GEARBOX

Abstract: The gearbox has a number of selectable gears which can be coupled one at a time to its input shaft (1). The selected gear is in mesh with a gear on an intermediate shaft (2) which has a further gear in mesh with one of a number of selectable gears which can be coupled one at a time to its output shaft (3). The total number of gears is the product of the gears available on the input and output shafts. The three shaft layout achieves a compact gearbox with a minimum component content. Minimum forces are required to disengage or engage gears as the synchronization of the relevant gears is achieved with a small dedicated electric motor (25). Complete automation of the gearbox is achieved by controlling the engine clutch, gear selector rods and the synchronizing motor with a gearbox control unit.

Description: GEAR BO X FIELD OF THE INVENTION This invention relates to gearboxes for automotive and general vehicle transport applications. BACKGROUND OF THE INVENTION In many conventional gearboxes, synchronization of gears to be engaged utilizes the frictional engagement of synchronizing cones which requires significant forces on the actuator mechanisms resulting in wear of the engaging friction elements, the generation of heat and often relatively slow gear changing operations. British Patent Specification No. 1,369,983 describes an automatic change-speed gear control system for a vehicle gearbox which is adapted to effect speed synchronization prior to- a gear changing operation. The speeds of the gearbox input and output shafts are monitored by an electronic control unit. When a gear change is demanded by the driver, a signal representative of the required gear ratio to be selected is transmitted to the control unit which then determines whether the gearbox input shaft needs to be accelerated or decelerated in order to effect synchronism before the gear dogs are engaged to select the newly required gear ratio. If the input shaft needs to be accelerated, the clutch is engaged to allow the input shaft to be accelerated by controlling the throttle of the engine of the vehicle. Other means may be used to produce this acceleration of the input shaft. On the other hand, if the output shaft needs to be decelerated, the clutch is disengaged and a shaft brake acting directly on the gearbox input shaft is brought into operati on . A primary object of the invention is to provide an improved synchronizing system for computer controlled automatic gear-changing operations. Another object of the invention is to provide 5 a gearbox having a large choice of ratios available with the selection of the correct gear ratio being made by a computer control . A further object of the invention is to provide a compact multi-speed automatic gearbox having a - o reduced axial length. SUMMARY OF THE INVENTION According to the invention, there is provided a gearbox having a torque receiving input, a torque transmitting output, and including a plurality of 15 gear carrying shafts for transmitting torque through the gearbox, means to effect isolation of one of said shafts from loads applied, in use, to said input and said output, means to accelerate said one shaft and means to decelerate said one shaft,' o as required, in order to effect synchronization preparatory to a gear selection operation, and means for controlling said isolation means, said accelerating means and said decelerating means to effect a synchronized gear-changing operation, characterized 5 in that said acceleration means and said deceleration means are constituted by an electric synchronizing motor adapted to operate directly on said one shaft to accelerate or decelerate said shaft when the shaft is isolated from loads applied to said input 0 and said output, for synchronization during a gear- changing operation, and in that an electronic computer control system is provided to control the sequential operation of said isolation means, gear selector means and said synchronizing motor including 5 acceleration or deceleration of the motor, to change the overall gear ratio to a newly required gear ratio in response to a command signal of the required new overall gear ratio. Such • an arrangement permits the use of simple engagement hubs to allow mesh engagement between a selected gear and the shaft upon which that gear rotates. The force required to move these engagement hubs is small , and the time required to move them is relatively short. Moreover, automization of the gear changing operations is achieved by controlling the synchronizing motor, and the actuation of the engagement hubs by means of a gearbox control unit, which controls said isolating means, e.g. a clutch or decoupling device, as part of an overall gear selection operation. A gearbox is a device which allows the selection of a coupling between a demanded load and the available power from an engine, utilizing a change in speed to match the demanded speed or torque of the load with the engine. In order to obtain good fuel efficiency, the gearbox ratio selected to couple the available power to the load should desirably 'be such that the engine supplying the power is able to operate at or ' close to its optimum point of minimum specific fuel consumption. Automotive vehicles with very good aerodynamic characteristics require relatively small power levels to maintain high cruising speeds; this power is capable of being provided by an engine running at relatively low speed and hence, to achieve the speed matching of the vehicle to the engine, a high output ratio is required in the gearbox. The total range of a gearbox from its lowest ratio to its highest ratio will be greater than found in conventional gearboxes of today. Preferred features of the invention provide a gearbox having a large choice of ratios available wherein the choice of the correct gear ratio is made by a computer control . A multi-speed automatic gearbox embodying this invention may have a number of forward gears ratios, this being dependent upon the number of gears chosen to be placed on the input and output shafts. The total range o.f the gearbox from the lowest ratio to the highest ratio depends upon the size of the gears specified, as do the steps between the ratios available. The overall size of the gearbox may be kept small , and the number of gear components reduced by placing all the forward gears on three parallel axes shafts. The automatic selection of gears may be accomplished by moving the gear selector rods with actuators, and the overall size of the actuators and gear selection mechanisms may be kept small by utilizing a speed synchronizing motor independent of the vehicle engine. BRIEF DESCRIPTION OF THE DRAWINGS A specific embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic representation in cross-section of a gearbox embodying the invention and adapted to achieve twelve forward speeds; Figure 2 is an end view in cross-section of a gearbox in accordance with the general layout represented in Figure 1 but illustrating the spatial location of the three gearbox shafts and the selector rods; Figure 3 is a side view of the gearbox utilizing the spatial shaft arrangement shown in Figure 2; Figure 4 is a diagrammatic representation of a control system for 'the gearbox of Figures 1 to 3 ; and , Figure 5 is a flow diagram giving the sequence of operation of the control system of Figure 4. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT Referring to the drawings, Figure 1 shows the schematic layout of all the major components with the exception of the reverse idler gear and its associated shaft. The input shaft (1) has four gears (16), (17), (18) and (19) located concentrically upon it and each able to freely rotate about the shaft. Two sliding hubs (8) and (10) are located upon splines on the shaft (1) and are able to slide into meshing engagement with the four gears (16), (17), (18) and (19). The sliding hubs are moved by actuator forks (9) and (11) which are fixed to control rods (4) and (5) respectively. The four gears (16), (17), (18) and (19) are continuously in mesh with four of the seven gears that are integrally formed with the intermediate or layshaft (2) of the gearbox. Three of the intermediate shaft gears are continuously in mesh with three gears (20), (21) and (22) which are located concentrically upon and each able to ' freely rotate about the output shaft (3). Two sliding hubs (12) and (14) are located upon splines on the shaft (3) and are able to slide into meshing engagement with the four gears (20), (21 ), (22) and (23). The sliding hubs are moved by actuator forks (13) and (15) which are fixed to control rods (6) and (7) respectively. Gear (23) is in constant mesh with a reverse idler gear [(24) in Figure 3] which in turn is in constant mesh with its associated gear on the intermediate shaft (2). With the three shaft arrangement of the illustrated embodiment, one of the intermediate shaft gears is in constant mesh with gears situated upon both the input shaft (1) and the output shaft (3) which ' allows a more compact arrangement to be achieved by reducing the overall axial length of the gearbox and also allowing the use of four actuator hubs of similar axial length to be used. This arrangement also obviates the need for intermediate shaft bearings thereby further reducing the overall length of the gearbox. The particular gear chosen depends upon the gear ratios available for the required gearbox, and is influenced by the centre distances between shafts (1) and (2) ' and shafts (2) and (3) that are acceptable and the gear ratios and diametral pitch which the chosen gears dictate. It can be seen that the output shaft (3) turns in the same direction as the input shaft (1) in the forward gear mode, and can be coupled to the rest of the drive train in either direction. It, therefore, is able to be used as a straight through gearbox principle or as a transaxle gearbox principle. The synchronizing motor (25) (Figure 3) can be fixed to any of the three shafts (1), (2) or (3), but its location depends upon the siting of a clutch or decoupling component which can isolate the shaft it is fixed to from any drive input. For example, when the clutch is associated with the input shaft (1 ) the synchronizing motor (25) is associated with that shaft. - Similarly if the clutch is associated with the output shaft (3) the motor (25) is associated with that shaft. The synchronizing motor could be associate-d with the intermediate shaft (2). In such an arrangement, clutches could be provided on both input and output shaft (1,3) or if only one clutch is used it would be necessary to de-couple one set of gears as well as releasing that clutch in order to isolate the intermediate shaft for synchronization, those gears being re-engaged after synchronization. Figure 2 shows the spatial layout of the three main shafts (1), (2) and (3) and the control rods (4), (5), (6) and (7) which select the appropriate gear to be coupled to the input and output shafts. Each control rod is operated by an electrically operated three position actuator (28). Inhibition of gear selection can be achieved through software control in the gearbox operating computer. Figure 3 shows a side view of a practical layout of the gearbox. In this figure, the reverse idler gear (24) is situated at the rear of the gearbox. The highest and lowest ratio gear sets associated with the input shaft (1 ) are grouped together at the front of the gearbox to be operated upon by the sliding hub and its associated actuator fork (9). In this way, sufficient space is now available to accomodate a second fixing point for the shaft of the reverse idler gear (24). It is anticipated that a conventional clutch position is used to disengage the vehicle engine from the gearbox input shaft (1 ). The output shaft (3) is in constant engagement with the wheels of the vehicle. The optimum position for the synchronizing motor (25) is with its rotor permanently attached to the input shaft (1 ). The synchronizing motor is an electric motor of _ a relatively small size, is easily controlled and requires no additional equipment to enable it to function. The * rotor of the motor (25) is permanently coupled to the input shaft (1 ) and in order to effect a synchronizing operation, an electric contact is made with the armature of the motor in order to speed up or slow down the motor shaft, and hence the input shaft ( 1 ) , as requi red . The example of the gearbox shown in Figure 3 has four gear ratios created between the input shaft (1 ) and the intermediate shaft (2), and these ratios are:- 19 47 42 21 27 39 33 28 These gear ratios are created between the intermediate shaft (2) and ' the output shaft (3), and these rat i o s are 26 37 28 28 31 37 By selecting one of the first set of gear ratios and combining it with one of the second set of gear ratios, twelve independent ratios can be achieved. The forward speed gears, the overall ratios and the percentage change from the preceding gear ratio can be tabulated as follows:- gear overall ratio change in ratio 1st 3.5199 2nd 2.9525 19.22% 3rd 2.4734 19.37% 4th 2.0555 20.33% 5th -I .7241 19.22%- 6th 1.4445 19.36% 7th 1.2074 19.64% 8th 1.0127 19.23% 9th 0.8485 19.35% 10th 0.7115 19.26% 11th 0.5968 19.22% 12th 0.5000 19.36% The ratio span of this gearbox is 7 to 1 and the change in gear ratios has a geometrical progression. The variation in diametral pitch between the largest and smallest gear sets is 17.6%. With a twelve ratio gearbox, any ratio span is possible, and the change in gear ratios does not have to be of a geometrical progression. More or fewer gear ratios can be created by adding or reducing the number of selectable gears respectively on the input and output shafts. The use of two sliding hub assemblies per shaft as shown in the example requires no intermediate bearing support of either shaft. Consequently, the overall length of the gearbox is kept to a minimum and the construction of the gearbox can be kept si p! e . The selection- of the appropriate gear ratio will be made by the gearbox control computer (36) which can be incorporated into the engine management or vehicle management system (34) already in existence on the vehicle. A conventional vehicle management system is responsive to various vehicle operating parameters, such as engine operating conditions and vehicle road speed, which are sensed by respective sensors as well as driver demand requi ements, e.g. throttle pedal position, to control the engine fuel supply and ignition systems to provide optimum engine operating conditions. Once a gearch ' ange has been decided upon, the vehicle engine is decoupled from the input shaft of the gearbox by operating a conventional dry plate clutch or a similar device, e.g. a modified torque converter. If one of the output shaft gear ratios has to be changed, the existing gear coupled to the output shaft is disengaged. The synchronizing motor is switched on such that it accelerates (or decelerates) the input shaft and hence the intermediate shaft to a speed which creates synchronization between the next gear to be selected and the output shaft. If one of the input shaft gear ratios has to be changed, a similar sequence of events takes place except that in this case the synchronizing motor has to achieve synchronization between the input shaft and the next gear to be selected. Once all gear selections have taken place, the vehicle engine can be coupled again to the input shaft of the gearbox. Particular advantages of using a synchronizing motor for gear changing operations, in accordance with the invention, are that no synchronizing mechanism is required between the hubs and the gears and that the force required to move the sliding hub into or out of engagement with a gear is relatively small compared to that required in a conventional gearbox with synchronizing cones since the force that must be overcome is only the sliding friction. The time taken to achieve speed synchronization for the next gear to be selected depends upon the power of the synchronizing motor and the mass moment of inertia of the shafts and gears to be operated upon. The electric motor chosen in the gearbox example is only required to operate intermittently and for a 200 bhp rated gearbox would require an operational electrical rating of 1 KW . The time taken to effect a gear change is calculated to vary between 200 • and 800 milliseconds depending upon the gearbox components to be operated upon. Figure 4 shows a schematic layout of a control system for the gearbox in which the gearbox selector rods are operated by solenoid actuators (28) and an electric motor (25) is used as the gearbox synchronizer. However, in Figure 4 only one gearbox selector rod ' together with its operating solenoid, is shown, whereas the gearbox shown in Figures 1 - 3 has a total of four such selector rods. Figure 5 is a flow diagram giving the sequence of operation of the control system of Figure 4. It is assumed that the vehicle to which the automatic gearbox described is fitted will have a microprocessor computer control system (36) which can calculate the correct gear ratio to be selected on the basis of information fed thereto through an input/output interface (35) from a conventional engine management system (34) provided in the vehicle, this being done in order to obtain the optimum operating conditions necessary for the vehicle speed as requested by the driver. This computer (36) acts through the interface (35) to receive information from a position sensor (29) associated with each selector rod (4,5,6,7); a speed sen'sor (27) associated with the gearbox output drive shaft (3); a speed sensor (26) associated with the synchronization motor (25); and a position sensor (33) associated with a clutch (32) between an engine drive shaft (31 ) and the gearbox input shaft (1). The computer gives command signals through the interface (35) to three position electrically operated actuators (28); the synchronizing motor (25) and the engine management system (34). In operation, when a change of gear is required, the clutch (32) is disengaged in order to remove the drive input (31 ) to the gearbox (30). Clutch movement is monitored, and as soon as disengagement has been achieved, the engine management system (34) causes the fuel supply to the engine to be shut off in order to prevent engine over-revvi ng . - With the gearbox design shown in . Figures 1 ,■ 2 and 3, it is necessary to know whether a gear change is required on the gearbox input shaft (1 ), the gearbox output shaft (3), or both, preference b.eing . given to changes on the output shaft gears in the flow diagram shown in Figure 5. To change gear, an electric signal is sent to operate the actuator (28) associated with the selector rod (4,5,6,7) required to be moved. The position of the selector rod is monitored, and the electric control circuit enables precise and fast positioning of the rod to be achieved. Once gear disengagement is obtained, the synchronizing motor (25) is employed to produce synchronization between the next pair of gears to be selected. The computer programme extrapolates the acceleration or deceleration of the synchronizing motor at each time step in order to predict if a synchronizing speed will be reached within the known operating time of the gearbox selector rod circuits. When synchronization is expected, the synchronizing motor is switched off and the actuator rod associated with the next gear to be selected is activated. Gear engagement is monitored by means of selector rod movement, and when this is accomplished, the gear change routine of one shaft is complete. If a gear change is necessary on another shaft, an identical process to that described above takes place except that the selector rods associated with the other shaft are now activated. When the required gear change or changes have taken place, the engine management system is operated to reconnect the fuel supply to the engine, usually with an initial short period of fuel enrichment, and the clutch is re-engaged automatically. The computer control system (36) may have programmed therein a number of different modes of operation based on respective different prescribed optimum operating conditions, for example for maximum fuel economy or for maximum performance or based on other such criteria. Each mode could be selected by a driver operated manual control or one mode could operate automatically as a default mode with a manual control being provided to allow the driver to select another mode. One such mode could be actuated by a throttle kick-down for example to demand a higher performance operation.

Claims: C LA I MS 1. A gearbox having a torque receiving input (1), a torque transmitting output (3), and including a plurality of gear carrying shafts (1,2,3) for transmitting torque through the gearbox, means 5 (8,10,12,14,32) to effect isolation of one of said shafts from loads applied, in use, to said input and said output, means (25) to accelerate said one shaft and means (25) to decelerate said one shaft, as required, in order to effect synchronization 10 preparatory to a gear selection operation, and means (36) for controlling said isolation means, said accelerating means and said decelerating means to effect a synchronized gear-changing operation, characterized in that said acceleration means and 1 said deceleration means are constituted by an electric synchronizing motor (25) adapted to operate directly on said .one shaft (1 ,2,3) to acceler.ate or decelerate said shaft when the shaft , is isolated from loads applied to said input and said output, for 20 synchronization during a gear-changing operation, and in that an electronic computer control system (36) is provided to control the sequential operation of said isolation means (32), gear selector means (8,10,12,14) and said synchronizing motor (25) including 25 acceleration or deceleration of the motor, to change the overall gear ratio to a newly required gear ratio in response to a command signal of the required new overall gear ratio. 30 2. A gearbox according to Claim 1, wherein said computer control system (36) is responsive to signals from a vehicle management system (34) representative of vehicle operating parameters and driver demand requirements and is adapted to generate 35 command signals of required optimum gear ratios in accordance with said signals for automatic control of the gearbox. 3. A gearbox according to Claim 1 comprising three parallel gear carrying shafts, an input shaft (1 ) constituting said torque receiving ' input, an intermediate shaft (2), and an output shaft (3) constituting said torque transmitting output. 4. A gearbox according to Claim 3 wherein selectable gears (16-23) are mounted on said input shaft (1 ) and said output shaft (3) for free rotation thereon to mesh with gears fixedly provided on said intermediate shaft (2), and releasable coupling means (8,10,12,14) are provided for coupling each selectable gear with respect to the shaft on which it is mounted to provide a number of different overall gear ratios which can be selected equal to the product of the number of selectable gears (16-19) provided on the input shaft and the number of selectable gears (20-22) provided on the output shaft, torque being transmitted through the -gearbox from said input shaft to said intermediate shaft and then to said output shaft whichever overall gear ratio is selected. 5. A gearbox according to Claim 4 wherein a gear fixedly provided on the intermediate shaft (2) meshes with a gear (18) provided on the input shaft (1 ) and also a gear (21 ) provided on the output shaft (3). 6. A gearbox according to Claim 4 wherein said coupling means comprise slidabl ' e engagement hubs (8,10,12,14). 7. A gearbox according to Claim 3, wherein said one shaft is said input shaft (1 ) and said isolation means include a releasable coupling device (32) which can be actuated to isolate the input shaft from an engine load applied thereto in use. 8. A gearbox according to Claim 3 wherein said one shaft is said output shaft (3) and said isolation means include a releasable coupling device which can be actuated to isolate the output shaft from loads applied thereto in use. 9. A gearbox according to Claim 3 wherein said one shaft is said intermediate shaft (2) and said isolation means include a releasable . load transmitting coupling device associated with the input shaft (1) and/or the output shaft (3) for isolating such shaft (1,3) from loads applied thereto i n use. 10. A gearbox according to Claim 2, wherein said computer control system (36) is adapted to have a plurality of modes of operation, at least some of which may be selectable by manual operation, corresponding to different required engine operating conditions and to provide signals of optimum gear ratios for each of such modes to effect automatic gearchangi ng .

Inventors: EVERTON JOHN MALCOLM, EVERTON, JOHN, MALCOLM
Applicants: EVERTON JOHN MALCOLM, EVERTON, JOHN, MALCOLM
Application year: 1985
Main classification: F16H3
IPC codes: B60W10, B60W30, F16H3, F16H61