The ZIU-5 trolleybus

Sándor Ambrus
The ZIU-5 trolleybus number 566 at Élmunkás tér (square), in the '70s.

The ZIU-5 type trolleybus was after the MTB-82 series the next, which was bought from the Sowiet Union. As the MTB 82 became a standard type in Budapest (since the IK-60T was built after the plans of the MTBs); the ZIU-5 also became a basic type of tht BKV (Budapest Transportation Company). Here also not the very construction was basic, but it was the first of a family, which had similar electric equipment - the ZIU-9 and the IK-280.T1 (100 series) are very similar electrically to the ZIU-5.
The prototype of the ZIU-5 trolleybus and the ZIU-6 autobus - which had similar body - were made in 1959. From 1961 the Uritsky factory in the city of Engels started the mass production of ZIU-5, on average annually 200 vehicles were made.

The first 7 pieces of ZIU-5 trolleybuses were put into service by the FVV (Capitol Tramways) in Budapest on 6th August 1966. These cars started their run on line 76.

The new 504 trolleybus on Élmunkás híd (overpass)
100 pieces of ZIU-5 trolleybus was bought alltogether by Budapest, between 1966-69. These obtained the numbers 500-599.

The supply of the ZIU-5s:
new vehicles (pieces)

The ZIU-5 was longer than the earlier trolleybuses, on this type the servo help of the steering and the automatic regulation of the acceleration were also introduced. 

The trolleybus 550 around 1970. at the corner of Bajza utca - Damjanich utca (street).
The ZIU-5 trolleybuses had only two side doors, so despite their large room, the vehicles were not really suitable to the city-centre traffic of Budapest. A further problem was, that the driver's cabin was not well designed: since there was no window before the first door, the door of the cabin and the first door together blocked the view to the right. That is why between 1971-75 the BKV reconstructed the front door: instead of the original four wings they replaced to three wings, and a window was made before the door. This worsened the speed of the passenger exchange at the stops.

The ZIU-5 did not last long, the scrapping of the first two was in 1975. The electric equipments of the vehicles scrapped until 1978 were moved to Ikarus bodies: e.g. the 100 IK-280 articulated and the 600 IK-260 solo car obtained the equipment of the first stalled two. This was the birth of the 100 series of articulated trolleybuses in Budapest.

Sándor Ambrus
The 575 at Podmaniczky utca (street) - with already grey doors. The image was taken before 1977.
The building of the Ikarus trolleybuses lasted until 1978: alltogether 79+1 new trolleybuses were made (possibly spare electric units were also used above the scrapped ZIU-5s).

Scrapping of ZIU-5:
scrapped vehicles (pieces)

The last 23 trolleybuses were stalled in 1981-82. Last time they ran in line 72. By this time these trolleybuses were operating rather unreliable comparing to ZIU-9s, so the drivers of ZIU-5 obtained extra bonus for the many lost courses because of technical failures.

The trolleybus 598 in the queue in front of Pongrác depot. Behind is the successor: one of the 100 series articulated trolleybuses
In Kőbánya, at a park in Kozma utca (street) the 552 was exhibited with the tram 3635 and an IK-620 autobus. Here children learned the rules of the traffic.
These vehicles were there until the '90s. 
Moszkva tér
Sándor Ambrus
A scrapped trolleybus used for a shack at Moszkva tér (square).
The 573 is exhibited in Szentendre, in the Museum of Urban Transport. The image was taken after its restore at the workshop of Gyömrői út (street). The trolleybus is full operable.

Data of ZIU-5:

11780 mm
2680 mm
height (without trolleys)
3160 mm
distance of the axles
6100 mm
weight (empty/full load)
9600 kg/19280 kg
DK 207 G-1
110 kW
seats / load (7 persons/m2)

Electric equipment:

As it was mentioned earlier, the electric equipment of the ZIU-5 is not just interesting by itself, but because similar ones were mounted into the ZIU-9, the IK-280.T1 (100 series), the Debrecen 400 series and Szeged 500 series of trolleybuses.

The electric circuit of the ZIU-5 is in many aspect the automatic version of the MTB-82's equippment. Both types have double coiled motors: with a main circuit (serially coupled to the rotating part) and a separate outer exciting circuit. Also the principle of the coupling is similar, both in acceleration and rheostatic brake. The main difference is, that there are less contactors in the ZIU-5, because the varying of the resistors are mainly done by the automatic starter device.

This brought some other changes, mainly because the starter works only "one way": it is not able to reopen the electric circuit.

The starter is also mounted on the chassis. This has two major parts: a knobby cylinder, which closes the coupling elements, and a 24 V motor to propel it. Alltogether there are 12 coupling elements.

On the image is the starter of one of the IK-280 trolleybuses in Debercen (401-404), which is fitted with ZIU-9 equippment. The starter of the ZIU-5 was almost like this: on the left there is the motor, on its right the cylinder and the coupling elements are visible.

Dániel Szigeti

Since the starter cannot get the resistors out of the circut, there are contactors to do so. The manouvre contactor LK3 can insert a large resistor in the main circuit and the line contactors LK1 and LK2 shut the main circuit completely out of the poles. At the end of the acceleration there is this two step of closing the circuit before the accelerator turns back the cylinder into the initial position.
At the beginning of the acceleration this happens opposite way: first the line contactors turn on the motor, then the LK3 gets out of the circuit the large resistor in less then a second. This is the manouvre stage: it is possible to go like this (with all the resistor coupled by the starter inside the main circuit) in low speed.

This is a contactor box open in a ZIU-9, on the right of the driver. In the ZIU-5 the order of the contactors were exactly the same.

The LK1 line- , T brake-, LK3 maneuvre contactors; the S2, S3 exciting circuit contactors, and the KDK compressor regulating contactor are visible. Also there are some relays: the zero voltage relay (RN), the maximal relay (RT) and the acceleration relay (RU) is there. The rest is covered by the wall of the driver's cabin.

The speed of the starter is regulated by the acceleration relay (RU), which stops the cylinder if the current is higher than a certain threshold. This threshold is 250 A in the second position of the accelerator pedal, and it is lower at the first position. In case there are some irregularities in the level of the current, first the maximal relay, then the fuse switch (which is above the head of the driver) can break off the circuit.

At the end of the acceleration, the R accelerator contactor short circuits all the resistors (and also with this the outer excitation is decreased). This happens around the speed of 30 km/h. After the shunt cascades come into the play, regulated also by the starter. Hereafter the speed of 60-80 km/h was possible to reach. There is three shunt possibility according to the accelerator pedal position.

Clicking on the image the full main voltage circuit becomes visible. To avoid the confusing parts, here a simplified version is shown.

The rotating part of the motor is between JA-JAJA, the main circuit's exciting coil is at K-KK, and the outer exciting coil is at S-SS sign.
LK1, LK2 - line contactors, LK3 - maneuvre contactor, R - accelerator contactor, T - brake contactor, S1-S3 are the exciting circuit contactors. 
1-11 (12 is missing!) are the starter's coupling elements.

The acceleration of the ZIUs are not very smooth: the beginning of the starter's operation, the coupling of the R contactors and the shunt cascades make a considerable kick to the car. However the articulated 100 series with ZIU equippment were much better: the larger weight of these trolleybuses nicely decreased the strength of these kicks, without considerably loosing the speed and accelerating power.

There is no possibility of recuperating brake on the ZIUs, since the shunts are regulated also with the starter. For decreasing the speed there is the rheostatic brake.
By pressing the brake pedal all the main circuit will be out of voltage by releasing the line contactors (so during the brake the starter can go back). However the brake contactor T makes the rotating part coupled on the resistor of the LK3 (which is also released). The S exciting-circuit contactors regulate the current of the braking in two stage: this gives a very smooth and not exremely powerful decrease of speed. During the brake pedal is pressed, the trolleybus uses a small current to supply the exciting magnets: if there is a dead section (e.g. tram crossing), then the rheostatic brake becomes ineffective. By pressing the pedal further down, the pressure air brake could always fully stop the vehicle.

Jumping the trolleys with ZIU-5 on Hungária körút (boulevard). Because of the broken sticks and torn supporters the trolleys have to be held down. If the continuity of the pole is broken, the trolleys have to be pulled away while the vehicle rolls under the faulty section.

The ZIU-5 had the old iron trolleys; if it got loose it could make more serious damage as todays' aluminum trolleys. Also the older trolleys were just painted, but had no insulating cover: so the side of the trolley could cause an electric shortcut stalling in the overhead wire-system.

All electric vehicles make radio noises, to compensate this effect electric filters are put in the circuit. The ZIU-5 had these on the roof without cover.

On the picture is the 521 at the entry of Pongrác depot, in the '70s. The radio-filters are visible on the roof: to the 600 V trolley belonged twice as large as to the 0 V. These were made of coils and capacitors.


Electric devices operating from accumulator:

The ZIU-5 had interestingly two low-voltage circuit: 12 V and 24 V. The microphone (installed posteriorly), the turn signals, the front lights, the speedometer and the windscreen wiper operated from 12 V, the rest from 24 V. The 24 V circuit was joint to a dynamo (with own motor running constantly) to charge the accumulator, the 12 V was probably simply branching from the accumulator cells. Later the 12 V devices were using 24 V with a resistor in the circuit.

Let's have a look in the driver's cabin:

Rudolf Lakos
The low-voltage equipment was put on the wall without any cover. Some devices are signed:
Heating switch (F), 17 low-voltage switches (K), windscreen wiper (A), 9 low-voltage fuse (b), emergency- and no-voltage bells (cs), amplifier (e). Behind the heating switches was the switch of the dynamo.
These parts are better hidden on ZIU-9.
As it is possible to see, the seat was not really comfortable on this type: there is no suspension. Some more devices:
direction selecter (Iv), handbrake (Kf), accelerator (M), brake (F).
The box of the direction selecter contains the also the KVP-22 type controlling cylinder: this is mechanically joint to the pedals. The arm of the direction selecter was removeable, this was supposed to be taken by the driver.
Those switches, which are situated on ZIU-9 on the right of the driver, on ZIU-5 was on left under the window. This was not really good for operating the doors or the blinking turning signals.

The doors ran with 24 V motors. The switches of the doors had three stages: in the middle stage it was possible to turn off the motor. This was neccessary when the door was shutting someone: the motors could quite heavily press the passenger, and if the doors did not go to the end, the motor could burn down. A get off requesting signal was only at the rear door.

Rudolf Lakos
The passangers' room of 535 and 558. Thanks to the wider body, between the double seats of the two side there was enough place for standing.
The cover of the seats was typical russian: the soft coushioning compensated the hard suspension of the trolleybus. It was a usual view as the passengers bounced together on the seats as the vehicle went through a bump on the road.
At the back was the conductor's seat, which was never used in Budapest, since by the time the trolleybuses went into the service, there was no conductor job.

Pressure air equipment:

With pressure air was working the air-brake, and - uniquely - the steering servo. Practically the servo was the same as the nowadays usual hydraulic devices, only the cylinders were pressed with air. That is why the ZIU-5 had the nickname "susy": the moving of the steering wheel caused a noise of the streaming air. The pressure of the air-circuit was around 8-10 bar.

A view to east:

It seems, that Budapest was the only city outside the Sowiet Union, where ZIU-5s were in service. Possibly it is because by the time of the production of these cars, the trolleybus networks were decaying around the world.
Ferenc Szántó
A ZIU-5 on line 5 in Leningrad (today Sankt-Petersburg).
A trolleybus on a dead street of Odessa (today in the Ukraine), in 1981.
Blickpunkt Strassenbahn
Blickpunkt Strassenbahn
Two exhibited trolleybuses in front of the depot of Cheboksari on the river Volga, in 1995.
The 007 trolleybus of Almati (until 1992 Alma-Ata) - as a working car in 1998.

Every comment is regarded!

Written an translated by: Zoltán Ádám Németh
Part of pictures and informations are from Blickpunkt Strassenbahn and