GB2352487A - Dissipation of drag rotation in synchronised transmissions - Google Patents

Abstract

In an automated manual transmission, upon selection of the reverse gear combination an hydraulic or pneumatic brake load L is applied via actuators 8 and/or 10 to a synchromesh synchronisation mechanism 1,2,3,9 of at least one forward gear combination in order to brake the transmission (drive shafts 4 and 5) into a substantially stationary condition whereupon potential unbalanced rotation of the transmission is diminished so that there is less likelihood of idle rattle. Several such synchronisation mechanisms may be combined to provide more rapid dissipation. The selected gear combination(s) may be alternated to reduce wear on the respective synchronisation mechanism(s). Alternatively, upon selection of the reverse gear combination, a forward gear combination synchronisation stage may be performed, whereby drag rotation is dissipated by proportional coupling to the bulk of the transmission ie. increasing the mass of inertia, prior to engagement of the reverse gear combination.

Description

2352487 A Transmission Control Arrangemen The present invention relates to

a transmission control arrangement and more particularly to a transmission control arrangement used within a motor vehicle with regard to selection of a reversing gear.

Clearly, within a motor vehicle it is necessary to provide a transmission tr through which, motive power can be distributed to the wheels of the vehicle. Normally, this transmission will comprise a gearbox including several respective gear ratio combinations in order to correlate the necessary torque for vehicle proportion to the engine power output etc. Typically, there will be four or more forward gears and at least one reverse gear in order to accommodate a full range of vehicle operational scenarios.

The present invention relates effectively to an automated manual transmission for a motor vehicle. In such an automated manual transmission gear changes are made through appropriate switches activating solenoids in order to displace the necessary gear sets within the transmission to a desired gear ratio combination indicated by such switching initiated by the vehicle driver or by a preprogrammed calibration map of appropriate gearing for the current operational conditions.

In order to effect smooth gear changes between respective gear ratios it is necessary to provide a synchronisation mechanism to bring the respective gears in a gear ratio pairing up to a substantially equivalent rotation speed before meshing the respective gear teeth gears together. Such a mechanism is referred to as a synchromesh. Clearly, synchromesh mechanisms are particularly required when changing between gear ratios whilst the vehicle is in motion. However, it will be understood that with regard to a reverse gear typically the vehicle will be substantially stationary when that gear is selected and so synchromesh mechanisms may be considered unnecessary in some applications.

Unfortunately, when a vehicle is stopped and the transmission therefore placed in neutral, particularly after a period of forward motion, there is a good 5 degree of gearbox momentum or drag rotation which overruns for a period of time. Thus, when a vehicle driver wishes to engage a reverse gear in such a scenario, it will be understood without a synchromesh mechanism smooth engagement of reverse gear is difficult and even with a synchromesh mechanism it may be necessary to reverse rotation against the gearbox momentum or drag. Such 10 difficulties with regard to reverse gear are at least inconvenient to a vehicle driver.

I The above described problems with regard to engagement of reverse gear are particularly apparent with regard to automated manual transmission arrangements in which simple switch activation is provided by the driver rather than in a fully manual transmission where there is typically at least a time delay involved in displacing a gear lever and overcoming a reverse selection gate or bridge during which gearbox drag rotation may diminish. Clearly, simple depression of a button switch in an automated manual transmission is more instantaneous and therefore more liable to incur problems with regard to drag rotation overrun.

It is an object of the present invention to provide a transmission selection arrangement which substantially avoids the above mentioned problems.

In accordance with the present invention there is provided a transmission control arrangement for a motor vehicle, the arrangement comprising transmission means including at least one forward gear combination and a reverse gear combination with selector means to select therebetween, the forward gear combination including synchronisation means used to synchronise, when selected by the selection means, that forward gear combination with vehicle drive means through progressive engagement prior to full engagement therebetween, the selection means including control means whereby, when that reverse gear combination is selected, the synchronisation means of one of the forward gear combinations is subject to a brake load determined by the control means in order to dissipate any momentum or drag rotation of the transmission means and so facilitate engagement between the reverse gear combination and the vehicle drive means despite that reverse gear combination being substantially stationary.

Alternatively, in accordance with the present invention there is provided, a transmission control arrangement for a motor vehicle, the arrangement comprising transmission means including at least one forward gear combination and a reverse gear combination with selection means to select therebetween, the forward gear combination including synchronisation means used to synchronise when selected by the selection means, that forward gear combination with vehicle drive means through a synchronisation stage of progressive engagement prior to full engagement therebetween, the arrangement being configured by control means associated with the selection means, whereby when the reverse gear combination is selected by said selection means then the control means arranges that said synchronisation means performs said synchronisation stage of at least one of said forward gear combinations in order to dissipate drag rotation of the transmission means through proportional coupling to the bulk of the transmission means prior to engagement of the reverse gear combination with the vehicle drive means.

Typically, the transmission means will be an automated manual 25 transmission. Thus, the selection means will comprise appropriate switches activated by paddles or buttons in order to select a respective forward gear combination or the reverse gear combination.

Typically, the brake load may be applied through displacement of a suitable brake pad or other actuation mechanism. However, more typically the braking load will be applied through the selector mechanism onto the synchro ring using the synchro ring as the friction material.

The control means may be arranged such that more than one synchronisation means in respective forward gear combinations may be subjected to a brake load in order to dissipate momentum or drag rotation of the transmission means.

Furthermore, the control means may alternate the respective synchronisation means utilised in different forward gear combinations in order to extend wear and/or provide more rapid dissipation of momentum or rotation of the transmission means. In such circumstances, initially all synchronization means in all forward gear combinations may be subjected to a braking load with an incremental reduction in the number of switch synchronisation means subjected to a braking load as momentum or rotation drag of the transmission means is dissipated.

The control means may also be coupled to appropriate indication means in order to indicate to a driver of a motor vehicle when the reverse gear combination can be selected through the selection means upon appropriate dissipation of momentum or drag rotation of the transmission means.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a pictorial cross-section of a transmission control arrangement to facilitate engagement of a rear gear combination; and, Figure 2 is a pictorial side cross-section of the transmission control arrangement depicted in Figure 1 with a forward gear combination engaged.

Operation of synchromesh gears is well known to those skilled in the art. Thus, specific description directed towards such operation is limited to reference to 5 that known understanding of synchromesh gear operation within motor vehicles. However, it should be noted that general description with regard to operation of synchromesh gear transmissions in motor vehicles is given in the text books "The Motor Vehicle" published by Butterworth-Heinemann (Newton, Steeds and Garret) twelfth edition, pages 651 to 683 and "Fundamentals of Motor Vehicle Technology" published by Stanley Thorns (Publishers) Limited - Hilher, fourth edition, pages 237 to 243.

In essence, the purpose of a synchromesh or other synchronisation mechanism used with regard to a transmission within a vehicle is to provide two stages of gear combination engagement. In a first stage, which is generally of a progressive nature, the respective rotational speeds of a two sides of the gear combination are brought to substantial equalisation such that in a second stage of full engagement there is a smooth coupling of the gear combination with less jerk and wear through initial gear teeth misalignment etc.

The drawings illustrate a transmission gear combination in accordance with the present invention. The underlying synchromesh synchronisation mechanism comprises a friction cone 1 and a selector collar 2 incorporating a reciprocal friction surface 3 to engage the friction cone 1. Thus, as the selector 2 is moved in the direction of arrowhead S, it will be understood that the friction surface 3 and the friction cone 1 are forced into progressive engagement such that the rotational speed of a primary shaft 4 and a main shaft 5 are substantially equalised. With the primary shaft 4 and main shaft 5 at approximately the same rotational speed a dog clutch 6 (Figure 2) is then engaged to provide full engagement between the primary shaft 4 and the main shaft 5 for normal power transmission therethrough.

It will be appreciated that the primary shaft 4 and the main shaft 5 are relatively substantial components and thus have momentum when rotated which must be dissipated when disengaged before rotation stops. Thus, when a vehicle stops from a period of forward motion it will be understood that the primary shaft 4 and/or the main shaft 5 may still have a degree of drag rotation as a result of momentum conservation which overruns vehicle motion. In such circumstances, particularly when the vehicle transmission is in neutral the primary shaft 4 or main shaft 5 will still rotate for a period of time.

Clearly, it is normally only prudent to engage a reverse gear combination when the vehicle has stopped. Thus, normally a reverse gear combination will not include a synchronisation mechanism as the shaft 4, 5 rotation will be contrary to that required for reverse gear combination drive and so more complicated synchronisation mechanisms would be required. Furthermore, the vehicle, and therefore the transmission, will almost certainly be stationary unless reverse is engaged immediately after a period of forward gear combination motion.

With regard to automated manual transmission arrangements it will be understood that the displacements such as that indicated by arrowhead S will be performed through solenoid or hydraulic actuators (not shown) displacing a selector fork 7 to select the desired gear combination. Similarly, with regard to a reverse gear combination in an automated manual transmission a simple switch will be operated in order to provide the selection of that reverse gear combination. In such circumstances, it will be understood that selection of reverse gear can be relatively rapid and so the transmission has had inadequate time in order to dissipate the drag rotation overrun of the shafts 4, 5 due to these shafts 4, 5 rotational momentum.

As indicated previously, with regard to a fully manual transmission there will be a gear lever displacement through selection slots and normally a specific reverse selection gate which must be overcome so that there is a greater possibility of rotation drag dissipation prior to reverse gear combination engagement. It is the relative rapidity of automated manual transmissions along with relatively robust solenoid selection which has no feedback for back-off in automated manual transmission arrangements which presents significant problems. Thus, for example, there may be excessive wear and even fracture between gear teeth as a result of the forced engagement between a relatively stationary reverse gear combination and a still rotating drive shaft as a result of drag rotation shaft momentum. Furthermore, the automated selection solenoids used to force such engagement will also tend to fail prematurely due to the inherent resistance of making such a reverse gear combination selection between such non- synchronised drive shaft and reverse gear combination. Clearly, if a driver feels resistance through a gear lever then that driver will alter the pressure applied whilst an automated arrangement may not have the facility for such feed-back control.

In accordance with the present invention a braking load is applied to the synchronisation mechanism of a forward gear combination in order to slow the drive shafts 4, 5 of that combination and so dissipate drag rotation due to momentum. Once such drag rotation is dissipated, it will be understood that engagement of a reverse gear combination is then much easier between a substantially stationary drive shaft and reverse gear combination. In such circumstances, as depicted in Figure 1 a brake actuator 8 acts through the selector 2 to engage a synchronizing member 9 which engages the main shaft 5. Thus, when a braking load L is applied to the actuator 8 rotation of the shaft 5 is resisted through the braking effect of the load L. In effect, the braking load L ensures dissipation of the momentum in the shaft 5 as a result of forward motion is more quickly dissipated than due to natural transmission configuration friction. Once the shaft 5 has been brought to a substantially stationary condition, it will be appreciated that a reverse gear combination can be brought into engagement with that shaft 5 relatively easily by a simple slide process. However, it will be understood to avoid problems of gear block out, generally the braking on the synchro ring of the shaft 5 will be removed just before selection of the reverse gear in order that the braking does not lock the shaft and so prevent indexing of gear 10 teeth together during slide engagement therebetween.

I Once the shaft 5 has been slowed or brought to a stationary condition it will be appreciated that the braking load L may be removed prior to or after engagement of the reverse gear combination so that the shaft 5 can provide drive to that reverse gear combination.

It will be understood that rather than the main shaft 5 being slowed that a similar brake actuator and brake load could be applied to the primary shaft 4 such that this shaft 4 is slowed to a substantially stationary condition for engagement with a reverse gear combination and subsequent transmission of drive to that reverse gear combination.

The braking load L may be provided by hydraulic or pneumatic pressure control through a control mechanism associated with selection of the reverse gear combination.

It will be understood that both the primary shaft 4 and the main shaft 5 may be slowed through an actuator combination of actuator 8 acting upon a peg actuator 10. Thus, the actuator 8 will slow the main shaft 5 through engagement with the peg 10 located in an aperture through the synchronisation member 9 and the peg 10 will be directly forced into braking abutment with the friction cone 1 of the primary shaft 4. In such circumstances both the shafts 4, 5 will be slowed by the braking load L to a substantially stationary state by the braking load L to enable and facilitate engagement with a similarly substantially stationary reverse gear combination. Thus, even though the selection fork 7 has arranged for there to be no transmission of drive between the shafts 4, 5 and so placed the transmission in a neutral configuration there is a braking load L applied between the shafts 4, 5 through the synchronisation progressive engagement surfaces of the friction cone 1 and surface 3 in order to enable the drag rotation of the shafts 4 due to their momentum of rotation to be dissipated quicker than as a result of their natural configuration or friction within a vehicle. By such means, it will be appreciated that selection of reverse gear within a motor vehicle is made substantially easier by the present invention and furthermore, where automated selection is conducted a similarly rapid selection of reverse gear consistent with such operation is achieved.

As indicated above, generally the present transmission control arrangement is used with regard to automated manual transmission systems. In such circumstances, selection of a respective forward gear combination or a reverse gear combination is made through switches which may take the form of paddles or button switches located adjacent the vehicle steering wheel or a Tiptronicigear lever. In any event, a single actuation of the selector switch alters the respective forward gear combination used by the vehicle or by a single switch actuation or combination selection of a reverse gear combination. The distinct advantage of automated manual gearbox transmissions is that the driver is less distracted by gear changes in that their hands can remain in contact and least adjacent to the vehicle steering wheel.

Typically, as illustrated in Figure 1, the brake actuator 8 or peg actuator 10 may take the form of abutting members into contact with the synchronisation mechanism surfaces of the friction cone 1, surface 3 and the synchronisation member 9. These abutment surfaces will generally take the form of brake pad type friction materials in order to facilitate dissipation of drag rotation in the transmission i.e. shafts 4, 5.

It will be understood that each respective forward gear combination of a motor vehicle transmission may include its own actuator 8 and/or actuator peg 10 in order to provide dissipation of drag rotation in the transmission and so facilitate engagement of the reverse gear combination. In such circumstances, the inherent problem f wear with regard to any load abutment mechanism can be avoided by the controller associated with selection of the reverse gear combination alternating which particular forward gear combination synchronisation mechanism is utilised in order to dissipate drag rotation on the transmission. In such circumstances, the period of time over which replacement of worn actuators 8, 10 will be significantly extended.

As each respective synchronisation mechanism may be utilised. to facilitate dissipation of drag rotation it will be understood that several such synchronisation mechanisms could be combined in order to provide more rapid dissipation where required. Thus, if a vehicle is rapidly decelerated to a full stop the drag rotation within the transmission will be relatively high and so if reverse gear is to be selected a more rapid dissipation of that drag rotation must be achieved by a more aggressive application through a single synchronisation mechanism or by a combination of several such mechanisms. It will also be understood that initially all the synchronisation mechanisms may be utilised in order to dissipate rotation and incrementally, one after another, each such synchronisation mechanisms are disengaged as the level of drag rotation is diminished.

It will be understood that the present transmission control arrangement may include an indicator coupled to the controller associated with selection of reverse gear combination such that once the drag rotation of the transmission has been diminished the driver is informed that reverse gear combination can be selected or more normally, the controller can then select such reverse gear combination without damaging the selector solenoids utilised in the automated selection mechanism.

As an alternative to inclusion of specific actuators 8, 10 it win be understood that drag rotation of the transmission means may be dissipated by increasing the mass of inertia of the transmission. Thus, through a law of conservation of a momentum if, for example, the primary shaft 4 should have a relatively high drag rotation then coupling to a main shaft 5 will transfer some momentum to that shaft 5 such that the coupled combination of shafts 4 and shaft 5 will rotate more slowly. Thus, rather than brake the shafts 4, 5 through specific actuators 8, 10 it will be understood that the normal synchromesh progressive engagement between the friction cone I and the surface 9 may be utilised in order to slow the transmission and so facilitate selection of a reverse gear combination. Clearly, the more forward gear combinations through their respective synchronisation mechanisms which are combined into the momentum distributive effect the slower the combined transmission will be. In such circumstances, the controller associated with selection of a reverse gear combination will determine the necessary number of synchronisation mechanisms in order to dissipate drag rotation of the transmission sufficiently for convenient engagement of that reverse gear combination by the selection mechanism.

Generally, with regard to the present invention when selecting a reverse gear combination a braking load is applied to one or more of the forward gear combination synchronisation mechanisms of sufficient force to substantially dissipate and normally stop drag rotation of the transmission clue to momentum. However, the forward gear combinations themselves are not selected as these will typically add rather than diminish drag rotation and normally this rotation will be contrary to that required for reverse gear combination drive. Furthermore, in order to improve wear and tear the or the selection of forward gear combinations chosen to dissipate drag rotation of the transmission means will be alternated or varied such that each respective synchronisation mechanism of the transmission is not overly burdened and therefore subject to early failure.

Clearly, when a forward gear combination is selected as depicted in Figure 2 then the brake load L is substantially removed or at least diminished such that normal synchronised transmission drive can be passed through the primary shaft 4 to the main shaft 5 via the synchronisation member 9 or vice versa. Thus, any wear of the actuator 8 or peg 10 is not significant during the long periods of forward gear combination operation. However, it will also be understood that the top or overdrive forward gear combination may be arranged such that there are no brake load actuators 8, 10 associated with their respective synchronisation mechanisms as long term operation will normally be in these forward gear combinations and so would result in excessive wear to these actuators 8, 10.

It will be appreciated that typically the primary shaft 4 or main shaft 5 will be coupled to the vehicle engine or other primary driving means either directly or through another gear transmission path.

Claims (12)

-13CLAIMS

1. A transmission control arrangement for a motor vehicle, the arrangement comprising transmission means including at least one forward gear combination and a reverse gear combination with selector means to select therebetween, at least one forward gear combination including synchronisation means used to synchronise when selected by the selection means, the forward gear combination with vehicle drive means through progressive engagement prior to full engagement therebetween, the selection means including control means whereby, when that reverse gear combination is selected, the or one of the synchronisation means of the forward gear combinations is subjected to a brake load defined by the control means in order to dissipate drag rotation of the transmission means and so facilitate engagement between a substantially stationary reverse gear combination and the vehicle drive means.

2. A transmission control arrangement for a motor vehicle, the arrangement.

comprising transmission means including at least one forward gear combination and a reverse gear combination with selection means to select therebetw.een, the forward gear combination including synchronisation means used to synchronise when selected by the selection means, that forward gear combination with vehicle drive means through a synchronisation stage of progressive engagement prior to full engagement therebetween, the arrangement being configured by control means associated with the selection means, whereby when the reverse gear combination is selected by said selection means then the control means arranges that said synchronisation means performs said synchronisation stage of at least one of said forward gear combinations in order to dissipate drag rotation of the transmission means through proportional coupling to the bulk of the transmission means prior to engagement of the reverse gear combination with the vehicle drive means.

3. An arrangement as claimed in claim 1 or claim 2 wherein the transmission means is an automated manual gearbox transmission.

4. An arrangement as claimed in claim 1, 2 or 3 wherein the selection means comprises an appropriate switch to activate a solenoid device in order to select one of the forward gear combinations or the reverse gear combination.

5. An arrangement as claimed in claim 1 and any claim dependent thereon wherein the brake load is applied by a brake actuator forced into braking abutment with the synchronisation means under a brake load dependent upon the control means.

6. Am arrangement as claimed in any preceding claim wherein the control means is configured such that more than one synchronisation means in respective forward gear combinations are utilised to dissipate drag rotation of the transmission means.

7. Am arrangement as claimed in claim 6 wherein the control means alternates the specific synchronisation mechanism of each respective forward gear combination used to dissipate drag rotation in order to ameliorate wear between respective synchronisation means of each respective forward gear combination.

8. An arrangement as claimed in claim 6 or claim 7 wherein the control means is arranged to utilise two or more synchronisation means of respective forward gear combinations in order to more rapidly dissipate drag rotation of the transmission means.

9. An arrangement as claimed in claim 8 wherein the control means is arranged to utilise, more than one synchronisation means in order to initially dissipate drag rotation of the transmission means and then incrementally reduce the number of synchronisation means utilised to dissipate drag rotation of the transmission means until the transmission means attains a substantially stationary status.

10. An arrangement as claimed in any preceding claim wherein the controller provides an indication to a driver of a motor vehicle that selection of the reverse gear combination is allowable.

11. A transmission control arrangement substantially as hereinbefore, described with reference to the accompanying drawings.

12. A motor vehicle including a transmission control arrangement as claimed in any preceding claim.