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The Formula 1 Power Unit By Brandon Speedie Modern Formula 1 engines have incredible performance despite their modest size. They owe their high power and astonishing efficiency to the clever use of two electric motors and some smart electronics. Image Source: Jay Hirano Photography/Shutterstock.com T he current specification for Formula 1 race car engines was introduced in 2014. It was a major shift for the sport from the previous V8 petrol engines, given its much higher reliance on electrical power and a strong emphasis on efficiency. These hybrid engines can generate over 750kW, a remarkable feat considering its compact design—a turbocharged 1.6-litre V6 weighing only 145kg. Even more astonishing is its efficiency, peaking above 50%, nearly twice as efficient as most other petrol engines and approaching the theoretical maximum efficiency of a heat engine (54% for the 18:1 compression ratio per FIA regulations). This exceptional efficiency allows a Formula 1 car to cover an entire Grand Prix (300km) circuit at race speeds using just 100kg of fuel despite the constant acceleration and braking inherent in motor racing. Internal combustion engine To explain how the electrical system works, we first need to understand the internal combustion engine (ICE). Similar to the engines in most road-going cars, air enters the intake manifold 56 Silicon Chip and is mixed with a hydrocarbon fuel similar to petrol (with 10% ethanol). It is ignited inside the engine cylinders, producing heat. This increased heat, and therefore pressure, pushes down on a piston, which attaches to a crankshaft and ultimately to the rear wheels for propulsion. Assuming perfect combustion and a 9:1 mixture by weight of octane (the closest single hydrocarbon to regular petrol) and ethanol, the chemical reaction is: 58 C8H18 + 16 CH3CH2OH + 773 O2 → 496 CO2 + 570 H2O The turbocharger After passing through the engine, the combustion byproducts are expelled as hot exhaust gas (a mixture of CO2 and steam). While they are considered waste to the piston engine, they still contain heat, which can do useful work. Some of that ‘waste’ energy is used to spin a shaft by attaching a turbine to the exhaust manifold. The shaft is connected to a compressor assembly on the intake manifold, which increases the intake fuel and air Australia's electronics magazine mixture density, allowing more molecules to enter the fixed volume of the engine. Burning this greater air/fuel volume produces higher cylinder pressures and therefore more power. This increased intake pressure is referred to as ‘boost’. The hybrid system The electrical system operates together with the ICE to increase power and efficiency. It consists of two electric motors, which can also work as generators: the Motor Generator Unit – Kinetic (MGU-K) and the Motor Generator Unit – Heat (MGU-H). There is also a small (4MJ or 1.1kWh) Energy Store (ES) unit, which can be used to keep power from these generators for later use. Some participating F1 teams initially experimented with a mechanical flywheel-style ES, or capacitors, but all have now adopted a lithium-ion battery. The type of motor used for the MGU-K and MGU-H is a closely guarded secret but they are almost certainly permanent-magnet synchronous reluctance (PMSynRM) types. The PMSynRM is a hybrid motor siliconchip.com.au An exploded view showing the components of the energy recovery system in an F1 engine. Source: Renault combining technology from permanent magnet motors and synchronous reluctance motors. Its theory of operation is similar to that of a hybrid stepper motor, which we previously covered in some detail (January 2019 issue; siliconchip.au/Article/11370). The rotor in a PMSynRM motor is designed to have a very low reluctance in one axis and a high reluctance in another axis offset by 45°. When the stator windings apply a rotating magnetic field, a reluctance torque is generated that rotates the rotor with very little power loss. Pure SynRM motors do not need permanent magnets; the PMSynRM motor is a hybrid type that includes some permanent magnets in the flux barriers for increased torque and power at a given motor size – see Fig.1. Recently, the PMSynRM motors have begun to gain widespread use. They have slightly higher efficiency than an equivalent induction motor, as there are lower resistive losses in the rotor (no squirrel cage with induced currents and therefore resistive heating). However, PMSynRM motors have high torque ripple, which makes them difficult to control. It has only been recent advances in power electronics and control algorithms that have made them attractive for general use. Tesla Motors has begun using PMSynRM in their newer vehicles, moving away from the induction motor their company siliconchip.com.au namesake, Nicola Tesla, so famously invented. The Motor Generator Unit – Kinetic (MGU-K) The MGU-K is a 120kW motor connected to the crankshaft of the ICE. Regulations limit the rotational speed to ‘just’ 50,000 RPM. By coupling the MGU-K to the engine crankshaft, the motor has a direct path to the wheels. When operated as a motor, the driver has 120kW of extra power available. When operated as a generator, electrical energy can be harvested and stored in the ES as the car is slowing for a corner, ie, regenerative braking. This also means the rear disc brakes can be much smaller and lighter than they would otherwise need to be; the MGU-K provides much of the stopping force, so the mechanical brakes have much less power and heat to dissipate. The Motor Generator Unit – Heat (MGU-H) Fig.1: PMSynRM motors use a combination of radially variable reluctance and permanent magnets to provide very high power and efficiency in a compact package. Flux lines are obstructed along the q-axis but not along the d-axis. Note that the flux guides/barriers don’t have to line up with the motor poles, and they are usually more gracefully curved in a real motor. Australia's electronics magazine The MGU-H is similar to the MGUK, except it is coupled to the turbocharger shaft rather than the engine crankshaft. The F1 rules allow a higher rotary speed limit of 125,000 RPM to better suit the typical operating speed of a turbo. Unlike the MGU-K, it has no mandated power limit. The MGU-H has two primary functions. One is to operate as a generator, harvesting electricity from the turbine. On a traditional engine, a turbo’s operating speed is controlled by a wastegate, which opens to bypass exhaust around the turbine as it approaches maximum speed. This gas is effectively wasted (although many people like the whooshing sound it generates on accelerator lift-off!). On a Formula 1 engine, the MGU-H May 2024  57 controls the turbine speed. Once the engine has enough boost, the motor begins generating electricity, which has the side benefit of acting as a turbo boost controller. In this way, no exhaust gas is wasted and the engine’s overall efficiency is drastically improved. This is known as “cogeneration”. It is worth noting that the engine also has a wastegate, as in a traditional turbocharged engine. However, it only opens in specific scenarios that will be described later. The MGU-H can also operate as a motor to help spool up the turbo when there is insufficient exhaust gas for the turbine to do it alone. This is most often done exiting a corner, where the driver is beginning to accelerate, but the turbo is not yet spinning fast enough to provide adequate boost. The MGU-H is thus used to eliminate ‘turbo lag’, a common complaint from drivers of turbocharged cars who suffer degraded throttle response and driveability. It’s less of a problem on a racetrack because you can anticipate needing to accelerate, but it’s still something that would otherwise need to be managed by the driver. Turbos suffer two related problems: turbo lag refers to the time the turbine takes to spin up from a sufficient exhaust flow, while the ‘boost threshold’ is the amount of exhaust required before the turbine can produce maximum boost. Both cause a delay in full power availability, and both are mitigated by the MGU-H being able to spin the turbine up on demand, regardless of exhaust flow. Energy flows The MGU-K, MGU-H, and ES all work together to optimise the racecar’s performance. This orchestration is performed by the control electronics, which can quickly redistribute power between each component. The control electronics can control when the MGU-K and MGU-H act as a motor or generator, the amount of power delivered or extracted, and where that energy goes. Regulations limit some power flows, while others are left unbounded – see Fig.2. The ES is capped at 4MJ of deployment each lap, which gives the driver 33 seconds of additional power through the 120kW MGU-K. Of this 4MJ, up to half can be provided by the MGU-K through regenerative braking. The rest of the ES charge comes from the MGU-H, which has no harvesting limit. Power can also flow directly from the MGU-H to the MGU-K, which bypasses the ES and is therefore not counted in the 4MJ limit. This ends up being a large proportion of the overall deployment energy in a typical race lap. Control algorithms Teams spend considerable resources modelling the system’s behaviour to develop optimum control algorithms. These ‘maps’ change to suit every track and will have different options depending on the driver’s needs at any given time. Let’s consider how the hybrid system might respond to one corner of a race track, with reference to Fig.3. As the car approaches the corner, the driver applies the brakes. During the stopping phase, the MGU-K operates as a generator, sending power to the ES to charge it up. The driver is neither braking nor accelerating through the corner apex, so the system is idle. Upon exiting the corner, the driver begins to open the throttle. Power is deployed from the ES to the MGU-H to spool up the turbocharger. As more throttle is applied, the exhaust gas begins to take over from the MGU-H in spinning up the turbo, so less and less power flows from the ES. Once the car has straightened out, the driver has the throttle fully open. Power flows from the ES to the MGU-K to give the driver maximum acceleration. The turbocharger is now fully spooled up, so the MGU-H crosses over from being a motor to a generator and starts supplying the MGU-K directly, rather than discharging the ES. The MGU-H continues to supply the MGU-K for much of the straight. On approach to the next corner, energy from the MGU-H is diverted from the MGU-K to charge up the ES. The driver will feel this as a sudden loss of power, as the MGU-K is no longer deploying. The drivers call this a ‘derate’, and it is a common source of complaint over the radio. While it may feel unnerving to a driver to suddenly lose power under the pressure of a race, it is the overall best choice as the ES needs to be recharged for deployment on the next corner exit, which is much more critical to overall lap time than corner entry. Once the driver applies the brakes, the entire cycle repeats. The driver can use different modes to help them execute their race strategy. For example, if a driver is approaching a slower car, they might opt for a charging mode, which will harvest slightly more power than usual, and the ES will charge up to its maximum of 4MJ. When the driver is ready to attempt an overtake, they can swap to a more Fig.2: a block diagram of a current, standard Formula 1 power unit. The ICE is combined with a turbocharger, two electric motors (MGU-K and MGU-H) and an energy storage system (Li-ion batteries), forming a hybrid power source. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au aggressive mode (via the buttons and flaps on the steering wheel), which will discharge the ES and give the driver extra power to complete the overtake. The car in front can also use its battery defensively to try to retain track position against the faster car approaching from behind. The hybrid system thus allows an element of catand-mouse between drivers. For this reason, overtakes can be many laps in the making; the attacking driver may need to mount multiple attempts to deplete the battery pack of the car in front before the move can be made. Qualifying mode An interesting configuration of the hybrid system occurs during qualifying, where the cars are timed over a single lap. During this session, it is all about power; there is less need to optimise efficiency. When in ‘quali mode’, there are periods where the wastegate is purposefully opened, venting otherwise usable energy. This reduces the back pressure on the engine, allowing it to make marginally more power. To retain boost, the MGU-H constantly takes power from the ES to spool the turbo. This can be thought of as an electric supercharger system. As the energy stored in the ES only needs to last a single lap during qualifying, this unusual mode actually provides peak performance. Fig.3: an example of how the MGU-H, MGU-K and energy storage system can recover kinetic energy during the entry to a corner and increase acceleration out of the corner. The exact profiles will vary depending on the corner speed, radius, what follows it etc. Formula 1 teams and drivers work to optimise the precise scheme used for each corner of every track. Road-going versions The technology behind the MGU-H and MGU-K has filtered down to production vehicles. The Mercedes-Benz SL 43 AMG features an “electrically assisted turbocharger” from Garrett (which they call an E-Turbo). It functions similarly to the MGU-H, eliminating turbo lag. The Mercedes-Benz AMG ONE is a sports car featuring a modified version of the Formula 1 engine, with the addition of two electric motors driving the front wheels. This system provides up to 360kW of electric propulsion, in addition to the 422kW from the ICE directly, for a total of 782kW. This vehicle has achieved numerous lap records for a road-going production car, including at the famed Nürburgring Nordschleife, beating the previous record by a staggering 13 seconds. SC siliconchip.com.au Fig.4: a top-down schematic view of the Mercedes-Benz power unit. Note the elongated turbocharger shaft, allowing the compressor and turbine to be positioned at either end of the engine. This is unusual as the turbine and compressor are normally next to each other, in the same housing. Intake air and fuel are in blue, while exhaust is in red/orange. The MGU-H is coupled to the turbocharger shaft and is in the engine V to save space, while the MGU-K connects to the engine crankshaft. Australia's electronics magazine May 2024  59