How does the type of route driven affect the fuel consumption of PHEVs

The type of route driven significantly affects the fuel consumption of Plug-In Hybrid Electric Vehicles (PHEVs) because of the differing energy demands and efficiencies in various driving conditions.

Impact of Route Type on PHEV Fuel Consumption

City vs. Highway Driving

• PHEVs experience different fuel consumption patterns in city and highway settings due to varying driving dynamics such as stop-and-go versus steady cruising speeds.
• City driving typically involves frequent stops and lower average speeds, leading to more regenerative braking opportunities where the electric motor can recover energy, potentially reducing fuel use and increasing reliance on electric energy.
• However, too much stop-and-go can also increase electrical energy consumption because of the repeated acceleration demands, although this is often still more efficient than gasoline alone.

Average Speed and Stops

• Studies on PHEVs like the Hymotion Prius model show that at average speeds below around 35 km/h (about 22 mph), fuel and electric energy consumption decrease as speed increases because there is less stop-and-go, enabling the powertrain to operate more efficiently.
• Above 35 km/h, fuel consumption begins to increase with speed, while electrical energy consumption decreases. This happens because more of the vehicle’s energy comes from fuel rather than electricity at higher speeds. This speed threshold roughly differentiates city driving (frequent stops, lower speed) from highway driving (higher speed, fewer stops).
• The number of stops per mile and idle time also correlate with fuel consumption, where more stops and idling generally reduce fuel efficiency.

Route Planning and Economical Driving

• Research indicates that the most economical route for a PHEV may differ from that for a conventional gasoline car. This is because PHEVs optimize energy use between electric and fuel sources differently depending on the route characteristics.
• Specialized route-planning methods can recommend routes that maximize the use of electric propulsion and minimize fuel consumption by considering factors like traffic, stops, speed changes, and elevation changes.

Distance Between Charges and Charging Frequency

• The distance driven between battery charges affects fuel consumption. If a PHEV is repeatedly driven without being plugged in to recharge, it will rely more on the internal combustion engine, increasing fuel use.
• In real-world usage, PHEVs are not always charged daily, leading to variable shares of kilometers driven on electricity versus fuel. Longer routes that exceed the vehicle’s electric-only range will increase fuel consumption since the engine must take over for the extended portion of the trip.

Summary

• City routes with frequent stops can reduce fuel consumption by maximizing electric driving and regenerative braking, but excessive stops and low speeds can increase electric energy use.
• Highway routes tend to increase fuel consumption as speeds rise above about 35 km/h, with more reliance on the gasoline engine.
• Optimal fuel economy for PHEVs depends on route characteristics, charging behavior, and intelligent route planning to maximize electric mileage and minimize fuel use.
• Therefore, the type of route—its average speed, stop frequency, and length relative to battery range—has a substantial effect on PHEV fuel consumption and overall energy efficiency.

This nuanced dynamic contrasts with conventional vehicles, emphasizing the importance of route selection and charging strategy in managing PHEV fuel consumption effectively.