We join the pacesetters...
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SOUTH Yorkshire PTE and CM have scored a double first. The Tykes are the first UK concern to fit a Voith DIVVA D851 fully automatic gearbox to a standard Leyland AN68 Atlantean double-decker — and I am the first British journalist to test it.
Recently, I had the opportunity to put the bus through its paces at MIRA and carry out an operational trial, unladen, in Sheffield.
The Voith Leyland combination was very impressive with the empty bus. The Europeanmade Voith transmission, in use in many Continental city buses and incorporated in the new Dennis Dominator, is a fully automatic differential torque converter transmission incorporating a built-in hydraulic retarder or converter brake.
The gear selection controls are electronic buttons mounted on a panel in front of the driver. There are three buttons, forward, reverse and one to lock the vehicle in second.
Safety measure
As a safety measure to avoid accidentally engaging reverse, a second button some way away from the main controls has to be simultaneously pressed with the main reverse button when selecting reverse.
A hard retarder control level is mounted at the left of the selecting controls.and is within easy reach of the driver's left hand. There is also a retarder warning light, but on the South Yorkshire bus it was obscured by the steering wheel.
At MIRA, I found the acceleration times and the braking capabilities of the bus favourable compared with other double deckers tested by CM.
The bus stopped smoothly and efficiently and accelerated quickly.
The Voith transmission smoothed out many of the jolts and jerks normally associated with self-changing and semiautomatic geared buses.
Carrying out brake tests with the empty Atlantean a Tapley meter was used; using the service brakes which automatically engaged the retarder crash stops at 32 18km/h (20mph), 48.27km /h (30 mph) and 64.36km/h (40mph). Figures of 71, 75, 78 per cent efficiency were obtained on the brake meter. Slowing down using just the retarder hand control which operates in three stages, Tapley performance meter readings using just the first stage at 32.18km/h, 48.27km/h and 64 36km /h (20mph, 30mph
and 40mph) were 3.6, 5.3, 7.1 per Cent g, using two stages were 6.25, 6.7 and 8.5 percent g and three stages were 8.9, 10.3 and 13.4 per cent g.
In comparison figures from the Tapley performance meter on engine braking only were 2.7 per cent g from 64.36km /It (40mph), 3.1 per cent g from 48.27km /h (30mph) and 2.2 per cent g from 32.18km / h (20mph).
Impressive
I drove the bus on MIRA's arduous ride and handling circuit where the transmission coped impressively with changes in gradients and cambers. On the horizontal straights, at MIRA the Atlantean covered the standing quarter mile in 31.5 seconds. 0-32, 18km ih (0-20mph) took 7.6 seconds, 0-48.27km /hi (0-30mph) took 13.8 seconds and 0-64 36km /h (0-40mph) took 25.6 seconds in our acceleration tests. The bus achieved 30.57km/h (19mph) maximum speed in first gear, 48.47km / h (30mph) a second and a maximum speed of 75 623km / h (47mph) Using the kickdown, the bus achieved a maximum 54.71km/h (34mph) in second.
I also drove the South Yorkshire AN68 No. 323 in normal operating conditions in Sheffield, selecting Route 51 which crosses the city from Herdings to Lodge Moor.
The route takes in most types of operating conditions including the extremely busy centre, the tight corners and narrow streets of housing estates and fairly fast country roads. It is also one of the hilliest routes in. Sheffield as the route gradient plan on the right shows.
I was also able to evaluate performance on a limited stop journey between MIRA at Nuneaton, and Sheffield.
Beautiful
I decided to follow a regular service bus on Route 51, an older, semi-automatic AN68. The bus was beautifully easy to drive and, although on several occasions I used the second gear lock control, the engine never felt as if it was labouring. My only criticism of the braking was that, when using the hand retarder control, there was a split second pause before I felt the vehicle stopping.
I was a little embarrassed when the bus we were following became full, even though we did not carry out our test during peak hours and its passengers expected to be able to board our CM test bus. This says a lot for South Yorkshire PTE's policy of keeping down fare levels and I understand that passenger levels are increasing.
At the terminus, I checked the brakes of our Atlantean and the standard one and noticed that the drums on the Voithequipped vehicle were cold while the standard bus's brakes were too hot to touch. Later, I carried out a similar comparison with an empty AN68.
The Voith bus achieved a remarkable fuel consumption of 28.9 litres/100km (9.75mpg) on the Route 51 test and 28.25 litres/100km (10mpg) on the trip from Nuneaton. The vehicle had been in service for some time before our test and had travelled about 10,000 miles but the brake linings had required no attention.
Our test bus was one of two East Lancashire-bodied 75-seat Atlanteans originally ordered by Fishwick Company but cancelled by them and bought by the PTE.
Twelve years
The fitting of the Voith transmission necessitated a considerable amount of engineering work by the South Yorkshire PTE which included resiting the radiator. The gear box costs over 1,000 — twice the price of most competitors — but this and the cost of development is more than justified by the improved driving characteristics and brake life. Voith expects the gearbox to last 12 years — four times the average life of an automatic — without a major overhaul.
The test bus, which started life as a standard AN68, has now been lent to Leyland Truck and Bus for evaluation.
My impressions of it were in common with several South Yorkshire bus drivers with whom I spoke. Their verdict was unanimous, the Voith box is outstanding with its smooth and effortless gear changing. The retarder braking system is revolutionary and a must for future automatic passenger vehicles.
The Voith DIWA D851 transmission is currently fitted to a Daimler CVG 6 doubl decker which has served as mobile test bed for the Denni companyThis vehicle is soo to enter experimental servic with London Transport and expect the transmission wi prove ideal for the capital' extreme traffic conditions.
Choosing the Voith tran5 mission must also give the ne% Dennis Dominator doubt decker chassis a promisin future.