Tested 25.11.17, Germany On sale 2019 (est) Price TBC
Wolfsburg reveals mild hybrid tech for mainstream models
The technology might be a year or two away from trickling down to mainstream family cars, but Volkswagen, like most manufacturers, already has 48-volt mild hybrid electric vehicles (MHEVs) under development. We drove a pair of prototype Golf 1.5 TSI MHEVs at the car maker’s Ehra-Lessien proving grounds.
Forty-eight-volt electrical systems such as those in the Golfs have been under development for a few years to power driver aids, infotainment systems and devices such as electrically assisted turbochargers.
The 48V belt-integrated starter alternator (BISG) replaces the normal 12V unit and produces 8kW, the equivalent of 15bhp if used as an electric motor to boost the engine’s torque. As a generator, it can recover energy and charge the 48V lithium ion battery when the car decelerates. This aspect is crucial as manufacturers come under ever-increasing pressure from emissions and CO2 regulations.
VW is working on two variants, the Golf 1.5 TSI MHEV and the MHEV Plus. The second of these has a 34bhp (25kW) electric motor driving the front axle in addition to the engine. The MHEV Plus can also be configured with a second motor driving the rear axle in pseudo all-wheel-drive fashion to help with traction on poor surfaces or to neutralise understeer.
The Golf 1.5 TSI MHEV proved surprisingly refined for a prototype, with seamless integration of the BISG. Stop-start events are much smoother than with a conventional 12V system, as the engine is spun up to higher revs before it fires. This also means the engine can be stopped and restarted fluently when the car is moving, allowing the driver to ‘coast’ with the engine stopped to save fuel.
The MHEV Plus felt slightly less seamless because synchronising the engine and the two electric motors is far more complicated. The aim is not to produce finished, refined software at this stage but test the system for efficiency. Even so, it was punchy to drive and the system restarts from coasting smoothly enough. The second motor recoups energy via regenerative braking when the engine is stopped for coasting, which isn’t possible with the basic MHEV.
The systems are estimated to give an improvement of around 7mpg (13%), which, given that MHEV powertrains could one day become standard, is not to be sniffed at.
VW Golf 1.5 TSI MHEV
Early versions of the MHEV Golf with 48V electric drive show promise, with punchy and refined power delivery
Engine 4 cyls, 1498cc, turbo, petrol
Gearbox 9-spd automatic
Kerb weight na
0-62mph 8sec (est)
Top speed 134mph (est)
CO2, tax band na