Belgium / UK - The BAE Systems’ electric drivetrain and accessories power system when compared with a generic competitor system has significant differences and advantages for the vehicle and vehicle manufacturer, according to Laurence Homer, Business Development Manager at BAE Systems Inc of Rochester, UK, when speaking with Truck & Bus Builder at Busworld Europe in Brussels held in October.

In explaining this, Homer said that a typical competitor system could comprise of nine separate components (or ‘boxes’), which are then connected using many cables, all of which then need to be fitted into the vehicle somewhere. Furthermore, as many of the components need to be actively cooled, this further adds to the cabling, pipework and space requirements!

On the stand BAE Systems displayed its current family of motors and inverters; these included the GPM-10 and GPM-12 direct drive motors alongside a GPM-5 motor with an Eaton MD4 (Medium-Duty 4-speed) gearbox, as well as the MAPS*, MPCS**, and GPI-10 inverters.

Homer stated that BAE Systems offers a federated system, which means that all of the same functionality is held in a smaller number of core units, meaning that BAE Systems will only fit four ‘boxes’ in the bus; the E-Motor, System Control Unit (SCU), Propulsion Control System, and Accessory Power System.

A short animation video by BAE Systems is now available on YouTube that explains the advantages of its modular federated system.

Homer said: “So, those typical nine boxes found in a competitor’s power system, are now replaced with just four. As a result, less cabling is required, as some of the connections have been internalised within the units; there are fewer cooling requirements, because only three units need to be actively cooled and, there is less space required to install the system components, making it less complex to integrate and easier to fit. Furthermore, when you combine the units, there is also the benefit of greater efficiency with less weight.”

Homer also pointed out that some of the heaviest parts on the components are the chassis frames, “So if you have nine ‘boxes,’ this requires nine chassis with mounts, brackets and fixings - all resulting in added weight and a significantly higher part count.”

BAE Systems’ ‘One-stop-shop’ solution

There is also the added advantage of having pre-integrated systems, stated Homer. He explained that if the component parts (‘boxes’) were sourced separately from different suppliers, the OEM may need to deal with possibly seven or eight different systems, which are not pre-integrated, and so the OEM would need to do this itself; meaning the parts would most likely be more costly, not to mention the difficulties with compatibility, cost and speed of integration.

With BAE Systems’ modular system, Homer pointed out, the company offers a ‘one-Stop-Shop’ solution. “By buying the whole system from us,” he remarked, “it will work together simply because we have already integrated it.” BAE Systems, Homer added, always works in partnership with the OEM to first configure what system is needed ahead of the installation work, so that when it takes place, it should be a simple case of plugging it together.

For example, according to Homer, the demonstrator vehicle BAE Systems has created with its currently un-named partner in South America – from completing the chassis build, to it driving on the road - took just seven weeks! “We gave them the ‘boxes,’ they fitted them, we loaded the software – there were a few niggles – but effectively, it worked first time.”

Fuel cell ready

BAE Systems has plans to integrate a converter for fuel cell applications into its MPCS (Modular Power Control System) unit, announced Homer. On the side of its MPCS will be a PIM (Power Interface Module), which will interface directly with a hydrogen fuel cell. This will provide a connection directly to the Hydrogen Fuel Cell (HFC) to enable high voltage DC input from the fuel cell into the MPCS, which would then be converted to the voltage(s) needed specifically for the different system requirements. The PIM will also provide power back to the HFC for its cooling fans and other ancillary systems.

Caption: A direct-drive GPM-12 (general purpose motor) + MAPS + MPCS

The integration of the fuel cell PIM again will reduce weight, complexity and integration time. Homer stated that currently, most systems for hydrogen fuel cell applications require a separate converter box or DC gateway between the HFC and the power system.

Power system for coach and truck applications

On display for the first time in Europe was BAE Systems GPM-5 with Eaton MD4 Gearbox – a direct drive motor coupled with a four speed EV gearbox for delivering both speed-on-highway, and speed-on-grade.

Caption: BAE Systems' GPM-5 with Eaton MD4 (Medium-Duty 4-speed) Gearbox V1

Homer explained the purpose of this traction drive configuration. He said that traditional electric drivetrains are directly geared to the wheels, so there is no gearbox, they are fixed geared, so when designing a vehicle with BAE Systems’ motors, it chooses a differential gear ratio that is suitable for the application. The disadvantage of this is that the top speed is fixed, meaning that by choosing a higher top speed there is a trade off with reduced torque at lower speeds. By introducing a gearbox in front of the motor, this allows an electric vehicle to run at a higher speed, when operating on a highway, for example, but then when operating at lower speeds, it removes the torque disadvantage of the direct drive by switching down through the gears to deliver higher torque. Another advantage, Homer pointed out is that a smaller electric motor can be used where torque, but not power, is required (hence the use of the smaller GPM-5).

One disadvantage of an electric drive with transmission is that it does have to shift, albeit it will be seamlessly smooth, Homer remarked. The automated gearbox shifting is controlled by the BAE Systems software based on the speed and torque of the motor. While the unit on the stand was a display model only, Homer said BAE Systems and Eaton were making good progress in working together on building a test vehicle.

*MAPS (Modular Accessory Power System), which provides the auxiliary AC and DC (28V) power for vehicle accessories, such as 3-phase AC control of systems like the air conditioning, power steering, air compressors etc.

**The MPCS (Modular Power Control System), for controlling the main traction motor and the ability to add modules for additional battery storage capacity and on-board charge capabilities.