GB1596358A

GB1596358A - Electrical control means for changespeed gearing

Info

Publication number: GB1596358A
Application number: GB12527/78A
Authority: GB
Original assignee: Thomas Electronics Ltd
Current assignee: Thomas Electronics Ltd
Priority date: 1974-11-27
Filing date: 1978-03-30
Publication date: 1981-08-26
Also published as: GB1492523A

Description

(54) AN IMPROVEMENT IN OR RELATING TO ELECTRICAL CONTROL MEANS FOR CHANGE-SPEED GEARING (71) We, THOMAS ELECTRONICS LIMITED, a British Company, of Garrison Works, Birch Vale, Stockport, Cheshire, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to electrical control means for change-speed gearing and has for its object to provide an improvement in or modification of the invention claimed in our prior patent No. 1,492,523.

There are certain conflicting requirements in the design of change-speed gearing, especially change-speed gearing for public service vehicles where the requirements for maximum public safety sometimes conflict with the requirement that the vehicle engine should be saved from damaging overspeed. The invention seeks to balance these requirements and in addition to provide a change-speed gear control means capable of different modes of operation according to driver requirements and road conditions.

According to the invention, there is provided an improvement in or modification of the invention claimed in our prior patent No. 1,492,523, that is to say an electrical control means for vehicle changespeed gearing, the control means including individual drive selection means for the various forward gear ratios available electrical signal amplifiers associated with the respective drive selection means for rendering said drive selection means operative or inoperative selectively, vehicle speed responsive means for bringing the electrical signal amplifiers into operation selectively according to vehicle speed, first switch means operable in response to vehicle throttle opening and closing movements whereby, during normal operation, at a small throttle opening (as when the vehicle is descending a hill and the throttle pedal is released) a change to the next upward gear ratio is prevented but down changes are permitted still under the control of the vehicle speed responsive means, and further switch means which are manually operable to effect the same function as said first switch means whereby, at will, the driver of the vehicle can operate said further switch means to effect a "gear hold" condition in which a change to the next upward gear ratio is prevented regardless of throttle opening and closing movements, the improvement or modification residing in the fact that means are also provided to prevent the selection of forward gears whilst the vehicle is moving rearwardly and to prevent the selection of reverse gear whilst the vehicle is moving forwards. Means will preferably also be provided whereby, when a fault condition arises in the control means, the highest available gear ratio is established for engine overspeed protection. Electrically operated means will preferably be provided whereby the torque transmitted through the changespeed gearing can be reduced during and immediately following a change of gear ratio and these means will preferably be adjustable whereby the period during which the torque is reduced can be varied from the briefest instant to several seconds. The electrically operated means for reducing the torque transmitted through the gearbox during this brief interval of time may operate to cut the fuel to the engine. The control means may include the facility for engaging an emergency low gear in the event of brake failure of the vehicle in which the change speed gearing is installed, such means canveniently including an electric switch located beneath the brake pedal of the vehicle, and may also include means for preventing the engagement of two gear ratios simultaneously. Means will preferably be provided whereby a neutral pause is brought about when downward changes or upward changes of gear ratio are being made. Means will preferably also be provided whereby the operation of the control means is modulated according to throttle opening so that as the vehicle is accelerating at full throttle the lower gear ratios are maintained for a longer period before upward changes are made and so that the lower gear ratios are re-engaged sooner, such means conveniently including an electric switch located beneath the throttle pedal.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, with reference to the accompanying drawing, which is a diagrammatic illustration of an electrical control means embodying the invention.

Referring now to the drawing, the electrical control means for change-speed gearing there illustrated includes a number of transistors, resistors, diodes, capacitors and the like electrically connected in circuit and designated in a conventional manner which will be readily understood by an electronics expert. The control means provides automatic selection of all forward gear ratios, the lowest ratio having three modes of operation that is to say: 1. Automatic selection 2. Selection by a switch means 3. Pre-selection by a switch means In the first mode of operation, switch 2 is permanenetly closed or the switch contacts bridged, switch 3 is left open or omitted and link A is removed from pin 11 on Icl (1A) and (3A). With the circuit connected as described, then first gear will be engaged and disengaged according to the rotational speed of the vehicle prop-shaft (hereinafter call shaft speed).

In the second mode of operation, switch 3 and link A remain as for the first mode.

Switch 2 may now be either hand or foot operated, in the latter case the switch being located beneath the vehicle throttle pedal to be closed automatically at maximum throttle. (Switch 2 may alternatively be controlled by other means, i.e. gradient operated switch, load operated switch or the like. Should switch 2 be closed, then first gear will engage providing the shaft speed is less than a predetermined maximum.

Should switch 2 be opened whilst the shaft speed is appropriate then the next highest ratio will engage. The arrangement is such that, unless switch 2 is closed, the control means will "see" the second ratio, i.e. 2nd gear as the lowest automatic ratio.

The third mode of operation is brought about by introducing link 'A' to Icl (sections 1A and 1C). Switch 2 is disconnected or left open and switch 3 is then used to present information to Icl (sections 1A and 1B2) which acts as a 'memory'. Should switch 3 be closed at any time, the 'memory' will store the information presented to it by its closure.

Should the shaft speed be appropriate for Ist gear engagement then the information contained within Icl (sections 1A and 1B) will agree with Ic2 and engagement of Ist gear will result. (Had the shaft speed been greater than that appropriate for Ist gear engagement, then Ic2 would not agree with Icl (sections 1A and 1B) and would therefore have no effect). Should the shaft speed now increase sufficiently to signal 2nd gear, then Ist gear will disengage and 2nd gear engage. At the same instant a signal will be received by Icl (sections 1A and 1B) via Ic4 (4B) and capacitor C3 to abandon its information. The 'memory' may receive information at any time but cannot be acted upon unless agreed with by Ic2. The selection by this mode of operation is therefore termed "Pre-select". As with mode 2, the control means will 'see' second gear as the lowest automatic ratio.

Frequency to Voltage Convertor The control means provides a frequency to voltage convertor which can have for its input signal a square, triangular or sine wave. The A.C. input signal is applied to R4 and a square wave is produced at the output of IC30, the frequency and mark space ratio being dependent upon the input signal.

Coupled to Tic30 output is Tl and its function is to switch in phase with the output of Ic30 causing its collector voltage to rise to the supply voltage and fall to 0 volts. Capacitors C4 and 5 are connected to the emitters of T2 and T3 and also to the collector of Tl.

The action of Tl is to cause the charge stored on C4 and 5 to be transferred to the collector circuits of T2 and T3 giving a mean current of I=Q/T which is equal to Q.F. where F is the input signal frequency.

It will be seen that the collectors of T2 and T3 have a variable resistor and this enables the mean current passing to provide a variable output voltage to the bases of T4 and T5. As T4 and T5 are connected as emitter followers they provide a high input independence and low output independence.

The ripple produced at the output is smoothed by capacitors C7 and C9 giving a low ripple D.C. output voltage relevant to the frequency of the input signal. The output voltage is then directed by Diodes D5, 6, 7 and 8 to the inverting inputs of Ic's 2, 5, 11 and 17 which are arranged to have their outputs brought to 'o' as the signal output voltage exceeds the reference voltage set at their non-inverting inputs.

Gear Shift Two shift sequences will now be described, i.e. 1st to 2nd and 2nd to 3rd.

(The shift from 3rd to 4th and 4th to 5th are identical to that of 2nd to 3rd).

Assume the shaft speed to be zero and mode 1 of the Ist gear operation in use, i.e.

Automatic selection of Ist gear and conditions to be described later are correct for engagement of a forward ratio.

First gear engagement is accomplished by Icl (section lc and lid), Ic2, T8, Ic3 (sections 3A and 3B) IC4 (section 4A T10 and T11.

The prevailing conditions are: Icl (section 1 c) will have its inputs held at '0' via the previously described link across switch 2 or its permanent closure, (section Ic) will therefore have its output at '1' and this is applied to (1D) which inverts the input to it and gives '0' at its output. This is then fed to one input of (3A) the other input being connected to the collector of T8. Since there is no propshaft movement then no signal voltage is being applied to the inverting input of Ic2, its output is at '1' and this in turn holds T8 off and maintains its collector at '0'. The state of (3A) inputs are therefore '0' '0' and its output is '1', this being inverted by (4A) and the '0' output being fed to one input of (3B). The other input of (3B) is connected to IcS which has at this stage its output at '0'. Therefore both inputs of (3B) are at '0' and its output is at '1'. As the output from (3B) is at '1', it causes T10 to conduct which in turn switches on the output transistor Till. This in turn energizes an external valve unit to engage Ist gear.

Ist to 2nd Up-shift Should the propellor shaft now begin to revolve, the voltage will begin to rise at the inverting input of Ic2 and should the shaft speed increase sufficiently the voltage at the inverting input of Ic2 will become greater than the reference voltage at the noninverting input of Ic2. When the signal voltage exceeds the reference voltage by 100 mv then the output of IC2 will become '0' and cause T8 to conduct causing its collector to go to '1'.

The logic now present at the inputs of '3A' will be '1' '0' and its output will go to '0'. This will be inverted by '4A' and its output will go to '1'. As '3B' will now have '1' '0' at its input, its output will fall to '0' causing T10 and Tl 1 to switch off and deenergise the external valve unit, causing Ist gear to disengage.

2nd gear engagement is accomplished by Ic3 (sections 3c and 3D) Ic4 (sections 4B and 4C) Ic6, Ic7, T12 and T13, together with all sections described for first gear engagement with the exception of (3B) T10 and Tll.

Engagement of 2nd gear on disengagement of Ist gear.

From the description of the logic state required for Ist gear engagement, it will be seen that (4B) is also connected to the output of (4A). To review the state of the first gear when engaged (Ic) input = '0' (Ic) output ='1', therefore (ID) output='0' and one gate of (3A)='0'. The output of IC2='1' therefore T8 is off and its collector is '0'. As one input of (3A) is connected to the collector of T8 then both of (3A) inputs are '0' giving an output '1' (4A) inverts the '1' to '0' and this is applied to (4B) along with (3B). (The remaining logic on 3B is as described for Ist gear engagement).

The input on (4B) '0' is inverted by (4B) to give '1' at its output. Ic6 output is at this stage '0'. Therefore the input to (3C) is '1' '0' and the output of (3C) is '0', (4c) inputs are connected to the output of 3c via a resistor and the '0' present at (4C) input becomes '1' at its output. One input of (3D) is connected to (4C) output and the other input of (3D) is at this stage '0' via R114.

The inputs to (3D) are therefore '1' '0' causing (3D) output to be '0' and holding off T12 and T13 which, in turn maintain the external valve in a de-energised condition.

Should the conditions now prevail as explained in the 1st to 2nd up-shift, then as (4A) goes to 'I' and disengages Ist gear via (3B) T10 and Til, (4B) input will also go to '1' and its output will go to '0'. The transition from 'I' to '0' of (4B) will cause the output to Ic6 to go to '1' for a given period of time (dependent upon the setting of VR3) and at the same instant one input (3C) will also go to '0'. Therefore (3C) will maintain its output state, maintaining (4C), (3D), T12 and TI3 in the same state. When Ic6 returns to '0' then (3C) inputs will both be '0' and its output will go '1'. (The inclusion of R77 and C19 are to prevent (4C) from giving a brief '1' output during the time it takes for Ic6 to rise to 1). The output from (3C) is now inverted by (4C) and gives an output '0', (the output'0' also being applied to Cl 8 to bring Ic7 output to '1' for a period set by VR4, this output causing T14 and T15 to switch on and energise a solenoid to be later described), causing (3D) inputs to become '0' '0'. As one input is at '0' via R114 (3D) output will now become '1' and switch on T12 and T13 which, in turn, energises an external valve unit to engage 2nd gear.

To summarise the output conditions to the external valve unit, Ist gear is engaged, 2nd gear is signalled, Ist gear disengages, a neutral pause is introduced and then 2nd gear engages along with separate timed output (see throttle dip).

2nd to 3rd Upshift Third gear is accomplished by IcS, Ic6 (sections 6A, 6B and 7B) Ic7 (sections 7A and 7B) Ic8, Ic9, T18, Tl9 and T20.

When the shaft speed is below that appropriate for 3rd gear engagement, the prevailing conditions are: The inverting input voltage on IcS is lower than that at its non-inverting input causing its output to remain '1' thereby holding off T18. As T18 is off its collector will be at '0'. The inputs of (6A) are connected to the collector of T18, therefore their inputs will be '0' '0' and the output at '1'. Connected to the output of(6A) are C33 and one input of (7A). The other input of (7A) is connected to the output of IC8 which has '0' at its output. The input conditions for (7A) are therefore '1' '0' and its output is '0'. The inputs of (6B) are connected to the output of (7A) via R76 giving an input of '0' '0' to (6B) which inverts this to give '1' at its output.

Connected to the output of (6B) is C37 and one input of (7B). The other input to (7B) is taken to '0' via R117. The input conditions on (7B) are therefore '0' '1' giving '0' at its output, causing Tl9 and T20 to be held off and maintain the external valve in a deenergized condition.

Should the shaft speed increase sufficiently to cause the inverting input to exceed the non-inverting input of IC5, then its output will go to '0' and cause T18 to switch on, causing its collector to go to '1'.

The inputs of (6A) will be '1' '1' and its output will go to '0'. As C33 and one input of (7A) are connected to the output of (6A) and the function of C33 is to trigger IC8 to '1' for a period of time determined by the setting of VR5, then (7A) will have for its input '0' '1' and its output will remain unchanged for the period during which Ic8 remains '1'. It will be seen also that as T18 now has '1' as its collector, D24 has become forward biased and now applies '1' to one input of Ic3 (section 3D) causing the output of (3D) to go to '0' which in turn switches off T12 and T13. This causes the 2nd gear external valve to de-energise and in consequence disenagage 2nd gear.

On completion of the period during which Ic8 is '1', it will revert to '0' and both inputs of (7A) will become '0' '0' causing its output to go to '1'. The inputs to (6B) are connected to the output of (7A) via R76 and therefore the input of (6B) will also go to '1' and its output will go to '0'.

Connected to the output of (6B) are one input of (7B) and C37. As 6B output goes to '0' Ic9 output will go to '1' for a period of time determined by setting of VR6 and switch on T14 and T15 for the same period Ic9 is at '1' (see throttle dip), the other input of (7B) is at '0' via R117 and the output therefore goes to '0'. As '1' is appearing at (7B) output it causes T19 and T20 to switch on, causing the external valve to energise which in turn causes selection of 3rd gear.

To summarise the events which led to 3rd gear selection with 2nd gear engaged, the shaft speed increased sufficiently to select 3rd gear; in selection of 3rd gear, 2nd gear was disengaged; a pause in the chain of events occurred and on completion of the pause 3rd gear engaged and an output was given to the throttle dip mechanism. The selection of 4th and 5th gear would have the same logic states as those described for 3rd gear selection, only the relevant sections for 4th gear would be: Icll, Ic12 (sections 12A and 12B), Ic13 (sections 13A and 13B) Ic14, Ic15, T23, T24 and T25 along with T14 and T15.

The relevant 5th gear sections are Ic17, Ic18 (sections 18A and 18B), Icl9 (sections 19A 19B), Ic20, Ic21, T28, T29, T30 along with T14 and T15.

Down Shifts The sequence of events for the down shift will be given for 3rd to 2nd and 2nd to Ist as those for 5th to 4th and 4th to 3rd are identical to that of 3rd to 2nd.

Down Shift 3rd to 2nd Assuming 3rd gear to be engaged and the shaft speed to become reduced sufficiently for the inverting input voltage to fall below the non-inverting input voltage of Ic5, then its output would retum to '1' and cause T18 to switch off. As T18 is now off then its collector voltage has returned to '0' causing (6A) (6B) (7A) and (7B) to return to their original conditions prior to engagement (see 2nd to 3rd upshift) thereby causing 3rd gear to disengage. As T18 collector is now '0' then D24 is no longer conducting and 2nd gear could re-engage. However, as T18 collector goes to '0' Ic 10 is triggered to '1' at its output via capacitor C76 (for a period determined by the setting of VR12) and forward biases D23 maintaining '1' '0' on the inputs of (3D). On completion of the period referred to IclO returns its output to '0' and D23 becomes reversed biased allowing '0' '0' to appear at the inputs of (3D) causing its output to go to '1' and switch on T12 and T13. This re-energises the external 2nd gear valve which in turn reengages 2nd gear.

Down Shift 2nd to Ist If the shaft speed is reduced further, the inverting input of Ic2 will become less than the reference voltage of the non-inverting input and cause its output to return to '1', causing T8 to switch off and return its collector voltage to '0'. '0' is now appearing on T8 collector. Consequently, (3A) (3B) (3C) (3D) (4A) (4B) and (4C) return to their original states prior to 2nd gear engagement (see 1st to 2nd upshift). Ic5 is however triggered to '1' at its output by C14 causing (3B) inputs to go '1' '0' for the duration of the period during which IcS is at '1'. Upon completion of this period IcS output returns to '0'. (3B) now has '0' '0 at its input giving '1' at its output causing TlO and Tll to switch on. This re-energises the external valve unit and engages Ist gear.

The sections involved in 5th to 4th down shift are Ic22 and D34.

The sections involved for 4th to 3rd downshift are Ic16 and D30.

Hysteresis In order to provide an adjustable margin between the upshift and downshift, hysteresis is provided once an upshift has occurred and is automatically removed on the completion of a downshift. Since the method employed is identical for each gear then a description of its operation will be given for the 3rd gear shift by way of example: The components relevant to the function for 3rd gear hysteresis are Ic5, T18, T17, VR20 along with their respective capacitors and resistors. Assuming the shaft speed to be lower than that appropriate for 3rd gear engagement, then the non-inverting input will be lower that the inverting input of Ic5 and its output will be '1' causing T18 to be off. As the base of T17 is connected to the collector of T18, and T18 is off, its collector will be '0' and will cause T17 to be reversed biased. As T17 is off then VR20 and R48 can have no effect upon VR16, R40 and R41.

The potential set by VR16 at the junction of R40 and R41 will therefore remain unaltered.

Should the shaft speed now increase and cause the inverting input of Ic5 to exceed the non-inverting input its output will go to '0' annd cause T18 and T17 to switch on. As T17 is now conducting VR16 and R41 are in parallel with VR20 and R48. The voltage appearing at the non-inverting input will now be modified and be dependent upon the setting of VR20 and R48. This action is to cause the voltage at the junction of R40 and R41 to be reduced. In consequence the voltage at the inverting input must also become proportionately lower before Ic5 may resume its original state and switch off T17 via Ic5 and T18. It will be understood that the downshift point may vary from the upshift point between the limits set by R41 and VR20 and also that T17 can only be effective after the shaft speed is sufficient to cause a higher gear to engage.

The relevant components for 2nd gear hysteresis are Ic2, T8, T9, VR19 and R21.

The relevant components for 4th gear hysteresis are Icll, T23, T22, VR21 and R66.

The relevant components for 5th gear hysteresis are Ic17, T28, T27, VR22 and R86.

Modulation of Change Point In order that a dual shift pattern may be obtained, means are provided to modulate the shift point according to closure of an externally mounted switch, which may be mechanically or otherwise closed. These means also provide a delayed return to the normal shift pattern on re-opening of the external switch. To obtain this function on upward shifts a master driver/timer is employed to operate T16, T21, T26 which in turn modify the potential on the noninverting input of Ic5, Icll and Ic17. Since the action is identical for 2nd, 3rd and 4th gears, only 3rd gear will be described: The master driver/timer consists of Ic33, T7, Z4, C63, R133, R134, R135, R136 and R137, along with its actuator SW4. With switch SW4 open then C63 will have charged to Vcc via R133 when power is first supplied to the unit and now lays in the correct state for its use. In view of this, the non-inverting input voltage will lie at a point set by R134 and R136 and this is arranged to be lower than Vcc. As C63 has charged to Vcc via R133 then the inverting input voltage will be higher than the non-inverting input voltage to Ic33 causing its output to go '0'. The base of T7 is connected to the output of Ic33 via Z4 and reverse biases T7.

The bases of T16, T21 and T26 are all connected to the collector of T7 and therefore their switching action is in phase with that of T7.

Assume now that switch SW4 is closed.

The potential on C63 will fall to '0' via R135 and SW4. The inverting input voltage will now be lower than the non-inverting input voltage and the output of Ic33 will go to '1' causing T7, T16, T21 and T26 to switch on.

As T16 is conducting VR23 and R47 are not in parallel with R40 and, dependent upon the setting of VR23, will cause a modified potential to exist at the junction of R40 and R41. The action is to lift the potential at the junction in order that a greater shaft speed must be reached to cause the inverting input of Ic6 to exceed the non-inverting input and so select 3rd gear. Should switch 4 be opened at any time then C63 will again begin to charge towards Vcc via R133 and when the voltage across C63 exceeds the voltage across R136 the output of Ic33 will again go '0' and switch off T7, T16, T21 and T26 causing the normal potential to be resumed at non-inverting input of Ic5.

Consequently, a period of time will lapse before C63 has charged sufficiently to cause Ic33 to return to its normal state and this provides a delayed return to normal range.

Gear Hold In order to limit the range of upshifts the control means are provided with upshift limit circuits and these are only effective if the shaft speed is below that appropriate for the selected range, Furthermore the limit circuits have no effect on the downshift pattern. The circuits are activated by the closure of an external hand operated switch SWI .

The following description assumes the vehicle to be in 2nd gear with a shaft speed less than that appropriate for selection of 3rd gear and assumes also the switch SW1 is in the Automatic position. With the switch in this position then the output transistors will be supplied with a potential nearly equal to the battery potential and the 2nd gear output will be on (see selection for Forward Drive). Should switch SW1 now be moved to position 2, D51 will conduct and maintain the potential at the output transistors. However, a feed path now exists to one input of Ic6 (section 6c), via D46 and it is this section which limits the gear changes to 2nd gear, should all other conditions be correct. With 2nd gear engaged the output of (3D) will be '1' and this is fed to the anodes of D25, D27, D28 and one input of (6C), the other input of (6C) is also at '1' via D46 and SW1 its output therefore is '0'. Connected to the output of (6C) is the cathode of D61 its anode being connected to the inverting input of Ic5. As the output of (6C) is now '0' D61 will become forward biased and cause the whole of the signal voltage to be dropped across R43. Consequently, the inverting input of Ic5 will remain at a lower potential than that on non-inverting input and maintain Ic5 output at '1' which will prevent selection of 3rd gear. Since diodes D27, D28, D29, D25 and D32 are also forward biased, (12C) and (18C) have their inputs at '1' '1' giving '0' at their outputs. The signal voltages at the inverting of Icl 1 and Ic17 will thus also be dropped across R67 and R84 causing their outputs to remain at '1' and prevent selection of 4th and 5th gears should the shaft speed increase to a figure appropriate for their engagement. Should switch SW1 now be moved from position 2 to position 3 a momentary loss of supply will occur and on restoration of the supply D50 will become forward biased restoring the supply to the output transistors. D47 will now become forward biased and provide '1' to one input of (12C). As D46 is no longer conducting the input condition of (6C) is '1' '0' and its output goes to '1' causing D61 to become reverse biased. As D61 is no longer conducting the voltage is restored to the inverting input of Ic5 and should it exceed the non-inverting input, selection of 3rd gear will take place.

Assuming 3rd gear has now selected, then D25, D27 and D28 will become reverse biased and (6C) will have at its input '0' '0' maintaining '1' at its output. As 3rd gear is now engaged then D26, D32 and D29 will become forward biased and (12C) inputs will be '1' '1' the collector of T37 is the base of T38 the collector of which is connected to the base of T39 and its collector is connected to the base of T40. T40 acts as series element to supply the anode of Thyristor TH I. When the control output condition is correct then all sections of Ic's 23, 24, 25 will see either '0' '1' or '0' '0' at their inputs and their outputs will be '1'. T37 will therefore be reverse biased as will T38 and T39. T40 will however be forward biased and cause the anode of TH1 to be positive.

Assume that TH1 has received a gate pulse and is now conducting, (see selection of Drive). If any two output transistors conduct simultaneously then a section of the detector stage (ic's 23, 24, 25) will see '1' '1' and its output will go '0'. T37 will now become forward biased as will T38 and T39.

T40 will however become reverse biased and switch off. This will cause the anode potential of THI to be lost and will therefore switch off all outputs. The Ic sections will now see '0' '0' and resume the safe state for T40, i.e. T40 in conduction.

THl can however no longer conduct as it has not received a further gate signal and the control remains with all outputs de energised and in consequence the control remains in neutral gear.

Selection of Forward Drive In order to obtain forward drive the air tank pressure must be sufficient to close the external air pressure switch and the gear lever must be placed in a neutral position.

Should the conditions described prevail, then on closure of the start switch the control circuitry will by supplied via Ic34 and will drive the base of either T10 or T12 dependent upon the selected lowest ratio.

Switch 1 will also have its moveable contact supplied and the anode of TH2 will also be supplied. Should the external air pressure switch be closed then the gate of TH2 will be positive with respetlto the cathode of TH2 and will conduct. Conduction of TH2 will cause a voltage to appear across R172 and will allow Ic29 to function on the application of a trigger pulse via 68. If switch 1 is now moved to positions 1, 2, 3 or 4 then either diodes D49, D50, D51, or D52 will conduct and cause the anode of TH1 to become positive via T40 which already has its base current initially provided by T37 and being amplified via T38 and T39, the amplification only occuring on the conductance of D49-52. Th2 will at the same instant receive a gate pulse from Ic39 and will then conduct, thereby feeding the emitters ofTll, T13, T15, T20, T25 and T30 and the collectors of their respective interface drivers.

In order that THl may receive its gate pulse on the conductance of D49-52, T42 also receives base current and its collector goes negative, causing a negative going pulse to Ic29 via C68. The negative going pulse drives the output of Ic29 positive for a delay period (determined by R169 and C70) thereby supplying the gate of TH1 via R137 and D54. The base of T14 is also connected to the output of Ic29 and in consequence will switch on causing T15 to switch on and energise an external valve which in turn will cause the engine throttle to be placed in a slow running position. On completion of the delay period, Ic29 remains with its output high, T14 will switch off, switching T15 off and de-energising the external valve leaving the throttle to return to any position at which it may be set.

However, should TH2 not have been conducting because of the external air pressure switch failing to close, then Ic29 would have remained dormant upon its trigger pulse and the emitters of the output transistors would remain unsupplied.

Selection of Reverse Drive Reverse drive is accomplished by TH4 along with Ic29, Ic28, T36 and T31. In order to select reverse there must be no propshaft movement, the air tank pressure must close the external pressure switch and the gear lever must be in a neutral position.

Assuming that these conditions prevail, then should switch 1 be moved to position R, TH4 will receive its anode potential, T14 will conduct as its base is connected to TH4 anode via D53 and R165 and trigger Ic29.

The output of Ic29 will go high and cause a gate pulse to TH4 causing it to conduct and energise an external valve, which in turn will cause reverse gear to select.

Prevention of Reverse Drive Should reverse have been selected whilst there was propshaft movement, then it would have been prevented from reverse gear engaging for the following reasons: Ic32 (section 32A 32B) are connected as a monostable. The input signal to the monostable is connected to the collector of T1.

As the fucntion of T1 is to cause its collector to rise to Vcc or fall to Zero volts, then the monostable Ic32 will be triggered from its dormant output state '0' to '1' (for the period determined by C61 and R139) when the collector voltage of Tl falls from Vcc to Zero volts. Therefore, whenever there is propshaft movement a train of pulses will be received by the base of T3 1 and T33.

In order to ground the gate signal of TH4 whilst there is propshaft movement the following circuitry is used:- Ic32 (sections 32A and 32B) Ic28, T31, Zil, R140, R141, R142, R143, R156 and C64.

Should there be no shaft movement when the unit is switched on C64 will rapidly charge to Vcc and a lesser potential will exist at the junction of R142 and R143 and the output of Ic28 will be '0'. Connected to the output of Ic28 is the base of T36 and whilst '0' exists at the output of Ic28, T36 will be off and will not effect the gate signal of TH4. If there is no shaft movement, then the pulse train emitted by Ic32 will cause T3 1 to switch on in phase with the pulse train and discharge C64. The peak voltage now appearing at the junction of C64 and R141 will be less than that at the junction of R142 and R143 causing the output of IC28 to go to '1' and switch on T36 which effectively grounds the junction of R157 and D64 and prevents the gate signal of TH4 rising much above zero volts thereby preventing TH4 from conducting and engaging reverse gear.

Prevention of Forward Drive Should reverse gear have been engaged and selection of a forward gear now be required, propshaft movement must cease and the gear lever moved to a neutral position whilst the shaft is stationary.

Forward drive may then be selected by positioning SW1 in the appropriate position.

The circuitry involved in this function is Ic32 (sections 32A, 32B), Ic26 (sections 26A, 26B, 26C, 26D) Ic27, T32, T33, T34, T42, Z12, C65, R148, R149, R150, R151, R152, R153, R174. Ic27 is arranged to have its output controlled by T33 (which is responsive to propshaft movement) or by T32. Whilst both T32 and T33 are off the output of Ic27 will be '1' and reverse bias T34, causing its collector voltage to be '0' and reverse bias T42.

Ic26 is arranged to have its output state (section 26B) dependent upon the output state of Ic27 and the input state of SW1, which in turn controls the output state of Ic27. Assuming reverse gear to be engaged and propshaft movement occuring then the input to 26C will be '1' and its output will be '0', this being fed to one input of 26A giving ' I ' at its output. The output of 26D will be '1' by virtue of its input logic causing the output of 26B to become '0'. As the base of T32 is responsive to the output of 26B then T32 will be reverse biased and the transistor controlling the output state of Ic27 is T33. As T33 is responsive to propshaft movement, it will switch on and off according to the frequency of the input signal from the propshaft. This will then discharge C65 and maintain its peak voltage at a lower potential than that at the junction of R151 and R152. The lower potential on C65 causes the output of 1C27 to go to '0' and switch on T34 which in turn switches on T42 and effectively grounds the gate terminal of THI. As the gate of THI is now grounded then any gate signal it may receive will also be grounded and prevent THI from conducting thereby preventing selection of forward drive.

Should propshaft movement now cease, T33 will no longer function and the potential on C65 will rise to Vcc and change the output state of Ic27 to '1' which in turn switches off T34 and T42. As it is necessary for forward drive to be constantly available once established the following provides for this: Assume there to be no shaft movement and the gear switch SWI to be in a neutral position. Should SWI now be moved to a forward drive position then the inputs of 26c will remain at '0' (the condition prevailing once SW1 is moved from the reverse position). One input of 26D will be at '1' from the output of Ic27 and awaits its other input to go to '1' by THl conducting. Should TH1 conduct (for the reasons given in selection of forward drive), then 26D will see '1' '1' at its input and its output will go '0'. The output of 26C will be '1' as it now has '0' '0' on its inputs, the combination of all three inputs causing 26B to change state to '1' at its output. The base of T32 is connected to the output of 26B and will switch on thereby grounding the base of T33. As TH1 must conduct to accomplish the logic, it is evident that the lowest selected ratio must be engaged. If the propshaft movement now occurs then again the base of T33 will receive a positive pulse train but these will be grounded by the action of T32 and have no effect upon T33.

This in turn will maintain the output of Ic27 at '1' and reverse bias T34 which in turn will hold off T42 and allow TH I to remain responsive to gate signals.

It can be seen therefore that, had shaft movement not ceased prior to selection of forward drive, the bistable could not have changed state as the output of Ic27 would remain at '0' due to the action of T33. This would prevent TH 1 from receiving a gate pulse as its gate would be grounded by T42 and therefore could not conduct.

Since one input of (26D) goes to the cathode of THI, unless a gate signal causes it to conduct (which is prevented by Ic27 output being '0' whilst there is shaft movement), then shaft movement must cease prior to the selection of forward drive.

Furthermore, should forward drive have been selected whilst there was shaft movement and then shaft movement ceases, the gear switch SWI will need to be placed in a neutral position and again placed in a forward drive position to enable another gate pulse to TH1 in order that it may conduct.

Signal Monitor The control means are provided with an incoming signal from a transducer or probe which is mounted externally and in a position that will detect the rotational speed of the gearbox output. It is necessary to constantly monitor the incoming signal and compare it with a known safe standard.

Should the comparison not be correct the control means must be set in a safe condition.

The only condition for the signal to be lost or not appear is when the lowest ratio is engaged and this is used as the safe standard. Should the signal be lost at higher shaft speeds than that set for the shift from 1st gear to 2nd then the control will automatically select a safe ratio. The input signal is monitored from the output of Ic32 therefore failure of (Ic32) (tl) (Ic30) and the transducer or probe will all be classed as the input signal. The description to follow is valid when the input signal is correct: Assume the vehicle to be stationary and the selected lowest forward ratio to be engaged, the components involved in the signal monitor are: (Ic2), (Ic31), T45, T6, TH5, D9, D10, Dll, D12, Z13, Z5, C62, R120, R121, R123, R124, R125, R126, R127, R129, R130, R131, R132.

As there is no shaft movement the (Ic2) will have its output at '1' which is connected to the base of T45. The output from (Ic32) will be '0'. As '1' is appearing at the base of T45 it will conduct and ground C62 causing (Ic31) to have its output at '1' and reverse biasing T6. The gate of TH5 will therefore remain negative and maintain TH5 cut off.

If the shaft movement should now occur, a train of positive pulses will also be received by T45 but can have no effect as T45 is already in conduction via (Ic2). As the shaft speed increases the output of Ic2 will go '0' and remove the forward bias it supplied to T45. Ic32 will however maintain to emit a positive pulse train to the bias of T45 and it will now switch according to the frequency of the input signal and maintain the peak voltage at the junction of C62 and R123 below that of the junction of R120 and R121, maintaining Ic31 output at '1'. As the output of Ic31 is maintained at '1' then T6 will remain reverse biased, preventing a gate signal to TH5. If the pulse train ceases due to the failure of the probe, T45 will no longer periodically conduct and C62 will begin to charge through R123.

When the potential at the junction of C62 and R123 exceeds that at the junction of R120 and R121 the output of Ic31 will go '0' and switch on T6 causing its collector to become '1' and apply gate current to TH5 which then conducts. In the cathode circuit of TH5 there comprises a divider network R127 and Z5. This network is necessary to reduce the anode voltage to the working voltage of the control means. The other output of TH5 is at the anode voltage and is fed to an external warning light bulb to indicate a malfunction. The regulated output from TH5 is directed by D9 and D10 to the inverting inputs of IC's 2, 5, 11 and 17. The voltage now on the inverting inputs is the maximum that may be developed by the frequency to voltage convertor should it still have its input signal present. Since the voltage now being applied to the voltage controller switches Ic's 2, 5, 11 and 17 is a maximum, then the highest ratio will select giving a safe condition for the final outputs of the control means.

In order to reset the control the main supply switch to the control must be opened and so remove the anode voltage from TH5, whereupon the external warning lamp will also extinguish If the propshaft movement now recommences, the control means will be limited to the lowest selected ratio as no evidence that there is propshaft movement exists.

Means to ignore Air Tank Pressure It was stated in the description 'selection of forward drive' that Ic29 must function to enable selection of drive.

It has also been stated that an external air pressure switch must close in order to supply gate current to TH2 and enable Ic29 to function. In order that the air tank pressure may be ignored after first establishing its adequacy (which may fail for many reasons) then the function of TH2 is twofold. Once TH2 has come into conduction its gate signal is no longer required as the device will maintain conduction, therefore should tank pressure now fall below the level required to maintain the external switch in a closed position, it can have no effect upon the operation of Ic29. However, if the supply to the control means is switched off, then TH2 will revert to it non-conducting state and air pressure will again have to be established prior to Ic29 being enabled.

Means to reduce Engine Speed Since it is necesary to reduce the engine speed on an upshift to synchronise with the higher ratio being engaged, and also since it is desirable to ensure the engine speed is a minimum when either forward or reverse drive is selected the control means provides for this, the sections of the control means involved being Ic29, Ic7, Ic9, Ic15 and Ic21.

These Ic's all drive a common output driver T14, the collector of which goes to the base of T15. T15 is in phase with the switching action to T14 and is the driving element of an external solenoid. Should any of the Ic's 7, 9, 15, 21, or 29 function as described elsewhere then T14 and T15 will switch on and energise the external solenoid.

The solenoid may simply pull the rack back on the fuel pump and act as a fuel cut or a more complex arrangement may be employed whereby the throttle linkage is returned to its slow running position. Since each of the IC's 7, 9, 15, 21 or 29 have a means to determine the length of time they switch on T14 and T15, it is possible to afford accurate synchronisation of the engine speed with the relative gear ratio.

Prevention of Door Opening with Propshaft Movement If the control means are intended for a public service vehicle, the arrangement is such that door operation can only be accomplished with the propshaft stationary.

The following provides for this and the components involved are, Ic28, TH3, R154 and R155. (As a description of the action of Ic28 has already been given in 'reverse gear selection', it will be evident that whatever action Ic28 has on T36 it must afford the same action to T35 as both bases are connected to the output of Ic28).

Assuming that there is no propshaft movement and SWI is moved to the door position, TH3 will receive its anode potential and since the gate is connected via R154 to the anode, it will cause the gate to bring TH3 into conduction. T35 will be reverse biased and therefore has no effect at this stage. The output of TH3 is used to operate an external relay or solenoid which, in turn, operates the door control.

However, had there been shaft movement then T35 would already be conducting and would ground the gate terminal of TH3.

Therefore when the anode received its potential via SWI, the gate would remain grounded and prevent operation of TH3 thereby preventing operation of the door gear.

Thus there is provided an electrical control means for change-speed gearing which is particularly suitable for use in a passenger service vehicle since it has the important safety features referred to above and since passenger service operation is particularly arduous. A particularly useful feature has been found to be that if the control means should fail the highest available forward ratio is selected so that the engine and transmission are safeguarded from serious damage (which would inevitably result if the transmission should suddenly change down to a low gear ratio whilst the vehicle was travelling at high speed and this would also constitute a road safety hazard). It will also be understood that the control means can be applied to any design of change-speed providing the requisite number of available ratios and capable of having the available gear ratios established by electrical signals.

WHAT WE CLAIM IS: 1. An improvement in or modification of the invention claimed in our prior patent No 1,492,523, that is to say an electrical control means for vehicle change-speed gearing the control means including individual drive selection means for the various forward gear ratios available, electrical signal amplifiers associated with the respective drive selection means for rendering said drive selection means operative or inoperative selectively, vehicle speed responsive means for bringing the electrical signal amplifiers into operation selectively according to vehicle speed, first switch means operable in response to vehicle throttle opening and closing movements whereby, during normal operation at a small throttle opening (as when the vehicle is descending a hill and the throttle pedal is released) a change to the next upward gear ratio is prevented but down changes are permitted, still under the control of the vehicle speed responsive means, and further switch means which are manually operable to effect the same function as said first switch means whereby, at will, the driver of the vehicle can operate said further switch means to effect a "gear hold" condition in which a change to the next upward gear ratio is prevented regardless of throttle opening and closing movement, the improvement or modification residing in the fact that means are also provided to prevent the selection of forward gears whilst the vehicle is moving rearwardly and to prevent the selection of reverse gear whilst the vehicle is moving forwards.

2. An electrical control means according to claim 1, in which when a fault condition arises in the control means, the highest available gear ratio is established for engine overspeed prptection.

3. An electrical control means according to either one of the preceding claims, in which electrically operated means are provided whereby the torque transmitted through the change-speed gearing can be reduced during immediately following a change of gear ratio.

4. An electrical control means according to claim 3, in which the electrically operated means are adjustable whereby the period during which the torque is reduced can be varied from the briefest instant to several seconds.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. These Ic's all drive a common output driver T14, the collector of which goes to the base of T15. T15 is in phase with the switching action to T14 and is the driving element of an external solenoid. Should any of the Ic's 7, 9, 15, 21, or 29 function as described elsewhere then T14 and T15 will switch on and energise the external solenoid. The solenoid may simply pull the rack back on the fuel pump and act as a fuel cut or a more complex arrangement may be employed whereby the throttle linkage is returned to its slow running position. Since each of the IC's 7, 9, 15, 21 or 29 have a means to determine the length of time they switch on T14 and T15, it is possible to afford accurate synchronisation of the engine speed with the relative gear ratio. Prevention of Door Opening with Propshaft Movement If the control means are intended for a public service vehicle, the arrangement is such that door operation can only be accomplished with the propshaft stationary. The following provides for this and the components involved are, Ic28, TH3, R154 and R155. (As a description of the action of Ic28 has already been given in 'reverse gear selection', it will be evident that whatever action Ic28 has on T36 it must afford the same action to T35 as both bases are connected to the output of Ic28). Assuming that there is no propshaft movement and SWI is moved to the door position, TH3 will receive its anode potential and since the gate is connected via R154 to the anode, it will cause the gate to bring TH3 into conduction. T35 will be reverse biased and therefore has no effect at this stage. The output of TH3 is used to operate an external relay or solenoid which, in turn, operates the door control. However, had there been shaft movement then T35 would already be conducting and would ground the gate terminal of TH3. Therefore when the anode received its potential via SWI, the gate would remain grounded and prevent operation of TH3 thereby preventing operation of the door gear. Thus there is provided an electrical control means for change-speed gearing which is particularly suitable for use in a passenger service vehicle since it has the important safety features referred to above and since passenger service operation is particularly arduous. A particularly useful feature has been found to be that if the control means should fail the highest available forward ratio is selected so that the engine and transmission are safeguarded from serious damage (which would inevitably result if the transmission should suddenly change down to a low gear ratio whilst the vehicle was travelling at high speed and this would also constitute a road safety hazard). It will also be understood that the control means can be applied to any design of change-speed providing the requisite number of available ratios and capable of having the available gear ratios established by electrical signals. WHAT WE CLAIM IS:

1. An improvement in or modification of the invention claimed in our prior patent No 1,492,523, that is to say an electrical control means for vehicle change-speed gearing the control means including individual drive selection means for the various forward gear ratios available, electrical signal amplifiers associated with the respective drive selection means for rendering said drive selection means operative or inoperative selectively, vehicle speed responsive means for bringing the electrical signal amplifiers into operation selectively according to vehicle speed, first switch means operable in response to vehicle throttle opening and closing movements whereby, during normal operation at a small throttle opening (as when the vehicle is descending a hill and the throttle pedal is released) a change to the next upward gear ratio is prevented but down changes are permitted, still under the control of the vehicle speed responsive means, and further switch means which are manually operable to effect the same function as said first switch means whereby, at will, the driver of the vehicle can operate said further switch means to effect a "gear hold" condition in which a change to the next upward gear ratio is prevented regardless of throttle opening and closing movement, the improvement or modification residing in the fact that means are also provided to prevent the selection of forward gears whilst the vehicle is moving rearwardly and to prevent the selection of reverse gear whilst the vehicle is moving forwards.

5. An electrical control means according

to either one of claims 3 and 4, in which the electrically operated means for reducing the torque transmitted through the gearbox during and immediately following a change of gear ratio operates to cut the fuel to the engine.

6. An electrical control means according to any one of the preceding claims, including means for preventing the engagement of two gears simultaneously.

7. An electrical control means according to any one of the preceding claims, in which means are provided whereby a neutral pause is brought about when downward changes or upward changes of gear ratio are being made.

8. An electrical control means according to any one of the preceding claims, in which means are provided whereby the operation of the control means is modulated according to throttle opening so that as the vehicle is accelerating at full throttle the lower gear ratios are maintained for a longer period before upward changes are made and so that the lower gear ratios are re-engaged sooner.

9. An electrical control means according to claim 8, in which the means for modulating the operation of the control means according to throttle opening include an electrical switch for location beneath the throttle pedal of the vehicle in which the change-speed gearing is installed.

10. An electrical control means for change-speed gearing, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.