Aids to economy
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Paper by Tim Blakemore, TEng AMIRTE, AMIMI
This paper traces the development of driver aids for fuel economy, from the simplest tachometer to the latest microprocessorbased gearchange advisory systems, and considers the possible impact of some even more sophisticated systems which are set to go into production soon. The question is discussed whether the proliferation of such systems will require some fundamental changes in hgv driver training. What, for example, is the relationship between safe driving and economical driving?
THE FIRST vehicle manufacturer to make a badly insulated cab probably unwittingly produced the first driver advisory system, an aural one, to aid fuel economy. Behind the wheel of such a vehicle, a skilful driver would listen attentively, unhindered by layers of noise insulation material, to the engine tone and change up or down through the gears at probably about the right engine speed for optimum fuel economy, most of the time. It might take some time to adapt to the characteristics of different vehicles, but he would take pride in being able to do so.
Meanwhile the less skilful driver was also using the first "aural advisory system" but not in quite the same way. When changing up through the gears he would wait until the in-cab noise level rose to a difficult-totolerate 95dB (A) (or thereabouts) which would tell him that governor run-out speed had been reached and therefore he might as well change up a gear. As for changing down — that was easy. Well everyone knows that when you reach a gradient, you select a lower gear, as early as you can, to keep the engine speed up.
The noisy cab was acting as a sort of crude fuel economy aid — after all if it had been better insulated, the less skilful driver might have stayed in the lower gears for a few more miles — and the mpg would have been even worse.
Tachometers
THE NEXT stage, in the development of economy aids, was hardly a quantum leap. It was the fitting of tachometers. Early examples of these, and even some more modern instruments, were not very informative. They were simply marked with engine speeds from just below idle to beyond governed. They did little more than visually confirm what drivers' ears were already telling them. It could be argued that as cab insulation began to improve, they became rather more useful.
However, again only the most skilful and conscientious driver would take the trouble to find out at what speed the engine's maximum torque was developed. Thus he would use the tachometer to good effect — and he was the man who probably was driving well, anyway.
The rather less skilful man, carried on as before, taking the engine speed up to the governor in each gear, though he might just occasionally glance at the tachometer to confirm that this Swedish engine really would go up to 2,600 rpm. Volvo managed to confuse some drivers for a while by calibrating its instruments in revs/second rather than revs/minute.
Long delay
IT DOES seem remarkable, that for a long time after the 1973 oil crisis little progress was made in providing the heavy goods vehicle driver with information he could use to improve fuel economy. Cummins became something of a trendsetter in this area in 1978 when it discovered that its, then new, Big Cam, E for economy series, 14litre engines were not so economical if drivers ignored the recommended driving technique. This was s. mmed up in the memorable phrase "let it lug."
This was only part of the sage. Cummins also rer mmended progressive up shiffrly That meant with a Fuller ninespeed gearbox, for instar re, a change up from second t id should be made gene.. about 1,250 rpm; from third to fourth at 1,350 rpm; fourth to fifth at 1,400 rpm and so on. It should never exceed 1,700 rpm, except on very steep hills. Above that figure was "the sting" in the tail of the E290's specific fuel consumption curve.
It is quite clear that in order to follow this recommendation, a driver needed to watch his tachometer closely. It helped if the tachometer had shaded segments.
As a matter of interest, shortly after the introduction of the E290, CM conducted a short comparative test, to attempt to quantify the effect on fuel consumption of not following the recommendation. It was surprisingly large.
In a Seddon Atkinson 400 Series with a flat semi-trailer laden to 32 tons gcw, the E200's average consumption on a 78mile route was 44.1 lit/100km (6.4mpg) when upshifts were made around 2,000 rpm and downshifts on gradients at 1,300 rpm. Over the same route, on the same day, this time following the Cummins recommendations, the average fuel consumption improved to 38.7 lit/100km (7.3 mpg), with very little variance in journey times between the two runs.
Other manufacturers soon followed Cummins in issuing more detailed recommendations concerning fuel efficient engine speeds. Tachometer faces began to become increasingly pretty, with dark and light green areas, shaded green areas, orange, red and even blue segments. But it is questionable whether the average driver took a lot of notice.
Then, quite suddenly it seems, everybody began to take notice of aerodynamics. Air deflectors of various shapes and sizes began to sprout all over vehicles, some of them set up correctly to do a good job. It did not take many operators long to discover that one effect of reducing a vehicle's aerodynamic drag can be to increase its powered speed.
In other words, if the driver chose to keep his right foot down, any fuel economy benefit to be gained from an air deflector would be lost in a few extra mph. That is when road speed governors began to sell in relatively large numbers.
There are now numerous proprietary types including those with pneumatic, hydraulic and electronic actuation. I do not propose to describe any in detail here. Some manufacturers may accuse me of being unfair when I say that, in general, road speed governors have not enjoyed a good reputation for reliability but I know many operators who would agree.
Perhaps the latest models are better. However, it seems to me that, when these devices began to sell in large numbers it marked a particularly significant point in the story of the development of fuel economy aids. It was the first step towards taking away some discretion from the driver. Again the manufacturers may argue this point but I believe many drivers resented that. Perhaps that is part of the reason why their reliability record has not been good.
It is interesting that vehicle manufacturers seem to have been reluctant to follow this particular path. Could it be because they want drivers on their side? Mercedes-Benz is an exception and fits 1,900 rpm engine speed limiter& as standard on its 330 hp, and above, vee-eight models, the 1633 tractive unit in this country, together with a road speed governor set at 68 mph but Mercedes is careful to emphasise that the driver has the facility to override the engine speed limiter, simply by pressing down the accelerator pedal far enough to activate a micro switch.
Some operators may say that any speed limiter which can be overridden by the driver, is a waste of money. I believe that the Mercedes system works quite well.
When I tested the 1633 in July 1983 I hardly ever felt it necessary to kick down the accelerator pedal and the Mercedes achieved a good average speed and reasonable fuel economy (42.1 mph and 6.70 mpg) around the 737-mile Scottish route. In other circumstances, however, with less than 330 hp at 38 tonnes gcw or perhaps with a more bloody-minded driver than me (if that is possible!) then the story might be different.
More recently Mercedes also introduced another type of fuel economy device, developed with Bosch, called the Ecometer. This is an advisory system and does not remove the driver's discretion in any way. It is similar in many ways to Daf's Visar, which was the first system of its kind, in that it uses a microprocessor and advises the driver which gear he should select for optimum economy.
I am told that Visar is a Dutch acronym standing for Consumption Indication and Gear Change Advice Display.
By means of three dashboardmounted lights, Daf's system simply advises the driver that he should change up or down a gear (or half a gear) whereas Mercedes', being a later development, is more sophisticated. It tells the driver which gear he is in and which one he should select for optimum economy. Both systems include gauges to indicate instantaneous fuel consumption in litres/100km. The Daf gauge, now integral with the tachometer is analogue and the Mercedes is digital.
I road tested a Visar-equipped Daf FT3300, at 32 tons gcw over GM's Scottish route in 1982. The fuel economy gauge proved to be rather more useful than the lights, which had an irritating single mindedness. They would persist in intermittently advising me to change up at 60 mph even though I was already in top gear.
The fuel economy gauge I found was more practical because, like any gauge, it was easy to ignore when necessary, such as when climbing steep hills. However, it could also provide useful information on which gear is best for optimum fuel economy. When there are sixteen ratios to choose from, as there are with the 3300, that information is worth having.
The development of microprocessor-based driver aids — mainly but not exclusively aimed at improving fuel economy, has really begun to gather pace. Scania broke new ground with its computer-aided gearshifting system which was first described in CM in January 1983.
At that time Scania engineers said they thought the system might become available as a production option within two years. Such has been the operator interest, and the speed of development of competitive systems, that CAG is an on line option now — just over one year after its introduction.
The main attraction to operators of the Scania system, and others which I shall mention shortly, is that in essence it can offer all the advantages and more, of a conventional fully automatic transmission without any of its disadvantages. It does not carry a high initial cost, or a weight penalty. There is no need for specialised maintenance, and there is no fuel consumption penalty. Indeed the system is included in this paper because it is designed to improve fuel economy.
Like Visar and Ecometer, Scania's CAG system has a microprocessor, programmed to advise the driver on the correct gear for optimum fuel economy. The parameters on which the microprocessor bases its gear selection, are engine load, road speed and rate of change of road, pertinent information on the engine and gearbox is also stored in its memory. The important difference with the Scania system is that the driver can leave choice of gear entirely to the computer if he so chooses.
The gearbox is mechanically identical to a standard Scania synchromesh model, either splitter or range-change. Its gear selector linkage on the top cover is replaced, or in some cases supplemented by, pneumatic control cylinders. These will select gears according to command signals received from the control unit.
The driver can select automatic or manual mode. In manual mode the driver shifts gear by means of a small toggle lever, pushing forward for up changes, back for down changes. He is advised of the computer's choice of gear, and which gear the vehicle is in, by means of a gear display panel.
He can select gears higher or lower than that recommended, provided it would not be likely to cause mechanical damage. If the computer senses "irrational" input parameters it will select neutral.
When wheels spin the microprocessor identifies this as an abnormal speed fluctuation and neutral is selected. The same happens in the event of an electrical failure. Scania also provides a stand-by conventional gear lever so that the vehicle is not immobilised by a simple electrical failure.
In automatic mode the driver does not have to move his hands from the wheel to shift gear. He simply depresses the clutch pedal and the gear chosen by the microprocessor is selected.
While gear selection is taking place, a clicker warns the driver to keep the clutch disengaged. If he lets up the clutch pedal too soon the microprocessor will select neutral.
Even in automatic mode, the driver has the facility to override the microprocessor gear choice. When an advisory gear change, say from 8 to 7, flashes on the display, the driver has seven seconds in which to exercise his override option. If he can see that the hill he is about to climb steepens suddenly, a little further on, he may decide to skip shift from 8 to 6, and with the toggle lever override the microprocessor's advice.
Whether in automatic or
manual mode, gearchanging cannot take place until the driver disengages the clutch. He is always left to choose when gearshifting occurs. Scania says that its pneumatic cylinders execute a single gearshift in 0.8 sec, compound shifts with rangechange or splitter take a little longer. This is faster than the average driver who will take 1.0 second. Nevertheless I found when I drove some CAGequipped lorries and coaches recently that the clicker warning is necessary. The natural tendency when you do not have to spend time moving a gear lever across a gate is to let the clutch pedal up too soon.
The retention of the clutch pedal by Scania is significant. It brings me back to the issue of driver's discretion. If somebody was intent on driving a CAG Scania in a way that wasted fuel he could do so. However, he could not cause serious damage by forcibly selecting too low a gear.
Scania's engineers say they have prototype developments of the CAG system with automatic clutch control but have not put this into production on the grounds that it is too expensive and complex.. They say it would take away too much control from the driver.
In a moment I proposed to describe briefly Eaton's automated mechanical transmission.
It is clear that this question of how much discretion the driver is left with is important. It is a question which is being addressed by the many manufacturers who are now working on systems similar in concept to Scania's and Eaton's.
They include ZF who might be ready to reveal some details at this year's British Motor Show. Lucas L understand are working along similar lines with DanaSpicer and RVI is developing its new 89 gearbox, as used in the G260.
Production of Eaton's automated mechanical transmission is still some way off, but the project has already attracted a "very positive response" from European-based manufacturers. Three prototypes have been built and only two weeks ago, I had the opportunity to drive one in the Iveco 170.30 belonging to Eaton's European Engineering Centre at Manchester.
The principle of the Eaton design is the same as Scania's. A conventional mechanical gearbox is used with its gearshifting effected by pneumatic cylinders, controlled by a microprocessor.
The Eaton system is different from Scania's in two important respects. It uses a constant mesh rather than a synchromesh gearbox and Eaton's microprocessor also controls clutch engagement, there is no clutch pedal.
Why has Eaton followed this route? The general thrust of its development work including that on its twin splitter transmission, a separate gearbox but one to which the AMT idea may be applied, is to make gearshifting easier. But improvement of fuel economy is an important factor.
The AMT's designers say that "programming for fuel economy can result in all drivers in a fleet achieving as good or better economy than is now available from the best drivers."
Remember the skilful driver who changes up and down through the gears, never crunching them, always double declutching, at the right engine speeds for optimum fuel economy? That is what the AMT does, but with no driver influence, apart from the position in which he holds the accelerator pedal.
At first, driving the AMT is a slightly unnerving experience, particularly when you slow down for a hazard and downshifts occur, complete with the characteristic throttle blips a skilled driver of constant mesh would make at a rate which depends only on the rate of deceleration. Other hgv drivers can be unnerved by somebody pulling alongside them on up gradients, making a show of keeping both hands on the wheel and then waiting for the microprocessor to sense increased engine load and falling speed and signal for a perfect downchange. The other drivers, knowing the vehicle has a Fuller Roadranger transmission will be left wondering how it is done!
The particularly clever part of the Eaton system is its clutch control. The prototype I drove was fitted with ceramic clutch facings which make smooth clutch engagement a little tricky on conventional manual clutches. I spent about an hour driving the Iveco, laden to 32 tons gcw, around Manchester in traffic, and up and down gradients. Clutch engagement was always remarkably smooth. I deliberately stopped on a hill of about 1 in 7 to try a restart. Again it was surprisingly easy — simply a matter of increasing engine speed to about 700-800rpm to begin clutch engagement, enough to hold the vehicle, releasing the park brake and accelerating away.
Another aspect of the AMT which impressed me was that, even with an uncoupled tractive unit, gearshifts occurred at what I felt was about the right time. This was unlike the unnatural shifts one sometimes finds on full automatics, so I hardly ever felt a need to override the microprocessor's choice.
It managed to win my sympathy in a very short time. That is an important factor on a system which goes a long way towards taking away driver discretion. Eaton's argument is that a driver's skill should be concentrated on steering his vehicle and observing what is going on around him. They have recognised that they will have to be able to demonstrate excellent reliability in the field if it is eventually to convince sceptical transport engineers of the AMT's worth.
I feel that Eaton's AMT, Scania's CAG and the many other similar current projects are exciting engineering developments. This is not just because they will give me plenty to write about for the next couple of years!
However, they raise a question in my mind, as to what their effect will be on hgv driver training, and ultimately road safety.
Many people argue that these developments are bound to improve hgv safety by taking from the driver the need to concentrate on gear changing. I understand that argument but I am not wholly conv-i-nced. Is it not equally possible that a driver with no gears to think about and perhaps with nothing to do with his left hand and leg becomes generally less attentive?
The current method of hgv driver training lays great emphasis on gear changing skill. This means anticipating far enough ahead to give time to double de-clutch, changing down a gear to meet a hazard. If these microprocessor-based gearchange systems become common, as seems likely, a quite fundamental change in driver training methods surely will be demanded.