Springs Self-adjusting to Load.
Page 10
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DEVELOrMENTS which enable the springs to be almost., if not quite, as efficient when a vehicle is employed partially loaded as when it is utilized with a full load, are of the greatest value, for this question of running a vehicle with alternately light and heavy loads has proved one of the most difficult problems which face the haulier, as well as those who run passenger vehicles of different types.
In certain cases use has been made of supplementary springs. We may give as an instance of the employment of these the London omnibuses, in which volute springs take an increasing proportion of the weight as the vehicle fills with passengers.
If the same results can be obtained by using a single spring in place of the ordinary spring and a further cushioning device, it is all to the good.
Such a spring was described in our recent article on the new Bristol 2-tonner, and we have reason to believe that the springing used on this vehicle has already aroused considerable inter est in the trade and amongst users. In this connection we have received the
following letter from William Foster and Co., Ltd., of Lincoln :—
"In your issue of the 3rd April we notice a description, on page 211, of a special type of spring used by the fl,,istol Tramways and Carriage Co., Ltd., which is claimed as affording a,
considerable saving in material employed, as well as an improvement in comfort on bad roads.
" We are pleased to say we can confirm this as the design has been incorporated in our steam tractors and some types of traction engines since 1911.
"We took out a patent for this at the time (No. 3010, of 1911), and have used this compensating device ever since. For simplicity it is hard to beat.
"We enclose herewith a blue print -of our current design, which is slightly different from the original patent in detail—although not. in principle—and no doubt the Bristol Co, will be pleased to know that 12 years' experience has confirmed our high opinion of its value.—Yours truly, " For WILLIAM FOSTER AND CO., LTD., (Signed) W..0. TRITTON, 'Managing Director."
For the information of our readers -we reproduced a portion of the blue print referred to in the above letter, and it will be noted that, although the principle adopted in this spring is practically i the same as that used n the Bristol springing, yet from the details given it would seem that the change in the strength of the spring caused by the shortening of the effective length appears to be abrupt, whereas in the Bristol spring (a drawing of which we also reproduce) the slipper pieces are so curved that the springs are gradually strengthened, or, perhaps, it would be better to say, that their periodicity is increased in proportion to the load.
We shall be glad to receive opinions on the two forms of spring from those of our readers who are particularly interested in any improvements which can be effected in springing.