Introduction
A system of valves using oil pressure to turn the cam with respect to its drive gear controls the cam positions on the BMW system shown in. The position of the cams is determined from a suitable map held in ROM in the control unit.
A system that not only allows changes in valve timing but also valve open periods is also starting to be used. The system is known as an active valve train (AVT) and was intended to be a development tool for the design of fixed camshafts. However, production versions are being developed.
Wide range lambda sensors
Most lambda sensors provide excellent closed control of the air-fuel ratio at or very near to stoichiometry. A sensor is now available that is able to provide a linear output between air-fuel ratios of about. This allows closed-loop feedback over a much wider range of operating conditions.
Injectors with air shrouding
high-speed air is introduced at the tip of an injector, and the dispersal of the fuel is considerably improved. Droplet size can be reduced to below 50 m during idle conditions. shows an injector with air shrouding.
Combustion flame and pressure sensing
Research is ongoing in the development of cost-effective sensors for determining combustion pressure and combustion flame quality. These sensors are used during development but currently are prohibitively expensive for use in production. When available, these sensors will provide instantaneous closed-loop feedback about the combustion process. This will be particularly important with lean-burning engines.
An accurate crankshaft speed sensor is used to monitor ignition and combustion in the cylinders. Misfiring alters the torque of the crankshaft for an instant, which causes irregular rotation. This can be monitored, thus allowing a misfire to be recognized instantly
On-board diagnostics (OBD)
Figure 10.9 shows the Bosch Motronic M5 with the OBD 2 system. On-board diagnostics are becoming essential for the long-term operation of a system in order for it to produce a clean exhaust. Many countries now require a very comprehensive diagnosis of all components which affect the exhaust. Any fault detected will be indicated to the driver by a warning light.
The OBD 2 system is intended to standardize the many varying methods used by different manufacturers. It is also thought that an extension to total vehicle diagnostics through a common interface is possible in the near future
2A number of further sensors are required for the functions of the OBD 2 system. Another lambda sensor, placed after the catalytic converter, monitors the operation of the OBD 2. An intake pressure sensor and a valve are needed to control the activated charcoal filter to reduce and monitor evaporative emissions from the fuel tank. A differential pressure sensor also monitors the fuel tank permeability.
Last word
As well as the driver’s fault lamp a considerable increase in the electronics is required in the control unit in order to operate an OBD system. A better integral-monitoring system will have a superior effect in reducing vehicle emissions than tighter MOT regulations.
