Speed Control - TDV8 3.6L Diesel (G1679444)

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The speed control system is integrated with the engine management system and uses fuelling 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:

• On/Off/Suspend switch
• '+' and '-' (set/accelerate and decelerate) steering wheel switches
• Resume 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 control module.

The speed control is operated by the driver using only the steering wheel switches. When speed is active, the ECM regulates the pulse width modulation (PWM) 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 speed control switches are located on the left-hand (LH) side of the steering wheel. The switches are connected via fly leads directly to the clock spring. All the speed control switches are non-latching momentary rocker switches. The minimum set speed is 18 mph (30 (km/h). Speed control is automatically suspended if the vehicle speed falls below 15 mph (24 km/h).

The speed control switches are resistive ladder type switches. There are three rocker switches associated with speed control, two of which are for adaptive speed control (where specified). The switches vary the resistance of a signal voltage sent to the ECM. The switches receive a 5 volt reference supply. The ECM measures the returned voltage to determine which switch has been pressed.

Suspend/Resume Switch

The suspend/resume switch controls the selection of speed control. When the ignition is in position II, a single press of the suspend switch will activate the suspend mode. This temporarily switches off the speed control system, but retains the previously set speed in the ECM memory.

Resume Switch

A second press of the switch re-activates the previously set speed after the speed control has been suspended by pressing the suspend switch or by depressing the brake pedal.

Accelerate/Decelerate (+/–) Switches

When the speed control system is active, pressing the '+' switch sets the controlled speed to the current road speed of the vehicle. Subsequent momentary presses of the switch increases the set road speed by 0.6 mph (1 km/h). If the switch is pressed and held the road speed will continue to increase until the switch is released. Momentarily pressing the '–' switch, decreases the set speed by 0.6 mph (1 km/h). If the switch is pressed and held, the set speed is decreased until the switch is released

Time Gap Adjustment Switches

The time gap adjustment switches allows the driver to adjust the length of time gap between the vehicle and the vehicle in front. The maximum time gap is 2.4 seconds and the minimum time gap is 1 second.

General

The adaptive speed control system comprises the following components:

• Adaptive Speed Control Sensor
• Adaptive Speed Control module
• Steering wheel control switches
• ECM
• Electric throttle
• ABS module and pump

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 (4 seconds) 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 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. 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 30 km/h (20 mph) 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 non Adaptive Speed Control variants.

Radar Sensing

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.

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 speed - 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 of target - using a narrow angle beam to scan horizontally 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.

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 20% of full pressure (0.2G) 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 override of 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 10 km/h), pedestrians, objects on the road and oncoming vehicles in the same lane are not recognized.

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.