What is a driven axle?

While direct-drive steering wheels have the advantages of high precision and fast response, they also have some limitations. For example, their high-torque characteristics may make them difficult for beginners to control in racing games, as they can easily deviate from the track due to oversteering and require a long adaptation period. Additionally, the hardware cost of direct-drive systems is relatively high, and they have stringent requirements for supporting equipment (such as high-strength racing rigs) and driver software. Insufficient driver optimization may compromise the smoothness of the actual experience. Structurally, direct-drive steering wheels eliminate the traditional steering column and gear set, but this also implies potentially higher costs when repairing or replacing motor components. For casual players with infrequent usage or limited budgets, belt-driven steering wheels may be a more economical and practical choice, whereas direct-drive systems are better suited for professional users seeking the ultimate simulation experience. It should be noted that the implementation of direct-drive technology still depends on the stability of the electronic system, and any sensor or control unit malfunction could directly impact steering performance.

The design of directly driving wheels (such as in-wheel motors or wheel-side motors) offers significant advantages in automotive applications, primarily manifested in three aspects: power transmission efficiency, handling flexibility, and structural simplification. Traditional drive systems require power transmission through components like gear reducers and drive shafts, resulting in energy losses of approximately 5%-10%. In contrast, direct drive integrates the motor with the wheel, shortening the power transmission path to nearly zero loss and significantly improving energy efficiency. Taking the in-wheel motor as an example, it embeds the motor within the wheel hub, with the rotor directly driving the tire rotation, enabling independent torque control for all four wheels. The electronic signal response speed is ten times faster than mechanical coupling, allowing dynamic adjustment of torque distribution between inner and outer wheels to enhance high-speed cornering stability, and even supporting complex maneuvers like tank turns. Furthermore, the elimination of traditional transmission components improves chassis space utilization, enables the front compartment to be designed as a large-capacity storage area, and reduces overall vehicle weight. However, the increased unsprung mass may adversely affect suspension response, while the motor demands higher heat dissipation and sealing requirements. Currently, brands such as BYD have adopted wheel-side motor technology (e.g., the "Yi Sifang" system in the Yangwang U8). Although some transmission structures remain, a single motor can deliver 200-300kW of power, achieving a balance between performance and handling. These technologies are likely to gain wider adoption as costs decrease, particularly for electric vehicle models with stringent space and energy efficiency requirements.

AWD (All-Wheel Drive) and FWD (Front-Wheel Drive) each have their own advantages and disadvantages, and the choice depends on specific needs. AWD distributes power to all four wheels, significantly enhancing grip and stability on slippery roads, during off-road driving or aggressive driving. It is particularly suitable for rainy areas or complex road conditions, but its complex structure leads to higher purchase costs and slightly increased fuel consumption. FWD, on the other hand, is more fuel-efficient due to its simpler structure and lighter weight, making it suitable for urban commuting. However, front-wheel slippage may occur during rapid acceleration or hill climbing, and its steering agility is slightly inferior. Taking the 2023 Toyota Prius as an example, its AWD version enhances driving safety in rainy weather through a rear-mounted motor, while the FWD version focuses more on the fuel efficiency of daily commuting. Overall, if the budget allows and one frequently encounters challenging road conditions, AWD is more practical; if the primary use is urban commuting, FWD offers better value for money. The technical differences between the two drive systems are also reflected in vehicle dynamics. For instance, AWD can automatically adjust torque distribution to optimize acceleration performance, whereas FWD relies on the front wheels to simultaneously handle both steering and propulsion.

Rear-wheel drive (RWD) has significant advantages over front-wheel drive (FWD) in terms of handling and driving experience, mainly reflected in the following aspects. First, the front wheels of RWD models focus on steering while the rear wheels are responsible for propulsion. This division of labor makes the vehicle more agile and precise when cornering, which is particularly suitable for high-performance cars or sports cars, offering a more stable body posture and greater driving pleasure. Second, during acceleration, the vehicle's weight shifts backward, enhancing the traction of the rear wheels and improving launch and hill-climbing performance. This is also why many sports cars employ the RWD design. Additionally, the mechanical layout of RWD is relatively simplified. The engine and transmission are typically arranged longitudinally, resulting in more balanced weight distribution. This not only mitigates torque steer but also reduces front tire wear, and maintenance costs may be lower—for instance, the differential doesn't require simultaneous repair when the transmission malfunctions. However, RWD demands more advanced driving skills on slippery surfaces, and the driveshaft design may compromise some cabin space, along with higher acquisition costs. For drivers prioritizing handling and acceleration performance, RWD is an ideal choice, whereas daily commuting may place greater emphasis on FWD's cost efficiency.

The working principle of the steering wheel is to convert the driver's steering operation into the actual steering movement of the wheels through mechanical linkage and power assist systems. When the driver turns the steering wheel, the steering column transmits the rotational torque to the rack-and-pinion mechanism inside the steering gear; the rotation of the pinion drives the rack to move laterally, which in turn pushes the wheels to steer via the tie rods. Modern vehicles are generally equipped with an Electric Power Steering (EPS) system. This system detects the steering wheel's rotation angle and torque through a torque sensor, and after calculation by the electronic control unit, drives the motor to provide assistive torque. This design can automatically adjust the assist intensity according to the vehicle speed—light steering at low speeds and stable steering at high speeds. A larger steering wheel diameter results in a longer lever arm, making operation more effortless, but requires balancing steering sensitivity. Currently, mainstream steering systems are divided into rack-and-pinion type and recirculating ball type. The former has a compact structure and direct response, and is predominantly used in passenger cars; the latter has strong load-bearing capacity and is commonly found in commercial vehicles. It is noteworthy that the steering system is closely related to suspension geometry design. Front wheel alignment parameters (such as caster angle) affect the steering wheel's return-to-center characteristics, while improper four-wheel alignment may cause steering wheel vibration or pulling.