Wiktor Wise
Hybrid vehicles have become increasingly popular in the automotive market, with consumers understanding the basics of the technology and its ability to reduce fuel consumption compared to traditional gas-only engines. While there are different types of hybrid systems, including series, parallel, and series-parallel, the discussion surrounding the absence of series electric vehicles in the mass market warrants further exploration. Series hybrids, also known as extended-range electric vehicles (EREV) or range-extended electric vehicles (REEV), offer unique characteristics that set them apart from other hybrid configurations. However, certain factors have influenced their limited presence in the automotive industry.
Characteristics and Values of Series Hybrid Electric Vehicles
| Characteristics | Values |
|---|---|
| Engine | Small |
| Electric Engine | Does most of the heavy lifting |
| Battery | Large and complicated |
| Motor | Large |
| Mechanical Transmission | None |
| Efficiency | 37% |
| Powertrain | Reduces weight of the plane by 100 kg |
| Mechanical Link between ICE and Wheels | None |
| Energy Buffer | Used to accelerate and achieve greater speed |
| Regenerative Braking Energy | Stored in a supercapacitor or flywheel |
| Traction Motors | Required if attached to the vehicle body |
| Engine/Generator Set Design | Lotus offered a design that runs at two speeds, giving 15 kW of electrical power at 1,500 rpm and 35 kW at 3,500 rpm |
| Electrical Power Transfer Pathway Efficiency | 70% efficient in Toyota Prius |
| Mechanical Power Transfer Pathway Efficiency | Over 90% efficient |
| Electrical Components | Need to be bigger for series hybrid operation |
| Power Requirements | Better for short distances |
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What You'll Learn
Series hybrids are more expensive to manufacture
Another factor that makes series hybrids more expensive to manufacture is the inclusion of a genset or fuel cell. This additional component is necessary to ensure the vehicle has enough electrical power to reach top speed. The genset or fuel cell adds to the overall complexity and cost of the system. Additionally, series hybrids may include a supercapacitor or a flywheel to store regenerative braking energy, further increasing the cost.
The manufacturing costs of series hybrids are also impacted by the type of battery and motor used. These vehicles typically employ traction motors, which are integrated into the wheels. While this design can improve efficiency and reduce weight, it also adds to the complexity and cost of manufacturing. Furthermore, the batteries in series hybrids tend to be larger and more complicated, as they need to store more energy to power the vehicle.
It is worth noting that while series hybrids may be more expensive to manufacture, they offer higher efficiency than parallel hybrids, especially at low and mixed speeds. Series hybrids achieve an efficiency of 37% compared to the internal combustion engine (ICE) average of 20%. This increased efficiency can lead to a significant reduction in fuel consumption and emissions, which can offset some of the higher manufacturing costs over the lifetime of the vehicle.
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They require bigger motors and larger batteries
One of the primary reasons why series hybrid electric vehicles (SHEVs) are not as commonly found on the market as their parallel hybrid counterparts is the larger motors and batteries they require. This is due to the unique operational characteristics of series hybrids, where the internal combustion engine (ICE) is solely dedicated to generating electricity, and the electric motor(s) are responsible for propulsion.
In a series hybrid configuration, the electric motor(s) must be capable of providing all the necessary torque and power to drive the vehicle, regardless of the speed or load. This is in contrast to parallel hybrids, where the ICE can assist or even take over during high-demand situations, such as
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Power transfer is more efficient in parallel hybrids
Hybrid vehicles combine a battery (or supercapacitor) with an internal combustion engine (ICE) to either recharge the batteries or power the vehicle. There are three types of hybrid systems: series, parallel, and series-parallel. In a series hybrid, the engine acts as an electric generator, attached to the battery via cable, and the electric motor is directly connected to the transmission. In contrast, a parallel hybrid system connects the ICE and the electric motor in parallel to deliver power to the wheels.
The power transfer is more efficient in parallel hybrids due to several reasons. Firstly, in a parallel hybrid, the engine and motor work together to power the drivetrain directly, without the need for energy conversion. On the other hand, a series hybrid requires converting the engine's mechanical energy into electrical energy and then back into mechanical energy through the motor, leading to energy losses in the process. Secondly, the mechanical connection in a parallel hybrid between the engine, electric machine, and vehicle wheels results in higher transmission efficiency. The parallel coupling of power sources also allows for further research and improvement of the vehicle's performance. Additionally, parallel hybrids have smaller battery packs, which can be recharged through regenerative braking, making them more efficient in urban "stop-and-go" conditions.
Furthermore, the elimination of the generator in a parallel hybrid leads to a single-stage power conversion, increasing efficiency and reducing the weight and cost of the vehicle. The larger engines in series hybrids also contribute to increased weight, impacting overall efficiency. The increased weight in series hybrids is due to the requirement for bigger motors and batteries to achieve higher speeds. In contrast, parallel hybrids can utilize engine downsizing to improve fuel efficiency by reducing frictional losses and weight.
While series hybrids have advantages in certain situations, such as slow or stop-and-go traffic, the overall power transfer efficiency of parallel hybrids makes them more suitable for long-distance driving and varying power demands. This is because efficient power transfer is achieved through mechanical power transfer, which is characteristic of parallel hybrids.
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Series hybrids are less efficient for long-distance travel
The electrical power transfer pathway in series hybrids, such as the Toyota Prius, is estimated to be around 70% efficient, while the mechanical power transfer pathway in parallel hybrids is likely to be over 90% efficient. This difference in efficiency becomes more pronounced over longer distances, where the power transfer from the gasoline engine to the wheels needs to be as efficient as possible, making mechanical power transfer the preferred option.
Additionally, series hybrids require larger electrical components to achieve the same level of performance as parallel hybrids. The motors, batteries, and gensets or fuel cells in series hybrids need to be bigger to provide enough electrical power to propel the vehicle to top speed. This adds weight and complexity to the vehicle, further reducing its efficiency over long distances.
The inefficiency of series hybrids over long distances is also related to the energy density of gasoline. Gasoline has a higher energy density, which means it can provide a significant amount of range with a relatively small weight penalty. In contrast, electric vehicles, including series hybrids, may require additional components like a generator, which add weight without providing the same level of range.
While series hybrids may be more efficient in certain scenarios, such as urban driving with frequent stops, their efficiency over long distances is not their strong suit. The need for efficient power transfer, the weight and complexity of larger electrical components, and the energy density of gasoline all contribute to the reduced efficiency of series hybrids when compared to parallel hybrids for long-distance travel.
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They are less efficient at high speeds
Series hybrids are less efficient at high speeds because the internal combustion engine (ICE) is not directly connected to the wheels, and the electric motor has to bear the burden of propulsion alone. This means that at higher speeds, the electric motor has to work much harder, drawing a significant amount of power from the batteries, which leads to increased energy loss in the form of heat.
In a series hybrid, the ICE is dedicated to charging the batteries, and the electric motor is solely responsible for driving the wheels. While this setup offers benefits in terms of simplicity and the ability to
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Frequently asked questions
Series-hybrid vehicles are a type of hybrid vehicle drivetrain where only the electric motor is directly connected to the transmission. The gas engine serves as a generator that powers the electric motor and, in combination with regenerative braking, recharges the battery.
Series-hybrid vehicles are not as common as parallel hybrids because they require bigger motors and bigger batteries. This makes them more expensive to manufacture. Additionally, the electrical power transfer pathway is less efficient than the mechanical power transfer pathway.
Yes, there are a few series-hybrid vehicles on the market, such as the BMW i3 REX, the Mazda MX-30, the first-generation Chevrolet Volt, and the Honda Clarity.
Series-hybrid vehicles are more efficient than parallel hybrids at low or mixed speeds, achieving up to a 50% increase in overall efficiency. They also do not require a mechanical transmission, which reduces weight, bulk, noise, cost, and complexity.
One disadvantage of series-hybrid vehicles is that the unsprung mass increases, and suspension responsiveness decreases, which can impact ride and safety. Additionally, the electrical components need to be larger, and the power transfer from the gasoline engine to the wheels may not be as efficient over long distances.
