HYDROACTIVE 2 ZASADA DZIAŁANIA.pdf

Hydractive 2 suspension system

In comparison to a regular hydropneumatic suspension, Hydractive 2 adds the following elements:

1) Additional hydraulic elements (compared to hydropneumatic):

- Two additional spheres with no damping elements (similar to accumulator spheres), one for the front

wheels, and one for the rear wheels.

- Two electro-hydraulically controlled suspension control blocks, which fit the spheres above, again one for

the front wheels and one for the back wheels.

The control blocks connect the left and right corner sphere and the height corrector, and depending on the

electric control, the center sphere. This enables the suspension to have two spring/damping settings, which

can be quickly selected by an electric signal. The suspension has a soft setting with low resonance

frequency, and a hard suspension setting with a higher resonance frequency. The roll characteristics of the

suspension also change depending on suspension setting. In hard mode the cross-flow of fluid between left

and right corner spheres is severely limited. This considerably dampens rolling motion. In the soft setting the

fluid passes through the double damper element arrangement. The roll motion damping of the suspension is

significantly lower than for the hard setting.

2) Electronic sub-system:

- A set of sensors that sense the dynamics of the vehicle

- A user command input enables the driver to choose the suspension mode between 'normal' and 'sport'

- An ECU (Electronic Control Unit) that uses the inputs from the sensor and the user select input to generate

the control signal for the suspension control block, and a status signal for the user

- A suspension status light on the dashboard that tells the driver which setting is selected

The ECU reacts to inputs from it's sensors to dynamically select the soft or hard mode of the suspension,

based on two sets of rules, one each for the normal and sport suspension setting. The ECU uses a relatively

simple but effective set of rules to be able to decide on the suspension setting within 25ms.

Hydraulic elements

1) Suspension control block

The suspension control block consists of several distinct elements:

- A standard Citroen sphere base which fits an accumulator type sphere (without a damper block)

- A hydraulically controlled valve that connects or isolates the sphere above from the rest of the suspension

circuit, in effect, a 'control piston' within the control block.

- A ball and piston valve arrangement that limits fluid cross-flow between the left and right suspension strut.

The arrangement is such that the ball valve limits cross flow, but is disabled for suspension height

corrections, to guarantee that the fluid pressure in the corner struts remains equalized.

- Two damping elements similar to the ones used on suspension spheres, that act as dampers for the center

sphere.

The suspension control blocks for the front and rear suspension are the same.

The picture below shows the suspension control block, with the electric valve already mounted.

2) Electrically controlled valve

The valve is located on the suspension control block and is driven by the ECU. It's resistance is 4 ohms and

the nominal voltage, for continuous duty is 2.6V. However, due to the inductance of the winding, the ECU

uses pulse width modulation to achieve a constant current through the winding. This makes the valve react

quicker by increasing the drive voltage when it is turned on, but also reduces heat buildup since the voltage

reduces once the inductive effects have been overcome, should the valve stay on for a long enough time.

The valve is designed to be on indefinitely as long as the proper current is driven through it. The cross-

section of the valve is shown below:

The valve itself does NOT control the flow of fluid into the center sphere. instead, it controls the fluid flow to

the hydraulically controlled valve inside the suspension control block body. The valve enables passage of

the main feed pressure from the main feed to the control piston located within the control block (orifice

marked LHM to orifice marked with the control block outline in the picture above), or it enables the pressure

activating the control piston to escape through a simple non-return valve through the valve body (to the

orifice marked with the LHM tank outline in the picture above). In this way the valve actually only controls the

control piston, in effect implementing an electro-hydraulic relay of sorts.

The electric portion of the valve is energized when the suspension is in it's SOFT setting. Electrically, the

default position of the suspension is HARD. However, due to the indirect action of the suspension valve

within the suspension regulator body, depending on the suspension pressure and the pressure in the main

feed, with the electric valve disconnected, the suspension can remain in either position for extended periods

of time. With the main suspension pressure feed at nominal pressure, both the electric and the hydraulic part

of the valve will remain in HARD mode.

3) The center sphere

The center sphere is an accumulator type sphere that is used to provide a lowering of the spring constant of

the suspension when the sphere is connected to the rest of the suspension circuit. The spheres differ

depending on the vehicle version and also depending on weather they are used for the front or rear

suspension.

Operation:

The picture above depicts the soft setting of the control block. The blue areas are LHM fluid under

suspension pressure, the red area is the suspension hydraulics feed, under the system feed pressure (equal

to the main accumulator pressure under normal operation).

The center element is the suspension control block. The electric valve (bottom left corner) opens the feed

pressure to move the control piston in the control block, which opens the center sphere to the rest of the

suspension. Note the blue area - the fluid passes through two damping blocks (one for each strut

connection) into the middle sphere. When both the struts move in unison, effectively, the middle sphere

behaves as a standard sphere with a damper element with a hole twice the area of a single damper element

in the suspension block. However, when the fluid moves from one strut to the other, as is the case when the

vehicle rolls left-right, it has to pass through both damper elements consecutively. In addition to that, the

middle sphere presents a 'spring' that dampens cross flow by absorbing quick changes in pressure between

the dampers, additionally slowing the flow of fluid between the corner spheres. In this manner the roll

behavior of the suspension is improved.

The above picture shows the suspension control block in the hard setting. The electric valve does not let the

main feed pressure pass and move the control piston. The pressure inside the middle sphere, which is

always higher than that of the return path under normal operating conditions, will move the control piston

into a position which closes off the middle sphere completely. The remaining pressure in the middle sphere

remains unknown (green area in the picture). The control rules for the electric valve are designed with this in

mind, so that the pressure is periodically equalized by enabling the control block to assume the soft setting

for a short period of time. This is done because it is possible that the suspension pressure (blue area) is

different at the time the control block goes into hard mode and at the time it returns to soft mode, due to

either the dynamics of the suspension (acceleration, braking, movement due to uneven surface), or the

vehicle height being set differently.

Cross-flow of fluid from one strut to the other still has to pass through both damper blocks, but it is

additionally limited using a simple piston and ball valve, which is now positioned between the damper

elements instead of the middle sphere. The ball is positioned in the fluid so that any cross flow moves the

ball and thus limits the cross flow. This dampens the cross-flow considerably (see picture below), and thus

also body roll.

In the picture above, a situation is shown where the vehicle is making a left turn, and tends to roll to the

right. This compresses the right strut and expands the left strut, causing a cross flow of fluid, from the

compressed strut to the expanded one. This moves the ball in the valve towards outlet to the left strut,

closing off further cross-flow. The remaining damping is left to the spheres on the strut.

Because it is possible that the vehicle needs to change ground clearance while body roll is present, such as

when the vehicle is braking in a curve, the ball valve has an additional piston arrangement in the fluid path

from the height corrector. In the pictures above, two situations are shown where height correction is needed.

In the left picture, the suspension needs to be raised. This would mean that the pressure on the height

regulator side becomes higher than that of the suspension. This situation presses down the piston, which

dislodges the ball in the anti-roll valve, to enable the pressure to raise equally in both the left and right strut.

If the ball was not dislodged, the pressure would increase only in one strut, thus locking the ball position,

and resulting in incorrect suspension operation.

The right picture shows the opposite situation, where the suspension needs to be lowered. In this case, fluid

needs to go out of both struts, which dislodges the ball. Because the pressure on the regulator side is now

lower than that of the suspension, and both sides of the piston part of the valve effectively present the same

surface area, the pressure of the suspension will open the piston towards the return line, and the fluid will

escape from the struts lowering the vehicle.

The electronic subsystem

The suspension ECU takes signals from the various sensors and based on two sets of rules (one each for

normal and sport suspension), activates the electric valves. Although there are two electric valves that select

the suspension setting (one for the front and one for the rear wheels), the ECU operates them as if they

were one valve, so in effect, the ECU only has a single output signal.

The ECU uses 7 sensors, which generate a total of 10 'input parameters':

1) Vehicle speed

2) Steering wheel position (2a) and speed (2b)

3) Body movement magnitude (3a) and speed (3b)

4) Gas pedal press (4a) and release (4b) speed

5) Brake pressure sensor

6) Door/boot open sensor

7) Ignition switch on/off

The sensors work as follows:

1) Speed sensor

The sensor is Hall effect based and produces 8 impulses per rotation, or approximately 5 impulses per

meter traveled (this depends somewhat on tire size). It is located on the gearbox where the speedometer

cable attaches, or in some versions, on the cable itself.

2) Steering wheel angle/speed sensor

The sensor is optoelectronic. It produces a quadrature signal from two optoelectronic sensors, by

interrupting the passage of an infra-red beam of light through 28 holes on the sensor corona. The ECU

senses signal changes on both optoelecronic sensors to effectively increase the resolution of the sensor (28

impulses per steering wheel revolution) by a factor of four. This produces one edge change every 3.214

degrees of steering wheel rotation.

The signal from the sensor is used in three ways:

a) The straight line position is assumed if the vehicle speed is more than 30km/h and the total accumulation

of full quadrature impulses generated was zero within a period of 90 seconds. This is then used as a

reference for steering wheel position. Accumulation of full quadrature impulses effectively means that for the

accumulation process, the sensor resolution is not multiplied by 4. This is done to avoid sensing small

movements which the driver might use to correct miniscule road irregularity or a steering wheel free-play. In

order for a pulse to accumulate in this mode, depending on the actual position of the steering sensor, a hole

or fill-in has to pass beneath both optoelectronic sensors. In addition, the number of pulses observed in each

direction is tallied and the zero position is also corrected using the resulting count. Because the number of

steering wheel turns is known (2.94 full left to full right), the sensor can generate a maximum of 84 pulses,

42 in each direction from straight. This process is a lesser rate correction, because up to a 5 pulse

difference is possible due to wheel alignment and similar phenomena. A total tally of anything more than 47

pulses in either direction from the current center line, automatically corrects the internal center line reference

by the difference between the actual number of pulses observed minus 47.

b) Pulse edges from both optoelectronic sensors within the steering wheel sensor are counted relative to the

zero position set in (a) to derive the steering wheel position. The sequence of edge changes from both

optoelectronic sensors is used to derive the direction the wheel is turning.

c) The time between the pulse edges is also measured, which is used to derive the steering wheel speed.

3) The body movement sensor

This is similar to the steering wheel sensor. It consists of two optoelectronic sensors with two infrared beams

being either blocked or alowed to pass by a disc which has 45 notches on it's corona, producing 45 full

quadrature pulse cycles per revolution. The ECU again uses the signal edges from the two optoelectronc

sensors to quadruple the resolution of the sensor. Excessively long intervals between impulses are taken as

suspension travel as a result of a different height setting being chosen, and are not taken into account.

Similar to the steering wheel sensor, the body movement sensor is used to derive the body movement

amplitude, as well as speed of movement.

Due to the way the sensor is set up, it is capable of detecting squat/dive and to an extent, roll. The sensor is

connected to the front anti-roll bar to the right of the height corrector linkage. Since the sensor is mounted off

center on the anti-roll bar, it's sensitivity to roll is about three times less than it's sensitivity to squat/dive.

Only a small amount of the full circumference of the corona is used due to this linkage arrangement,

unfortunately, the documentation is not exactly clear as to what number of impulses from the sensor

corresponds to what amount of body movement. The picture below shows how the sensor looks. Note the

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