1, the power head is the power heart of the outboard engine, which is actually a complete internal combustion engine. The crankshaft of the traditional internal combustion engine is arranged horizontally, which outputs power in the horizontal direction, and the crankshaft of the outboard engine is arranged vertically, which is convenient for the downward output of power. In addition to the crankshaft, piston, connecting rod, cylinder liner, cylinder head and cylinder block, the power head also includes a complete valve train (camshaft, ejector pin, air valve, etc.). ), fuel system, cooling system, lubrication system, air intake system and other components, etc.
Power head is the component with the highest cost, the largest technical content and the largest weight and volume in the whole outboard engine. The "much-anticipated" power head is at the top of the outboard, so the fuel outboard looks top-heavy.
2. The gear box is located under the power head, which is responsible for transmitting power to the propeller and providing a reduction ratio. Because the internal combustion engine has too high speed and too low torque, it is not suitable for ship propulsion, so it needs a gear box to reduce the speed and increase the torque. Gear box is mainly composed of transmission shaft, gear and shell. Its main performance indexes are transmission efficiency, water resistance coefficient, reliability and durability. This is very challenging. In order to improve transmission efficiency and reduce water resistance, it is necessary to "slim down", but it will reduce reliability and durability. "Thick material" will increase reliability, but it will reduce transmission efficiency and increase water resistance. Therefore, the key to the problem is how to find a balance between the two.
3, the propeller is actually a propeller, which is also very particular. The most basic index of the propeller is the pitch, which is defined as the distance that the propeller rotates once without slipping. This pitch is essentially the same as the pitch of the screw, that is, when the screw is screwed into the wood, it is screwed once and the distance the screw advances. The greater the pitch, the greater the thrust required by the propeller, and the greater the distance before each turn (it is very difficult to screw up, but it will soon be all screwed in); Small pitch requires small thrust, but the distance per revolution is also short (easy to screw up, but time-consuming).
Usually, for heavy ships, we hope that the outboard engine can provide more torque, larger propeller pitch and higher propulsion efficiency. For a very light ship, the requirement for torque is not so high, the propeller pitch is smaller, the rotation speed is higher and the propulsion efficiency is higher. According to fuel types, there are gasoline outboard, diesel outboard, liquefied petroleum gas outboard and kerosene outboard.
1, gasoline outboard: the mainstream fuel of outboard is gasoline, which has the advantages of wide application, mature technology and wide power range. In combustion technology, it can be divided into two-stroke, four-stroke and two-stroke direct injection. Two-stroke acceleration is good (because the crankshaft does work once per revolution), but the emission is too poor to sell in Europe and America. Four-stroke is relatively environmentally friendly, but two-stroke people are not suitable for its acceleration ability (the crankshaft needs to turn twice to do a job); Two-stroke direct injection hopes to combine the advantages of both, that is, to realize direct injection of gasoline in cylinder on the basis of two-stroke instead of mixing with air through carburetor. Major outboard manufacturers, such as Yamaha and Mercury, all have these three technical capabilities, while Evinrude in the United States pays more attention to the dual-flushing direct injection technology.
2. Diesel outboard: Due to the technical characteristics of diesel engines, diesel outboard cannot be widely used. Even if the high-voltage rail technology is popularized, its compression-ignition working principle is doomed to have greater vibration and noise when working. It is not a problem for the outboard engine installed in the engine room, but it is fatal for the outboard engine hanging on the stern plate. Diesel engine usually has a large torque, and transmitting large torque also brings greater challenges to gearbox. The outboard attraction of diesel comes from diesel. First, it is safer (safer than gasoline); Second, there is no need to provide another (gasoline) tank for transport boats placed on large ships fueled by diesel. Japan Yangma Company is one of the few diesel outboard engine manufacturers.
3. LPG outboard: It was born for only one reason-environmental protection. With the increasing attention to environmental protection in various countries, the gasoline/diesel outboard can no longer meet the environmental protection requirements in many areas or lakes, so the LPG outboard was born. In essence, this is a slight modification of the traditional gasoline outboard engine, just like changing domestic cars into liquefied gas cars. LPG outboard engines occupy a considerable share in the United States, and have also been used in China. However, because they are too easy to volatilize and leak, the security concerns hanging over people's heads can never be shaken off. The most common one in China is the outboard modification of Honda's gasoline.
4. Kerosene outboard engine: There is a huge market in Southeast Asia and South Asia, and low-quality kerosene is used as fuel. Advantages: saving money; Disadvantages: great pollution. The advantages and disadvantages of various fuel outboard engines have been mentioned above, and only the advantages and disadvantages of gasoline outboard engines are emphasized here.
Advantages: 1, easy to install, directly hung on the stern plate, no complicated links such as stern shaft centering. 2, no engine room, saving valuable space in the engine room. 3. It is a complete propulsion system, which simplifies the purchase and procurement process for users and shipyards. 4. Generally, light weight is beneficial to improve the navigation performance of ships, especially high-speed boats.
Disadvantages: 1, due to the limitation of installation mode, lightweight design must be adopted to reduce the weight and greatly reduce the reliability and life of the outboard engine. The service life of general commercial outboard is 2-5 years. 2. Low energy utilization rate, poor fuel economy and high use cost. 3, the structure is complex, there are many moving parts, and a lot of maintenance is needed in the later stage, so the failure rate is high. 4. It is inconvenient to store and transport, and gasoline leakage is inevitable, which not only brings safety problems, but also pollutes the surrounding environment. In many areas of China, the Maritime Safety Administration has banned ships with more than 12 seats from using gasoline outboard engines as power.