Control for Automatics—and Component Reliability
Page 71
If you've noticed an error in this article please click here to report it so we can fix it.
rOLLOWING the usual pattern, two 1 technical papers were read at the C.A.V. Ltd. annual conference, held at Torquay on Tuesday.
Mr. W. D. Sutherland, assistant chief engineer of C.A.V., dealt with the electrical control aspect of automatic transmission for p.s.v. in his paper entitled "The application of transistors to automatic transmission control ". In reviewing past history he said that whereas in early C.A.V. automatic transmission controls transistors were rarely used because of their expense, now the situation was completely reversed and semi-conductors, both diodes and transistors, were universally available and widely used in electric control circuits.
Mr. Sutherland said it was now time that users should reconsider their assessments of automatic transmission control In view of the changing pattern of operation and economics. The increased numbers of vehicles on the road made reduction in driver fatigue more necessary in the interests of safety. Whilst automatic transmission would help this, it was said to be a necessity in one-man bus operation.
Next, Mr. Sutherland dealt with features required from an automatic transmission system under six main headings. These were: gear sequencing, ombination of fixed speed gearchanging and accelerator pedal position, flexibility, elimination of jerk in gear changing, idling in neutral and holding third or fourth gear. Going on to deal with equipment required for automatic transmission control which, it was assumed, would be applied to a directacting epicyclic gearbox, the author said that a selector switch to enable automatic, reverse or a manual gear to be obtained plus three other items—a speed signal generator, an accelerator switch and a control unit—were required.
Lighter and Smaller It was in the control unit that the semiconductor was of great advantage. Mr. Sutherland compared a conventional unit and one using semi-conductor circuitry with which it could be replaced, and apart from illustrating the much reduced bulk and weight—the transistor board is one quarter the volume and one fifth the weight of the equivalent relay unit— showed the manufacturing advantages through the use of printed circuits made practicable by the use of transistors. Checking and fault tracing is easier and since the transistor is basically a reliable device the need for replacement should be much less than with the equivalent relay unit.
A considerable number of transistorized control systems were said to have been operating successfully over the past four years and this had enabled the detail weaknesses inherent in any new product to be discovered and eliminated. Further proof of the reliability of the C.A.V. unit, had been obtained from extensive laboratory tests, said Mr. Sutherland, who, in concluding his paper, remarked that in the light of present-day trends, traffic density and operating economics, automatic transmission for p,s.v, would necessarily be on a much larger scale than previously.
Unreliability is Costly Following Mr. Sutherland, Mr. R. G. C. Messervy, director, equipment sales. C.A.V. Ltd., presented a paper entitled "Quality and reliability factors in vehicle and engine equipment ". Unreliability. said Mr. Messervy, was a form of waste which could be measured in monetary terms, and could be costly to manufacturer and user alike. A reliable product was one that gave customer satisfaction, and the ability to do a stated job for a given length of time decided whether the product was a good or bad one.
To understand the problem of reliability, Mr. Messervy said it was interesting to consider why any product should be unreliable. In the first place it might be underdesigned; obviously not intentionally, but design was always a compromise where individual experience and judgment played an important role. His company's task as manufacturers of -equipment was to produce better and more reliable designs at the lowest feasible cost. To achieve continual improvements in this direction not only better designers but better proving and testing facilities were required. Mr. Messervy explained some of the problems in designing and testing new products before going on to the second cause of unreliability—operation of the product beyond its rating.
Here specification of the right product for the job was beset by competitive pressure which could lead to equipment being used above its reliable rating. Adequate product operating specifications were in the course of preparation and these would enable vehicle makers to specify the correct equipment. Operators and vehicle and equipment makers had a responsibility in this matter, said the author, and by paying a little more in the first place, economies through greater reliability could be achieved.
Poor location of the equipment also played a part in unreliability; sometimes it was impossible to reac-h for routine maintenance, sometimes it was in such an exposed position that mud and so on caused the product to deteriorate.
The fourth aspect covered in the paper was inadequate quality. The product might not have been well manufactured; perhaps it had a defective component, it might have been badly assembled. damaged in transit or fitted to a chassis which was then stored in the open for some weeks. To help combat the first two possibilities the latest quality control techniques were developed by C.A.V. and efforts were made to promote greater interest in quality among personnel.
In dealing with the four major factors affecting reliability, said Mr. Messervy, he had omitted any mention of lack of maintenance as he did not feel it was a key factor. The obvious and most immediate effect of poor maintenance was frequent breakdowns. In the reliability context it was easy to shelter behind a blanket excuse of bad maintenance, he said, when in reality the problem lay in imperfect design, defective manufacture. improper application or a combination of these factors.
Interesting Discussion After Dr. Sutherland's paper, p.s.v. operators commented on the use of automatics and Mr. J. W. Wicks related London Transport's experience. But, as expected, many more questions had been submitted for the discussion on Mr. Messervy's paper and these were dealt with by a panel. This consisted of Mr. Messervy, Mr. J. Cook, deputy sales manager, Mr. C. W. Billington, service manager, and Mr. R. Reymer, technical sales manager, with Mr. H. Astbury, sales director, in the chair.
The greatest interest was in starters, and Mr. Cook admitted that a lot of trouble had been experienced with the C-change version of the CA45 4.5-jn. starter—though very little with some engine applications. He said that about 80 per cent of CA45s were for 12 v. earthreturn systems and the latest D-change for this use was available as original equipment last December. Of the remaining 20 per cent, most were 24 v. earthreturn (which had given less trouble than the C-change 12 v.) and other models such as 12 v. and 24 v. insulated-return. D-change versions of all these would be available to manufacturers by the last quarter of 1964.
Results with the D-change CA45 had been very good, said Mr. Cook, but C.A.V. was nevertheless working on a new basic range of starters which would incorporate a clutch and would be less "installation-conscious" and more amenable to abuse.
Questioned after the discussion, Mr. Cook said no D-change CA45 starters were available as replacements and he did not know when they would be. But he said that when the C-change was sold as a replacement C.A.V. recommended that, with engines which picked up speed quickly after firing, a special version of the Lucas 2ST solenoid be wired into the starter solenoid circuit, it being actuated by dynamo charging current to prevent the starter engaging when the engine was running, even if the driver kept the starter control engaged. This prevented overspeeding and guarded against possible damage to bearings or commutator.