Related Manuals for Audi A6 242
Summary of Contents for Audi A6 242
- Page 1 Service. Pneumatic suspension system Part 1 Selflevelling suspension in the Audi A6 Design and Function Self-study programme 242 For internal use only...
- Page 2 Self-levelling suspension, A6 The rear axle air suspension system for the Audi A6 Avant is described here. 242_046 The 4-level air suspension of the Audi allroad quattro is described in self- study program 243. You will find further information on the Audi allroad quattro in self-study programme 241.
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Page 3: Table Of Contents
Contents Page Principles Vehicle suspension..............4 The suspension system ............6 Vibration ................... 8 Characteristic values of springs .......... 12 Conventional running gear without self-levelling .... 14 Principles of air suspension Self-levelling air suspension ..........16 Characteristic values of air spring ........21 Vibration damping.............. -
Page 4: Principles
Principles Vehicle suspension When a vehicle travels over irregular road When we talk about the vehicle suspension surfaces, impact forces are transmitted to the we can basically distinguish between the suspension system and the vibration wheels. These forces pass to the bodywork via the suspension system and the wheel damping system . - Page 5 During driving operation, the vehicle body is The correct matching of the springs and subject not only to the forces which cause the vibration damping system is therefore of upward and downward motion of the vehicle, great significance. but also the movements and vibrations in the direction of the three spatial axes.
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Page 6: The Suspension System
Principles The suspension system As ”supporting” components of the In the case of the passenger vehicle we can suspension system, the suspension elements differentiate between sprung masses (body form the connection between the wheel with drive train and parts of the running gear) suspension and the bodywork. - Page 7 The unsprung masses The aim in principle is to minimise the volume of unsprung masses and their influence on the vibration characteristics (natural frequency of the bodywork). Furthermore, a low inertia of masses reduces the impact load on the unsprung components and significantly improves the response characteristics of the suspension.
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Page 8: Vibration
Principles Vibration If a mass on a spring is deflected from its rest The natural frequency of the bodywork position by a force, a restoring force develops in the spring which allows the mass to The vibrations are defined by the degree of rebound. - Page 9 The natural frequency of the bodywork is Definitions essentially determined by the characteristics of the springs (spring rate) and by the sprung Vibration Upward and downward mass. motion of the mass (body) Greater mass or softer springs produce a Amplitude The greatest distance of lower natural frequency of the bodywork and the vibrating mass from...
- Page 10 For instance, the natural frequency of the matched to a higher natural frequency bodywork of the Audi A6 is matched to 1.13Hz of the bodywork because when the on the front axle and 1.33Hz on the rear axle vehicle is loaded, it is principally the (design position).
- Page 11 Engine code / gearbox code letters Paint no. / interior equipment no. M-equipment number Stamp of the Audi delivery Weight class of centre front axle Weight class of the rear axle Un-laden weight / consumption figures / CO...
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Page 12: Characteristic Values Of Springs
Principles Characteristic values of Progressive characteristic curve springs Linear characteristic curve Hard spring Characteristic curve/spring rate of springs We can obtain the characteristic curve of a spring by producing a forces/travel diagram. The spring rate is the ratio between the effective force and the spring travel. - Page 13 (Example: Suspension strut with auxiliary polyurethane springs). 242_020 -120 Rebound in mm Compression in mm Parallel springing Spring Auxiliary spring Advantages of progressive characteristic curve of spring: • Better matching of the suspension system from normal to full load. • The natural frequency of the bodywork remains practically constant during loading.
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Page 14: Conventional Running Gear Without Self-Levelling
Principles Conventional running gear (steel springs) without self- levelling Spring travel The overall spring travel s required for When the vehicle is stationary, the vehicle running gear without self-levelling is body retracts by a certain spring travel comprised of the static compression s depending upon the load. - Page 15 The static compression ... Definitions: ... is the starting point (zero) for the dynamic The un-laden position ... spring movements, compression travel (plus) ... is the compression exerted onto the wheels and rebound travel (minus). when the vehicle is ready for the road (fuel tank completely filled, spare wheel and ...
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Page 16: Principles Of Air Suspension
Principles of air suspension Self-levelling air suspension Air suspension is a controllable form of • Ground clearance is maintained, whatever vehicle suspension. the load. With air suspension, it is simple to achieve self-levelling and it is therefore generally • There are no track or camber changes integrated into the system. - Page 17 In addition to the main advantages offered by (sprung masses) remains at one level (design self-levelling, its realisation by means of air position) because the air spring pressure is suspension (Audi A6) offers another adapted accordingly. significant advantage. As the air pressure in the air springs is...
- Page 18 In the self-levelling suspension systems in the Audi A6 (on the rear axle) and in • Raised driving position for travel off-road the Audi allroad quattro (rear and front and on poor road surfaces.
- Page 19 Design of the air springs: In passenger vehicles, air springs with The outer and inner surfaces are made of an U-bellows are used as suspension elements. elastomer material. The material is resistant These allow greater spring travel in restricted to all weather influences and is largely oil- spaces.
- Page 20 Principles of air suspension Air springs must not be moved in an High-quality elastomer material and unpressurised condition since the air polyamide cord woven inserts (stability bellows cannot unroll on the piston and supports) provide the U-bellows with good would be damaged. unrolling characteristics and a sensitive In a vehicle in which the air springs are response of the spring system.
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Page 21: Characteristic Values Of Air Spring
Air spring parameters Piston and cylinder Supporting force Resilience/spring rate The resilience (supporting force) F of an air spring is determined by the effective surface and the excess pressure in the air spring p F = p The effective surface A is defined by the effective diameter d In the case of a rigid structure, such as piston... - Page 22 Principles of air suspension Characteristic curve of springs Owing to the functional principle, the characteristic curve of an air spring is Small spring volume progressive (in the case of cylindrical pistons). Large spring volume (+ piston volume) The progress of the characteristic curve of the spring (flat/steep inclination) is determined by the spring volume.
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Page 23: Vibration Damping
Example of the contour of a piston (suspension strut in the Audi allroad quattro) U-bellows Piston Compressed 242_079 Vibration damping Vibration dampers are available in different Without vibration damping, the vibration of designs but their basic function and purpose the masses during driving operation would be increased to such an extent by repeated are the same. - Page 24 Principles of air suspension Sprung mass Direction of travel Unsprung mass Uneven ground Damped vibration Un-damped vibration 242_022 The term “shock absorbers” is As previously mentioned, vibration damping misleading as it does not precisely has a fundamental effect on driving safety describe the function.
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Page 25: Shock Absorbers (Vibration Dampers)
Shock absorbers (vibration dampers). Dual pipe gas-pressure shock absorber Cavitation is the formation cavities and the creation of a vacuum in a rapid The dual pipe gas-pressure shock absorber liquid flow. has become established as the standard damper. In the dual pipe gas-pressure shock absorber, the working cylinder and the housing form two chambers. - Page 26 Principles of air suspension Function During compression, damping is determined During rebound, the piston valve alone by the bottom valve and to a certain extent by carries out the damping action and exerts a the return flow resistance of the piston. predetermined resistance against the oil The oil displaced by the piston rod flows into flowing downwards.
- Page 27 Single pipe gas-pressure shock absorber With the single pipe gas-pressure shock absorber, the working chamber and the oil reservoir are located in a single cylinder. Volumetric changes caused by the piston rod and the temperature changes in the oil are compensated by another gas chamber which 242_082 is separated from the working cylinder by a...
- Page 28 Principles of air suspension Function During rebound, oil is forced out of the upper During compression, oil is forced out of the chamber through the suction valve integrated lower chamber through the discharge valve into the piston which exerts a defined integrated into the piston which exerts a resistance against the oil.
- Page 29 Damping matching We can basically distinguish between Advantage of this matching: compression and rebound in the damping Good response of the vehicle suspension process. ensures greater driving comfort. The damping force during compression is The disadvantage of this matching occurs in generally smaller than during rebound.
- Page 30 Principles of air suspension The degree of damping describes how The degree of damping much kinetic energy a vibration system been dissipated between two vibration ... (the factor which determines how quickly cycles as a result of damping. the vibrations are eliminated) The damping coefficient is just another of the vehicle body is dependant on the term for degree of damping.
- Page 31 Damping force The force/stroke diagrams thus obtained can The damping force depends upon the oil be converted into force/velocity diagrams (f-v volume to be displaced (surface of the diagrams). damping valve), the flow resistance of the damper valves, the speed of the damper These characteristic curves show the piston and the viscosity of the damping oil.
- Page 32 Principles of air suspension Note: Measures are taken during the design stage to adapt the characteristic curves to the A distinctive feature of damper requirements of suspension matching. matching is described in SSP 213, page 28, “Shock absorbers with load Shock absorbers with decreasing and travel-dependent damping characteristic curves are normally used.
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Page 33: Pdc Shock Absorbers
Audi A6 self-levelling air suspen- sion and the Audi allroad quattro 4-level air suspension both have a continuously variable load recognition system fitted to the rear axle. - Page 34 Principles of air suspension The damping force is altered by means of a separate PDC valve integrated into the damper. It is connected to the air springs via a hose. 242_087 1 00 A variable throttle in the PDC valve is Rebound controlled by the air spring pressure acting as 1 00...
- Page 35 Design and function The PDC valve influences the flow resistance of the working chamber on the piston rod side (working chamber 1). Working chamber 1 is connected to the PDC valve via bore holes. The PDC valve has a low flow resistance when the air spring pressure is low (no load or small partial load).
- Page 36 Principles of air suspension Function during rebound at low air spring pressure The piston is drawn upwards, part of the oil flows through the piston valve, the remainder flows through the bore holes in working chamber 1 to the PDC valve. As the control pressure (air spring pressure) and consequently the flow resistance of the PDC valve is low, the damping force is reduced.
- Page 37 Function during compression at low air spring pressure The piston is pushed downwards and damping is determined by the bottom valve and to a certain extent by the flow resistance of the piston. The oil displaced by the piston rod flows partly via the bottom valve into the reservoir.
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Page 38: Self-Levelling Suspension, A6
In the case of the Audi A6, an air suspension- based self-levelling system is offered as an A level sensor detects the actual vehicle level. - Page 39 Along with the principle advantages of self- levelling (see Principles), the system realised in the A6 has the following advantages: • Virtually load-independent suspension • Environmentally friendly, uses air and vibration behaviour. • Good operating safety due to great • Little space requirement due to compact stability.
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Page 40: Air Springs
Self-levelling suspension, A6 The air springs The installation of the air springs on the front- Air springs may not be moved while wheel drive and the quattro drive is the same at atmospheric pressure since the as in the steel spring version. This allowed the U-bellows cannot uncoil on the piston use of the axle design from the production and would be damaged. - Page 41 O-ring Air suspension strut design In the case of the quattro suspension strut, the connection/seal between the air spring (piston) and the damper is made via a double- sealed bayonet connector. The bayonet connector must be absolutely clean and is greased before assembly with a special lubricant (see Workshop Manual).
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Page 42: Air Supply Unit
Self-levelling suspension, A6 The air supply unit The following components are contained in a metal box inside the air supply unit: Specially adapted rubber bushes prevent any significant vibration transfer to the bodywork. – the V66 compressor with integrated air Ensure that rubber bushes are installed dryer and discharge valve N111, correctly! -
Page 43: Diagram Of Pneumatic System
Diagram of pneumatic system Suction filter Discharge valve N11 Compressor with motor V66 Valve for suspension strut HL N150 Non-return valve 1 Valve for suspension strut HL N151 Air dryer Rear left air spring Non-return valve 2 Rear right air spring Non-return valve 3 Throttle Discharge filter... -
Page 44: Compressor
Self-levelling suspension, A6 The compressor The compressed air is generated by means of The discharge valve N111 and the pneumatic a single stage piston compressor with discharge valve are integrated into the dryer integrated air dryer. In order to avoid oil cartridge housing. - Page 45 Suction/compression Suction/compression When the piston moves upwards, air is sucked into the Non-return valve 1 crankcase via the sinter filter. The Air dryer air is compressed above the piston and enters the air dryer via non-return valve 1. The compressed and dried air passes via non-return valve 2 to the pressure connector which leads to the transverse check...
- Page 46 Self-levelling suspension, A6 Discharge/lowering The air spring valves N150 and N151 and discharge valve N111 open during compression. The air spring pressure flows to the pneumatic discharge valve and out of the system from there via the air dryer and the pressure limiting valve (see description of Pneumatic discharge valve pneumatic discharge valve).
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Page 47: Air Dryer
The air dryer Because the air dryer is regenerated only with waste air, the compressor cannot be used to fill any other The air must be dehumidified in order to components. As this compressed air is prevent condensate and the associated not fed back via the air dryer, no problems of corrosion and freezing. -
Page 48: Discharge Valve N111
Self-levelling suspension, A6 Regeneration The air dryer is regenerated during discharge As outlined above, the compressed air is (lowering). During discharge, the dried initially fed through the air dryer and dried. compressed air (“waste air”) is fed back into The moisture is temporarily stored in the air the air dryer where it re-absorbs the moisture dryer and the dried compressed air passes stored there and discharges it into the... - Page 49 Pneumatic discharge valve The pneumatic discharge valve performs two At an air spring pressure of >3.5 bar, the valve tasks: body lifts against the resilience of both valve springs and opens valve seats 1 and 2. The air • It is a residual pressure retaining device spring pressure then passes to the air dryer •...
- Page 50 Self-levelling suspension, A6 The pressure limiting function protects the In such cases, the pressure limiting valve system against inadmissible high pressure opens against the resilience from approx. e.g. when the compressor fails to switch off 13.5 bar upwards, and the pressure is due to a defective relay contact or defective discharged via the discharge filter.
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Page 51: Valve For Suspension Struts N150 And N151
242_012 above (not in the case of a one-sided load). The self-levelling system in the Audi A6 is not able to compensate for one-sided loads (level difference between left and right). To prevent differing pressures in... -
Page 52: Self-Levelling Suspension Sender G84
This connection allows self-levelling to operate using only one level sensor. The self-levelling system in the Audi A6 is not able to compensate for different levels on the left and right-hand sides (e.g. due to one-sided loads). - Page 53 Function The angle sensor described here is also used for the automatic A ring magnet is connected to the axle of the headlight range control system. sensor crank (rotor). A total of 3 sensors are fitted into vehicles with automatic headlight A hall IC is positioned eccentrically between a range control.
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Page 54: Self-Levelling Suspension Control Unit J197
Self-levelling suspension, A6 Self-diagnosis system G84 VAS 5051 If the G84 fails, no self-levelling is possible. The system initiates the appropriate emergency operation mode. The G84 is adjusted by adapting the reference level with the aid of the diagnostic tester and spacer gauges T40002 (see Workshop Manual). -
Page 55: Self-Levelling Suspension Warning Lamps K134
<–55 mm/>+30 mm. the system is switched off. The driver is requested to contact the ..flashes during final control diagnosis. nearest Audi service centre..flashes when the control system is switched off (only possible with diagnostic tester). -
Page 56: Function Diagram
Self-levelling suspension, A6 Functional diagram Condenser Diagnostic interface Self-levelling suspension sender Driving speed signal J197 Self-levelling suspension control unit Door contact signal J403 Relay for self-levelling suspension Terminal 50 signal compressor K134 Self-levelling suspension warning lamp Discharge valve N150 Rear left strut valve N151 Rear right strut valve = Input signal... -
Page 57: Interfaces
The interfaces 1 wheel revolution The driving speed signal (a square wave signal processed by the dash panel insert, the frequency of which changes analogously to the speed) is required in the evaluation of the driving Driving speed signal (4 pulses) condition (stationary/driving mode) and thereby for the selection of the control criteria (see “Control concept”). -
Page 58: The Control Concept
Self-levelling suspension, A6 The control concept Driving mode Stationary mode Control process Run-on mode/run-up mode Sleep mode Stationary mode Driving mode The stationary mode is recognised at a speed The driving mode is recognised at a speed of of <5 km/h. >10 km/h. - Page 59 Run-on mode/run-up mode Sleep mode After “Ignition OFF”, the control system is in To minimise electricity consumption the the so-called run-on/run-up mode. The control system switches to “system idle” control unit remains active for a maximum of (sleep mode) after 15 minutes. 15 minutes (via terminal 30) until it goes into sleep mode.
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Page 60: Other Features Of The Control Concept
Self-levelling suspension, A6 Other features of the control concept Lifting platform mode System behaviour: If the vehicle is raised on a lifting platform the It is normal for the rear axle to sink system will react in the same manner as for a after placing the vehicle onto the lifting level increase, by discharging the air spring platform as a certain amount of time... - Page 61 Overheating protection In order to protect the compressor from overheating, it switches off at excess temperatures. 242_011 A temperature module is integrated into the control unit. This monitors the temperature and is used to calculate the compressor temperature. The calculations are based on the running and cooling times of the compressor.
- Page 62 Notes...
- Page 64 All rights reserved, including the right to make technical changes. AUDI AG Dept. I/VK-5 D-85045 Ingolstadt Fax 0841/89-36367 940.2810.47.20 Technical status 11/00 Printed in Germany...
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