Not only about the vehicles themselves, but also their own operations. Richard Simpson finds out more about MAN’s electric tractor unit, the eTGX
The 6x2 tractor unit, which forms the backbone of the UK’s long-haul transport parc, may not be the optimum solution for an electrified industry. As MAN Truck & Bus UK product manager Ashlea Awbery pointed out at the UK launch of the company’s eTGX tractor, by taking advantage of a legal dispensation for low-emissions vehicles, an electric 4x2 tractor can actually carry more payload at 42 tonnes gtw than a diesel 4x2 can at 40 tonnes gtw. Adding the extra axle to run at 44 tonnes (the legal limit for both diesel and zero-emissions) means that the payload advantage of a 6x2 wouldn’t be that great. A 46-tonne limit would be required for payload parity, but the chassis length required to accommodate both the battery packs and a centre undriven axle would mean that full-length trailers could not be used.
Achieving something close to payload parity requires careful attention to the vehicle’s specification, which means customers have to balance payload against range requirements.
The eTGX can be specified with four, five or six battery packs (or systems), each of which weighs in at 800kg. The payload advantage over a 4x2 diesel is lost as soon as more than four packs are specified. Range requirements are determined by charger availability, MAN’s electric vehicle consultant David Watts asserts. “The most important part of the transition is charging: it’s 70% charging, 20% the vehicle and 10% the driver.”
“Charging a truck requires five times as much energy as charging a car,” continues Watts. “The MAN product is perfectly suitable for long haul, but the UK’s charging infrastructure does not yet enable it.”
Seasonal variations
Watts’ claim is backed up by Awbery, who points out that, fitted with six packs, the eTGX had a daily range in the region of 600m to 800km with an intermediate charge. “If you drove a full shift on the speed-limiter you would cover 890km, but that’s an impossible achievement in UK operations,” he says. Range would vary seasonally, as batteries needed to be heated and cooled in use according to the ambient temperature. However, waste heat from the motor’s cooling circuit was used to warm the cab in winter.
There are three possible charging options: back-to-base; base and destination; and on-route. The first would be possible for all operators providing their grid connection was good enough, the second for some operators and the third would have to wait for suitable infrastructure as there was currently only one public truck charging station in the UK.
While desired range and payload were the two main constraints on battery specification, there were others. There was a two-tonne leeway on gross weights, but axle weight limits remained unchanged. Hence, while the MAN drive axle (carried over from the diesel truck) was technically rated to 13 tonnes, legally it could only bear 11.5 tonnes. Choosing the correct position for each pack was crucial to avoiding axle overloads. Also, operators requiring additional equipment to be fitted to the chassis might find that space constraints limited them to no more than five modules. An additional benefit of fewer batteries was a reduction in front-end price: they were, according to sales engineer Andrew Telling, the single most expensive component on the truck.
In contrast to the batteries found in electric cars, which might last up to 300,000km, MAN’s truck batteries would last for 1.5m kilometres – and MAN was obliged to take responsibility for them at end of life. The German OEM produced the batteries in-house using lithium nickel manganese cobalt (NMC) cells provided by CATLG (the German subsidiary of the giant Chinese CATL concern, which builds batteries for Apple). Each cell was around the size of an old VHS video-cassette and 15 were assembled to form a module. Twelve modules made up a system, or pack.
Belief in the batteries
The systems were tested to withstand dust, crash impact, fuel fires, water immersion, vibrations and other hazards. One of the benefits of NMC was that the system would keep working, even if a cell failed. The systems were built at MAN’s historic base in Nuremberg.
Battery monitoring will be a key task for fleet engineers on electric fleets, with some key terms to keep an eye on, as Telling explains, based on MAN’s experiences. State of Health (SoH) was the percentage of original capacity retained. A new battery started at 100% and was regarded as being serviceable until it fell below 80%. State of Charge (SoC) was the energy currently held by a battery at a given moment.
To preserve battery life the MAN system would only make from 60% of the potential capacity available to the driver: the top and bottom 20% were inaccessible to maximise battery life. Depleting a battery to below 20% and charging it beyond 80% had a detrimental impact on its overall life. Telling draws an analogy: “You wouldn’t brim a diesel tank without leaving room for expansion – and nor would you run it until it was nearly empty because of the contamination risk from sediment.” With this protection, the batteries could last up to 15 years. They are covered by a 10-year warranty.
Depth of Discharge (DoD) was the percentage of the battery’s original charge that was left at any point in the operation. Battery life was mainly determined by the total amount of energy that had flowed through it and the number of charging cycles it had been subjected to. However, there were steps that operators could take to preserve their batteries. In particular, battery use could be reduced by setting the internal cab temperature and defrosting it while it was still tethered to the battery charger.
Numerous other factors would have an impact: “Even the type of tyre on the trailer will have an impact: low rolling resistance tyres reduce the wear on the battery,” says Telling.
Ready to recycle
MAN’s preferred solution to disposal of end-of-life batteries was recycling, and it already met all current and known future standards regarding this. “All the components can be recycled, and all materials have been ethically sourced,” adds Telling, also pointing out that renewable energy companies regard expired vehicle batteries as useful resources for static storage.
Roger Turnbull, head of e-truck sales, says it is vital that operators take on the manufacturer’s consultation package as part of the acquisition process. His team would work with customers from pre-order, through the ordering process and after delivery of the truck. The trucks could handle most transport tasks but could not be just dropped in to replace diesels.
On the positive side, operators accustomed to replacing diesel trucks when they were three to five years old could look forward to longer lives from electrics over which to amortise the greater capital costs. MAN’s experience with city buses indicated that BEVs lasted longer and cost less to maintain than their diesel counterparts. Turnbull adds that residual values would be predominantly determined by battery condition rather than the vehicle’s age or mileage.
MAN has already taken some UK orders outside of government-supported schemes, and deliveries are expected to commence in Q3 of next year.
Beside the 4x2 tractor, MAN has also unveiled a wide range of rigid trucks in its German home market in 4x2 and 6x2 form, suited for a variety of vocational applications in addition to distribution.
Power for the people
A conventionally mounted, permanently excited synchronous motor delivers 330kW of power and 1,150Nm of torque through a four-speed MAN TipMatic automated transmission. There is no reverse gear: the motor runs backwards to reverse the truck. Drivers can switch between a ‘one-pedal’ mode, where regenerative braking is initiated as soon as the accelerator is released, or a conventional mode where braking is only actuated when the brake pedal is pressed. Regenerative and friction braking is integrated in the pedal action.
Drive functions are controlled by a stalk on the steering wheel column, just as they are on the diesel truck, and the diesel’s rev counter is replaced by a multi-function battery state indicator on the TFT ( thin-film transistor) instrument panel. Charging capacity is 375kW DC, with front-mounted CCS charging connections to the left and right.
