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The reciprocating piston petrol engine
Published in M.J. Nunney, Light and Heavy Vehicle Technology, 2007
However, it also seems to follow that a harmonic balancer would be unnecessary if only we could go out and buy ourselves a set of infinitely long connecting rods! Since the notion of infinitely long connecting rods may seem rather obscure to the motor vehicle service engineer, let us now try to understand its significance in simple terms. Referring to Figure 1.79a it will be seen that instead of using a conventional hinged connecting rod between the piston and crank, we have substituted a crank and slotted-bar or ‘Scotch yoke’ mechanism, which was sometimes employed in early steam and pumping engines. Comparing this arrangement with the conventional one shown in Figure 1.79b, it will be noticed that there is no inequality of piston travel towards the dead centres for corresponding angular movements of the crank. In fact by conferring a straight-line, instead of a swinging, motion on the connecting rod we have arrived at the practical equivalent of an infinitely long connecting rod. As a result the piston acquires a simple, as opposed to non-simple, harmonic motion. That is, it now oscillates about its equilibrium or mid-stroke position in such a way that its acceleration (positive or negative) towards this position is directly proportional to its displacement therefrom. So in the case of our in-line four-cylinder engine, the common centre of gravity of the four pistons would remain stationary and there would be no unbalanced secondary inertia forces.
Prototyping of automated systems
Published in Fuewen Frank Liou, Rapid Prototyping and Engineering Applications, 2019
Reciprocating motion can be converted into linear motion by pistons as shown in Figure 8.53, oscillation by linkages in Figures 8.54 and 8.55, and intermittent motion by ratchets as shown in Figure 8.69. This piston is used to convert rotary motion into reciprocating motion and vice versa. Notice how the speed of the piston changes. The piston starts from one end and increases its speed. It reaches maximum speed in the middle of its travel and then gradually slows down until it reaches the end of its travel. The oscillation mechanism and the Scotch yoke mechanism function like the piston or crank–slider mechanism.
Control Valves
Published in Don Renner, Hands-On Water/Wastewater Equipment Maintenance, 2017
2.138 Other styles of cylinders use piston rods that are more controlled and travel in only a straight line (Figure 2.29). The straight line motion is converted to rotary motion through the use of a pivoting arm or a scotch yoke (slotted arm) connecting mechanism. When a scotch yoke is used, the piston rod is usually extended past the valve stem into or through the opposite side of the actuator housing for support.
Optimum design and analysis of a novel planar eight-bar linkage mechanism
Published in Mechanics Based Design of Structures and Machines, 2023
Recep Halicioglu, Assylbek Jomartov, Moldir Kuatova
Another alternative to press manufacturing has been the development of different mechanisms to achieve the desired motion gain. These mechanisms have been also driven by a servo motor for flexibility. Soong (2014) developed two types of 1DOF seven-bar geared linkage mechanisms consisted of a slider-crank mechanism or scotch yoke mechanism. In his study, one input cycle was corresponding to two output cycles. Disadvantages of the scotch yoke are the rapid wear of the slot in the yoke and sinusoidal slider motion having a higher forming acceleration. Pennock and Israr (2009) carried out a kinematic analysis and a kinematic synthesis of an adjustable six-bar linkage proposed as a variable-speed transmission mechanism. They tried an angular dwell without slider. He et al. (2010) introduced a turret punch press with an eccentric-toggle mechanism driven by a servomotor for a dwell motion. But a sinusoidal slider motion was obtained without a servo motor. Bai, Gao, and Guo (2011) proposed a design method based on the combination of the dual screw actuation unit, the parallel mechanism with kinematic redundancy, and the toggle mechanism with the symmetric arrangement where screws were driven by multi-servomotors. Losses are likely to be high due to the screw drive and the complexity of the toggle mechanism. Also, lower speed capacity can be considered as a disadvantage of the screw actuations in presses. Halicioglu, Dulger, and Bozdana (2014) conducted a study on the kinematics of a slider-crank mechanism by using Matlab/Simulink platform. They showed that it was possible to extend motion scenarios for the slider with servo inputs. Jomartov et al. studied on the implementation of the four-class kinematic chain to synthesize the crank press mechanism (Jomartov and Tuleshov 2018, 2019; Jomartov et al. 2019; Tuleshov, Jomartov, and Kuatova 2019). Liu et al. (2019) proposed a synthesis strategy for four-bar, six-bar, and eight-bar linkages for a rectilinear movement task and compared the resulting performances of the designs. There are different types of linkage mechanisms in the literature, and they have some disadvantages, such as inability to produce long dwell motion without servo motor or increase in complexity and losses. In addition, since force is transmitted to the slider from a single point in most mechanisms, the unbalanced slider and nonuniformly distributed force affect the forming precision and quality.