Did you know that Liebherr is a pioneer of hydrostatic drive systems for mining dozers? While the majority of the industry uses hydrodynamic systems in its dozers, we’ve been using hydrostatic technology since 1954. But if hydrodynamic systems are the norm, why did Liebherr take a different approach? We’re so glad you asked!

Hydrodynamic and hydrostatic systems couldn’t be more different from one another. Even though both have a diesel engine and a final drive, that’s where the similarities end. At the core of a hydrodynamic system is a torque converter – a fluid coupling that transfers torque from the engine to the mechanical transmission. While this system is great for vehicles like trucks that maintain high speeds during operation, it introduces some inefficiencies with fuel consumption and drawbar pull in dozer applications where speeds need to be kept low but drawbar pull needs to be kept high. This is why Liebherr opted for a hydrostatic system for its dozers.

The hydrostatic difference

Instead of using torque converters and gear boxes, hydrostatic systems use hydraulic pumps with swash plates. The swash plate is a revolving disc that sits at an angle within the pump. When the swash plate’s angle changes, so does the oil flow within the pump. The closer the swash plate gets to its maximum angle, the more oil flow there is. This determines the speed and the direction of the system as the oil flow from the pump moves the motor.

But what moves that swash plate in the first place? The operator, in the cab, with the joystick.

This direct connection between the joystick and the swash plate is a big part of why there are no gears in a hydrostatic system. There’s no need to choose a gear when the joystick is telling the dozer exactly how fast it should be moving. The other piece of this no-gears puzzle is that the system itself automatically changes its internal pressure in response to environmental load so it can generate the torque needed to achieve the operator’s desired speed. The amount of torque needed depends on a number of different factors: material density under the machine, slope of the ground and even how much weight the dozer is currently pushing. But no matter what the machine is doing, the hydrostatic system continuously matches the amount of torque it puts out to meet activity requirements.

Hydrostatic drives in practice

But what does all of this mean for everyday operations?

Well, for one thing, because hydrostatic systems have no use for gears, they have far fewer components than their hydrodynamic counterparts. No gears? No gearbox, clutch or differential steering gear. With fewer components there are fewer things that experience wear or need replacing, so maintenance personnel don’t have to spend as much time maintaining hydrostatic machines. Which is a big win for uptime.

Not having gears also allows the hydrostatic engine to run at a constant rpm the entire time it’s operating. For our mining dozers, the engines stay at 1,600 rpm – the most efficient operating pace for these machines. The swash plate in the pump always rotates at the same speed, which in turn means the motor maintains that same pace. This means the engine never has to speed up or slow down to reach target speeds; it just keeps chugging along at the same rate. This consistency can reduce our customers’ fuel consumption and related greenhouse gas emissions – depending on the operating conditions and the type of fuel used – and therefore their fuel costs.

Another benefit of zero gear changes? Uninterrupted pushing power. In a hydrodynamic drive system, changing gears disrupts the connection between the engine and the final drive. Even though each disruption only lasts for a fraction of a second, it still causes dips in the machine’s pushing force, or drawbar pull.

We don’t have this problem with hydrostatic drives. No gear changes, means no disruptions, means consistent drawbar pull. Over the course of a shift that consistency translates to hydrostatic machines pushing material more effectively than hydrodynamic ones. Case in point: the PR 776 G8 has the highest drawbar pull in the 70-tonne class.

Importance of independence

There are two independent sets of these pumps and their motors in our hydrostatic system – one on each side of the transmission – and each controls its respective track. This setup is one of the key reasons our hydrostatic dozers are highly manoeuvrable. Because operators can control each track independently, they’re able to turn the dozer much more tightly than they could in a hydrodynamic machine. To accomplish these tight turns, operators simply slow the outer track with the joystick to reduce its oil flow. All the while, the dozer never loses drawbar pull, so no productivity is lost. This comes in handy not only when operators steer the dozer with a loaded blade but also when they’re pushing with an unevenly loaded blade, like at a waste dump.

We carefully considered the best way to connect the hydraulic pumps and motors to each other. Instead of using rigid pipes as our connectors, we used flexible hoses. These hoses gave us the, well, flexibility to organise the drive system’s components in a way that would give our customers the most benefits: better weight distribution, fewer vibrations, less noise and more straightforward access for maintenance teams. All of which helps to make working in and around our hydrostatic dozers an enjoyable experience.

No brakes (sort of)!

The relationship between the engine and the hydraulic pumps and motors is what puts the ‘static’ in ‘hydrostatic drive system’. When all of these components work together, they form a closed loop circuit. The oil within the circuit moves from the pumps to the motors then back to the pumps, rather than returning to a tank first. This continuous flow keeps the circuit under constant pressure, making it nearly impossible for the motors to create enough force to turn the pumps on their own. And so the dozer stays at a standstill. This is why hydrostatic systems are self-locking. Operators can bring these enormous machines to a stop just by using the joystick – no mechanical brakes required. But just to be extra sure that our dozers don’t go anywhere once they’re stationary, they do still have a parking brake. This brake can also be used as a fallback solution in an emergency in the unlikely event it’s needed. Think of it like a handbrake in a car.

Not needing brakes has much the same benefits as not needing gears: consistent rpm and drawbar pull. This can support efficient pushing power and lower fuel consumption – depending on the application and operating conditions the dozer is working in.

Hang on a second…

But perhaps you’re reading this and thinking, ‘I’ve sat in a Liebherr dozer before and there’s definitely a brake pedal!’.

Technically speaking the thing you’re thinking of as a brake pedal is an ‘inching pedal’, which can also be called a ‘deceleration pedal’. This pedal works in much the same way as the joystick in terms of speed. Pressing on it will reduce the oil flow to the pump, which stops the machine moving forward. Once the pedal is fully depressed, the mechanical brake engages. But by that point the machine has already come to a complete stop. Which means no brake wear.

Having a pedal that replicates the actions of another component seems redundant. But we absolutely have our reasons.

Including this inching pedal in our hydrostatic machines helps operators to acclimatise to Liebherr dozers. As mentioned, the majority of mining dozers have hydrodynamic drive systems, which are always primed to move at full speed. To manage this, these hydrodynamic machines use inching pedals to slow the machine down by taking power away from the transmission and reducing the engine’s rpm. Most operators in the industry will be used to handling dozers this way, so not having an inching pedal can make operating Liebherr dozers feel strange. As such, while there’s no technical need for this pedal, we include it to make operating our dozers feel more familiar. Because, at the end of the day, the person behind the joystick is the one moving material day in, day out, and so their comfort is one of our top priorities.

The bottom line

So what does it all mean?

Well, at the end of the day, it boils down to this: hydrostatic drives offer a range of advantages for mining dozers. They support fuel-efficient operation, consistent pushing power, simplified maintenance, streamlined operator controls, a quieter cab and a self-locking drive system. Not bad for a drive system we’ve been using and refining for more than 70 years!

Published October 2026