Intake string for a reciprocating internal-combustion engine

What is described is an intake system for a reciprocating internal-combustion engine for vehicles, especially for passenger motor vehicles, which has intake pipes which lead to the individual cylinders of the internal-combustion engine and which are each divided into at least two intake strings (3, 4) connectable in succession by shut-off members (6, 8) as a function of the engine speed. In order, under full load, to increase the torque of the internal-combustion engine within wide engine-speed ranges by utilising gas-oscillation phenomena in the intake pipe, the shut-off member (6) of the first intake string (3) connected alone at low engine speeds is to be designed as a non-return flap which can be loaded in the opening direction, counter to a return spring (7), by the working medium flowing through the intake string. In order, particularly at the lowest engine speeds, to prevent the cylinder charge from flowing back through the still open intake valve towards the end of the inlet stroke, there is to be provided an actuating device which releases the non-return flap (6) in a first lower engine-speed range, so that it is subjected only to the effect of the return spring (7), and which keeps the non-return flap constantly in the opening position in a second upper engine-speed range.