The centrepiece of the ŠKODA all-wheel drive is a fifth-generation electronically controlled multi-plate clutch. It is the latest evolution of the all-wheel-drive technology that was first used at ŠKODA nineteen years ago. The all-wheel drive is fully automated and ensures optimum traction in any driving situation. A series of sensors (e.g. for wheel speed, steering angle, longitudinal and lateral acceleration, accelerator pedal position, engine speed) continuously evaluates the current driving situation, while the all-wheel-drive electronics take all of the incoming parameters into account. Within milliseconds, the electronics can alter the distribution of torque between the individual wheels, thereby ensuring the optimum distribution of power.
All-wheel-drive technology offers many benefits. The all-wheel drive only intervenes when the driving situation requires it. At the same time, the system’s electronics proactively precondition the all-wheel drive for anticipated driving situations. In normal driving conditions, only the front axle is driven – which keeps fuel consumption low.
From a technical point of view, the multi-plate clutch has barely changed compared to the previous fourth generation, though there are some important new features and improvements. One of the most important is the system’s new design: it means that the fifth-generation multi-plate clutch no longer requires a pressure tank or control valve. Due to the lower minimum amount of oil, the clutch is altogether more compact and 1.4 kg lighter than the previous generation. The 4×4 drive control unit controls the rotational speed of the drive pump, which consists of an electric motor, a piston pump and a control valve. Thanks to the control valve, the rotational speed of the pump controls the oil pressure in the main piston. The higher the rotational speed of the pump, the greater the torque which the multi-plate clutch can transfer to the rear wheels. At a low pump speed, the forces are primarily transferred to the front axle. With the aid of the fully electronically controlled multi-plate clutch, the 4×4 drive control unit detects the wheels on the rear axle even when the vehicle is at a standstill.
The multi-plate clutch is positioned on the rear axle, together with the fixed gear and the rear axle differential. The system reacts within milliseconds, virtually unnoticed by the occupants, meaning that its reactions are just as fast as the transmissions in the previous generation of the system, despite the simplified design.
The HISTORY of the ŠKODA 4×4 drive
… All-wheel drive was first used in 1999 in the first generation of the ŠKODA OCTAVIA COMBI 4×4 and used a mechanical pump. Its drive was dictated by the difference between the speeds of the front and rear axles. In order to bring the mechanical pump into its working position, an additional electric pump was required. The clutch could be adjusted via a control valve, which was also regulated by an electric motor.
The second generation of the ŠKODA OCTAVIA was equipped with a multi-plate clutch in a new design. To fully close the clutch, here it was enough to spin the wheels on the front axle slightly, by around 20°, in relation to the rear axle. A slight spin of the wheels on one axle was sufficient to activate the system.
Thus, these systems differed significantly from the current fifth-generation multi-plate clutch. Compared to the current state-of-the-art technology, the dynamic performance of the systems was considerably inferior.
As a central component of the overall all-wheel-drive system, the electronically controlled multi-plate clutch interacts with the vehicle’s electronics and assistance systems perfectly and reacts to every change in the driving situation immediately. Just as in its sibling with front-wheel drive, under normal conditions, engine torque in all-wheel-drive models is transferred to the front wheels. As soon as sensors and control units engage the rear axle due to the driving conditions – because the front wheels are losing traction, for example – the control unit alters the pressure on the plates. The torque is then transferred in the ideal ratio to the rear wheels, too. At the same time, the Electronic Differential Lock (EDL), which is active on both axles on ŠKODA 4×4 models, also prevents individual wheels on the same axle from spinning. The spinning wheel is slowed down and more torque transmitted to the wheel with better traction. The XDS+ system is an extension of the EDL. It reacts when the load on the inner wheel is reduced when cornering, automatically applying the brakes to prevent the wheel from spinning. As a result, the vehicle holds its line noticeably better on bends.
HOW DOES THE CURRENT FIFTH-GENERATION MULTI-PLATE CLUTCH DIFFER FROM ITS PREDECESSOR?
The main difference is the simplified system design. It no longer requires a pressure tank or control valve. The fifth generation has a new six-piston axial pump, which is driven by an electric motor and can react to instructions from the control unit within milliseconds. Moreover, the entire component is 1.4 kg lighter.
All of the ŠKODA 4×4 system’s outlined interventions take place automatically, the redistribution of the driving forces between the individual wheels is imperceptible to the driver. In this way, the system ensures maximum traction and outstanding driving stability, even when cornering and performing difficult manoeuvres on rough terrain.