| Automotive consultancy Zytek is using a diesel hybrid powertrain, installed in a Smart forfour, for its ultra low carbon car challenge (ULCCC) vehicle, funded by the UK Department of Transport.
In the scheme, vehicles must be capable of mass production at a sensible price, offer C-segment interior space, accelerate to 62mph (100kph) in under 16s, be Euro IV compliant and emit less than 100g/km CO2 on the combined cycle.
Zytek’s vehicle reaches 62mph in under 12s before a limited top speed of 155kph and emits only 85g/km CO2, returning 88mpg (3.2l/100km) combined.
Zytek’s solution, like its Smart EV vehicle, requires no changes to the BIW of the DaimlerChrysler platform and addresses packaging and cost. A small turbodiesel engine was the obvious starting point so the three cylinder 1.5l CDi unit with 50kW/160Nm was retained, though a diesel particulate filter was added.
The hybrid is dual mode and uses advanced control strategies to replace the clutches and epicyclic gears used in other designs, making the powertrain lighter, cheaper and more compact. A 288V Li-ion battery provides 45kW of power and can be recharged using a 240V mains supply.
The design uses two electric machines: a 43kW/130Nm DC starter/generator permanently engaged with the engine and a 50kW/105Nm AC traction motor mounted on to the end of the two speed custom gearbox (only 138mm long), designed by transmission specialist Xtrac.
Integrated into the bellhousing, the starter generator provides torque assist to aid acceleration and enable a high gear ratio to be used at low revs, keeping the engine at its most efficient range. The traction motor spins up to 11,500rpm and is more than 97 per cent efficient. They engage the drivetrain via a dog synchromesh system: advanced control replaces the synchro cones to provide smooth shifts without torque interruption.
The new drivetrain is packaged in the same space as the original six speed gearbox.
Launch is via electric toque only from the traction motor, supplemented by the engine between 45-50mph until the electric effort ceases at approx. 70mph, ensuring that all machines operate only at their most efficient levels.
The engine has a new controller, designed by Zytek – it’s first for a diesel, developed and calibrated in less than 14 months. The unit ensures the most efficient and clean operation possible and communicates with existing vehicle data buses plus the extra CAN bus added for the hybrid components.
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Zytek's drivetrain including gearbox, motors and controllers |
Integrated with the controller is Zytek’s engine and hybrid control module (EHCM) which performs the complex task of managing the hybrid systems, including the diesel/electric torque split and the degree of regenerative/hydraulic braking required.
Zytek’s compact inverter, packaged under the bonnet, supplies the 300V supply to the motors and 1.8kW of 12V power for the main electrical system.
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Engine bay offers limited space for hybrid components |
Launch is via electric torque only from the traction motor, supplemented by the engine between 45-50mph until the electric effort ceases at approx. 70mph, ensuring that all machines operate only at their most efficient levels.
The driver chooses one of three operating modes, each available with high/low regen braking levels:
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Economy for city use; engine use minimised and max power limited to boost electric range (max speed 45mph)
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Drive for mixed use; full power available with engine/stop start for efficiency
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Sport; disables stop start and offers maximum power and acceleration.
Zytek says that the hybrid elements represent an on-cost of £2500 at production volumes of 20,000 units a year. “An important objective for this vehicle is that it is totally ready for production,” says Neil Cheeseman, programme manager. “It has the design detail and sophistication needed to enter the market immediately.”
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