Unlike cruise control, which typically works only above a certain speed, HDC systems typically aren’t activated if the vehicle is moving slower than 15 or 20 mph. The specifics vary from one automaker to the next, but it’s generally a low-speed technology.
How Hill Descent Control Works
Hill descent control typically works in a multistep process:
Low-Speed Cruise Control for Rough Terrain
Like many other automotive safety features and advanced driver assistance systems, HDC automates a task that a driver otherwise would do manually. In this case, that task is controlling the speed of a vehicle on a downslope without losing traction. Drivers usually accomplish that by downshifting and tapping the brakes, which is also the same basic method of HDC systems. HDC works like traction control and electronic stability control do. Just like those systems, HDC can interface with the ABS hardware and pulse the brakes without any input from the driver. Each wheel can be independently controlled in this manner, which allows the system to maintain traction by locking up or releasing individual wheels as the need arises.
How to Use Hill Descent Control
The operation of each manufacturer’s system differs slightly, but all share one trait: The vehicle’s speed must be below a specific threshold for HDC to work. These systems are designed to maintain a safe speed, not reduce a dangerous speed to a safe speed. Most automakers require the vehicle to be below about 20 mph, with some exceptions. In some cases, such as the Nissan Frontier, the speed threshold changes depending on the gear setting. Typically, a vehicle must be in forward or reverse gear (not neutral) and on a grade before you can activate HDC. Most systems have an indicator on the dash that shows when all the conditions are met and the feature is available. Pressing a button typically activates HDC. Depending on the manufacturer, the button might be on the center console, below the instrument cluster, or elsewhere. Some automakers such as Nissan use a rocker switch instead of a simple button. Upon activation, every system operates a little differently. In some cases, you can control the speed of the vehicle with the cruise control buttons. In other cases, you can increase speed by tapping the gas and decrease it by tapping the brake.
History of Hill Descent Control
Bosch developed the first HDC system for the Land Rover Freelander. The Freelander lacked the low-range gearbox and differential locking features of other 4x4 offroad vehicles, and HDC was billed as a fix. The initial rollout of the technology suffered from a few drawbacks, including a preset speed that was too high for many situations. Later implementations by Land Rover and other automakers set a “walking pace” speed or allowed the driver to adjust the speed on the fly. Vehicles equipped with this style of HDC are better suited for use in rough terrain with loose or muddy surfaces and very steep hills.
Who Offers Hill Descent Control?
HDC is still available on the Land Rover Freelander and Range Rover. Other automakers such as Ford, Nissan, BMW, and Volvo have introduced HDC in some SUVs, crossovers, station wagons, sedans, and trucks, and the technology is added to more model lines each year.
