SyTech Engine: Exploring Scotch Yoke Mechanism in Automobiles
Hybrid vehicles are automobiles that combine IC engines with electric propulsion systems. These vehicles represent a solution to the need for more environmentally friendly modes of transportation. Hybrid vehicles offer a promising alternative by reducing the overall carbon footprint. The slider-crank mechanism, integral to traditional internal combustion engines, has been the driving force behind the automotive industry for more than a century. However, the imperative for hybrid vehicles arises from the need to address environmental concerns, minimize fuel consumption, and lower emissions. We aim to uncover hybrid vehicles’ potential to revolutionize the automotive industry, offering a more sustainable and efficient path forward while challenging established paradigms in the process.
Few companies are pioneering the development of alternatives to the conventional mechanism. Their primary objective is to address the myriad challenges associated with the existing mechanism. In addition, their innovation efforts revolve around the reduction in engine size, which consequently yields a more compact and lightweight design. This enables various different enhancements such as noise reduction, engine efficiency, vibration mitigation, and a significant reduction in exhaust emissions.
SYTECH Powertrain Technologies Co., Ltd is committed to advancing New Energy technologies. In collaboration with FEV Germany, SYTECH has introduced a ground-breaking range of ICEs designed to run on various fuel sources, including Gasoline, LPG, CNG, and Hydrogen. These engines feature a modular design, encompassing a spectrum of engine displacements and power outputs, ranging from 30kW to 250kW. Notably, this innovative engine technology has been conceived and engineered by a team of Australian professionals, with support from FEV Germany, who have played a pivotal role in its development. This design incorporates a Scotch Yoke Mechanism as a key component in the construction of the engine. Within this mechanism, two pistons are connected through a singular connecting rod, positioned in an opposing horizontal orientation. As outlined by the company, the engine is available in three distinct configurations, featuring 2 cylinders, 4 cylinders, and 8 cylinders.
The innovative design leads to a family of SYTECH engines based on the commonality of modules from:
● 2-cylinder, 0.8L, 30/55kW
● 4-cylinder, 1.5L, 65/110kW
● 8-cylinder, 3.0L, 130/250kW
The configuration of the SyTech engine design involves the synchronized movement of two pistons and two connecting rods along the cylinder axis, generating a precise sinusoidal motion pattern. This motion eliminates the occurrence of higher-order inertia forces that are commonly associated with traditional crankshaft arrangements. A pivotal element within this design is the bearing block, which moves vertically between the parallel surfaces of the connecting rods and rotates relative to the crankcase, following a circular path around the crankshaft axis. To counterbalance the centrifugal forces arising from the mass of the bearing block, counterweights are incorporated into the crankshaft.
Notably, the connecting rods in this design do not engage in any vertical motion concerning the cylinder axis. This characteristic permits them to be designed with shorter lengths without the typical adverse effects, such as increased piston noise, heightened cylinder wear, elevated piston friction, and amplified engine vibrations commonly observed in engines featuring shorter conrods. Furthermore, the SyTech engine achieves a compact engine height and a low centre of gravity without incurring the significant increase in engine width like the conventional engines.
The applications of SyTech technology yields several notable advantages for the vehicle, some of them being,
1. Engine Size and Weight:
The SyTech design features two cylinders in direct opposition, devoid of any offset. This arrangement permits the development of exceptionally short connecting rods, which can be reduced by 30% in equivalent length. Consequently, the engine block’s height is more than 20% smaller compared to conventional “Boxer” engines. The dry weight of the engine stands at a mere 75 kg, which starkly contrasts with the typical weight of 1.4-liter four-cylinder engines, underscoring its remarkable lightweight design.
2. Noise and Vibration:
In serial hybrid systems, the engine functions autonomously in response to energy storage levels and traction motor requirements. This automated engine cycling, while efficient, can introduce disturbances when engine activation leads to abrupt increases in noise and vibration. Notably, SyTech engines distinguish themselves with significantly lower Noise, Vibration, and Harshness (NVH) levels in comparison to conventional engines. The notable reduction in both vibration and noise emissions can be attributed to three primary factors:
Firstly, SyTech engines achieve a state of balance, facilitated by the sinusoidal motion of the pistons. This motion eliminates the presence of higher-order inertia forces, yielding reduced vibrations.
Secondly, the first-order inertia reaction moments in all SyTech engines are balanced by a singular balance shaft, which exclusively operates at engine speed. This contributes to the mitigation of vibrations and noise, enhancing the overall driving experience and comfort within serial hybrid vehicle applications.
In a high-volume production vehicle of a German car manufacturer, a 2.2-liter SyTech engine was found to show the lowest cabin noise levels of all tested competitor vehicles at wide-open throttle accelerations.
3. Fuel Efficiency:
The sinusoidal motion of the pistons within the SyTech engine exerts a discernible influence on the combustion dynamics of the air/fuel mixture. The extended dwell time experienced around the top dead center, coupled with the disparities in the rates of cylinder volume change, yields notable distinctions in fuel efficiency and exhaust emissions when comparing conventional engines to the SyTech design. Remarkably, these variations persist even when the initial conditions for combustion, such as the quantities of fuel and air confined within the cylinder, remain identical.
4. Exhaust Emissions:
When optimized for peak performance, the ideal spark timing for an engine featuring sinusoidal piston motion typically averages approximately 4 degrees later than the optimal timing required for a conventional engine. In both engine variants, whether SyTech or conventional, the application of this delayed spark timing reduces NOx emissions while elevating the specific fuel consumption. However, the relationship between these parameters is intricate, and influenced by numerous factors.
A series of test results conducted on a SyTech engine in comparison to a conventional counterpart offer insights into the anticipated outcomes. When focused on fuel efficiency rather than low NOx emissions, the fuel consumption reduces to 6% in 2.2L engines.
5. Engine Applications:
The versatility of a SyTech crank mechanism extends to all piston engines characterized by reciprocating piston motion. Notably, both Diesel and Spark Ignition (S.I.) engines have been successfully constructed and rigorously tested, spanning across the domains of 2-stroke and 4-stroke engines. This adaptability offers a host of compelling advantages, encompassing reductions in weight, size, noise, and vibration. These advantages render SyTech technology particularly well-suited for a wide array of applications, including automotive, motorbike, small aircraft, and sports boat engine configurations, as well as in the realms of mobile compressor and power generator systems.
In a hybrid vehicle, SyTech Engine can be placed in any of the configurations, as shown in the figure:
The CMC SyTech Engine in the new aXcessaustralia Hybrid Car. The ‘aXcessaustralia II,’ an Australian concept car, is an example of the “New Generation Hybrids” in HEVs. Designed as a medium-sized, four-door family car with front-wheel drive, it integrates an essential power system at the core of its architecture. The heart of the ‘aXcessaustralia II’ is an ESU (Electrical Storage Unit) mounted in the rear of the vehicle, consisting of a 4-cylinder Spark Ignition (S.I.) engine with a 1.4-liter displacement.
The internal combustion engine takes on the role of driving an electrical power generator. The wheels, in turn, are exclusively propelled by an electric traction motor, which sources its energy from a dynamic combination of batteries, capacitors, and the aforementioned electrical power generator.
Within this drive train, comprising a combustion engine, generator, traction motor, dual systems for electrical energy storage, and the electronic controls for optimizing fuel efficiency, every component is subject to weight optimization. This approach ensures that the fuel savings achieved through the system are not offset by increased overall vehicle weight. Additionally, a premium is placed on the individual efficiency of each component.
One notable feature is the role of the petrol engine in this serial hybrid system, which serves as a generator and doubles as the starter motor for the combustion engine. This innovative configuration results in remarkably low noise levels during frequent engine starts. The electrical power generated by the generator is channelled to the electric traction motor, and any surplus energy is stored in electric storage units that encompass a combination of batteries and capacitors. These storage units also receive electrical energy derived from recuperated brake energy. The interplay between the energy storage levels in the batteries and capacitors, the driver’s input, and the prevailing road conditions is finely orchestrated by a sophisticated energy management algorithm, which governs the operation of the combustion engine, ensuring a harmonious and efficient power strategy.
Usually, there are only three different operating conditions for which the engine has to be optimized in a Serial Hybrid System.
(1) Starting the Engine: In the case of the aXcessaustralia hybrid vehicle, a distinct methodology is applied during engine activation. The generator/motor is engineered to rapidly accelerate the crankshaft to a significantly higher speed before initiating the first fuel injection sequence. This higher initial starting speed ensures that the first firing cycle, following the introduction of fuel, achieves complete combustion. The stored energy in the inertia of the rotating components plays a pivotal role in overcoming the next cycle of negative torque, which typically occurs during the compression stroke of the subsequent cylinder. Consequently, this rapid sequence of events ensures that the engine promptly transitions into normal operation. Once the engine/generator speed surpasses a predefined threshold, the control algorithm seamlessly shifts from motor to generator operation. This transition serves to further increase engine speed, ultimately leading to the generation of electrical power.
(2) Normal Engine Operation: In the aXcessaustralia hybrid car, the engine, once initiated, is controlled to operate within a speed range spanning from 1,800 to 3,300 rpm. The electrical power generated by the engine is distributed to the traction motor, the batteries, and the storage capacitors. It’s noteworthy that while the capacitors have the capacity to be charged with a substantially higher current, their energy storage capacity is limited. This develops the energy management strategy of the vehicle.
(3) Sustained High Power Requirement: In HEVs, the battery storage capacity falls short of the capacity found in electric-only vehicles. This reduces vehicle costs and overall weight. This arrangement poses limitations during extended, high-load journeys, such as extended uphill drives with a heavy vehicle. Here, the combustion engine must directly provide the traction motor with a high-power output, surpassing the levels attainable during normal operation at lower engine speeds. Under these conditions, the engine operates at 5,000 rpm, generating an output torque of approximately 95 Nm, equivalent to 50 kW of power. As long as the generated power exceeds the demands to overcome driving resistances and meet the maximum battery charging current, the vehicle operates in this mode. However, as soon as the capacitor storage units reach full charge, the operational mode transitions back to normal operation within the lower speed range. This return to normal engine operation ensures the vehicle’s efficient and balanced performance.
Finally, the new SyTech engine is well-suited to Range Extended Vehicles and uses many common parts across the family of engines to reduce part, tooling and manufacturing costs, and assembly tooling. The SYTECH engine has very good NVH with no 1st order vibration. Due to its dimensions, the SYTECH engine can be fitted to vehicles in many positions The SYTECH engine performs better than many of its competitors, and with the addition of VVT, EGR, and other technologies, the SYTECH engine performance can be further improved.
References:
1. Karan C. Prajapati, Ravi Patel, Rachit Sagar, “Hybrid Vehicle: A Study on Technology” International Journal of Engineering Research & Technology (IJERT) Vol. 3 Issue 12, December-2014.
2. Muhammad Yousaf Iqbal, Tie Wang, Guoxing Li, Dongdong Chen, Mohammad Al-Nehari, “A Study of Advanced Efficient Hybrid Electric Vehicles, Electric Propulsion and Energy Source” Journal of Power and Energy Engineering, 2022.
3. Rogelio León, Christian Montaleza, José Luis Maldonado, Marcos Tostado-Véliz, Francisco Jurado, “Hybrid Electric Vehicles: A Review of Existing Configurations and Thermodynamic Cycles” Thermo, MDPI 2021.
4. M. Yaich, M. R. Hachicha and M. Ghariani, "Modeling and simulation of electric and hybrid vehicles for recreational vehicle," 2015 16th International Conference on Sciences and Techniques of Automatic Control and Computer Engineering (STA), Monastir, Tunisia, 2015.
5. M. T. Al-Atabi and T. F. Yusaf, "Experimental investigation of a single cylinder diesel engine as a hybrid power unit for a series hybrid electric vehicle," Student Conference on Research and Development, Shah Alam, Malaysia, 2022.
6. Richard Tamba, “USING THE SYTECH ENGINE IN Range Extended Electric Vehicles; Performance, Simulation and Durability” 31st Aachen Colloquium Sustainable Mobility, October 2022.
7. ASF Group, “Technology - ASF Group”, ASF Group ltd., https://www.asfgroupltd.com/technology/
