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ERS In F1: How The MGU-H and MGU-K Work

ERS stands for Energy Recovery System, and it is a fairly new innovation within the world of F1. First bursting onto the scene in 2009, it has evolved over time to become integral to the powertrains within the F1 cars. So, what are the MGU-H and MGU-K, and how do they work?

The MGU-H uses excess exhaust gases from the engine to feed power to the energy store, which is then used to power the turbocharger’s compressor. The MGU-K feeds waste energy from the decelerating wheels back to the energy store for later use.

Although the two systems work in similar ways, there are also some big differences. Plus, they are used in different parts of the car, and so it is key to look at each one individually and consider the benefits that each one gives in terms of power.

The Basic Components Of An F1 Powertrain

What Is The Powertrain?

The powertrain is the mix of components that drives the F1 car. Most people think of simply the engine powering the car, but instead it is actually known as a Power Unit, or PU, as it is made up of several vital components that work together to give the car the enormous amount of power required to go through corners at speeds upwards of 100mph, and 200+mph on the straights.

The powertrain is made up of many different components, but the main ones to consider are the engine, the turbocharger and both the MGU-H and MGU-K. We will talk about these more specifically in later sections, but MGU stands for Motor Generator Unit, while the H is for Heat and the K is for Kinetic.

Engine Size

Since 2014, the engines used in F1 cars have been 1.6-liter hybrid V6s. These are internal combustion engines, or ICEs, and they work using a traditional 4-stroke system you would find on your normal car. With a few extra components, like special spark plugs and precise fuel injection systems, it draws fuel and air into the cylinders, compresses and ignites them, and discharges exhaust gases.

Where the powertrain differs from your road car’s is in the power they can provide to the cars. They are capable of more than 1000BHP, which is a massive amount of power for a car that weighs less than a ton. The engine itself produces around 700BHP, with the remaining power coming from the motor generator units that this article will explain.

Energy Storage

These units generate and make use of energy that is stored in an extra Energy Store (ES) or Energy Storage System (ESS), which is essentially a large lithium ion battery. It is regulated to weigh between 20 and 25kg. They are also regulated with regards to how much energy they can store and provide.

When deployed, the power boost translates into totals of around 300BHP for around 30 seconds each lap, which is obviously of massive advantage to the drivers. The MGU-K is used to harvest “waste” energy from the wheels under deceleration and provide this to the energy store to be used later. The MGU-H works in a similar way, although it is linked with the turbocharger.

The MGU-K can harvest 2MJ per lap and deploy 4MJ per lap, while the MGU-H can harvest an unlimited amount, but only deploy 2MJ per lap. Energy from the MGU-H can either be used to power the MGU-K or sent to the Energy Store.

Turbocharger

The turbocharger is a key component of these engines, and itself is made up of two main parts. The turbine is the first part, and this is connected to the waste gate of the engine. The exhaust gases from the engine flow out of the waste gate to the turbine, and they then spin the turbine, which is connected via a shaft to a compressor.

This compressor spins with the turbine, drawing in extra air and pushing this air into the engine. This increases the amount of oxygen available to be sent into the engine, which allows the engine to burn more fuel faster for more power. The MGU-H is attached to the turbocharger and works in a similar way to the MGU-K to send “waste” energy to the energy store.

Some Energy Basics

Waste Energy

We have mentioned the word energy quite a lot already, and especially waste energy. This word has been in inverted commas for a good reason. Essentially, the car’s powertrain can only be so efficient, as there is a lot of energy lost at each stage due to friction, which results in heat which is lost to the atmosphere. This is common of all mechanical equipment and is a challenge for engineers.

Thus, the waste energy in question is not wasted just for the sake of it, as it is instead inevitable when it comes to combustion engines. The second idea to note concerns the first law of thermodynamics. This states that energy cannot be created nor destroyed, only transformed. Essentially, it can only be shifted from one form to another, rather than “made” or “lost”.

So we need to consider what is happening to the energy within a car when it is being driven. The engine uses fuel and oxygen to generate mechanical energy through combustion. This is a result of the chemical energy of the fuel and oxygen being burned, and the mechanical energy of the pistons is converted into kinetic energy in the wheels, driving the car forwards.

Heat Loss

At every stage of the process, heat is generated, which is another form of energy. This occurs due to friction of components rubbing against each other, as well as a by-product of combustion itself. But there is a lot of heat generated at the wheels in particular, most notably when the car is braking intensely. It is friction between the brake pads and the brake discs that slow the car down.

This results in a lot of “lost” heat energy. This is important to consider for the MGU-K. Both the MGU-K and the MGU-H use heat, or thermal, energy to provide power back to the energy store. They do this by converting the thermal energy into electrical energy by means of a motor system. Hence the name, motor generator unit.

The Motor

A motor is an electrical component that turns when it receives an input of energy. As part of a circuit, that input energy is electrical energy, and the motor turns by converting it into kinetic energy. These motors can be used to turn things like wheels and turbines. Turning the motor mechanically however can also turn the kinetic energy back into electrical energy.

This can be seen with the common dynamo which you might have on your bicycle. Essentially, as the wheels turn, the motor in the dynamo turns, which through some complex electronics that we will hopefully simplify below, provides power to another electronic device, such as your bike light. This energy can also be stored, which is the basis of the MGUs.

Some Electricity Basics

The last section gave some very basic explanations of energy and some common concepts that relate to the motor generator units we are finally about to discuss in more detail. But just how does the motor in these units turn the kinetic, or rotational, energy of the motor into electrical energy, which can then be stored for a power boost later on?

Understanding The Motor

As mentioned, the motor can turn as a result of electrical energy being applied, or it can turn via the input of kinetic or mechanical energy. Think of a fan on your desk that keeps you cool in the summer. You turn it on, and electrical energy spins the fan’s blades. But you can also spin them with your hands even when the power is disconnected.

What happens with both the MGUs in an F1 car is a similar process. They both contain motors, as the name suggests, and these motors can be made to turn via the input of electrical energy from the energy store, like a traditional motor. Or they can be used like a dynamo, using external kinetic energy to turn the motors, and then converting that into electricity.

Generating Current

The way they do this is quite complex. Essentially, the motor consists of wires and magnets. When wires are placed in a rotating magnetic field, current can be generated within the wires, even when they are not connected to a power source. This rotating magnetic field is created by the spinning of the motor, which is being spun by external forces that are different for the MGU-H and MGU-K.

So the movement of a rotor can be used in the opposite direction to generate electrical energy, or simply electricity, from kinetic energy. This is a vital concept for both MGUs. Let us first look at how this works for the MGU-H, and it will hopefully start to make more sense if it does not already.

The MGU-H

Extra Power Through The Turbo

The MGU-H is connected to the turbocharger. The turbocharger works by using the waste exhaust gases to rotate a turbine. This turns a compressor, boosting the air intake of the engine, increasing the power output. The turbocharger relies on the engine to be working hard in order to provide enough exhaust gases to rotate the turbine.

When the driver releases the accelerator the engine stops working so hard, and there are much less exhaust gases coming out of the waste gate. This is not enough to rotate the turbine, so the compressor also stops spinning. This is fine, as the engine doesn’t need extra power when the driver is decelerating. The problem is when they put the foot down again.

Turbo Lag

When the car starts to accelerate again, the turbine takes a second or two to get up to speed with the exhaust gases provided to it, so the compressor does not instantly provide the extra air to the engine. This delay from when the driver presses the accelerator pedal to when the engine gets the boost of power from the extra air from the compressor is called turbo lag.

This is where the MGU-H comes in. When the driver presses the gas pedal, the turbine experiences the full force of the exhaust gases coming out of the engine. The compressor can only spin so fast, so there needs to be some regulation of the turbine. This is achieved by bleeding off some of the exhaust gases away from the turbine.

More Energy Conversion

The MGU-H is located between the turbine and the compressor, and this excess exhaust gas is sent through it. The MGU-H has a motor in it, which spins when the exhaust gases pass through it, converting the kinetic energy of the hot exhaust gases into electrical energy through the process described above, with the spinning magnets in the motor generating electricity in the wiring.

This energy is sent to the energy storage system. After the driver releases the gas pedal, the exhaust gases stop going through the MGU-H, and then when they press the accelerator again, the energy storage system sends electricity directly to the compressor to get it spinning straight away.

Eliminating Turbo Lag

This means there is no delay between the driver pressing the gas pedal and the compressor spinning, meaning the MGU-H eliminates turbo lag. This means the driver can get a big boost of power right away. There is no limit to the power that the MGU-H can generate, although the ESS is still limited in how much energy it can send to the power unit each lap

One thing to note about both of these units is the fact that they are very advanced pieces of technology, so are expensive to build. The MGU-H is one of the most expensive parts of the car, and it is for this reason that from the 2021 season, there is the removal of the MGU-H from the powertrains.

The MGU-K

A Bit More Complex

The MGU-K is the more complex of the two systems. As we have said, when wires are placed within a rotating magnetic field, a current is produced. The faster the motor rotates, the more current is produced. The MGU-K is made of a motor, similar to the MGU-H. In this case however, it is connected to the crank shaft, which is what turns the engine’s piston movement into the wheels’ rotational movement.

When the wheels are spinning, the motor in the MGU-K is spinning, which means the magnets are spinning. Now, when the MGU-K is in motor mode, it is taking electrical energy from the energy store and convert it into kinetic energy just like the MGU-H does with the compressor. This provides a power boost to the wheels.

Under Acceleration

The MGU-K is in motor mode when the car is accelerating, which is in contrast to the MGU-H, as it is in generator mode when the car is accelerating, taking waste gases from the engine and storing their kinetic energy as electrical energy in the ESS. In motor mode, the boost of power from the ESS is working alongside the mechanical energy from the engine that is driving the wheels constantly.

Now, when the accelerator is released or when the brakes are applied, the MGU-K goes into generator mode. When the car is decelerating, the wheels are still spinning, and they are spinning in the same direction as when they are accelerating. The difference here is that the motor in the MGU-K stops being rotated by the electrical energy from the ESS.

Harvesting Waste Energy

Instead, the motor continues to spin solely due to the rotational energy of the wheels. This means the motor is spinning without an electrical power source, and the magnets in the still-spinning motor rotate, causing the current to flow back to the energy storage system. This occurs under deceleration or braking, making use of the “wasted” energy lost from the wheels slowing down.

This sends electrical energy back to the ESS which equates to a maximum of around 160BHP. However, the way it does this is quite complicated. Essentially, the electricity is generated by the MGU-K due to the fact that the wheels spinning causes the current to be generated in the opposite direction to that in which the motor would “prefer” to be spinning.

Essentially, when the MGU-K is in motor mode, it takes electrical energy from the ESS and sends it to the wheels via the spinning of the motor in a certain direction. Think of this direction as the direction which provides the least resistance, and thus allows for the most efficient transfer of energy from the ESS to the wheels, and thus the most power.

Resistance

However, when the MGU-K is forced to work in the opposite direction, taking kinetic energy from the wheels and turning it into electrical energy, it is forced to send current in the other direction. It would prefer to rotate in the opposite direction to the wheels, as that would generate less resistance in the circuit. Instead, it is essentially forced to work against itself.

This extra resistance that the motor needs to overcome to generate the current requires a lot of kinetic energy. Luckily, it can take this kinetic energy from the wheels, which it does so very quickly. Under deceleration, such as when the driver hits the brakes, the wheels “lose” their kinetic energy due to friction, which slows them and the car down.

Not Enough On Its Own

The MGU-K harvests some of this “lost” energy while also aiding in slowing the car down faster. The MGU-K would not provide enough resistance on its own to completely stop the car, as this would need a massive motor and a large battery to store the huge amount of electrical energy that it would generate. But slowing it down is not its main purpose anyway.

Instead, its main purpose is to do what the MGU-H does, and harvest otherwise “wasted” kinetic energy from the decelerating wheels and turn it into electrical energy, which can then be sent to the energy store. From there, it can be sent to both the turbocharger’s compressor or the wheels themselves when the accelerator is pressed, giving the car that massive boost in power.

Final Thoughts

The ERS system of an F1 car is used to recover what may be called wasted energy, and use it to give the car a boost in power of several hundred horsepower every lap. It is made up of many different components, all part of the powertrain of the car. The two main components are the motor generator units, the MGU-H and the MGU-K.

The MGU-H uses waste heat energy (technically kinetic energy) from the exhaust gases to spin the compressor of the turbocharger and eliminate turbo lag. The MGU-K transforms wasted kinetic energy from the decelerating wheels into electrical energy, which can also be stored in the car’s energy storage system. They both work together to give the cars massive power boosts.