Chain drive

“ On cars with double-chain drive, the differential is fitted to the jack shaft, and of course receives the drive from the change-speed mechanism through its housing.
Both the driving-shaft and double-chain drive have points of advantage and of weakness, and each type has its advocates. For the double chain, great strength can be claimed with light weight, as the axle is in one piece, and perfectly adapted to support the car. ”

“ It runs at three times engine speed, operating directly from the crank shaft through a silent chain drive. Being a single unit machine, it employs but one armature with only one commutator, one set of field windings and one set of brushes for the performance of all of its functions both as a starter and as a generator. ”

“ Great Britain and the United States the worm drive was in most extensive use. Of the lorry models manufactured in Great Britain in 1920 roughly 50% had worm drive, 25 % chain drive and 25% the double-reduction drive, or drive by one pair of bevel and one pair of spur gears enclosed at the middle of the axle. In the United States the most popular drive next to the worm was the internal gear drive, in which there was a first reduction by bevel gears at the middle of the axle and a second by internal gears at the driving wheels. ”

“ In many instances the steering mechanism is unnecessarily exposed, and placed very far forward so as to be liable to injury in the case of slight collision or passage over any considerable obstruction. The chain drive is very popular among French manufacturers. The chains are usually not protected by cases, and in very many instances an attempt is made to obtain through the medium of the chain a very large gear reduction, resulting in the use of absurdly small chain pinions, which will certainly need frequent renewal under the conditions of rough service. ”

“ The hub is thus driven at a higher speed than the chain-wheel. For normal gear, the striking gear draws the internal mechanism of the hub towards a central position, compressing a spring, disengaging the sun-wheel and locking the drive-ring hub and annular wheel together. At low gear, the internal mechanism is drawn to the right-hand side, where the planet carrier engages with the end plate of the hub by means of claw-clutches. The annular wheel is still engaged with the drive-ring, and the sun-wheel is again locked to the spindle. The hub is thus driven at a lower speed. ”

“ A fan is generally employed, either situated behind the radiator and driven by the engine, or the flywheel is vaned so as to induce a current of air through the radiator. To deal now with the transmission mechanism, the drive is taken through a clutch and gear-box as in the earliest days, but, for the final drive, chain transmission to the road wheels running on a fixed axle has largely given place to propeller drive on to a live axle. ”

“ Or the driving wheels may be mounted on a live rear axle, the motor driving on to the compensating gear, either by a chain, by spur gearing, or by means of worm gearing, which gives a nice silent drive, and is used in the Oppermann cars. In any case the use of a single motor involves, in addition to the motor, a differential gear. What is to be avoided is a live rear axle with the motor so mounted that any large proportion of its weight comes on this live axle. ”

“ Gib and cotter attachment for long link flat suspension chains.
[31]
Larger plate.
[32]
204 & 205. Drive chains. See Ewart’s patent, No. 2752-76, and others. These chains are replacing belts for many purposes, as they give a positive drive, do not stretch so much, and last longer, besides which they are easily detached at any point, and a damaged link can be readily replaced.
206 & 207. Thrust chains, with friction rollers at each junction, used in hydraulic multiplying cylinder gear in some cases.
208. Ewart and Dodge’s patent chain, with renewable seatings between the links. ”

“ Bearing in mind that B is not only a loss from the normal contact but also a loss of the extra contact that A gives, it will readily be seen how important a power-saving factor the right sort of [Pg 18] a drive is—especially on high-speed small-pulley machines, such as dynamos, motors, fans, blowers, etc. ”

“ The locking together of the square shaft and sleeve gives what is known as the direct drive, which is of comparatively recent development; many designs of sliding gears still use a third pair of gears which, being of the same size, give the square shaft the speed of the crank shaft. By the use of the direct drive, the power of the engine is directly applied to the square shaft, avoiding the loss that occurs through the friction of the teeth of the gears. ”

“ The wheels of such a truck turn freely on the axle stubs of a dead axle.
Objections to Chains.—Few pleasure cars are now equipped in this manner, as the shaft drive is more desirable for several reasons: The use of chains is always objectionable, as the efficiency decreases with wear quicker than the shaft drive, and requires the jackshaft, sprocket chains and sprocket wheels, besides the noise and excessive wear, by stretching of chains, which are always inherent in the use of chains. ”

“ This is the disagreeable characteristic of a differential, (54) that makes one wheel spin when it touches a slippery spot on the road, and stalls the car, because the other wheels cannot get any driving power.
(55)
CHAPTER VI
THE DRIVE
The term used to designate the transmission of power from the engine to the wheels, is called the drive.
In nearly all cars the engine shaft runs fore and aft, and consequently is at right angles to the axles. This, of course, necessitates some sort of gearing between the engine shaft and axle. This change is made in the bevel gear drive hereafter explained. ”

“ Constant Speed Drive. The invention of the gear type of drive, or, as it is better known, the "constant speed drive," is, without doubt, the most valuable improvement in design brought out in many years. It is the result of a demand for a machine in which the feeds would be entirely independent of the spindle speeds, and all speeds and feeds would be self-contained, thus doing away with complicated overhead works, or permitting the machine to be driven by a constant speed motor. ”

“ Such systems include Vehicles which carry heavy batteries of accumulators, the current from which is utilized for the driving of the vehicle by means of electric motors. Other variations include the Hallford-Stevens system, shown in fig. 32, in which it may be seen the petrol engine drives a dynamo, and the current is then caused to drive an electric motor at each side of the chassis. Each motor drives one of the back road wheels, through a worm and worm wheel. ”

“ The straight line drive is most desirable, in every way, as the full power of the engine is available, and this is usually arranged for by lowering the engine bed sufficiently so that the shaft will point straight to the axle when the car is loaded. ”

“ If it is found that the speed of the water wheel drops 25 per cent between no load and full load, a dynamo with field coils over-compounded to this extent would give a fairly constant regulation. If you are buying a special dynamo for direct drive, your manufacturer can supply you with a machine that will maintain constant voltage under the normal variations in speed of your wheel. ”

“ Furthermore, a wider belt can be employed than on cone drive machines. As a result, a maximum amount of power is delivered to the machine pulley, and is transmitted through heavy gearing to the spindle, under all conditions, thus fitting this style of machine particularly well to the heavier classes of work. Another advantage of this drive is its particular adaptation to the application of a motor. The constant speed type of motor, which is more economical, both in first cost and in the amount of power consumed, than the variable speed motor, can be employed. ”

“ The wheel carrying the sensitised film is driven by an electric motor, the shaft of the wheel being extended beyond the box on one side to carry a small grooved pulley, the drive from the motor being transmitted through a small belt. The motor may be driven at varying speeds, so that the number of exposures per second may be varied according to the revolutions of the box completed in that period of time. ”

“ On the automatic regulator, the worm shaft is connected to the motor through a spur gear and pinion, which constitutes a compact driving device having very little friction. Provision is made for either alternating current or direct current motor drive. When a motor driven regulator is operated by hand, the brake must be held in the release position, otherwise it will be impossible to operate the regulator. In the hand operated regulator the spur gear is replaced by a hand wheel and the regulator is driven directly from the worm shaft. ”

“ Another plan, employed however only by one or two firms, substitutes for the bevel gearing what is known as skew or screw gearing, a very smooth and silent drive without the spreading or bursting action of the bevels, the end of the driving shaft being fitted with a screw which drives a series of teeth cut diagonally around the circumference of the driven wheel. ”

“ While this type is in general use, the gears are often so arranged that the direct drive combination is reached when the control lever is in the third-speed position, the gears meshed by the fourth-speed position driving the square shaft at a still higher speed. This high speed can only be used for running under the best road conditions. ”

“ It is desirable, therefore, so far as the shafting is concerned, to place the machines requiring the most power to drive as near as possible to that end of the shafting that receives power from the motor. ”

“ An admirable example of the application of this drive is shown in Fig. 139, the 24 inch reflector at the Harvard Observatory. The mount is a massive open fork, and the motor drive is seen on the right of the mount. There are here two motors, ordinary fan motors in size. The right hand motor carries the fly-wheel and runs steadily on under the pendulum control. ”

“ It is a positive drive, that is, there can be no slip. Less liability of becoming detached, and, because it is not dependent on frictional contact, the diameters of the sprockets may be much less than pulley diameter for belt drive. ”

“ In arranging the belt drive so as to run slightly out of synchronism, if the pulleys be of the same size, the desired result is obtained by pasting a thin strip of paper around the face of one of the pulleys thus altering the velocity ratio of the drive slightly from unity. ”

“ Once we have installed a sufficiently powerful dynamo and a steam or other engine to drive it, we can place motors just where they are required, either close to the dynamo or miles away, driving them simply by means of a connecting cable. In factories, motors can be placed close to the machines they are required to drive, anywhere in the building, thus doing away with all complicated and dangerous systems of shafting and belts. ”

“ The motor may be geared direct to a very small dynamo, if the latter is designed to run at high speeds. If a geared-down drive is needed, a small pulley—such as is used for blinds, and may be bought for a penny—should be attached to the shaft, and a bootlace be employed as belt. Avoid overloading the wheel, for if it is unable to run at a high speed it will prove inefficient.
[Illustration: FIG. l08.-Water motor working a photographic dish-rocker.]
Lubrication.—The water will keep the bearings cool, but the bearings should be well lubricated. ”

“ From the last change-speed shaft the power must be transmitted to the road wheels through a differential gear and through one or other of the types of final drive which are now employed by representative makers. The great distinction from the axle of a horse-drawn vehicle is that there must be both a mechanical connexion, yet a differential action, between the two back wheels. ”

“ The early power presses were worked by horses, by men known as crank-men, and even in the case of small machines by dogs. These crude power appliances soon gave way to steam, and within a few years steam has been largely supplanted by the electric drive, with a tendency to a preponderance of individual motor-driven machines. ”

“ It is cheaper to buy good oil than to run the risk of damage to bearings from overheating or scoring.
Care of Driving Chain on Motor Driven Machines. The care of the driving chain on motor driven machines is important. ”

“ The power which has been transferred to the driving shaft from the motor is in turn transferred to the two rear wheels of the carriage by a combination gear and sprockets. An endless chain connects the sprockets on the carriage wheels to the sprocket wheels on the driving shaft. All of the motive power is located under the body of an ordinary phaeton, the hight of which is not increased by the machinery. The motor is started by a crank which is easily applied to a shaft in the rear of the carriage and the gasoline is ignited in the cylinder by electricity. ”

“ With direct drive the engine and dynamo must run at the same speed; this is a disadvantage because the desirable speeds of the two machines may not agree.
Since the usual engine speeds are slower than dynamo speeds, direct drive involves the use of a larger dynamo for a given output than would be necessary with belt connection, and involves a corresponding increase in cost and greater friction loss due to the rotation of larger and heavier parts.
Fig. 444.—Belt clamp for stretching belt and holding the ends while making joint. ”

“ These cranks are removed by unscrewing in the opposite direction to which they revolve in the propulsion of the machine.
DEVICES FOR TIGHTENING CHAIN BY MOVING REAR AXLE.
The next part of the wheel we will turn our attention to is the chain—the medium through which the motion is imparted from the driving-gear to the rear sprocket. Frequently after a long ride on rough roads, or perhaps a few days of usage, the chain will be found to have slackened up considerably. ”