## 3 Engine Modifications and Mechanism Design  
### Engine Modifications  
Cylinder balancing is a well-established technique for reducing torsional vibrations arising from unbalanced cylinders in common-rail engines and attenuating transmitted disturbances to the vehicle's passengers. In this approach, cylinder fuel injectors are controlled electrically to adjust the injection durations and timings, by stabilizing the dynamic loads and providing a uniform mechanical strain distribution in engine components, such as the crankshaft through time- and frequency-domain analyses [4]. Time-domain balancing method is more demanding in the automotive industry [5; 6] as it only requires measurement of the speed at the flywheel and taking the numerical integration of the estimate torques applied to it. On the other hand, in frequency-domain methods, the ultimate goal is to directly reduce the harmful vibration frequency components through computationally -efficient calculations, such as DFT-based control of cylinder injections [7] and artificial neural networks for pattern-recognition of crankshaft angular speed waveforms [8]. [PERSON] et al. [9] applied time- and frequency-domain power balancing algorithms to adjust the fuel-injection and reduce power unbalance of a 7-cylinder diesel engine-generator, with a flexible crankshaft, through speed measurements at 750 rpm. The proposed approach was able to balance the estimated powers via reconstructing the produced torque at the flywheel in four iterations and tuning the fuel injection durations without affecting the total power of the engine. The outcome was an 82% reduction in undesirable torsional vibrations induced by power unbalances. Figure 1 illustrates an excellent consistency between the simulation and full-scale test results on the engine, using their power balancing algorithm. Engine mounting system plays an inevitable role in isolating the driver and passenger from the noise, vibration, and harshness (NVH), produced by power-intensive engines in modern lightweight vehicles [10; 11]. An ideal engine mount should feature (i) high stiffness and excellent damping capability to isolate the frequency-dependent disturbances excited by powertrains and road vibrations; (ii) support static powertrain weight and dynamic engine torque; and (iii) hinder engine bounce from shock excitation [12; 13]. Therefore, the performance and reliability of these systems require further improvements for a better NVH refinement. Engine mounting transmission ratio (EMTR), or transmissibility, which is defined as the ratio of the vibration generated at the engine to the one that is transmitted through the mounting system to the body of the vehicle, is a useful metric for expressing isolation efficiency of the engine mounts at a specific frequency or speed [14]. While many statistical tools have been developed to detect and analyze different physical and natural phenomena [15; 16; 17; 18], a well-established measure in vibration diagnosis and analysis is the power content (root mean square or RMS) value of the measured vibration signal [19; 20; 21]. [PERSON] et al. [14] performed time- and frequency-domain analyses on a 4-cylinder engine, running at 800-4000 rpm, to evaluate the vibration isolation and transmissibility of three rubber engine mountings (REM), including cylindrical (A), cone-and-shear (B), and center-bonded mounts (C). They concluded that a cone-and-shear system offers the minimum RMS of vibration accelerations (Figure 2) and optimum transmission ratio when it is mounted on the engine and chassis (Figure 3). A further enhancement was achieved by adding a concentrated mass (steel block) of \(\sim\)1.5 kg, to the location of the rubber cone-and-shear engine mount, on the chassis. In that way, the spike acceleration of the chassis dropped more than two times, when the engine was operating at 1600 rpm. This modification also improved the transmission ratio of the mount, from 14% at 800 rpm, up to 19% at 4000 rpm (Figure 4).