Cruise Control: Description and Operation
Speed Control
5.0L V8 SPEED CONTROL COMPONENT LOCATION
GENERAL
There are two variants of speed control available, a standard system and an adaptive system. The standard system maintains a set speed selected by the driver until operation is suspended or cancelled by a further input from the driver and is controlled by the Engine Control Module (ECM). The adaptive system includes the same functionality as the standard system, but also has the ability to:
- Reduce vehicle speed, to less than the set speed, in order to maintain a selected distance behind a slower moving vehicle
- Accelerate the vehicle back to the set speed, once the way ahead is clear, after reducing the set speed because of a slower moving vehicle
- Alert the driver when the vehicle comes within a given distance of a slower moving vehicle.
The standard system and the adaptive system both have the following components:
- A set + switch
- A - switch
- A RESUME switch
- A CANCEL switch.
Both systems also use:
- The ECM
- The brake switch
- The Accelerator Pedal Position (APP) sensor.
The adaptive system incorporates the following additional components:
- An adaptive speed control module
- An adaptive speed control sensor
- Forward alert selection in the instrument cluster set-up menu
- The Anti-lock Brake System (ABS) module.
STANDARD SPEED CONTROL
The standard speed control system is integrated with the within the ECM and uses fueling intervention to automatically maintain a set vehicle speed. Once engaged, the system can also be used to accelerate the vehicle without using the accelerator pedal.
The standard speed control system also uses inputs from the Stop lamp switch, the APP sensor, the ECM and the ABS module.
The standard speed control is operated by the driver using only the steering wheel switches. When standard speed control is active, the ECM controls the electronic throttle to adjust the fuel supply as required to maintain the set speed.
The minimum set speed for standard speed control is 20 mph (32 km/h). Speed control is automatically suspended if the following conditions apply:
- Vehicle speed falls below 20 mph (32 km/h)
- The brake pedal is pressed
- The cancel button is pressed
- Neutral, park or reverse gear is selected
- The difference between actual speed and the set speed is too great
- When the vehicle speed reaches a maximum speed of 150 mph (240 kph)
- If the accelerator pedal is used to accelerate beyond the set speed for too long
- Engine speed too high (cancel limit set just below red line).
Speed Control Switches
The speed control switches are located on the Left Hand (LH) side of the steering wheel. The switches are connected via fly leads to the clock spring. The speed control switches are resistive ladder type switches which vary the resistance of a 5 volt signal sent to them. The signal is returned along a Local Interconnect Network (LIN) bus to the instrument cluster. The instrument cluster routes the control signals to the Engine Control Module (ECM) on the high speed Controller Area Network (CAN) bus.
Speed control is engaged by pressing the set/increase switch. Once engaged the speed can be varied by the speed adjustment switches. Each press of the speed adjustment switches will increase or decrease the set speed in steps of 1 mph (2 kph).
ADAPTIVE SPEED CONTROL
The adaptive speed control system uses a forward looking radar sensor to scan the road ahead, looking for objects that are moving at a different rate to itself. When a target is identified the adaptive speed control system will monitor the time gap between it and the target vehicle. When that gap falls below a set driver selected level, the adaptive speed control system will intervene slowing the vehicle by backing off the throttle and/or applying the brakes, until the correct gap is attained. The driver can choose between four gap settings, 1, 1.4, 1.8 and 2.2 seconds.
The system will detect but not react to the following:
- Vehicles in the oncoming lane
- Stationary vehicles
- Pedestrians
- Vehicles not in the same lane.
Adaptive speed control is active when the vehicle is moving at a minimum speed of 20 mph (32 km/h) and a maximum speed of 112 mph (180 km/h). Adaptive speed control only functions when a set speed is entered in standard speed control mode. The adaptive speed control system only intervenes with the set speed when it detects a target vehicle, and then only if the minimum time gap is breached.
It is important to note that the system is intended for use in limited driving situations, does not remove control and responsibility from the driver, and at all times can be quickly overridden. The adaptive speed control system is not a collision warning system and will not react to stationary objects. The system does not operate below a minimum speed of approximately 20 mph (32 km/h) since it is unsuitable for use in cities or congested traffic. The system is best suited to main roads/ highways with gradual bends.
The ECM, throttle body and throttle control are unchanged from those used for the standard speed control variants.
Adaptive Speed Control Module
The adaptive speed control module is located on the drivers side at the bottom of the A pillar. The control module is connected to the other vehicle systems via the high speed CAN bus. Signals from the adaptive speed control forward looking radar sensor are received on a dedicated CAN bus between the two modules.
Adaptive Speed Control Radar
The adaptive speed control radar sensor is located in a central position, behind the front bumper. The sensor is connected to the adaptive speed control module via a private CAN bus. If the unit is replaced in service the unit must be mechanically leveled vertically. Horizontal alignment is achieved by putting the sensor in service mode using an approved Land Rover diagnostic system. The vehicle is then driven for a short period while the sensor calibrates itself. Calibration is complete when the 'follow' icon in the instrument cluster stops flashing.
The radar sensor monitors reflections from stationary roadside objects such as street lighting poles, signposts and barriers, and the road surface itself. In areas with few of these features it may incorrectly judge that the radar is blocked. In these cases, confirm that the radar horizontal alignment is correct, and that the vehicle has not had a front end protective cover or film applied.
OPERATION
Speed Control
The speed control system is integrated with the engine management system and uses fueling intervention to automatically maintain a set vehicle speed. Once engaged, the system can also be used to accelerate the vehicle without using the accelerator pedal. The speed control system comprises the following components:
- '+' and '-' (set/accelerate and decelerate) steering wheel switches
- Resume switch
- Cancel switch
- Clock spring
- Speed control warning lamp.
The speed control system also uses inputs from the brake pedal switch, the APP sensor, the ECM and the ABS module.
The speed control is operated by the driver using only the steering wheel switches. When speed control is active, the ECM regulates the PWM (pulse width modulation) signals to the fuel injectors to adjust the fuel supply as required to maintain the set speed.
During speed control operation, the ECM controls vehicle speed by adjusting fuel injection duration and timing. When the accelerator pedal is pressed with speed control active, the ECM outputs a calculated throttle angle signal in place of the actual throttle angle signals produced by the APP sensor. The calculated throttle angle is derived from fuel demand.
The minimum set speed for speed control is 20 mph (32 (km/h). Speed control is automatically suspended if the following conditions apply:
- Vehicle speed falls below 20 mph (32 km/h).
- The brake pedal is pressed
- The cancel button is pressed
- Neutral, park or reverse gear is selected
- The difference between actual speed and the set speed is too great
- When the vehicle speed reaches a maximum speed of 150 mph (240 kph)
- If the accelerator pedal is used to accelerate beyond the set speed for too long
- Stability control system intervention
- System error causes shut-off.
Adaptive Speed Control
The adaptive speed control system comprises the following components:
- Adaptive speed control sensor
- Adaptive speed control module
- Steering wheel control switches
- ECM
- Throttle intake manifold - Electric throttle
- ABS module and pump
- Adaptive speed control warning indicator (in the instrument cluster).
The adaptive speed control system uses a forward looking radar sensor to scan the road ahead, looking for objects that are moving at a different rate to itself. When a target is identified the adaptive speed control system will monitor the time gap between it and the target vehicle. When that gap falls below a set driver selected level the adaptive speed control system will intervene slowing the vehicle by backing off the throttle and/ or applying the brakes, until the correct gap is attained. The driver can chose between four gap settings, 1, 1.4, 1.8 and 2.2 seconds.
The system will detect but not react to the following:
- Vehicles in the oncoming lane
- Stationary vehicles
- Pedestrians
- Vehicles not in the same lane
- Motorcycles.
Adaptive speed control is active when the vehicle is moving. Adaptive speed control only functions when a set speed is entered in normal speed control mode. The adaptive speed control system only intervenes with the set speed when it detects a target vehicle, and then only if the minimum time gap is breached.
It is important to note that the system is intended for use in limited driving situations, does not remove control and responsibility from the driver, and at all times can be quickly overridden. The adaptive speed control system is not a collision warning system and will not react to stationary objects. The system does not operate below a minimum speed of approximately 20 mph (32 km/h) since it is unsuitable for use in cities or congested traffic. The system is best suited to main roads/ highways with gradual bends.
The ECM, electric throttle and throttle control are unchanged from those used for non adaptive speed control variants.
The adaptive speed control system is based on the use of a front mounted radar sensor. The sensor transmits a 1.5° wide beam forward of the vehicle and detects the returning signals reflected off other vehicles and objects ahead.
The 1.5° wide radar beam is mechanically scanned at a rate of 10 sweeps/second across a total arc of 15° centered on the longitudinal axis of the vehicle. The radar operates at millimetric wavelengths (76 - 77 GHz) and transmits a frequency modulated continuous wave signal at a relatively low power level (no high power pulses).
With the ignition switched ON, the adaptive speed control module is powered up but no radar transmissions are emitted until the vehicle is in motion.
In follow mode a set speed is selected in the normal speed control manner and this speed is maintained until a slower vehicle is encountered in the lane ahead. When the vehicle ahead comes within the effective range of the radar sensor, the system identifies it as a target vehicle and an icon is illuminated on the instrument cluster to indicate that the system is in "follow mode". When the distance between the two vehicles closes to a set time gap, the adaptive speed control system closes the throttle and if necessary applies the brakes to maintain the set time gap. Follow mode is effectively a closed loop system. If several vehicles are ahead, the closest vehicle is chosen as the target to follow. If the target vehicle moves out of radar range, or if either vehicle changes lane, the system exits follow mode and the follow mode icon is extinguished. The adaptive speed control system will only raise its speed to the originally set speed, it will not accelerate past this
speed to maintain a time gap.
Driver operation of the foot brake or control switches will immediately cancel adaptive speed control. A 'cruise cancelled' message will be displayed to the driver in the message center.
When the vehicle is in follow mode, the Follow Mode warning indicator is illuminated in the instrument cluster.
The radar sensor detects three primary parameters of objects within the scanned arc. These are:
- Range
- Relative velocity
- Angle.
Range: The radar sensor detects the presence and ranges of different vehicles and objects within the scanned arc up to a distance of approximately 130 meters. The transmitted signal frequency changes continuously in a cyclic pattern (modulation). This means that, in the time taken for the signal wave front, to travel to and from a target vehicle (or other object), the transmission frequency will have changed. The difference between the received signal frequency and the new transmission frequency is proportional to the distance between the transmitting vehicle and the target vehicle.
Relative velocity: When the signal is reflected off a vehicle moving at a different speed (opening or closing gap) an effect known as the Doppler shift causes an extra frequency modulation to be imposed on the signal. This Doppler frequency varies with the relative speed of the vehicle being followed, enabling the system to differentiate between vehicles traveling at different speeds and also between moving vehicles and stationary objects.
Angle: Using a narrow angle beam to scan horizontally enables the system to distinguish between vehicles in different lanes and between vehicles and roadside objects.
System Restrictions
The adaptive speed control system is only intended to provide enhanced speed control as described above in certain restricted conditions. The following points should be noted:
- Automatic braking is limited to approximately 30% of full pressure (0.3G deceleration) and is intended to provide a smooth, gradual deceleration in follow mode conditions. Harsh braking by the target vehicle or following the target vehicle down to very low speeds or to a halt will require driver to intervene and override the brakes. A 'driver intervene' message will be displayed in the message center accompanied with an audible chime.
WARNING: It must be emphasized that the adaptive speed control system is not a collision warning or avoidance system and that, other than the limited conditions of follow mode, driver intervention will be necessary to control the vehicle speed.
The following illustration shows circumstances where the adaptive speed control system may brake late or unexpectedly. The driver is required to intervene in these situations.
In follow mode, some situations may cause target ambiguities for the detection system. These situations include:
- The nearby presence of a third vehicle when driving on a line slightly offset to the target vehicle.
- Vehicles edging into the lane ahead which are not detected by the system until they have moved into the radar beam.
On the approach to, or exit from a bend, a target vehicle may be lost or a new target acquired as vehicles ahead change their angular position with respect to the radar sensor. On a straight road, if the sensing vehicle is in follow mode below its selected set speed, losing the target vehicle will cause the sensing vehicle to accelerate to this set speed. This acceleration is undesirable either on, or entering a bend when the target is suddenly lost, and in this situation the system inhibits the resumption of the set speed.
The speed control system compares vehicle speed data from the ABS system with the relative speed of an external object as detected by the radar sensor to ascertain whether the object is stationary or not.
If tires are fitted which are different in diameter from those specified for the vehicle, the vehicle speed calculated by the ABS will not be the true road speed. This situation may cause stationary objects to be falsely identified as moving vehicles and result in automatic deceleration on a clear road.
Forward Alert
The forward alert system utilizes the adaptive speed control system components. Forward alert is turned on and off independently of adaptive speed control, using the vehicle set-up menu in the instrument cluster. Forward alert will notify the driver by means of a chime, and warning indicator in the instrument cluster and indication in the message center, when a target vehicle comes into range. The system will NOT use throttle or brake intervention to slow the vehicle.
NOTE:
This system is intended as a driver aid and should be used as such. The system is NOT a collision warning or avoidance device.
The system sensitivity can be adjusted in the same manner as the Adaptive Speed Control, via the steering wheel mounted switches. Each adjustment is accompanied by a message in the message center.
Advanced Emergency Brake Assist
WARNING: Advanced Emergency Brake Assist is an additional safety system and is not intended to override driver responsibility for driving with care and attention.
On vehicles fitted with the Advanced Emergency Brake Assist system, brake response is improved during emergency braking when a moving vehicle is detected close ahead. The system activates if the risk of collision increases after the Forward Alert warning is issued.
After a Forward Alert warning is displayed, the brakes are automatically applied gently in preparation for rapid braking. If the brake pedal is then pressed quickly then braking is fully implemented by the Emergency Brake Assist system, even if the pressure on the brake pedal is light. For additional information, refer to Anti-Lock Control - Traction Control Description and Operation
Advanced Emergency Brake Assist is available at speed above 5 mph (7 km/h) and will function even when Forward Alert and adaptive cruise control are switched off.
If a fault occurs in the system a message Forward Alert Unavailable is displayed in the message center. Advanced Emergency Brake Assist will not be available until the fault is rectified.
CONTROL DIAGRAM
NOTE:
A = Hardwired; D = High Speed CAN Bus
