GB2459711A

GB2459711A - Locking arrangement having teeth/splines

Info

Publication number: GB2459711A
Application number: GB0808031A
Authority: GB
Inventors: Kevin Wayne Dempsey; John Charles Cooke
Original assignee: JACK KNIGHT DESIGN Ltd
Current assignee: JACK KNIGHT DESIGN Ltd
Priority date: 2008-05-01
Filing date: 2008-05-01
Publication date: 2009-11-04
Also published as: GB0808031D0

Abstract

A lock arrangement for a transmission, in particular in the form of a parking-lock arrangement for a large or heavily loaded vehicle. The lock arrangement makes use of two interlocking splines or gears, the first gear 1 is rotationally fixed and the second gear 2 is capable of rotation. The lock is applied by the first gear 1 being axially brought into mesh, via lever 23, with the second gear 2 to enact the locking action. The teeth/splines may be formed on internal or external circumferences of the gears (figs 1 and 2 or figs 3 and 4). The locking mechanism delivers a high load capability within a far smaller space envelope than previous lock designs and can optionally provide a positive engagement within the mechanism itself due to a special form of the engaging gears.

Description

TRANSMISSION LOCK AND PARKING LOCK MECHANISM

Field

This invention relates to mechanical transmission lock mechanisms and parking locks, as are commonly used to establish a positively locked condition of an output shaft in an automatic transmission (park condition) or other automotive transmission systems which are required on occasion to be in a positively locked condition.

Background

According to the current state of the art, mechanical transmission locks or parking locks commonly operate through the use of a pawl mechanism configured to engage with a gear form as described most recently in US2007283735 and previously in GB2036212. US2007283735 describes a lock arrangement for a transmission, in particular a parking-lock arrangement for an automated transmission, the lock arrangement being pre-stressed by a first spring accumulator into a locking position in which the transmission is locked, and the lock arrangement being capable of being shifted by means of an actuator from the locking position into a release position in which the transmission is unlocked. Parking-lock arrangements of this type are known for automatic transmissions, including automatic converters, automated shift transmissions, double clutch transmissions, etc. GB2036212 describes a manually operable locking mechanism with a pawl for engagement with a toothed member connected to the transmission output shaft. The pawl is controlled for engagement and disengagement with the toothed member by the action of a manually operated cam, spring and lever arrangement. Whereas this configuration has been successfully used over a number of years for mechanical transmission locks or parking locks, in conditions of high load, such as exist in large off-road or commercial vehicle applications, this type of mechanism can suffer failure. The typical failure mode of this design of locking mechanism occurs when the loading on the pawl and locking tooth reaches a level where the pawl and/or it's mounting flexes elastically and plastically and the gear tooth, which is usually formed from a hard but brittle material, is subjected to a greater tensile and shear stress than it's material can withstand. The resultant failure of the locking system can result in the vehicle becoming mobile, creating a serious danger to people and property. Another, generally less severe failure mode can result from wear of the pawl giving degraded retention of the toothed member of the locking arrangement.

Brief Summary of the invention

Against this background, the object of the present invention is to overcome the failure mode described above, enhancing vehicle safety and reliability and furthermore enabling a far more compact locking configuration than would normally be possible. The inventive locking mechanism outlined in this document achieves a locking action by means of at least a pair of interlocking sets of radially arranged tooth-like forms or splines where the rotationally mobile component of the transmission is brought into mesh with the rotationally static locking component through relative axial movement between the static and mobile components. The rotationally static toothed or splined gear form part enables the locking action provided in current locking systems by the pawl and gives a radically increased level of mechanical engagement between the rotationally mobile and rotationally static components of the lock. Preferably, the toothed form on the rotationally static component of the mechanism is disposed around the outside of the part and the matching toothed form of the rotationally mobile component is arranged on an internal section of the part such that when locked, the rotationally static component is positioned within the rotationally mobile component. More preferably, the rotationally static component of the mechanism is attached to a splined shaft or hub which reacts any rotational loading into the housing of the locking mechanism.

Depending on space constraints or bearing requirements, the splined shaft or hub can be configured either with the splines arranged on an internal bore or on an external diameter. Most preferably, the teeth on the rotationally static locking component are wider at the end of the form nearest the mating rotationally mobile component or components than at the end furthest from the mating components, thus creating a negative rake on each gear tooth and ensuring that once engaged the lock will remain engaged until released. In this embodiment, the present invention has a very high strength compared to the pawl lock configuration due to the number of locking teeth engaged and a mechanical structure in which the locking forces can be fully resolved. Moreover, the negative rake of the locking teeth enables the mechanism to provide a very secure lock which requires a relatively high disengagement force. Finally, the locking configuration described can be incorporated within a relatively compact space envelope, enabling reductions in cost, material usage and weight for the overall mechanism. The negative rake described can alternatively be incorporated into the gear form on the rotationally mobile component of the lock.

In certain operating conditions or design configurations, it may be necessary for the lock to engage the rotationally static locking component with the rotationally mobile component when the drive train is in motion. In this situation, a preferable arrangement uses the rotationally static locking toothed or splined component actuated in concert with a rotationally fixed, spring loaded cone clutch mechanism, such that during engagement, the cone clutch engages with and stops the rotation of the rotationally mobile transmission component before the toothed or splined locking component is brought into mesh with the rotationally mobile component.

It will be appreciated that the features mentioned above and those yet to be explained below may be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention as will be clear to a person skilled in the art.

Brief description of the drawings within the patent document Figure 1 shows a diagrammatic view of the first configuration of the transmission lock component in an un-locked state with the with the locking components shown is section view Figure 2 shows a diagrammatic view of the first configuration of the transmission lock component in a locked state with the with the locking components shown is section view Figure 3 shows a diagrammatic view of the second configuration of the transmission lock component in an un-locked state with the with the locking components shown is section view Figure 4 shows a diagrammatic view of the second configuration of the transmission lock component in a locked state with the with the locking components shown is section view Figure 5 shows a diagrammatic view of a typical yoke mechanism used to drive the rotationally static locking component towards the rotationally mobile component. The view shows the mechanism in a locked condition Figure 6 shows a view of the rotationally static locking component Figure 7 shows a close up detail view of the gear form on the rotationally static locking components

Detailed description of the invention

A first embodiment of a parking lock or transmission lock arrangement according to the invention is designated in general by 10 in FIG. 1. The lock arrangement 10 consists of a rotationally static component 1 and a rotationally mobile component 2 attached to shaft 8. Arranged on the inner diameter of a blind bore in component 2 are locking teeth 6. Around the outer diameter of component 1 are axially aligned splines 5 which are designed to interlock with teeth 6. A further arrangement of axially aligned splines 4 are positioned on the internal bore of component 1.

Component 1 is positioned onto a shaft and hub unit 3 which has splines on its outer diameter 7 to correspond with the internal splines 4 on component 1 such that component 1 is free to move in the axial direction but restrained by the splines 4 and 7 in the rotational direction. The shaft and hub unit 3 is attached to the casing of the transmission housing 21 (figure 5).

Figure 2 shows the same parking lock or transmission lock arrangementlO in a locked position. In order to lock, component 1 is urged in an axial direction by yoke 22 (figure 5) attached to lever 23 (figure 5) towards the teeth 6 on component 2. When the splines 5 on component 1 align with the teeth 6 on component 2, component 1 is driven to a position where the splines 5 and teeth 6 fully interlock. In this condition, any load which would cause component 2 to move radially relative to component 1 is fully reacted through teeth 6 to splines 5 then to splines 4 and, via splines 7 and shaft and hub unit 3 to the transmission housing 21 (figure 5).

Figures 3 and 4 shows an alternative locking arrangement for situations where space constraints prevent the use of an internal shaft and hub 3. In figure 3, the mechanism is shown in an un-locked condition. The lock arrangement 20 consists of a rotationally static component 11 and a rotationally mobile component 12 attached to shaft 18. Arranged on the inner diameter of a blind bore in component 12 are locking teeth 16. Around the outer diameter of component 11 are axially aligned splines 15 which are designed to interlock with teeth 16. A further arrangement of axially aligned splines 14 are also positioned on the external bore of component 11 on the opposite side of the part from the splines 15. Component 11 is positioned within hub unit 13 which has splines 17 on its inner diameter to correspond with the external splines 14 and 15 on component 11 such that component 11 is free to move in the axial direction but restrained by the splines 14, 15 and 17 in the rotational direction. The hub unit 13 is attached to the casing of the transmission housing 21 (figure 5).

Figure 4 shows the same parking lock or transmission lock arrangement 20 in a locked position. In order to lock, component 11 is urged in an axial direction by yoke 22 (figure 5) attached to lever 23 (figure 5) towards the teeth 16 on component 12. When the splines 15 on component 11 align with the teeth 16 on component 12, component 11 is driven to a position where the splines 15 and teeth 16 fully interlock. In this condition, any load which would cause component 12 to move radially relative to component 11 is fully reacted through teeth 16 to splines 15 then to splines 14 and, via splines 17 and shaft and hub unit 13 to the transmission housing 21 (figure 5).

Figure 5 shows the mechanism 10 in a locked condition where an externally applied force shown by arrow) on lever 27 acts on lever 23 via linkage 26. This action causes lever 23 to pivot around components 24 and 25 and urge yoke 22 to move rotationally static component 1 towards rotationally mobile component 2, locking the mechanism. An unlocking action is achieved by reversing the direction of the externally applied force on lever 27. This action causes lever 23 to pivot around components 24 and 25 and urge yoke 22 to move rotationally static component 1 away from rotationally mobile component 2, unlocking the mechanism.

In Figure 6 component 1 is shown as a 3D view. The splined tooth form 31 is shown. Figure 7 shows the tooth form 31 where faces 32 and 33 are angled with respect to each other so that the thickness of the tooth furthest from engagement is smaller than the thickness closest to engagement. This configuration creates a negative rake and when component 1 is locked into component 2, reacts any rotational load on component 2 to urge the two gears more tightly together. This configuration creates a higher level of locking security, while still enabling the design to be tuned so that unlock loads applied to lever 27 are acceptable to the vehicle user.