GB2025546A - Transmissions for motor vehicle - Google Patents

Abstract

A transmission for a motor vehicle comprises a gearbox and printed circuit cards 1-7 for controlling the gearbox. The output card 6 produces electrical output signals which actuate electropneumatic or electrohydraulic elements which cause respective gear ratios to be selected. A two-gear protection card 7 senses the electrical output signals and, if signals for more than one gear are present, actuates a disabling means to disable all the output signals for a predetermined period. After that predetermined period, if the signals for one of the gears was spurious, the genuine signal reappears and the gear is engaged. If signals for two or more gears re-appear, the disabling means operates for a further disable period. Since the output gear-selecting signals are sensed, as opposed to input signals from, for example, a gear selector, faults in the circuitry for producing the output signals as well as faults in the input circuitry will be detected. <IMAGE>

Description

SPECIFICATION Transmissions for motor vehicle This invention relates to transmissions for motor vehicles and especially to the control systems of such transmissions.

The invention provides a transmission for a motor vehicle, which comprises a gearbox, means for producing a plurality of electrical output signals for selecting the respective gear ratios, sensing means for sensing when the electrical signals for more than one gear ratio are simultaneously produced, and disabling means arranged to disable the gear-selecting signals for a predetermined time period in response to the simultaneous sensing of the electrical signals for more than one gear ratio.

After the disable period, if the signals for one of the gear ratios was spurious, the signals for the genuine gear will reappear and the respective gear will engage. If signals for two or more gears re-appear after the disable period, the disabling means will operate for a further disable period. Since it is the output gear-selecting signals that are sensed, as opposed to various input signals from for example, a gear selector, faults in the circuitry for producing the output signals as well as faults in the input circuitry will be detected.

Advantageously, the disabling means is so arranged that the simultaneous sensing of the electrical signals for more than one gear ratio must be maintained for a pre-determined time delay period before the disabling means becomes operative to disable the gear-selecting signals, the delay period being small compared with the disable period. It has been found that gear-selecting signals may overlap briefly during gear changes and the provision of the delay period prevents the disabling means from being brought into action in such a case. Preferably, the disable period is at least fifty times, and preferably at least a hundred times, longer than the delay period.

The delay period may be between fifty and two hundred microseconds duration, and the disable period may be between half a millisecond and two seconds, and preferably between one millisecond and one second.

The sensing means may include three twostate logic devices so coupled that the delay period takes place between the switching of the first and second devices and the disable period takes place between the switching of the second and third devices, the disable period preferably only occurring on switching to the state where the disabling means is not operative, that is, when the sensing means senses signals for more than one gear, the switching of the third two-state logic device should follow the switching of the second immediately. The two-state logic devices may be for example NAND gates. Alternatively, if a single electrical signal corresponds to each gear ratio, the sensing means may comprise means for summing the electrical signals present at any time and a comparator connected to the output of the summation means for detecting when more than one signal is present.

The arrangement of the invention may be provided with its own power supply, for example, a zener diode and a capacitor; a low power supply for the whole control system of the gearbox may itself be a cause of spurious signals and if the power supply for the arrangement of the invention was itself low, it might not be able to itself function properly.

The gearbox may be an epicyclic transmission of the type known as the 'Wilson' gearbox, an example of which is disclosed on pages 492 and 496 of the 9th Edition of 'The Motor Vehicle' by K Newton, W Steeds and T K Garrett. In this kind of transmission, gear engagements are effected by the application of brake bands or clutches to either the reaction members or other elements of various epicyclic gear trains. In this case the gearselecting signals may be to elements (for example, electrohydraulic or electropneumatic valves) for applying the brake bands or clutches, one signal per brake band or clutch, that is one signal per gear ratio. The control system of the gearbox may be semi-automatic, that is, pre-select type, or automatic, and may employ a torque converter.

The electric output signals may be fed to elements for example electrohydraulic or electropneumatic valves which produce the respective gear ratios by means of fluid pressure. If the gearbox is an epicyclic gearbox, the elements may be for applying brake bands or clutches in the gearbox to select the gears.

The disabling means may comprise an electronic switch in series with the means for producing the electrical output signals for selecting the respective gear ratio. A transmission for a motor vehicle will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block digram of a part of the control system of the gearbox; Figure 2 shows a block diagram of part of the control system shown in Fig. 1; Figure 3 shows the circuit of the output printed circuit card; and Figure 4 shows the circuit of the two-gear protection printed circuit card.

The gearbox of the transmission controlled by the control system may be a Wilson gearbox, an example of which is described and illustrated on page 492 to 496 of the 9th Edition of 'The Motor Vehicle' by K Newton, W Steeds and T K Garrett. The control system of the gearbox receives input signals from the driver of the vehicle and other sources and translates them into output signals which act on electrohydraulic or electropneumatic valves which operate the brake bands or clutches of the control system. An example of such a gearbox and such a control system is described in United Kingdom Patent Specification No. 1,505,817. The present invention is concerned with means to prevent two or more output signals being simultaneously produced; this would cause the gearbox to stall, causing severe damage.

Referring to Fig. 1, the control system comprises seven printed circuit cards or modules 1 to 7, the functions of which are as follows: The interface and power supply card 1 converts 28 volt driver command signals to 10 volt noise free control signals. The driver command signals include 'automatic' and 'hold 3' where the gearbox may select ratios up to and including third gear. The frequency to voltage card 2 converts an a.c. frequency dependent signal from a sensor measuring road speed to a d.c. voltage dependent signal.

This signal is fed to the speed level switch card 3, which generates switched output signals as various speed thresholds are crossed.

From these signals and from driver command signals fed from interface and power supply card 1, the logic card 5 selects a gear ratio.

The signals from the logic card corresponding to the respective gears are amplified by power output transistors contained in the output card 6 and fed to a six-way electropneumatic valve unit (not shown). This valve unit converts the electrical signals received from the output card to pneumatic signals, which directly operate the brake bands of the gearbox. A time generation card 4 generates a throttle dip signal (fed to the output card 6), a neutral gap (fed to the logic card 5) and is controlled by a time trigger signal fed from the logic card 5.

The two gear protection card 7 monitors the output signals and detects more than one ratio being selected. The card has its own power supply.

Referring to Fig. 2, the two-gear protection card 7 comprises a circuit 7a for receiving signals GS1 to GS6 which sense the output gear-selecting signals G1 to G6 and a circuit 7bfor generating a disabling signal D when more than one gear-selecting signal is present.

Signal D is fed to the output card to where it switches off all the gear-selecting signals.

The sensing circuit 7athen no longer senses two gears but because of a delay inherent in the circuit 7b, the disable signal is held for the duration of the delay.

Referring to Fig. 3, the output circuit includes a number of transistor amplifiers Al to A6 which amplify signals L1 to L6 from the logic card 5 and feed the output gear-selecting signals G1 to G6 to the electropneumatic valve (not shown). The amplifiers each have an additional transistor connected into their output circuits for providing gear sense signals GS1 to GS6. The output card also includes a gear disable electronic switch in the form of a transistor TR1 which is controlled by disabling signal D from the two-gear protection card. When disabling signal D is operative, transistor TR 1 is switched off and amplifiers Al to A6 are also switched off. Thus gear-selecting signals G1 to G6 are switched off, as are gear-sensing signals GS1 to GS6.

Referring to Fig. 4, both the sensing circuit 7 a and the disabling circuit 7behave an independent power supply comprising a zener diode ZD1 and a capacitor C1. In the sensing circuit 7a, GS1 corresponds to fifth gear and GS2 to GS6 correspond to fourth gear to reverse, respectively. Sensing circuit 7a also comprises an array of NAND gates, NAND 1 to NAND 1 6 and the signals corresponding to each gear are fed to the inputs of NAND 1 to NAND 8 as shown.

The NAND gates 1 to 1 5 are so arranged that the output of NAND 1 5 is in logic state '0' for two or more gears and logic state '1' for when one gear-sensing signal is present.

However during a normal gearchange, there can be a slight overlap in gear-selecting signals and, to prevent a disabling signal being generated every time there is such an overlap, R8 and C2 have the effect of delaying the signal by approximately 100 microseconds before it reaches NAND 1 6.

In the event of two or more gears, NAND 16 and 17 switch to logic state '1' TR3 is turned on, thereby operating a warning light (not shown) and TR4 is turned off. Disable signal D is generated and amplifiers Al to A6 are turned off. All gear selecting signals G1 to G6 are thus turned off.

NAND 1 5 thus immediately returns to logic state '1'. However this change does not reach NAND 1 7 for approximately half a second delay because of capacitor C3, and thus the disable signal D is held for this period. When the delay expires, the gear will try to reengage. If the fault condition still exists, the gear disable signal D will be immediately generated (the half second delay only applies to a '1' to '0' transition of NAND 16). If a permanent two-gear condition exists, G1 to G6 appear as a series of pulses whose width is approximately 100 microseconds (due to R8 and C2) and whose repetition frequency is approximately two times a second (due to C3). The electrical time constants of the electropneumatic valve are such that it does not respond to such pulses.

The control means of the invention thus protects the gearbox from damage resulting from simultaneous selection of two ratios by sensing the gear-selecting signals to the electropneumatic valve, and removing the supply to all output devices if two or more gear selecting signals are sensed. In this way the gearbox is protected from faults occurring both within the control means and in the wiring of the vehicle (for example, a bus).

Various modifications may be made to the circuit without departing from the scope of the invention. Thus, for example, the two-gear sense circuit 7a may be modified to consist of analogue elements instead of logic circuitry as described. The voltages G1-G6 measured on the output terminals could be summed using conventional operational amplifier techniques, and a comparator could be used on the subsequent output signal to detect more than one gear. This would be suitable for the "one gear-one output signal" gearbox described.

The illustrated gear sense logic circuit 7c however could be modified to detect two gears even if more than one electrical signal was associated with each gear.

Among the advantages of the system of the invention are that: the system monitors the gear selecting signals directly on the output terminals of the gearbox controller and thus caters for vehicle wiring faults; the system caters for failure of the transistors in amplifiers Al to A6 because the disable device is in series with all these amplifiers; and the system works on a continuous basis and does not "lock up" when two gears are sensed in such a way that it must be reset before it is operational again.

Claims (11)

1. A transmission for a motor vehicle, which comprises a gear box, means for producing a plurality of electrical output signals for selecting the respective gear ratios, sensing means for sensing when the electrical signals for more than one gear ratio are simultaneously produced, and disabling means arranged to disable the gear-selecting signals for a predetermined time period in response to the simultaneous sensing of the electrical signals for more than one gear ratio.

2. A transmission as claimed in claim 1, wherein the disabling means is so arranged that the simultaneous sensing of the electrical signals for more than one gear ratio must be maintained for a predetermined time delay period before the disabling means becomes operative to disable the gear-selecting signals, the delay period being small compared with the disable period.

3. A transmission as claimed in Claim 2, wherein the disable period is at least fifty times longer than the delay period.

4. A transmission as claimed in claim 3, wherein the disable period is at least one hundred times longer than the delay period.

5. A transmission as claimed in any one of claims 2 to 4, wherein the delay period is between fifty and two hundred microseconds duration, and the disable period is between half a millisecond and two seconds.

6. A transmission as claimed in any one of claims 2 to 5, wherein the sensing means includes three two-state logic devices so coupled that the delay period takes place between the switching of the first and second devices and the disable period takes place between the switching of the second and third devices, the disable period only occurring on switching to the state where the disabling means is not operative.

7. A transmission as claimed in any one of claims 1 to 5, wherein a single electrical signal corresponds to each gear ratio, and the sensing means comprises means for summing the electrical signals present at any time and a comparator connected to the output of the summation means for detecting when more than one signal is present.

8. A transmission as claimed in any one of claims 1 to 7, wherein the electric signals are fed to elements which produce the respective gear ratios by means of fluid pressure.

9. A transmission as claimed in claim 8, wherein the elements are electrohydraulic or electropneumatic valves.

1 0. A transmission as claimed in claim 8 or claim 9, wherein the gearbox is an epicyclic gearbox, and the elements are for applying brake bands or clutches in the gearbox to select the gears.

11. A transmission as claimed in any one of claims 1 to 10, wherein the disabling means comprises an electronic switch in series with the means for producing the electrical signals for selecting the respective gear ratios.

1 2. A transmission for motor vehicle substantially as hereinbefore described with reference to, and as shown in, Figs. 1 to 4 of the accompanying drawings.