The Cummins VGT Exhaust Brake
The ISB diesel engines we have been running since 2009 have been very dependable. The only failures have been 2 turbochargers that were pumping oil. I’m still praising the VGT (variable geometry turbocharger) because the failure rate is low and the up time far exceeds any inconvenience we had to deal with.
All the failures incurred were covered by warranty as well so that is a big factor. We get 5 years of powertrain warranty which is well worth it. I would recommend this extra coverage to anyone. The down time for a fleet like ours is manageable because of the spare buses we have on site. They are older units but the wheels still turn and they start up ready to go when needed.
Some VGT Background Info
The VGT system is a patented Cummins design that controls boost pressure much more effectively. The desired boost pressure can be regulated for various engine loads creating more efficiency. The Cummins Holset design uses a set of guide vanes that controls exhaust gas through the turbine.
The difference between the Cummins and conventional design is the standard design pivots the vanes to get variations in nozzle areas while the Cummins VGT vanes don’t pivot but slide on it’s axis. The VGT raises the exhaust turbine efficiency because of the accurate angles it can achieve.
The sliding nozzle ring design can easily increase exhaust gas flow onto the turbine wheel. As the geometry changes inside the turbo the boost is increased as the nozzle is closed down. The increased exhaust pressure speeds up turbocharger speed. When the nozzle rings open boost decreases to maintain the best boost levels according to engine rpm. The variations are endless with the VGT to suit all engine loads.
Other benefits include improved fuel economy, EGR emission control and assistance with regeneration of the DPF exhaust system. I am sold with the ISB diesel and we are very happy to be ordering our buses with nothing else but the ISB option planted in the IC conventional school buses.
