With the shortage of petroleum resources and the increasing environmental pollution, countries began to tighten their fuel consumption and emission standards. Therefore, more energy-efficient and environmentally-friendly vehicles began to be favored by people. For an internal combustion engine with a history of more than 100 years, if you want to continue to maintain its vitality, you must make a breakthrough in energy saving and emission reduction technology.
From the perspective of technological innovations in the engine field by OEMs and component suppliers, miniaturized engines have long been the focus of chasing. Relatively speaking, smaller, more power-intensive engines can reduce friction losses and improve vehicle fuel economy. In addition, small-displacement engines of 1.6L and below in China can also enjoy preferential policies for halving the purchase tax.
What is the miniaturization of the engine?
Miniaturization of the engine reduces exhaust emissions and greenhouse gas emissions while improving fuel efficiency by reducing engine displacement or reducing the number of cylinders. Global emissions regulations and ever-increasing fuel economy standards are driving the development of traditional engines toward miniaturization. Currently, this technology is widely used in light gasoline engines by OEMs. Test data shows that engine miniaturization can increase fuel efficiency by 20% to 30%.
However, in the case of reducing fuel consumption and emissions, how can a miniaturized engine ensure that its dynamic performance is not impaired during actual driving? Previously, Gasgo has conducted an industry survey on the miniaturization of the engine. "The engine miniaturization trend shows that the dynamic performance is a market pain point." The results show that the industry's biggest question about engine miniaturization is whether its power performance is strong enough, which is the root cause of the impact of miniaturized engines in the end market. Regarding the factors restricting the performance of the engine miniaturization market, Geshi Automobile will explain in depth in the later expert interviews, and this article will not go into too many details.
Engine miniaturization related technology
Smaller engines with fewer cylinders are possible, and are inseparable from key component technologies such as turbocharging technology, gasoline direct injection technology, and variable valve timing. The following is a brief analysis of the working principle of these technologies, and analyze the advantages and disadvantages of each technology.
Turbocharging technology
The turbocharger (Turbocharger) uses the exhaust gas emitted by the engine to impact the turbine to compress the intake air, thereby improving the engine's power and fuel efficiency.
As we all know, the fuel needs to be ignited in the engine. The more oxygen, the more complete the combustion, the better the engine works. Turbocharging is a form of intake air for automobile engines. Its main function is to compress air and increase the intake air volume of the engine, thereby increasing the power and torque of the engine and making the car more powerful. At the same time, fuel combustion is more sufficient, fuel economy is improved and exhaust emissions are reduced.
When a turbocharger is installed in an engine, its maximum power can be increased by 40% or more compared to when the turbocharger is not installed. This means that the same engine can generate more power after being pressurized. Take our most common 1.8T turbocharged engine, after boosting, the power can reach the level of 2.4L naturally aspirated engine, but the fuel consumption is slightly higher than the 1.8L naturally aspirated engine.
Advantage:
1, have a good acceleration and sustainability, full of stamina. The maximum torque output has a wide range of speeds and a straight torque curve.
2. Improve fuel economy and reduce exhaust emissions.
3. Use the energy of the exhaust gas without consuming the power of the engine.
Disadvantages:
1. Ride comfort needs to be improved. At low speed, the turbine cannot be intervened in time, and there is a certain lag. Turbo hysteresis and non-linear power output are the biggest drawbacks of turbocharging.
2. The overall system temperature is increased and additional high heat effects need to be addressed. In order to solve the high heat impact, it is necessary to use a high temperature and oxidation resistant cooling and lubricating medium, and a cooler.
3. The maintenance cost is higher in the later period.
Therefore, when using a turbocharged engine, it is necessary to focus on the selection of engine oil and the oil change interval. The key bearings in the turbocharger need to be lubricated with engine oil and cooled with engine coolant. Most designs allow the engine coolant pump to continue working for a few minutes after a warm stop to cool the turbine cover. Since the turbine is driven by engine exhaust, the turbine cover may become red hot. In addition, since the oil has its established flow path, the oil is drained through these channels when the engine is turned off. Without proper cooling and emptying, the engine oil on the bearings burns (coking), turns into tar, and blocks the flow path of the oil, causing a catastrophic failure of the turbine.
Gasoline cylinder direct injection technology
Direct injection in the cylinder, as the name suggests, is the technology of directly injecting fuel into the cylinder and mixing with the air. Different from the traditional manifold injection, the direct injection in the cylinder further increases the injection pressure, making the fuel atomization more detailed, realizing the precise proportional control of the injection and mixing with the intake air, while eliminating the out-of-cylinder injection. Disadvantages. When the engine is low-speed and low-load, the injection is delayed, and the piston is injected at the final stage of the compression stroke. The air vortex is used to concentrate the fuel near the spark plug, and the stratified combustion achieves the purpose of fuel saving, but when the engine speed is up, the load is up. It is still necessary to inject in advance, and the fuel is injected into the intake stroke to uniformly mix and burn the oil and gas.
In addition, the special design of the nozzle position, spray shape, intake air flow control, and piston crown shape enables the oil and gas to be fully and uniformly mixed throughout the cylinder, so that the fuel is fully combusted and the energy conversion efficiency is higher. Compared to conventional PFI (port fuel injection) engines, GDI engine fuel consumption can be reduced by 20% to 50%.
Advantage:
1. Fuel combustion is more complete and energy conversion efficiency is higher.
2. More precise control of engine intake and injection timing to promote energy saving and environmental protection.
3. The transient response of the direct injection in the cylinder is fast and the startup is faster.
Disadvantages:
1. The combustion chamber is in an oxygen-rich environment and is prone to nitrogen oxides.
2, the combustion temperature is low, the three-way catalytic converter can not reach a good working temperature, the conversion of harmful media is not complete.
3. For the poor adaptability of oil, the sulfur in gasoline will poison the nitrogen oxide catalytic device.
Variable valve timing technology
The engine variable valve timing technology "VVT" (Variable Valve Timing), commonly known as "variable valve timing". The working principle is to adjust the amount of intake and exhaust according to the running condition of the engine, control the time and angle of valve opening and closing, so as to optimize the amount of air entering, thereby improving combustion efficiency.
Generally speaking, the four-stroke gasoline engine is divided into four steps of inhaling, compressing, working, and exhausting. Because the engine is running at a high speed, a working stroke of a four-stroke engine takes only a few thousandths of a second. The time often causes the engine to have insufficient intake air and the exhaust gas is not clean, resulting in a drop in power. Therefore, it is necessary to utilize the intake inertia of the airflow, and the valve should be opened early and closed at night to meet the requirements of sufficient intake and clean exhaust.
In the case of taking into account the torque characteristics of the engine in the low speed zone and the power characteristics of the high speed zone, a device that adjusts the valve lift, namely the "variable valve timing technology", emerges. This technology can guarantee low speed and high torque, and can achieve high speed and high power, which is a great breakthrough for the engine. Almost every company today has its own variable valve timing technology, such as VVT-i developed by Toyota, Variocam developed by Porsche, DVVT developed by Hyundai... A series of variable valve technologies have different trade names, but they have different names. The design idea is very similar.
Advantage:
By controlling the valve distribution and changing the opening and closing time of the intake valve, the intake charge can be increased, and the torque and power of the engine can be further improved.
Disadvantages:
1. The mid-speed torque is insufficient.
2. Due to the intervention of multiple rocker arms and cam mechanism, the engine runs loudly.
3. The cost of maintenance and use has also increased significantly.
Variable displacement technology
The variable displacement technology, also known as the cylinder dormancy technology, refers to when the engine is operating in a small load state, a part of the cylinder is stopped (sleep) through a series of "means", and the remaining cylinders work normally, and the technology can 6-cylinder combustion intelligently switches to 3-cylinder combustion, achieving the dual functions of saving fuel and reducing emissions; when the acceleration or climbing requires more power, the variable displacement technology will start all cylinders and quickly increase the engine's power output energy. .
To make the cylinder dormant (not working), the mainstream way of many manufacturers is to cut off oil and cut off gas. For current EFI engines, "off oil" is relatively simple because the fuel nozzle is actually a solenoid valve. When the solenoid valve is energized, it will spray oil. If it is not energized, it will not spray oil. "Break gas" is relatively complicated. Because the intake and exhaust valves of the engine are the only way for gas to enter and exit the cylinder. Therefore, as long as the intake and exhaust valves are not opened, "off gas" can be achieved.
At present, various manufacturers have their own methods. For example, Honda's method is to break the linkage between the rocker arm and the camshaft by moving the plug, so that the rocker arm no longer pushes in and out of the exhaust valve to achieve "breaking gas".
Advantage:
Low fuel consumption, saving oil, it is obvious for small-displacement economy cars
Disadvantages:
1. The cost of car purchase and car use increases, and the cylinder dormancy technology uses a more complex engine mechanical structure and a matching control strategy, which will definitely bring about an increase in the cost of the entire vehicle, which will inevitably be passed on to consumers. .
2. Complex technology brings the possibility of failure and increases maintenance costs.
Automatic start-stop technology
The engine automatic start-stop technology refers to the automatic flameout when the vehicle is temporarily parked during driving (for example, waiting for a red light). When it is necessary to move on, the system automatically restarts the engine's system. Its core technology is automatic control of flameout and start-up. This technology can effectively reduce the idle time of the engine idle, which can reduce emissions and improve fuel economy in the city's stop-and-go traffic conditions.
The start-stop function of the intelligent stop-and-stop "stop-start" system is automatically turned on by default when the key is energized. When the vehicle speed drops below the limit, in the neutral state and the clutch pedal is completely released, the automatic stop system will be turned on. When the engine is successfully started, if the driver does not have any pedal and gear operation within a certain period of time, the system will assume that the driver has no intention to start, and the engine will automatically stop. At this time, the compressor also stops working. When the brake pedal is released to continue, the engine starts automatically.
Advantage:
Save fuel and save money.
Disadvantages:
1. If the traffic jam time is long, long-term stop and stop will inevitably increase the burden on the starter.
2. The start-stop logic of some models is not very good, and the intervention time is not accurate.
3. The noise and vibration are large at startup.
The original intention of the engine automatic start-stop technology is to save energy and environmental protection. In the theoretical environment, it can indeed achieve this goal. However, if combined with the road conditions in China - the traffic jam time is long, long-term stop and stop will inevitably increase the burden on the starter. Therefore, in the case of long-term congestion, it is best to turn off the automatic start-stop function, which is more conducive to extending the life of the starter and battery.
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