Zi U-9 - History and Development

History and Development

The explosion-like development of trolleybus systems in the Soviet Union in the 1960s required a large number of trolleybus vehicles. The mainstay of the contemporary Soviet trolley fleet, the ZiU-5, was not sufficient for huge urban passenger transfers. It was more suited for medium-size cities rather than large megapolises such as Moscow or Saint Petersburg. In addition the ZiU-5 had an aluminium hull, which was expensive and complicated from a technological point of view. The two doors in the ZiU-5 hull ends did not work well in overcrowded situations which were quite common in Soviet public transportation.

The ZiU-9 was a quite successful attempt to solve this problems. It has one extra door compared to the ZiU-5. Two doors are wide and placed in the middle and rear end of the vehicle hull. One small door in the front end of the vehicle was/is comfortable for the driver and for outgoing passengers. The hull of the ZiU-9 is a welded steel one and it is significantly cheaper and simpler in production than the hull of the ZiU-5. The external appearance of the ZiU-9 was influenced by contemporary German-made MAN trolleybuses.

The electrical equipment of the ZiU-9 had some minor differences from the ZiU-5. The power of the main motor was increased. The indirect resistor-based control system of electric current was slightly modified to deal with the increased power of the main motor. While western designers developed new semiconductor-based control devices, Soviet engineers decided to leave the old resistor-based system for service simplicity. The first prototype vehicles were tested in Moscow in 1971 and were approved for mass production after some minor design adjustments.

The '9' in the vehicle name was the initial project index of the design team. However, after launching mass production, the new trolleybus received a new index '682' from the united classification of non-rail public transport vehicles. So all series vehicles had a ZiU-682 designation. But the number 682 is difficult to pronounce and the shorter '9' still lives in the everyday language of drivers and servicemen. In 1986, the new classification was introduced and the former ZiU-682 was designated as HTI-682. But this was not an end of renaming the same vehicle. The Russian acronym HTI in the Cyrillic alphabet is ХТИ and these three Cyrillic letters in 1995 were confused with the Latin letters XTU. This Latin acronym became an official name of the vehicle.