The damping suspension system is able to vary the regulation of the shock absorbers, second by second, in real time, on all four wheels. This system is electronically controlled and allows the setting of the shock absorbers to be varied in relation to the type of driving and the road conditons. This ensures maximum comfort, road holding and safety in every given moment. The controlled damping suspension (SCS) is able to operate in accordance with two different intervention logics: "Auto" or "Sport", which can be selected using two buttons positioned on the central control console. These two intervention logics operate on the basis of two different shock absorber conditions which can work with soft or hard settings. In the "Auto" function the electronic system sets the shock absorbers in real time converting them from soft to rigid and vice versa, automatically, in relation to the information supplied by the series of sensors which read, second by second, different driving conditons. In the "Sport" function the setting of the shock absorbers is always for sports driving, without any compromises; favouring maximum road holding over comfort. The system is protected by one fuse located in fuse box G1 and one fuse located in fuse box G2:
Fuse F1 (10A) in G1
Fuse F2 (10A) in G2
FUNCTIONING OF THE SYSTEM IN "AUTO"
The system parameters are identified during, vertical acceleration, variations in the steering angle and the speed with which these changes take place., exceeding certain pressure values in the hydraulic brake circuit and the opening of the throttle valve in 1st and 2nd gear. The "Auto" logic has two different functioning ranges dependent on the vehicle's speed.
1) Up to 3 MPH the setting of the shock absorbers is rigid to avoid excessive springiness during manoeuvres on rough surfaces.
2) The system switches the setting from soft to rigid when one of the following conditions occurs:
- sudden changes in direction to avoid obstacles or particularly tight bends: these conditions are detected by a "steering wheel rotation angle and steering wheel rotation speed" sensor (L40);
- bumps or roughness which cause the body to vi-brate: these conditions are detected by a "vertical acceleration or accelerometer" sensor (N47);
- vehicle braking with a braking pressure in excess of 20 bar (290 psi); this condition is detected by the "braking pressure" sensor (L41):
- sudden accelerations in 1st or 2nd gear; this condition is detected by the "engine throttle sensor' (H47) and the "gearbox sensor" (H46) at speeds lower than 30 MPH.
To better understand the system functioning, we shall analyze in detail the system's various components.
- BOGE SHOCK ABSORBERS
- SENSORS
- ELECTRONIC CONTROL UNIT
- SELECTION/CONTROL ASSEMBLY
- SHOCK ABSORBER SOLENOID VALVE CONTROL RELAY
Boge shock absorbers
The pressurized hydraulic shock absorber is equipped with an oil flow regulating solenoid valve fixed to the outer tube of the shock absorber. The solenoid valve, on the basis of the input received from the control unit, regulates the passage of oil between the two chambers of the shock absorber, proportionally modifying the damping action. The intervention times, ie. valve opening and closing, are extremely short, around 5 milliseconds.
SENSORS
There are six sensors which supply the: electronic control unit with specific information.
They are:
- vertical acceleration sensor (accelerometer);
- steering wheel angle and steering wheel rotational speed sensor;
- braking sensor;
- speedometer sensor;
- engine throttle sensor;
- gearbox sensor.
We will examine them one at a time.
Vertical acceleration sensor (accelerometer)
This is fixed to the control unit itself which, in turn, is housed in the trunk. It detects the body's vertical accelerations These accelerations provoke variations in the resistance value within the sensor. In the "AUTO" condition the control unit, by analyzing the signals on the basis of their intensity and comparing them against vehicle speed, sets the shock absorber setting to rigid or soft.
Steering wheel angle and steering wheel rotational speed sensor
The sensor is fixed to the support oi the steering column close to the joint between the upper and lower steering shaft.
From the steering wheel angular position, the sensor detects the radius of the bend and the speed with which the steering wheel has reached that angular position. This sensor perceives the emergency manoeuvres necessary to avoid unexpected obstacles., eg. sharp steering. Three LEDs are present in the sensor, A, B, C which are interfaced to three receiving photodiodes STRZ, STR1, STR2. between which a phonic wheel is positioned, integrated into the steering column. This has 20 slits positioned at equal distances along the circumference, and a notch, which is located in correspondence with LED A and photodiode STRZ, corresponding to straightline driving, if hit by the light of the LED, the photodiodes send a series of signals to the control unit corresponding to the number of light intermittences from the slits between the LED and the photodiodes. As there are 20 slits on the phonic wheel, each signal corresponds to a rotation of 18". In the "AUTO" condition, the control unit sets the shock absorbers to soft or rigid in accordance with the require ments, by measuring the steering wheel rotational speed. This is received by the control unit on the basis of the frequency of the signals which arrive from the sensor.
Braking sensor
This is fitted on the front part of the brake master cylinder. This sensor is set for a hydraulic brake pressure equal to 20 bar (290 psi). If this threshold is exceeded, the control unit will set the shock absorbers to rigid. The sensor operates through a switch whose contacts are normally open; once closed: they can only be reopened if the brake pedal is released, when the pressure in the hydraulic circuit falls below 18.5 bar (268 psi). The information which the control unit receives from the braking sensor is of the on/off type.
Speedometer sensor
This sensor detects the current speed of the vehicle It is positioned on the gearbox and transmits the information to the control unit through an electonic module located on the instrument panel. The speed detection is a more crucial factor for the behaviour of the control unit compared with the information originating from the other sensors.
Engine throttle sensor
This is located on the throttle body. It detects the position of the throttle by closing a contact if it opens more than 20". This closure is detected by the control unit in 1 st and 2nd gears only.
Gearbox sensor
This is the device which signals the control unit when 1 st or 2nd gears have been engaged. It is made up of 1 microswitch fitted on the gearbox. The information obtained is transferred to the electronic control unit and is processed together with the information originating from the throttle sensor.
Electronic control unit
It is located, as we have already seen, in the trunk. The control unit is made up of a microprocessor developed by MARELLI-AUTRONICA. As already mentioned, the information originating from the various sensors is correlated in the control unit and processed on the basis of a logic pre established by the manufacturer. Following this processing: command impulses are directly emitted by the control unit to the shock absorber solenoid valves. The control unit can be connected to the ALFA TESTER in order to allow any faults to be immediately detected.
Selection/control assembly
The operating logic for the two different types of driving can be selected by pressing either of the two buttons situated next to the hand brake. For an automatic driving logic, "AUTO" button; for a sports driving logic: "SPORT" button.
Shock absorber solenoid valve control relay
The shock absorber solenoid valves, are energised by a relay situated on the lefthand side of the trunk. The duration of the energising times differs according to the sensor which determined the energising.
Operating logic
We will now analyse some typical cases of "AUTO" operation.
GRAPH 1
We are travelling on a straight line, over a smooth surface at 75 MPH. The shock absorbers are set to soft (point A), as none of the parameters have exceeded the thresholds to switch from soft to rigid. If the road surface becomes uneven, the body will be subjected to vertical stress detected by the accelerometer; if this acceleration reaches a value of 0.2 g, the control unit will switch the shock absorber setting to rigid {point B}. From the graph it can be noted that at any speed the system will switch to rigid when the vertical acceleration exceeds 0.2 g.
GRAPH 2
Let's assume that we are travelling at 40 MPH on a straightline followed by a bend; the steering wheel rotational angle, necessary to take the bend detected by the sensor, exceeds 54 degrees and the shock absorber setting is switched from soft to rigid. It can be noted that the threshold angle varies in relation to the speed: indeed, at 68 MPH, a steering wheel rotational angle of 9* is enough to provoke the switch.
GRAPH 3
In this example, let's assume we are sharply accelerating in first or second gear. If this acceleration corresponds to an engine throttle opening in excess of 20 the system switches the shock absorber setting from soft to rigid; this will only happen at speeds below 31 MPH.
GRAPH 4
The fourth example concerns the switching from soft to rigid setting in relation to the braking intensity. The graph demonstrates how the switch takes place every time the sensor detects a pressure value greater than 20 bar {290 psi), regardless of the vehicle speed.
GRAPH 5
In the last example, let's assume that we are travelling on a straightline at 75 MPH and we suddenly see an unexpected obstacle crossing our path; the movement required to avoid the obstacle is detected by the steering wheel rotational speed sensor. If the steering wheel rotational speed exceeds the threshold of 30*/sec (corresponding to a steering wheel rotation of 7.5° in 1/4 sec), the system will switch the setting from soft to rigid. Here too the threshold value varies in relation to the speed; in particular the steering wheel rotational speed limit is inversely proportional to the vehicle speed.
SHOCK ABSORBER FUNCTIONING IN THE RIGID SETTING
When the piston (1) moves upwards (extension/stroke), the oil passes from the upper chamber (A) to the lower chamber (B) of the cylinder, and from the reserve Cham ber (C) to the lower chamber (B) through the regulating valves (3) and (4) to compensate for the different quantity of oil due to the presence of the stem. When the shock absorber is compressed, the piston (1) moves downwards, the oil passes through the valves in the lower chamber (B) to the upper chamber (A) and from the reserve chamber (C) to the lower chamber (B). During this stage, the solenoid valve is not energised. The function of the gas present in the air space between the external body and the internal cylinder is to guarantee a constant pressure for the oil present in the reserve chamber.
SHOCK ABSORBER FUNCTIONING IN THE SOFT SETTING
In this condition, the solenoid valve for each shock absorber is energised by a signal with a frequency of 1 KHz; in this way the oil passes from the central channel of the support (5} to the reserve chamber (C) and the damping action is softer. During the extension/ stroke with a soft setting, the oil is also able to pass directly from the upper chamber (A) to the reserve chamber (C) through the central channel of the support (5) and valve (6) as well as through the valves (3} and (4). Vice versa, when soft setting is chosen and when the shock absorber is compressed, the volume of oil which must pass from the upper and lower chambers to the reserve chamber, does not find itself up against strong resistance because the passage is open through the solenoid valve.
FUNCTIONAL DESCRIPTION
The controlled damping suspension is controlled by an electronic control unit N46. The control unit N46 is sup plied at pin 3C (with the key in the "RUN" position) through fuse F2. This receives information from the various sensors which are correlated and processed on the basis of a logic pre-establised by the manufacturer. Following this processing, the control unit sends command impulses directly to the solenoid valves of the shock absorbers M17/18/19/20. The vehicle's vertical acceleration is detected by the accelerometer N47 which sends signals "ACCH" and "ACCL" to pins 4B and 10C of the control unit. The steering wheel rotational speed is detected by the accelerometer L40 which sends the signals "STR2": "STR1", "STRZ" at pins 1 A, 6A, 11A of the control unit. Through pin 6C the control unit detects the pressure of the brake pedal through the pressure contact L41, whilst at pin 2B, the control unit detects the position of the gearbox (switch H46) and that of the accelerator (switch H47). At pin 4A of the control unit, the speedometer signal is detected and sent to the instrument panel C10. The selection of ''Auto" or "Sport" functioning is made using the buttons located on the panel B67 and the condition is "detected" at pins 8A and 2A of the control unit N46.
