43:

just a height where the car would still stand poised on the two wheels on which it rested.

The experiment made with the conventional construction outlined at A demonstrated that when the car was tipped so that a line joining the bottoms of the two wheels was at an angle of 43 degrees with the ground that the car would tip over. When the same experiment was tried as shown at B with an underslung car it was demonstrated that the car could be tipped to an angle of 55 degrees without becoming overbalanced. These tests would indicate that there is a considerably greater degree of safety when

Fig. 193.-Comparison to Show Relative Stability of Two Types of Frame Suspension. A-Angle at Which Overhung Car Ceases to Be in Stable Equilibrium. B-Angle to Which Underslung Car May Be Tipped Without Danger of Overturning.

the underslung frame is used as compared to the conventional method of construction.

Q. Describe construction of typical frame made of pressed steel.

A. A typical frame of the pressed steel form consists essentially of two side members joined together by means of cross members which act as spacers to separate the two frame sides, as well as form a supporting means for the power plant and transmission elements. It will be noted at Fig. 190-A the one piece frame sides

are joined by four cross members, one at the front practically over the front axle, which serves as a radiator support, two at the intermediate points in the frame under the body and a fourth at the rear end. The cross members are well braced with gusset plates or triangular pieces of pressed steel in order to stiffen the construction. Some forms of frames have a shorter inner member or subframe carried between the two side members.

Q. What is the sub-frame for?

A. The sub-frame is employed to support the power plant and change speed gearing when the main frame side members are too far apart to permit these units being attached directly to the frame sides.

Q. How are the springs attached to a frame?

A. The springs are attached to special spring horns or brackets securely riveted to the frame side members.

Q. How are running board supporting irons, radius rods, spring end brackets and other parts attached to the frame?

A.

The usual method of attaching auxiliary parts not likely to be removed to the frame is by some permanent means of securing as by riveting.

Q. Name common types of springs.

A.

The common forms of springs utilized in motor car construction are the helical coil and laminated leaf forms.

Q. Where are coil springs used in automobile construction? A. Coil springs are generally employed in various parts of the mechanism such as on the valves, in the clutch and to return various rods or operating levers to their proper position when released. Some forms of automobiles have been made in which coil springs were utilized as supporting mediums for the frame but these have not been generally used on account of various structural defects.

Q. Why are laminated leaf springs so generally used?

A. When the laminated leaf construction is employed it is possible to so proportion the springs that members having great strength and resiliency are used and the strength may be varied easily by using different numbers and widths of leaves. If one of

the spring leaves should break the member is still serviceable, whereas if one of the coils of a helical spring breaks the member can be used no longer. Coil springs are especially desirable where quick action is required and it is because of this quality that they are employed as valve springs and in motor car seat cushions or where great strength is needed in small space, which is the reason that coil springs are used in clutches. The springs used for frame suspension must be more gradual in action and it is for this reason that the leaf form is preferred because in the few cases where coil springs

A

B

Fig. 194.-The Two Most Popular Forms of Automobile Springs. A-Semi-Elliptic Type. B-Three-Quarter Elliptic Forms.

have been used their action had to be dampened or retarded by means of friction shock absorbers or other devices of that character. Q. Name principal types of leaf springs.

A. Leaf springs used for supporting automobile frames are either of the semi-elliptic, three-quarter or full elliptic type; or the platform spring, which is a composite form composed of three semielliptic members.

Q. Describe construction and state advantages of semi-elliptic springs.

A. The semi-elliptic spring is shown at Fig. 194-A and as will be noted it is composed of a number of strips of steel graduated in length so the longest member is at the top and the shortest member is at the bottom. The upper leaf is turned over at the ends to form eyes by which the spring is attached to the frame and the other leaves are held to the top leaf or main member by means of small clamps. The semi-eliptic form of spring is suited for carrying great weight and is well adapted for use at points where a stiff suspension is desired.

Q. What are three-quarter and full elliptic springs and why are they used?

A. A three-quarter scroll elliptic spring is shown at Fig. 194-B. This member is composed of a semi-elliptic spring and an auxiliary member which is a quarter elliptic spring secured to one end of the lower member by means of a spring shackle. The free end of the upper member is attached to the motor car frame, as is the free end of the semi-elliptic or lower member. A full elliptic spring is composed of two semi-elliptic members joined together either in the manner indicated for the three-quarter elliptic as outlined at B, or by inverting one member and have it fit into suitable sockets at the ends of the other member. The advantage of the full elliptic and threequarter form is greater flexibility on account of the construction permitting greater spring movement than is possible with the semieliptic form of the same length.

Q. What is the platform spring suspension ?

A. Two forms of platform springs are shown at Figs. 195 and 196. The platform spring consists of three semi-elliptic members, two of which are placed parallel with the frame side members while the other is placed at the rear end of the frame parallel to the cross member. The front end of the side springs are secured to the frame, they are attached to the axle at their center and to shackles carried by the cross spring ends at the rear. The frame is supported by one point at the center of the rear cross member which rests at the top of the arc of the cross spring. The cross spring shown

at Fig. 195 is used on a pleasure car chassis and it will be noted that the frame side members are raised directly over the axle in order to permit the proper degree of axle movement. The heavier construction outlined at Fig. 196 shows the application of a platform spring assembly to the frame and axle of a motor truck.

Q. Outline the conventional spring suspension system.

A. As a rule the front end of the car is supported on semi-elliptic springs while the rear end may be carried on three-quarter elliptic, as shown at Fig. 190-A, or by full elliptic or by the platform spring as shown at Figs. 195 and 196. On some heavy commercial car frames, as shown at Fig. 190-B, semi-elliptic springs are utilized at both front and rear of the frame, though in most forms of pleasure cars the semi-elliptic springs are utilized only at the front end.

Q. Why are semi-elliptic springs desirable for supporting front ends of frame?

A. On account of the front end of the frame carrying the power plant and also having the front axle, which is depended on for steering the car, attached to it, it is not desirable or necessary to have great flexibility at that point. The semi-elliptic forms carry