2.2 Operation and powerflow in individual gears
2.2.1 Powerflow of 3-speed transmissions (D 823.3E, D 851.3E, D 863.3E)
Neutral position
1st gear
(DIWA drive range)
2nd gear
3rd gear
Braking in 3rd gear
Braking in 2nd gear
Braking in 1st gear range
ANS activation
ANS activation via parking brake
Reverse gear
6 Voith. Oil and Control Circuit Diagrams DIWA.3E
Refer to the principle view in chapter 1. See chapter 2.1 for the transmission structure with an explanation of the items in brackets. See chapter 3. for the hydraulic circuits.
Neutral position
The transmission is in neutral when the engine is running and the N button on the button switch is pressed. Neutral means all clutches are disengaged and all brakes are released. When the input clutch EK (c) is disengaged, only the gear pump (n) is driven which supplies oil under pressure for power transmission, gear changes and transmission lubrication (see chapter 3).
1st gear (DIWA drive range)
When input clutch (c) is closed, engine power is transmitted to the crown gear in the differential (B).
When setting off, the output shaft (h) and the planet carrier (q) connected to it are stationary. The pump (p) and sun gear (o) are driven in opposing directions by planet gears (p) in the differential (B).
In the converter, oil from the pump (P) is driven through the stator (L) and turbine (T) in a closed circuit. Torque transmitted and converted, i.e. increased by the turbine is transmitted to the output shaft (h) by the planet gears and planet carrier on the turbine transmission (I) pumpwhose turbine brake TB (f) is closed.
2nd gear
Shifting to 2nd gear with completely mechanical power transmission occurs automatically and is dependent on roadspeed and engine filling.
The pump brake PB (e) is closed, meaning that pump (P) is stopped and hydrodynamic power transmission is inactive.
At the same time, the turbine (T) is switched off because turbine brake TB (f) on the turbine transmission (I) is open. The 2nd gear has the same ratio as the differential (B).
3rd gear (3-speed transmissions)
At about 60-70% of top speed, the input clutch EK (c) opens automatically while the lock-up clutch DK (d) closes. This means that input shaft (a) is directly connected to output shaft (h) - ratio 1:1.
Braking
In the braking range of the 2nd, 3rd or 4th gear, if installed, the turbine (T) is driven by the turbine and reverse gear transmissions (k) and (l) by the coasting vehicle. At this point, the disks of the pump brake PB (e) and reverse gear brake (g) are closed. The turbine is driven in the opposite direction to that of 1st gear (DIWA drive range) and acts as an axial pump which supplies oil to the stationary pump and stator. Kinetic energy is converted into heat and dissipated by the heat exchanger (i).
The input clutch EK (c) is engaged and the turbine brake TB (f) is applied during braking in the 1st gear range. The pump brake PB (e) is disengaged as for traction in the 1st gear. The principal deceleration of the vehicle in all three braking stages is provided by activating the reverse gear brake RB (g). In some applications, the service brake is engaged instead of the reverse gear brake RB (g) in the first braking stage.
Voith. Oil and Control Circuit Diagrams DIWA.3E 7
2.2.2 Powerflow of 4-speed transmissions (D 854.3E, D 864.3E)
Neutral position
1st gear
(DIWA drive range)
2nd gear
3rd gear
4th gear
Braking in 4th gear
Braking in 3rd gear
Braking in 2nd gear
Braking in 1st gear range
ANS activation
ANS activation via parking brake
Reverse gear
8 Voith. Oil and Control Circuit Diagrams DIWA.3E
The power flow in 1st and 2nd gear of 3- and 4-speed transmissions is achieved in the same way.
3rd gear (4-speed transmissions)
At about 40-50% of top speed, the input clutch EK (c) opens automatically while the lock-up clutch DK (d) closes. This means that input shaft (a) is connected directly to the output shaft (h) - ratio 1:1.
4th gear
At about 60-70% of top speed, the transmission automatically shifts from 3rd to 4th gear. The step-up gear clutch SK (d1) closes while the lock-up clutch DK (d) opens. This high ratio gear makes it possible, when the specific design speed is taken into account, to use the same axle ratio in a city bus with D 851.3E and in a long-haul or intercity bus with the D 854.3E f.i.
ANS activation
ANS means Automatic Neutral at Standstill.
The ANS activation, dependent on the number of bus-stops and prevailing traffic conditions, results in fuel savings.The powerflow from the engine to the transmission can be interrupted when the vehicle is stationary and with the engine running by opening the input clutch EK (c) under certain conditions:
–driving speed below 1 km/h
–accelerator in idling position (L0)
–service or bus parking brake applied
–forward gear selected.
This process differs from the neutral position in that the vehicle is stopped by activation of the turbine brake and reverse gear brake (f and g) are engaged. The parking brake function may be installed, its use is not essential for actuation of the ANS activation, however.
ANS activation via parking brake
This function differs from the one described above in that the parking brake must be activated. The turbine brake (f) is closed, the reverse gear brake (g) is open. The vehicle is therefore stopped by the parking brake only.
Reverse gear
Power transmission combines the hydrodynamic and mechanical systems in the same way as the 1st gear (DIWA drive range). The pump (P) is driven by the sun gear (o) and planet gears (p) of the differential (B) when the input clutch EK (c) is closed. The turbine (T) transmits torque to the turbine and reverse gear transmissions (I) and (k) when the turbine brake TB (f) is opened and the reverse gear brake RB (g) on the output shaft (h) is closed. The max. vehicle speed in reverse is roughly equivalent to 10% of maximum forward speed.
Voith. Oil and Control Circuit Diagrams DIWA.3E 9