An electronic control system for a hydrokinetic power-shift transmission for a motor vehicle

Claim 1

An electronic control system for a hydrokinetic transmission for a motor vehicle, particularly a lift truck with an internal combustion engine the speed of rotation of which can be controlled by an accelerator, the transmission including a hydraulic converter (CI), and a power-shift gearbox (PS) coupled to the output shaft (2) of the converter (CI) and including a plurality of hydraulic clutches (DI) which are associated with the gears, which can be activated selectively by the manual operation of a selector (MS), and which are controlled by a plurality of enabling on-off solenoid valves (V1-Vn), and an electrically-operated pressure-modulator (EVP) connected to a source (P) of pressurised fluid, the control system including: sensor means (GM, GT, GU1, GU2, PA, MS) for supplying electrical signals indicative of the speed of rotation of the input shaft (1) and the output shaft (2) of the converter (CI), of the speed and sense of rotation of the output shaft (3) of the gearbox (PS), and of the positions of the accelerator (A) of the engine (MT) and of the selector (S), and an electronic processing and control unit (MCU) which is arranged to pilot the pressure modulator (EVP) and the enabling solenoid valves (V1-Vn) in a predetermined manner in dependence on the signals supplied thereto by the sensor means, the control system being characterised in that it also includes a manual or pedal-operated control (I) connected to the electronic unit (MCU) and associated with a position sensor (PI), and in that the electronic unit (MCU) is arranged to effect an automatic control procedure for advancing the vehicle slowly at a predetermined speed (V T ) when the sensor means (GM, GT, GU1, GU2, PA, MS, PI) indicate that the selector (S) is set at a gear ratio and the accelerator (A) and the manual or pedal-operated control (I) are operated, the unit (CU) automatically regulating, by means of the modulator (EVP), the pressure of the fluid supplied selectively to the clutch or clutches (DI) associated with the gear engaged during the slow advance procedure so that the deviations of the speed of the vehicle from a predetermined reference value (V T ), which depends on the detected extent of operation of the manual or pedal-operated control (I) and on the gear engaged, are kept within a predetermined range.

Claim 7

A system according to one of the preceding claims, characterised in that the unit (MCU) is arranged to put into effect a stopping procedure (Figure 3) in which the unit simultaneously engages two opposing gears by means of the solenoid valves (V₁...V n ).

Claim 10

A system according to one of Claims 5 to 9, characterised in that the unit (MCU) is arranged to calculate incremental variations of the fluid pressure according to the equation: Δ ¯ p = Δ p* · TF in which the symbols have the meanings defined in the foregoing description.

Claim 14

A system according to one of Claims 9 to 13, characterised in that the unit (MCU) is arranged to increase the pressure until a predetermined value of the ratio (V GT /V GM ) between the output and input speeds of the converter is reached, this value being close to the value which corresponds to the stall condition of the converter.

Claim 15

A system according to one of the preceding claims, characterised in that the unit (MCU) is adapted to carry out an automatic deceleration procedure (Figure 4), in which it brings about successive calculated increments in the fluid pressure, each calculated increment being effected only if the expression: β = p·|V GT - τ · V GU | is less than a predetermined value β o , the symbols in the expression having the meanings defined in the foregoing description.

Claim 18

A system according to one of Claims 15 to 17, characterised in that the unit (MCU) is also adapted to effect a procedure for reversing the drive (Fig. 6).

Claim 19

A system according to one of the preceding claims, characterised in that the unit (MCU) is adapted to effect a procedure for moving the vehicle off, during which it brings about the engagement, by means of the solenoid valves (V₁...V n ), of the first gear or of another gear according to whether the ratio between the speed of rotation (V GU ) of the output shaft (3) of the gearbox (PS) and the speed of rotation (V GM ) of the engine (MT) is less than or greater than a predetermined value (W), the unit (MCU) then controlling the increase of the fluid pressure in a predetermined manner.