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Technical Nuances Of EV & Hybrid Race Cars

Our contacts took us deep inside the technology required to start, run and stop alternative-power race vehicles.

By Rick Carlton

While both hybrid and electric vehicles are engineered for improved mileage and fewer harmful emissions, the technologies are gaining traction in motorsports alongside gains in general automotive markets.

However, because these are entirely different technologies, it’s worthwhile to explore what separates them. So let’s compare the technology used in all-electric, short-stint sprint events like FIA’s Formula E with hybrid powertrains that lend themselves to endurance racing such as the WEC Championship.

Regardless of the nature of one powertrain versus the other, both approaches require highly integrated systems development utilizing cutting-edge components to get the job done. Here’s what we’re talking about:

Central Electric Formula E (FE) Components

  • Lithium-ion battery package
  • Power inverter system
  • Rechargeable Energy Storage System (RESS)
  • Motor Generator Unit (MGU)
  • Electronic control unit
  • Electric Motor (eMotor)
  • 5/6 gear transmission

Powertrain

  • Max power (limited): 200 kW (268 hp), approximately 230 N·m (170 ft-lb) torque
  • Race mode (power-saving): 170 kW (228 hp equivalent)
  • Fanboost: Additional 30 kW (40 hp equivalent)
  • Power-to-weight ratio: 0.30 hp/kg

Maximum power is available during practice and qualifying sessions. During races, power-saving mode applies, with a ‘Push-to-Pass’ system temporarily enabling maximum power for a limited time.

The amount of energy that can be delivered to the Motor Generator Unit (MGU) by the Rechargeable Energy Storage System (RESS) is limited to 30 kWh and is monitored by FIA race stewards.

Performance

  • Acceleration: 0–100 km/h (0–62 mph) in 3 seconds (estimated)
  • Maximum speed: 225 km/h (140 mph) (FIA limited)

When it comes to hybrid powertrains, however, different goals and consequent performance specs apply. Let’s examine what makes the TS050 Hybrid of Toyota Gazoo Racing that competes in the WEC excel on-track:

Central Hybrid WEC Components

  • Fossil-fuel, V6 ICE
  • Four-wheel, electrically driven hub motors
  • Lithium-ion battery package
  • Power inverter system
  • Electronic control unit
  • Seven-gear sequential transmission

 Powertrain

  • 2.4-liter V6 – direct-injection, dual-turbo
  • ICE (rear) – 368 kw/500 PS
  • Hybrid (front/rear) – 368 kw/500 PS
  • Aggregate power total (ICE/front/rear) - 735kw / 1000 PS
  • Lithium-ion battery package
  • Front/rear electric hub motors

 While big fish such as Toyota Motorsport and Andretti Autosport continue to plow deeply into the market in terms of global brand extension—and consumer product innovation—smaller organizations are focused on delivering individual component refinements in order to create their own milestones in the alternative racing segment. As a major player in the electric vehicle space, France’s Venturi Automobiles is not only working on an active Formula E racing program, but has also supported the FE Championship’s sole battery provider, Williams Advanced Engineering (WAE), by offering its own iterations on battery system developments that are applicable to both racing and electric road car programs.

We recently caught up with Dr. Eric Prada, Venturi’s Performance and Simulation Engineer, who gave us a sense of what goes into the engineering associated with a racing battery package. “When it comes to battery technology for consumer electronics, or automotive-derived racing applications,” he told us, “the key words are autonomy, performance, safety and durability.

“In order to better understand battery pack specifications for consumer or race applications, let’s first introduce notions of electrical power and energy related to battery use,” he explained.

“From a technical perspective battery power, P, (expressed in kW—kilo-Watt) can be seen as the image of the car performance while battery energy, E, (expressed in kWh—kilo-Watt-hour) is generally related to the autonomy of the car. Consequently, when designing a battery package, the goal is to safely use the energy (E) required, by hitting a particular power (P) target.

“However, before comparing a typical EV versus a race car package like a Formula E, let’s start by accepting that a battery is used to store and provide electricity via various electrochemical processes,” Prada added.

Whatever the application, he noted, a battery package is generally composed of multiple elementary components called cells, mounted in series and/or parallel to achieve energy and power requirements; electronic components for safety like fuses or for management such as monitoring/balancing boards; and a thermal system composed of fans (air cooled system), pumps and/or radiators (liquid cooled system).

He explained that these cells contain the “chemical identity” of the technology, and different chemistry families can be used in automotive applications like Lead-Acid (for start/cranking), Ni-MH (Nickel Metal-Hydride) for HEVs like the Prius, or Li-ion (Lithium-Ion) systems. Each of these chemistries offer different properties and characteristics when it comes to energy storage capability expressed in Watt-hour (Wh).

“Energy density is a key parameter, and is commonly used to compare different technologies that describe the ability to store certain amounts of energy per volume (Wh/L) or per mass (Wh/kg),” Prada continued. “Similarly, power density (W/kg or W/L) is used to describe the ability of a particular chemistry to provide for a certain amount of energy, within a certain duration.

The temperature range of operation of the battery is generally between 20° C to 60° C, he explained. “Above 40° C, important and fast degradation can occur. 60°C is generally set as an upper limit to not reach. Consequently, thermal hazards and safety issues associated with fire risk can be triggered when going above 80°C to 90°C for some Li-ion technologies, for example.

“Onboard conventional electrified vehicles, whether it is a hybrid electric vehicle or a pure electric vehicle, applies electrical energy used to drive various components stored in the battery packs. For example, a Formula E battery pack offers 28 kWh of usable energy with a power reaching 200 kW.”

Prada stressed that due to the Formula E race format and car design specification, the car’s battery pack energy and power densities become key features. The chosen battery cell design must store as much energy as possible within volume and mass constraints authorized by the FIA’s regulations.

“On top of the energy-density target, the important power requirement of the Formula E duty cycle generates a lot of heat in the battery pack during operation, inducing engineering challenges to keep using the battery in a safe operating zone,” he said. As a result, the FE battery is liquid cooled in order to extract as much as heat as possible during this operation.

“Therefore, then, key features for a race car application are No. 1, energy density and No. 2, thermal management, particularly since the FE series is generally located in hot climates with ambient temperatures reaching 38° C.

“Venturi Automobiles encompasses many years of experience in battery integration, design, and battery management system, as illustrated by our various EV vehicle projects including our VVB3, AMERICA, and VOLAGE road variants,” Prada concluded.


Stopping Power


Another important component to electric and hybrid motorsports technology can be found in the brakes. In addition to the full electric Formula E series, Alcon in Tamworth, Staffordshire, United Kingdom, works directly with series employing hybrid and regenerative braking technologies, which include, but are not limited to, WEC and Formula 1.

According to Garry Wiseman at Alcon, “Currently in Formula E, the braking system is fully independent from the regen braking system. This means that all of the ‘torque blending’ between electrical torque, and torque from the hydraulic brake system, is done by the driver. At the moment, regenerative braking is only taking place on the rear axle of the car. So to avoid excessive rear torque, the drivers (and team engineers) have to manage the independent controls of brake bias and regen map setting manually (whilst racing!).

“As the amount of electrical energy that can be generated via regen increases through season three, four and beyond, the demands on the rear hydraulic brakes will reduce,” he continued. “This means that disc operating temperatures will reduce on the rear axle (when the regen system is active). It’s worth noting that there are periods in the races currently where little/no regen is active, so the system has to be capable of working under full loads, as well as performing consistently when the rear hydraulic braking demands reduce.

Thinking beyond the next couple of seasons, “the hydraulic and electrical braking systems in Formula E will most likely be more ‘coupled,’ as to increase performance and range you will need to be as efficient as possible in harvesting electrical energy during braking. Doing this will lead to opportunities to tailor the braking system to suit the ‘normal’ operating mode of the car during a race, and lead to further weight savings on hydraulic brake components,” said Wiseman.

Regarding upcoming developments at Alcon, Wiseman explained that all current systems use a combination of conventional and electrical braking torque, and he doubts this could be abandoned entirely. “The high-tech systems in F1 and WEC all rely on a high-performance foundation braking system running alongside the regen system. This is because the ability to provide electrical torque can be influenced heavily by battery charge level, battery temperature and regen system failure. All of these rely on the hydraulic system as either a top-up mechanism, or as a ‘failsafe.’ The system must allow the driver to decelerate the car in a controlled and predictable manner. As technology progresses, I guess the hydraulic brake componentry will just get smaller and lighter,” he added.




Technical Nuances Of EV & Hybrid Race Cars

Debuting in 2014, the FIA Formula E Championship is the world’s first fully electric motor race series, with participation from American team Andretti Autosport (seen here). Maximum power for the motors is limited to 200 kW (268 hp), but during races, power-saving mode applies, with a Push-to-Pass system temporarily enabling maximum power for a limited time.


Technical Nuances Of EV & Hybrid Race Cars

Hybrid powertrains lend themselves perfectly to endurance racing such as the FIA World Endurance Championship (WEC). For example, the TS050 Hybrid of Toyota Gazoo Racing that competes in the WEC uses a fossil-fuel, V6 ICE; has four-wheel, electrically driven hub motors; and a lithium-ion battery package.


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