Cruise Control: Description and Operation

Speed Control

COMPONENT LOCATION 5.0L V8









INTRODUCTION
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. 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 rapidly approaching a slower moving vehicle.
Both systems are controlled by the Engine Control Module (ECM).
The standard system and the adaptive system both have the following components:
- Accelerate set + switch
- Decelerate - switch
- RESUME switch
- CANCEL switch.
Both systems also use:
- The ECM
- The stop lamp switch and the CANCEL 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 - selected by RH (right-hand) instrument cluster menu button on steering wheel
- A time gap switch
- An interface to the Anti-lock Brake System (ABS).

STANDARD SPEED CONTROL
The standard speed control system is integrated with the within the ECM (engine control module) 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 (accelerator pedal position) sensor, the ECM (engine control module) and the ABS (anti-lock brake system) module.
The standard speed control is operated by the driver using only the steering wheel switches. When standard speed control is active, the ECM (engine control module) 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 maximum (limited) vehicle speed is reached
- 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).

Standard Speed Control Switches









There are 4 standard speed control switches:
- Set speed + accelerate switch
- Decelerate - switch
- Cancel switch
- Resume switch.
The standard speed control switches are located on the LH (left-hand) side of the steering wheel. The switches are resistive ladder type switches which vary the resistance of a 5 volt signal sent to them. The resistive ladder is wired to the Steering Wheel Module (SWM), the SWM is a LIN (local interconnect network) node which transmits the data to the CJB (central junction box) which gateways the data onto the high speed CAN (controller area network) bus. In the event of the ECM (engine control module) logging a cruise switch fault DTC (diagnostic trouble code), fault finding should start at the SWM and clockspring. The ECM (engine control module) diagnostic detects that the SWM hasn't provided an updated live counter.
The LIN (local interconnect network) bus is shared with the keyless vehicle module and docking of the key may cause cruise to become unavailable. This is due to the security module taking over the LIN (local interconnect network) bus during the key check.
Engage Speed Control
Speed control is engaged by pressing the set speed accelerate + switch. Once engaged the speed can be increased by one of 3 methods:
- Press and hold the set speed accelerate + switch which will cause the vehicle to accelerate. When the switch is released the attained speed will be set as the cruise speed.
- Repeatedly pressing the set speed accelerate + switch. Each press increases the vehicle speed by 1 mph (2 km/h).
- Use the accelerator pedal to increase the vehicle speed. Once the required speed is reached, a single press of the set speed accelerate + switch will set the cruise speed.
When the target speed has been set, a green marker will appear on the outer circumference of the speedometer in the instrument cluster, adjacent to the set speed. If the set speed is changed the marker will move accordingly.
Reduce Cruising Speed
The set speed can be reduced by pressing and holding the decelerate - switch until the required speed is reached. When the switch is released the speed is reset at that value. The set speed can be reduced incrementally by pressing and releasing the decelerate - switch. Each press will reduce the speed by 1 mph (2 km/h).
Set Speed Adjustment
Speed control adjustment is limited around the current vehicle speed. This means speed adjustment won't occur when resuming or if the vehicle speed is noticeably different to set speed. This is noticeable when resuming speed control and a large difference exists between the set speed and the current speed. The driver can set a new speed, but can't adjust the old speed.
Suspend Speed control
Suspending Speed Control means speed control has been deactivated without loss of the memory speed. In all suspend events the memory speed is maintained. Speed control can be suspended numerous events, as described in the general description, there are some additional suspend conditions:
- Park, Reverse or Neutral selected using transmission gear selector
- Hill Descent Control (HDC) has been selected
- Low range has been selected on the transfer box
- Cancel button has been pressed.
A single press of the RESUME switch will resume speed control at the previously set speed.

NOTE:
In the event that a memory speed has been lost during a driving cycle, confirm with the customer if the "Cruise Not Available" message was observed. Loss of memory speed implies a fault has occurred.


ADAPTIVE SPEED CONTROL
The adaptive speed control system uses a forward looking radar module 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). Activate adaptive speed control by pressing the set speed + switch to select a set speed, as described for standard speed control. The adaptive speed control system will maintain the set speed, but will reduce the vehicle's speed when it detects a slower vehicle ahead.
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 (engine control module), throttle body and throttle control are unchanged from those used for the standard speed control variants.

Radar Sensing
The adaptive speed control system is based on the use of a front mounted electronic radar module. The module transmits a radar beam forward of the vehicle and detects the returning signals reflected off other vehicles and objects ahead.
The radar beam is electronically scanned at a rate of 20 sweeps/second across a total arc of 20° 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). The radar provides a list of 64 targets.
With the ignition ON, the adaptive speed control radar module is powered up but no radar transmissions are emitted until the vehicle is in motion. The radar module detects three primary parameters of objects within the scanned arc. These are:
- Range
- Relative velocity
- Angle.
Range
The radar module detects the presence and ranges of different vehicles and objects within the scanned arc up to a distance of approximately 130 meters (426.5 feet). 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
The antenna consists of several receivers; if an object is offset from the vehicle centre line, there will be a small time difference between the receive time on the near side compared to the far side. The radar can use this time difference to measure the angular position of the object. This enables the system to distinguish between vehicles in different lanes and between vehicles and roadside objects.

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 or drops below the minimum operating speed, 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.
When the vehicle is in follow mode the Forward Alert warning indicator is illuminated in the instrument cluster and the current gap setting will be displayed in the message center.









System Restrictions
The adaptive speed control system is only intended to provide enhanced speed control as described above in certain restricted conditions. The following illustration show circumstances where the adaptive speed control system may brake late or unexpectedly. The driver is required to intervene in these situations.
The following points should be noted:
- Automatic braking is limited to approximately 30% of full pressure (0.3 G 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 intervention on the brakes
- While the radar sensor detects moving and stationary targets for assessment of the environment ahead, the system does not react to or provide any control in situations other than follow mode conditions. Stationary or slow moving vehicles (below 6 mph (10 km/h)), pedestrians, objects on the road and oncoming vehicles in the same lane are not recognized.

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 module with the relative speed of an external object as detected by the radar sensor to ascertain whether the object is stationary or not.

NOTE:
If tires are fitted which are different in diameter from those specified for the vehicle, the vehicle speed, calculated by the ABS module, 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.
The radar continuously monitors both moving vehicles and stationary objects to determine if it can 'see' normally. If the radar can detect only a few objects it may be blocked by an accumulation of snow or mud or a physical blockage such as wet paper or an incorrectly located number plate. In a few empty roads areas where there are few roadside objects or other vehicles to detect, it may determine that it is blocked and inhibit adaptive speed control; a DTC (diagnostic trouble code) is recorded in this instance. The system will reset after the ignition is cycled. In this case the module is not faulty and should not be replaced.

Adaptive Speed Control Switches









The adaptive speed control system is controlled from the LH steering wheel switches. The switches are the same as used for normal speed control with the addition of 2 time gap setting switches. The time gap setting switches allows the driver to adjust the time gap to one of four pre-set time gaps. The selected time gap is displayed in the vehicle message center.
The time gap will return to the default gap (the third setting) each time the ignition is cycled.

Adaptive Speed Control Radar Module
The adaptive speed control radar module is located on the RH (right-hand) side behind the front bumper cover. The radar module is connected to the other vehicle systems via the high speed CAN (controller area network) bus. If the unit is replaced in service the unit must be re-levelled vertically using a level gauge (digital or bubble type).
Horizontal alignment is achieved by putting the module in service mode with 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.

Forward Alert
Limited detection and warning of objects ahead is provided during adaptive speed control operation by the Forward Alert warning. The enhanced Forward Alert warning provides additional warnings when the adaptive speed control is not engaged. If an object is detected close ahead, a warning tone will be emitted and a Forward Alert message will be displayed. The brake will not be applied.
The Forward Alert system is active when the warning indicator in the instrument cluster is illuminated. Forward Alert does not initiate any action, the driver must take the appropriate action when the message is displayed. The system monitors driver intervention and may not issue the warning if the driver has taken the appropriate action (braking, steering or indicating) early enough.
The sensitivity of the warning can be changed using the gap increase and decrease switches when the adaptive cruise control is not active. Confirmation of the gap change is given by Forward Alert being displayed in the message center.
Forward Alert can be switched on or off by the driver using the instrument cluster menu selection.

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
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, O = LIN bus; U = Private CAN bus