Patent ID: 7322804

Claim:
A Metering pump device for a vehicle heater, comprising an inlet chamber ( 40 ), an outlet chamber ( 54 ), a first valve assembly ( 66 ) between the inlet chamber ( 40 ) and the outlet chamber ( 54 ), which permits fluid exchange substantially only from the inlet chamber ( 40 ) to the outlet chamber ( 54 ), a displacement piston element ( 12 ), which is movable to and fro in an opening ( 16 ) formed in a piston housing ( 14 ) between a first piston position, in which it minimizes the volume of the inlet chamber ( 40 ) and a second piston position, in which it minimizes the volume of the outlet chamber ( 54 ), a reduction (V 1 ) in the volume of the inlet chamber ( 40 ) being greater than an increase (V 2 ) in the volume of the outlet chamber ( 54 ) on movement of the displacement piston element ( 12 ) from the second piston position to the first piston position, wherein the opening ( 16 ) is of stepped construction, with a portion ( 20 ) of smaller diameter and a portion ( 26 ) of larger diameter, the displacement piston element ( 12 ) comprises a portion ( 28 ) of smaller diameter, the size of which is conformed to the smaller diameter portion ( 20 ) of the opening ( 16 ) and which is guided in the smaller diameter portion ( 20 ) of the opening ( 16 ), the displacement piston element ( 12 ) comprises a portion ( 30 ) of larger diameter, the size of which is conformed to the larger diameter portion ( 26 ) of the opening ( 16 ) and which is guided in the larger diameter portion ( 26 ) of the opening ( 16 ), the piston housing ( 14 ) is surrounded by a coil ( 32 )of an electromagnetic drive ( 34 ) in the region in which the smaller diameter portion ( 20 ) of the opening ( 16 ) is formed, the displacement piston element ( 12 ) is inserted with its smaller diameter portion ( 28 ) into the coil ( 32 ) and forms an armature ( 36 ) of the electromagnetic drive ( 34 ), a fluid feed line is provided in the displacement piston element ( 12 ), which line is open at the smaller diameter portion ( 28 ) of the displacement piston element ( 12 ) to the smaller diameter portion ( 20 ) of the opening ( 16 ), which comprises an orifice leading to the inlet chamber ( 40 ) at the larger diameter portion ( 30 ) of the displacement piston element ( 12 ) and which is closable by a second valve assembly ( 76 ), which permits fluid exchange substantially only from the fluid feed line ( 12 ) to the inlet chamber ( 40 ).