Smaller engines, greater dynamics, lower fuel consumption: downsizing and turbocharging
Gasoline direct injection with turbocharging forms the basis for innovative downsizing concepts. For engines with a specific power output of 60 to 100 kW/l engine displacement, fuel consumption and CO₂ emissions can be reduced by some 15% – with substantially improved driving dynamics. At the same time, there is an improvement in responsiveness, map utilization, and transient behavior during start-up, i.e. the load-change characteristics at high engine speeds. In conjunction with widely spaced transmissions and downspeeding, downsizing of 50% plus is also possible.
Exhaust-gas turbochargers pump fresh air into the combustion chamber using overpressure, enabling more air-fuel mixture to be burned with the same cylinder volume, and power output and torque to be increased sharply. This means a smaller engine can generate the same power output as an engine with a much larger displacement. The fuel consumption saving is primarily achieved by the smaller engine’s ability to operate in the optimum efficiency range for more of the time. In addition, exhaust-gas turbochargers are driven solely by the flow of exhaust gas and do not consume any mechanical drive energy.
No turbo lag, more dynamics: scavenging
Turbochargers are driven by the flow of exhaust gas and achieve the standard boost pressure only from a certain engine speed. At low engine speeds, the flow of exhaust gas is weak and the compressor cannot compress the air sufficiently. The engine power output is correspondingly low – an effect dubbed “turbo lag”. Scavenging, which was developed by Bosch, eliminates the turbo lag through an intelligent combination of gasoline direct injection, variable camshaft timing control, and turbocharging.
With scavenging the valves are timed so that the intake and exhaust valves briefly open simultaneously in the low engine speed range. Between the engine’s intake and exhaust side there is a dynamic pressure differential; this draws larger volumes of fresh air into the combustion chamber and purges the residual gases more efficiently. Bosch Motronic boosts this effect by means of variable camshaft timing control with optimized valve timing. Early closing of the intake valve at low engine speeds and later injection produces a substantial increase in charging since less air is pushed back into the intake port. The higher mass throughput moves the exhaust-gas turbocharger to a higher boost speed level with much higher boost pressure. Scavenging can be used to increase torque at full load below 2,000 rpm by up to 50% so that the responsiveness is on a par with large displacement engines. Compared with intake manifold engines with the same power output, fuel consumption can be reduced by up to 15%.
Highest precision, constantly: controlled valve operation (CVO)
State-of-the-art combustion processes are characterized by high pressure even under partial load and multiple injections for optimized mixture formation. This translates into ultra-short injection times and increased metering tolerances.
Thanks to Bosch’s CVO mechatronic system solution, the precision of the gasoline direct injection is significantly increased and is maintained throughout the fuel injector’s entire service life. The basis for this solution is provided by the consummate interplay between Bosch electronic control unit and Bosch high-pressure injector, which form a closed loop. Unlike conventional precontrolled injection, with CVO the electronic control unit records the triggering signal during the injection and determines the optimum timing for opening and closing the valve needles. This enables the electronic control unit to calculate individually the actual injection quantities of each injector and even allows minute quantities of fuel to be injected with minimal tolerances. The combustion process remains stable and particulate emissions are reduced, especially during the catalytic converter warm-up phase. Bosch offers a solution that is as innovative as it is cost-effective in the shape of CVO to meet future emissions standards.