Geely JL481Q, Руководство пользователя, Страница: 74 / 198

Because of high mechanical and thermal loads and complicated stress distribution on the piston, it’s hard to control the gap
width between piston and cylinder body. For achieving steady control of the gap, the piston of engine adopts the structure
of drum skirt and elliptic cross section, with long axis vertical to the pin hole and short axis parallel to it.
Piston uses an intact strengthening rib to transfer force. Its pin seat sinks into the rounded outer piston surface by 9mm,
reducing support distance between piston pins and weakening deformation of piston pins and pin seat. Apart from that, an
appropriate lead angle at the internal edge of pin seat lightens edge loads on the pin seat, the unequal thickness of pin seat
and biasing of outer circle’s center towards piston top by 2cm strengthen the upper half piston which endures larger stress.
To eliminate the destroying stress caused by heat expansion of piston skirts and deformation of piston’s pin seat, concavi-
ties are drilled under the piston pin holes, with one concavity in each skirt.
Forward marks on piston top and group marks on skirt recesses provide ease of mounting and fitting.
2. Piston pin
Piston pin connects piston and connecting rod, and endures various loads including pull, thrust, wallop caused by alternat-
ing movements of connecting rod and pin seat. Periodical changes of loads on connecting rod small end and pin seat, as
well as slight glide of piston pin in pin hole, lead to bad conditions of abrasion and lubricating on all parts of piston pin. The
inner hollowed piston pin of engine is made of low carbon alloy steel. After treatments of outer-surface carburization, preci-
sion grinding and polishing, it acquires sufficient rigidity and intensity, fine wear resistance property on surface and excel-
lent impact toughness on central part. In the semi-floating structure, magnitude of interference between connecting rod
small end and pin varies from 0.12mm to 0.003mm, while oil film thickness between pin and pin seat varies from 0.002mm
to 0.013mm. Such structure has the advantages of omitting copper sleeves and piston pin clamp rings, reducing connect-
ing rod small end width and lengthening pin seat. But connecting rod must be mounted at the temperature of about 100
o
C
or be squeezed by press machine at the temperature of -40
o
C in cold state, which will cause difficulties in disassembly.
3. Piston ring
Piston rings of engine include two gas rings and one oil ring connected by flat ends.
The main functions of cylinder are to prevent the exchange of burned gas with high temperature and high pressure in
cylinder and waste gas in crankshaft case, and transfer most heat from piston top to cylinder wall in order to minimize heat
in piston head and piston skirt and minimize deformation of piston.
The cross section of the first gas ring is illustrated as Fig. 175. It’s a symmetrical barrel-shaped ring with small interface and
good leak tightness. It also possesses fine lubrication property and can provide constant lubricant films both in its upward
movement and downward movement. The rounded outer surface of the first gas ring is nitridation treated and the rest
surfaces of it are bonderite. The first gas ring is 2.7±0.1 in thickness and 1.2 in height. Free ends distance is 10mm
and radial elasticity is 18.4-27.6N. Back clearance after mounting is 1.25mm.
The cross section of the secondary gas ring is illustrated as Fig. 176.It’s a conic ring with pitch of 1 . It can provide
lubricant film in its upward movement while scraping lubricant in its downward movement. The secondary gas ring is made
of nodular graphit castiron or tungsten vanadium titanium alloy,and possesses good wear-in property, fine thermal stability
and excellent wear-resistance. Surfaces of the secondary gas ring are bonderite. This ring is 3.0±0.1 in thickness and
1.5 in height. Free ends distance is 13mm and radial elasticity is 18.4-27.6N. Back clearance after mounting is
1.3mm. A “π”sign for mounting is marked on the side of the ring, take care not to mount it in the reverse direction.
Fig 176 The cross section of the second gas ring
Fig 175 The cross section of the first gas ring
-0.010
-0.025
-0.010
-0.025
+30’
0
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