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       CONNECTING ROD SUPPORTING NEEDLES & RETAINER ASSEMBLY

            RTL  Connecting rod supporting needles retainer assembly is applicable to the 
medium and small size diesels.
           The needle bearings , due to its special operational conditions , must bear the 
shock force from the explosion in the cylinder, the inertia forces of the piston, the c-
onnecting rod and the crank shaft. Therefore , needles and the retainer must sustain
 the great centrifugal forces and acceleration forces. Besides, it is responsible for the 
heat dissipation  . So, the flow of lubricant oils must be taken into account during the
 entity designing of the bearing so that enough cooling area is increased , or coating 
copper, silver on the surface to prevent the abnormal abrasion during the starting p-
eriod.
           To conclude, the  Connecting rod supporting needle retainer assembly has the 
following merits:
           Light weight, lower inertial force, the use of highly anti-fatigue , highly rigid and
 highly abrasion-resistant materials, low abrasion force in low speed operation and 
high cooling capability.

Structure

KZK	Crank pin supporting needle and retainer assembly
KBK	Piston pin supporting needle and retainer assembly

KBK Piston pin supporting needle and retainer assembly(small end bearing)

                Piston pin supporting needle and retainer assembly transmit the engine poser through the piston pin. To reduce the impact and lower
                     the noise, the inner diameter of the retainer is often close to the piston pin which means inner guiding method is used.
                               The retainer  of  RTL piston pin supporting needle retainer assembly is generally made of 20 steel . The small end bearing retainer of 
                     high torque force and high speed. is always made of 15CrMo steel .

KZK Crank pin supporting needle and retainer assembly(big end bearing)

                              The crank is driven by the big end of the connecting rod. Therefore , the outer diameter of the retainer should be as close as possible
                    to the inner diameter of the big end of the connecting rod so that the impact can be reduced and the noise lowered.. That means out guiding 
                    method is used.
                               The big end of the bearing revolute around the center of the crank shaft and it the same time it rotates itself. When the speed reaches
                    very high (over 8000rpm) , the centrifugal force will be very huge and thus extremely big load resulted on the retainer creating very poor conditions.
                               The retainer of the RTL crank pin supporting needle retainer assembly is generally made of suitably heat treated 15DrMo steel  , this
                    greatly increase the strength and abrasion resistance. Meanwhile this will ensure the material the same as the piston pin steel so that they have
                    the same heat expansion factor under the same condition. When the working speed exceeds 8000rpm or the temperature is very high, silver
                    coating to the retainer is suggested.

应用资料

                                It is suggested that 15CrMo be used for connecting rod material. After carbonization quenching and tempering, its toughness is increased.
                       The tray surface hardness of the apertures of both small and big ends are no less than HV700 with effective hardened layer no less than 0.5mm.
                       the surfaces of seat holes and the pin tray must be ground very precisely till its surface roughness doesn抰 exceed Ra0.2. the circularity, cylind-
                       ricity will be controlled within 0.003mm. the parallelism of the two ends : for high speed  0.02/100.  For general purpose 0.03/100. For low sp-
                       eed , 0.04/100.
                               If the above mentioned precision can not be reached, it is suggested to widen the radical combination gap. Or damage will happen on the
                        bearing due to the abnormal load resulted from over heat.
                              BIG END GUIDANCE AND SMALL END GUIDANCE
                              Big end guidance (lower guidance) and small end guidance (upper guidance) are constituted as shown in Fig 1. Big end guidance is more 
                        commonly used. Lower end guidance is considered only in case of very high speed or the overheat  resulted from big end guidance.
                              Big end (lower ) guidance:
                              The big end of the connecting rod and the needle bearings are mounted between the two cranks. So when big end guidance is used, the
                       oil film lubrication among the crank, connecting rod big end and the bearings must be noticed. On the big ends of the connecting rod, the end 
                       surfaces are always made into slit , hole or groove shapes so that the lubricating oil can enter the needle bearing smoothly and normal lubric-
                       ation oil circulation can be maintained.
                              The width of the big end needle bearing is the same as the connecting big end. To ensure the effective guidance to the big end bearings 
                        and to prevent the connecting from slanting, two washers made of phosphorus bronze are added by the two sides of the big end and a gap 
                        of 0.2~0.5mm between cranks are ensured.
                              SMALL END GUIDANCE (UPPER GUIDANCE)
                              The small end of the connecting rod and the needle bearings are mounted between the piston and the pin and are guided by piston body.
                       To reduce the axle gap ,  two hardened washers are added onto the end surface of the small end bearings to limit the axial movement of  the 
                        connecting small end.

Figure1

Radical gap

          
          The radical gap should be selected as per the engine type and the operational conditions. The speed , 
        load , lubrication, temperature , the material and machining precision of the engine must be specially
        noticed. The selection of smaller gap can be used to increase the efficiency of the engine but all the
        parts must be guaranteed by the matched precision. Or the bearing might be burnt. Suitable radical gap
        should take experience and the test values.

Recommended radical gap

Small end ： 0.002 _ 0.012mm

Double stroke big end ： 0.015 _ 0.030mm

4 stroke ： 0.007 _ 0.024mm (for high speed, 20-35% can be increased)