Bosch has produced the 20 millionth electrically driven auxiliary water pump at its Bühl plant in Germany, after the company went into the world-wide large-scale production with the original version 35 years ago.

The pumps are now installed in an increasing number of vehicles due to the quick interior heating available during normal driving as residual engine heat is redirected into the cabin. It is also possible to cool the engine and turbocharger after the 'ignition' key or card has been removed. In auxiliary heaters, these pumps circulate coolant around the system.

Main water pumps are connected to the drivetrain and provide a reliable circulation of cooling water. However, the direct coupling to the engine makes the delivery capacity dependent upon engine speed and not necessarily adjusted to the actual requirement. This is where additional electrically driven water pumps can help. If the car stops at a traffic light or in traffic congestion in cold weather, for instance, they increase the throughflow to the heat exchanger of the heater.

As a result, more heat is available for warming the car interior. This is of particular benefit in vehicles equipped with modern diesel engines, which dissipate only a little heat due to their efficiency. The available heat is therefore put to the greatest possible use.

Some vehicles have separate cooling circuits which work with electric auxiliary water pumps. Since these pumps also operate when the engine is switched off, they can keep the cooling or heating circuits functioning in vehicles with start/stop function or hybrid drives which are independent of the combustion engine.

Bosch has continually improved its auxiliary water pumps in terms of function, size and weight. In 1988, the company started installing solenoid operated couplings, which provided magnetic connection torque transmission from the drive motor to the pump wheel. The absolute segregation of pump and drive guarantees tightness throughout the service life. In 2001, this was followed up by brushless electric motors, which dramatically increased the service life and brought size and weight down even further.