GB2462474A

GB2462474A - Transmission control which reduces shock when first gear is engaged with stationary vehicle

Info

Publication number: GB2462474A
Application number: GB0814662A
Authority: GB
Inventors: Martin William Wesley
Original assignee: Zeroshift Ltd
Current assignee: Zeroshift Ltd
Priority date: 2008-08-09
Filing date: 2008-08-09
Publication date: 2010-02-10
Also published as: GB0814662D0

Abstract

A transmission system comprises first and second shafts (1, 3, fig 1a) including a first gear train having a first gear element (8) rotatably mounted on one of the shafts (1, 3) and a second gear element (8') mounted on the other shaft (1, 3). A control system 90 arranged to control operation of a selector assembly (29, fig 1c) and to send control signals to a drive system such as an engine 80 and clutch 86, wherein in response to a request to select the first gear train in a condition when at least one of the first gear element 8 and sets of engagement members (35,36) is not rotating, the control system 90 is arranged to actuate the engine 80 or the clutch 86 to provide relative rotational movement between first gear element (8) and the sets of engagement members (35,36) prior to actuating the selector assembly (29) to engage the first gear element.(8). The selector assembly (29) operates the engagement members (35, 36) so as to include several selection modes which, for example, may be: locking the first gear element (8) for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction.

Description

Transmission system and gear selection method The present invention relates to transmission systems, in particular to dog-type transmission systems, and a method for selecting a gear.

In conventional single clutch synchromesh transmission systems for vehicles it is necessary to disengage the transmission from the power source, such as an engine or motor, by operating the clutch before the current gear is deselected and the new gear is engaged. If the power is not disengaged when attempting to engage a new gear the synchromesh is unable to engage the new gear wheel or has to be forced into engagement with the risk of damaging the transmission and creating torque spikes in the transmission. This is because in most cases the speed of the engine is not matched to the speed of the new gear. For motor vehicles such as cars having conventional gearboxes and powered by an engine, the selection of a new gear ratio typically takes between 0.5 and 1 second to complete. So, for example, when a higher gear is selected the time delay allows the engine to reduce its speed [due to its own inertia] to more closely match the speed of the new gear before the clutch re-connects the engine and the transmission, thereby reducing the possibility of torque spikes occurring when the power is reapplied.

An instantaneous transmission system is arranged such that a new gear can be selected before the current gear is disengaged under power. These transmission systems include at least one instantaneous gear selector mechanism, which typically has four modes of operation with respect to each of the rotatably mounted gear wheels associated with it: Fully engaged in both torque directions (fully in gear); Disengaged in both torque directions (neutral); Engaged in the forward torque direction while disengaged in the reverse torque direction; Disengaged in the forward toque direction while engaged in the reverse torque direction.

It is the last two modes that enable a discrete ratio gearbox to have the ability to shift up or down ratios instantly under load without torque interruption. In some embodiments it is not necessary to have a neutral mode.

In instantaneous type transmission systems selecting first gear when the vehicle is stationary can be a problem. This is because the transmission system may accidentally lock out because drive formations on first gear can be aligned with respect to its gear selector assembly such that the drive formations prevent the selector assembly from properly selecting first gear.

Typically each drive formation includes a substantially planar surface that is oriented towards the selector assembly and if the planar surfaces are positioned when the vehicle comes to rest such that the selector assembly engages them instead of the spaces between the drive formations when selecting first gear, the transmission locks out and there is no way for the driver of the vehicle to reset or adjust the transmission system to enable the vehicle to be moved.

A further problem in transmission systems where the selection of a new gear ratio takes place almost instantaneously without substantial power interruption, such as the transmissions described in WO 2004/099654, WO 2005/005868, WO 2005/005869, WO 2005/024261 and WO 2005/026570 the contents of which are incorporated by reference, large torque spikes can be generated when the new gear is engaged under certain shift conditions because the load impacting the gear wheel can be as high as 6OkN.

The torque spikes cause shock waves to propagate through the transmission that can be heard and felt by the occupants of the vehicle. The shockwaves can produce a jerky ride for the car occupants and can lead to wear of transmission components and the possibility of components failing. Nevertheless it is highly desirable to use this type of transmission in vehicles since for many shift types there is no loss of drive during a gear change. This makes the vehicle more efficient thereby requiring less fuel and producing lower emissions while at the same time increasing the performance of the vehicle since the vehicle does not noticeably decelerate during an instantaneous shift.

WO 2005/005868 has addressed the torque spike problem by using a control system that reduces the vehicle clutch pressure prior to making a shift to at least partially absorb the large torque spikes generated when a new gear is engaged by relative rotational movement of the input and output sides of the clutch. However even with this system in place, known instantaneous transmission systems can be noisy, falling below acceptable limits of Noise, Vibration and Harshness (NVH) tests. This is because absorption of the torque spikes takes place at the vehicle clutch, which is too far away to be fully effective.

WO 2008/062192 discloses an instantaneous transmission system that includes damping mechanisms in each of the gear wheels andlor the gear selector mechanisms to reduce the effects of torque spikes. For transmission systems having several gear ratios this requires multiple damping devices in order to achieve quiet shifts. However, without appropriate control when a new gear is selected there can be significant backlash experienced due to the rebound effect of the damping mechanisms.

Accordingly the present invention seeks to provide an improved transmission system and a method of selecting a new gear that mitigates at least some of the aforementioned problems.

According to one aspect of the invention there is provided a transmission system including first and second shafts, means for communicating drive between the first and second shafts including a first gear train having a first gear element rotatably mounted on one of the shafts and a second gear element mounted on the other shaft, a selector assembly including first and second sets of engagement members that are independently moveable into and out of engagement with the first gear element for selectively locking the first gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the first gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the first gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the first gear element for rotation with the shaft in the clockwise and anti-clockwise directions, and a control system arranged to control operation of the selector assembly and to send control signals to a drive system, wherein in response to a request to select the first gear train in a condition when at least one of the first gear element and the sets of engagement members is not rotating, the control system is arranged to actuate the drive system to provide relative rotational movement between first gear element and the sets of engagement members prior to actuating the selector assembly to engage the first gear element.

The invention prevents the first gear element from being oriented relative to the selector assembly in a maimer that prevents a proper engagement being achieved and thereby prevents the transmission system from locking out. In the context of a vehicle, the invention enables first gear to be selected when the vehicle is stationary, that is when there is no rotational output from the transmission system to the drive wheels, for example when the vehicle is parked or has come to a temporary halt at traffic lights. Of course the invention is also applicable to the selection of other gears, for example in the situation where a driver decides to select second gear to pull away from a stationary position. In this instance, the first gear element can refer to a gear element associated with second gear.

Typically, the control system is arranged to actuate the drive system to provide relative rotational movement between first gear element and the sets of engagement members when there is no relative rotational movement between the first gear element and the sets of engagement members and / or when there is no rotational output from the transmission system, for example an output shaft of the transmission system is not rotating. Thus the invention essentially provides a transmission system arranged to perform a controlled spin-up procedure prior to engaging the new gear to ensure that lock out cannot occur.

The control system can be arranged to determine whether or not there is relative rotational movement between the first gear element and the sets of engagement elements.

Advantageously the control system can be arranged to receive inputs from sensor devices such as a vehicle speedometer, a sensor device arranged to determine whether a transmission output component is rotating and a speed sensor for monitoring the speed of an output side of a clutch device that drives transmission components and determines whether or not there is relative rotational movement between the first gear element and the sets of engagement elements according to the signals received.

Advantageously the control system can be arranged to determine whether or not there is rotational movement of a transmission output component. For example, the transmission can include an output shaft and a sensor device arranged to measure the rotational speed of the output shaft and the control system can determine whether or not there is a rotational output from the transmission system from the signals received from the speed sensor. Additionally, or alternatively, in the context of a vehicle, the control system can be arranged to receive signals from a vehicle speed sensor such as a conventional speedometer. Signals from other devices can be fed to the control system to enable it to determine whether or not there is an output from the transmission system, such as signals from a vehicle ignition system or motion detectors such as accelerometers.

Advantageously the drive system can be arranged to rotate either the first or second shaft and the control system can be arranged to move the selector assembly to a neutral position before rotating the shaft. This ensures that there is no rotational output from the transmission system when the drive system is actuated by the control system. In the context of the vehicle, this prevents the vehicle from lurching forward and / or stalling when drive is applied.

Advantageously the transmission system includes means for determining the operational status of the gear selector assembly. For example, the transmission system can include position sensors for detecting the positions of the first and second sets of engagement members and the control system can use the signals received form the position sensors to determine the operational status of the selector assembly.

Advantageously the control system can be arranged to send control signals to a clutch device in the drive system to selectively open and close the clutch device and thereby control the application of drive to the first gear element or the sets of engagement members via the first or second shafts.

The control system is arranged to actuate the selector assembly to engage the first gear element within a predetermined range of relative rotational speed between the first gear element and the first and second sets of engagement elements occurs. Preferably the relative rotational speed is in the range of 20 to 500 rpm, more preferably still in the range 50 to 200 rpm.

Advantageously the transmission system can include a speed sensor for measuring the speed of rotation of the first gear element or a component connected directly or indirectly thereto, and wherein the control system is arranged to receive inputs from the speed sensor and to determine when to select the first gear element according to the inputs received. For example, the speed sensor can be located on or around the output side of the clutch and the control system can determine the speed of the first gear element or the shaft on which the gear selector assembly is mounted either from the direct measurements or by calculation based on the geometry of the transmission system. The transmission system is arranged to actuate the selector assembly to lock the first gear element for rotation with the first shaft when the relative rotational speed between the first and second sets of engagement members and the first gear element is in the predetermined range.

Advantageously the control system can be arranged to calculate a time delay and to actuate the gear selector assembly to select the first gear element after the period of time has lapsed.

When the clutch device is closed, the output side of the clutch device is substantially matched to the input side of the clutch device and the speeds of the first gear element or the sets of engagement members are set according to the geometry of the transmission system. When the control system opens the clutch device, the rotating components are then slowed by friction in the transmission system, for example in the bearings and due to the drag of the lubricating fluid. The control system is programmed with information relating to the frictional effects on speed retardation on the gear element and the sets of engagement members and determines when the rotating component will have slowed down to a speed that is within a predetermined range. The control system is arranged to actuate the gear selector assembly to engage the first gear element when this period of time has elapsed.

Advantageously the transmission system can include a temperature sensor for measuring the operating temperature of the transmission lubricating fluid. The control system can be arranged to determine the time delay according to values received from the temperature sensor. The frictional effects in the transmission system are in part determined by the temperature of the lubricating fluid. Using the temperature measurements, the control system can calculate the frictional effects of the lubricating fluid by reference to data stored in a memory device, and determine the time delay for engaging the first gear element accordingly.

The transmission system can include a damping device for damping locking engagements between the first gear element and its shaft. Advantageously at least one of the first gear element and the gear selector assembly can include the damping device.

The damping device is arranged to allow lost motion between the first shaft and at least one of the first gear element and the selector assembly after the selector assembly engages the first gear element. For example, the damping device can be arranged to allow relative rotational movement between the first shaft and at least part of the first gear element after the selector assembly engages the first gear element. Additionally, or alternatively, the damping device can be arranged to allow relative rotation between the first shaft and at least part of the selector assembly after the selector assembly engages the first gear element. Advantageously the selector assembly can be mounted on the first shaft and is arranged to rotate therewith.

The damping device includes first and second parts that are arranged to rotate relative to each other. The first gear element can include first and second parts that are arranged for relative rotational movement. The first part can be rotatably mounted on the first shaft and the second part can be arranged for limited rotational movement relative to the first part. The first part can include drive formations that can be selectively engaged by the selector assembly to drive the gear element. The second part can include gear meshing means for meshing with other gear elements. For example, the gear meshing means can be gear teeth. Advantageously the damping device can be arranged to allow lost motion between the selector assembly and the second part of the gear element when the selector assembly drivingly engages the first part.

The gear selector assembly can include first and second parts that are arranged for relative rotational movement. The first part can be fixed for rotation with the first shaft and the second part can be arranged for limited rotational movement relative to the first part. The second part can include engagement members for selectively engaging drive formations formed on the first gear element. Advantageously the damping device can be arranged to allow lost motion between the first part of the selector assembly and the first gear element when the engagement members drivingly engage the first gear element.

Advantageously the damping device can be a fluid damping device, and preferably a hydraulic damping device. Advantageously the fluid damping device can be arranged such that as the angle of relative rotation between the first gear element and the selector assembly increases the damping fluid opposes the relative rotation and thereby absorbs energy. For example, the fluid damping device can be arranged such that increasing the angle of relative rotation between the first gear element and the selector assembly increases the fluid pressure, which absorbs energy and ultimately arrests the relative rotation. Advantageously the fluid damping device can include means to enable damping fluid to flow out of a compression zone as the angle of relative rotation between the first gear element and the selector assembly increases. Advantageously the transmission system can include an enclosure, which substantially surrounds at least the first gear element and the selector assembly and which includes a lubricating fluid such as oil. Advantageously the lubricating fluid can be fed into the fluid damping device to provide the damping action. Advantageously the fluid damping device can be arranged to discharge the lubricating fluid back into the enclosure. Alternatively a separate supply of damping fluid can be supplied to the fluid damping device, for example in the manner of a closed system.

Advantageously the fluid damping device can include at least one piston device that is arranged to damp the locking of the first gear element for rotation with the first shaft. The or each piston device is arranged to damp the locking of the first gear element for rotation with the first shaft in clockwise and anti-clockwise directions and includes a piston member that is arranged to apply pressure to the fluid when the gear element is engaged by the selector assembly. Advantageously the fluid damping device can include a recess, pathway, channel, bore or similar that enables damping fluid to bypass or pass through the piston member as it compresses the damping fluid within a piston device chamber. Controlling the rate at which operating fluid can bypass the piston member is an important factor in determining the damping effect of the damping device. Advantageously the fluid damping device can include an exit port that enables the damping fluid to exhaust from the gear element.

Advantageously the or each piston member can be arranged to move along a curved path. The pathway(s) can be substantially circular, or a substantially circular segment, and can be formed substantially coaxially with the first part of the gear element. Preferably the or each piston member is arranged to move along a substantially actuate pathway that subtends an angle from a start position to an end position of between 20 and 180 degrees. Advantageously the fluid damping device can include a valve device for controlling the flow of operating fluid into the damping device. Advantageously the valve device can be arranged to close a fluid entry port in response to movement of the or each piston member. Advantageously the fluid damping device can be arranged to move the or each piston member to the start position by recharging the device with operating fluid.

Advantageously the fluid damping device can include first and second piston devices, wherein the first piston device is arranged to damp locking of the first gear element for rotation with the first shaft in a clockwise direction and a second piston device arranged to damp locking of the first gear element for rotation with the first shaft in an anti-clockwise direction. Advantageously the first and second piston devices can include first and second piston members respectively, which are arranged to be driven by the second part of the gear element when the selector assembly engages the drive formations formed thereon: the first piston member being driven when the torque direction is in the clockwise direction and the second piston member being driven when the torque direction is in the anti-clockwise direction.

Advantageously the first gear element and/or the selector assembly can include means for opposing relative rotational movement between the first and second parts thereof. Preferably the first gear element and/or the selector assembly includes resilient means for opposing relative rotational movement between the first and second parts thereof. The means for opposing relative rotational movement between the first and second parts can include stiffening elements, such as metallic elements such as steel balls. Preferably the resilient means includes at least one block of rubber or spring element. Advantageously the resilient means can be arranged to bias at least one of the first and second parts to a neutral position.

The control system is arranged to actuate the selector assembly such that the first and second sets of engagement members engage the first gear element before the relative rotational movement of the first and second parts of the damping device ceases. This ensures that the rebound effect of terminating relative rotational movement between the first and second parts of the damping device is mitigated since the backlash between the first gear element and the gear selector device is lower when the gear element is fully engaged by the first and second sets of engagement members (typically in the range 0 to 5 degrees) than when it is only engaged by one of those sets (typically in the range 80 to 100 degrees).

Preferably the first shaft is an output shaft and the second shaft is an input shaft. The input shaft is connected to a drive source via the clutch device. The first gear element is mounted on the output shaft together with the selector assembly and the second gear element is fixed for rotation with the input shaft. It will be apparent to the skilled person that first gear element can be mounted on the input shaft, together with the selector assembly, and the second gear element can be mounted on the output shaft.

The transmission system can include a third shaft, wherein the first shaft is an output shaft, the second shaft is a lay shaft and the third shafi is an input shaft, wherein the transmission system includes means for transferring drive between the input shaft and the lay shaft. The first gear element is mounted on the output shaft, together with the selector assembly, and the second gear element is fixed for rotation with the lay shaft. It will be apparent to the skilled person that first gear element can be mounted on the lay shaft, together with the selector assembly, and the second gear element can be mounted on the output shaft. Similarly, the first gear element can be mounted on the input shaft, the selector assembly can be mounted on the input shaft or the output shaft, and the second gear element can be mounted on the lay shaft.

The transmission can include a second gear train having a third gear element rotatably mounted on the same shaft as the first gear element a fourth gear element mounted on the same shaft as the second gear element, wherein the first and second sets of engagement members are arranged to independently move into and out of engagement with the third gear element thereby enabling the gear selector assembly to selectively lock the third gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the third gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the third gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the third gear element for rotation with the shaft in the clockwise and anti-clockwise directions.

The selector assembly is arranged such that when one of the first and third gear elements is engaged by the selector assembly the other gear element can be selected before disengaging the current gear element for at least some of the operational modes. For example, the selector assembly can be arranged such that when one of the first and second gear elements is engaged by the selector assembly the other gear element can be selected before disengaging the current gear element for the following operational modes: locking the gear elements for rotation with the first shaft in the clockwise direction and not locking in the anti-clockwise direction; and locking the gear elements for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction.

Advantageously the selector assembly is arranged to select the following operational mode with respect to the first and second gear elements: not locking the gear elements for rotation with the shaft in the clockwise and anti-clockwise directions. This provides a neutral condition.

The transmission system can include a third gear train having a fifth gear element rotatably mounted on one of the first and second shafts and a sixth gear element mounted on the other of the first and second shafts and a second gear selector assembly including first and second sets of engagement members that are independently moveable into and out of engagement with the fifth gear element for selectively locking the fifth gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the fifth gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the fifth gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the fifth gear element for rotation with the shaft in the clockwise and anti-clockwise directions. The fifth gear element is preferably mounted on the same shaft as the first gear element and the sixth gear element is preferably mounted on the same shaft as the second gear element.

Advantageously the transmission system may include additional gear trains for communicating drive between the shafts and additional gear selector assemblies for selectively locking the rotatably mounted gear elements for rotation with the first shaft, similar to those described above. Advantageously the gear selector assemblies can be mounted on the shafts between gear trains and alternately on the first and second shafts.

Advantageously the or each gear selector assembly can be arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition. In some embodiments the actuator system is arranged to move the unloaded set of engagement members into driving engagement with the unengaged gear element to effect a gear change. In other embodiments, the unloaded set is moved out of engagement with its current gear to a neutral position and a new gear is selected by another selector assembly.

Advantageously the or each selector assembly can be arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear wheel, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged / gear wheel, and the first set of engagement members is then in an unloaded condition.

Advantageously the or each selector assembly can include an actuator system having a first actuator device for actuating the first set of engagement members and a second actuator device for actuating the second set of engagement members independently of the first actuator device.

Advantageously the or each rotatably mounted gear element includes drive formations that can be engaged by its respective selector assembly or assemblies.

Advantageously the control system is arranged to issue control signals to adjust the output of a drive source. Preferably the control system is connected to an engine control unit via a communication means such as a Controller Area Network (CAN) bus. The control signals instruct the engine control unit to adjust the engine output as required. The control system can also be arranged to issue control signals for controlling the clamp load between input and output sides of a clutch device. Preferably the control system controls the operation of a clutch actuator, which in turn controls the clutch device. Controlling both the clutch and the engine control system provides the best gear shift results.

According to another aspect of the invention, there is provided a transmission system including first and second shafts, a first gear train for communicating drive between the first and second shafts having a first gear element rotatably mounted on the first shaft, a second gear train for communicating drive between the first and second shafts having a second gear element rotatably mounted on the first shaft, wherein the first and second gear elements each having drive formations formed thereon, a selector assembly for selectively transmitting torque between the first shaft and the first gear element and between the first shaft and the second gear element, wherein the selector assembly includes an actuator assembly and first and second sets of engagement members that are moveable into and out of engagement with the first and second gear elements independently of each other, said selector assembly being arranged such that when one of the gear elements is selected by the first and second sets of engagement members and a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition, and a control system arranged to control operation of the selector assembly and to send control signals to a drive system, wherein in response to a request to select the first gear train in a condition when at least one of the first gear element and the sets of engagement members is not rotating, said control system is arranged to actuate the drive system to provide relative rotational movement between first gear element and the sets of engagement members prior to actuating the selector assembly to engage the first gear element.

Advantageously aspects of the control system and sensor devices described above are also applicable to this aspect of the invention.

Advantageously the or each selector assembly can be arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear element, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear element, and the first set of engagement members is then in an unloaded condition.

Advantageously the actuator system for the or each selector assembly can be arranged to include a first actuator device for actuating the first set of engagement members and a second actuator device for actuating the second set of engagement members independently of the first actuator device. Preferably the actuator system includes a first actuator member for moving the first set of engagement members and a second actuator member for moving the second set of engagement members, which can be actuated by the first and second actuator devices respectively.

The actuator assembly can be arranged to bias at least one of the first and second sets of engagement members towards the first or second gear element when the engagement members are drivingly engaged with a gear element.

Preferably the or each selector assembly is arranged such that when the first and second sets of engagement members engage one of the first and second gear elements the backlash when moving between acceleration and deceleration is less than or equal to five degrees.

Preferably each of the rotatably mounted gear elements includes drive formations that can be engaged by the first and second sets of engagement members. For example, the first and second gear elements can include first and second groups of dogs respectively. For example, the first and second groups of dogs can each comprise between two and twelve dogs, evenly distributed on the first and second gears respectively. Preferably the first and second groups of dogs each comprise between two and four dogs, and more preferably three dogs.

Advantageously the first gear element includes first and second sets of drive formations, wherein the first set of drive formations are arranged for engagement by the first selector assembly and the second set of drive formations are arranged for engagement by the second selector assembly.

Advantageously the transmission system can include a second selector assembly similar to the first selector assembly.

Advantageously the transmission system can include additional gear trains for transmitting drive between the first and third shaft.

According to another aspect of the invention there is provided a drive line including a drive source and a clutch device and a transmission system according to any configuration described above. The control system is arranged to control operation of the clutch device to selectively apply drive to the first or second shaft in response to a request to select the first gear train to provide relative rotational movement between the sets of engagement members and the first gear element prior to engaging the first gear element.

According to another aspect of the invention there is provided a vehicle including a transmission system or drive line according to any configuration described above, and wherein the control system includes means for determining when the vehicle is stationary.

According to another aspect of the invention there is provided method of selecting a gear train in a transmission system, said transmission system including first and second shafts, means for communicating drive between the first and second shafts including a first gear train having a first gear element rotatably mounted on one of the shafts and a second gear element mounted on the other shaft, a selector assembly including first and second sets of engagement members that are independently moveable into and out of engagement with the first gear element for selectively locking the first gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the first gear element for rotation with the shaft in the clockwise direction and not locking in the anti- clockwise direction; locking the first gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the first gear element for rotation with the shaft in the clockwise and anti-clockwise directions, and a control system arranged to control operation of the selector assembly and to send control signals to a drive system, said method including, in response to a request to select the first gear train in a condition when at least one of the first gear element and the sets of engagement elements is not rotating, the control system actuating the drive system to generate relative rotational movement between the sets of engagement members and the first gear element prior to engaging the first gear element.

Advantageously the method may include any of the following: determining the operational positions of the first and second sets of engagement members; moving the first and second sets of engagement members to a neutral position prior to actuating the drive system to generate relative rotational movement between the first and second sets of engagement members; and the control system determining whether or not there is any rotational output from the transmission system and actuating the drive system to provide relative rotational movement between first gear element and the sets of engagement members only when there is no rotational output from the transmission system. For transmission systems including more than one selector assembly, the step of moving the sets of engagement members to a neutral condition can apply to all of them.

Advantageously the transmission system can include a damping device for damping the locking engagement of the first gear element with its shaft, said damping device having first and second parts that are arranged for limited relative rotational movement and wherein after one of the first and second sets of engagement members has engaged the first gear element, thereby causing the first and second parts to rotate relative to each other, the method includes the control system actuating the other set of the first and second sets of engagement members to engage the first gear element before the relative rotational movement between the first and second parts of the damping device ceases. This reduces the rebound effect of the damping device by limiting the amount of backlash in the transmission when the rebound takes place.

Advantageously the transmission system can be part of a vehicle and the method is performed when the vehicle is stationary.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 a is a schematic representation of a first transmission system layout according to the invention; Figure lb is a schematic of a vehicle drive system including a transmission system in accordance with the invention; Figure 1 c is a schematic representation of a selector mechanism used in the transmission system of Figure 1 a; Figures ld and le are sectional views of a gear including a damping mechanism in first and second operational positions; Figure if is a sectional side view of the gear of Figures ld and le mounted on an output shaft; Figure 2 is a schematic illustrating the arrangement of a group of dogs on a side of a gear wheel (teeth not shown for clarity); Figure 3 is a schematic that illustrates the interaction of a selector mechanism and the dogs on the side of a gear wheel; Figure 4 is an isometric view of an engagement element from the selector mechanism; Figures 5a-f illustrate diagrammatically the operation of one of the selector mechanisms; Figure 6 is a flow diagram showing the steps taken to select first gear when there is no relative rotational movement between first gear and the selector assembly; Figure 7 shows a second transmission system layout according to the invention; and Figure 8 shows a third transmission system layout (HGV transmission system) according to the invention.

Figure la shows a transmission system 88 that includes an input shaft 3, an output shaft 1, a lay shaft 6. The lay shaft 6 is arranged substantially parallel to the input and output shafts 3,1.

Drive is transferred between the output shaft 1 and the lay shaft 6 via five gear trains 8-8',lO- 10',12-12',14-14',16-16' each having a gear 8, 10, 12, 14, 16 mounted on the output shaft I via a bush 203 (see Figures 1 d and 1 e) so as to be rotatable relative to the output shaft 1 and gears 8',10',12',14',16' mounted on the lay shaft 6 so as to be fixed for rotation therewith. As seen from right to left in Figure Ia, the gear trains are first gear 8, 8', second gear 10, 10', third gear 12, 12', sixth gear 14, 14', and fifth gear 16, 16'.

Drive is transmitted between the input shaft 3 and the lay shaft 6 via a transfer gear train 18- 18' comprising a gear 18 fixed for rotation with the input shaft 3 and a corresponding gear 18' fixed for rotation with the lay shaft 6. The transfer gear 18 is also fourth gear.

To transfer drive from the input shaft 3 to the output shaft 1, each gear has associated with it a selector mechanism 29,31,33. The gear selector mechanisms 29,21,33 are arranged to select the gear trains in order to create torque paths between the shafts. The first selector mechanism 29 is mounted on the output shaft 3 and is arranged to selectively lock the first and second gears 8,10 for rotation therewith. The second selector mechanism 31 is mounted on the output shaft 3 and is arranged to selectively lock the third and sixth gears 12,14 for rotation therewith. The third selector mechanism 33 is mounted on the output shaft 3 and is arranged to selectively lock the fifth and transfer/fourth gears 16,18 for rotation therewith.

The transmission system layout uses a multi-gear multi-path layout, which uses discrete gear ratios and instantaneous selector mechanisms 29,31,33 to facilitate instantaneous torque handover gear shifts for a variety of different ratios. In the example given, the layout is a six speed transmission. It will be apparent to the skilled person that additional (or less) gear trains can be used in the transmission system to make it suitable for different vehicles.

The first selector mechanism 29 is mounted on the output shaft 1 in between the first and second gears 8,10 and is arranged to selectively lock those gear wheels for rotation with the output shaft I in the manner described below. By selecting the gears 8,10 it is possible to transfer drive between the selected gear and the output shaft 1. The selector mechanism 29 is arranged such that when one of the first and second gears 8,10 is engaged it can select the unengaged gear before while the current gear is still engaged for at least some shift types and thus there is no appreciable interruption in the torque transferred through the transmission when selecting the new gear.

The second selector mechanism 31 is similar to the first selector mechanism 29 and is mounted on the output shaft 1 between the third and sixth gears 12,14. The second selector mechanism 31 is arranged to selectively lock the third and sixth gears 12,14 for rotation with the output shaft 1 thereby transferring drive between that the selected gear and the output shaft 1.

The third selector mechanism 33 is similar to the first selector mechanism 29 and is mounted on the output shaft 1 between the fifth and the transfer/4th gears 16,18. The third selector mechanism 33 is arranged to selectively lock the fifth and the transfer/4th gears 16,18 for rotation with the output shaft I thereby transferring drive between that the selected gear and the output shaft 1.

Power enters the transmission through the input shaft 3, is transferred to the lay shaft 6 through the transfer gear 18 and to the output shaft 1 via the gear trains 8-8', 10-10', 12-12', 14-14', 16-16' according to the operational conditions of the first, second and third selector mechanisms 29, 31, 33.

When the fourth gear 18 is selected by the third selector mechanism 33 power travels directly from the input shaft 3 to the output shaft 1 and is not transferred through the lay shaft 6.

Each of the selector mechanisms 29,31,33 enables at least some instantaneous gearshifts and are arranged as described below. Alternatively, the selector mechanisms can be arranged as disclosed in W02004/099654, W02005/005868, WO 2005/005869, W02005/024261 and Figure lb is a schematic diagram of a drive system including a transmission system 88 in accordance with the invention. The drive system can be used in lorries and other heavy vehicles such as cars, lorries, agricultural vehicles, excavators, cranes, military vehicles, etc and includes an engine 80, an engine control unit 82, a sensor system 84 for determining the direction of torque in the transmission, a clutch device 86 such as a friction clutch, a transmission system 88, and a transmission control unit 90.

The engine 80 is typically an internal combustion engine in a vehicle but may be an electric motor for electric vehicles or any other suitable drive source. The output of the engine 80 is largely determined by the driver loading a throttle input device 81 (typically a throttle pedal), which is connected to the engine via a throttle interface 83 and the engine control unit 82. The engine control unit 82 is arranged to monitor and adjust the output of the engine 80 in accordance with instructions received from the user and the transmission control unit 90. The engine control unit 82 may be a throttle potentiometer type system or alternatively an electronic control system (sometimes called a "drive by wire" system).

The engine control unit 82 communicates with the transmission control unit 90 via a Controller Area Network (CAN) bus.

The transmission control unit 90 is a software driven automatic control system that is programmed to produce smooth gearshifts and prevent certain transmission failure modes occurring, for example transmission lockup due to impermissible gearshifts. In order to fulfil its primary functions the transmission control unit 90 controls the sequencing of shift operations in the transmission system 88, the torque in the transmission system via the clutch 88 and engine 80 using a clutch actuator 92 and the engine control unit 82 respectively. In order to achieve this, the transmission control unit 90 receives inputs to determine the direction of torque in the transmission. This can be calculated from existing vehicle sensors for detecting engine and road speeds and from a knowledge of the geometry of the transmission system or can be from clutch sensors 93 or a transmission torque direction sensor 84. The transmission control unit 90 also detennines the operational conditions of selector assemblies 29,31,33, for example by determining their positions from a knowledge of the transmission system and controlling actuation of the selector assemblies 29,31,33 and / or by using one or more transmission position sensors 96. Optionally, the transmission control unit 90 can also receive inputs from one or more of the following devices: a transmission output shaft speed sensor 98, and a user operated gear selection input device 94 for manual and semi-automatic transmissions.

The torque value in the transmission is determined in part by the output of the engine 80 and in part by the operational condition of the clutch 86, which determines the maximum permissible torque that can be transmitted to the transmission (clutch torque limit) according to the clamp load between the input and output sides of the clutch. The clamp load between the input and output sides of the clutch is determined by the transmission control unit 90 via the clutch actuator 92. Reducing the clamp load between the clutch plates allows controlled relative rotational movement between the input and output sides of the clutch device 86 to control the value of torque transmitted. A typical value for speed difference can be 25rpm when operating around 4000rpm (4000rpm on one side of the clutch to 4025rpm on the other side).

The input and output clutch sensors 93 detect the speeds of the input and output sides of the clutch 86 respectively. The readings from the sensors 93 are monitored by the transmission control unit 90, which determines whether relative rotational movement is occurring and the direction of torque according to the values received from the sensors 93. The transmission control unit 90 is arranged to control the clutch actuator 92 and select the clutch clamp load in order to transmit the desired amount of torque to the transmission 88.

The drive system may include one or more clutch clamp load sensors (not shown) in order to detect slip between the input and output sides of the clutch 86.

The optional sensor system 84 for determining the direction of torque in the transmission, may include an accelerometer for determining whether the vehicle is accelerating or decelerating such as a mercury switch, a pair of load cells arranged to detect strain in transmission components wherein from a comparison of the outputs of each load cell it is possible to determine the torque direction (see WO 2005/005 869), a sensor for detecting throttle position andlor a sensor for determining the rate of change in velocity in a rotating transmission component, such as an output shaft. In each case, it is the transmission control unit 90 that determines the direction of torque based on signals received from the sensor(s) used.

Any other suitable way of determining the direction of torque in the transmission can be used.

Optionally, the system can include a speed sensor 98 for detecting the output speed of the transmission. This can assist the transmission control unit 90 to determine which gear is engaged, since it can be programmed with details of the gear ratios and knows the input speed from the output side of the clutch sensor 93. Also, the readings from the speed sensor 98 can be used by the transmission control unit 90 to take into account the effect of changing road conditions on the direction of torque in the transmission 88.

Output shaft gears The output shaft gears 8,10,12,14,16 each include a damping mechanism 200 that is arranged to soften the selection of the gears 8,10,12,14,16 by their respective selector mechanism 29,31,33 thereby reducing the noise generated to acceptable levels. The damping mechanism effectively increases the time that it takes for the gears 8,10,12,14,16 to be locked for rotation with the output shaft 1 and thereby provides a greater period of time over which the energy generated by the collision is dissipated. The input shaft gear 18 is similarly arranged to the output shaft gears 8,10,12,14,16.

The damping mechanism is shown in Figures id and le with reference to the first gear 8, however all of the other output shaft gears 10,12,14,16 are similarly arranged.

Each gear includes an outer part 202 an inner part 204 arranged for limited rotational movement with respect to the outer part 202 (see Figure 1 f). The outer part 202 of the gear wheel includes gear teeth that are arranged to mesh with the gear teeth of the other gear in the gear train 8' that is mounted on the lay shaft 6. The inner part 204 includes three drive formations 20 in the form of dogs 20 on a side face arranged to be engaged by one of the selector mechanisms 29,31,33.

The first dog group 20 is located on one side of the first gear 8 on the inner part 204. The dogs are preferably formed integrally with the first gear 8, but this is not essential. The first dog group 20 comprises three dogs evenly circumferentially distributed about the gear face, i.e. the angle subtended between the centres of a pair of dogs is approximately 1 2d (see Figures 2 and 3). The second dog group 20, comprises three dogs and is similarly arranged on one side of the second gear 10. Three dogs are used because this arrangement provides large engagement windows, that is the spaces between the dogs, to receive the engagement elements and because of its inherent self-centring affect and even load distribution. Large engagement windows provide greater opportunities for the first gear selector mechanism 29 to fully engage the gear wheels 8,10 before transmitting drive thereto. If the first gear selector mechanism 29 drives a gear wheel when only partially engaged it can lead to damage of the dogs and / or the first gear selector mechanism 29.

A substantially annular groove 206 is fonned in one side face of the outer gear part 202. A substantially kidney-shaped drive member 208, which is attached to the inner gear part 204 on a side face opposite to the dogs 20, is located in the groove 206 and is arranged to drive a first piston 212 along the groove 206 in a clockwise direction and a second piston 212 along the groove 206 in an anti-clockwise direction. The movement of the pistons 212 is limited by abutments 215 at a start position and by a shuttle valve 218 and a stop member 219 at an end position, which is located approximately 180° from the start position around the annular groove 206. Thus the first piston 212 can be driven along the groove 206 by the drive member 208 through an angle a little under 180° in the clockwise direction. The second piston 212 can be driven along the groove 206 in the anti-clockwise direction through an angle of a little under 180°. Each piston 212 includes a substantially U-shaped body that is arranged to mate with the drive member 208 and a pointed leading end.

The first groove 206 is arranged coaxially with the outer gear part 202. The side wall 217 of the groove 206 has first and second undercut portions 214. Each undercut portion 214 extends around a substantial portion of one half of the groove 206 (approximately 25 degrees) and gradually increases in depth from a start position adjacent the stop member 219 to a maximum depth a short distance from the abutments 215, wherein the undercut portions 214 terminate. Each undercut portion 214 provides a fluid pathway to allow oil to escape from the groove 206 as the first and second pistons 212 are driven along the annular groove 206. Oil can vent to the gear wheel surrounds from the groove 206 through a hole 210 formed in the drive member 208, via the undercut portions 214.

The gear wheel is mounted on the output shaft 1 via a bush 203 and a first feed ring 222. Oil is supplied to the interior of the gear wheel via a second feed ring 217 mounted on the input shaft 3, an axial feed line 22 formed in the input shaft 3 along its central axis, and at least one radial feed line 220 (four shown in Figures id and le), which connects the interior of the gear wheel to the axial feed line 22 via holes formed in the bush 203 and the first feed ring 222 and a port 216 formed in the outer part 202 of the gear wheel. The first feed ring 222 includes an annular groove formed in its outer surface to enable it to continuously supply oil to the interior of the gear wheel.

The port 216 is arranged to feed oil to both sides of the annular groove 206 in clockwise and anti-clockwise directions. The supply of oil to the groove 206 is controlled by a shuttle valve 218. The arrangement is such that in an unloaded state the port 216 is fully open and oil can be supplied to both sides of the annular groove. When the shuttle valve 218 is loaded by one of the pistons 212 the shuttle valve 218 closes the port 216 on the same side as the loading piston but remains open on the opposite side and therefore oil can still be supplied to the opposite side of the groove 206.

In operation, the groove 206 is substantially filled with oil via the feed lines 22, 220 and the port 216. When the gear wheel is selected by one of the selector mechanisms 29,31,33, engagement of the dogs 20 on the inner part 204 of the gear wheel causes the drive member 208 to drive one of the pistons 212 along the groove 206 in the direction of torque applied by the selector mechanism 29,31,33. As the piston 212 moves along the groove 206 the oil located in the corresponding part of the groove 206 is pressurised, which causes the shuttle valve 218 to close the port 216 at the compression side, but still allows oil to flow into the opposite (unloaded) side of the groove 206. As the piston 212 continues to move along the groove 206 the oil begins to slip past the piston 212 via the undercut portion 214 and is able to vent to atmosphere, which is typically the inside of the gear box, via the hole 210 in the drive member. The oil passes from the undercut portion 214 into a gap between the base of the groove 206 and the drive member 208 and into the hole 210. This absorbs a significant proportion of the engagement energy thereby reducing the noise and shockwave of the impact and hence damping engagement.

The movement of the piston 212 within the groove is arrested when it reaches the shuttle valve 218 and stop member 219. When this happens, the inner part 204 of the gear wheel is then locked for rotation with the outer part 202 and thus drive is communicated between the input and output shafts 3,1 When there is a change in the torque direction, or if the torque applied becomes less than the torque applied to the piston 212 by the oil pressure, oil can be pumped into the groove 206 to restore the piston 212 to its start position adjacent abutments 215. If the force in the new torque direction is sufficiently large, the drive member 208 will move around the groove 206 and engage the other piston 212 and drive it into the oil reservoir located in the other half of the groove 206. This causes the piston 216 to load the oil in a similar manner to that described above. Thus there is a similar damping action.

Thus damping takes place in both the clockwise and anti-clockwise directions.

The extent of movement of the pistons 212 can be varied to provide different damping effects, for example the movement can be along an arcuate path extending through ten to 180 degrees.

Also, in some variations it is only necessary to use a single piston, for example the free moving pistons 212 can be removed from the embodiment described above and the piston action can be provided by the drive member 208 alone moving within the groove 206. The size and shape of the drive member 208 can be adjusted to provide a tighter fit within the groove 206. In some embodiments, a plurality of piston elements that are similar to the drive member 208, in that they are fixed to the inner part 204 of the gear wheel can be included.

The exact number will depend on the damping effect that is suitable for a particular application. The damping mechanism 200 can include four piston chambers, two arranged to absorb load in a clockwise direction and two arranged to absorb load in the anti-clockwise direction and two drive members, wherein each drive member is arranged to load one of the pistons in the clockwise direction and one of the pistons in the anti-clockwise direction. Also, in addition to, or instead of, providing one or more undercut portions 214 the piston elements 208 can have at least one hole formed in its body to enable pressurised oil to pass through the piston element 208 when the oil is compressed by the piston element 208. The size and shape of the hole is an important factor in determining the damping effect.

The oil supply system can be a closed system or an open system. For example, an open system can use the gearbox lubricating oil and include a system for pumping it from the sump of the gearbox to the interior of each gear wheel including the lost motion mechanism.

Other types of lost motion mechanism can be used, for example, those disclosed in WO 2008/062 192, the contents of which are hereby incorporated by reference.

Selector and actuator mechanisms Each selector mechanism 29,31,33 is similar and is mounted on the output shaft 1 in a similar manner. The structure of the first gear selector mechanism 29 and the way that it selectively engages the first gear 8 and the second gear 10 will now be described. However the general structure and principles of operation are applicable to the second and third gear selector mechanisms 31,33 and their respective gear wheels.

The first and second gears 8,10 are mounted spaced apart on the output shaft I and are arranged such that the sides including the first and second dog groups 20 face each other. The gear selector mechanism 29 is arranged to engage the drive formations 20 located on the first gear 8 and the second gear 10.

The first gear selector mechanism 29 includes the first and second sets of engagement elements 35,36 and the actuator assembly 38.

The first and second sets of engagement elements 35,36 are mounted on the output shaft I between the first and second gears 8,10. The first set of engagement elements 35 comprises three engagement elements 28 that are evenly distributed about the output shaft 1 such that their bases face inwards, and the axes of the elements 28 are substantially parallel. The second set of engagement elements 36 comprises three engagement elements 30 which are similarly arranged about the output shaft 1 (see Figure 3).

The sets of engagement elements 3 5,36 are mounted on a sleeve 34 which is mounted on the output shaft 1 between the first and second gears 8,10 (see Figures la, ic and 3). The sets of engagement elements 35,36 are arranged to rotate with the output shaft 1 but are able to slide axially along the sleeve 34 and the output shaft 1 in response to a switching action of the actuator assembly 38. To facilitate this, the sleeve 34 includes six keyways 41 formed in its curved surface with each engagement element 28,30 having a complementary formation in its base. The keyways 41 can be arranged to be non-radially restraining or to be radially restraining. If the keyways 41 are radially restraining, they may have substantially T-shaped profiles such that the elements are radially and tangentially (but not axially) restrained within the keyways 41 (see Figure 3). Alternatively, the keyways 41 can have slotted or dovetailed profiles to radially restrain the elements, or any other suitable shape.

Preferably the engagement elements 28,30 are configured to be close to the output shaft I to prevent significant cantilever effects due to large radial distances of loaded areas thus reducing the potential for structural failure.

The arrangement of the element sets 35,36 is such that elements of a particular set are located in alternate keyways 41 and the element sets 35,36 can slide along the sleeve 34. The elements in each set are rigidly connected to each other by an annular connector member 100 and move as a unit. The connector member 100 also acts to radially restrain the engagement elements. Each element set 35,36 can move independently of the other. The connector member 100 has a groove 102 formed in its outer curved surface that extends fully around the circumference of the connector member. The elements 28 in the first set of engagement elements 35 are preferably integrally formed with its connector member 100, though this is not critical. The elements 28 are evenly distributed about the connector member 100. The second set of engagement elements 36 comprises three elements 30, which are held in a similar fixed arrangement by a second connector member 100. When there is relative movement between the first and second sets of elements 35,36, the connector member 100 of the first element set 35 moves over the second set of elements 36 and the connector member of the second element set 36 slides over the first set of elements 35.

Each element 28 in the first element set 35 has a first end 28a arranged to engage the first group of dogs 20 attached to the first gear 8 and a second end 28b arranged to engage the second group of dogs 20 on the second gear 12. The first and second ends 28a,28b typically have the same configuration but are opposite handed, for example the first end 28a is arranged to engage the first group of dogs 20 during deceleration (reverse torque direction) of the second gear 10 and the second end 28b is arranged to engage the second group of dogs 20 during acceleration (forward torque direction) of the second gear 10 (see Figure 4). Each element 30 in the second element set 36 is similarly arranged, except that the first end 30a is arranged to engage the first group of dogs 20 during acceleration of the first gear 8 and the second end 30b is arranged to engage the second group of dogs 20 during deceleration of the second gear 10.

When both the first and second sets of engagement elements 35,36 engage a gear wheel drive is transmitted between the input and output shafts 3,1 whether the gear is accelerating or decelerating.

The first and second ends 28a,30a,28b,30b of each element include an engagement face 43 for drivingly engaging the dogs 20, a ramp 45, an end face 42 and may include a shoulder 44 (see Figure 4). The engagement faces 43 are arranged to lock the gear for rotation with the shaft when the faces 43 engage the dogs 20. The faces 43 may be angled to complement the sides of the dogs 20a so that as the engagement elements 28,30 rotate into engagement, there is face-to-face contact to reduce wear. Each ramp 45 is arranged to prevent locking engagement of the gear with the shaft. Preferably each ramp 45 is helically formed and slopes away from the end face 42. The angle of inclination of the ramp 45 is such that the longitudinal distance between the edge of the ramp furthest from the end face 42 and the plane of the end face 42 is larger than the height of the dogs 20. This ensures that the transmission does not lock up when there is relative rotational movement between the engagement elements 28,30 and the dogs 20 that causes the ramp 45 to move towards engagement with the dogs 20. The dogs 20 do not crash into the sides of the engagement elements 28,30 but rather engage the ramps 45. As further relative rotational movement between the dogs 20 and the engagement elements 28,30 occurs, the dogs 20 slide across the ramps 45 and the helical surfaces of the ramps cause the engagement elements 28,30 to move axially along the output shaft 1 away from the dogs 20 so that the transmission does not lock up. Thus each set of engagement members can lock the first gear 8 for rotation with a shaft in a first torque direction but cannot lock it for rotation in the second torque direction and can lock the second gear 10 for rotation in the second torque direction but not in the first torque direction. When the first or second gear 8,10 is engaged by both sets of engagement members 35,36 it is locked for rotation in the acceleration and deceleration torque directions. The end faces 42 limit the axial movement of the engagement elements 28,30 by abutting the sides of the gear wheels The arrangement of the gear selector mechanism 29 is such that it inherently prevents lockup of the transmission occurring when selecting a new gear.

When the elements of the first and second sets 35,36 are interleaved, as in Figure 3, the engagement faces 43 of the first ends 28a of the first set of elements 35 are adjacent the engagement faces 43 of the first end 30a of the second set of elements 36. When the first and second sets of elements 3 5,36 are fully engaged with a gear, a dog 20 is located between each pair of adjacent engagement faces 43. The dimensions of the dogs 20 and the ends of the elements are preferably such that there is little movement of each dog between the engagement face 43 of the acceleration element and the engagement face 43 of the deceleration element when the gear moves from acceleration to deceleration, or vice versa, to ensure that there is little or no backlash in the gear.

The actuator assembly 38 includes first and second actuators 46,64 and first and second actuator members 48,58. The first and second actuators 46,64 are force generator actuators and preferably part of an electrical system for example, an electro-mechanical system or an electro-hydraulic system. The first and second actuator members 48,58 are mechanical drive members that transmit force from the first and second actuators to 46,64 to the sets of engagement members 35,36 and are preferably in the form of independently controllable forks. Accordingly, the first set of engagement elements 35 is driven by the first actuator 46 via the first fork 48 and the second set of engagement elements 36 is driven by the second actuator 64 via the second fork 5 8. Thus the first and second sets of engagement elements 35,36 move totally independently of each other. Alternatively, the first and second sets of engagement members 35,36 can be arranged to have some interdependence such as the arrangement of WO 2004/099654, which only has a single actuator for controlling actuation of both sets of engagement elements.

Each fork 48,58 is arranged to extend approximately 180 degrees around the groove 102 of its respective set of engagement elements and includes a semi-annular part that is located within the groove 102. Each set of engagement elements 3 5,36 can rotate relative to its respective fork 48,58 and is caused to move axially along the input shaft 3 by the actuator member 48,58 applying a force to the connector member 100.

The actuator assembly 38 can optionally include resilient devices, such as helical springs (not shown). The springs are arranged to bias the first and second sets of engagement elements 35,36 to move in an axial direction when they are in driving engagement with a gear wheel and are unable to move. For example, the forks 48,5 8 can be suspended at their remote ends in a cradle and can be arranged to move a limited amount with respect to the cradle 68 against the action of the springs 66.

Operation of the first and second actuators 46,64, and hence movement of the first and second sets of engagement elements is controlled by the transmission control unit 90. When transmission position sensors 96 are used, they are arranged for determining the operational conditions of selector mechanisms 29,31,33 in the transmission. Typically the position sensors 96 monitor the positions of the actuator members 48,58 and hence the positions of the sets of engagement elements to determine whether they are engaged with a gear wheel or not.

However, they can be arranged to monitor the positions of the sets of engagement elements directly in some applications to obtain the same effect. Typically there are the same number of position sensors 96 as there are sets of engagement elements or actuator members 48,58. In this case, there are two position sensors per selector mechanism 29,31,33, giving six in total.

Conveniently the position sensors 96 can be included in the actuators 46,64 to provide a compact arrangement. The position sensors 96 can be of any suitable type such as hall effect type sensors.

If position sensors 96 are not used, the positions of the sets of engagement elements 35,36 are calculated by the transmission control unit 90 from the known geometry of the transmission and the controlled actuation of the sets of engagement elements 35,36.

The transmission control unit 90 is an electronic logic control system driven by software that is arranged to control operation of the first and second actuators 48,64 and hence the first and second sets of engagement elements 35,36. It is the sequence programming that enables the transmission control unit 90 to automatically control the transmission to prevent conflict shifts occurring. Being able to control the actuation of the first and second sets of engagement elements 35,36 totally independently by use of first and second actuators 46,64 and the first and second actuator members has the advantage that the magnitude and the timing of application of the biasing force applied by each actuator can be independently and accurately controlled. This means that even at low rotational gear speeds the engagement elements sets 35,36 do not accidently disengage from the engaged gear wheel and thus no loss of drive is experienced.

The transmission control unit 90 is programmed with a control algorithm that is arranged to select first gear when the vehicle is stationary in a manner that ensures that the engagement elements enter into the windows between dogs 20 and do not engage the planar surface of the dogs which would prevent gear selection, and can lock the transmission from further operation. The transmission control unit 90 avoids this scenario by ensuring that when first gear (the first gear wheel 8) is selected when the vehicle is stationary there is relative rotational movement between the first gear wheel 8 and the second set of engagement elements 36 when engagement takes place. Thus even if the second set of engagement elements 36 initially engage the planar surfaces of the dogs 20 the relative rotational movement ensures that subsequently the engagement elements move into the windows between the dogs 20 to properly select the first gear wheel 8. This is achieved for a stationary vehicle, by moving the selector assemblies 29,31,33 to the neutral position and then closing the clutch 86 to rotate the gear wheels 8,10,12,14,16 mounted on the output shaft 1. The transmission control unit 90 then actuates the first selector mechanism 29 to select the first gear wheel 8 with the second set of engagement elements 36 when the relative rotation between the first gear wheel 8 and the second set of engagement elements is in a predetermined range. The transmission system can include a sensor for detecting the relative rotation or the transmission control unit 90 can be programmed to select the first gear after a predetermined amount of time has elapsed, which is calculated from a knowledge of the transmission arrangement and the current operating conditions, e.g. the transmission system can include a temperature sensor 87 to measure the temperature of the transmission lubrication fluid and the transmission control unit 90 can use the measured values to determine the frictional effects of the lubricating fluid and hence determine the period required for the lubricating fluid to slow the gear wheel to an appropriate speed for the selector mechanism to engage the gear wheel.

The transmission control unit 90 is also programmed to complete the selection of the first gear wheel 8 by engaging it with the first set of engagement elements 35 of the first gear selector while there is relative rotational movement between the first and second parts 202,204 of the first gear wheel 8. This reduces the amount of backlash in the system at the point when the relative rotational movement between the first and second parts 202,204 ceases and there is a recoil effect for the second set of engagement elements 36. The reduced backlash significantly reduces the loudness of the sound generated by the recoil effect such that it is imperceptible by the driver.

Optionally, the transmission control unit 90 can have two layers of control: a first layer for controlling operation of the selector mechanisms 29,31,33 and a second level that monitors operation of the first level of control to ensure that the first layer of control is operating correctly.

The transmission 88 can be fully automatic, that is gear selections are made by the transmission control unit 90 when the engine control unit 82 detects predetermined operational conditions, for example when the engine 80 reaches a particular speed in a particular gear. Alternatively, gear selection can be made by the user of the drive system by initiating the gear selection input device 94, for example a gear lever (manual) or switches located adjacent the steering wheel (semi-automatic). The transmission 88 can be arranged such that it is possible to select between the automatic and manual modes.

Operation of a single gear selector mechanism The operation of the first gear selector mechanism 29 will now be described with reference to Figures 5a-5f which for clarity illustrate diagrammatically the movement of the first and second sets of engagement element 35,36 by the relative positions of only one element from each set, and Figure 6.

Figure 5a shows the first and second element sets 35,36 in a neutral position, that is, neither element set is engaged with a gear wheel. This is the typical condition at engine 80 start-up, or when the vehicle has come to a temporary halt such as at traffic lights or a stop sign and the driver selects neutral while waiting. At this time, the engine 80 is at, or around, its idling speed, the output shaft us not rotating and the transmission control unit 90 holds the clutch open.

Figure 5b shows the first and second element sets moving into engagement with the first gear 8 under the action of the first and second actuators 46,64 in response to a gearshift request from the input device 94. When a user or the transmission control unit 90 calls for first gear 8, the transmission control unit 90 first checks whether the selector mechanisms 29,32,33 are in neutral by receiving signals from the positions sensors 96 or from other inputs and data stored in its memory. If the selector mechanisms are not in the neutral condition, the transmission control unit 90 actuates them to move to the neutral positions. The transmission control unit then closes the clutch 86 such that drive is transmitted from the engine 80 to the input shaft 3 and from the input shaft 3 to the lay shaft 6 via the transfer gear 18-18'. Since the lay shaft gears 8',10',12',14',16' are fixed for rotation with the lay shaft 6 they rotate therewith. The gears 8,10,12,14,16 that are mounted on the output shaft 1 are constantly in mesh with the gears 8',l0',12',14',16' mounted on the lay shaft 6 and therefore they are driven to rotate about the output shaft I. However, since all of the selector mechanisms 29,31,33 are in the neutral condition, no torque is applied to the output shaft I by rotation of the gears 8,10,12,14,16 mounted thereon.

Thus by connecting the transmission system to the engine 80, the transmission control unit 90 has provided a rotational speed difference between each of the gears 8,10,12,14,16 mounted on the output shaft 1 and the selector mechanisms 29,31,33, without transmitting power to the wheels. This prevents a transmission failure mode occurring. If there is no relative movement between the first gear 8 and the second set of engagement elements 36 of the first selector mechanism 29 and the gear 8 is in a rotational orientation such that when the second set of engagement elements 36 move along the output shaft I into engagement with the gear 8 their end faces 42 engage with the planar surface of the dogs 20 proper engagement is prevented.

This is because the second set of engagement elements 36 are unable to move into the windows between the dogs 20 and therefore cannot drive the gear 8. The transmission is stuck in a non-operational condition.

Closing the clutch 86 with the selector mechanisms 29,31,33 in the neutral position to cause first gear 8 to rotate relative to the first selector mechanism 29 overcomes this failure mode.

Closing the clutch 86 brings the input shaft 1 up to, or around, the idling speed of the engine 80. The transmission control unit 90 then opens the clutch 86 and monitors the rotational speed of the output side of the clutch with speed sensor 93. From this speed sensor 93 and knowledge of the arrangement of the gear ratios, the transmission control unit 90 knows the speed of the first gear 8. When the clutch is open, the speed of the first gear 8 decays due to friction in the transmission system. When the speed reaches a predetermined value the transmission control unit 90 is arranged to activate the first selector mechanism 29 to engage the first gear 8 with the second set of engagement elements 36. Engaging the dogs 20 on the second part of the gear 204 acts to brake the rotation of the first gear 8 since the output shaft 1 is connected to the vehicle wheels and has a significant retarding inertia however there is relative rotation between the first and second parts of the gear 202,204 in the damping mechanism 200, which effectively provides some lost motion between the output shaft 1 and the first gear 8 enabling there to be some limited relative rotation between them. The damping mechanism 200 also absorbs a significant proportion of the energy in any torque spikes generated by the engagement. This is because a significant proportion of the energy in the torque spike is used to move the drive member 208 to drive the piston 212 against the resistance of the oil in the groove 206, thereby causing damped relative rotational movement between the first and second parts of the gear 202,204. This significantly reduces the amount of noise generated.

The transmission control unit 90 then moves the first set of engagement members 35 into engagement with the first gear 8. The transmission control unit 90 does this while there is still relative rotational movement between the first and second parts of the gear 202,204. The correct rotational speed of the first gear 8 for engagement will be determined by the application however it should be sufficiently high to ensure that the second part 204 of the first gear 8 continues to rotate until at least the shift is completed when the gear 8 is engaged by the first set of engagement elements 35. This is because the output shaft 1 is stationary and is connected to the car wheels and thus has sufficient inertia to stop the input and lay shafts 3,6 from rotating after the first and second parts 202,204 of the gear 8 have reached the limit of their relative rotation. When this happens, there is some rebound in the system. If the first set of engagement elements 35 has not engaged the gear, thereby completing the shift, there is backlash of around 80 to 100 degrees, which leads to a large impact that is noticeable by the driver. However, if the shift is completed, the backlash is typically less than 5 degrees. This reduces the rebound affect thereby producing a quieter gear selection.

Typically the speed of the gear 8 to enable the shift to be fully completed before the reboundl occurs is in the range 20 to 500 rpm, and preferably is in the range 50 to 200 rpm, for most applications.

The clutch 86 remains open until the driver activates the throttle, for example by pressing down on the accelerator pedal. When this occurs, the transmission control unit 90 closes the clutch to enable the vehicle to pull away.

Instead of using the sensor 93 to detect the speed of the output side of the clutch in order to determine when to select the first gear 8, the transmission control unit 90 can be arranged to close the clutch 86 to bring the input shaft 3 up to the engine 80 idling speed and then to select the first gear 8 after a predetermined amount of time has lapsed. The time delay will be dependent upon the transmission layout, which determines how much friction there is in the system, which in turn determines how quickly the first gear 8 slows to the engagement speed.

This will of course be affected by parameters that vary according to the operation of the vehicle, such as oil temperature. In this arrangement the transmission system can include a temperature sensor 87 for monitoring the temperature of the oil in the gearbox and the transmission control unit 90 is arranged to determine the period of delay in accordance with temperature measurements received.

In the situation where the vehicle slows to a temporary stop, for example at traffic lights or a stop sign, and is in gear, the transmission control unit 90 automatically opens the clutch to prevent the engine 80 from stalling as the vehicle speed approaches zero. If the driver then applies the throttle the transmission control unit 90 automatically closes the clutch.

Alternatively, if the driver wants to select first gear 8 (or another gear) after coming to a complete stop the transmission control unit 90 initially moves all of the selector mechanism 29,31,33 to the neutral position and then closes the clutch 86 in order to provide the required relative rotational movement when selecting first gear (or another new gear) and the shift takes place as described above.

Figure 5c shows the condition when the first gear 8 is fully engaged, that is, the elements 28,30 are interleaved with the first group of dogs 20. The first and second actuators 46,64 are activated such that the actuator members 48,58 maintain the first and second element sets 35,36 in engagement with the first gear wheel 13. Accordingly, drive is transferred through the first gear 8 to the output shaft 1 via the first element set 35 when decelerating and via the second element set 36 when accelerating.

Whilst accelerating using the first gear 8 (first gear 8 rotating in the direction of arrow B in Figure Sc), the engagement faces 43 of the elements of the first element set 35 are not loaded, whilst the engagement faces 43 of the elements of the second element set 36 are loaded. When a user, or an engine control unit 82 wishes to engage the second gear 10 an input signal is sent from the input device 94 or the engine control unit 82 to the transmission control unit 90. The transmission control unit 90 sends a signal to the clutch actuator 92 to reduce the clutch clamp load until the transmission control unit 90 detects relative rotational movement between the input and output sides of the clutch 86, based on signals received from the clutch sensors 93.

For example, the transmission control unit 90 may detect around a 1% difference in rotational speeds. The transmission control unit 90 also actuates the first actuator 46 to drive the first actuator member 48, which causes the elements 28 of the first element set 35 to slide axially along the keyways 41 in the sleeve 34 thereby disengaging the first element set 35 from the first gear 8 (see Figure Sd).

The second actuator 64 is activated to move the second actuator member 58 and hence the second element set 36 towards the second gear 10. However, because the second element set 36 is loaded, i.e. is driving the first gear 8, it cannot be disengaged from the first gear 8, and the second element set 36 remains stationary, with the second actuator 64 and when used at least one helical spring 66 biasing it towards the first gear wheel 12.

When the first element set 35 slides axially along the output shaft 1, the engagement faces 43 engage the second group of dogs 20 (see Figure 5e). The torque spike caused by the engagement is significantly reduced by relative rotation between the first and second parts of the gear 202,204 in the damping mechanism 200. This is because a significant proportion of the energy in the torque spike is used to move the drive member 208 to drive the piston 212 against the resistance of the oil in the groove 206, thereby causing damped relative rotational movement between the first and second parts of the gear 202,204. This significantly reduces the amount of noise generated. The engagement elements 28 are then driven by the second gear 10 in the direction of Arrow C in Figure 5e and drive is transmitted between the output shaft 1 and the lay shaft 6 via the second gear train 10,10'. As this occurs, the second element set 36 ceases to be loaded, and is free to disengage from the first group of dogs 20. Since the second element set 36 is biased by the second actuator 64 (and the helical spring 66 if used) it slides axially along the keyways 41 in the sleeve 34 thereby completing the disengagement of the first gear 8 from the output shaft 1. The second element set 36 slides along the keyways 41 until it engages the second gear 10, thereby completing engagement of the second gear 10 with the output shaft 1 (see Figure Sf).

The transmission control unit 90 restores clutch clamp load using the clutch actuator 92 and returns control of the engine 80 to the driver. This is done smoothly so that it is imperceptible to the driver.

This method for selecting gear trains substantially eliminates torque interruption since the second gear 10 is engaged before the first gear 8 is disengaged, thus momentarily, the first and second gears 8,10 are simultaneously engaged and locked for rotation with the output shaft 1, until the newly engaged gear overdrives the original gear. Thus gearshifis are instantaneous since there is no loss of drive when changing gear because a new gear is selected while the current gear is still engaged.

When a gear is engaged by both the first and second element sets 35,36 it is possible to accelerate or decelerate with very little backlash occurring when switching between the two conditions. Backlash is the lost motion experienced when the dog moves from the engagement face 43 of the acceleration element to the engagement face 43 of the deceleration element when moving from acceleration to deceleration, or vice versa. A conventional dog-type transmission system has approximately 30 degrees of backlash. A typical transmission system for a car in accordance with the current invention has backlash of less than five degrees.

Backlash is reduced by minimising the clearance required between an engagement member and a dog during a gearshift: that is, the clearance between the dog and the following engagement member (see measurement A' in Figure 5b). The clearance between the dog and the following engagement member is in the range 0.5mm -0.03mm and is typically less than 0.2mm. Backlash is also a function of the retention angle, that is, the angle of the engagement face 43, which is the same as the angle of the undercut on the engagement face of the dog 20a.

The retention angle influences whether there is relative movement between the dog and the engagement face 43. The smaller the retention angle, the less backlash that is experienced.

The retention angle is typically between 0 and 15 degrees.

Transition from the second gear 10 to the first gear 8 whilst decelerating is achieved by a similar process.

Whilst decelerating in the second gear 10 the engagement surfaces 43 of the elements of the first element set 35 are not loaded, whilst the engagement surfaces 43 of the elements of the second element set 36 are loaded. When a user, or an engine control unit 82 wants to engage the first gear train 12 a signal is sent from the input device 94 or the engine control unit 82 to the transmission control unit 90. The transmission control unit sends a signal to the clutch actuator 92 to reduce the clutch clamp load until the transmission control unit 90 detects relative rotational movement between the input and output sides of the clutch based on signals received from the clutch sensors 93. The transmission control unit 90 then synchronises the engine speed via the engine control unit 82 to the new gear wheel to be selected. The transmission control unit 90 actuates the first actuator 46 to move the first actuator member 48 axially, causing the first element set 35 to slide axially in the keyways 41 along the input shaft 3 in the direction of the first gear 8, thereby disengaging the first element set 35 from the first gear wheel 12.

The transmission control system activates the second actuator 64 however since the second element set 36 is loaded, i.e. it is drivingly engaged with the dogs 20 on the third gear wheel 17, it remains stationary but is urged towards the first gear wheel 13.

As the first element set 35 slides axially in the keyways 41 and engages the dogs 20 on the first gear 8, it is driven by the first gear 8 such that energy is transmitted between the output shaft I and the lay shaft 6, via the first gear train 8-8'. The torque spike caused by the engagement is minimised due to the combination of the speed synchronisation step, and the relative rotational movement between the first and second parts of the gear 202,204 in the damping mechanism 200. This is because a significant proportion of the energy in the torque spike is used to move the drive member 208 to drive the piston 212 against the resistance of the oil in the groove 206, thereby causing damped relative rotational movement between the first and second parts of the gear 202,204. This significantly reduces the amount of noise generated. As this occurs, the second element set 36 ceases to be loaded and biasing of the second actuator 64 (and the helical spring(s) 66 if used) causes it to slide axially within the keyways 41 along the input shaft 3 towards the first gear 8, thereby completing disengagement of the second gear 10. The second element set 36 continues to slide within the keyways 41 along the output shaft 1 until it engages the first gear 8, thereby completing engagement of the first gear 8 with the output shaft 1.

The transmission control unit 90 restores clutch clamp load using the clutch actuator 92 and control of the engine 80 is returned to the driver.

Kick-down shifts, that is a gearshift from a higher gear train to a lower gear train but where acceleration takes place, for example when a vehicle is travelling up a hill and the driver selects a lower gear to accelerate up the hill, require a brief torque interruption to allow disengagement of the driving element set. For example, when accelerating in first gear 8, the first gear 8 is fully engaged by the first and second sets of engagement elements 3 5,36 and the first element set 35 drivingly engages the dogs 20. When a kick-down shift is requested by the user via the input device 94 or the engine control unit 82, the transmission control unit 90 reduces the clutch clamp load using the clutch actuator 92 until controlled relative rotational movement between the input and output sides of the clutch is detected by the transmission control unit 90 via the clutch sensor 93 readings. The engine speed is then adjusted to synchronise with the new gear speed (first gear 8 in this case), which typically involves increasing the engine speed. The transmission control unit 90 is able to synchronise the speed since it is programmed with information relating to the gear ratios for each gear train and can determine the currently engaged gear and the new gear to be selected. Synchronising the engine speed in this manner has a smoothing effect when engaging the new gear and prevents the vehicle from lurching when the gear is selected. The clutch clamp load is then further reduced as is the throttle in order to maintain the new ratio speed. The loaded 35 and the unloaded element sets 36 are then disengaged from the third gear wheel 17 by actuating the first and second actuators 46,64 such that loaded set disengages the second gear 10 prior to the unloaded set 36 engaging the first gear 8. The torque spike caused by the engagement is minimised due to the speed synchronisation step. However if a torque spike is generated its effect is mitigated by further relative rotation of the first and second parts of the gear 202,204 in the damping mechanism 200. This significantly reduces the amount of noise generated. In practice, it is preferable to reduce the torque transmittable by the clutch to zero, or near zero, or at least sufficiently low such that the actuators 46,64 are able to move the sets of engagement before disengaging the loaded set of engagement elements 35. Although the shift is not entirely instantaneous, it is very quick and the power interruption is lower than previous methods and may not even be noticed by the driver. The first element set 35 is then moved across into engagement with the first gear 8 to complete the kick-down shift. After which, the torque is reinstated by the engine control unit 82, the clutch clamp load is restored by the clutch actuator 92 and control of the engine 80 is returned to the user.

When the unloaded second element set 36 is disengaged from the second gear 10, it can alternatively be held in the neutral position until after the loaded first element set 35 is disengaged from the second gear 10. The second element set 36 can then be moved into engagement with the first gear 8, after which the torque and clutch are reinstated. This shift is not instantaneous.

Figure 7 shows a second transmission layout to which the method of selecting first gear is applicable. The transmission system includes an input shaft 303, an output shaft 301, first to sixth gear trains 308-308',3 10-3 10',3 12-3 12',3 14-314',3 16-3 16',3 18-318' and first to third selector assemblies 329,331,333 for selectively engaging the gear trains to create torque paths between the input and output shafts 303,301.

The selector mechanisms 329,331,333 and gears are similar to those of the first embodiment.

The transmission layout of the second embodiment is as follows: the gears 308,310,312,314,316,318 are mounted on the output shaft 303 on bearings and arranged to rotate relative to the output shaft 301. The corresponding gears 308',310',312',314',316',318' are fixed for rotation with the input shaft 301 and are arranged to be in constant mesh with their respective output shaft gears 308,310,312,314,316,318.

The first selector mechanism 329 is mounted on the output shaft 301 between the first and second gears 308,310 and is arranged to selectively lock them for rotation with the output shaft 301. The second selector mechanism 331 is mounted on the output shaft 301 between the third and fourth gears 312,314 and is arranged to selectively lock them for rotation with the output shaft 301. The third selector mechanism 333 is mounted on the output shaft 301 between the fifth and sixth gears 316,318 and is arranged to selectively lock them for rotation with the output shaft 301.

The method of selecting first gear described in relation to the first embodiment is applicable to this embodiment.

Noise Vibration and Harshness improvements can be achieved through clutch modulation during shift events.

The method of selecting first gear is also applicable to HGV multi-path transmission systems for example those that include a splitter gear arrangement and a range changing device such as that shown in Figure 8. The transmission system includes an input shaft 403, an output shaft 401 and a countershaft 406. Drive is transferred between the various drive shafts 401,403,406 by a set of six mainshaft gears 408,410,412,414,416,418 carried by the input and output shafts 403,401 and six countershaft gears 408',410',412',414',416',418' carried by the countershaft 406.

The six countershaft gears 408',4 1 0',4 1 2',4 1 4',4 1 6',4 18' are attached directly to the countershaft 406 for rotation therewith. As seen from right to left in figure Ia, these countershaft gears are a reverse gear 408', crawler gear 410', first gear 412', second gear 414', splitter high/third gear 416' and splitter low gear 418'. The mainshaft gears 408,410,412,414,416,418 carried by the input and output shafts 403,401 are mounted on bearings (not shown) so as to be rotatable relative thereto. Five of these mainshaft gears are rotatably mounted on the output shaft 1: these are from right to left a reverse gear 408 (R), crawler gear 410 (C), first gear 412 (1st), second gear 414 (2') and splitter high/third gear 416 (HI3''). A mainshaft splitter low gear 418 (L) is rotatably mounted on the input shaft 403. The transmission system also includes a reverse idler gear 419 that transfers drive from the mainshaft reverse gear 408 to the countershaft reverse gear 408', and a conventional epicyclic range changer mechanism 422.

As previously mentioned, the mainshaft gears 408,410,412,414,416,418 are rotatably mounted on the respective input/output shafts 403,401. To transfer drive from the respective shaft to the primary gear, each gear has associated with it a selector mechanism 429,431,433.

Each of these selector mechanisms may, for example, be of the type described in one or more of described in W02004/099654, W02005/005868, W02005/005869, W02005/024261 and W02005/026570, the contents of which are incorporated by reference herein. However, the selector mechanisms 429,431,433 are preferably arranged as described above in relation to the first embodiment.

The transmission system layout uses a multi-gear multi-path layout, which uses discrete gear ratios and instantaneous selector mechanisms 429,431,433 to facilitate instantaneous torque handover gear shifts for a variety of different ratios. In the example given the layout is a twelve plus two transmission with twelve main gear ratios plus one crawler ratio and one reverse gear ratio. It will be apparent to the skilled person that additional (or less) gear trains can be used in the transmission system to make it suitable for different vehicles.

The first selector mechanism 49 includes first and second sets of engagement elements 435,436 for selectively locking respectively the crawler gear 410 and first gear 412 to the output shaft 201. Each set of engagement members 435,436 is connected to an actuator assembly 438, which is described below. By actuating the sets of engagement members 435,436 it is possible to connect the crawler gear 410 andlor first gear 412 to the output shaft 401 to transfer drive between that gear and the shaft 401. Moving the actuator assembly 438 engages one gear and disengages the other without any appreciable interruption in the torque transferred through the transmission.

The second selector mechanism 431 is similar to the first selector mechanism 429 and includes a first and second sets of engagement members 435,436 for selectively locking respectively the second gear 414 and third/splitter high gear 416 for rotation with the output shaft 401 and an actuator assembly 438. By activating the actuator assembly 438 it is possible to connect the second gear 414 and/or third/splitter high gear 416 to the output shaft 401 to transfer drive between that gear and the shaft.

The third selector mechanism 433 is again similar to the first selector mechanism 429 and includes first and second sets of engagement members 435,436 for selectively locking respectively the third/splitter high gear 416 and the splitter low gear 418 to the input shaft 403 and an actuator assembly 438. By activating the actuator assembly 438 it is possible to connect the third/splitter high gear 416 and/or the splitter low gear 418 to the input shaft 403 to transfer drive between that gear and the shaft. The third/splitter high gear 416, the splitter low gear 418, their complementary countershaft gears 416',42W, and the third selector mechanism 433, together comprise an input splitter 460.

In order to achieve the different ratios an input splitter 460 is used on the input side of the transmission and a range changer 422 is used on the output shaft of the transmission. It is feasible to incorporate a neutral position between the splitter ratios which will aid engine synchronisation during certain shifts.

Power enters the transmission through the input shaft 403 and is transferred to the countershaft 406 through either one of two gear ratios (split low and split high) provided by the input splitter 460. The first selector mechanism 429 with no neutral position transmits the input power to the countershaft 406 through either the split low gear ratio or the split high gear ratio.

The mainshaft gears 412,414,416 are then selectively locked for rotation with the output shaft 201 and power is transferred to the output shaft 401 through the selected ratio, according to the operational conditions of the first, second and third selector mechanisms 429, 431,433.

The high splitter gear 416 is also third gear. This means that when third/split high is selected by the second and third selector mechanisms 431,433 power travels directly from the input shaft 403 to the output shaft I and is not transferred through the countershaft 406.

The range changer 422 provides a two ratio final drive for the transmission. The torque paths for the various selected ratios remain the same once the range changer 422 has been changed from its initial low ratio to its alternative high ratio.

This layout is further described in PCT/GBO8/000422, the transmission layout of which is hereby incorporated by reference.

It will be appreciated by the skilled person that the invention is not to be considered as strictly limited to the above embodiments and that modifications can be made that fall within the scope of the invention, for example the number of gear trains included and the specific type of selector assemblies used. The rotatable gears 8,10,12,14,16 can be mounted on the lay shaft, or input shaft together with the selector mechanisms. In some layouts it is possible to have selector mechanisms on more than one shaft together with rotatably mounted gears.

The transmission can be of the type that does not include a layshaft, for example, it may only include an input shaft and an output shaft. In this type of transmission the rotatably mounted gears and their respective selector mechanisms can be mounted on the output shaft and/or the input shaft.

The damping mechanism 200 can be included in each of the selector mechanisms 29,31,33 as an alternative to each of the gear wheels, or if additional damping is required, in addition to the gear wheels.

Claims

Claims I. A transmission system including first and second shafts, means for communicating drive between the first and second shafts including a first gear train having a first gear element rotatably mounted on one of the shafts and a second gear element mounted on the other shaft, a selector assembly including first and second sets of engagement members that are independently moveable into and out of engagement with the first gear element for selectively locking the first gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the first gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the first gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the first gear element for rotation with the shaft in the clockwise and anti-clockwise directions, and a control system arranged to control operation of the selector assembly and to send control signals to a drive system, wherein in response to a request to select the first gear train in a condition when at least one of the first gear element and the sets of engagement members is not rotating, the control system is arranged to actuate the drive system to provide relative rotational movement between first gear element and the sets of engagement members prior to actuating the selector assembly to engage the first gear element.
2. A transmission system according to claim 1, wherein the control system includes means for determining whether or not there is relative rotational movement between the first gear element and the sets of engagement elements.
3. A transmission system according to claim 1 or 2, wherein the control system includes means for determining whether or not there is rotational movement of a transmission output component.
4. A transmission system according to any one of the preceding claims, wherein the drive system is arranged to rotate either the first or second shaft and the control system is arranged to move the selector assembly to a neutral position before rotating the shaft.
5. A transmission system according to any one of the preceding claims, wherein the control system is arranged to send control signals to a clutch device in the drive system to selectively open and close the clutch device and thereby control the application of drive to the first gear element or the sets of engagement members.
6. A transmission system according to any one of the preceding claims, wherein the control system is arranged to actuate the selector assembly to engage the first gear element within a predetermined range of relative rotational speed between the first gear element and the first and second sets of engagement elements. Preferably the relative rotational speed is in the range of 20 to 500 rpm, more preferably still in the range 50 to 200 rpm.
7. A transmission system according to any one of the preceding claims, including a speed sensor for measuring the speed of rotation of the first gear element or a component connected directly or indirectly thereto, and wherein the control system is arranged to receive inputs from the speed sensor and to determine when to select the first gear element according to the inputs received.
8. A transmission system according to any one of the preceding claims, including a temperature sensor for measuring the operating temperature of the transmission lubricating fluid.
9. A transmission system according to any one of the preceding claims, wherein the control system is arranged to calculate a time delay and to actuate the gear selector assembly to select the first gear element after the period of time has lapsed.
10. A transmission system according to claim 9 when dependent on claim 8, wherein the control system is arranged to determine the time delay according to values received from the temperature sensor.
11. A transmission system according to any one of the preceding claims, including a damping device for damping locking engagements between the first gear element and its shaft.
12. A transmission system according to claim 11, wherein at least one of the first gear element and the gear selector assembly includes the damping device.
13. A transmission system according to claim 11 or 12, wherein the damping device is arranged to allow lost motion between the first shaft and at least one of the first gear element and the selector assembly after the selector assembly engages the first gear element.
14. A transmission system according to claim 13, wherein the damping device includes first and second parts that are arranged to rotate relative to each other.
15. A transmission system according to any one of claims 11 to 14, wherein the damping device is a fluid damping device, and preferably a hydraulic damping device.
16. A transmission system according to claim 14, wherein the control system is arranged to actuate the selector assembly such that the first and second sets of engagement members engage the first gear element before the relative rotational movement of the first and second parts of the damping device ceases.
17. A transmission system according to any one of the preceding claims, wherein the first shaft is an output shaft and the second shaft is an input shaft.
18. A transmission system according to any one of claims 1 to 16, including a third shaft, wherein the first shaft is an output shaft, the second shaft is a lay shaft and the third shaft is an input shaft, wherein the transmission system includes means for transferring drive between the input shaft and the lay shaft.
19. A transmission system according to any one of the preceding claims, including a second gear train having a third gear element rotatably mounted on the same shaft as the first gear element a fourth gear element mounted on the same shaft as the second gear element, wherein the first and second sets of engagement members are arranged to independently move into and out of engagement with the third gear element thereby enabling the gear selector assembly to selectively lock the third gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the third gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the third gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the third gear element for rotation with the shaft in the clockwise and anti-clockwise directions.
20. A transmission system according to claim 19, wherein the selector assembly is arranged such that when one of the first and third gear elements is engaged by the selector assembly the other gear element can be selected before disengaging the current gear element for at least some of the operational modes.
21. A transmission system according to claim 20, wherein the selector assembly is arranged such that when one of the first and second gear elements is engaged by the selector assembly the other gear element can be selected before disengaging the current gear element for the following operational modes: locking the gear elements for rotation with the first shaft in the clockwise direction and not locking in the anti-clockwise direction; and locking the gear elements for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction.
22. A transmission according to any one of the preceding claims, wherein the selector assembly is arranged to select the following operational mode with respect to the first and third gear elements: not locking the gear elements for rotation with the shaft in the clockwise and anti-clockwise directions. This provides a neutral condition.
23. A transmission system according to any one of the preceding claims, including a third gear train having a fifth gear element rotatably mounted on one of the first and second shafts and a sixth gear element mounted on the other of the first and second shafts and a second gear selector assembly including first and second sets of engagement members that are independently moveable into and out of engagement with the fifth gear element for selectively locking the fifth gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the fifth gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the fifth gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the fifth gear element for rotation with the shaft in the clockwise and anti-clockwise directions.
24. A transmission system according to any one of the preceding claims, wherein the gear selector assembly is arranged such that when a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition.
25. A transmission system according to claim 24, wherein the actuator system is arranged to move the unloaded set of engagement members into driving engagement with the unengaged gear element to effect a gear change.
26. A transmission system according to any one of the preceding claims, wherein the or each selector assembly is arranged such that when a braking force is transmitted the first set of engagement members drivingly engages the engaged gear wheel, and the second set of engagement members is in an unloaded condition, and when a driving force is transmitted the second set of engagement members drivingly engages the engaged gear wheel, and the first set of engagement members is then in an unloaded condition.
27. A transmission system according to any one of the preceding claims, wherein the or each selector assembly includes an actuator system having a first actuator device for actuating the first set of engagement members and a second actuator device for actuating the second set of engagement members independently of the first actuator device.
28. A transmission system according to any one of the preceding claims, wherein the or each rotatably mounted gear element includes drive formations that can be engaged by one of the selector assemblies.
29. A transmission system including first and second shafts, a first gear train for communicating drive between the first and second shafts having a first gear element rotatably mounted on the first shaft, a second gear train for communicating drive between the first and second shafts having a second gear element rotatably mounted on the first shaft, wherein the first and second gear elements each having drive formations formed thereon, a selector assembly for selectively transmitting torque between the first shaft and the first gear element and between the first shaft and the second gear element, wherein the selector assembly includes an actuator assembly and first and second sets of engagement members that are moveable into and out of engagement with the first and second gear elements independently of each other, said selector assembly being arranged such that when one of the gear elements is selected by the first and second sets of engagement members and a driving force is transmitted, one of the first and second sets of engagement members drivingly engages the engaged gear element, and the other set of engagement members is then in an unloaded condition, and a control system arranged to control operation of the selector assembly and to send control signals to a drive system, wherein in response to a request to select the first gear train in a condition when at least one of the first gear element and the sets of engagement members is not rotating, said control system is arranged to actuate the drive system to provide relative rotational movement between first gear element and the sets of engagement members prior to actuating the selector assembly to engage the first gear element.
30. A drive line including a drive source and a clutch device and a transmission system according to any one of the preceding claims.
31. A vehicle including a transmission system or drive line according to any one of the preceding claims, wherein the control system includes means for determining when the vehicle is stationary.
32. A method of selecting a gear train in a transmission system, said transmission system including first and second shafts, means for communicating drive between the first and second shafts including a first gear train having a first gear element rotatably mounted on one of the shafts and a second gear element mounted on the other shaft, a selector assembly including first and second sets of engagement members that are independently moveable into and out of engagement with the first gear element for selectively locking the first gear element for rotation with its shaft, said selection being made from operational modes that include the following modes: locking the first gear element for rotation with the shaft in the clockwise direction and not locking in the anti-clockwise direction; locking the first gear element for rotation with the shaft in the anti-clockwise direction and not locking in the clockwise direction; and locking the first gear element for rotation with the shaft in the clockwise and anti-clockwise directions, and a control system arranged to control operation of the selector assembly and to send control signals to a drive system, said method including, in response to a request to select the first gear train in a condition when at least one of the first gear element and the sets of engagement elements is not rotating, the control system actuating the drive system to generate relative rotational movement between the sets of engagement members and the first gear element prior to engaging the first gear element.
33. A method according to claim 32, including determining the operational positions of the first and second sets of engagement members.
34. A method according to claim 32 or 33, including moving the first and second sets of engagement members to a neutral position prior to actuating the drive system to generate relative rotational movement between the first and second sets of engagement members.
35. A method according to any one of claims 32 to 34, including determining whether or not there is any rotational output from the transmission system and actuating the drive system to provide relative rotational movement between first gear element and the sets of engagement members only when there is no rotational output from the transmission system.
36. A method according to any one of claims 32 to 35, wherein the transmission system is part of a vehicle and the method is performed when the vehicle is stationary.
37. A method according to any one of claims 32 to 36, wherein the transmission system includes a damping device for damping the locking engagement of the first gear element with its shaft, said damping device having first and second parts that are arranged for limited relative rotational movement and wherein after one of the first and second sets of engagement members has engaged the first gear element, thereby causing the first and second parts to rotate relative to each other, the method includes the control system actuating the other set of the first and second sets of engagement members to engage the first gear element before the relative rotational movement between the first and second parts of the damping device ceases.