The heart of the Benz Patent Motor Car was a single-cylinder, four-stroke engine with a displacement of 0.954 litres. This design already incorporated several of the key features found in most internal combustion engines today, including a crankshaft with counterweights, electric ignition and water cooling. The unit developed a peak output of 0.55 kW at 400/min.
By the standards of the day, this engine was positively lightweight, tipping the scales at around 100 kilograms. Other characteristic features were its open crankcase, the intake slide valve controlled by an eccentric rod, the exhaust poppet valve operated via a cam disc, rocker arm and pushrod, and the drip-feed lubrication system. Benz’s design had the large flywheel mounted horizontally on the chassis, because he feared the gyroscopic effect of a vertical arrangement would interfere with the steering and stability of the vehicle.
Preparation of the fuel-air mixture was handled by the surface or evaporative carburettor, another Benz design, which also doubled as a 4.5 litre fuel reservoir. The vehicle required around 10 litres of petrol for every 100 kilometres travelled. The fact that fuel capacity was inadequate for longer distances was not initially a major concern. First and foremost, the purpose of the Benz Patent Motor Car was to demonstrate that the overall design was fit for purpose.
The precise composition of the petrol-air mixture was controlled by a sleeve valve, the position of which determined power output by opening or closing holes for the auxiliary intake duct. This sleeve valve was easily accessible beneath the driver’s seat. The engine was started with a hearty swing of the flywheel.
Benz spent a great deal of time experimenting with the ignition, before he eventually came up with a solution that suited the low battery voltage of the day. He transformed it up to a higher voltage using a Ruhmkorff spark coil. The spark plug was also one of his own designs.
Cooling the internal combustion engine presented a particular problem, since unlike a stationary engine it could not merely be attached to a cold water supply housed inside a building. Benz opted for simple evaporation cooling, which proved highly effective and more than adequate for the low engine output. The steam produced was simply allowed to escape, meaning that water consumption during a journey was considerable. More efficient closed-loop cooling systems were not developed until around ten years later, when increased engine outputs and the higher demands placed on a vehicle’s reliability made this a necessary improvement.
- horizontal flywheel
- mounted at the rear
Bore x stroke
- 90 x 150 millimetres
- 0.55 kW at 400/min
- approx. 10 litres per 100 kilometres
- 1 speed
- engaged by shifting the drive belt from the idler disc to the fixed drive disc
- 16 km/h