Steyr prototype hybrid tractor ready before the end of 2022

In March of 2022, the Austrian tractor manufacturer Steyr officially presented a new type of tractor transmission: the Hybrid Drive Train concept, with a partially electric drive.

The new Hybrid Drivetrain Konzept as the system is officially called builds on the futuristic tractor Steyr showed at Agritechnica in 2019. It was never the manufacturer’s goal to actually bring this concept to market. However, it spurred a new way of thinking.

The Hybrid Drivetrain Konzept is a transmission concept with a partially electric drive. Besides a diesel engine, the hybrid tractor prototype has a generator, storage capacity for generated power and an electric motor.

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Generator and supercapacitators

The hybrid transmission works as follows. The concept’s power source is a six-cylinder diesel engine. This drives a new transmission that has been enhanced with, among other things, a generator. The generator sits on the right-hand side of the transmission housing and is connected to the gearbox input shaft with a mechanical claw clutch. Coupling of the claw clutch is mechanical, but is electrically controlled. For safety, the clutch can mechanically disengage in an emergency.

A gearing ensures that the generator always runs in the most efficient range. The generator stores the generated power in three supercapacitors. These are linked together with a series connection.

From the outside, the supercapacitors look like normal batteries. The difference compared to a normal battery is that a supercapacitor can store a lot of energy in a short time. They can also release this stored energy very quickly. Normal batteries typically have more storage capacity, but do not release the stored power as quickly.

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Electric boost

On the left side of the transmission housing, we find an electric motor. The generator and electric motor together account for 136 hp of constant power, and can temporarily boost to a maximum of 280 hp.

The electric motor is coupled to the pinion shaft in the transmission. This directly drives the differential. The electric boost (e-Boost) thus becomes available only at the wheels. So the electric boost does not go through the gearbox gears, but skips this step and comes directly to the differential and rear wheels via the pinion shaft.

Steyr’s thinking behind this is that with a more powerful engine, you don’t necessarily need a heavier transmission. You route the extra power around the transmission, and use the boost on the wheels only when called for. That driveline is calculated well enough to handle the extra forces, according to the manufacturer.

The PTO and hydraulic system cannot use this so-called electric e-Boost. You don’t always need the full boost. For that, there are three electric gear ratios. Which ratio fits best is determined by the power needed at the time.

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Charging while braking

The hybrid tractor concept also incorporates an electric brake retarder. It works on the basis of electromagnetic induction and generates current during braking. With this, the system charges the supercapacitors. When these are full, the electrical power goes to the front and drives the cooling system there. This, in turn, saves fuel.

In hilly areas, such a brake retarder that generates electricity is ideal. It allows you to maintain speed without straining the brakes. In the process, you charge the supercapacitors, and you can then use that generated electricity by boosting up to 150 hp via the electric motor when you need to go up another hill. That 150 hp e-Boost is considerably more than the boost Steyr generates with its current tractors. The boost goes up to a maximum of 30 hp extra.

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Independent front axle drive

The transmission has a separate front axle drive. This is powered by an electric motor. In the field, this allows you to adjust the front axle to the best conditions. In doing so, Steyr uses it to reduce the turning circle. This is achieved by having the front axle actively pull the tractor when cornering. The front axle pulls the tractor through the bend, instead of the rear axle pushing it into the outer bend.

We see the same thing in the larger Fendt tractors, which use a separate driveline in the transmission for the front axle. Steyr does this electrically.

To reduce wear, the traction control system monitors slippage. It adjusts the speed accordingly.

Electrically driven implements

The energy generated or stored by the system can also be used for implements. For example, a plough or cultivator with an electrically driven wheel (set). The implement can then push along, reducing the slip and power requirements of the tractor. This saves diesel and thus wheel slip. Steyr is not working on its own machines for the time being.

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Analyses indicate that fuel savings of up to 8% are possible with Steyr’s Hybrid Drivetrain Konzept. The model we saw in real life is a non-working model. According to the manufacturer it could work, however, with some modifications.

Steyr wants to introduce the hybrid transmission on a new model, and later bring it to the Terrus and smaller tractor models. Before that can happen, the concept has to pass all the tests and prove itself practical. This is not due until 2024 at the earliest.