From the by Graham Montgomerie )0MPAY E J I ME 1 07 8' reduced the weight of u - ter motor with three Fication changes in
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one of its new opment. The second involves two further jes which have yet to roduced on a wide STARTER MOTOR is red at best by the operator as assary evil to be used once ?fully) and then carted d as dead weight for the
f the day. From the outside (s the same as the starter .s of 20 years ago, but is fair comment?
len Davies is the product eering and sales manager Butec Electrics division of atec ahd he is in no doubt future starter motor dement will proceed. Based yland, Butec includes g its customers, Rolls:, Leyland (both truck and iivisions), Cummins and s.
le of the major dements in starter motor de(and alternator design as has been a reduction in
it. .
the search for lighter es, the chassis manufac, have looked at various as to keep the kerb weight
including aluminium alloy ,eas like wheels and fuel
ERF was one manufacwhich started looking at potential areas for weight g with the result that the lbach-based company cted Butec with a view to ig weight out of starter rs and alternators.
reported that US oil corns will pay up to five dollars ound weight saved and Bu,timates that the UK equivaompanies will pay up to E3 lo.
basic request was for a ction in weight without iromising reliability and duty. As Rupert Davies reI: "It appeared simple on ;urface but in practice it involved some deep consider ations."
Taking the starter motor first, the switch assembly contains a fair amount of copper in the coil. The pull generated to engage the starter depends upon the magnetic flux and this is rated in ampere-turns. Butec swapped amps for turns and made the materials work harder with the result that the coil could be made about one pound lighter.
Making it work harder means that it will get hotter and part of the art is to effectively dissipate this heat. The normal ambient temperature for a starter motor is standardised at 93°C (200°F) by Butec as this figure (which is based on a US military specification) has become the norm for the industry. Within the core of the coil it is possible to get up to 150/170°C (300/400°F) on a prolonged crank which is about 15° hotter than before.
The next weight-saving tech nique was to move to aluminium in certain areas. With electrical components, this is not easy as sorve pieces, for example, have to be steel because they are part of the magnetic circuiting. EffectivIy, what Butec tried to do was to change everything that did ot need to be magnetic and this 'ncluded the structural components.
Howevs r, aluminium is not the panacea for all weight problems as some engineers (and operators) seem to think. Bulk for bulk it is not as strong as steel so the metal sections need to be beefed up. With the shift housing this proved impossible to do because the thicker sections would foul the fixing bolts. And the fixings could not be moved because they are part of an SAE standard which fixes the pitch circle diameter for starter motor mountings . .
All this meant that Butec had to go for a "fairly special" alloy to get the strength required using the existing metal sections. The company arrived at a component of the necessary strength which incorporated inserts to cope with the point loadings associated with the six fasteners holding the nose on to the shift housing. The result was a casting capable of taking the full weight of the motor and passing the Butec vibration test while at the same time retaining the same versatility of fit of the original starter motor. The commutator end housing was easier to make in more conventional aluminium as its ability to carry load is less critical.
The three specification changes mentioned so far brought the weight down from 28 to 23kg (62 to 521b) which Butec refers to as Phase 1. Phase 2 includes two further changes which have yet to be introduced on a wide scale. This second stage incorporates a switch to aluminium for the nose housing and a change in the construction of the commutator.
Previously, the commutator was a built-up component with a steel centre with copper segments clamped into place. This is a big and heavy arrangement, but it has a major advantage in that the heat can pass from the segments into the core via the steel shaft.
Butec is currently working on a moulded commutator where the segments are keyed into a moulded core. Rupert Davies explained that the problem has been to get a moulding material which could withstand high temperatures — not only during operation but also during manufacture. Butec predicts that the Phase 2 package will be introduced early next year to bring the weight down still further to 22kg (481b).
The next stage? Rupert Davies said that this will involve "swapping electrical intelligence for existing mechanical pieces". This could involve the mechanical leverage for advancing the pinion where a torque drive twists it round to prevent abutment, which is where the pinion and ring meet tooth to tooth and thus will not mesh properly.
Butec argues that this can be done electronically on a time basis. Only when the pinion is fully engaged with the ring gear will the contact be completed. if complete meshing does not take place within half a second, the unit will de-energise and try again.
Replacing the existing torque drive could save a further three pounds. its electronic replacement is likely to become available within the next 18 months.
On the alternator side of the business, the traditional bus type of alternator has been the totally enclosed unit. The main limitation of this desigr been that a machine of a output tends to produce a sponding amount of self-c ated heat. This heat has radiated or convected from the outside of the all tor envelope and so the assembly becomes phys large for the output it is ca of offering.
The US principle is to p1 through the machine to co components inside, whicF well known principle for and trucks. On buses, tot; closure is required for goc vironmental protection so 1 is protected from road sal can even pass through a sl cleaning operation wit harm.
Butec has adopted a duct approach for buses whi. claimed to offer satisfactoi vironmental protection wh the same time, allowing a output to be realised withi smallest possible physical lope.
The company has not ci out a deliberate weight-s exercise with alternator: comparing output for with the opposition, it is pa to offer an alternator pa which already gives a signi weight advantage. Accordi Rupert Davies, the Butec alternator weighs about (31Ib) compared to the (531b) of some of the oppos Butec's involvement wit commercial vehicle does stop at alternators and s motors, however. The corr has also been involved in matic transmission control the introduction of the Le G2 system.
In 1976 Butec sought t place the then state-of-ti equipment with micro-pr sor-based controls. The ori! this work was the Univers Manchester Institute of Sc and Technology (UMIST). and UMIST have been look the susceptibility of micr cessor-based controllers t coming voltage fluctuatior in the vicinity of a high-pm radio transmitter.
It is possible that future niques will allow the uni withstand these physical tions through manageme the software. The first pr. tion units are scheduled foi trials in early 1984.
Butec developments in field are being designed to with future generations of • mission control, an all-ening expression which inc such items as the Leyland tinuously variable transmis