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New “2-in-1” EV unit integrates traction motor and A/C compressor for increased range in hot climates

Engineers from Nanyang Technological University (NTU) and the German Aerospace Centre (DLR) have designed a “2-in-1” electric motor unit which can increase the range of electric vehicles in hot climates. This innovative electric machine integrates the A/C compressor, the compressor drive motor and the traction motor into a single housing physically clutching with the compressor during braking events.

The approach unifies the EV traction and compressor drives into a single housing which drive together during braking events. Based on simulations and analysis, the team expects the system to reduce battery consumption by at least 3% compared to existing mechanisms while improving the regenerative energy capturing capacity of the system by 8%. Overall, the novel design could increase the range of electric vehicles by an additional 15 to 20% with other modifications, the researchers suggested.

The design allows the electric motor to be more efficient in powering the car’s wheels, while its integrated compressor uses less power due to synergy between the engine and the compressor, which can also draw on energy regenerated directly from the car’s brakes.

Ntu
Design concept of the integrated A/C compressor-traction motor unit. Hybrids and EVs use regenerative braking to capture kinetic energy and store it; this requires the conversion of the kinetic energy first into electricity to transport to the battery, resulting in extra energy conversion steps.

The integrated compressor with drive motor, however, uses the recuperated energy immediately through the clutch connecting it to the traction motor. Coaxial shafts eliminate any interference that might occur between the two drives, while providing independent speed control during normal operations. Click to enlarge.

The biggest challenge with electric cars in tropical megacities is the range that they can travel on a full-charge, because their batteries are needed to power both the engine and the air-conditioning. In tropical countries like Singapore, up to half the battery’s capacity is used to power the air-conditioning system.

—Prof Subodh Mhaisalkar, Executive Director of the Energy Research Institute at NTU

The development of the machine took place in the course of an exchange program between the DLR and the NTU, with Singaporean PhD student N. Satheesh Kumar working on the project with the support of his German DLR-supervisor Dr. Michael Schier. (The cooperation between DLR and NTU has existed since 2012 and emphasizes electric mobility, energy storage, air conditioning systems, and hybrid lightweight construction as well as multifunctional materials.)

For electric vehicles, the air conditioning uses a lot of electrical energy, thereby cutting down the range of electric cars by up to 50%. To increase the energy efficiency and therefore the range of electric cars, the thermal management and the integration of additional functions into existing powertrain components play a major role.

By integrating the refrigerant compressor directly into the electric motor, we save components, weight and cost. Simultaneously, the more regenerative braking part of the kinetic energy is passed directly to the refrigerant compressor and thus the efficiency is further increased.

—Dr. Michael Schier, DLR’s Institute of Vehicle Concepts

With the potential boost in range through the efficient use of energy, the joint invention recently won the Best Originality Award in the TECO Green Tech International Contest held in Taiwan. (TECO, a Taiwan-based company, is one of the largest manufacturers of electrical drive technology.)

The competition saw 19 entries from top universities including Boston University, University of California (UCLA), Waseda University, and universities from China and Russia.

NTU’s partner DLR will conduct further tests and improvements to the new engine with the aim of eventual commercialisation. The team is applying for a Proof-Of-Concept (POC) grant in Singapore. After the development of the prototype, test bedding and refinements will be done at DLR’s facilities in Germany.

Prof Mhaisalkar said this innovation will pave the way for extending the range of electric cars, as the integrated design combines the two of the most important parts of an electric car, thus reducing its complexity into one highly efficient solution.

For the automobile manufacturers, the new electric motor will also cost less to produce, as it requires less material than its counterparts. Both the weight and size of the electric motor are reduced, creating more space for other components such as an auxiliary battery source.

Resources

Comments

Sublime

This is really clever. It's always more efficient to stay in the same energy domain. So if you can use the vehicles kinetic energy to drive the compressor that is way more efficient than converting that energy to electric energy, then converting to DC, storing in the battery, then converting back to kinetic energy to drive the AC compressor.

HarveyD

Reducing total dead weight of e-vehicles and battery pack + using ultra light high efficiency solar panels on roof, hood and booth areas could certainly improve range and performances in hot sunny places?

SJC

Sublime,

Good comment, welcome to GCC.

Roger Pham

The savings of 3% of battery energy consumption and 8% of recuperated energy is minor. A disadvantage to this is slow leakage of refrigerant via the drive shaft that over time, will render the A/C system less efficient, therefore, negating initial gain in efficiency.

The beauty of a separated electric powered A/C compressor is that it is hermetically sealed, thereby no leakage of refrigerant that can contribute to Global Warming, because many refrigerants have very high GHG index.

When the car sits idled in traffic, the motor is not moving while the A/C still needs to run, therefore, the A/C compressor and traction motor need to be separated, or else, a clutch will be needed to disengage the motor from the car that will increase weight and complexity. A larger traction motor that is used to pull a relatively light load of running A/C compressor at idle will not be as efficient as a dedicated motor optimized just to pull the A/C compressor's load. Those two factors further negate any minor gain in efficiency, and can adversely effect overall efficiency.

SJC

This does not seem to be a major advancement, I agree with Roger that you could "can" the compressor and motor to reduce refrigerant loses.

Engineer-Poet

Must agree with Roger.  Unless the refrigerant is something cheap and environmentally harmless in the quantities required (like isobutane or CO2), leakage past seals is probably a bigger deal than a bit of energy savings.  Just getting rid of the need for regular service will be a big advantage that this scheme foregoes.

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