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The Governed Vehicle in Service
Page 95
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Economies That Can be Effected by Governing Maximum Engine Revolutions By a Service Manager
A RECENT survey of commercial
vehicle fleets throughout the country reveals a rapidly increasing growth in the popularity of enginespeed governors. There is a number of such governors at present available, and it is not proposed, in this article, to describe the various systems employed.
Arising from the investigation, however, there is a number of points of interest which go to show that the value of a governor on a commercialvehicle engine is far from being properly appreciated, and that many misconceptions prevail in regard to the performance of machines, the engines of which are fitted with such a device.
It has been clearly established by many owners of large fleets that speed limitation has a marked effect upon running costs, and this is confirmed in reports received from America, where a much wider use is made of governors on commercial vehicles than is the case in this country.
Savings in Unsuspected Directions.
General statistics show results which are of an illuminating nature, and there seems to be no doubt that, where a governor is employed, considerable savings are effected in directions that, at first sight, are unsuspected.
First, let us consider the question of fuel consumption. In recent years the design of commercial-vehicle engines has approached closely that of units used in private cars ; in fact, there are many examples of commercial vehicle in which the engine was specifically designed and is extensively used in private cars. This development, whilst it may, in certain directions, increase the efficiency of the commercial vehicle, opens the way to abuse by careless drivers, resulting, in many cases, in excessive petrol consumption and other heavy running costs which will, later, be exemplified.
There are few classes of service where the maximum speed of which many makes of commercial vehicle are capable is required, but, in considering the question of road speed and its relation to m.p.g., it is necessary to translate these terms into engine r.p.m. to realize the • significant 'effect on petrol consumption of a fully open throttle. Many a commercial engine, were it driven at its maximum speed in top gear, would be turning over at 4,000 or more r.p.m., and the point is that
it is capable of revving " at that speed in any intermediate gear, and it is this feature which determines fuel consumption.
It is well known that a moderate road speed is productive of considerably better results in fuel consumption than continuous high-speed travel. Translated, therefore, into r.p.m., it will be appreciated that, other things being equal, an engine speed of, say, 3,000 r.p.m. is far more economical than
one of 4,000 r.p.m. Thus, in any intermediate gear gross wastage of fuel occurs if the engine be " revved to the maximum.
As applied to the commercial vehicle, it is obvious that maximum r.p.m. in the intermediate gears is the prime cause of heavy fuel consumption for, by comparison, there are few opportunities for a driver to "rev." the engine to its maximum in top gear, even if the law permitted.
The object of a governor, then, is -to limit engine speed, and as a result of this limitation marked economy in fuel consumption can be achieved.
High Engine Speeds Mean Wastage.
Any operator of a fairly large number of vehicles can, as a rule, point to a driver who invariably obtains a better fuel consumption than the average. The reason is that he is a good driver ; he does not " rev." the engine to its maximum in intermediate gears, but only to the limit necessary to make an effective change to a higher ratio.
By governing engine speed, therefore, indifferent drivers are forced to make gear changes at the correct economical engine speeds, and so driving ability is, as it were, levelled up and the fleet average mileage per gallon is substantially improved.
In considering the economies made possible by governing the engine speed, fuel consumption is not the only factor. More than one tyre company has issued figures which go to show that high road speeds have a marked effect upon tyre wear, whilst oil consumption is raised to a marked extent with increased engine revolutions. The value of governing in relation to these two sources of wastage—not forgetting, too, that brake facings suffer equally with tyres—is worthy of consideration.
Now for the alleged disadvantages of using an engine-speed governor. From the driver's angle, the only objection, not influenced by prejudice, is that there is not sufficient latitude in the intermediate gears for rapid overtaking. If the engine be governed within reasonable limits, it is questionable whether this is a complaint to be taken seriously.
When Performance is Accepted.
It has, in fact, been noted that, in the case of a vehicle fitted with a governor at the time of being put into service, this complaint never arises, because the driver accepts its performance, which would not be the case if he had driven the same vehicle without a governor.
In actual fact, there is, perhaps, only one circumstance in which the governed-engined vehicle is at a genuine , disadvantage, and this is in service such as is encountered at gravel pits. In such cases it may frequently be necessary to make use of maximum engine revolutions to release the vehicle from
axle-high sinkage. Here, of course. the torque represented by the high" revving," ungoverned engine would help in extricating the vehicle, whereas a governedengine would, in this respect, be at a disadvantage.
The cost, however, may be high, and the writer is conversant with a case where governors have been installed to prevent this practice, because broken axle shafts have discounted all the advantages of being able to drive out the fully laden vehicle under such conditions. It is realized that lighter loads, necessitated by the employment of a governor, are a much better paying proposition.