Although skid steer loaders are not widely used in China, they are by no means a new thing. On the one hand, foreign manufacturers have been promoting them in China for many years; on the other hand, due to the low barrier to entry, many domestic companies have been producing them for a long time as well. With their unique structure and traveling method, combined with a variety of attachments, skid steer loaders have become versatile players in various work situations.

▲ Early transmission method of a skid steer loader manufactured by Zoomlion

As a compact piece of equipment that also features skid steering, the transmission method of a skid steer loader is very distinctive. Today, the vast majority of skid steer loaders use a configuration with one hydraulic motor on each side, driving the two wheels on that side via a chain drive. When the motor speeds on the two sides are controlled to be different, the corresponding wheel speeds on each side also differ, thus achieving steering. Reversing the motors can even achieve zero-turn (in-place) steering.

▲ The simplest and most common transmission principle of a skid steer loader

Of course, in the early development of skid steer loaders, hydraulic motors were not yet widespread. At that time, power was transmitted using drive shafts along with multiple sets of chains and gears, supplemented by a braking system. Today, the simplest transmission method is a hydraulic motor directly driving a duplex sprocket. This method is adopted by many manufacturers, including Caterpillar, Zoomlion, Volvo, and others.

▲ Inside a Caterpillar skid steer loader: The blue circle indicates the travel hydraulic pump, and the blue arrows point to the travel motors on each side.

Of course, different manufacturers have different designs. Some manufacturers have a slightly more complex design, adding an extra chain set for speed reduction, while others use a pair of gears for speed reduction. Additionally, some manufacturers equip their loaders with a chain tensioning device.

▲ Some manufacturers equip a chain tensioning device; there are two tensioning gears in the picture.

The travel hydraulic system of a skid steer loader generally uses a dual-circuit closed-loop system. Because the hydraulic circuit is closed, the vehicle brakes when it stops, eliminating the need for a separate service brake. However, some manufacturers also equip brake discs for parking brake.

▲ Some manufacturers use gears for speed reduction before driving the chains.

When we typically refer to skid steer loaders, we usually mean the wheeled chassis. In fact, those with a tracked chassis are also skid steer loaders. However, manufacturers often call these compact or multi-terrain tracked loaders. But their structure is actually very similar to wheeled skid steer loaders. Except for using a tracked traveling device, their internal structure is nearly identical to the wheeled version, only the position of the hydraulic motors changes slightly, and of course, chains are no longer needed.

▲ A tracked skid steer loader. It can be seen that its internal structure is essentially the same as the wheeled version.

In summary, the skid steer loader has a simple structure and a relatively simple transmission system, yet its performance and functionality are far from simple. However, constrained by the cost of hydraulic components and the lack of diverse attachments, the widespread adoption of skid steer loaders in China still needs time.