Device and method for transmission control

Control device for a transmission unit comprising a clutch and a gear shift which are coupled respectively to a first and a second actuator unit in order to operate the actuation of the clutch and the selection and engagement/disengagement of the gears. The device comprises a transmission control circuit in which a main microprocessor formulates control signals for the first and second actuator unit and an auxiliary microprocessor determines a state of malfunctioning of the main microprocessor in order to transfer the control of the transmission unit to the auxiliary microprocessor in the event of a fault.

BACKGROUND OF THE INVENTION 
The present invention relates to a device and a method for transmission 
control. 
Control devices for vehicle transmission units are known, in which an 
electronic circuit supplies control signals for a first and a second 
actuator unit which are able to operate, respectively, the actuation of a 
clutch and the selection and engagement/disengagement of the gears of a 
shift associated with this clutch. The known electronic circuits comprise 
at least one microprocessor which generates the clutch and shift actuation 
signals on the basis of a plurality of input signals, for example 
representative of a manually selected gear, of the working conditions of 
the engine, etc. 
In the event of a malfunctioning of the microprocessor, the control signals 
may be completely lacking or may be generated in an entirely chance manner 
making the transmission unit unusable and giving rise, as a consequence, 
to the unmanageability of the vehicle. In particular, in the event of a 
malfunctioning of the microprocessor while the vehicle is travelling at 
high speed, any failing in traction due to the accidental opening of the 
clutch or to the accidental disengaging of the engaged gear, may give rise 
to the loss of control of the vehicle. Similar considerations may hold in 
the event of a malfunctioning of the microprocessor while the vehicle is 
travelling along a steeply descending stretch of road. 
SUMMARY OF THE INVENTION 
The object of the present invention is to produce a transmission control 
device which overcomes the drawbacks of the known devices. 
The above object is achieved by the present invention as the latter relates 
to a transmission control device of the type described in claim 1. The 
present invention furthermore relates to a method of transmission control 
of the type described in claim 14.

DETAILED DESCRIPTION OF THE INVENTION 
With particular reference to FIG. 1, a transmission control device is 
indicated 1, as a whole, cooperating with an internal combustion engine 3, 
for example a petrol engine or a diesel engine. The engine 3 cooperates 
with an electronic engine-control facility 5 which receives as input a 
plurality of information parameters P measured mainly in the engine 3 and 
supplies control signals for the ignition system (not illustrated) and an 
injection system (not illustrated) of the engine 3. 
The engine 3 has an output shaft 8 able to provide mechanical power to the 
input of a transmission unit 10 having an output shaft 12 able to transmit 
mechanical power to the wheels of a motor vehicle (not represented). The 
transmission unit 10 comprises a clutch 15 input-connected to the shaft 8 
and a shift 17 input-connected to the output shaft of the said clutch 15. 
The transmission unit 10 furthermore comprises a first actuator unit 19 
(represented schematically) for opening and closing the clutch 15 and a 
second actuator unit 21 for operating the selection and 
engagement/disengagement of the gears of the shift 17. 
The transmission unit 10 cooperates with a transmission control circuit 24 
able to formulate a plurality of input signals G and able to control the 
first and the second actuator unit 19, 21 for the selection and 
meshing/unmeshing of the gears. For example, the control circuit 24 can 
receive input signals from a manually actuatable selector device 26 usable 
for the selection of the gears. The transmission control circuit 24 
furthermore cooperates with the engine control facility 5 to which it is 
connected via a bidirectional data transmission line (BUS) 29. 
In particular, the first actuator unit 19 comprises a hydraulic actuator 31 
coupled with an electric control valve 32 receiving pressurized oil from 
an electric pump 35. The hydraulic actuator 31 is able to actuate, in a 
known manner, the clutch 15, opening or closing the clutch 15 on the basis 
of an electrical control signal OP/CL supplied to the electric valve 32 
from the circuit 24. The actuator unit 21 comprises two double-action 
hydraulic actuators 37a, 37b coupled with respective control valve devices 
39a, 39b receiving pressurized oil from the electric pump 35. The actuator 
unit 21 is able, in a known manner and on the basis of a control signal 
GEAR supplied to the valve device 39a, to engage/disengage the gears of 
the shift 17 and is furthermore able, in a known manner on the basis of a 
command SEL supplied to the valve device 39b, to select the setting of the 
gears of the shift 17. 
The transmission control circuit 24 furthermore controls a relay 41 for 
energizing the electric pump 35. According to the present invention the 
transmission control circuit 24 comprises a first microprocessor 44 and an 
auxiliary microprocessor 46 working together according to the procedures 
which will be made clearer subsequently with the help of FIG. 2. 
FIG. 2 illustrates a preferred example of the operation of the transmission 
control circuit 24 working in accordance with the present invention. 
To start with there is a block 100 in which the auxiliary microprocessor 46 
determines the state of operation of the main microprocessor 44, for 
example by monitoring a CLOCK signal CK from the main microprocessor 44. 
In the event that the monitored state of operation corresponds to normal 
operation of the main microprocessor 44 (for example in the event that the 
CLOCK signal is present and regular) the block 100 is followed by a block 
110, otherwise, in the event that a malfunctioning of the main 
microprocessor is determined, we go from block 100 to block 120. The state 
of malfunctioning can be determined, for example, in the event that the 
CLOCK signal is absent or irregular. 
Block 110 carries out, in a known manner, control of the transmission unit 
10 via the main microprocessor 44 and on the basis of the signals G 
supplied to the circuit 24 (and possibly of the state of the engine 3 as 
determined from the data coming through the data line 29). From block 110 
we return to block 100, although remaining within the loop formed by the 
blocks 100, 110 so long as the main microprocessor 44 is operating 
correctly. 
Block 120 transfers the control of the transmission unit 10 to the 
auxiliary microprocessor 46 and possibly generates a signal in order to 
execute a malfunctioning and danger signalling (optical, audible) 
addressed to the user of the vehicle (not illustrated). The auxiliary 
microprocessor 46 comprises a first data exchange interface 46a 
(illustrated in FIG. 1) receiving the signals identifying the state of 
malfunctioning of the microprocessor 44 and a second data exchange 
interface 46b (illustrated in FIG. 1) which is normally configured as an 
input interface (INPUT). With the determining of the state of 
malfunctioning the second interface 46b becomes configured as an output 
interface (OUTPUT) for the purpose of allowing the generation of control 
signals by the auxiliary microprocessor 46 heading for the transmission 
unit 10. 
The auxiliary microprocessor 46 determines a first and a second working 
condition of the vehicle by observation of the state of the clutch 15 as 
prevailing before the determining of the malfunctioning. In particular, 
the block 120 determines a first working condition in which the clutch 15 
is closed and the vehicle is proceeding normally or is stationary and a 
second working condition in which the clutch 15 is at least partially open 
and a shift of gear or a pull-away is in progress. In the event that the 
first working condition is determined the block 120 is followed by a block 
130, otherwise, in the event of the determining of the second working 
condition the block 120 is followed by a block 140. The determining of the 
state of the clutch 15 can be undertaken by sequentially storing the 
clutch control signal OP/CL generated by the main microprocessor 44 and 
retrieving the last stored value of this signal before the determining of 
the malfunctioning. Alternatively, the determining of the state of the 
clutch can be carried out by determining the actual position of the clutch 
15, for example with a position sensor (not illustrated) or by determining 
the strength of the control current of the electric valve 32. 
The block 130 acts on the transmission unit 10 in order to maintain this 
unit in the working condition in use before the detection of the 
malfunctioning; in particular, the block 130 operates on the controls of 
the unit 10 in order to prevent the opening of the clutch 15 and the 
modifying of the currently set transmission ratio. 
In particular, the block 130 controls: 
the opening of the relay 41 so as to switch off the electric pump 35 
thereby disabling the supply of pressurized oil to the actuator units 19 
and 21; 
the deactivation of the electric valve 32 so as to disable the hydraulic 
actuator 31 thereby preventing the actuation of the clutch 15; and 
the deactivation of the valve devices 39a, 39b so as to disable the 
double-action hydraulic actuators 37a, 37b thereby preventing the 
actuation of the shift 17 and in particular the disengaging of the gears. 
Block 130 is followed by a block 150 which checks whether the speed of the 
vehicle is below a near-zero threshold value; if so (vehicle stationary or 
almost stationary) block 150 is followed by a block 160, otherwise 
(vehicle moving with non-negligible speed) block 150 is followed by a 
block 170. Block 160 maintains the deactivation of the controls of the 
transmission unit 10 as done in block 130 and possibly sends a 
malfunctioning signalling (for example of the optical or acoustic type) to 
the driver of the vehicle. 
Block 170 waits for the speed of the vehicle to drop below a preset 
threshold value corresponding to a safety speed; upon the reaching of this 
safety speed, we pass from block 170 to a block 180. Alternatively, block 
170 may wait for the angular speed of the engine to drop below a preset 
threshold value corresponding to a safety rotation range; upon reaching 
this safety range, we pass from block 170 to block 180. 
Block 180 commands the closure of the relay 41 in order to reactivate the 
electric pump 35 and resupply the actuator units 19 and 21 with 
pressurized oil. Block 180 is followed by a block 190 which commands the 
supplying to the electric valve 32 of an electrical signal able to effect 
the opening of the clutch 15. Block 190 is followed by a block 200 which 
commands the supplying to the valve devices 39a, 39b of a signal able to 
effect the putting into neutral of the shift 17. Block 200 is followed by 
a wait block 210 (TIME OUT) which effects a closed loop for a preset 
period of time T; on termination of the period T, we return from block 210 
to block 130. 
Block 140 comprises a block 140a which commands the closure of the relay 41 
in order to reactivate the electric pump 35 (if deactivated by the faulty 
main microprocessor) and supply the actuator units 19 and 21 with 
pressurized oil. Block 140a is followed by a block 140b which commands the 
supplying to the electric valve 32 of an electrical signal able to effect 
the opening of the clutch 15. Block 140b is followed by a block 140c which 
sends the valve devices 39a, 39b a signal able to effect the putting into 
neutral of the shift 17. From block 140c we go to block 210. 
In use, the malfunctioning of the main microprocessor 44 is immediately 
determined (block 100), transferring the control of the transmission unit 
10 from the main microprocessor 44 (faulty) to the auxiliary 
microprocessor (block 120). Therefore, the state of the vehicle is 
monitored (block 120) and if the vehicle is stationary or is travelling 
along at normal speed, all the commands to the transmission unit 10 are 
removed (block 130) so as to prevent the vehicle from lacking traction (in 
the event that the vehicle is travelling along) or to prevent the starting 
of the vehicle (in the event that the vehicle is stationary). In the event 
that the vehicle is travelling along at normal speed, the slowing down of 
the vehicle is awaited (block 170) in order to reactivate the electric 
pump 35 (block 180), open the clutch (block 190) and put the shift into 
neutral (block 200). Therefore, the shift is put into neutral at low speed 
without the danger that the lack of traction might cause the loss of 
control of the vehicle. Subsequently, the vehicle stops, for example 
because the driver has actuated the brakes, and is no longer able to set 
off again (block 130). In the event that the malfunctioning of the main 
microprocessor occurs during a gear shift or a pull-away (block 120), the 
electric pump 35 is reactivated if it was switched off following the fault 
in the main microprocessor (block 140a). Following this, the 
microprocessor 46 commands the opening of the clutch (block 140b) and 
places the shift into neutral (block 140c). 
From the foregoing it is clear how the device which is the subject of the 
present invention enables the transmission unit 10 to be placed in a 
safety condition following a fault in the main microprocessor. 
Indeed, in the event of a fault, the following actions are possible: 
if the vehicle is stationary and the clutch is closed (for example because 
the vehicle is stationary with the engine switched off), the following are 
prevented: the engaging or disengaging of the gears, the opening of the 
clutch and the generating of hydraulic power (blocks 130, 150, 160) and 
the consequent starting of the vehicle with the circuit 24 defective; 
if the vehicle is moving and the clutch is closed, traction is maintained 
so long as the speed of the vehicle has not dropped below a safety 
threshold (blocks 130, 170)--this prevents lack of traction from being 
able to render the vehicle unmanageable; 
if the vehicle is stationary and the clutch is open (for example while the 
vehicle is waiting at traffic lights), control of the pump is effected and 
so the clutch is opened and the shift put into neutral (block 140); 
if the vehicle is moving at low speed, the clutch is opened and the shift 
is put into neutral (blocks 170, 180, 190 and 200); and 
if a gear shift or a pull-away is being operated, the shift is put into 
neutral (blocks 170, 180, 190 and 200). 
Finally, it is clear that modifications and variants may be made to the 
device described and illustrated without however departing from the 
protective scope of the present invention. 
For example, the main microprocessor 44 could in turn diagnose the state of 
operation of the secondary microprocessor 46 and in the event of a 
malfunctioning or defect in the secondary microprocessor 46, a signalling 
could be sent to the user of the vehicle.