THE ROLE OF THE

104 The Role of the Chemist in Automotive Design
7.10 syntHetIc esters
Synthetic esters like polyol esters or neopentyl polyol esters are made from monobasic
fatty acids and polyhedric alcohols with a neopentyl structure (see Figure 7.6).
On these molecules, there are no hydrogen atoms on the beta carbon. This carbon
is where thermal attack occurs on diesters and eliminating it improves the thermal
stability of the molecule. Polyol esters have an increased number of ester groups
versus diesters. This feature increases polarity, which will affect the lubricity of
the oil at elevated temperatures and give it an advantage over PAOs.
7.11 PolyoleFIns
Polyolefins—specifically, polyalpha olefins—are made from polymerizing alpha
olefins where the double bond is located at the alpha carbon atom. Figure 7.7 shows
1-hexene. The double bond is located between the first and second carbon atoms
and, as a result, they have flexible alkyl branching groups on every opposite carbon
in the chain. The flexibility due to the different configurations makes crystallization
difficult. Because polyalpha olefins are able to remain flexible at lower temperatures,
they are ideal as a synthetic motor oil. Some advantages versus disadvantages of
synthetics are shown in Table 7.4
7.12 automatIc transmIssIon FluId (atF)
The severity of the life of automatic transmission fluid is less severe than that
of engine oil. Without the microscopic coke particles, soot, fuel interaction,
and other contamination associated with motor oil, ATF must contend only
with particles from friction plates and bearings from inside the transmission.
Transmissions typically contain a nylon screen or filter of around 150 µ to filter
out these particles; however, changing the fluid is the only way to eliminate them.
The metallic particles present can contribute to the oxidation of the fluid and
hasten its demise.
H
H
C
H 3 C
H 3 C
FIgure 7.6 Neopentyl glycol ester.
FIgure 7.7 Structure of 1-hexene.
C
CH 2
H
CH 2
O R
n
CH 2
O
Neopentyl glycol ester
CH 2
CH 3