WO2015067937A1

WO2015067937A1 - Transmission control system

Info

Publication number: WO2015067937A1
Application number: PCT/GB2014/053289
Authority: WO
Inventors: Sam JENNINGS
Original assignee: Hi-Lex Cable System Company Limited
Priority date: 2013-11-06
Filing date: 2014-11-05
Publication date: 2015-05-14
Also published as: GB201319602D0

Abstract

The present invention relates to a transmission control system to be used in a vehicle. Such transmission systems utilise transmission cables what provide mechanical actuation of the gear box from the gear shifter. The invention comprises a transmission cable and a transmission cable housing having a conduit therethrough having a conduit wall, the conduit having longitudinal length and being configured to receive the cable such that the cable is able to move in the conduit in the longitudinal length. The conduit wall comprises undulations in the longitudinal length defining a plurality of peaks and troughs, wherein the transverse spacing between the cable and the peaks of the conduit wall is in the range of 0.02mm to less than 0.11mm.

Description

Transmission Control System

The present invention relates to a transmission control system to be used in a vehicle. Known transmission cables provide mechanical actuation of the gear box from the gear shifter as presented schematically in Figure 1. They can be manual cables (2 legs) or automatic cables (1 leg) (2). They connect directly to the gear box at one end passing through the vehicle bulk head into the passenger cell, attaching to the gear shifter at the opposite end.

Such transmission control systems generally have two main components. The first is the inner cable (7) which provides the mechanical movement. This is usually constructed from a series of wound steel filaments (8) which forms the cable and is generally coated with a low friction polymer (10) such as Nylon 66 which is housed in a transmission cable housing (1) forming a conduit therethrough. At each end of the inner cable (7) is an 'eye end' which allows connection to the gear box and shifter. Thus actuation of the inner cable by the gear shifter causes corresponding actuation of the gear box. A cross- sectional view of the cable (7) and conduit (1) presently in use is represented in Figure 2a, and a perspective representation of the cable (7) and conduit (1) with each layer from radially inwardly to radially outwardly peeled back to clearly show the layers of the cable and the conduit is represented in Figure 2b.

Referring to Figures 2a and 2b there is provided a housing ( 1 ) comprising a housing covering (la), and a plurality of steel wires (lb) which are embedded with the housing covering (la). The housing (1) further comprises a cable liner (2) through which the cable (7) passes. The cable liner (2) beneficially comprises a low friction material such as PTFE or PBT. As represented in Figure 2c the cable liner (2) may be of a multi- layered construction comprising an inner liner of, for example, PTFE and an outer liner comprising a nylon jacket identified by reference numeral (4). The cable (7) passes through the liner (2) and the cable (7) comprises a cable covering (7a) encasing a plurality of wires (7b). With reference to Figure 1, at a point along the conduit is a fixing element (19), often termed an 'abutment' which attaches to the body of a vehicle. In particular, the practice has developed of anchoring the conduit to an opening in a bracket (21) or bulkhead across which the conduit (12) passes.

As represented in Figures 2a and 2b, the outer profile of the cable covering (7a) may be non-cylindrical. A plurality of peaks (6) are provided which in use communicate with the inner wall of the liner (2). The separation or distance radially between the peaks (6) and the wall of the liner (2) when the cable (7) is radially central in the conduit (36) defined by the liner (2) is 0.113mm. This has been found to provide the optimum balance of friction between the cable (7) and the liner (2) and the feature of backlash of the cable as the cable (7) is actuated during a gear change. Backlash is apparent as lost motion under a push or pull input force which is caused by the cable (7) moving from the inside to the outside of the bends in the conduit (36) with the change in direction of the movement. Accordingly, it is a function of a clearance between the cable (7) and liner (2), the input force and the total number of degrees of bend in the cable (7). It will be appreciated that each cable (7) and thus cable housing routing in a vehicle depends on the route required to connect to the gear box to the gear shifter. This may involve a plurality of bends. Accordingly, the separation radially of the cable (7) and liner (2) is a balance of friction and backlash. A user of a vehicle does not want significant friction as the gear shifter will be difficult and require significant force. They also do not want significant backlash as this reduces the preciseness of the shift.

The present invention provides an improved arrangement reducing the effect of backlash whilst also minimising friction characteristics.

According to the present invention there is a transmission control system comprising: a transmission cable having a first end arranged to be secured to a gear box and a second end arranged to be secured to a gear shifter, and a transmission cable housing having a conduit therethrough defined by a conduit wall, the conduit having a longitudinal length and being configured to receive the cable such that the cable is enabled to move in the conduit in the longitudinal length;

wherein the conduit wall comprises undulations in the longitudinal length defining a plurality of peaks and troughs, wherein the average transverse spacing between the cable and the peaks of the conduit wall is in the range of 0.02mm to less than 0.11mm.

Also according to the present invention there is a transmission control system

comprising:

a transmission cable having a first end arranged to be secured to a gearbox and a second end arranged to be secured to a gear shifter, and a transmission cable housing having a conduit therethrough defined by a conduit wall, the conduit having a longitudinal length and being configured to receive the cable such that the cable is enabled to move in the conduit in the longitudinal length;

wherein the conduit wall comprises undulations in the longitudinal length defining a plurality of a peaks and troughs, wherein the transverse spacing between the cable and the peaks of the conduit wall is manufactured to be in range 0.02mm and less than 0.11mm.

As shown in the specific description the presently claimed invention provides a significantly improved transmission control system. Irrespective of the cable housing routing the effect of backlash is significantly reduced as a result of a combination of undulations in the longitudinal length of the conduit wall and the transverse spacing between the cable and the peaks of the wall. It will be appreciated that the transverse spacing is measured when the cable is radially equidistant from a peak. Alternatively, the spacing may be defined as when the cable is centralised in the conduit. The peaks are beneficially at the radially inner most point or portion of the conduit wall and the troughs form a point or portion of the radially outermost part of the wall. The average transverse spacing can be taken as the average spacing over the entire length of the portion of the transmission control housing that defines the conduit.

The average transverse spacing between the cable and the peaks of the conduit wall is beneficially in the range of 0.02mm to less than 0.11mm. The average space between the cable and the peaks of the conduit wall is beneficially manufactured to be in the range of 0.02mm to less than 0.11mm.

The average transverse spacing between the cable and the plurality of peaks of the wall is beneficially in the range of 0.05mm to 0.09mm. The average transverse spacing is preferably substantially 0.07mm.

The transfer spacing between the cable and the peaks of the wall is manufactured to be substantially 0.07mm. The spacing is therefore specified or selected to be substantially 0.07mm and is beneficially designed to have such a spacing value. It will be appreciated, however, that due to manufacturing tolerances there may be some variation in the spacing.

A plurality of peaks and troughs may be formed by a projection or protrusion extending helically from the wall. This helical projection may extend generally longitudinally from the wall. Alternatively, or in addition, the plurality of peaks and troughs are formed by longitudinally spaced ridges, wherein the ridges are spaced apart in the longitudinal axis and isolated from each other by a trough. Each ridge effectively, therefore, may form a loop. The ridges are beneficially regularly spaced apart. A benefit of the provision of peaks and troughs formed by longitudinally spaced ridges is that grease is retained in the troughs improving lubrication of the cable in the cable conduit. The ridges may also be termed protrusions or projections extending from the wall defining the conduit.

The peaks are beneficially regularly spaced apart.

The present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic perspective view of a transmission control system with a cable secured at two points to a vehicle body as currently known in the art. Figure 2a is a cross-sectional view of a transverse cable housing including a cable therein as known in the art.

Figure 2b is a schematic cutaway view of a transmission cable housing and cable as known in the art.

Figure 2c is a further schematic perspective cutaway view to show an alternative liner as known in the art.

Figure 3 is a schematic cutaway view of a transmission cable housing for use according to an exemplary embodiment of the present invention, together with a cross-sectional view of the conduit liner.

Figure 4 is a schematic longitudinal cross-sectional view of a transmission cable housing and cable according to an exemplary embodiment of the present invention also showing the cable and conduit liner in further detail.

Figure 5a is a cross-sectional view showing a transmission cable housing and cable identifying the location of the lubricant between the cable and conduit wall as known in the art and Figure 5b is a transmission cable housing and cable according to an exemplary embodiment of the present invention. Figure 5c is a detailed view of the area identified "Y" of Figure 5b.

In prior art transmission cable systems as shown for example in Figures 2 and 5 a there is a nominal separation value of 0.113mm as represented by reference number (30) between the conduit liner (2) and the radially outermost points of the cable (3). This clearance specification or spacing specification results in backlash characteristics that are measured together with friction and efficiency values. Typical values are as follows:

Backlash: 0.6mm

Efficiency (high load): 92%

Friction: 4.5N

The present invention enables improved backlash characteristics without significantly changing the friction and efficiency values.

Referring to Figure 3 there is a cutaway representation of a transmission cable housing

(1) comprising a conduit (36) according to an exemplary embodiment of the present invention and there is further shown a longitudinal cross-section of the cable liner (2). As represented in Figure 3 the conduit liner (2) has a substantially cylindrical outer dimension which is substantially constant along the longitudinal length of the cable liner

(2) . The internal wall that defines the cable conduit (36) comprises a plurality of peaks (32) and troughs (24) formed by projections, protrusions or ridges (32) extending radially into the conduit (36). The peaks defined by the projections (32) form the radially inwardly points of contact for a cable extending through the conduit (36). The projections (32) are regularly spaced in the longitudinal axis and may be provided in a number of different forms. For example, as represented in Figure 3 the protrusions (32) are formed to extend non-parallel to the transverse axis. In an alternative embodiment the projections (32) may be annular. In an alternative embodiment there may be a singular elongate projection (32) extending helically along the wall defining the conduit (36). It is important, however, that the wall defining the conduit is undulated meaning that there are a plurality of peaks and troughs formed by projections extending inwardly radially from the wall in the longitudinal length.

Referring to Figure 4 there is a cross-section through the longitudinal length of the transmission cable housing (1) where the cable (7) is provided within the conduit (36). The peaks formed by the projections (32) are clearly shown defining a point of contact with the cable (7). The troughs (34) effectively form pockets that are configured to receive grease to aid lubrication of the cable (7) passing through the conduit (36). The projections (32) as represented in Figures 3 and 4 extend non-parallel to the transverse axis and as represented in Figures 3 and 4 the peak of the projection (32) extends between approximately 30 and 60 degrees relative to the longitudinal or transverse axis meaning that there are few points in the longitudinal length where the cable (7), around its peripheral transverse outer surface, is not adjacent a peak of a protrusion (32). The protrusion (32) can therefore effectively be described as being offset in the transverse axis, or tilted relative to the transverse axis.

Referring to Figures 5a, 5b and 5c, Figure 5a compares a prior art cable liner (2) and cable (7) for comparison with a cable liner (2) and cable (7) according to an exemplary embodiment of the present invention represented in Figures 5b and 5c. As represented in Figure 5a the cable liner (2) has a substantially constant internal diameter and the spacing (30) between the cable (7) and the internal wall of the liner (2) is represented by reference numeral (30). When the cable (7) is centrally located in the conduit (36) there is a substantially constant separation or spacing or clearance (30) of approximately 0.113mm. This separation includes therein a lubricant (38). This lubricant (38) aids movement of the cable (7) through the conduit (36). A nominal separation (30) of 0.113mm gives an optimised combination of minimal backlash of 0.6mm and friction of 4.5N at an efficiency of 92%. In the present invention, however, the separation has been reduced to a value of between 0.02mm and less than 0.11mm. It has further been found that a preferred separation is 0.07mm. This separation is defined when the cable (7) is positioned centrally in the conduit (36) meaning that the cable is equidistant from the peaks of the projections (32).

Represented in Table 1 is a comparison with a prior art cylindrical liner conduit and an undulating cable liner (2) where the respective clearances or separation are 0.11mm and 0.7mm respectively. These are shown for three different cable routings between a gear shifter and a gear box. It is clear that whichever routing on the vehicle is selected, through the provision of a clearance or separation of 0.07mm utilising an undulated cable liner the reduction in backlash is significant. For example, in Routing 1 backlash is reduced from 0.55mm to 0.35mm. In Routing 2 backlash is reduced from 0.75mm to 0.45mm. In Routing 3 backlash is reduced from 0.75mm to 0.35mm. It will also be identified that the friction remains substantially the same. In Routing 1 there is a slight increase, in Routing 2 the friction value is the same, and in Routing 3 the friction value reduced for the separation of 0.07mm with the undulated cable liner.

Table 1

In Table 2 there is a comparison of a clearance or separation value of 0.02mm for both a cylindrical cable liner and an undulated cable liner where the backlash is similar, however, for a cylindrical cable liner the friction value is significantly increased meaning that a significant force would need to be input to the gear shifter in order to change gear. This would clearly be undesirable, and shows true effect that reducing the separation value has on friction values for prior art arrangements. Table 2

As identified with respect to Figure 5, lubrication is important between the cable and the cable liner (2) in order to ensure durability. In a prior art cylindrical liner conduit the grease acts as a resistance whereby providing a majority of the friction to movement. There are, however, negative consequences of this in that the science of tribology explains that if an object passes through a lubricant at an increasing speed, the greater the increase in friction will be. This is represented below in Graph 1 whereby line "A" is representative of a high grease quantity comparing friction and speed of movement of the cable through the cable liner with a cylindrical cross-section and line "B" is

representative of a reduced grease quantity for the same cable liner and cable. It is apparent that using lower grease quantities has an effect, as expected, of a reduced friction value.

raph 1

Referring now to Graph 2, there is a comparison of a transmission control system according to the present invention and a prior art arrangement. As shown, in line "C", the effect of the claimed separation together with the provision of the troughs to receive grease provide a substantially constant friction value irrespective of speed of movement of the cable through the conduit. This is for a high grease quantity. Accordingly, the present invention provides improved consistency in feel of gear change irrespective of the speed of the gear change. This further retains the durability effect of the provision of high grease quantity.

Graph 2

The present invention has been described by way of example only and it will be appreciated to the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the appended claims.

Claims

1. A transmission control system comprising:

a transmission cable having a first end arranged to be secured to a gear box and a second end arranged to be secured to a gear shifter, and a transmission cable housing having a conduit therethrough defined by a conduit wall, the conduit having a longitudinal length and being configured to receive the cable such that the cable is enabled to move in the conduit in the longitudinal length;

2. A transmission control system comprising:

3. A transmission control system according to any preceding claim, wherein the transverse spacing between the cable and the peaks of the conduit wall is manufactured to be substantially 0.07mm.

4. A transmission control system according to claim 2, wherein the average transverse spacing between the cable and the peaks of the conduit wall is in the range of 0.02mm to less than 0.11mm.

5. A transmission control system according to claim 1, wherein the average spacing between the cable and the peaks of the conduit wall is manufactured to be in the range of 0.02mm to less than 0.11mm.

6. A transmission control system according to any preceding claim, wherein the average transverse spacing between the cable and the plurality of peaks of the wall is in the range 0.05mm to 0.09mm.

7. A transmission control system according to any preceding claim, wherein the average transverse spacing between the cable and the plurality of peaks of the wall is substantially 0.07mm

8. A transmission control system according to any preceding claim, wherein the plurality of peaks and troughs are formed by a projection extending helically from the wall.

9. A transmission control system according to any preceding claim, wherein the plurality of peaks and troughs are formed by longitudinally spaced ridges, wherein the ridges are spaced apart in the longitudinal length and isolated from each other by a trough.