Is it possible for a four-wheel drive vehicle like the Toyota Land Cruiser to possess flat, confidence-inspiring handling characteristics on the road and yet offer generous axle articulation during off-road use?
Traditionally, these are mutually exclusive qualities. This is partly because the anti-roll bars that connect both sides of the vehicle and help maintain a horizontal cornering attitude for road use also place limits on an individual wheel’s range of vertical travel when negotiating uneven surfaces.
Toyota’s solution to this seeming paradox is its Kinetic Dynamic Suspension System (KDSS), fitted to Land Cruiser Icon and Invincible models. As the name suggests, KDSS is designed to react dynamically to forces being applied across the suspension, optimising chassis performance whether on- or off-road. It achieves this by using an electrically modulated network of hydraulics to modulate or even disable the anti-roll bars.
As you can see in the above cutaway and simplified schematic below, a hydraulic cylinder with a separate upper and lower chamber is fitted to each of the Land Cruiser’s anti-roll bars. The upper chambers of the front and rear cylinders are connected by one hydraulic line, while both lower chambers are similarly connected. Each hydraulic line is plumbed with an electronically controlled accumulator valve.
When cornering in normal road use, equal pressure is applied to the outer wheels. As a result, the hydraulic fluid remains still within the lines, holding the front and rear cylinder pistons in place. This allows the anti-roll bars to twist as normal, suppressing the suspension stroke and reducing body roll, improving the feeling of stability. The difference this can make to the car’s angle of attitude is pictured below.
On rougher roads, slightly uneven forces are exerted between the front and rear wheels. When this is sensed, the accumulator valves rapidly open and close to control fluid movement within the hydraulic lines. This dampens vibrations by absorbing surface undulations, delivering a more comfortable ride.
In the more serious off-road condition illustrated above, the wheels are at different heights in relation to one another. This generates unequal forces between and across the axles, causing the pistons in each hydraulic cylinder to stroke in opposite directions. This counteracts the normal resistance of the anti-roll bar and allows maximum articulation of the suspension. With both front and rear anti-roll bars now effectively disengaged, all four wheels can remain in contact with the ground for as long as possible.
Toyota models equipped with KDSS therefore enjoy optimised on-road stability as well as greater freedom and ability in extreme off-road situations.
Learn more: History of the Toyota Land Cruiser