What is an I4 in cars?

[ReidDella]

Automotive L4 can have three meanings: it can refer to an inline-four engine; or it can denote high-level autonomous driving, which can achieve full driving without any driver intervention but with certain limitations; or L4 can mean low-range four-wheel drive, where the vehicle uses part-time four-wheel drive with options for high-range and low-range four-wheel drive. Inline-Four Engine: Generally, L4, V6, and W12 refer to the cylinder layout of an engine, which is the most critical factor affecting engine performance. Common layouts include L-type (inline), V-type, VR-type, W-type, horizontally opposed, and rotary. "Inline" can be represented by L, followed by the number of cylinders, forming the engine code. Modern cars mainly feature L3, L4, L5, and L6 engines. L-type (inline) engines refer to inline engines, the most common cylinder layout, where all cylinders are arranged in a straight line. Depending on the number of cylinders, there are L3, L4, L5, and L6, representing three-, four-, five-, and six-cylinder engines, respectively. Since the cylinders are arranged in a straight line, the more cylinders there are, the longer the engine block becomes, so inline engines typically do not exceed six cylinders. Their advantages include compact size, ease of vehicle layout, excellent stability, low-speed torque characteristics, fuel efficiency, and low manufacturing costs. High-Level Autonomous Driving: In the "SAE Levels of Driving Automation" published by SAE (Society of Automotive Engineers), besides Level 4 autonomous driving, there are five other levels. Level 0 is manual driving, where, according to SAE's definition, the driver is fully responsible for all driving operations, including steering, braking, and throttle. The vehicle only executes commands, so this level is not considered autonomous driving. Level 2 is partial automation, where the vehicle can simultaneously automate acceleration, deceleration, and steering, meaning adaptive cruise control and lane-keeping systems can work together. Most car manufacturers have already achieved Level 2 autonomous driving technology. Level 3 is conditional automation, where the vehicle can automate acceleration, deceleration, and steering in specific environments without driver input or monitoring of the surroundings. However, the driver must remain attentive and ready to take over if the autonomous system encounters situations it cannot handle. The Audi A8 is the world's first production car capable of Level 3 autonomous driving on public roads. Level 5 is full automation, requiring no driver intervention whatsoever. It enables all-weather, all-terrain autonomous driving and can adapt to environmental and geographical changes, allowing the driver to focus on rest or other tasks. However, this level involves legal and high-tech breakthroughs and requires further development. Low-Range Four-Wheel Drive: The difference between high-range and low-range four-wheel drive lies in the change in the vehicle's gear ratio. Different terrains require different four-wheel-drive modes. Vehicles equipped with part-time four-wheel-drive systems can distribute power to all four wheels via a transfer case during driving. The driver can switch between 2H, 4H, and 4L using a four-wheel-drive lever or electronic buttons to enhance the vehicle's performance. Here, 2H refers to two-wheel drive, 4H to high-range four-wheel drive, and 4L to low-range four-wheel drive. Switching to high-range four-wheel drive allows the wheels to gain better traction. Compared to 4L, 4H has broader applications. If the vehicle is driving uphill, low-range four-wheel drive provides better traction due to the engine's higher torque, enabling it to overcome more obstacles. With increased engine torque, the vehicle performs more stably on rough terrain, meaning its off-road capability improves.