torque converter clutch tcc

25.21 - 007 TCC/retarder components

Cutaway view of converter

1 Clutch discs (lockup

clutch)

2 Overrun freewheel

3 Disc carrier

4 Output rotor

5 Input rotor6 Stator (reaction wheel)

7 Freewheel for stator

8 Drive gear for oil pump and engine-dependent power take-off, if necessary

General

The number 400 in the model designation TCC400 indicates the diameter (B) of the converter in mm. For economic reasons the converter must be accurately tuned to the output or torque of the engine. Therefore, depending on the vehicle model, various converter versions are installed in the TCC housing. The different converter characteristics are achieved by modifying the converter components, but maintaining the same diameter. The converter characteristic is stated with the characteristic value for the torque take-up (Nm) at an engine speed of 1000 rpm with a "permanently braked" (stationary) output rotor (e.g. TCC400/61 = 400 mm dia., 610 Nm torque take-up).

There are converter housings which are completely welded up. These converters must be replaced complete in the event of a complaint (mechanical defect). In the event of transmission damage, visually inspect the area behind the oil filter of the TCC (C, clean side, refer to illustration on next page) for metal chips. The converter must be replaced if metal chips are found here.

Note

The bolted-on converter housing can be opened for cleaning and troubleshooting. In the event of a defective lockup clutch or defective overrun freewheel the complete converter must also be replaced as this subassembly is welded.

of 21© Daimler AG, 3/3/11, G/09/10 / ra2521w400007x / 21-0007 - TCC/retarder components Torgue converter clutch unit (MB Transmissions / WSK separate)

Oil circuit

Oil extraction

An internal gear oil pump (2) is installed in the TCC housing. The gear connected to the input rotor drives the oil pump drive gear. When the engine is running oil is constantly extracted from the storage chamber in the transmission via the oil gallery and filter (1) (C, clean side) and pumped into the valve body casing (A). The relief valve in the valve body casing limits the oil pressure to 8 to 10 bar. The oil flow (B) is fed through the oil supply flange (3) to the input rotor (4) via an oil gallery in the TCC housing.

Converter function

The converter housing is attached to the flywheel with diaphragms. The input rotor in the back of the converter housing is therefore permanently connected to the engine. The input rotor converts the mechanical energy of the engine into flow energy:


The oil pressure and centrifugal force cause the oil to be accelerated outwards, under high pressure, into the baffles of the output rotor.

In the output rotor the flow energy is again converted into mechanical energy. The power is transmitted by the oil flow (no wear) as the input rotor and output rotor are not connected directly to each other:

The oil flow is deflected against the blades of the stator (reaction wheel or reversing wheel) (2) in the output rotor (3). The blades of the stator are directed against the direction of flow of the output rotor. The rotor, with a one-way freewheel, which locks against the direction of incoming flow, is located on the splines of the oil supply flange. The oil flow is therefore once more diverted into the input rotor (1) in the direction of rotation of the engine. The backpressure on the output rotor and the additional acceleration in the input rotor cause a torque, which has been increased up to 2.5 times, to be transmitted to the output rotor and then to the transmission drive shaft via the turbine shaft/converter clutch (refer to Table 25.21 - 008/2 or 25.21 - 008/5).

The converter operates in two ranges:

1. If the output rotor is stationary (when starting off) the maximum torque is transmitted. After this the increased torque reduces progressively, the more the speed of the output rotor adjusts to that of the input rotor (converter phase).

2. An increase in torque is no longer effective from a speed ratio of 0.8 (clutch phase). The input rotor, output rotor and stator turn in the same direction in the clutch phase.


Oil return and cooling

When the engine is running the oil pump constantly delivers oil to the converter. The excess oil is forced into the valve body casing (6) between the oil supply flange (1) and output rotor (5, A) via an oil gallery in the TCC housing. A valve in this valve body casing is located at this oil gallery, which adjusts the converter back pressure between 3.9 and 4.3 bar.

The pilot pressure in the converter of approx. 5 bar is required to prevent bubble formation (results in cavitation) in the oil flow. With insufficient pilot pressure (oil level too low, loss of oil), the converter characteristics change and bearing damage due to a shortage of lubrication would be the consequence.


When driving in converter operation, high temperatures occur and therefore a heat exchanger (2) must be installed in the converter and transmission oil circuit. The heat exchanger can be an oil/air cooler (rear end cooling system on a heavy-duty transporter) or an oil/coolant cooler depending on the type of vehicle model:

On the new TCC version (with retarder) the oil is fed from the valve body casing (C) through an oil gallery in the retarder housing to the heat exchanger (D, connection 156). The return flow to the transmission oil pan is done via the right-hand oil gallery in the retarder housing.

These oil ducts are shut-off and switched over to the retarder cooling circuit when braking with the retarder. In this case excessive converter oil is fed back to the transmission via the leakage oil gallery (G). On the TCC version without retarder the oil is fed directly from the valve body casing (4, connection 9) to the heat exchanger. Depending on the construction, the return flow to the oil pan in the transmission takes place at the TCC housing (3, connection 10) or at the transmission housing (with ZF transmission only).

Oil temperature display

In order to avoid damage to the converter due to excessive oil temperatures, a display instrument (1) for the driver is fitted to the center waist rail.

Converter operation is only permissible in the green range. If during driving the temperature rises to the red range, the transmission must be shifted down or the vehicle stopped and the transmission shifted to the neutral position. If the temperature does not drop back within the normal range within a minute, the following may be the causes:

- Defect/leakage in cooling system,

- Insufficient oil level (TCC), loss of oil (TCC, transmission).


The oil temperature sensor (2) for the instrument display is located in the oil pipe between the heat exchanger and retarder housing.

The oil temperature sensor is a NTC resistor, i.e. the ohmic resistance decreases as temperature increases.

Note

In the event of a short-circuit or short-circuit to ground at the oil temperature sensor, the instrument displays an excessive temperature when the transmission is cold (> 160°C).

Lockup clutch


As, in the clutch phase, the torque converter (speed ratio approx. 0.8) operates without a tractive effort increase and with loss (efficiency 0.85 to 0.9), a lockup clutch is installed. This automatically makes a mechanical connection between the output rotor and input rotor. As a result the converter can only be operated in its range of highest efficiency:

When the engine is running the oil pressure for the lockup clutch is adjusted to 6 to 6.8 bar by the lockup clutch pressure valve in the valve body casing. When the lockup clutch is open, the shift valve in the valve body casing shuts off the oil pressure to the oil gallery (A) in the TCC housing. If the lockup clutch is to close, the shift valve is opened by the electromagnetic pilot control valve (4). As a result the pressurized oil can reach behind the lockup clutch pressure plate (C, enlarged view) through the bore (B) in the hollow turbine shaft (2) and stretch bolt (3). The clutch discs (1) are pushed back into the converter housing by the oil pressure.

As the clutch discs (1) engage in a spline (5) on the output rotor, there is now a mechanical connection to the input rotor. A pilot pressure against the closing direction of the lockup clutch pressure plate (D) exists as a result of the bore in the input rotor (arrow), so that when the lockup clutch is opened the oil pressure behind the pressure plate can be reduced quickly enough by the valve in the stretch bolt (3).

Lockup clutch control

So that the lockup clutch automatically switches in the correct range further components are required in and outside of the TCC housing.

The lockup clutch closes depending on the load. If as the engine speed increases a particular speed ratio (A, depending on the converter or control module) is achieved between the input rotor and output rotor, the lockup clutch is closed. As engine speed reduces the lockup clutch opens at approx. 950 rpm (applies to all types of converter).

1 Torque at transmission (tractive effort)

2 Converter torque characteristics

3 Engine torque characteristics

4 Engine speed5 Lockup clutch closed

6 Converter range

7 Kick-down range between 950 rpm and closing point of lockup clutch


TCC indicator lamp

A yellow indicator lamp is installed to indicate whether the vehicle is operated in the converter range or with a closed lockup clutch, : If the vehicle is driven in the converter range, the indicator lamp is illuminated. The indicator lamp goes out when the lockup clutch is closed.

Control module

The pilot control valve is actuated by the TCC control module via a relay (A31/K2 on the previous version, and A35/K1 on the new TCC version). On the new TCC version (with diagnostics facility), the TCC control module and retarder control module are located in one housing (1). As the opening and closing times for the lockup clutch differ for the various converter versions, a corresponding number of control module variants are also required (refer to Table 25.21 - 008/5).

The new control modules (EST33) have a diagnostics facility (refer to function description 25.21 - 007/14).

On the older TCC versions the TCC control module and, if necessary, retarder control module are fitted separately. Various control modules are fitted depending on the type of converter.

On the new TCC version, both control modules are fitted in a housing with a 25-pin connector.


Turbine rpm sensor

The rpm sensor for recording turbine speed is located in the manual transmission or in the TCC housing, depending on the transmission version: Turbine rpm sensor (1) on MB transmissions. The speed is recorded at the countershaft on this version.

Note

The position of the splitter unit also has to be recorded in the control module due to different speeds. The switch is located on the transmission.

Screw lock (2) for turbine rpm sensor on ZF transmission (previous version).

Engine rpm sensor

An rpm sensor is located underneath the valve body casing (1) for recording engine speed. The speed is recorded from the drive pinion (34 teeth) for the oil pump on the converter housing.


Kick-down switch

The range between automatic engagement and disengagement of the lockup clutch is very large. The kick-down switch (1, previous version) is installed so that the driver can also shift to converter operation in this range, if necessary.

The switch must be adjusted so that it switches after the full load position (A) and before the mechanical stop for the accelerator pedal (2).

The kick-down switch is located in the accelerator pedal sensor (3) on vehicles with EMR or FMR/EDC. The kick-down switch is also required to exceed the limit speed set by the Temposet.

Control with power take-off

A constant operating speed is required to operate most power take-offs. In addition losses occur due to slip when the lockup clutch is open. Therefore on vehicles with a clutch-dependent power take-off, the lockup clutch must close automatically when the power take-off is engaged. On these vehicles the power take-off can only be engaged in the transmission neutral position. For this, an additional relay (K5/A31) is incorporated for switching on the pilot control valve. The relay is actuated at the I module and M module. The pilot control valve is switched on via this relay only if the neutral position switch on the transmission and the pressure switch in the power take-off are switched on.

A Relay fitted in electrical compartment of previous TCC version:

Note B Relay fitted in electrical compartment of new TCC This circuit is not fitted to dumper trucks with version (with diagnostics facility):TCC. The power take-off is only in operation for a short period and the driver can compensate for slip by means of the accelerator pedal.


Overrun freewheel

So that the braking effect of the engine can also be used when the lockup clutch is open, there is a jamming roller freewheel in the converter. The output rotor is connected to the jamming roller freewheel (1) via the internal spline (arrow).

A jamming roller freewheel allows a vehicle fitted with TCC to be tow-started.

Function: The freewheel outer race (2) is welded to the converter housing. If the engine turns faster than the turbine shaft there is no permanent mechanical connection (A). If the turbine shaft (3) turns faster than the engine (B, overrun operation) the jamming rollers bring about a permanent connection between the freewheel outer race and the freewheel inner race (5) due to the jamming rollers (4).

Converter clutch


A conventional diaphragm/dry converter clutch is mounted on the turbine shaft. The converter clutch is only required to shift the gears (without the usual starting off with the slipping clutch). The actuation takes place by means of the clutch pedal with compressed-air assistance from the clutch booster (servo unit). A protective device is required for the converter clutch on account of the increased torque occurring in converter operation.

Accelerator pedal shut-off to protect the converter clutch (without electronic engine control)

In order to prevent the converter clutch being used as a starting off clutch, an accelerator pedal shut-off is installed on vehicles without electronic engine control: When the converter clutch is operated, the engine speed is throttled back to idle speed irrespective of the accelerator pedal position.

1 Accelerator pedal 4 Stop position 7 Compressed-air from 3/2-way valve

2 Stop cylinder 5 Closed throttle position 8 Throttle shut-off cylinder

3 Injection pump 6 Wide open throttle position 9 Travel limiter

On these vehicles the pneumatic throttle shut-off cylinder on the injection pump is actuated via a solenoid valve (3/2-way valve). The solenoid valve is switched via a relay (K4/31 on previous version, K3 and K6/A35 on the new version). The throttle shut-off cylinder can also not be overpressurized by using force. The travel limiter (9) on the throttle shut-off cylinder must be adjusted as follows: If the accelerator pedal (1) is in the wide open throttle position, the lever on the injection pump must be in the idle position (5 mix. + 100 rpm) when the throttle shut-off cylinder (8) is pressurized. If the travel limiter is incorrectly adjusted, the engine may be switched off during clutching.


Pneumatic diagram - TCC accelerator pedal shut-off:

P20.1 iston cylinder A to engine brake

20.1 Piston cylinder B to injection pump governor

28.1Two-way valve

33.1 3/2-way valve, engine brake foot brake switch

33.2 3/2-way valve, from speed switch (under the electrical compartment) actuated at > 900 rpm

V Compressed-air from reservoir

Accelerator shut-off control

The accelerator shut-off is not required or not wanted

in transmission neutral position,

during starting,

when the lockup clutch is closed.

A positive circuit is installed for this:

The voltage for the relay (A31/K4 or K6/A35 on the new version) for the throttle shut-off cylinder is supplied by the relay for the pilot control valve (K2/A31 or K1 and K3/A35 on the new version). This means when the lockup clutch is closed there is no voltage at the clutch switch or at the relay for the throttle shut-off cylinder. This relay

A (K4/A31, K6/A35 on the new version) is actuated Relay fitted in electrical compartment on old TCC

by the M module: If the starter is operated, or version:the transmission is shifted into a neutral position, A31/K1 Kick-down switch relay the throttle shut-off cylinder is switched off. A31/K2 Pilot control valve relay for lockup clutch

A31/K3 TCC indicator lamp relay

A31/K4 Throttle shut-off relayNoteA31/K5 Pilot control valve relay for lockup clutch for On vehicles with GBL (linear speed limitation) or

power take-offelectronic engine control (EMR, FMR/EDC) no A31/K6 Retarder proportional valve relaythrottle shut-off valve is required. This circuit B Relay fitted in electrical compartment on new TCC described above is connected to the module that version:is installed (V or E module). The function of the A31/K5 Pilot control valve relay for lockup clutch for throttle shut-off cylinder is taken over by the

power take-offmotor electronics.A35/K1 Pilot control valve relay for lockup clutch

No adjustment work is required on EMR and A35/K2 TCC indicator lamp relay

FMR/EDC and the circuit described above can be A35/K3 Throttle shut-off relaychecked by actual values using the HHT.A35/K4 Retarder shut-off relay*


A35/K5 Retarder indicator lamp relay

A35/K6 Throttle shut-off relay

* is either connected to the stage switch (wiring diagram 625 540 36 00 and 625 540 37 00) or to the control module (wiring diagram 080 540 89 00 and 080 540 90 00).

Clutch switch, clutch booster

The clutch switch is located on the clutch booster (servo unit) on the previous and new TCC versions.

Note

- On the ZF transmission the clutch booster (servo unit) is located above the transmission.

- The switch must be open in the normal position (N.O. contact).

Retarder

General

The retarder integrated in the TCC housing is a single-flow hydrodynamic permanent brake. The ZF retarder works as a primary retarder due to its location between the converter and converter clutch. In contrast to a secondary retarder (mounted on the transmission output), the braking effect for a primary retarder decreases as speed increases in the higher gears.

Main constituent parts of the retarder in the TCC housing

Stator (2, is bolted to the retarder or TCC housing)

Rotor (5, is connected to the turbine shaft by a spline).

Pneumatic/hydraulic retarder control valve (9)

Connection for heat exchanger (8)

Function

When operated the retarder is supplied with oil from the oil pump. As no power transmission through the converter is required when braking, in this case only the retarder is connected to the oil circuit between the transmission and heat exchanger (refer to Section "Oil return flow and cooling", 25.21 - 007/4).

In principle the retarder works as a fluid clutch:

When braking, oil is controlled under pressure in the retarder housing. The rotor is driven in one direction by the drive shaft of the moving vehicle (direction of rotation of engine). The rotor collects the oil in the retarder housing with its vane chambers and presses into the vane chambers of the fixed stator. The rotor is braked as the oil flow cannot discharge instantaneously. The braking torque generated depends on the oil pressure and the rotor speed.


1 Control air connection (from proportional valve)

2 Stator

3 Pressure pipe

4 Vane chambers/discharge spiral

5 Rotor

6 Coolant

7 Heat exchanger

8 Oil pipe

9 Retarder control valve

Retarder indicator lamp, stage switch

An electric stage switch (4 braking stages) is mounted on the steering wheel for the driver to adjust the retarder braking torque. The green retarder indicator lamp illuminates when braking with the retarder (stages 1 to 4).

Note

On the new control modules (EST33) a fault in the retarder or TCC is indicated by the retarder indicator lamp flashing.


Retarder control module

The stage switch is connected to the retarder control module (previous version).

The current to the proportional valve is monitored by the control module corresponding to the selected braking stage. At the same time the control module constantly monitors the oil temperature during the braking process. With an excessive oil temperature, the control module switches back the retarder without any stages and a warning buzzer sounds.

On the new TCC version, the retarder and TCC control module are in one housing. On this version an additional warning buzzer is required for the retarder (behind the instrument panel). New control modules have a diagnostics facility, i.e. components connected are monitored constantly or during actuation. A fault code is stored in the control module (EEPROM) in the event of a malfunction. This fault code can be displayed by the HHT diagnosis unit or the EPS display on vehicles with FDS.

Troubleshooting instructions (guided testing) can also be called up in the HHT.

Inputs and outputs from the control module can be checked with actual values, without first having to remove trim panels etc.


The mechanical components can also be checked indirectly by means of the test facilities of the electronic system: e.g. without spending a lot of time it can be established by means of an actual value whether a fault is located in the control electronics or the connected area. If no fault is found here, the troubleshooting can take place selectively on the mechanical components (pneumatic valves etc.).

Oil temperature sensor

The oil temperature sensor (1) for the control module is located on the retarder control valve. The oil temperature sensor is a NTC resistor as with the display instrument. The ohmic resistance decreases as temperature increases.

Proportional valve

The electropneumatic proportional valve (1) adjusts the control pressure at the retarder control valve corresponding to the braking stage.

The pressure switch (2) on the proportional valve switches the supplementary oil cooler on from a particular pressure (on heavy-duty tractor units only).


Retarder control valve

The retarder control valve switches over the oil cooling circuit between TCC operation and retarder operation and controls the quantity of oil in the retarder. In the rest position, the oil cooler circuit is connected to the TCC. To change over the oil circuit, the spring back pressure in the retarder control valve must be overcome with compressed-air at a pressure of approx. 2 bar.

Retarder control by ABS

On vehicles with ABS/ASR braking with the retarder is monitored by the ABS/ASR control module.

If ABS recognizes one or several locking wheels, the retarder is switched off. On the previous TCC version the voltage supply from the stage switch is interrupted via the relay K4/A32 on relay K5/A31. On the new TCC version the retarder is switched off in the control module. The ABS control module is connected directly to the TCC control module via the B module.

Oil accumulator

So that the braking torque is available without any delay when the retarder is operated, approx. 1.5 l of oil must be delivered from the oil accumulator (2) into the retarder housing immediately. At the end of braking stage 1, the contents of the oil accumulator are forced into the return line from the heat exchanger and thus into the retarder chamber by means of the pneumatic accumulator charge valve (1).


On the new TCC control modules the accumulator charge valve is actuated electrically. The retarder is automatically switched off when an ABS control process is activated. When the ABS control process is completed, the retarder is active again, but the accumulator charge valve is no longer actuated.

Note

There are vehicles without oil accumulator and accumulator charge valve. So that no fault (fault code 100, accumulator charge valve interrupt) is stored in the control module, a ballast resistor (3) is connected to the TCC control module.

Cutoff valve (retarder shut-off)

So that it is possible to shift down smoothly, comfortably and without clutch wear when braking with the retarder, a pneumatic cutoff valve was required on the previous TCC version. On vehicles equipped with cutoff valves, this valve is connected to the control pressure from the clutch booster (servo unit). This function is integrated in the control module on the new TCC version.


Closed throttle switch

If because of traffic, the driver has to "accelerate" (even briefly) while braking with the retarder, the retarder is shut off by the closed throttle switch by the relay K5/A31 and on the previous TCC version it is shut off by the stage switch. The closed throttle switch (1) is located on the throttle linkage on the left side of the engine.

On the new TCC version the stage switch is switched off by the closed throttle switch via relay K4/A35 when the accelerator pedal is operated.

On vehicles with EMR or FMR/EDC the closed throttle switch is installed in the accelerator pedal sensor (2). In the event of a defective closed throttle switch the fault is displayed and a fault code is stored in the EMR control module or FMR control module.

Engine-dependent power take-off (NMV) combined with TCC


An engine-dependent power take-off (1) can be installed on the TCC 400. The specific properties of this engine-dependent power take-off (NMV) are as follows:

The drive takes place by means of a ring gear on the converter, i.e. directly on the engine

Common oil supply with TCC and manual transmission

Direction of drive is opposed the direction of rotation of the engine

High speed: Engine speed x 1.03

Max. load carrying capacity 12 Nm

Can be used when the vehicle is stationary or on the move

Can be engaged and disengaged under load by the built-in hydraulic multiple-disc

Note

- The procedure for repair work is not fundamentally different from a TCC without NMV. Only the designs of the TCC housing, valve body casing, the converter and the oil supply flange differ. Two drive gears for the NMV are also installed in the TCC housing.

- The engine-dependent power take-off must not be engaged or disengaged when the engine is not running.

- When engaging, the engine speed must be at least 600 rpm to achieve the necessary shift pressure of 9 to 10.5 bar. If the shift pressure is too low, the clutch discs in the power take-off wear prematurely.

- The permissible max. engine speed of 1800 rpm must not be exceeded when engaging the power take-off while driving.

The multiple-disc clutch is actuated at the valve body casing (arrow) via a pneumatic 3/2-way shift valve in the cab. It is technically feasible to retrofit with engine-dependent power take-off but is very expensive.


torque converter clutch tcc

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