Wilhelm Maybach (1846-1929), and the Development of Closed Circuit Cooling and the Honeycomb Radiator

• Effective cooling as a prerequisite for powerful engines
• Wilhelm Maybach used the honeycomb radiator for the first time in the Mercedes 35 hp
• The distinctive radiator grille became the hallmark of Mercedes-Benz vehicle design

Effective cooling of the combustion engine was, and still is, a prerequisite for producing powerful engine output. Vehicle designer Wilhelm Maybach was the first to demonstrate this fact 120 years ago. On 20 September 1900, he took out a patent for the honeycomb radiator design: as the car moved, the airstream was forced through a multitude of tubes mounted side-by-side, similar to a honeycomb when viewed from the front, which efficiently cooled the cooling water – that had been heated by the combustion action in the engine – as it passed through the radiator. The system was constructed as a protruding, vertical radiator and debuted in the Mercedes 35 hp in 1900. Form follows function – and so the high-performance radiator became a central characteristic of the modern car. What's more: that distinctive heat exchanger at the front of the vehicle became a defining stylistic element for the Stuttgart car manufacturer over the decades, and the front grille remains so today.

Sectional drawing of the tube-based radiator made by Wilhelm Maybach. The design, registered as a utility model in 1897, is the forerunner of the honeycomb radiator of 1900.

The background: The first vehicles after the invention of the car by Carl Benz in 1886 did not have a closed cooling circuit. Instead, the cooling water heated by the engine just evaporated. Refilling the water supply was part of the motoring experience – but, as engine power increased, it was no longer a practical solution.

Taking up the challenge: Wilhelm Maybach (1846 to 1929) was the first car designer to develop a solution, and quickly, at that. As early as 1897, that resourceful engineer, together with Gottlieb Daimler, introduced the tube-based radiator. Maybach himself described it as an "apparatus for cooling the water flowing around the cylinders of internal combustion engines, consisting of a flat vessel traversed by a large number of tubes, whereby a stream of air generated by a suitable ventilation device passes continuously through the tubes and extracts the heat from the cooling water". The tubes were made of brass because that alloy of copper and zinc has very good thermal conductivity. The new cooling system was first used in September 1898 in the world's first road vehicle with a four-cylinder engine: the engine of the "Phoenix" horseless carriage initially developed 5.8 kW (8 hp) from a 2.1-litre engine.

Wilhelm Maybach (1846 to 1929) was a close associate of Gottlieb Daimler until Daimler died on March 6, 1900. In the same year, the honeycomb radiator developed by Maybach was patented with effect from 20 September 1900. The cooling system made a considerable increase in the performance of car engines possible.

The breakthrough: On 20 September 1900, Maybach applied for a patent for the honeycomb radiator design as a "cooling and condensation device based on the cross-flow principle". From 8 August 1901, German Reich Patent (DRP) number 122 766 came into force to protect the invention, which was a further development of the tube-based radiator. Wilhelm Maybach had a new type of radiator soldered, made up of 8,070 square tubes measuring six by six millimetres in cross-section. The increased inner surface area of the square tubes in comparison to round tubes, combined with the smaller gaps between the individual tubes, increased the cooling effect considerably and made significantly higher engine performance possible.

Better efficiency: Compared to the Phoenix horseless carriage from 1898, the water consumption in the new 26 kW (35 hp) Mercedes engine from 1900 was reduced by half, from 18 litres to nine per 100 kilometres. In other words: for each horsepower, rather than requiring 2.25 litres of water for cooling purposes, only 0.26 litres was needed over that distance. A small fan located behind the radiator additionally improved the cooling effect at low speed. In this way, the new high-performance radiator solved the car cooling problem permanently – to this day, vehicle radiators are based on exactly the same principle.

Première The honeycomb radiator found its first practical application in the Mercedes 35 hp, the epoch-making new high-performance car manufactured by Daimler-Motoren-Gesellschaft (DMG). After the long-legged early motorised, horseless carriages, the design of this, the first modern car in history was trend-setting and triggered a landslide design change: the elongated silhouette, high engine output, honeycomb radiator, low bonnet, long wheelbase, a gear-change gate, inclined steering column, equally sized wheels on both axles and low weight were pioneering core features.

A design feature for decades: The vehicle design of the Mercedes 35 hp was defined to a large extent by the radiator that presented itself to the airstream, which was copied by many manufacturers. "Allgemeine Automobil-Zeitung", (issue 51-52/1902), commented on the Mercedes Simplex at the Paris Motor Show: "The honeycomb radiator, which also influences the lines of the vehicle in some respects, was virtually unknown at the last Paris Motor Show, but has since become 'de rigueur' for most French construction engineers." This was followed by the vertical, pointed radiator, also a defining design feature for decades. From the Mercedes-Benz 170 (W 15) model series, from 1931 on, the flat radiator was hidden behind a grille. It was incorporated as part of the bonnet and, with its house-roof shape, resembled the pointed radiator. The chrome-plated grille became the central distinctive feature of the brand. Now flatter, more elongated and redesigned many times over, it still is today.