AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

• The Latest Guy Trolleybus Chassis

4th October 1935, Page 53
4th October 1935
Page 53
Page 54
Page 53, 4th October 1935 — • The Latest Guy Trolleybus Chassis
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

WHEN, some eight or nine years IN ago, Guy Motors, Ltd., Wolverhampton, first introduced a. trolleybus with regenerative control, many people were inclined to view the design with some trepidation. Nowadays, however, practically all transport undertakings using trolleybu.ses specify regenerative control, so it is clear that the enterprise shown by Mr. Sydney S. Guy and his designing staff was in no way misplaced. Naturally the original design introduced by Guy Motors, Ltd., has been modified and improved from time to time and the latest chassis produced for Newcastle Corporation Transport Department include all the improvements which experience of trolleyhus operation over a number of years has indicated as being desirable.

Abont two years ago an entirely .new design of chassil was.eyolYed .ancl.it is that particular machine which forms the basis of the Newcastle design. In this article it is necessary merely to point out a number of points about the chassis which seem worthy of mention, rather than to describe the whole of the mechanical and electrical features in detail.

The motor, of 80 b.h.p. at 1 hour rating, is mounted in a forward position at the front of the chassis, and it is claimed that many advantages accrue from this form. of construction. In the first place the size and shape of the motor are quite divorced from the combination of dimensions which restricts floor height. With a centrally disposed motor of a similar h.p. rating it is impossible to use the ideal circular-sectioned machine, without it being necessary to make an appreciable increase in floor height.

• Without any such restriction in the forward position, however, .. there is room enough loput a:large:number, of turns into the shunt windings, resulting in a small current of 2 amps being passed which, of course, results in the motor maintaining a low mean temperature. Furthermore, this low amperage of the shunt circuit enables a drum controller to be employed and as there are no fewer than 13 steps, the progress of the vehicle during acceleration is extremely smooth. Another point is that.the maintenance of the contacts on a drum controller with a low shunt current should be extremely small.

The forwa:rd. position of the motor, too, is conducive to effective coaling of the power unit, especially under heavy service conditions, as all the dust and mad thrown up by the front wheets is avoided.

Whilst it is true that placing the motor in the front of a vehicle necessitates a longer propeller-shalt than in the case of a vehicle having a motor in the centre of the chassis, it is interesting to note that in the Guy design the three propeller-shafts which form the transmission line from the motor to the offset rear ale have universal joints so disposed that the angular velocity of the joints—primarily the cause of vibration in a trolleybus—is balanced rather more effectively than when a centrally disposed motor with a 'horizontal armature is used in conjunction with an unclerslung wormdriven rear axle.

With. regard to the regenerative con-trol, nun of ,the patented features of the Guy system is that the .shunt circuit is never broken, piad it is-claimed that a good deal of high-voltage stirg,

lug is avoided thereby. This is quite a reasonable assumption, for, when a vehicle is run at a fairly high speed with the shunt field disconnected, a high-voltage surge will be created so soon as regeneration commences by reconnecting the shunt circuit. There is another important point concerning the regeneration of current by utilizing the inertia of the vehicle—the control is fully, automatic in action and is entirely outside the jurisdiction of the driver.

• In these days of high schedule speed, it is of paramount importance 'for any public service vehicle to be capable of rapid acceleration and even more rapid retardation, and there is generally no time left for free coasting. • Thus, if the driver has to be instructed to use a control for regeneration of current there is a great temptation not to male full use of the potential economy. This has, indeed, been proved by experience and all Guy trolleybuses now incorporate a system whereby the moment the pedal is released, regeneration commences. Any further retardation of the vehicle can, of course, be obtained by depressing the brake pedal, the first part of the movement of which applies a progressive rheostatic brake followed immediately upon further depression by the application of the mechanical brakes.

The rheostatic brake has no fewer than nine steps ensuring a progressive action and, for ordinary purposes, the retardation provided electrically is sufficiently • powerful to preclude any extensive use of the mechanical brakes. The whole system is, therefore, conducive to long life for the shoes, drums and the brake mechanism generally.

The Newcastle trolleybuses are equipped with an interesting system of run-back preventer. In designing this device the worst possible condition was imagined—an occasion when a driver collapses at the wheel and the vehicle starts to run backwards down a steep hill. Normally, the ordinary run-back preventer only operates when the vehicle has got into sech a difficult situation that it has become de-wired. A lot of damage could be done, however, previous to such a contingency, and, realizing this, the Guy designers have evolved a system whereby the rheostatic system of braking conies into operation so soon as the motor reverses its direction of rotation, no matter what the position of the controls. Thus the vehicle would merely slide slowly backwards at about 2 m.p.h.—the point where the rheostatic braking ceases.

One other point worthy of mention is the advantage gained by the use of four-shoe brakes. By using four shoes in line with each other the friction area obtained is, of course, enormously increased over the two-shoe variety, but the most important point is that with equal pressures the four shoes expand within the drum without causing any distortion. This, of course, increases the life of the liners appreciably and precludes any possibility of shriek occurring.

The acceleration of a trolleybus can be, and usually is, much greater than the equivalent size of petrol or oilengineel vehicle, and with unlimited current from the power station the lowspeed torque to the back axle is frequently much higher than in the equivalent size of internal-combustionengined bus. Realizing this, Guy Motors, Ltd., has used worm gears having 8-in, centres for the driving axle instead of the usual 7-in., thereby providing lighter loading and lower rubbing pressures.

Tags

Locations: Wolverhampton, Newcastle

comments powered by Disqus