L322 Range Rover System Description and Operation
BRAKES
70-30
DESCRIPTION AND OPERATION
Hill Descent Control Enable Criteria
The target speed used by the HDC varies in response to driver inputs. Current target speed will lie in the range
between Maximum Target Speed and Minimum Target Speed.
Hill Descent Control Target Speeds
When HDC is first activated, if the driver does not press the brake or accelerator pedals, then current target speed is
set to default target speed. If HDC is activated and the driver presses the brake pedal, the vehicle brakes operate as
normal. While the brake pedal is pressed:
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If vehicle speed is equal to or more than current target speed, current target speed is unchanged
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If vehicle speed is less than current target speed, current target speed is set to vehicle speed
When the brake pedal is released:
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If vehicle speed is equal to or more than minimum target speed, then current target speed is unchanged
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If vehicle speed is less than minimum target speed, then Current Target Speed is set to minimum target speed.
If HDC is activated and the driver presses the accelerator pedal, current target speed is defined by a characteristic as
follows:
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If current target speed is less then default target speed, then the target speed is set to current speed.
When the accelerator pedal is released:
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If current target speed is greater than default target speed and vehicle speed is equal to or more than default
target speed, then current target speed is set to default target speed
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If current target speed is more than default target speed and vehicle speed is less than default target speed,
then current target speed is set to vehicle speed
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If current target speed is less than or equal to default target speed, and vehicle speed is less than current target
speed , then current target speed is set to vehicle speed
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If current target speed is less than or equal to default target speed , and vehicle speed is equal to or more than
current target speed , then current target speed is unchanged.
To ensure that the vehicle is in an appropriate gear during HDC activity the ABS ECU communicates with the EAT
ECU. A unique gearbox map is activated when HDC braking activity begins. The characteristics of the map are that
lower gears are selected sooner than normal, and higher gears are selected later than normal. This reduces the work
done by the foundation brakes, and improves the response time of HDC.
Gear Detected
Neutral
Auto Transmission D, 1-5, R
Throttle less than 5%
Enabled
Enabled
5% to 20%
Stand by
Enabled
Throttle more than
20%
Stand by
Stand by
Low
High
Gear
selector
position
D
1
2
3
4
5
R
N
D,1,2,3,
4,5
R
N
Maximum
target
speed
35 km/h
(22 mph)
35 km/h
(22 mph)
35 km/h
(22 mph)
35 km/h
(22 mph)
35 km/h
(22 mph)
35 km/h
(22 mph)
35 km/h
(22 mph)
—
35 km/h
(22 mph)
35 km/h
(22 mph)
—
Standard
target
speed
6 km/h
(4 mph)
3.5 km/h
(2 mph)
6 km/h
(4 mph)
6 km/h
(4 mph)
6 km/h
(4 mph)
6 km/h
(4 mph)
3.5 km/h
(2 mph)
6 km/h
(4 mph)
10 km/h
(6 mph)
6 km/h
(4 mph)
10 km/h
(6 mph)
Minimum
target
speed
3.5 km/h
(2 mph)
3.5 km/h
(2 mph)
3.5 km/h
(2 mph)
3.5 km/h
(2 mph)
3.5 km/h
(2 mph)
3.5 km/h
(2 mph)
3.5 km/h
(2 mph)
6
km/h
(4 mph)
6 km/h
(4 mph)
6 km/h
(4 mph)