at idle and in the lower partial load, because the intake mixture is accelerated enormously in the narrow valve gap and the resistance of the throttle valve and damping volume are eliminated. Eventually, the engine's cold start capability is dramatically improved. BMW also mentions a reduction in fuel consumption of 10% compared to the very good predecessor engine and an increase in torque in the lower speed range. This means that the consumption benefits mentioned for direct petrol injection can be achieved in a simpler way. BMW is by no means fundamentally against direct injection, but the previous systems are considered to be in great need of improvement because of the jagged piston crowns with the result of increased consumption at high load and speed and the increased tendency to form soot.
However, like most diesel engines, the BMW engine has a throttle valve, which is only used for correction and not for load control. This takes place exclusively via the variable lift of the inlet valves, with the timing of the inlet and outlet also being adjusted using the well-known Doppelvanos system by turning the camshafts. The lift of the exhaust valves, on the other hand, is not adjusted; the exhaust valves are operated as usual by the camshaft via roller rocker arms.
Stroke between 0 and 10 mm
VALVETRONIC and the Otto direct injection
Theoretically, there is hardly anything more natural for an engine developer than a direct-injection gasoline engine - with this concept, he can combine the performance potential of the gasoline engine with the unsurpassed consumption behavior of diesel. To date, however, this project has failed due to two factors: The availability of sulfur-free fuel required for a gasoline direct injection engine and the lack of durability of the indispensable and complex catalyst systems.
VALVETRONIC manages without the complex exhaust gas aftertreatment, which is essential for the gasoline direct injection engine., In contrast to the direct injection engine, a VALVETRONIC engine does not depend on sulfur-free fuel. The low consumption is achieved with all commercially available petrol fuels, so that the advantages of VALVETRONIC can be used without additional financial or time expenditure.
see also | Variable timing | Performance increase | Filling | Performance | Multi-valve | supercharging | Compare P / M |
Sources: BMW and various unknown sources
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Author: Johannes Wiesinger
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