malvernmugadzikwa
IN my previous articles, I talked about hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs).
This week, I introduce you to extended-range electric vehicles (EREVs).
When comparing the different electric vehicle (EV) drivetrains, motorists and mostly technicians should understand that each has been designed for a particular purpose and application.
The HEV utilises a full-sized internal combustion engine (ICE), which is similar to that of a conventionally powered vehicle.
The HEV battery is used to provide power to the electric machine.
The electric machine will be used for acceleration and load levelling.
Therefore, the battery pack capacity is much smaller (1,3 kilowatt hours), when compared to a PHEV’s (8,0 kilowatt hours) or BEV’s (24 kilowatt hours to 100 kilowatt hours).
This application still requires the ICE to operate to charge the battery pack and propel the vehicle.
The combination of mechanical and electric drive provides control for using electric propulsion primarily in low-speed operations, blending electric power and ICE during mid-range speeds and primarily ICE propulsion at high speeds. Combining these two technologies permits the control system to use electric ICE propulsion or a blend of the two technologies when either system is efficient.
It also allows the driver to benefit from the ability to charge the battery without the need to plug in the vehicle.
The PHEV application is similar to that of the HEV, except it has the ability to plug in to household 110 volts alternating current (VAC) or 220 VAC to provide the first 40 kilometres (km) to 80km under full electric power.
PHEV and EREV systems are not designed to be charged with direct current (DC) fast-charging systems. Therefore, only the lower-voltage system can be utilised to charge them.
In the United States, they use mostly 110 VAC in their household applications, but here in Zimbabwe, we use the 220 VAC electric vehicle supply equipment (EVSE) charger.
The 220 VAC EVSE system is significantly faster when compared to the 110 VAC EVSE system.
Most driving distances in Zimbabwe are within 16,1km of operator residence, which allows the PHEV to operate exclusively under electric power.
If the driver wants to go further, they have an ICE that will provide propulsion power and maintain the battery at a minimum state of charge (SOC).
The PHEV application can drive the vehicle under the full electric mode or “assist” the ICE so that the torque from both systems can be used to propel the vehicle.
This will decrease the load on the ICE and increase efficiency and fuel economy because the electric propulsion efficiency is significantly higher than in an ICE system.
Multiple charging and propulsion systems provide the operator with a familiar feel, whether in electric or blended modes, to enhance the acceptance of PHEV systems.
A full BEV application is only equipped with a high-voltage battery pack to provide power to the electric machine that propels the vehicle.
This application requires the driver to recharge the vehicle each time the battery pack is depleted.
Depending on the application, the availability of DC (480 volts) fast-charging capability is six to 16 times faster than a 220-volt charger (vehicle-dependent).
A trip with a BEV will require the driver to plan when and where to access a charging station to recharge the battery pack.
An EREV application utilises the ICE to generate power for the drive motor and sustain the high-voltage battery pack once it has depleted to the lowest permissible SOC operating point.
This application is different to the one for the HEV because it always uses the drive motor to propel the vehicle, with assistance from the engine and generator to provide electrical power to the drive motor and battery pack.
The EREV system is designed to operate only on electric propulsion during the first 40,2km to 80,5km of driving (battery depletion mode).
Once the battery has reached its lowest/minimum SOC (approximately 20 percent), the system will command the engine to start.
The engine will drive a generator, which will provide electrical power for the drive motor, while charging the battery to sustain its minimum 20 percent SOC.
Once the trip is completed, the driver can connect the vehicle to a charging station to recharge the battery to 100 percent SOC.
The EREV system uses one driving mode, in which the engine will augment the electric propulsion torque with engine torque that is delivered directly to the drive axles.
The EREV uses a smaller four-cylinder engine for propulsion, when compared to a conventional application, because the engine is not the primary method of propulsion.
Therefore, the engine size (litres and horsepower) can be reduced, which lowers fuel economy
and increases overall system efficiency.
Additionally, without the need to accelerate the ICE to propel the vehicle during the first 48,2km to 80,5km, multiple timing and operation strategies can be employed to make the ICE extremely efficient.
Some of these engine control strategies utilise the Atkinson cycle, instead of the typical Otto four cycle.
The Atkinson cycle increases the time the intake valve is open, which can decrease the pumping losses of the ICE.
It is also significantly more efficient than the Otto cycle when the engine speed and load are low, which increases fuel efficiency.
This type of engine operation is perfect for the EREV system because the electric propulsion system is extremely efficient during low- and medium-vehicle loads and speeds.
To be continued . . .
*Taurayi Raymond Sewera is ASE and AutoCate Association-certified World Class Master Technician with 39ASEs, ASE Advanced Level Specialist L1, L2, L3 and L4, AMI-Accredited Master Electric Vehicles and Master Automotive Manager, and ACDC-certified Master Hybrid and Electric Vehicles Technician. He is the founder and CEO of TauRay Automotive. He can be contacted on: +263772341193, +263772357296 or [email protected]
Online Reporter