Figure 1 depicts the principle layout of a 4-bar linkage which can be used to move a piston of an engine along a straight line. Point 4 in this figure is uch a point which moves almost exactly along a straight vertical line by an amount equal to the Stroke provided that the other parameters are chosen correctly. A straight-line motion is highly desirable to minimize the lateral forces acting on the piston which in turn minimizes friction and wear and tear of the piston. Ratios of vertical to lateral extent of the motion of the connecting point 4 of over a hundred can easily be realized.
To give you a feeling for the range of curves (orbits) point 4 moves on as the crank ( center at point 0 ) rotates once around click on the following links : oval , ovals with cusps , ovals with "ears" , leaning double-8 , double-8 with vanishing waist , and perfect double-8 orbit.
Program 4bar can do one of two things for you by filling out the boxes either on the left or right below. On the left side - labeled "Find an optimal Configuration ...." - you provide the smallest amount of information the program needs to determine the remaining parameters. On the right hand side - labeled "Or enter your values ...." - the program will determine the orbit of point 4 for your configuration.
Sample Input for Optimization :
Desired stroke 10 ratio e/a 0.4 x4_diff 0.1Result from program :
r 0-1 4.188803 a 18.689442 b 11.822348 c 2-3 18.925111 d 1-3 12.010892 e 4-5 7.475779 f 3-5 0.075418 Vbox 16.930246 Hbox* 25.934334 Stroke 10.000000Nobody can machine the various parts exactly to the demanded dimensions. But you can check now what happens if you round the above numbers and re-enter them as your configuration :
r 0-1 4.200000 a 18.700000 b 11.800000 c 2-3 18.900000 d 1-3 12.000000 e 4-5 7.500000 f 3-5 0.100000The program gives you back the following information :
Vbox 16.979104 Hbox* 25.928940 Stroke 10.028491 x4_diff 0.124848and you have to judge whether you can live with that.