Hydraulic Pumps

Early free piston hydraulic pump

1920's

As early as in the twenties, free-piston hydraulic systems have been proposed, but never realized.

1937 Raul Pateras Pescara

1937 Raul Pateras Pescara

Based on the work on free-piston compressors, Pescara suggested this opposed piston version of a free piston hydraulic pump.

Full patent download

1997, Tampere University of Technology Finnland

1997, Tampere University of Technology Finnland

Based on the double-acting free-piston engine, a hydraulic system was developed and tested.

At least two engines were built, one was tested in a mobile unit.

Tampere University of Technology Finnland

To eliminate the vibrations, it was proposed to run two serial coupled engines phase-shifted at 180°.

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Brandl engine

Single-piston hydraulic system according to Brandl

2006 - 2011 TU Dresden

2006 - 2011 TU Dresden

Single-piston hydraulic system according to Bosch-Rexroth

Thermohydraulic Free Piston Engine, TU Dresden

Forklift Test Drive

The INNAS Chiron Engine

Single-piston hydraulic system according to INNAS BV.
All these versions work stroke by stroke, i.e. they fire only when the hydraulic accumulator need to be recharged.

The engine was named the Chiron Engine. There was an intense collaboration with several licensees, including Caterpillar.

CAT hydraulic drive concept

On the other part, Caterpillar patented the application of this machine for a hydraulic hybrid drive.

Full patent download

All versions above have a common problem: vibration. Very early, Pescara realized that a free-piston engine - whatever the application is - must be inherently balanced.

Ingocar

Ingocar: The idea of the hydraulic hybrid drive system is being promoted by Valentin Technologies. Please note an opposed-piston engine is used. This is the first widely published use of an inherently balanced free-piston engine with hydraulic power take-off.

Ingocar

INNAS hydraulic drive concept

INNAS BV is working on the same drive technology. Caused by the Caterpillar patent, INNAS dropped the self-developed free-piston engine (see above) and proposed a conventional internal combustion engine instead.

Download the HyDrid concept

Hydraulic drive systems develop - physically caused - high friction losses. It is therefore an illusion to believe that such drives could be highly efficient.

Meili hydraulic powertrain

Old wine in new bottles

The hydraulic components are neither lighter nor more effective than the solution with a manual or automatic standard transmission, but the friction losses are much higher.

Since many years, this drive system is used in a similar way in municipal vehicles, heavy construction machinery, etc. where it is important to have variable speed and high torque. The disadvantage is the extensive heat generated by the hydraulic drive train, that must be cooled through large surface coolers.

Download Patent (CH)

2010 Beijing Institute of Technology

2010 Beijing Institute of Technology

Experimental Study on Hydraulic Free Piston Diesel Engine.
Zhao Zhenfeng, Ying Huang, Fujun Zhang, Changlu Zhao and Kai Han