3. The hydraulic shifts

3.1 Main components

See chapter 3.4 for the illustrations showing the assignment of the items in brackets ( ).

The gear pump (F) pumps oil from the oil sump via the suction screen, the heat exchanger (G), the oil filter (H) and the operating pressure valve OPV (C) to the control block

(D) with the electrohydraulic control system, to the converter drain valve CDV (A) and via the converter filling valve CFV (B) to the transmission (E) with converter and lubrication system. The operating pressure valve (C) maintains the oil pressure at a largely constant level for supplying the multi-disc brakes and clutches, irrespective of the speed of the gear pump. The operating pressure is set by the preloading of the spring of the spool (8).

The solenoid valves in the control block (D) are subjected to operating pressure. Converter and operating pressure are present at the shuttle valve (10). The task of this valve is to allow the higher of the two pressures to flow through to the solenoid valves TB, RBG and RBK. The solenoid valves direct the oil from the operating pressure valve (B) or from the converter to the piston of the multi-disc brakes and clutches and to the converter drain valve (A).

Two types of valve are used: on/off solenoid valves (WP, WR, RGB) and pressure control solenoid valves (EK, DK, SK, PB, TB, RBK). The function of the latter type is to control the pressure profile whilst the multi-disc brakes and clutches are closing so that torque fluctuations at the transmission output are as small as possible within a specified time period. This results in a good shift quality, reduces load peaks and prevents premature wear on the discs. The most important components are the hydraulic control spool and an electromagnet which is connected to it. As well as the excitation coil, there is also a measuring coil installed for picking up the actual electrical values. It is possible to set any required pressure which is lower than the operating pressure. The pressure setpoints are specified by the control unit depending on the engine load status, the gearshift to be performed and the speeds at the transmission input and output. The on/off solenoid valves are used for less demanding control functions, with the WR pressure being altered by cyclic, pulse-width modulated (PWM) signals depending on the operating status.

The converter drain valve (A) is used for open and closed-loop control of the converter pressure.

The converter filling control reduces the oil supply to the converter by means of a throttle port in the converter filling valve (B); air is included in the oil fill of the converter via the open breather valve BV (13).

Overview: in all gearshift functions without converter filling control CFC, the converter filling valve (B) is open and the breather valve (13) is closed. The situation is the reverse in the functions with CFC (figures 6, 7, 8 and 9): the converter filling valve is closed with the exception of the throttle port, the breather valve is open.

10 Voith. Oil and Control Circuit Diagrams DIWA.3E

3.2 Shift description

Neutral position (figure 0)

The oil pressure in the operating pressure valve OPV (C) pushes spool (8) against the force of the corresponding spring and thereby opens the oil flow into the converter via the open converter filling valve (B). The transmission is supplied with lubricating oil through spool (9) and a throttle port in the OPV housing.

In neutral position, the operating pressure is higher than the converter pressure, so all solenoid valves of the control block (D) have operating pressure applied to them. The solenoid valves are closed, so all clutches are disengaged and all brakes released.

The spools (1-4) of the CD valve (A) are moved to their initial position by the corresponding spring. This means the converter is closed by the CDV. The converter pressure increases accordingly, so the breather valve (13) is closed.

1st gear (DIWA drive range - figure 1)

The input clutch EK (17) is engaged via the EK solenoid valve and the turbine brake TB (12) is applied via the TB solenoid valve.

Operating pressure is applied to spool (2) in the converter drain valve (A) via the WR solenoid valve which is 100 % open. This reinforces the spring force applied to spool (1), and spools (1-4) remain in their initial positions. The converter drain valve (A) closes and the converter pressure rises to values corresponding to the speed.

Because the converter plays an active part in power transmission, the operating pressure in this operating status is lower than the converter pressure which acts on the solenoid valves TB, RBG and RBK due to the position of the shuttle valve (10).

Upshift 1st-2nd gear (figure 2)

This gearshift is a transitional function which is only briefly activated.

The WR solenoid valve closes and the turbine brake (12) opens after the TB solenoid valve has switched off.

The pump brake (14) is applied via the PB solenoid valve and the pump pump is braked. The pump pump is additionally braked by the converter pressure which is still present; this improves the shift quality.

Operating pressure is also applied to spool (5) in the converter drain valve (A) when the pump brake closes. The spool (5) remains in its initial position because the converter pressure is higher.

2nd gear (figure 3)

The WP solenoid valve switches on about two seconds after the transitional function described above.

Spool (6) in the converter drain valve (A) moves to its end position, the converter pressure acts on spool (4) via spool (5). On the one hand, the force of the spring on spool (1) and, on the other hand, the converter pressure on (4) result in a control position being established for spools (1-4) by way of the control edge of (3). The converter pressure drops, spool (5) moves to its end position and converter pressure also acts on spool (3) as a result. A value of about 0.5 bar is established, which is required for the 1st braking level. The converter is ready to brake when this pressure is established.

When spool (5) and (6) are in their end positions, operating pressure acts on spool (9) of the operating pressure valve OPV (C). Spool (9) also moves to its end position and opens a large lubrication oil hole in the OPV housing. As a result, increased transmission lubrication is achieved from the 2nd gear onwards.

Operating pressure acts on both sides of the spool (7), so the converter filling valve (B) remains open. The breather valve (13) is closed.

Voith. Oil and Control Circuit Diagrams DIWA.3E 11

3rd gear (figure 4)

The input clutch EK (17) is disengaged via the EK and the lock-up clutch DK (16) is applied via the DK solenoid valve. Valves CDV (A), CFV (B), OPV (C) and BV (13) remain in the same switching status as the 2nd gear.

4th gear (figure 5)

The lock-up clutch DK (16) is disengaged via the DK and the step-up gear clutch SK (15) is applied via the SK solenoid valve. Valves CDV (A), CFC (B), OPV (C) and BV (13) remain in the same switching status as the 2nd gear.

3rd and 4th gear with converter filling control (CFC) (figures 6 and 7)

The clutches and brakes are set as in the 3rd or 4th gear (figures 4 and 5).

As mentioned in chapter 1, the purpose of the CFC is to improve the application of the converter brake, even when the vehicle is travelling at high speed in the 3rd or 4th gear. The following gearshifts serve as preparatory measures:

a)The WP solenoid valve is switched off to open the converter drain valve fully above a certain limit speed of the transmission output (f.i. about 2000-2200 rpm at 4-speed transmissions). The corresponding spring moves spool (6) to its initial position and allows the operating pressure to act on piston (3) and (4) via spool (5). Spools (1-4) move to their end positions and the converter pressure drops to values approaching 0 bar.

b)The breather valve (13) opens and thereby allows air into the converter oil circuit.

c)When the WP valve is switched off, this also means that operating pressure only then acts on one side of the spool (7) of the converter filling valve (B) and it moves to its end position. The converter is then only supplied with a reduced volume of oil via the throttle port in the CFV housing. See "Braking with CFC" for more information (figures 8 and 9). The WP valve switches back on below the limit speed and the gearshift status is the same as in the 3rd or 4th gear without CFC (figures 4 and 5).

1st, 2nd and 3rd braking stage - 3rd and 4th gear with CFC (figures 8 and 9)

Braking with CFC is a transitional function active for a limited time above the mentioned limit speed.

All clutches, brakes and valves are initially set as in traction in the 3rd or 4th gear with CFC (fig. 6 and 7).

The converter braking effort is channelled through the drive of the turbine wheel (see chapter 2.2.1). To do this, the RBK solenoid valve switches on after the converter brake has been actuated. This solenoid valve allows the operating pressure to act on the small piston surface of the reverse gear brake RB (11). As a result, the reverse gear transmission is synchronised, i.e. its outer crown gear is braked to a standstill (see also chapter 2.1).

The low pressure, the oil/air mixture and the reduced oil supply to the converter mean the braking torque is reduced when the turbine wheel starts moving, thereby facilitating synchronisation of the reverse gear discs when the vehicle is travelling at high speed.

1st braking stage - 4th gear with CFC preceding it (figure 10)

The step-up gear clutch SK (15) is engaged and the pump brake PB (14) is applied as in „Braking in 4th gear with CFC“ (fig. 9).

The RBG valve is switched on, allowing the operating pressure to act on the large piston surface of the reverse gear brake RB (11) which causes the pressure on the RB piston to be increased. The WP solenoid valve is then switched on. Spool (6) in the converter drain valve moves to its end position allows the operating pressure to act on spool (3) and (4) via (5). Spools (1-4) move into their control position, the converter pressure and the brake torque increase to the values for the 1st braking level. The converter filling valve (B) opens and the breather valve (13) closes.

„1st braking stage in 3rd gear with CFC preceding it“ takes place accordingly.

12 Voith. Oil and Control Circuit Diagrams DIWA.3E

1st braking stage - 4th gear without CFC preceding it (figure 10)

The step-up gear clutch SK (15) is engaged and the pump brake PB (14) is applied as in operating status „4th gear“ (fig. 5).

The reverse gear discs are synchronised after the converter brake is actuated. This synchronisation is performed by the RBK solenoid valve and thereby the drive of the turbine wheel. The RBG solenoid valve is then switched on, allowing the operating pressure to act on the large piston surface of the reverse gear brake (11) which causes the pressure on the RB piston to be increased.

„1st braking stage in 2nd and 3rd gear without CFC preceding it“ takes place accordingly.

2nd and 3rd braking stage (2nd-4th gear) (figures 11, 12 and 13)

The clutches, brakes and valves are initially in the same positions as for traction in the 2nd, 3rd or 4th gears (figures 3, 4 and 5); in addition, the reverse gear brake RB is activated as in the 1st braking level (figure 9).

The WR solenoid valve (for converter pressure control) is activated to increase the braking effort in the 2nd and 3rd braking stages. This solenoid valve channels the pressure onto the spool (2) in the converter drain valve (A) and thereby alters the braking effort by way of the converter pressure.

Braking in 1st gear range (figure 14)

Solenoid valves RBG and RBK are switched off for the downshift from the 2nd into the 1st gear with the converter brake active. This means the reverse gear brake RB (11) is released. The pump brake PB (14) is then opened as well, after which the turbine brake TB (12) is applied. In this operating status, the transmission is initially shifted as for traction in the 1st gear (figure 1).

In order to re-activate the reverse gear brake, the pressure is increased to the corresponding level by the RBK solenoid valve whilst the RBG valve remains switched off. At the end of the switch-on time, a pressure of about 1.2 bar acts on the small piston surface of the reverse gear brake. In this status, the predominant braking effort for the vehicle is provided by the slipping RB discs alone. The RBK pressure is reduced continuously as the vehicle decelerates until a value of about 0 bar is reached when the vehicle has come to a halt. The RBK pressure is then boosted to about 2.5 bar in order to lock up the transmission by means of the two brakes RB and TB.

ANS activation (figure 15)

The input clutch EK (17) is disengaged via the EK and the turbine brake TB (12) is applied via the TB solenoid valve.

The RBK solenoid valve establishes and maintains a certain pressure on the small piston surface of the reverse gear brake RB (11). The transmission is mechanically locked up because the two brakes TB and RB are applied. The vehicle is braked.

Operating pressure is applied to spool (2) in the converter drain valve (A) via the WR solenoid valve which is 100 % open. This reinforces the spring force applied to spool (1), and spools (1-4) move into their initial positions. The converter drain valve (A) closes and the converter pressure rises to values corresponding to the speed.

ANS activation via parking brake (figure 16)

This gearshift function is differentiated from the "ANS activation" in that the reverse gear brake RB (11) is released and the vehicle is braked by the parking brake (see chapter 2.2.1). The parking brake is activated by the transmission control unit.

Voith. Oil and Control Circuit Diagrams DIWA.3E 13

Reverse gear up to 1 km/h (figure 17)

This operating status is normally only in effect briefly when setting off in reverse.

The input clutch EK (17) is engaged via the EK solenoid valve and the reverse gear brake RB (11) is applied via the RBK and RBG solenoid valves.

Operating pressure is applied to spool (2) in the converter drain valve (A) via the WR solenoid valve which is 100 % open. This reinforces the spring force applied to spool (1), and spools (1-4) move into their initial positions. The converter drain valve (A) closes and the converter pressure rises to values corresponding to the speed.

Because the converter plays an active part in power transmission, the operating pressure in this operating status is also lower than the converter pressure which acts on the solenoid valves TB, RBG and RBK due to the position of the shuttle valve (10).

Reverse gear above to 1 km/h (figure 18)

The WP solenoid valve is activated in addition to the gearshift operations in reverse gear up to 1 km/h (figure 17).

Spool (6) in the converter drain valve (A) moves to its end position. Spool (5) and (6) allow the converter pressure to act on spool (4) and the operating pressure to act on spool (1), which also moves to its end position. The pressure of the WR solenoid valve is controlled according to the engine speed and is applied to spool (2). As a result, it is possible to control the converter pressure between about 0 and 20 bar by way of the control edge of spool (3).

14 Voith. Oil and Control Circuit Diagrams DIWA.3E

3.4 Pipes

Classification and Function

16 Voith. Oil and Control Circuit Diagrams DIWA.3E

Voith. Oil and Control Circuit Diagrams DIWA.3E 17

Classification and Function

18 Voith. Oil and Control Circuit Diagrams DIWA.3E

8

4

2

3

1

9

6

10

7

11

Pipes in the diagram

10

1

7

6

4

8

3

11

5

9

2

Voith. Oil and Control Circuit Diagrams DIWA.3E 19