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28th April 1931, Page 49
28th April 1931
Page 49
Page 50
Page 49, 28th April 1931 — Novelty in
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FUEL-PUMP DESIGN

Vernier Adjustment of Individual Cylinders of New Benes Pump. Ingenious Trip Device for Starting

IN the issue of The Commercial Motor, dated March 3rd, we gave full details of the fuel pump for oil engines, made by Benes, Ltd.' 24, Holborn, London, E.0.1. Since that date two interesting additions to the design have been made ; they are of an exclusivenature and of considerable importance.. The all-British Benes pump for compression-ignition engines is now in production; the example of the latest model which we illustrate is one of those made by the well-known concern, John I. Thornycroft and CO., Ltd.. of Reading.

The balancing of the individual elements in a multi-element oil-fuel Pump has always been a tedious operation, kit the development of the high-speed, compression-ignition engine, particularly for aircraft,now demands that this operation must not only be capable of execution While the engine is runnirig, but also must be done rapidly and with extreme accuracy. Provision for this has been made in the latest design of Benes fuel pump, the balancing or changing of the quantity of fuel delivered by individual elements being effected quickly and accurately, without the use of tools.

A further requirement of the multicylinder engine is economy, when starting, of electrical energy, compressed air or manual energy. If a number of cylinders be decompressed, this output can be much reduced.

Some of the methods hitherto in use for placing the corresponding pump elements in the " no injection" position, when engine cylinders are decompressed, are inconvenient.

In the latest Benes pump this object is attained by a simple movement of the control shaft—which can be remotely actuated from the dash—and is actually incorporated with the mechanism for output balancing. Reference to two of the illustrations shows that the usual toothed control c27 sleeves are retained, whilst the control shaft, which is screwed over its entire length, has mounted upon it collars, provided with projecting rings which form rack teeth and engage in the corresponding toothed control sleeves, so that endwise movement of the shaft rotates the control sleeves in unison. If one of the rack collars be rotated about the shaft on which it is screwed, it will move along the shaft to the right or left, according to the direction in which it is turned, thus altering the relative angular setting of its corresponding control sleeves and, consequently, the amount of fuel injected by this element.

These rack collars have four equidistant axial grooves in which a flat locking spring engages, thus preventing the collar from turning around the shaft whilst leaving it free to be moved for normal control; the spring is easily lifted out of the groove with the finger, yet prevented from leaving the groove when running, by the closely fitting inspection Cover. Thus it will be seen that a quarter turn of a rack collar will move it along the shaft a quarter of the pitch of the screw thread, the angular movement thereby imparted to the plunger being minute, resulting in an extremely accurate adjustment of the quantity of fuel injected ; actually the variation is in the order of .5 per cent.

In order to place all the elements in the "no injection" position, except the one connected to the engine cylinder employed for starting, the control shaft is provided with a sleeve on which is carried the rack collar operating the element used for starting, through which sleeve the control shaft projects. This end of the shaft is hollow, and is provided with a trip device; the trip pawl engages in a cam slot in the bar when the control shaft and its sleeve are to be moved together for running.

The slotted part of the trip bar is formed with a radius or cam face, so that when it is desired to start the engine, the bar is given half a turn (which raises the trip pawl) and is then pushed back, the pawl engaging in the slot in the control shaft, which allows the shaft to move backwards, carrying with it its rack collars. By this movement the three or five plungers required to idle are set at the "no injection" position, while the single rack collar on the sleeve remains in the normal active position ; the control is, of course, attached to the sleeve.

After starting up, the trip bar is given a half turn in the reverse direction and pulled forwards, when the trip pawl drops into its slot, interlocking the shaft and sleeve, thus bringing all the elements under the influence of the running control. This operation in either direction is effected in a moment, A great advantage in having these

adjustments all on the control shaft, quite apart from the addedconvenience in operation, is that everything is made accessible by removing the inspection cover, whilst the actual pump mecban

ism is not further complicated, and the pump is not increased in size, the expense of providing costly external fittings for these operations is eliminated. The whole shaft assembly may be removed and reversed in a few minutes should it be necessary to control the pump from the other end.

A simple and inexpensive method of completely decompressing any desired number of cylinders has been evolved which is applicable to all high-speed oil engines; when desired drawings will be supplied to users of the pump, in order that they may have the advantage of incorporating this arrangement.

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Locations: Reading, London

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