Hilberg Engine Technology – the solution for VCR

Linear Rod Technology (LRT)

The LRT represents a radical simplification of the engine’s Crankshaft – Rod – Piston connection.

The conventional crankshaft – rod – piston sets limits for interventions to achieve variable compression ratio. The rotating and reciprocating movement of the rod makes it virtually inaccessible to mechanisms capable of changing the distance from the crank to the piston top without a quite complex system which also affects the inertia of the moving parts.

Unlike all engines today, the LRT unique construction works with linear moving connection rods. This eliminates the piston’s sideway friction against the cylinder walls, which significantly reduces the internal mechanical losses.

As the two pairs of pistons, rods and yokes always move in the same direction, a counter moving weight is required to achieve full reciprocating inertia balance. This counterweight comprises a third yoke system having the equal mass of the two first yoke systems, connected to the crank midways between the other two. This third yoke is equipped with four pistons which forms two compressors and two exhaust gas expanders, further explained below (about DCE). As the system invokes true reciprocating and rotating parts only, with all internal inertia forces fully balanced, LRT provides a virtually vibration free engine.

Variable Compression Ratio (VCR)

Variable compression ratio has for decades been a recognized method of improving the efficiency of engines, especially for IC engines running at lower and varying operating loads. Several attempts have for various reasons failed. Foremost, if not for all proposals, because they were based on modifications of the conventional piston – rod – camshaft system. Consequently, they became too complicated, too heavy, too large and mostly too expensive

Changing challenges to become options by eliminating the cause of the issue often seems better than fighting the problems. The innovation of LRT has released the design of a practical, robust and fuel-efficient VCR solution. The linear moving piston rods run through coaxial worm gears, which by turning the rods can elevate the rods up and down on the yoke’s furnished threads, thereby changing the top dead position of the piston.
The compression ratio can be adjusted automatically at run-time between 7:1 and 15.4:1, depending on the engine’s actual load. When cruising, a car engine works at an average of 15 – 25% of full effect. Within this range the compression ratio will stay at 15,4:1, and the engine efficiency remains high. The VCR mechanism is moving only when the compression rate is changed, otherwise it will remain passive.

Photo showing the internal mechanism controlling VCR

Double Compression and Expansion (DCE)

Downscaling has become a trend in engine development. Simply explained, downscaling (also called downsizing) aims to achieve more power output of a certain size of an engine.

The available means for downscaling are methods of increasing the engine thermal efficiency and increasing the amount of charge flow through the engine. The latter is usually provided by an exhaust driven turbocharger. However, turbochargers cause a certain pressure to remain in the exhaust manifold and in the cylinders, thereby lowering the amount of fresh charge that is filled into the cylinders. Besides this, the turbochargers are inefficient and increase the temperature of the charge, which in turn causes the compression ratio to be kept lower in order to avoid knocking. Furthermore, these devices cannot convert any residual exhaust power to the main shaft.

As for VCR, the LRT is also the freedom key to design an engine where both high supercharging without a turbo device, as well as an effective double exhaust where recovered residual power of the exhaust is fed to the engine shaft, becomes realized. The latter process takes place in the upper part of the set of expansion cylinders, which common piston area has twice the size of the main piston area.
The lower part of the expansion cylinders forms a compressor, driven by the very same expansion pistons. When supercharging is needed, the expander’s regenerated energy is shared by the shaft and the compressor. However, when the load increases, the resident exhaust gas pressure from the main cylinders rise accordingly, so that even at full load, still a significant amount of recovered energy will be transferred to the engine shaft.
This method of supporting the main cylinders by pressurized charge has several advantages over the traditionally turbochargers:

  • Instant response to speed and load changes. (Turbo is slow)
  • Empties the main cylinders to atmosphere by discharging. (Turbo cause residual pressure in the exhaust manifold.)
  • Higher level of supercharging than turbo.
  • Built-in and away.
  • Silent operation.
  • Lower cost.


Downscaling has become a trend in engine development. Simply explained, downscaling (also called downsizing) aims to achieve more power output of a certain size of an engine.

The patented VCR-DCE engine design based on the LRT innovations, may be scaled with additional cylinders and up- or downsized to meet the needs of various engine producers.

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Patentec AS is the patent holder for the technologies described and licenses these rights to engine manufacturers and engine developers globally.