APAX designed the VRHEC technology to provide an energy management system for one of its HPVs (human-powered vehicles). The VRHEC (variable ratio hydraulic energy converter) is the key component of a hydraulic circuit which captures, stores, and recycles energy. The constraints inherent in an HPV require the VRHEC to be highly efficient, physically small, inexpensive, lightweight, and reliable. These objectives have been achieved.

Functionally, the VRHEC allows:

  1. Recapture of energy otherwise lost when braking (also known as regenerative braking). This energy is then available for reuse. The rider brakes the vehicle, thereby storing energy. They re-use this energy to accelerate, or propel them up the next hill, minimizing pedaling effort.
  2. Storage of energy provided by the rider. Energy generated by pedaling can be stored, rather than (or in addition to) used for propulsion. This storage can occur when pedaling while coasting, stopped, or pedaling in excess of what is required for propulsion.
  3. Continuous, smooth, "dialable" release of energy. This can occur at far higher rates than that available from the rider. An HPV could accelerate much faster than is possible by simple pedaling; however the rider can choose whatever acceleration rate they desire.

The VRHEC replaces the drive train. An HPV would have no derailleur, no gearing, no need for "gear changes". The HPV rider would control acceleration via a motorcycle-like throttle, with no attendant gear changes.

Note: in the HPV, the VRHEC is the size & shape of a tuna can.

VRHEC technology can be applied to any cyclic energy process. For example:

  1. Hydraulic-hybrid automobiles with considerable advantages in efficiency, cost, and longevity over the current electric-hybrid models.
  2. Elevators in modern buildings. These cyclic energy users represent considerable energy costs. The VRHEC could recycle 75% of this energy, while providing precision control of the elevator.
  3. Construction cranes
  4. Amusement park rides
  5. Ore haulers in open-pit mining
  6. Any process requiring infinite control, from heavy industrial processes, to the fine control of artificial arms

In most of the above applications, the control of the hydraulic circuit requires expensive electro-hydraulic interfaces. Since the VRHEC requires only a low-control force, the need for the electro-hydraulic interface is eliminated or reduced.

Functionally, the VRHEC is the hydraulic analog of the electric "Variac", (variable electric transformer). In many cases, a "Variac" can be used in place of a rheostat or potentiometer to control a load. It saves energy by not having the large resistive losses associated with rheostats and potentiometers. The VRHEC has 2 basic forms. One is the "2 chamber" VRHEC, a 3-port device analogous to a "Variac" autotransformer. The other is a "4 chamber" VRHEC, a 4-port device analogous to a "Variac" transformer. Each design has slight advantages over the other for a particular application, and both serve to control and conserve energy.

Physically, the VRHEC consists of a free-spinning rotor with vanes, (similar to a vane pump, but with no external shaft). It is connected to the hydraulic circuit, and with control by the operator via a small control rod, allows the hydraulic energy in the circuit to be managed. The operator sets the pressure ratio in the VRHEC, which tries to maintain this ratio between the accumulator and the load. This is accomplished by rotating, and delivering or receiving oil flow from the accumulator with no throttling losses. Control without the throttling losses represents energy conservation. Low friction and low internal leakage also contribute to efficiency.

The VRHEC is the key component in an efficient energy management system. It is lightweight, and comparatively small in size. It is highly reliable due to its fundamental design, and the fact that it operates in a sealed-oil environment. Due to its small size, and limited number of parts, it is comparatively inexpensive. The VRHEC is a versatile device, serving a number of applications.


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