5105 Description of major hydraulic and electronic components

Hydraulic control unit (Fig. 5.38) The hydraulic control unit is housed in the oil-pan position underneath the transmission gears. A fluid pump operates the hydraulic circuitry; it is driven directly from the engine via the torque converter casing, fluid is directed by way of a pressure regulation valve to the interior of the torque converter and to the various clutches and brakes via passages and valves. The hydraulic control circuit which operates the gear shifts are activated by three electromagnetic operated open/close valves (solenoid valves) and four electro-magnetic progressive opening and closing regulation valves (electronic pressure regulation valve 'EPRV'). Both types of valves are energized by the electronic transmission control unit 'ETCU' which in turn receives input signals from various speed, load, temperature and accelerator pedal sensors; all of these sensors are simultaneously and continuously monitoring the changing parameters. In addition a position selector lever or button operated by the driver relays the different driving programs to the electronic transmission control unit 'ETCU'.

Electronic transmission control unit The function of the electronic transmission control unit 'ETCU' is to collect, analyse and process all the input signals and to store program data so that the appropriate hydraulic circuit pressures will bring about transmission gear changes to match the engine speed and torque, vehicle's weight and load, driver's requirements and road conditions.

Control program The stored program provides data to give favourable shift characteristics for gears and the torque converter lock-up clutch, it co-ordinates parameters for pressure calculations, engine manipulation and synchronizing gear change phases, it provides regulation parameters for smooth gear shifts and the converter lock-up and finally it has built-in parameters for fault diagnoses.

Transmission input signal sensors The various signals which activate the electronic transmission control unit 'ETCU' can be divided into three groups: (1) transmission, (2) engine and (3) vehicle:

1 Transmission

(a) input turbine speed sensor

(b) output drive speed sensor

(c) transmission temperature sensor

(d) position switch signalling-selector lever position to the electronic transmission control unit

2 Engine

(a) engine speed sensor

(b) engine load-injector opening duration

(c) throttle valve opening-potentiometer

(d) engine temperature sensor

3 Vehicle

(a) kickdown switch

(b) position PRND432 indicator

(c) manual gear selection program

(d) brake light switch

Selector lever

Selector lever

Output speed sensor transmission

Input speed sensor transmission

Oil temperature transmission sensor

Cruise control

Cruise control

Gear change position switch

MV1

MV2

MV3

Electro/hydraulic transmission control unit

\

EPRV 1

\

EPRV 2

\ \

EPRV 3

EPRV 4

Electronic transmission control unit (ETCU)

Electronic injection control unit (EICU)

Selector lever position indicator

Selector lever position indicator

Diagnosis connection

Diagnosis connection

Throttle valve potentiometer

Throttle valve potentiometer

Kickdown switch

Kickdown switch

Brake light and switch

Engine speed sensor

Fig. 5.38 Basic electronic control system layout

Engine Fuel injection ignition quantity

5.1O.6 Description and function of the electro/ hydraulic valves valve SV-3. Solenoid valve MV3 activates the traction/coasting valve (T/QV.

Solenoid (electro-magnetic) valves (MV1, MV2 and MV3) (Fig. 5.39) The solenoid valves MV1, MV2 and MV3 are electro-magnetic disc armature operated ball-type valves which are energized by current supplied by the electronic transmission control unit. The ball-valve is either in the open or closed position, when the valve is de-energized the ball-valve closes the inlet port and vents the outlet port whereas when energized the ball-valve blocks the vent port and opens the inlet port. Solenoid valve MV1 when energized activates shift valve SV-1 and SV-3.

Solenoid valve MV2 activates shift valve SV-2 and shuts down the switch over function of shift

Electronic pressure regulating valves (EPRV-1, EPRV-2, EPRV-3 and EPRV-4) (Fig. 5.39) The electronic pressure regulating valves EPRV-(l-4) are variable pressure electro-magnetic cylindrical armature operated needle-type valves, the output pressure delivered being determined by the magnitude of the current supplied at any one time by the electronic transmission control unit to the electronic pressure regulating valves. With increasing current the taper-needle valve orifice is enlarged, this increases the fluid spill and correspondingly reduces the actuating control pressure delivered to the various valves responsible for gear shifts.

Hydraulic/electronic automatic transmission control system abbreviation key for Figs 5.39-5.46.

A list of key components and abbreviations used in the description of the electro/hydraulic control system is as follows:

Hydraulic/electronic automatic transmission control system abbreviation key for Figs 5.39-5.46.

A list of key components and abbreviations used in the description of the electro/hydraulic control system is as follows:

1 fluid pressure pump

P

2 selector position valve

SPV

3 main pressure valve

MPV

4 pressure reducing valves

PRV-1 and PRV-2

5 modulation pressure valve

MOD-PV

6 shift valve

SV-1, SV-2 and SV-3

7 reverse gear valve

RGV

8 clutch valves

CV-A, CV-B, CV-C and CV-D

9 brake valves

BV-E, BV-F and BV-G

10 retaining valves

RV-E and RV-G

11 traction/coasting valve

(T/C)V

12 traction valves

TV (4-5) and TV (5-4)

13 converter pressure valve

CPV

14 converter pressure control valve

CPCV

15 converter lock-up clutch valve

CLCV

16 lubrication pressure valve

LPV

17 solenoid (electro-magnetic) valves

MV1, MV2 and MV3

18 electronic pressure regulating valves

EPRV-1, EPRV-2, EPRV-3 and EPRV-4

19 multiplate clutch/brake

MPC-A, MPC-B, MPC-C and MPC-D/MPB-E, MPB-F and MPB-G

20 pressure relief valve

PRV

21 non-return valve

NRV

Table 5.6 Hydraulic/electronic automatic transmission control system solenoid valve, clutch and brake engagement sequence for different gear ratios for Figs 5.39-5.46

Table 5.6 Hydraulic/electronic automatic transmission control system solenoid valve, clutch and brake engagement sequence for different gear ratios for Figs 5.39-5.46

Solenoid valve - clutch - brake engagement sequence

Gear range

Solenoid valve logic

Clutch and brake logic

Solenoid valves

Pressure regulating valves

Clutch

Brake

1 2 3

12 3 4

A B C D

E F G OWC

N/P neutral/park D 1st gear D 2nd gear D 3rd gear D 4th gear D 5th gear 2 1st gear R = reverse

A A (A) AA

Control current (A)

Fig. 5.40 Electronic pressure regulating valve current-pressure characteristics

Control current (A)

Fig. 5.40 Electronic pressure regulating valve current-pressure characteristics

Thus control pressure delivered is inversely proportional to the amount of current supplied, that is, as the current rises the pressure decreases and vice versa. The characteristics of control pressure versus control current is shown in Fig. 5.40.

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