II. Case Analysis

The observations in this section are based on examination of individual accident cases for different car models and are illustrative, rather than statistical, in nature. Although case analysis cannot usually be defended as being typical or representative it serves a useful purpose by providing guidance to engineers in detecting weaknesses and making design corrections. It should be stressed however that in this study all cases involving a 1962 or 1963 car, as well as cases involving earlier model cars-about 1,500 in all-were examined individually. Cases were then selected to illustrate the various types of latch damage observed, and comments concerning the relative frequency of different types of damage were recorded.

1. Door latch damage. The series of door latch photographs that follow illustrate the influence of design changes on damage associated with door opening. Data for Chrysler, Ford, and General Motors cars are presented and major changes in latch design are noted and illustrated. For presentation purposes, factual data pertaining to latch type, damage, or other observed information in each case are recorded as "observations." All data interpretation, inferences, or conclusions are recordel separately as "comments."

A summary of observations and conclusions is also provided at the end of this section. The summary includes a discussion of observed patterns or trends that may not be apparent in examining individual cases.

Ford

The basic components and operation of the 1962-63 Ford latch are illustrated in figure 1. The striker (or pinion) is the component mounted on the door post. The latch is mounted on the door and consists of the latch jaws and housing that are visible on the door, and the latch mechanism contained inside the door.

The latch is shown in the "open" position. In actual operation, closing the door brings the latch jaws and pinion shaft into contact (dotted arrow) thus rotating the latch jaws and connected ratchet to the left until the pinion is encircled by the latch jaws. The pawl is spring loaded so that it holds the rachet at point A when the door is closed. (Point B represents the secondary or semilatch position.)

Release of the latch is accomplished through a linkage system from the interior and exterior door handles connected at points C1 and C2. Arrows indicate direction of latch release. D1 and D2 are linkage points for the interior locking device. Arrows indicate direction for activation. When the door handle is activated to open the door, the pawl is moved down (arrow) releasing the lower half of the ratchet. The upper half of the ratchet, which is spring loaded to hold in the "open" position, then moves both parts of the ratchet to the right into the position illustrated.

49-959-66-pt. 2--4

The photographs of Ford latches arranged chronologically below illustrate Ford latch design changes and the effect of these changes on damage to the latch, striker, and surrounding area. The first three photographs show the types of damage typically observed for pre-1956, 1956, and 1957 Ford latches. The remainder illustrate various types of damage to 1962-63 Ford door latches. Figure 2

Observations: The 1955 Ford latch and striker in figure 2 illustrate the appearance of many pre-1956 latches when doors opened. It was reported that this door opened, but neither the latch components nor the surrounding areas were damaged.

Comments: Prior to 1956, the latch and striker were not designed to resist longitudinal displacement and, when subjected to this type of load, could separate without damage. Consequently, damage to the latch or surrounding area was not observed under longitudinal loads. When subjected to lateral or vertical loads latch damage was possible, but was observed infrequently.

Figure 3

Observations: A hardened steel plate was added to the striker of the 1956 Ford latch, illustrated in figure 3, to prevent longitudinal displacement of the latch and striker. (Another version, introduced on 1957 models, and used until 1961, is shown in fig. 4.) The upper rotor tooth in figure 3 is broken off completely and it was reported that this door opened.

Comments: The type of damage illustrated in figure 3, a broken rotor tooth, was observed most frequently for both the 1956 and 1957 latches. Damage to the sheet metal surrounding the latch and striker, and associated with latch resistance, was not observed.

Observations: The striker of the 1957 Ford door latch shown in figure 4 was twisted, but it was reported that the latch was undamaged. The door sur

face to the left of the rotor, and the top of the rotor housing, were also scratched. It was reported that this door opened.

Comments: It appears that the rotor housing twisted the upper part of the striker in figure 4 (note scratches on rotor housing) permitting the rotor teeth to slip free over the striker plate. The scratches beside the rotor apparently were caused by the damaged striker as the door opened. Note the absence of deformation to the area surrounding the latch components for the three Ford latches illustrated in figures 2-4.

The 1957-61 Ford latch could also be disengaged in the fashion described, without damaging the latch, by separating the upper parts of the latch and striker so that the rotor teeth could slip over the plate vertically. Although this phenomenon can be demonstrated with the unmounted latch, it is difficult to determine if this actually caused door opening in accidents.

Figures 5, 6, and 7

Observations: Three cases involving the 1962-63 Ford latch, the next major Ford redesign, appear in figures 5, 6, and 7. All three latches remained closed and were reported to be undamaged.

Comments: Each of the three latches illustrated was subjected to longitudinal loads, as evidenced by the gap between the door and doorpost, but each latch successfully resisted these forces. The 1962-63 Ford latch was the first latch observed to hold under the conditions illustrated. It was also the first latch rigid enough to damage surrounding sheet metal by transferring part of the load to that area. Previous American latches tended to fail before surrounding sheet metal was damaged.

Figure 8

Observations: Part of the lower latch jaw which encircled the pinion was broken off the Ford latch shown in figure 8, and the upper left jaw appears to be bent to the left. Note that the pinion was gouged as well. The investigating officer reported that the door opened.

Comments: The latch jaws are shown in the "closed" position. The latch housing appears to be intact but surrounding sheet metal is deformed. The head of the pinion is intact while the shaft is scored. It appears that this latch failed in a lateral direction gouging the pinion and breaking the lower tooth on the latch.

Figure 9

jaw was broken off in a The pinion and doorpost outside of the car. Note,

Observations: In figure 9, part of the upper latch front impact that compressed the door longitudinally. have assumed a rather acute angle tilted toward the also, the torn sheet metal to the left of the latch jaws. It was reported that this door opened.

Comments: It appears that the latch and pinion were compressed longitudinally until the doorpost started to buckle, introducing a lateral component of force. As the post (and pinion) twisted, the upper latch tooth failed and released the pinion. Still under compression, the pinion was driven into the sheet metal beside the latch and then tore through it laterally allowing the door to open. Figure 10

Observations: Figure 10 illustrates a type of failure frequently observed for the 1962-63 Ford latch. In the photograph, the lower jaws of the latch are twisted or deformed. This type of damage was also observed but less frequently for the upper latch jaws. It was reported that the door opened and that the pinion alone was damaged.