Electronic air-process unit (EAPU), component description

W42.60-1162-05

Location

6.17 Electronic Air Processing Unit (EAPU)

Die Electronic Air-Processing Unit (EAPU) (6.17) is located inside on the left longitudinal frame member, at the height of the fuel tank.

Task

The electronic air-process unit (EAPU) (6.17) has the following tasks:

 Regulation of cut-in and shutoff phases of the pressure regulator

 Drying of the compressed air

 Distribution of the compressed air delivered by the compressor to the brake circuits and auxiliary consumer circuits

 Limitation of the operating pressures in the pressure circuits

 maintaining the reservoir pressures of all pressure circuits at the specified level

 protection of the intact pressure circuits against a possible defective pressure circuit

 regulation of compressed air desiccant cartridge regeneration

 Record and forward measurement value for condensation level

W42.60-1160-06

Design

6.17 Electronic Air Processing Unit (EAPU)

Pneumatic connections

3 Bleeding

4 Control connection (to compressor)

11 Compressed air supply (from compressor)

12 Compressed air supply (external filling)

21 Compressed air release (RA brake circuit supply)

22 Compressed air release (FA brake circuit supply)

23 Compressed air release (trailer control)

24 Compressed air release (ancillary consumers)

25 Compressed air release (parking brake)

26 Compressed air release (transmission control and clutch operation supply)

27 Compressed air release (air suspension)

28 Tire inflation connection

Electrical components

A121a1 Electronic Air Processing Unit (EAPU) control unit

A121b1 RA brake circuit pressure sensor

A121b2 FA brake circuit pressure sensor

A121b3 Trailer control pressure sensor

A121b6 Transmission control and clutch operation pressure sensor

A121r1 Heating element

A121y1 Pre-control solenoid valve

A121y2 Regeneration solenoid valve

A121y3 Trailer control solenoid valve

PL2 Auxiliary consumer pressure limiter

PR Pressure regulator drain valve

SV C1 RA brake circuit overflow valve

SV C2 FA brake circuit overflow valve

SV C3 Trailer control overflow valve

SV C4 Auxiliary consumer overflow valve

SV C5 Air suspension overflow valve

SV C6 Transmission control and clutch operation overflow valve

SV PB Parking brake safety valve

TH REG Regeneration throttle

Pneumatic components

A Non-return valve

CV C1 RA brake circuit check valve

CV C2 FA brake circuit check valve

CV C6 Transmission control and clutch operation check valve

CV EG Check valve

CV PB Parking brake check valve

CV PR Pressure regulator check valve

CV REG Regeneration check valve

CTR Compressed air desiccant cartridge

EX ESS Energy-saving system quick vent valve

Function

 The functions described below are only available with the ignition switched on. If a system is faulty, a warning indication is displayed in the instrument cluster (INS).

Filling operation (with empty system)

Compressed air reaching via the connector of the compressed air supply (11) from the compressor into the Electronic Air-Processing Unit (EAPU) (6.17) is cleaned and dried in the compressed air drier cartridge (CTR). The compressed air flows through the pressure regulator check valve (CV PR) to the air suspension overflow valve (PV C5), RA brake circuit overflow valve (PV C1) and FA brake circuit overflow valve (PV C2). For reason of the lower opening pressure of the overflow valves of the rear axle brake circuit (PV C1) and front axle brake circuit (PV C2) with an empty system the brake circuits of the rear and front axle are filled as a priority over the pressure circuit for the air suspension.

The compressed air drain (21) for the rear axle brake circuit is monitored by the pressure sensor for the rear axle brake circuit (A121b1) and the compressed air drain (22) for the front axle brake circuit is monitored by the pressure sensor for the front axle brake circuit (A121b2).

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 Via the non-return valve only attached to the rear axle brake circuit overflow valve (PV C1) (A) in addition compressed air can flow into the rear axle brake circuit so that here an earlier pressure rise takes place in the front axle brake circuit.

If the pressure rises at the compressed air drains (21 and 22), the solenoid valves for precontrol (A121y1), regeneration (A121y2) and trailer control (A121y3) as well as the pressure limiter for electrical accessories (PL2) are also applied with pressure. The auxiliary consumer pressure limiter (PL2) limits the pressure to 8.5 bar. The compressed air flows further to the trailer control overflow valve (PV C3), auxiliary consumer overflow valve (PV C4) and transmission control and clutch operation overflow valve (PV C6).

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The solenoid valve for trailer control (A121y3) is energized by the control unit for Electronic Air-Processing Unit (EAPU) (A121a1) and locks the overflow valve for trailer control(PV C3) by the set pressure so that first the compressed air drain (24) for electrical accessories and the compressed air drain (26) for the transmission control and clutch operation are vented.

The compressed air drain (26) for the transmission control and clutch operation is monitored by the pressure sensor for transmission control and clutch control (A121b6).

The regeneration solenoid valve (A121y2) is also energized as of a certain reservoir pressure which causes pressure to be applied to the pressure regulator drain valve (PR). This prevents the pressure regulator drain valve (PR) from being opened by the rising reservoir pressure and ventilating the system.

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Via the RA brake circuit pressure sensor (A121b1) and FA brake circuit pressure sensor (A121b2) the electronic air-process unit (EAPU) control unit (A121a1) detects the current reservoir pressure in the brake circuits. After the reservoir pressure guarantees the auxiliary braking effect specified by the legislator, the solenoid valve for trailer control (A121y3) is switched de-energized and as a result the locking of the overflow valve for trailer control (PV C3) is canceled. Now the compressed air drain is also vented (23) for the trailer control and compressed air drain (25) for the parking brake.

The compressed air drainage (23) for the trailer control is monitored by the pressure sensor for trailer control (A121b3).

 The filling sequence is also influenced by the engine speed and can therefore differ from the sequence described above. If the system is partially filled, different filling sequences may also result depending on the position of the overflow valves.

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Deceleration phase control

Via the communication with the engine control (MR) control unit the Electronic Air-Processing Unit (EAPU) (A121a1) control unit detects when the engine is in deceleration mode (e.g. when downhill driving). In this case, the electronic air-process unit (EAPU) (6.17) switches to the filling phase, even if the reservoir pressure has not yet dropped to the cut-in pressure.

Shutoff with regeneration

If the RA brake circuit pressure sensor (A121b1) and FA brake circuit pressure sensor (A121b2) signal that the operating pressure (shutoff pressure) has been reached in the brake circuits, the electronic air-process unit (EAPU) control unit (A121a1) energizes the precontrol solenoid valve (A121y1). The regeneration solenoid valve (A121y2) remains energized. The pressure from the precontrol solenoid valve (A121y1) causes the pressure regulator (PR) drain valve to switch to open. After the pressure regulator (PR) drain valve has switched over, the compressed air delivered by the compressor flows undried into the surrounding air via the vent line (3).

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At the same time dried compressed air flows out of the system by the engaged regeneration solenoid valve (A121y2), via the regeneration check valve (CV REG) and the regeneration throttle (TH REG) to the compressed air drier cartridge (CTR). The desiccant is regenerated as the compressed air flows through the compressed air desiccant cartridge (CTR). The compressed air carrying the moisture flows through the pressure regulator (PR) drain valve and along the vent line (3) into the surrounding air.

Regeneration ends when the electronic air-process unit (EAPU) control unit (A121a1) no longer energizes the regeneration solenoid valve (A121y2).

 The electronic air-process unit (EAPU) control unit (A121a1) processes various items of information (e.g. compressor speed and pressure level) to calculate the regeneration time.

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Shutoff without regeneration

If the RA brake circuit pressure sensor (A121b1) and FA brake circuit pressure sensor (A121b2) signal that the operating pressure (shutoff pressure) has been reached, the electronic air-process unit (EAPU) control unit (A121a1) energizes the precontrol solenoid valve (A121y1). The regeneration solenoid valve (A121y2) is de-energized. The pressure from the precontrol solenoid valve (A121y1) causes the pressure regulator (PR) drain valve to switch to open. After the pressure regulator (PR) drain valve has switched over, the compressed air delivered by the compressor flows undried into the surrounding air via the vent line (3).

Each time a shutoff operation is performed, the energy-saving system quick vent valve (EX ESS) also admits air to the control connection (4) to the switchable compressor.

The reservoir pressure in the pressure circuits is prevented from escaping by the pressure regulator check valve (CV PR).

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Ventilation of compressed air desiccant cartridge

After the ignition has been switched off, the electronic air-process unit (EAPU) control unit (A121a1) energizes the precontrol solenoid valve (A121y1), even if the shutoff pressure has not yet been reached. This causes both the compressed air line from the compressor and the compressed air desiccant cartridge (CTR) to be ventilated. The previously delivered and possibly damp compressed air does not remain in the compressed air desiccant cartridge (CTR).

 In the service and repair case the compressed air drier cartridge (CTR) can thus be replaced without any danger.

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Switching on

If the rear axle brake circuit pressure sensor (A121b1) and front axle brake circuit pressure sensor (A121b2) signal that the cut-in pressure has been reached, the electronic air-process unit (EAPU) control unit (A121a1) no longer energizes the precontrol solenoid valve (A121y1) and energizes the regeneration solenoid valve (A121y2) again. The pressure regulator (PR) drain valve switches over so that ventilation is no longer possible and the system is filled again.

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 When stationary the cut-in pressure can lie under the normal value, if beforehand much air was delivered or the system was filled by a remote source.

By changing over the jiggle valve of the pressure regulator (PR) a pressure drop also takes place at the quick-action vent valve for the energy saving system (EX ESS), the control line to the compressor being vented.

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Protection of pressure circuits

With the exception of the pressure circuit for the trailer control system, protection of the pressure circuits corresponds to the previously implemented pneumatic protection of a four-circuit protection valve.

 In the event of a circuit failure the static safety pressure (closing pressure) remains in the intact pressure circuits, if no post delivery takes place.

 The dynamic protection pressure is safeguarded in the intact pressure circuits, if no post delivery takes place.

If there is a reduction in pressure at the trailer control pressure circuit, the electronic air-process unit (EAPU) control unit (A121a1) uses the signals from the trailer control pressure sensor (A121b3), RA brake circuit pressure sensor (A121b1) and FA brake circuit pressure sensor (A121b2) to detect whether this reduction is due to normal compressed air consumption or whether there is a fault.

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In the case of normal compressed air consumption, the trailer control solenoid valve (A121y3) remains de-energized and the control line to the trailer control overflow valve (PV C3) also therefore remains unpressurized. This overflow valve is therefore not locked pneumatically. Since the RA brake circuit overflow valve (PV C1) and FA brake circuit overflow valve (PV C2) can allow compressed air to flow in the reverse direction, the compressed air required for the trailer control system can be drawn from the reservoirs of these brake circuits.

In the event of a defect the Electronic Air-Processing Unit (EAPU) (A121a1) control unit energizes the solenoid valve for trailer control (A121y3) and the overflow valve for trailer control (PV C3) is locked pneumatically by the set pressure. The intact pressure circuits are therefore protected.

 If the trailer control solenoid valve (A121y3) was energized after a fault was detected, the ignition must be switched off upon completion of repair work so that a system reset is performed.

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Protection as per ECE-regulation no. 13

In the event of a pressure drop (leakage) in the rear axle brake circuit, the compressed air discharge (23) for trailer control and parking brake are vented (ECE function) via the check valve (CV EG) and via the overflow valve for rear axle brake circuit (PV C1). The compressed air flows through the leakage point and into the surrounding air.

When the parking brake is disengaged, the pressure in the compressed air discharge (25) is maintained for the parking brake through the check valve (CV PB) and the parking brake remains disengaged. After engaging the parking brake, a renewed disengagement is not possible unless the reservoir pressure in the brake circuits of the service brake enables the legislator's specified secondary braking to be achieved.

 When the pressure circuits for trailer control and for the parking brake are vented and the lever of the parking brake valve is in the driving position (parking brake released), in the event of a pressure rise or adequate pressure the spring-loaded actuator combination brake cylinder is vented (brake released) and the vehicle can roll away.

Breakaway coupling

If there is a defect in the compressed air line to the trailer, the compressed air release (23) to the trailer control system is depressurized. The parking brake check valve (CV PB) prevents the compressed air drain (25) to the parking brake being vented and the spring-loaded actuator combination brake cylinder goes into the brake position.

Overpressure in auxiliary consumer circuits

If with a remote feed (e.g. via the supplies coupling head) the maximum pressure of the pressure limiter for electrical accessories (PL2) is exceeded, the parking brake safety valve (SV PB) vents the overpressure via the vent (3).

Heating

The heating element (A121r1) installed in code (B65) Heated compressed air drier (single-chamber system), heats up the area around the drain valve for pressure regulator (PR), in order to prevent freezing. The request and duty cycle for the heating element (A121r1) is determined with the aid of a temperature sensor.