Mobile hydraulics – fundamentals and examples

The fluid-powered transmission of forces on vehicles is referred to as mobile hydraulics. This primarily refers to vehicles that operate with high forces and therefore carry their own hydraulic pump. Brake lines in standard motor vehicles are not considered part of mobile hydraulics.

Specific challenges in mobile hydraulics

In theory, hydraulics can generate virtually unlimited forces. Only the permissible compressive stresses on the components limit the forces that can be applied. In vehicles, the installation space and the design of the components used are another limiting factor.

Generating high operating pressures within the limited space of a moving machine housing is therefore one of the greatest challenges in mobile hydraulics. While many technical issues can be solved by using adapted components, this comes at the expense of purchase price. Components in mobile hydraulics are significantly more expensive than comparable components in stationary hydraulic systems. If mobile hydraulics is used not only in vehicles but also in avionics, the factors of reliability and weight are added. This further increases the cost of drives and actuators.

What tasks does mobile hydraulics face?

Mobile hydraulics on vehicles is divided into the following areas:

• Pressure generation
• Pressure transmission
• Pressure application
• Pressure monitoring
• Emergency systems

In mobile hydraulics, pressure is generated by pumps

The simplest pumps with high pressure generation are gear pumps. These are used, for example, on agricultural tractors. Gear pumps are also easy to clean and service. For particularly high operating pressures, piston pumps are used. Depending on the available installation space, either flat but wide radial piston pumps or narrow but long axial piston pumps are used. This pump type is standard on construction vehicles such as excavators, hydraulic cranes, or crawler machines.

In mobile hydraulics, the generated pressure is primarily used to move attachments. The hydraulic cylinder is the standard component used for this purpose. In addition, radial motors are used to drive the undercarriage, and occasionally also to rotate an upper carriage (or gun turret). When used for propulsion, the hydraulically driven undercarriage ensures high torque. However, hydraulically operated propulsion systems are usually slow.

This is why reliable monitoring is important

Access to mobile hydraulics components is always limited. This makes the use of high-quality components and reliable monitoring necessary. This is achieved through particularly pressure-resistant lines and highly advanced sensor technology.

Emergency systems in mobile hydraulics

Depending on the relevance of the hydraulic sub-circuit, it must be equipped with an emergency system. In most cases, this emergency system is used to be able to shut down the machine in a safe condition. Emergency systems cannot maintain continued operation under normal conditions.

High-priced, high-performance excavators have emergency valves that allow the boom to be lowered safely and in a controlled manner. Another example is the mechanical extension of an aircraft landing gear.