3D Crank Slider, with 4 revolute joints (hinges), one slider, a universal and a ball joint. The SW model details how they are defined.

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SW design tree

CSmotion IntelliMotion builder, (there is also a browser)

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Interference checking is very cpu intensive so the parts and the intervals are identified to improve response time

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Valve, rocker and cam assembly.The moments, forces and torques are indicated as the motion takes place. The spring parameters have to be defined specifically as stiffness and preload, they are not derived from physical dimensions of the spring. The model of the spring shown may be defined but is just decorative.

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Contact_camshaft-1_rocker-1Time(sec) Normal Force Friction Force(newton)

X Y Z Magnitude X Y Z Magnitude0 97.7089 -8.20E-13 -4566.17 4567.215 -228.308 2.95E-14 -4.88544 228.3607

0.0003 99.09613 -9.37E-13 -4530.41 4531.493 -226.52 4.42E-14 -4.95481 226.57470.0006 99.82533 -5.79E-13 -4504.38 4505.488 -225.219 4.33E-14 -4.99127 225.27440.0009 100.3737 -1.19E-12 -4482.74 4483.866 -224.137 4.36E-14 -5.01869 224.19330.0012 100.7007 -7.62E-13 -4460.78 4461.919 -223.039 4.29E-14 -5.03503 223.0960.0015 100.8917 -1.16E-12 -4439.61 4440.761 -221.981 4.29E-14 -5.04459 222.0380.0018 100.9896 -1.18E-12 -4419.73 4420.888 -220.987 4.26E-14 -5.04948 221.04440.0021 101.0193 -5.64E-13 -4401.31 4402.465 -220.065 4.20E-14 -5.05097 220.12320.0024 100.9983 -1.19E-12 -4384.33 4385.489 -219.216 4.20E-14 -5.04992 219.27440.0027 100.9389 -2.75E-13 -4368.68 4369.846 -218.434 4.15E-14 -5.04695 218.49230.003 100.8503 -1.50E-12 -4354.23 4355.393 -217.711 4.16E-14 -5.04251 217.7697

0.0033 100.7418 -1.47E-12 -4340.85 4342.02 -217.043 4.13E-14 -5.03709 217.1010.0036 100.6145 -7.95E-13 -4328.4 4329.569 -216.42 4.10E-14 -5.03072 216.47850.0039 100.4776 -5.04E-13 -4316.84 4318.006 -215.842 4.07E-14 -5.02388 215.90030.0042 100.3348 -7.46E-13 -4306.09 4307.263 -215.305 4.06E-14 -5.01674 215.36310.0045 100.1898 -9.52E-13 -4296.14 4297.303 -214.807 4.04E-14 -5.00949 214.86520.0048 100.0461 -7.97E-13 -4286.94 4288.105 -214.347 4.02E-14 -5.0023 214.40520.0051 99.90633 -7.92E-13 -4278.49 4279.655 -213.924 4.00E-14 -4.99532 213.98270.0054 99.77302 2.21E-13 -4270.78 4271.947 -213.539 3.98E-14 -4.98865 213.59740.0057 99.64817 1.24E-12 -4263.82 4264.981 -213.191 3.96E-14 -4.98241 213.24910.006 99.53352 -5.13E-13 -4257.6 4258.759 -212.88 3.95E-14 -4.97668 212.9379

0.0063 99.43051 -4.32E-13 -4252.12 4253.283 -212.606 3.94E-14 -4.97153 212.66420.0066 99.34033 4.50E-14 -4247.4 4248.559 -212.37 3.92E-14 -4.96702 212.42790.0069 99.26546 -6.42E-15 -4243.52 4244.68 -212.176 3.91E-14 -4.96327 212.2340.0072 99.15446 -7.37E-13 -4240.23 4241.388 -212.011 3.90E-14 -4.95772 212.06940.0075 99.13128 8.61E-13 -4238.86 4240.018 -211.943 3.88E-14 -4.95656 212.00090.0078 99.1766 4.16E-14 -4240.47 4241.632 -212.024 3.87E-14 -4.95883 212.08160.0081 99.24509 2.95E-13 -4243.11 4244.269 -212.155 3.87E-14 -4.96225 212.21340.0084 99.33023 -5.58E-13 -4246.48 4247.641 -212.324 3.86E-14 -4.96651 212.38210.0087 99.13779 -5.63E-13 -4237.04 4238.198 -211.852 3.84E-14 -4.95689 211.90990.009 99.24525 2.18E-13 -4240.36 4241.519 -212.018 3.83E-14 -4.96226 212.076

0.0093 99.38844 6.97E-13 -4246.27 4247.428 -212.313 3.83E-14 -4.96942 212.37140.0096 96.31969 2.59E-13 -4299.95 4301.033 -214.998 3.86E-14 -4.81598 215.05170.0099 48.50443 1.98E-13 -4324.26 4324.531 -216.213 3.89E-14 -2.42522 216.22660.0102 -67.4103 -2.07E-13 -4321.83 4322.357 -216.092 3.97E-14 3.370517 216.11780.0105 -264.755 -6.65E-13 -4334.1 4342.18 -216.705 4.13E-14 13.23776 217.1090.0108 -535.449 -4.01E-13 -4332.95 4365.904 -216.647 4.31E-14 26.77245 218.29520.0111 -818.372 -1.98E-13 -4354.15 4430.39 -217.707 4.52E-14 40.91859 221.51950.0114 -1118.21 0 -4404.66 4544.386 -220.233 4.75E-14 55.91033 227.21930.0117 -1444.69 -1.67E-14 -4487.65 4714.461 -224.383 5.03E-14 72.23443 235.72310.012 -1809.86 -8.26E-17 -4607.64 4950.352 -230.382 5.34E-14 90.49311 247.5176

0.0123 -2172.85 9.78E-13 -4770.8 5242.309 -238.54 5.65E-14 108.6426 262.11550.0126 -2323.32 1.90E-13 -4970.86 5487.011 -248.543 5.83E-14 116.1661 274.35060.0129 -2265.66 8.17E-13 -5175.66 5649.835 -258.783 5.89E-14 113.2829 282.49170.0132 -2036.31 1.38E-13 -5376.47 5749.175 -268.824 5.83E-14 101.8153 287.45870.0135 -1699.6 1.37E-12 -5562.03 5815.908 -278.101 5.80E-14 84.98 290.79540.0138 -1324.92 1.63E-12 -5711.15 5862.82 -285.558 5.72E-14 66.24588 293.1410.0141 -931.578 9.52E-13 -5816.53 5890.655 -290.826 5.59E-14 46.57888 294.53280.0144 -527.095 9.80E-13 -5881.33 5904.906 -294.067 5.45E-14 26.35474 295.24530.0147 -117.143 1.62E-12 -5910.94 5912.099 -295.547 5.31E-14 5.857147 295.60490.015 284.1474 1.12E-12 -5692.11 5699.201 -284.606 4.95E-14 -14.2074 284.96

0.0153 682.6359 7.24E-14 -5670.5 5711.438 -283.525 4.77E-14 -34.1318 285.57190.0156 1084.283 1.70E-12 -5630.9 5734.342 -281.545 4.61E-14 -54.2141 286.71710.0159 1492.947 3.79E-13 -5576.76 5773.135 -278.838 4.41E-14 -74.6473 288.65670.0162 1911.89 1.50E-12 -5511.95 5834.12 -275.598 4.21E-14 -95.5945 291.7060.0165 2283.125 1.28E-12 -5443.06 5902.506 -272.153 3.99E-14 -114.156 295.12530.0168 2502.036 3.50E-13 -5392.52 5944.702 -269.626 3.84E-14 -125.102 297.23510.0171 2441.965 0 -5371.77 5900.769 -268.588 3.78E-14 -122.098 295.03840.0174 2028.244 -4.43E-13 -5271.17 5647.921 -263.559 3.82E-14 -101.412 282.39610.0177 1608.103 -4.36E-13 -5117.14 5363.872 -255.857 -6.64E-11 -80.4052 268.19360.018 1226.542 -2.72E-13 -4976.43 5125.351 -248.821 -3.15E-12 -61.3271 256.2676

0.0183 877.7092 -5.76E-15 -4855.85 4934.538 -242.793 -3.11E-11 -43.8855 246.72690.0186 556.0637 1.08E-15 -4757.89 4790.277 -237.895 1.88E-10 -27.8032 239.51380.0189 326.5573 1.01E-12 -4689.9 4701.257 -234.495 7.68E-11 -16.3279 235.06280.0192 187.9032 0 -4644.91 4648.705 -232.245 7.16E-11 -9.39516 232.43530.0195 124.1942 2.52E-13 -4707.56 4709.195 -235.378 -1.20E-10 -6.20971 235.4598

An Excel s.s. generated from a csv file provided by Csmotion.

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The displacement of the piston, along the horizontal centre line shown, is the sum of the complete oscillatory movement of the crank pin and the partial oscillatory movement of the big end of the connecting rod. The result is in part higher acceleration at TDC (top dead centre) than at BDC. The force transmitted to the main bearings due to the inertia loads has harmonics, the highest component of which is at twice the engine speed.

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A model of a Mitsubishi engine showing the position of the engine at maximum bending moment in the connecting rod

The highest vertical acceleration at the connecting rod little end is at TDC, the next highest is at BDC. The alternating loads on the big end bolts occur at TDC, accelerating the piston up then down.

The highest lateral acceleration of the big end is shown at left, for an engine of the given dimensions.

The lateral inertia loads on the stem of the connecting rod occur at this point. These may bend the connecting rod.

The compression loads may not be damaging unless the engine fills with oil or liquid fuel.

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A con rod undergoes a number of ‘separable’ motions: it accelerates vertically up & down a). It rotates at variable angular accelerations b) that induce a bending moment in in its stem c). It rotates at variable angular velocities, that result in centripetal forces d).

a)

b)

c)

d)

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Vertical force at the big end with engine running at 8000 rpm

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Max gudgeon pin vertical acceleration against rpm. The horizontal axis is rpm the vertical is m/sec^2

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Bending moment in stem at 8000 rpm assuming stem of uniform section along its length.

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Top right are forked connecting rods for RR Merlins and Griffons.

At lower right the master and articulated con rod assembly for a radial engine

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Con rod assembly and retaining screws for a MB V8 1970s engine

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The connecting rod experiences tension, compression and a bending moments, while swinging from side to side, fortunately not all at the same time.

The loads caused by the combustion process become much smaller than the dynamic loads (F=mass x acc), at a relatively high ~7000 rpm.

Pressure and force due to combustion at higher rpm

14Jeri Svec 2003

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Jeri Svec 2003 UG thesis

simulation of 1300 cc Mitsubishi engine

Stress analysis of connecting rods under static conditions

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Assem Yamak 2013, MeSc thesis

Comparing conrods - while being spun at high rpm, the conrod with bolt holes showed a different stress pattern than the one piece conrod. This provides the first insight as why an H rod may be the better design than I for high revving engines.

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Our drag car conrod, end cap screw, piston and gudgeon pin

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