We recently expanded our collection of electric vehicle drive units, adding a unit from a Smart Fortwo Electric to our Leaf drive unit. This particular Smart EV unit is quite intriguing, almost a unicorn in terms of available information. Publicly accessible details are scarce, but we know it incorporates a Bosch SMG 180/120 motor, rated at 55kW. What makes this unit especially interesting is the use of the SMG 180/120 motor, an off-the-shelf component that should simplify integration into various vehicle projects. This motor also boasts a notable pedigree, having been used in vehicles like the Fiat 500e and even in the front axle of the Porsche 918. Let’s delve into our initial look at this drive unit before we fully disassemble it.
Initial impressions of integration complexity suggest it isn’t designed for straightforward component swaps. This aligns with the Smart Fortwo Electric Drive’s history as a low-volume model. Likely conceived as a compliance car to enhance Mercedes’ overall fleet fuel economy, its production probably relied heavily on electric vehicle subsidies to achieve profitability, rather than focusing on modular design for ease of part integration. For future reference, here’s the donor vehicle’s identification tag.
Before diving into the main power components, we took a detour to examine the air conditioning compressor.
This compressor is a fully integrated unit, incorporating DC power and CAN bus communication directly. Internally, it utilizes a scroll compressor mechanism, a design known for its efficiency and compactness.
It also features an interior permanent magnet (PM) motor, further contributing to the unit’s compact and efficient design.
A small inverter is mounted directly to the back of the compressor motor. While technically interesting, the practical use of this AC unit as a standalone component is limited unless a 370VDC air conditioning system is specifically required. With the AC compressor examined, we shifted our focus to the more substantial components of the Smart Fortwo electric drive unit.
The integrated charger is a 6.6kW unit manufactured by Lear Corporation, a well-known automotive supplier.
Similar to other components in this drive unit, accessing the charger required significant coolant draining, a common step in dismantling liquid-cooled EV systems.
Once the coolant was drained, the charger was easily detached by removing a few bolts, revealing a neatly packaged, self-contained module.
Our exploration of the charger was brief as our primary interest wasn’t in its operational functionality. However, getting it operational should be reasonably straightforward. It’s important to note that this charger is solely responsible for AC-DC conversion and does not handle battery balancing functions, which are managed separately within the Smart Fortwo Electric’s battery management system.
Next, we turned our attention to the inverter. Upon inspection, we found a part number, identifying it as an EFP 2-3 model manufactured by Continental and marketed by Zytek.
Further investigation revealed that this inverter is rated for 235A continuous current and 355A peak current. Detaching the inverter from the rest of the drive unit was accomplished by removing a few bolts, similar to the charger.
The inverter is remarkably small and compact. It’s almost comical how the high voltage cables likely outweigh the power electronics within. With the inverter and charger removed, we could finally separate the motor-gearbox assembly from the rest of the drive unit. The motor-gearbox unit immediately appeared promising – the motor’s cylindrical shape and manageable weight suggested it could be handled by a single person, simplifying integration into custom EV projects.
| Say hi to Charles! Inspecting the Smart Fortwo Electric drive unit motor. |
After separating the gearbox from the motor, we were left with a truly diminutive traction motor.
The motor’s mounting pattern appears quite user-friendly, which is beneficial for custom installations.
However, suspending the 32kg motor solely from these mounting tabs might not be structurally ideal for all applications. The gearbox design closely mirrors that of the Nissan Leaf, albeit in a smaller form factor, suggesting a similar internal configuration and operational principles.
Internally, the gearbox exhibits a very similar design to the Leaf’s unit, indicating a common approach to single-speed reduction for electric vehicle powertrains.
Our next step was to attempt to open the inverter housing to examine its internal components. Initial access looked promising with visible pin-style channels, presumably designed to minimize pressure drop within the cooling system.
However, we encountered a challenge with the high voltage cable harness connection.
The harness is plugged in using large blade terminals, indicating a robust high-current connection. Unfortunately, our attempt to further disassemble the inverter housing was thwarted by the presence of delicate ribbon cables connecting internal boards. It was unclear how to safely separate the housing halves without risking damage to these critical cables, so we decided to halt further disassembly of the inverter at this stage.
Overall, the Smart Fortwo electric drive unit shows significant potential for conversions in smaller vehicles or projects requiring compact EV components. The somewhat clunky integration in its original application turns out to be advantageous for repurposing, as individual components feature sensible mounting points. There also remains a possibility of obtaining datasheets for the inverter and motor directly from their respective original equipment manufacturers (OEMs), Bosch and Continental/Zytek. However, the 55kW continuous (80kW peak motor rating from Bosch) and 200Nm torque output of a single unit may be insufficient for full-size car conversions, suggesting that utilizing a pair of these units might be necessary to achieve more substantial power levels for larger vehicle applications.
