Micro Hybrid technology captures the energy generated from a bus’s braking system, and redistributes this energy to power pneumatics, hydraulic and electrical systems which would otherwise require power from the engine.
The result is a reduction in fuel consumption of up to 10%, leading to substantial savings over a bus’s typical 15-year operational service life.
the Micro Hybrid equipment – which charges the batteries during braking to power auxiliaries – deliver a significant fuel saving, it also entitles the operator to enhanced BSOG payments without the extra costs associated with a full hybrid’s complexity and batteries.
StreetLite Micro Hybrid range has achieved Low Carbon Emission Bus Certification. The StreetLite Micro Hybrid is a very low cost hybrid system that allows the bus to recuperate lost braking energy to power the vehicle electrics and the vehicle compressed air system for free. This improves fuel efficiency by approximately 10% on a typical city bus drive cycle.
The StreetLite Micro Hybrid uses the same engine, transmission and rear axle as the conventional StreetLite, but re-jigs the auxiliary systems to give the vehicle smart control of energy generation and usage on the vehicle.
A standard bus driveline has three important extra bits powered by the engine:
1. Air compressor (for brakes) which runs when the air tank pressure is below a given set point
2. Alternator (to charge battery and power lights etc.) which runs continually with a load proportional to the electrical load on the bus
3. Hydraulic pump for cooling fan (to stop the bus melting) which runs continually with a load proportional to engine speed.
Now in the Micro Hybrid, when the driver presses the brake pedal, some of the waste energy is stored in compressed air tanks and the compressor only runs when really, really needed (which is hardly ever on a busy stop-go city route - lots of brake presses.Likewise with the alternator, but here the spare energy is stored in the batteries. Again the alternator is hardly ever used on a busy city service. The hydraulic pump becomes an electric pump, again running only when needed.In this way, the load on the engine is significantly reduced, and the auxiliary systems are powered by waste energy that would otherwise be lost. This has the additional benefit of reducing the load on the retarder and brakes, which will also reduce the load on the cooling pack and extend the life of the friction brakes. The overall efficiency gain when Micro Hybrid is added to a conventional StreetLite is around 9.2% and this additional fuel saving is enough to place the vehicle comfortably below the threshold for Low Carbon Emission Bus Certification.
Wrightbus’ “Micro Hybrid” recovers braking energy, but rather than use it to directly benefit propulsion as in full hybrid systems, this energy is stored in storage systems already on board and is used to power pneumatics, hydraulics and electrical items. These components would otherwise require power from the engine and, by using the energy harvested from the braking system, reduces overall fuel consumption by around 10%.
Forgive me, but there's nothing there that explains to me exactly how these savings are achieved - ie what device does what - maybe it's that the hydraulic pump is now electrically driven - and the alternator does what?
I've read that the system uses the standard vehicle batteries (so there is no added storage equipment), but when a battery is fully-charged there's not much else you can do with electricity - other than use it to drive electric pumps - and the system is said to harvest energy during braking (so we aren't talking about an engine-driven generator - maybe it is driven from the gearbox retarder?)
It seems to me to be smoke and mirrors - but that is only because I haven't found a plausible technical explanation yet despite extensive searching . . .
You would think that for a pioneering system that there would be a treatise published explaining exactly how the saving is achieved - but maybe they don't want the competition to cotton on?