« НазадПродовжити »
ELECTRIC STARTING SYSTEMS
Q. Name principal types of motor starters, and give advantages of most popular system.
A. Automatic motor starters may be of three general types, mechanical starters, which include various leverage, spring and. gearing combinations that replace the starting crank, air starters, in which compressed air is admitted to the motor cylinders from a. tank where it is stored under pressure, and electric starters where a small motor is employed to rotate the crank shaft by some direct mechanical connection. The electric starter is the most popular type because on most cars electric lighting systems may be operated from the same battery and dynamo that supplies current for the starting motor. The electric starter is an easily operated form. and can be proportioned so that it will turn an engine over positively. In fact, some electric starters are powerful enough to actually propel the car a short distance.
The disadvantage of the mechanical starters, which comprise the various spring and lever type, is that they depend to a certain extent on human power. The spring of a spring starter is capable of giving the motor eight or ten brisk turns before the spring will be unwound and provision is made for automatically rewinding the spring by the motor power as soon as the engine starts. If the engine fails to start, owing to some defect in carburetion or igni. tion, and the spring becomes unwound, it is necessary for the operator to rewind the springs by means of a small crank provided for that purpose, a somewhat tedious proceeding. The usual form of mechanical starter requires almost as much energy to start the motor as is needed at the starting crank of the ordinary pattern, the only advantage being in most cases the power plant may be put in motion from the seat.
An air starter system has a disadvantage in that the air is apt to cool the cylinders and prevent proper starting on account of condensing the gas and also preventing the cylinder from taking in a charge of good rich gas, as it does when cranked by external
It is evident that the air supplied the cylinders must dilute the entering charge of gas to some extent as well as prevent the motor from taking in the proper charges. Several air starters have been designed that have given good results in practice, how
Q. Describe typical air starter system.
A. A typical air starter system is shown at Fig. 351. The air is supplied by a four cylinder air pressure pump which directs it to a storage tank, through a suitable return check valve. A pipe leading from the storage tank goes to a distributor fitting, driven by the motor, which directs an air current only to the cylinder which is at the firing point when the main operating valves are opened. The air is directed against the top of the piston and as it has a pressure of 150 or 160 pounds per square inch it will give a series of initial impulses to the pistons and turn over the crank shaft until the charge of gas drawn into one of the cylinders while the shaft is rotating explodes and permits the engine to take up its cycle of operation. The system shown was used on early Chalıners cars and a similar system was incorporated in the Winton automobile as well. An advantage of the air starting system is that one always has a supply of fresh cool air under pressure to blow up tires with. A simple valve is included in the pipe line so a rubber hose may be run from the dash to any one of the tires needing inflation.
Q. How do mechanical starters work and describe some typical forms.
A. While different makes of cars have been marketed using air starting systems, there has been no car offered with a mechanical starter, so wherever these are used they have been applied by the owner of the vehicle and not the manufacturer. Owing to the wide distribution of the Ford automobile, and the fact that the
makers make no provision for a self-starting motor, various forms of simple starters by which the motor may be cranked from the seat have been offered. Two of these are shown at the top of Fig. 352. That at A consists of a rachet clutch which is attached to the starting end of the crankshaft and which is operated by means of chain connection with the smaller pulley of a two diameter pulley wheel. The larger wheel carries a wire cable which is attached to a straight rod running through the dash board and terminating in a handle convenient to the driver's hand. A pull on the spade type handle provided at the end of the rod will move the pulley wheel and produce a corresponding movement of the starting rachet which turns the engine crankshaft over in the same way as the hand crank does. A modification of the device shown at A is outlined at B. This works on the same principle, except that an odd-shaped member is used to turn over the engine crankshaft. These devices are in no sense of the word “self-starters," but on light motor cars they provide an effective substitute in that the engine may be turned over without undue exertion and without leaving the seat. This is an advantage of some moment when the engine stalls in traffic, or under conditions where it would be inconvenient to get out of the car.
Q. Do all mechanical starters attach to the front of the engine crankshaft?
A. Two types of mechanical starters known as the Wilkinson are shown at the bottom of the illustration, Fig. 352. The one at D is operated by pulling a handle on the dash, the one at C by a pedal designed for foot actuation. The mechanism is such that the flywheel is pushed around by a lever which will engage with either a stud or a shoulder on the flywheel. The type at the left uses the studded flywheel, there being four of these marked "S." When the arm C is moved by depressing a pedal, the finger A contacts with one of the stubs and turns the flywheel. Return engagement is produced by the large spring shown. In order to minimize liability of injury from backfire, the Wilkinson device is constructed so that the pawl D rises on the cam which bears against the collar E, and thus throws the finger out of engage
ment with the stud. One thrust of the pedal will turn the flywheel of a four-cylinder engine sufficiently to cylinder to fire should ignition and carburetion systems be functioning properly. The type at D. is just as simple, but is
Fig. 352.-Showing Construction of Mechanical Devices for Starting Gaso
line Engine from the Operator's Seat.
modified somewhat in its construction. In this a hand lever is used to rotate the flywheel, and instead of using studs on the flywheel rim, four shoulders in the interior periphery do the work. These shoulders may be cast with the wheel, or in some cars it is possible to have them cut in the flywheel. The operation is the same as that of the type previously described as the movement of