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Mobile machinery

Converting a conventional tractor into an electric vehicle

Terberg (Netherlands) produces the YT 182, an electric version of one of their terminal tractors. The company met the challenge of delivering power to the large number of auxiliary systems with the help of Lenze Schmidhauser (Switzerland).

The solution features a CANopen and J1939 interface (Photo: Lenze Schmidhauser)

THE TASK WAS TO COMBINE A 24-VDC CONVERTER and a 600-V inverter into a compact system that would meet all vehicle requirements. “One of the hardest things to do when converting a traditional terminal tractor into an electric vehicle is powering the auxiliaries,” says Erik-Wim Vos from Terberg. “In our combustion engine designs, it is all pretty straightforward. You need air or hydraulic pressure? Just run a compressor or pump off a V belt or PTO and that is basically it. But an electric vehicle has no moving parts to borrow from. All the energy comes straight from the battery pack and needs converting or inverting.” In the commercial vehicle domain, electric vehicles are mostly uncharted terrain. Industrial components are too big and can’t comply with the requirements for utility vehicles. This would result in a costly and bulky enclosure that would not offer the kind of protection against operating conditions that a cast-aluminum housing does.

Terminal tractors are like city buses and refuse-collection trucks, always on duty, running for 30 000 to 50 000 hours before they “retire”. Terberg’s tractors are mainly used for logistic operations in ports, industry, distribution centers and other transshipment locations, where up to 115 tons of freight in 8-to-10-hour shifts are moved, day in, day out. At first glance, these are hardly the ideal conditions for electric vehicles. For one thing, no matter how big your battery pack, it will always run out of power eventually. Also, it will probably be a very long time until we can charge a vehicle with electricity anywhere near as quickly as we can fill a tank with diesel. For another thing, the total operating costs of the YT 182 electric tractor are still more expensive compared to its combustion engine counterpart. “But we expect that this will even itself out within a few years,” says Vos. “The vehicles with short repetitive cycles of operation are most likely to have a viable electric alternative. It is true that clients will have to adjust their operation when going electric. In the case of the YT 182, which can run for 8 hours to 10 hours straight and needs two hours of charging on a CEE 125-A grid charging point, it would be unwise for every driver to take a coffee break at the same time.” If you want to be on the safe side with grid requirements and charging points, as well as vehicles, you need to balance the number of terminal tractors, operators and their shifts. But people often neglect the fact that a combustion-engine-based fleet not only needs diesel, but also an infrastructure for refueling. Build a filling station costs money, as does maintaining it and taking measures to minimize the soil contamination that occurs when dealing with diesel.

Among environmental arguments such as CO2 emission, health and safety regulations can also come into play when going electric. Noise reduction can be a reason to turn your back on traditional combustion technology. When unloading large ships, exhaust fumes pose a health risk for operators, since the holds are often poorly ventilated. It is the trend towards stricter regulations for dealing with these issues that made the company decide to try a different solution. Another factor was the probable return of investment after eight to ten years – the expected lifetime of the vehicle – due to rising fuel prices.

The solution features a CANopen and J1939 interface (Photo: Lenze Schmidhauser)

How do you go about transforming a terminal tractor with a combustion engine into an electric one? You start with the drive train. Vos explains: “When designing the drive train, you start with getting the numbers right. In our case, we need to pull up to 85 tons gross combined weight (GCW), yet require a relatively low top speed of 40 km/h. This means that besides plenty of battery power with a reliable power management system and an electric motor (720 Nm and 138 kW) with integrated inverter, we also needed a gearbox, and in our case an additional gear to drive the hydraulic pump for the lift frame. Getting all these parameters working well together and translated into an integrated solution that also fits the YT182 frame is quite a challenge.

The way we resolved this was to work with specialist partners that offer integrated solutions, instead of connecting all the different dots ourselves. This was certainly also true for a second obstacle that we encountered: powering the auxiliary systems.” Lenze Schmidhauser provided the company with an integrated solution that took care not only of powering the 230-VAC compressor, but also delivered the 24 V needed for most dashboard functions. Integrating these converters into one robust cast-aluminum housing saves space and cuts the costs of buying and installing two separate units.

Modular platform with CAN

Lenze Schmidhauser has developed a modular platform approach called Mobile. Sales and Marketing Manager Jonas Schuster explains: “We noticed that more and more manufacturers of utility vehicles were looking for an electric alternative. But when it comes to the converters, it is hard to find ones that really meet the vehicle requirements, especially when it comes to life expectancy, the number of starts/stops and in general all the harsh operating conditions (shock, vibration, temperatures, water and so on). Typically, industrial converters are big and bulky and have moving parts, such as a fan for cooling. We figured that if we could come up with a platform where we could easily install a variety of converters of different voltages and power in a single water-cooled or glycol-cooled aluminum enclosure, the benefits for the manufacturers of utility vehicles would be similar to the benefits for car manufacturers. And this could be done without having to increase the production run.”

The solution features a CANopen and J1939 interface (Photo: Lenze Schmidhauser)

Since the launch of Mobile in 2012, various multi-inverters and DC/DC converters have been available. The Mobile platform consists of several intelligent double inverters (DCUs), different DC/DC converters (PSUs) and various combined modules. They can be used to control both synchronous and asynchronous motors, making them suitable for controlling auxiliary equipment, but also as small traction drives. As for the DC/DC converters, there is a 5-kW and a 10-kW version available with a 14 VDC or 28 VDC output (200 A or 400 A output current). They are intended for on-board electrical systems and can replace alternators. If more power is required, multiple converters can always be connected in parallel.

“In the case of Terberg, the on-board monitoring was another important Mobile platform feature. In order to be able to safely disconnect the power, we wanted a locking function. Thanks to the available CAN bus, we can easily integrate the system into the overlying vehicle management system,” says Schuster. The product platform complies with CANopen and J1939 and can thus be integrated into vehicle management systems.