A valve control is responsible for letting the gases (air-fuel mixture and waste gases) into and out of the cylinder at the right time. This technology is generally summarized under the term "valve train."
In today's modern systems, valve control is variable and dependent on various parameters. Several different systems for this have been developed and been established on the market.
Variable valve trains – that is, with variable opening time, variable valve stroke and/or variable spread – reduce the fuel consumption of gasoline engines through the influence of charge cycle work, mix preparation and combustion.
Newer variable valves also allow the deactivating of one of two inlet valves. This allows the effects of variable valve control and direct injection to be combined.