One application for the hydrostatic blower can be relatively well explained using the city-bus as an example. In general, the difference to the tour-coach, is that the city-bus has a much shorter wheelbase and a much lower floor. Thereby, the engine is moved right to the rear, e.g,. mounted flat in the rear, left corner. The relatively large cooler is thus, forced to take it's place on the rear, left-hand side.
Why is it like this? Because either it has too little space under the deep lying windscreen, which would increase the already large front overhang, or the access and possibly the also the path to the ticket-buying area would be limited.
Underneath the vehicle it's also not possible because of the low-lying floor and because the rear flap must remain free to get access to the engine compartment. At the rear and on the right it would without a doubt, not in the cooling air-flow, which would be the case if it were to be mounted up front. Thus, a blower is necessary, but not in the shape of an additional fan like in the motor car, but rather as the main cooling aggregate.
An electric motor for this blower, would have to be about the same size as a starter motor, and about the same amount of space would be needed to cool it. Converting mechanical- into electrical energy and then back again into mechanical, would reduce the efficiency. The generator would then also have to be vastly upgraded, whereby buses already need a great deal of current anyhow.
How can this problem be solved? The rotary movement is converted by a pump into a hydraulic oil flow. This drives a motor connected to the axle of the blower. Because the highest RPM is not always needed by the blower, an electronic control is necessary, which diverts a variable amount of the hydraulic oil away from the motor and directly to the flow-back. 02/12