Electronic device for gear selection in an automatic transmission for motor vehicles

Abstract: An electronic device for gear selection in an automatic transmission for motor vehicles, comprising a plurality of digital sensors for determining the angular position of rotation of a gear selection shaft emerging from the automatic transmission and rotatable to engage the various gears by a stepping motor operable in both directions, the digital sensors and the stepping motor being electrically connected to a digital electronic operating and control unit which can process coded electrical signals emitted by the plurality of digital sensors as the angular position of the selection shaft varies, a pair of electrical actuators being provided to drive the stepping motor through at least one step at a time in one direction of rotation and/or the other.

Description: This invention relates to an electronic device for gear selection in an automatic transmission for motor vehicles. In motor vehicles comprising an automatic transmission, a gear selection lever is provided which, when suitably positioned, determines the various transmission operating states and/or positions. The lever positions for selection mainly comprise a park position, a drive position, a reverse position and a neutral position. As stated, the various possible gear selection positions have to be selected by the vehicle driver, with the result that during the gear shifting operation the driver may make an unacceptable or dangerous lever movement which could endanger driving or damage the transmission. For example it is always possible, particularly at the moment of vehicle stoppage, for the driver to inadvertently forget to position the gear lever in the park position, with the result that the vehicle is free to move, hence constituting a dangerous condition. FR-A-2 638 402 relates to an electronic device for gear selection according to the preamble of claim 1. An object of the present invention is to provide a device for gear selection in an automatic transmission which overcomes these drawbacks, and in addition totally eliminates the need for direct manual operation of the selection lever associated with the transmission. A further object is to provide a gear selection device of the aforesaid type having maximum reliability in terms of the correct variation and/or succession between one gear and another and also allowing the transmission position to be checked with the vehicle at rest. These objects are attained according to the present invention by an electronic device for gear selection in an automatic transmission for motor vehicles according to claim 1. Advantageously, by means of the device according to the present invention, the manipulation of the gear selection lever is replaced by the operation of two electrical actuators. These latter are conveniently connected to an electronic processing unit which controls the operation of the automatic transmission on the basis of signals received and emitted in a predetermined succession and/or correlation of relative sensor positions. The structural and operational characteristics and the advantages of a gear selection device according to the present invention will be more apparent from the description given hereinafter by way of non-limiting example with reference to the accompanying schematic drawings, in which: Figure 1 shows a schematic embodiment of the device according to the invention associated with an automatic transmission, shown partly in perspective; Figure 2 is an enlarged side elevational view of part of the sensor unit consisting of a rotatable non-magnetic support carrying a plurality of permanent magnets forming part of the device of Figure 1; and Figure 3 is a table which schematically represents the correlation between the series of gear-indicating permanent magnets arranged on the support of Figure 2, as the position of the gear selection lever varies. Figure 1 shows schematically an electronic device for gear selection in an automatic transmission for motor vehicles according to the present invention, it comprising at one end a stepping motor 11 mechanically connected by a first shaft 12 and levers (not shown) to a second gear selection shaft 13 entering an automatic transmission 14. The electronic device according to the present invention comprises essentially an electronic processing unit 15, such as an electronic logic control and power centre, connected on one side to a switching and powering device, indicated schematically as a switch 16. The electronic unit 15 is also connected to a speed measuring device 17 consisting of a tachometer sensor which measures the vehicle running speed by the rotation of a shaft 18, such as a vehicle wheel axle. The electronic unit 15 is also connected to and operationally controlled by a pair of electrical actuators 19 and 20, usually consisting of two pushbuttons or switches, which cause the first stepping motor shaft 12 and the second gear selection shaft 13 to rotate in one direction or the other, with consequent successive gear shifts. A plurality of permanent magnets are mounted on the shaft 12 of the stepping motor connected to the gear selection shaft 13, and a plurality of magnetic sensors are mounted on the casing of the stepping motor 11. The use of permanent magnets enables magnetic fields to be generated which are practically constant with time without undergoing wear, as would happen if using for example sliding contacts. For example the magnetic sensors consist of Hall effect sensors comprising a conducting foil traversed by electric current, a potential difference being induced in this foil whenever it is immersed in a magnetic field. In this manner the magnets act on the magnetic sensors without any mechanical contact, so minimizing wear and damage. The gear selection shaft 13 can undergo predetermined rotations in the sense that it can assume only a finite number of positions, with each of which a determined engaged gear of the automatic transmission 14 corresponds, so that using digital sensors it is possible to determine which gear has been engaged. Figure 1 is a partly perspective view of two supports of non-magnetic material such as aluminium, these being a first support 21 fixed to an extension 22 of the shaft of the stepping motor 11, and a second support 23 to be fixed to the casing of the stepping motor 11. In the illustrated embodiment, the plurality of permanent magnets fixed to the rotatable support 21 consists of five series of permanent magnets indicated respectively by A, B, C, E and F, the plurality of magnetic sensors fixed to the casing of the stepping motor 11 comprising five sensors indicated respectively by 24, 25, 26, 27 and 28, they being connected to the electronic unit 15. The illustrated embodiment is merely a preferred embodiment in that a different number of sensors and magnets could be used in a different arrangement. The series of sensors 24, 25, 26, 27 and 28 is connected to the electronic unit 15. The first support 21 is shaped as an isosceles trapezium or a circumferential sector and carries the series of permanent magnets along concentric circumferential arcs of decreasing diameter. At its top, for example within radial recesses in the peripheral circumference 29, the support 21 contains the first series A of permanent magnets corresponding to the various gears or positions assumable by the automatic transmission. In the illustrated embodiment these permanent magnets are seven in number and correspond to the park position P, the reverse position R, the neutral position N, the drive position D, the 3rd gear position 3, the 2nd gear position 2 and the 1st gear position 1. The second series of magnets B consists of a magnet 30 aligned radially on one side with the centre of rotation of the extension 22 of the stepping motor shaft 12, and on the other side with the magnets D, N and R of the peripheral series A. The third series of magnets C consists of four magnets 31, 32, 33 and 34 radially aligned with the peripheral magnets 1, 3, N and P of the series A. The fourth series of magnets E consists of two magnets 35 and 36 radially aligned with the peripheral magnets 1, 2, N and R of the series A. Finally, the fifth series of magnets F is arranged on an inner circumference of smaller diameter than the preceding, and consists of a long magnet 37 radially aligned with the peripheral magnets 1, 2, 3 and D of the series A. The table of Figure 3 is a binary representation of the correspondence between the sensor series C, E and F in indicating the automatic transmission gears. In this respect, it is important to note that the Hall effect digital magnetic sensors, as used for example in the present invention, have the property of electrically generating a logic "0" whenever they are exposed to a magnetic field, and of generating a logic "1" in the opposite case. In this manner, a doubly unambiguous correspondence between the engaged gears and the corresponding coded electrical signals generated by the sensors is obtained, such that these signals can be unambiguously identified and used by any digital electronic circuit or electronic unit. A display unit 38 and a relay 39 with normally open contacts (closed when the ignition key is inserted) connected into an engine power line 40 are connected to the electronic unit 15. The electronic device for gear selection in an automatic transmission for motor vehicles according to the present operates in the following manner. On inserting the ignition key, the vehicle engine can be started only if in the park or neutral position, ie when the sensor 24 faces the permanent magnet in position P or the permanent magnet in position N of the first series of magnets A. These positions are also indicated on the display unit 38 by virtue of the mutual arrangement of the magnet series C, E and F shown in the diagram of Figure 3. For example, when in the park position the sensors 24 and 26 are exposed to the magnetic field generated by the magnets P and 34, whereas when in the neutral position the sensors 24, 26 and 27 are exposed to the magnetic field generated by the magnets N, 33 and 36. By virtue of its preset logic, the electronic unit 15 allows the engine to be started when the sensors and magnets are in these relative positions. If the electrical pushbutton 19 is now pushed once, the reverse position is achieved as the electronic unit 15 feeds a signal for rotating the stepping motor 11 through one step. The required operation of the automatic transmission 14 is therefore achieved, and the position attained is confirmed by the fact of the magnet R of the first series A being in a position corresponding with the sensor 24. This selection is also indicated by the display unit 38, in that the sensor 27 is exposed to a magnetic field generated by the magnet 36 of the series E. When in this position the reversing lights (not shown) are also operated. It should be noted that as in the case of all automatic transmission vehicles the brake governs the vehicle movement in the normal manner. If it is required to put the vehicle into gear from the park position while keeping the brake pressed, the pushbutton 19 has to be pressed a number of times sufficient to attain first gear (1). The sensors 24, 26, 27 and 28 are thus exposed to a magnetic field generated by the magnets 1, 31, 35 and 37. This arrangement is achieved by the stepping motor undergoing the required number of steps under the control of the electronic unit 15. For every other position either the pushbutton 19 is operated in the described manner, or the pushbutton 20 to return or to shift gear by reverse movement of the stepping motor 11. The second permanent magnet series B, consisting in the illustrated example of the magnet 30, acts when in the automatic drive position as a safety device should the signal obtained by the tachometer sensor 17 indicate a vehicle speed exceeding a first level, for example 5 km/h, or exceeding a second level, for example 180 km/h. As the magnet D faces the sensor 24, the magnet 30 will face the sensor 25, to actuate a logic safety device. In this respect it prevents gear shift into the neutral, reverse or park position of the automatic transmission at permanent magnets N, R and P above the first level by acting on the pushbutton 20. In addition to gear shift into the stated positions, above the second speed level , detected by the tachometer sensor 17, it also prevents shift into third gear by acting on the pushbuttons 19 and 20, hence preventing over-running. An LED indicator 41 is also provided, it lighting only below the first level, indicating operation of the tachometer sensor 17, and being extinguished above said threshold. If it lights above this threshold, it indicates malfunction of the tachometer sensor 17. Advantageously in a device according the present invention, when the ignition key is removed the electronic unit 15 automatically returns the automatic transmission to the park position. In this respect, the engine power line 40 contains the relay 39 which remains closed until the automatic transmission reaches the park position. Only at this point do the contacts of the relay 39 open to cut power to the electronic unit or control centre 15. Hence even if the driver forgets to operate the pushbuttons 19 and/or 20 to shift the automatic transmission into the park position on vehicle stoppage, the electronic unit 15 does this completely automatically. Advantageously an electronic gear selection device according to the present invention is also provided with means which enable gears to be selected even if the stepping motor 11 is faulty. To achieve this, a manual gear actuator device operable from the interior of the motor vehicle is provided associated with the shaft 12 of the stepping motor 11. This manual actuator device consists essentially of a knob 50 rotatable into a series of positions corresponding to the gear positions. Rigid with the knob 50 there is a semi-flexible transmission 51, consisting for example of a remote control such as a Bowden cable, at the end of which a male hexagonal engagement element 52 is provided An extension 53 to the gear selection shaft 13 is provided, emerging from the opposite side of the transmission 14 to that on which said gear selection shaft 13 is connected to the shaft 12 of the stepping motor 11. In the extension 53 there is provided a female hexagonal seat 54 able to receive the male hexagonal engagement member 52. To ensure that the male hexagonal engagement member 52 and the female hexagonal seat 54 of the extension 53 are aligned but not in continuous mutual engagement during normal operation of the electronic gear selection device, a cylindrical guide shaft 55 is provided able to slide freely within a complementary cylindrical hole 56 provided in the extension 53. It is apparent that if the stepping motor 11 develops a fault, the gears can be selected by operating the knob 50. This operation is achieved by firstly pushing in the direction of the arrow 57 until the male hexagonal engagement member 52 is inserted in the female hexagonal seat 54, and then turning the knob 50 through an angle such as to engage the desired gear. In this manner the transmission can be operated even if the stepping motor 11 is faulty.

Claims: An electronic device for gear selection in an automatic transmission for motor vehicles, comprising a plurality of digital sensors (24-28) for determining the angular position of rotation of a gear selection shaft (12,13) emerging from said automatic transmission (14) and rotatable to engage the various gears by a stepping motor (11) operable in both directions, said digital sensors (24-28) and said stepping motor (11) being electrically connected to a digital electronic operating and control unit (15) which can process coded electrical signals emitted by said plurality of digital sensors (24-28) as the angular position of said selection shaft (12, 13) varies, a pair of electrical actuators (19,20) being provided to drive said stepping motor (11) through at least one step at a time in one direction of rotation and/or the other, wherein said plurality of digital sensors (24-28) are fixed to the casing of said stepping motor (11) and are a plurality of Hall effect sensors sensitive to a magnetic field, characterised in that said gear selection shaft (12,13) is selectively connectable to a manual gear actuator device (50-56). A device as claimed in claim 1, characterised in that the magnetic field sensed by said plurality of Hall effect digital sensors (24-28) is generated by a plurality of permanent magnets (A,B,C,E,F). A device as claimed in claim 2, characterised in that said plurality of permanent magnets (A,B,C,E,F) are rigid with a shaft (22) of said stepping motor (11) positively connected to said gear selection shaft (13) of said automatic transmission (14). A device as claimed in claim 1, characterised in that said plurality of Hall effect digital sensors (24-28) consist of five Hall effect sensors. A device as claimed in claim 2, characterised in that said plurality of permanent magnets (A,B,C,E,F) consist of five series of permanent magnets. A device as claimed in claim 1, characterised in that said digital operating and control unit (15) is able to activate a display unit (38) indicating which gear is engaged in said automatic transmission (14). A device as claimed in claim 5, characterised in that said five series of permanent magnets (A,B,C,E,F) are fixed onto a support (21) of non-magnetic material rigid with said shaft (22) of said stepping motor (11), said support (21) being in the shape of a circumferential sector and said five series of permanent magnets (A,B,C,E,F) being positioned on concentric circumferences of decreasing radius. A device as claimed in claim 5, characterised in that the most outer (A) of said series of permanent magnets consists of seven permanent magnets (1,2,3,D,N,R,P) inserted into peripheral radial recesses in said support (21) of non-magnetic material and corresponds to the gears of said automatic transmission (14). A device as claimed in claim 5, characterised in that a second series (B) from said series of permanent magnets is provided as protection against shifting the automatic transmission (14) into the neutral (N), reverse (R) or park (P) position when the vehicle is travelling at a speed exceeding a first level. A device as claimed in claim 5, characterised in that a second series from said series of permanent magnets is provided as protection against shifting the automatic transmission (14) from the automatic drive position into a lower gear when the vehicle is travelling at a speed exceeding a second level. A device as claimed in claim 1, characterised in that a tachometer sensor (17) is associated with said digital electronic unit (15). A device as claimed in claim 1, characterised in that said manual gear actuator device comprises a knob (50) rigid with one end of a flexible remote control transmission (51) connectable to said gear selection shaft (13) by engagement elements. A device as claimed in claim 12, characterised in that said engagement elements are male and female hexagonal elements (52,54) positioned at the end of said gear selection shaft (13) and at the end of said flexible transmission (51) respectively. A device as claimed in claim 12 or 13, characterised in that said flexible transmission (51) is a Bowden cable.

Inventors: MOSCATELLI SAVERIO, MOSCATELLI, SAVERIO
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1992
Main classification: F16H59
IPC codes: F16H59, F16H61