Since there is a lack of pressure monitoring on the 722.6, The Ultimate-NAG52 TCU tries to estimate the following pressure rails with simple maths and derrivation from solenoid current.
For the simplification of this page, the pressure rail names are assigned the following variables. These variable names are noted in Mercedes' WIS:
pA - Working pressurepRV - Regulating valve pressurepSv - Shift valve pressurepSRmv - SPC solenoid output pressurepSKub - TCC solenoid output pressurepMod - MPC solenoid output pressurepU - Overlap pressurepKub - Torque converter lockup clutch pressurepSm - Lubrication pressureThe TCU has a complex calculation system which tries to match the requested pressures for each pressure rail, by only controlling the 3 pressure solenoids (MPC, SPC, and TCC). The influence of the solenoids and pressure rails can be viewed in the below diagram:
There are actually 3 Command valves, overlap regulators, shift pressure valves and shift solenoids in the gearbox, but the connections are the same, so only 1 is shown in the diagram for simplicity
When not changing gears, the overlap valve and shift solenoids are off, meaning overlap regulator, command valve, and shift pressure valve get 0 pressure.
Each regulator has a spring inside, which is tuned to a certain pressure. Since pressure is additive in the gearbox, output pressure of a regulator valve can be expressed as the sum of hydralic pressure and spring pressure (Or hydralic pressure minus spring pressure if the spring is working against the incomming hydralic pressure).
The TCU has a complex model of the 722.6's valve body, which is augmented by calibration data from OEM EGS52/53 ECUs. These stock calibrations contain various control points for the hydraulic simulation algorithm.
The hydraulic simulation algorithm is reverse engineered from EGS52, and might change over time to make additional improvements
The TCU (Gearbox.cpp) will assign target pressures for all 3 main working rails of the gearbox. pA is actually derrived from a clutch coefficient map, which in turn is used to set pRV (MPC) target. SPC Solenoid pressure (pSv) is only set during shifting, otherwise, it is pSV_MAX (The maximum pressure of the solenoid when turned off).
pA = (1.0/fac_gear * pLPReg) + extra_p - spc_reduction
fac_gear represents the influence pump pressure has on the LP regulator valve.
fac_gear = HYDR_PTR->p_multi_1fac_gear = HYDR_PTR->p_multi_otherpLPReg is the pressure (Before factor compensation). On the LP regulator.
pLPReg = pRV_Targ + HYDR_PTR->lp_reg_spring_pressure
extra_p is the additional force on the main pressure regulator due to the gearbox pumps speed.
extra_p = interp_linear(engine_rpm, 0, p_adder, HYDR_PTR->extra_pressure_pump_speed_min, HYDR_PTR->extra_pressure_pump_speed_max)
where p_adder:
p_adder = HYDR_PTR->extra_pressure_adder_r1_1p_adder = HYDR_PTR->extra_pressure_adder_other_gearsThis creates a inerpolation like so:
The pressures for the shift (In all its stages), are tracked with the following 6 variables:
p_on_clutch - Pressure at the applying clutch's clutch packp_off_clutch - Pressure at the releasing clutch's clutch packp_overlap_mod - Pressure at the overlap slider (Modulating pressure side)p_overlap_shift - Pressure at the overlap slider (Shift pressure side)p_shift_sol_req- Pressure requested for the shift solenoidp_mod_sol_req - Pressure requested for the modulating solenoidNOTE: The pressure names here are different to what Mercedes calls then in WIS, since the TCU is calculating the influence of one pressure rail over another, it requires a much more granualar understanding of pressures in the valve body. Where as WIS diagrams are more simplified to show simply how fluid flows in the hydraulic valve body.