HC V8 MANBATOR/BOBEN 12-TON-GROSS ARTIC
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by A. J. P. Wilding
LAST WEEK saw the official release of one of the most open secrets in the commercial vehicle industry—the AEC V8 engine. With it came news of the first vehicle to be fitted with the unit—the AEC V8 Mandator 32-ton tractive unit which is available with semi-automatic gearbox. To match the importance of the new model we decided to put the vehicle through a much more rigorous trial than usual; to be exact, two tests in one. The normal road test coupled with an extended run—from London to Scotland and back. This simulation of varied and searching operational conditions will increasingly become a feature of COMMERCIAL MOTOR'S test programme.
In every respect that matters the Mandator came through with flying colours. It will be seen from the map on page 46 that the route taken for the extended operational trial included motorways, good-class "trunk" roads and arduous, hilly and twisting roads in the south of Scotland and in Northumberland.
Ron Cater accompanied me on the test and we agreed that the Mandator with V8 and semi-automatic transmission was a fine ma
chine. On the twisting sections of the test route power steering would have been a benefit and we felt that the brake actuation could have been better to allow for finer control to be given. But probably the high qualities of the new engine and transmission showed up these features which are retained from the normal Mandator—previous tests have not drawn criticisms in this respect.
Total distance covered was almost 750 miles, which took up less than 21 hours total time on the road and required just under 126ga1 of fuel. Overall average speed was 35.8 mph and consumption 5.95 mpg. These are certainly impressive figures and they were matched by very good consumption returns on the normal test over our usual circuits-7.2 mpg at up to 40 mph and 6.4 mpg on the motorway.
Braking results on initial tests were just about acceptable although a little below current standards—persistent locking of the wheels on the three-axle trailer did not help —but after modifications to the semi-trailer air-pressure circuits and operating valves, good figures were obtained. Acceleration times were excellent.
The engine and gearbox were the main components under test and these performed very well indeed. The VS was found to be a quiet unit and an important benefit is that it fits under the seat pressing of the Ergomatic cab, eliminating the large central engine cover, making for more spaciousness, giving across-cab access and allowing room for a two-man passenger seat. The Mandator has first-class suspension and is thus a very comfortable vehicle to drive; in fact, the, whole atmosphere was of a vehicle up to the standard of any available in Europe.
Good average speeds
To get the best out of the V8 we found it necessary to keep the engine speed above 1,800 rpm but on long gradients the engine "hung on" well when allowed to go down to about 1,300 rpm or so.
When I tested a vehicle with a similar semi-automatic gearbox previously I reported that using the unit gave the practical effect of about 15 bhp extra output from the engine. The Mandator test confirmed this, while incorporation of the two-speed splitter gearing in the box was found preferable to having the two-speed rear axle. On the tough part of the route the facility to make instantaneous ratio changes was a particular benefit and helped very good average speeds to be maintained. On this sort of country dozens of gear changes are needed every mile or so. It is easy to imagine the saving on effort which the two-pedal semi-automatic offers over a conventional transmission—not only in the left arm but more particularly in the left leg.
As full details of the AEC V8 engine and new version of the Mandator were published last week it will not be necessary to go into any detail regarding the specification of the test vehicle. To be brief. the V8 produces 241 bhp net at 2,600 rpm and a maximum torque of 580 lb.ft. at 1,400 rpm. The drive is through a 17.75in.-diameter fluid clutch which gives a "lock-up" condition at about
800 rpm. The rear axle ratio in the test vehicle was the highest offered-6.25 to 1—this being chosen by AEC as the outfit was to be put through its paces primarily as a trunking vehicle for use mainly on the better roads now available—such as motorways and the greatly improved Al. With 10-ratio transmissions such as the semi-automatic box it is possible to have the higher axle ratios without impairing gradient performance on normal roads. But as the lowest ratio in the box on the Mandator was 7.25 to 1, gradient ability was only just adequate to cope with one or two of the most severe hills on the main test route. For these a lower axle ratio would have been better; if we had had to stop on one particular gradient on A68 we would have been unable to restart and on a diversion in Penrith a restart after traffic ahead had come to a sadden and unexpected halt was a ticklish business.
The semi-trailer used for the test was a Boden Mark 3 three-axle unit. Although it is certainly a well-designed and soOndly constructed model, I would have preferred a tandem-axle trailer. With three-axle semitrailers, unless one pair of the lwheels is steered, there must be extra drag and tyre scrub; although I appreciate that for the same gross weight as a four-axle design they allow a shorter outer-axle spread (and overall length), normally they have two less tyres than a .two-axle and are not necessarily any heavier. But now that the 15-metre overall length limit makes a 32-ton fourtaxle outfit feasible, I feel that this layout will tend to become the standard for maximumgross artic iioperaton. Results of the tests wI en on the
straighter sections would have been only marginally affected and it is impossible to say what difference there would have been on the twisting sections. But a lot of rubber was left on the road by the trailer tyres on tight turns and they, with the hub assemblies, came in for a lot of stress when manoeuvring.
Some idea of the resistance to motion when on bends is indicated by the tyre wear recorded during the test. Readings were taken before we took over the outfit and at intervals during the journey and final readings were recorded just before this article was written when the outfit had covered a total of 2,400 miles since our first check. When new, tread depth was 12.4mm and average wear on the outfit tyres was 1.65mm. But while the wear on the tyres of the front two axles of the trailer had worn by only 1.6mm those on the
rearmost axle had 3,25mm less rubber on them. Average wear on the semi-trailer tyres was 2.1mm and on the tractive unit tyres 1.2mm.
The route for the long-distance test was chosen to provide maximum use of the motorways, balanced by a section of heavy going on hilly, second-class roads. Also we passed our normal consumption test routes--and the Motor Industry Research Association test ground at Nuneaton-so that our usual test programme could be carried out.
Brakes, hill starts and acceleration were checked at MIRA and, on the third leg, the journey was broken at the Luton turn off M1 to check trunk-road consumption over the six-mile circuit on AS. But time did not allow the full high-speed consumption test over the usual circuit of M1 and this was done later, as were empty consumption tests and hill-climb and brake-fade tests.
The route proved just about perfect for a test of this type as we had hoped, and it certainly enables the true capabilities of a vehicle to be assessed. And although daily distances are above what would have been considered feasible for any vehicle a decade ago, they were shown to be well within the scope of a modern outfit, even one grossing 32 tons.
With three men in the cab the test outfit was just over its maximum legal figure with a load of 21 tons 12.25cwt on the semi-trailer. It will be seen from the accompanying table that the first day's run of 207 miles on Ml, A5 and M6 between Bushey and Preston was made at an average speed of 40.4 mph, the total running time needed being only 5 hours 7min. The 55.4 miles of M-1 and 85.8 miles of M6 were covered at exactly the same average speeds of 50.5 mph, while the figures for the two stretches of A5 were fairly close, with 32.1 mph up to MIRA and 33.9 from there to M6—even though the second part included a one-mile hold-up through Tamworth which took 10min.
A strong north-westerly wind was expected to have affected fuel consumption which worked out at 5.9 mpg to MIRA and 5.6 mpg from MIRA to the Keels service area on M6. This proved to be the case,. The figures were up to 1 mpg worse than on the motorway run south two days later in spite of the fact that consumption while on AS would have been close to the 7.2 mpg obtained on the A6 set-circuit test.
Acceleration-test results at MIRA were good for a 32-ton outfit and some part of this is due to the ease in gear changing and the ability to do so with full power on. Some of this advantage may have been lost by the slip, when starting off, through the fluid coup, ling, but this unit gives one of the more important benefits of the transmission in that it cuts out all chance of the drive line and rear axle being maltreated. Even the most ham-fisted person could not over-stress the transmission. As well as a stop to prevent inadvertent selection of first and reverse there is a restriction in the path between the two sides of the "gate" when in top so that Second or third can only be selected from fourth; although necessary, this was felt a nuisance when wanting to go from top to second or to first after a stop.
Braking tests at MIRA were marred (as already recorded) by locking of the trailer wheels. The tractive unit brakes performed well, there being only the slightest of marks from each of its tyres on the stops, showing that the correct effort was being achieved.
Another reason for the extended stopping distances was lag in full application. This felt greater than is now usual and made braking in normal driving difficult. Operation of the brake treadle was heavy and in conjunction with the lag made it hard to get progressive braking. At first I felt uneasy when braking to slow down (no difficulty when coming to a complete stop) and found it necessary to "drive a good way ahead" to get satisfactory operation. There was also lag in release of the brakes (probably those on the trailer).
After attention by AEC to the air-pressure circuits of the outfit—including replacement of the light /laden valve of the semi-trailer —repeat brake tests were carried out. Some improvement in the feel of the brakes was noted and much better figures were obtained —largely because there was very little locking of the semi-trailer wheels. The results quoted in the table are from the second test and compare with original stopping distances of 33.6ft from 20 mph and 70.2ft from 30 mph; there were no changes in the efficiencies recorded for the secondary brakes and handbrake.
On the 20 mph stops the only wheel locking was from those at the offside of the two rear axles, and from 30 mph all three tyres on the offside of the trailer left heavy marks (for 20ft) indicating that they were completely locked. The other tyres left light marks for a similar distance showing that they were on the point of locking and therefore giving their best efficiency.
But while the main tests were carried out on a perfectly dry road, just before a further stop from 30 mph a very small amount of rain fell. It was not enough to make the road appear even damp, but it was sufficient to reduce the adhesion by a small amount and bring about the condition on the original test. All six trailer wheels locked for 45ft and swung with the camber 3ft into the kerb.
It was not expected that a restart would be possible on either the 1 in 5 or 1 in 6 gradients at MIRA but it was decided to try the latter and at least check the handbrakeholding ability. With a short run up, the 1 in 5 was just managed in bottom gear and the handbrake held the outfit comfortably on the 1 in 6 on the other side of the "hill". As reverse gear in the semi-automatic gearbox is 5.97 to 1 there was no real hope of starting back up the slope and this was confirmed.
When stopped facing up the 1 in 6 slope the handbrake again held the outfit but restarting or attempts to do so produced considerable difficulties. The surface of the "hill" at MIRA is edged with kerbs and the road is relatively narrow. Attempts at restarting, perhaps without adequate concentration on the attitude of the outfit, resulted in the unit and trailer finishing up at an angle to each other. It was not possible to straighten them without going on the grass or up the hill first—and the latter was impossible! In taking to the grass the outfit got into a fold which stretched and fractured the "emergency" line hose, but the outfit was eventually straightened and the position retrieved.
On the second day of the test an early start was made from Preston with a stop at the first service area on M6 for fuel and breakfast. With only 15 more miles before the end of M6, we soon had more difficult roads. But the Mandator made easy work of A6 to Carlisle which was covered at an average speed of 23.3 mph including delays in the town.
Shap was climbed fairly easily although heavy traffic at the time hampered progress. Total time taken from the Jungle Cafe to the actual summit was 9min 47sec. Most of the climb was made at about 7 mph in the queue of traffic with second /high engaged throughout. For one short stretch the speed dropped to about 4 mph and at the top it was 10 mph after a climb which had taken a total of 9min 47sec.
After Shap it was all relatively easy going to Gretna with only the traffic in Carlisle and in Penrith to worry about. Average speed between Carlisle and Gretna had been 33.3 mph and soon we were on the good stretch to Beattock. This was covered at, an average speed of 42 mph and at Beattock we turned on to A701 for the more arduous section of the route.
But even here the AEC could be kept at a good average, making 30.6 mph to Broughton and 31.6 from there to Monklaw by way of Dalkeith where we had picked up A68 (and got lost through bad road signs in the process). A fill-up at Monklaw and we were only 30 miles or so from our planned night's stop at West Woodburn. This took just over an hour for an average of 28.2 mph including the climb of Carter Bar which was taken in fine style alternating on the main "drag" between third low and high.
Total distance covered in the day was 254 miles in a total time of 8 hours 20min. to give an average speed for the day of 30.4 mph, compared with the 40.4 mph for the 206 miles to Preston.
If we had thought that the second half of the previous day's run was severe we were to change our opinion on the stretch of A68 from West Woodburn to the start of Al. This was where the real value of the semi-automatic transmission was felt. The road is never flat for more than 100 yards at a time and virtually continuous gear changing was called for. Even with the 241 bhp engine, bottom gear with the low splitter ratio was called for on numerous occasions, but nevertheless the average for the 36 miles to Tow Law was 23.4 mph and from there to the start of Al, 27.1 mph.
A big factor in the production of these good
average speeds in the conditions was the • excellent "recuperation" of the Mandator after the speed had been pulled down by the hills. The quick gear changes played a big part in this.
During the difficult section, rough consumption checks had been made over one or two stretches and these indicated that between 3.0 and 3.4 mpg was being averaged. At the next fill-up point—at Scotch Corner —this was confirmed; the consumption worked out at 4.45 mpg from Monklaw, including about 10 miles of Al where a check had shown that 9.3 mpg was being returned.
We were now running downhill: or so it seemed after the morning's -work-. A stop in Boroughbridge for lunch, and the Doncaster by-pass was reached just under 2 hours 30min. later. The start of M1 proper after the long drag on M18 from the Doncaster by-pass needed another 41min—average speed 45.7 mph—and from here to "homewas 140 miles of motorway.
Average speed on the motorway varied between 47.2 and 56 mph, and over the major part of it worked out at exactly 50 mph. In the day 287 miles had been covered in a total running time of 7hours 24min, making the average 39 mph, an extremely high figure taking into account the terrain for the first 50-odd miles.
Total distance on the test was 747, miles—the actual figure with the speedometer error taken into account. Total time on the road had been 20 hours 51min, making the average speed 35.8 mph and 125.9gal of fuel had been used with the consumption rate 5.95 mpg.
Ron Cater and I shared the driving on the test and although we are not full-time professional drivers we were not unduly tired at the end of the run. In fact it had taken little more effort than is needed to drive a car. Heaviness in the steering was only evident on the twisting sections and when manoeuvring. On the better roads it merited no criticism. The steering was completely positive and direct and little attention was needed to keep the outfit on the chosen path. After the long-distance test and the various checks made on the journey little was needed to complete the picture. A laden high-speed consumption check was made on M1 and following this hill performance and fade were checked, but after the experience at MIRA hill restarts were not attempted as the 1 in 6.5 gradient of Bison would have been beyond the scope of the laden Mandator with the axle ratio fitted. After these an empty tandem-axle trailer was coupled to the Mandator for unladen consumption checks and as will be seen in the table very good figures were returned.
In between the empty tests maximum speeds in the gears were checked. Alternating between the low and high ratios in the splitter section of the transmission and with the engine speed at its maximum of 2,600 rpm, these were 6,8, 11, 14, 19, 26, 30, 38, 48 and 63 mph. These figures also take into account the speedometer error which varied from between 5 per cent at 30 and 8 per cent at 60 mph. It will be seen that the spacing of the ratios allows each one to be effective and this is one reason why good progress could be made on the hilly sections. The fitting of an engine rev counter also helped, as the engine could be kept at its best speed.
Our verdict: a really fine vehicle which appears well able to work hard, and to make a particularly good showing on fast trunk operations.
The list price of the AEC V8 Mandator in the standard form as tested (with semi-automatic transmission) is £5,065. Specification of the optional six-speed overdrive constantmesh box reduced the price to £4,375 and with the new 10-speed sOlitter box the price is £4,550.