Daimler’s first engine, built together with his long-time congenial companion Wilhelm Maybach, was a horizontal four-stroke single-cylinder unit. Its most important innovation was the hot-tube ignition which provided reliable ignition and made the desired increase in engine speed possible; the first experimental engine reached a speed of up to 600 rpm, significantly more than the previous maximum of 120 rpm for gas engines. The exhaust valve was precisely operated by Daimler’s invention of radial groove control, while the intake valve, known as the “snifting valve,” opened automatically by vacuum pressure.
The horizontal engine was soon replaced by the so-called grandfather clock, a vertical, considerably smaller engine which was perfectly suitable for installation in vehicles. This engine saw the first use of the float carburetor developed by Maybach, a type nowadays referred to as a surface carburetor, which enabled reliable operation with gasoline. The patent application contains an interesting explanatory note that is remarkable for its foresight: “Instead of the evaporator unit it would also be possible to use an atomizing pump”, an idea that later gave rise to the injection pump.
The world’s first motorcycle (1885)
Daimler first installed this air-cooled, 0.5 hp (0.4 kW) engine in the “riding car,” a wooden two-wheeler that was used as a test vehicle and quite incidentally went down in history as the world’s first motorcycle. Power was transmitted from the engine’s belt pulley to the rear wheel via a drive belt. Two speeds were possible depending on the belt pulley chosen: 6 or 12 km/h.
The horseless carriage (1886 – 1888)
In the summer of 1886, installing the engine in a coach was the next step. Still air-cooled but now with an output of 1.1 hp, the engine was centrally located in front of the rear bench seat to produce the world’s first gasoline-powered, four-wheel car. In 1887 the engine became water-cooled but still lacked an efficient radiator. The crucially new feature of this vehicle was its power transmission. Depending on the chosen ratio the engine’s belt pulley drove discs of different sizes on a lay shaft. The power was transferred to gears on the rear wheels via pinions on both sides. Instead of a differential a slip clutch was mounted on each side of the lay shaft.
V-engine and gear-only transmission (1889)
In 1889 this was followed by the world’s first V2 engine, which at 40 kilograms per hp was only half as heavy as its predecessor and initially delivered 1.5 hp (1.1 kW), later 2 hp (1.5 kW). This unit was first used in the very advanced design of the four-wheel Daimler steel-wheel car, whose tubular frame also served as a coolant ducting system. Next to the right wheel the rear axle featured an encapsulated bevel gear differential, while the left wheel was fitted with a brake drum and band brake. As if to confirm its technical exclusivity, the car had a four-speed gear-only transmission developed by Maybach, the first in the world. This became the forerunner of all subsequent automotive transmissions.
From closed cooling system to honeycomb radiator (1890 – 1901)
In 1890 the first four-cylinder four-stroke in-line engine was produced by Daimler. It had been designed to power a boat, had an output of 10 hp (7.4 kW) at 390 rpm and weighed 451 kilograms. A version developed at the same time generated 6 hp (4.4 kW) at 620 rpm and weighed as little as 25 kilograms per hp. Maybach equipped this engine with a closed cooling system consisting of 3.8 meters of coiled tubing with an air-contact cooling surface of 2.1 square meters. Though this was indeed an advance, the large coolant tanks were not big enough for longer journeys, and repeated refills were necessary.
In 1892 Maybach came up with the idea of “recooling” through the inside face of the flywheel, reducing the water requirement per horsepower and hour to two to three liters, one third of the previous amount and a considerable improvement. In 1897 Maybach was granted legal protection for the registered design of the tubular radiator, which at last made an engine output exceeding 10 hp (7.4 kW) possible. This consisted of numerous small pipes which allowed a greater volume of air to pass across the coolant reservoir, which still had a capacity of 18 liters.
The most sensational and still fundamentally unchanged invention, which was realized for the first time in the first 35 hp Mercedes in late 1900, was the honeycomb radiator. This radiator consisted of more than 8000 small tubes with square cross-sections and a side length of six millimeters. The square tubes, which facilitated significantly better cooling performance due to the higher air flow, were soldered together to form a new type of rectangular radiator with an integral coolant reservoir. A fan behind the radiator improved the cooling performance at slow speeds. The 35 hp engine (26 kW) in the Mercedes now required only nine liters of water, with a further reduction to just 7 liters one year later. The arrival of the honeycomb radiator finally put an end to automotive cooling problems.
Phoenix engine and spray-nozzle carburetor (1892 – 1893)
In 1892 the first two-cylinder in-line version of a new Daimler engine known as the “N” engine gave a major impulse to engine technology. The engine was heralded as a sensation by automotive specialists who spontaneously christened it the “Phoenix engine ... rising from the ashes of previous engine designs.” To reduce the weight, the two vertical, parallel cylinders were cast in one block. The cylinder block was bolted to the spherical crankcase. The smaller distance between the cylinders reduced crankshaft torsion.
The now outdated radial groove control system was replaced by a camshaft which moved the upright exhaust valve – the overhead intake valve operated automatically – and the unit featured flywheel cooling and the brand-new spray-nozzle carburetor. The output ranged from 2 to 8 hp (1.5 to 5.9 kW), depending on engine displacement. From 1897 it was available with a tubular radiator, the hot tube ignition was replaced by low-voltage magneto ignition in the fall of 1898, and a four-cylinder version appeared in the same year.
Maybach’s pioneering invention of the 1893 spray-nozzle carburetor became the model for all carburetors for decades to come. It permitted the immediate and flexible adjustment of mixture formation according to changes in engine output and made for increased engine efficiency. It also saved space, as it was much smaller than the float carburetor.