BMW S58, Owner'S Handbook Manual

Page: 72 / 102

S58�Engine
8.�Intake�Air�and�Exhaust�System
66
8.1.4.�Venturi�nozzle�pressure�sensor
The�flow�of�scavenging�air�is�generated�by�the�vacuum�in�the�intake�pipe.�In�order�to�be�able�to
scavenge�in�turbocharged�mode�as�well,�vacuum�is�generated�by�means�of�a�venturi�nozzle.�The
venturi�nozzle�is�powered�by�an�air�mass�flow�which�is�tapped�downstream�of�the�intercooler�and�fed
back�in�upstream�of�the�impeller.�The�venturi�nozzle�pressure�sensor�in�the�tank�vent�pipe�is�used�to
diagnose�the�second�feed-in�point�of�the�tank�ventilation�system.
Strain�gauges�are�used�to�determine�the�pressure.�A�steel�diaphragm�in�the�sensor�fitted�with�strain
gauges�is�deformed�by�the�pressure�present.�The�changes�in�resistance�of�the�strain�gauges�are
electronically�analyzed�by�a�Wheatstone�bridge.�The�voltage�measured�is�then�included�in�the�tank
ventilation�diagnosis�as�an�actual�data�reading.�The�venturi�nozzle�pressure�sensor�is�a�differential
pressure�sensor.
8.1.5.�Carbon�canister
To�meet�emission�standards�in�the�US,�a�carbon�canister�with�a�larger�volume�is�used.�The�basic
function�of�the�carbon�canister�has�not�changed.�The�increase�in�volume�is�solely�for�the�purpose�of
collecting�larger�amounts�of�fuel�vapor�and�retaining�them�for�longer�before�a�flushing�operation�by�the
tank�vent�valve�takes�place.
8.2.�Exhaust�emission�system
8.2.1.�Overview
The�exhaust�emission�system�has�a�different�structure�in�the�S58�engine�with�the�two�exhaust
turbochargers�than�in�the�B58TU�engine�with�a�twin-scroll�exhaust�turbocharger.�The�exhaust�system
is�a�cylinder-dependent�twin-pipe�design.
The�exhaust�system�was�designed�for�minimum�exhaust�gas�pressure.�With�this�dethrottling�of�the
exhaust�system,�the�efficiency�of�the�gas�exchange�could�be�optimized�even�further.