GB2076484A - Control Means for a Continuously Variable Ratio Vehicle Transmission - Google Patents

Abstract

The control means comprises a three dimensional control map 11 and a probe (not shown) which moves over and is spring pressed towards the surface of the map. Movement of the probe is controlled in two dimensions to fix road speed and accelerator pedal coordinates, the third dimension perpendicular to the plane of the figure, representing the required ratio of the continuously variable ratio transmission. The probe is carried by a bracket by which it is moved in the X direction in response to accelerator pedal movement and is mounted for sliding movement in the bracket in the Y direction so that, when it is away from the idling region 19 of the map, it tends to move in the Y direction downhill towards a valley 15 bounded by a contour 14 thereby establishing high ratio. Such movement in the Y direction is limited by a stop blade or blades positioned by road speed responsive means. <IMAGE>

Description

SPECIFICATION Control Means for a Continuously Variable Ratio Transmission This invention relates to means for controlling the ratio provided by a continuously variable ratio stepless transmission for a vehicle, and to vehicles that incorporate such transmission and control means.

Continuously variable transmission for control by the control means of the invention may typically comprise a mechanical variator in series cooperation with a lockable torque converter or centrifugal clutch; or an arrangement embodying a variator with an epicyclic gear-set constituting a regenerative type transmission. This latter arrangement can intrinsically incorporate a range of stepless ratios between reverse, through geared neutral to highest forward ratio, or a unidirectional range between geared neutral and maximum forward ratio only in which case a separate reverse, neutral, forward selection facility is provided. Such arrangements are termed 'single regime' systems and involve a varying level of torque recirculation throughout the operating range.

An extended concept involves the integration of two clutches which are operable to judiciously change the mode of the torque transfer within the transmission circuit and thereby establish a two regime system.

The initial regime commonly designated low regime provides a transmission range, involving the full ratio range of the variator element, which incorporates the reverse speed ratios through geared neutral to a maximum forward ratio approximately equivalent to conventional first gear selection, when a synchronous change by clutch actuation to high regime enables the total range of the variator element to be again fully utilised to provide forward transmission ratios between first gear analogy and an extended equivalent overdrive ratio by locking out the dynamic function of the epicyclic and thereby promoting higher mechanical efficiency of the system with lower internal torque transfer.For example, low regime using the total range of a belt type variatorfrom highest to lowest ratio, with torque recirculation, providing a stepless transmission range of say 5 mph/i 000 engine rpm in reverse though zero output shaft speed to 5 mph/i 000 rpm in forward vehicle direction.

High regime utilising the total range of the variator element from lowest to highest ratio, without torque recirculation, providing a stepless transmission range between 5 mph/1000 rpm and say 40 mph/1000 rpm for forward vehicle motion.

The invention is concerned with means for so controlling the members of the transmission that vary the ratio provided by the transmission that the transmission operates at a suitable ratio. Thus it should be understood that such control means can ensure that the ratio is so varied that the vehicle engine operates efficiently within the confines of the requirements of the driver and the prevailing conditions.

According to the invention control means for a continuously variable ratio, stepless, vehicle transmission includes a) a three dimensional control map calibrating predetermined ratios, accelerator displacements and road speeds; b) a probe adapted to be connected to members of the transmission that vary the ratio the probe being urged into contact with the surface of the control map; c) means for moving the probe across the surface of the map to an accelerator displacement co-ordinate determined by the displacement of the accelerator pedal; d) means limiting movement of the probe to below a road speed co-ordinate determined by the road speed, such as to limit the ratio for any given displacement of the accelerator pedal to below a predetermined value; and the arrangement being such that within the limits imposed by the said means for moving the probe and for limiting the movement of the probe, the probe will tend to move to a position on the surface of the map that gives the highest ratio.

Advantageously the control means may include means for providing a lower ratio than that normally determined by the position of the probe. For example, the probe may incorporate solenoid or other means for lifting the probe when there is a requirement for a lower ration as determined by, for example, engine manifold depression and/or under the manual control of the driver.

The means for limiting movement of the probe to below a road speed coordinate determined by the road speed of the vehicle may comprise a pair of interconnected profiled blades arranged to pivot across the surface of the control map; and furthermore the profile of the blades may be such that for any position of the blade - at least at low speeds (e.g. under 40 mph) - under steady state conditions the ratio will not vary irrespective of the accelerator pedal displacement.

Moreover the control means may incorporate means operated by the probe movement limiting means at low (say below 5 mph) road speeds to actuate a torque limiting coupling in the continuously variable transmission.

Furthermore the means for limiting movement of the probe to below a road speed co-ordinate determined by the road speed of the vehicle may include provision for optionally setting the limiting means under the control of the driver such that the transmission can be limited to operation below a ratio determined by the limiting means irrespective of the road speed. Thus, for example, the arrangement may be such that a pair of blades, which limit movement of the probe can be moved by the driver to a selected one of a number of positions that, under steady state conditions, cause the transmission to operate at ratios corresponding to those given by the various gears of a conventional gearbox.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1, is a plan view of a three dimensional control map as embodied in a control means in accordance with the invention for a composite two regime transmission arrangement.

Figure 2, is a section elevation of the map taken on the line I-I of Figure 1, as viewed in the direction indicated by the arrows.

Figures 3 and 4, are section elevations of the cam taken on the lines li-li and cranked line 111- 111 respectively of Figure 1, as viewed in the direction indicated by the arrows.

Figure 5 is a diagrammatic representation of the control map of Figure 1 in combination with a probe and means for controlling movement of the probe, said probe being positioned for the low speed forward motion mode of regime for the vehicle.

Figure 6, is a diagrammatic representation of part of the view shown in Figure 5 with the probe positioned for 'geared neutral' with associated switching circuitry.

Figure 7, is a view in elevation of the displacement transducer in contact with the cam section substantially on the line IV--IV in the direction indicated by the arrows on Figure 6, with further clarification to the switching circuit and diagrammatically indicating the servo actuation, by the probe of a typical belt variator incorporating a two regime capability.

Figure 8, is a section elevation of the probe and control map on the line IV--IV indicated on Figure 6 in enlarged and greater detail again cooperative with the associated circuit integration.

Figure 9 is a diagrammatic representation of the control means of Figure 5 with the probe positioned for the higher regime mode for forward vehicle motion with ratio analogous 1:1 (conventional top gear) ratio.

Figure 10, is a diagrammatic representation of the control means of Figure 5 with the probe positioned for high regime mode with the probe control means in the positions assumed during decreasing vehicle speed.

Figure 11, is a diagrammatic representation of the control means of Figure 5 with the probe positioned for high regime mode with the probe control means set to allow a typical maximum cruise status for vehicle forward motion.

Figure 12, is an isometric schematic display of the control means, with parts omitted for clarity, to illustrate the operation of the control means to obtain vehicle reverse motion within the low regime mode.

Figure 13, is a diagrammatic representation of an alternative embodiment of a control means suitable for single regime control only with the probe positioned for geared neutral status.

Figure 14, is a sectioned elevation of the control means of Figure 13, taken on the line V V in the direction indicated by the arrows on Figure 1 3 with circuitry and diagrammatic representation of servo actuation to a belt type variator composite with single regime and unidirectional capability.

A three-dimensional control map 11, shown in plan in Figure 1 and in section in Figures 2, 3 and 4, comprises a contoured surface 12 and a boundary wall 13. As will be appreciated from Figures 2, 3 and 4, a line 14 in figure 1 marks the edge of an area 1 5 of minium height. The area around 1 5 increases in height with distance from line 14, with varying gradient, as shown by the contour line 16. The area 17 and the line 18 represent points where the surface height is a maximum, while the area 19 represents a ramp leading down to an area 20 which is at the same height as contour 1 6.

Figure 8 shows a probe 21 comprising a body 22 arranged to be moved over the map 11 at a fixed height, and a probe head 23 which slides within the probe body 22, and is biased into contact with the surface of map 11 by a spring 24. As body 22 is moved over the map a ball point 25 at the top of the head 23 rolls over the surface of the map. The position of the probe head relative to the body changes in response to movement up or down a gradient on the map.

Probe movement is controlled by a guide rail member 27 which carries the probe body in a slot 28 along which the probe is free to slide subject to the constraints imposed by the control map and a pair of interconnected profiled blades 29 and 30 (figure 5). Member 27 is connected to the accelerator pedal 31 by a linkage which caused the member 27 and thus the probe also, to be moved in a direction parallel to a slot 32 and perpendicular to slot 28, the member 27 being constrained to this direction of movement by a pair of pegs 33 and 34. The members 27 thus provides means for moving the probe across the surface of the map to an accelerator displacement co-ordinate determined by the displacement of the accelerator pedal.The connection between accelerator pedal 31 and the movement of member 27 need not be a directly proportioned connection to accord with the invention, but the movement should be related in some way.

The interconnected blades 29 and 30 are controlled by a governor 35 which runs at a speed proportional to the vehicle roadspeed. The blades thus assume fixed positions for a given road speed and are so profiled that their probe contacting edges are aligned with the contours of the map, at least for road speeds below a given value, which in the present example is 40 miles per hour. Thus movement of member 27 is responsible to acclerator movement will not alter the map height reading by the probe if the probe remains in contact with the profiled edge of a blade.

Figure 7 shows a two-regime continuously variable ratio transmission (CVT) with a belt-type variator having a pair of pulleys 36 each with a variable effective diameter connected by a belt 37, which variator is coupled to an epicyclic gearset, comprising a sun gear 38, planets 39 and annulus 40, by a spur gear set 41. Annulus 40 is connected to the transmission output shaft 42. A pair of clutches 43, 44 enable an input shaft 45 to the variator to be locked to the input gear of the gear set 41, and the sun gear to be locked for rotation with the planet carrier 46 (effectively locking the gearset), respectively. With clutch 43 only engaged the transmission is in low-regime enabling overall ratios from reverse through geared neutral to forward to be obtained. Higher forward ratios are available in high-regime in which clutch 44 only is engaged.Control of the clutches 43, 44 is by a logic circuit 46 which operates in response to probe position as sensed by eiectrically conducting elements 47, 48 set in the control map walls and by a switch 49 on the guide rail 27 which detects movement of the probe past the line 18. The ratio of the variator is controlled by hydraulic pressure in the sheaves 36, which is determined by a valve 50, which valve is in turn controlled by a combination of feedback from the sheaves and in response to the height of the probe head 23, as shown diagrammatically at 51.

Thus the height of the control map on which the probe head 23 rests determines the variator ratio and hence the overall transmission ratio in a given regime. Means (not shown) are provided for modifying the sensed height of the map terrain. In particular the stylus head can be raised by means of a solenoid 52 controlled by logic circuit 46 this provides an effective override for use for example, in the case of the vehicles engine labouring with too low a manifold depression and speed, when a lower transmission ratio is required. Further, when a reverse speed control is selected the accelerator pedal 31 is disconnected from the guide rail member 27 and instead is operable to lower the control map relative to the probe, so that accelerator pedal movement operates directly to open the engines throttle and adjust the variator ratio.Figure 1 2 shows diagrammatically at 53 the means for altering the accelerator pedal connection.

The function of the control system can be demonstrated by describing a typical excursion of a vehicle fitted with a two regime CVT illustrated.

Neutral:-- Accelerator pedal 31 (A/P) disconnected from the control map 11 and guide rail member 27 with input shaft and output sheave clutches -- 43, 44 disengaged. In this mode the status is as for conventional neutral enabling engine start with or without choke incorporating fast idle with corresponding partial displacement of the A/P.

Reverse:-- A/P connected to control map with input shaft clutch 43 engaged. In this mode active low regime at geared neutral is established when depression of A/P displaces the control map away from the static probe body, thereby first disconnecting the electrical contact between map and probe which has maintained reduced reference pressure of the sheave hydrostatic circuit, hence initiating traction and subsequently a progressively increasing transmission ratio in parallel with increasing engine revs. Return of A/P to 'foot off position' progressively reduces speed of reverse traction to re-establish of geared neutral. Forward:-- A/P connected to probe guide rail 27 with input shaft clutch 43 engaged.

In this mode potential forward vehicle motion in active low regime is established for A/P in 'foot off position'.

Description of stylus motion with reference to figures and axis notation are subsequently designated:- Movement in direction of positive X (Fig. 1) as eastward, movement in direction of positive Y as northward et. al.

Initial slight displacement of the A/P, or displacement due to fast idle selected by an engine choke control will move the probe eastwards and, since the A/P is conventionally linked to the carburettor butterfly, engine speeds of say 1,500 to 2,000 rpm will also be established. However, electrical contact between the south boundary wall plate 48 and probe will not yet be broken, thus hydrostatic reference pressure to the pulley sheaves will remain nominally low and maintain an active status of geared neutral when belt variator ratio will constantly re-adjust to maintain a simulated static vehicle mode.

Further displacement of the A/P to say 2,500 rpm steady state engine speed equivalence will move the probe on a derived locus along 19 by forced contact with the east boundary wall of the control map to the limit of the low regime territory 1 8. Over the displacement the sheave reference pressure will be normalised for torque transfer due to the breaking of electrical contact between wall plate and probe, and the variator ratio proportionally decreased to its limit value by this probe displacement consistent with its riding up the incline of the map terrain.If, at the north limit of low regime terrain the vehicle road speed has not yet reached a design selected speed of say 1 6 mph, escape from the low regime terrain will be prevented by the ratio limiter blade 29 which is linked to the road speed sensing device 35, or the ratio limiter blade may have been manually selected to remain in this probe inhibiting position. Under these conditions the A/P might be further depressed, thereby increasing engine speed only, by the compression of an overload spring 54 interposed between A/P and the probe guide rail. As soon as the road speed exceeds the prescribed speed of say 1 6 mph, with selection in drive position, the ratio limiter blade will continue its angular displacement in proportion to the signalled road speed, hence allowing the probe to enter into high regime territory.Simultaneously with the probe traversing the demarcation ridge 1 8 of the terrain the northward displacement of the probe body in the guide rail will trip the switch 49, mounted on said rails, which signals the change in status of the transmission from low to high regime by disengaging the input shaft clutch and engaging clutch 44. The operation of this switch into high regime also activates a potential override signal provided by a minimum engine manifold depression value indicating excessive torque requirement. The effect of this signal is to energise the solenoid integrated in the probe assembly to lift the probe from contact with the map surface and consequently reduce transmission ratio until overload situations for the engine cease to be signalled.Also integrated with the probe assembly is a unidirectional damping facility to enable a judged impulse and dwell characteristic in cooperation with this signal.

Thereafter, following this synchronous change of transmission regime and the corresponding migration of the probe into high regime territory, then whatever displacement eastward or westward is orientated by the A/P actuation the probe will constantly tend to ride down the surface incline (constrained northward by the guide rail 27) thus increasing transmission ratio but at no greater rate than abutment of the probe body against the retreating ratio limiter blade, linked to road speed, will allow. For example if engine power and conditions of external resistance to vehicle motion are such that rapid acceleration is possible, the R.L. blade 29 will retreat quickly allowing more rapid change of probe displacement and corresponding increase in transmission ratio.Conversely if conditions of external resistance to motion are such that vehicle deceleration results, the R.L. blade will push the probe southwards and up the map surface incline thus effecting a decrease in transmission ratio. This aspect of 'wipe-down' activity is supplemented by the additional blade 30 kinematically linked to the profiled R.L. blade 29; the function of this supplementary blade is solely to apply a component of force to the probe body in a direction more nearly due south over approximate areas of the terrain which the activity of the R.L. blade 29 in isolation does not geometrically comply for this function.The continuing activity of this 'wipe-down' action will at the chosen road speed (instanced previously at 16 mph) and with A/P released to a low equivalence of engine speed (say less than 2,500 rpm), implement regime change from high to low regime for the probe activity.

At vehicle speeds in excess of say 40 mph the entire map area will be free from any restrictive activity by the ratio limiting/wipe down blade acting on the probe. Under these circumstances, the terrain surface, as derived by the specified isoratio pattern east of the valley plain, is such that for selected positions of the A/P the spring loaded probe head 23 will seek the lowest point on the terrain in abutment against the north boundary.

Among these situations with the probe in abutment against the north boundary is the position of maximum speed where the iso-ratio of 1 :1, (usually corresponding to the vehicle power load curve) intersects the boundary. The specified iso-ratio pattern east of the valley plain contains a family of iso-ratio curves ranging from highest overdrive iso-ratio line (bounding the plain) to the lowest gear iso-ratio over which the angular profiled sweep of the ratio limiter blade approximately shadows each iso-ratio line thus enabling the ratio to be limited to a number of chosen values by choice of static position of the ratio limiter blade.

With exception of 'foot off' A/P position, for all other steady state positions of the A/P the probe will have migrated northward analogous to highest vehicle speed for that particular foot setting of the A/P. If however deceleration is required, 'foot off' A/P position will result in the probe abutting the west boundary against which the terrain profile comprises a ramp and plateau such that at higher speeds of say greater than 40 mph no lower ratio than 1:1 will result to avoid over revving the engine; thereafter as the vehicle speed decreases, wipe-down action will progressively decrease the transmission ratio to first gear analogy at say about 20 mph. Hence overrun control whatever rate of deceleration will always be appropriate with terrain actuated acceleration when the probe is again moved eastward by A/P movement.These intrinsic attributes regarding control under deceleration with 'foot off' are continued when the speed is decreased below say 16 mph at which speed the transmission is reverted to low regime status by continuous wipe-down action on the probe.

Within this regime the ratio is maintained under further deceleration at the first gear ratio analogy until very low vehicle speeds results, say 2/3 mph when the steep ramp inter-action on the probe of the local terrain reverts the ratio rapidly to geared neutral. The control in the low regime remains similarly poised for immediate reactivation of traction from deceleration right down to zero speed by A/P actuation when displacement eastwards of the probe re-establishes appropriate ratios between geared neutral and finite bottom gear analogy at which ratio high regime mode is again available with control actuation et sequentia.A conscious analysis of A/P foot operation when driving vehicles with conventional manual transmissions with discrete ratios particularly in top gear reveals a tendency to slightly over throttle to accelerate the vehicle and then to ease back the foot to the maximum to just maintain a chosen cruising speed. This modus operandi is entirely appropriate strategy for the probe actuation when easing back the A/P will move the stylus westwards into higher ratio consistent with decreasing engine revs ultimately into maximum overdrive ratio if external resistances to motion permit.

Rate of operation of the A/P will also impart an appropriate differentiation of probe locus in that gradual A/P depression will tend to maintain constant ratio by following a particular iso-ratio as witnessed by following profiled edge of a manually set position for the ratio limited blade, and whereas rapid A/P depression will reduce ratio simultaneously with increasing engine revs for maximum acceleration before seeking higher ratios or re-establishing set ratio.

By analogy these aspects of differential control represent a considerable extension and variation over conventional kick-down provision in that the rate of, as well as the extent of displacement of the A/P aligned with steplessly variable ratio promotes an infinite range of compliance between driver inclination for leisurely increase in vehicle speed coupled with minimal rate of variation in engine revolutions and drivers demand for maximum vehicle acceleration consistent with total utilisation of maximum engine power.

A further embodiment of the present invention shown in Figures 13 and 14 includes a single regime transmission arrangement in which an epicyclic gearset 55 is geometrically derived to provide a unidirectional range of traction. ie.

Geared neutral at one limit of the variator range to maximum overdrive transmission ratio at the opposing limit of the variator range. In this arrangement input to gearset 55 is from a belt drive 56 and a spur gearset 57, and recirculation torque to a varying degree is always evident over the range. Neutral and reverse is selected independantly by alternative gear engagement in the drive line, by way of clutches 58 and 59. The control system is identical to that previously described with the following exceptions Ref. Fig.

13:-The control map is confined to the previously described high regime territory and is at a permanently fixed height relative to the probe body.

The ratio limiter blade range of sweep is confined to this single territory.

No switching facility is necessary on the guide rail member.

Geared neutral belt variator ratio and the variator range between geared neutral and finite torque transfer ratio is signalled by the probe activity riding down a west, eastward orientated ramp walled into the terrain at the junction 60 of the west and south boundary corresponding to minimal speed. Traverse of the probe within this walled adjunct is actuated by initial 'free' displacement of the accelerator pedal prior to throttle actuation of the engine. Choke control actuation of fast idle is independant of guide rail displacement.

Within the territory adjunct a west wall plate 62 can signal release of clutch on 62 in series with the transmission recirculation loop and south wall plate 63 can act as potentiometer over chosen linear displacement to control reference pressure of sheaves.

Yet a further embodiment (not illustrated) of the present invention is aligned with the control of a CVT incorporating a conventional type torque converter combining a hydrostatically actuated clutch between stator and impellor, in series with a mechanical variator.

The control map retains the form as for the single regime torque recirculation regenerative example but without the adjunct of geared neutral terrain. The hydrostatic clutch in the hydrokinetic converter is released below road speed of say 10 mph. At all other times of dynamic activity the clutch remains engaged unless actuated by a vacuum signalled engine over-ride facility.

Some attributes of embodiments are: A minimum number of input signals are required viz. Road speed signal, a suitable linkage coupling to the accelerator pedal and an induction manifold pressure switch.

The existing type of selector lever and console currently used for conventional automatic gear boxes could be retained.

The concept is very tolerant in accepting the usual performance variations of particular engine specification in quantity production and will accommodate the restrictive 'running in' requirements for new power units and the usual loss of performance due to wear and deviations in maintainance over the later life span of the engine.

It is relatively easy to acquire a working picture of the unit function which can facilitate the development process and help subsequent diagnosis and maintainence in the normal service industry.

Production manufacture of the unit could be accommodated by familiar industrial techniques, eg. the control map demands no greater accuracy than adequately accommodated by known standards of pressure diecasting technology.

The proportions of the control unit need be no greater than a typical facia instrument. Infact the construction can incorporate a transparent 'lid' when visual observance of the terrain and stylus position contributes an analogue display which can be instantly interpreted by the driver regarding dynamic and steady state engine and transmission inter-relation.

Hence by further application the control unit not only performs the function of automatic continuously variable transmission management for optimum exploitation of fuel economy but will complement this service with a visual feedback to assist driving technique to this end.

Claims (12)

Claims

1 A control means for a continuously variable ratio vehicle transmission including a) a three dimensional control map calibrating predetermined ratios, accelerator displacement and road speeds; b) a probe adapted to be connected to members of the transmission that vary the ratio; the probe being urged into contact with the surface of the control map; c) means for moving the probe across the surface of the map to an accelerator displacement co-ordinate determined by the displacement of the accelerator pedal; and d) means limiting movement of the probe to below a road speed co-ordinate determined by the road speed, such as to limit the ratio for any given displacement of the accelerator pedal to below a predetermined value; and the arrangement being such that within the limits imposed by the said means for moving the probe and for limiting the movement of the probe, the probe will tend to move to a position on the surface of the map that gives the highest ratio.

2 A control means as claimed in claim 1, including means for altering the ratio from that as predetermined by the road speed and accelerator pedal co-ordinates of the probe.

3 A control means as claimed in claim 2, wherein said means for altering the ratio comprise means for moving the control map in the ratio dimension.

4 A control means as claimed in claim 2, wherein said means for altering the ratio comprise means for moving the probe out of contact with the control map.

5 A control means as claimed in claims 3 or 4, wherein movement of the probe out of contact with the control map is undamped, while return movement into contact is damped.

6 A control means as claimed in any one of claims 2 to 5, wherein said means for altering the ratio operate in response to pressure in the intake of an internal combustion engine driving the transmission.

7 A control means as claimed in any preceding claim, wherein said road speed coordinate limiting means comprises a profiled blade arranged to pivot across the surface of the control map.

8 A control means as claimed in claim 7, wherein the profile of said blade is such that under certain steady state conditions at a given road speed, the ratio will not vary irrespective of acceleratorpedal displacement.

9 A control means as claimed in any preceding claim, wherein said road speed co-ordinate limiting means can be fixed at a given setting by the driver.

10 A control means as claimed in claims 8 and 9, wherein a plurality of fixed ratios can be set by the driver.

11 A control means as claimed in any preceding claim wherein said road speed coordinate limiting means cause actuation of a torque limited coupling in the transmission when the road speed is below a predetermined value.

12 A control means as claimed in any preceding claim, wherein said transmission is operable in two regimes and said control map has regions associated exclusively with each regime, including means for detecting movement of the probe from one said region to another and means for causing the transmission regime to change accordingly.

1 3 A control means for a continuously variable ratio vehicle transmission substantially as hereinbefore described with reference to Figures 1 to 12 or Figures 13 and 14 of the accompanying drawings.