1. Weight and size restrictions
For most mobile machines, weight is a really important factor. In machine design, the easiest way to make sure a machine is strong and lasts long is by using thick steel plates. This makes the machine tough and reliable. But mobile machines usually have weight limits, and these limits can be different depending on the vehicle's size and the rules it needs to follow. So, to make machines lighter, manufacturers have to try different methods, like using computer design tools, lighter materials, or switching from mechanical or hydraulic parts to electric ones. The surprising thing is that cutting down on weight can be very expensive-sometimes the steel ends up being cheaper.
Now, let's talk about power density. This is one of the key differences between mobile hydraulic systems and similar industrial ones. Power density is the amount of power a system can give compared to the size of the part that does the work. Right now, no other system can match the power density of a hydraulic actuator, and honestly, it might be a long time before that happens.
For example, a bulldozer's wheel drive motor can work at pressures over 400 bar, which is twice the standard for industrial hydraulics. Imagine this: a 300-horsepower (220 kW) drive motor weighing just 120 kg. If you think that's heavy, let's compare it to an industrial electric motor. A 300-horsepower electric motor might weigh 1,360 kg-about 11 times heavier than the hydraulic one.
The power density ratio of radial piston motors is already high enough. If you look at the power density ratio of inclined axis piston motors, you will find that radial piston motors are still inferior. The inclined shaft piston motor has a unique combination of fixed inclined plates and heavy-duty bearings, and works in equipment with application requirements close to 400 bar under most working conditions. At a power of 35 horsepower (26 kilowatts) with a 5cc A2F5 motor from Rexroth, it weighs only 2.5 kilograms and can even fit in a rice bowl.
By increasing the power density, the weight of the entire machine has been reduced. For OEMs, this means that machines can meet strict emission standards and reduce the size of engines or motors, which are usually the most expensive parts of the machine.
