GB2036204A - Speed controlled pulley system - Google Patents

Abstract

A pulley (6) with a half sheave (8) which is biased by spring (12) axially towards a half sheave (7) drives, through an endless member (23) such as a Vee-belt, steel ring, or chain, a pulley (18) of which a half sheave (20) is axially displaceable on a shaft (17) by variations of fluid pressure in a chamber (26) to which fluid is admitted or exhausted by a spool valve (27) controlled by a centrifugal governor (28) so as to maintain a substantially constant speed of the pulley (18). In a modification, dispensing with the governor and spool valve, the chamber (26) is in constant communication both with the output from a pump driven to provide an output pressure which is in proportion to the speed of rotation of the pulley (18), and with a temperature- compensated discharge orifice. <IMAGE>

Description

SPECIFICATION Improvements in or relating to speed con trol devices This invention relates to a speed control de vice.

More particularly the invention concerns a speed control device of the kind comprising two V-pulleys mounted for axial rotation; an endless transmission member engaging under tension between the two pulleys to transmit rotational drive from one to the other; each pulley having at least one half sheave which is axially displaceable with respect to its other half sheave; control means associated with a first of the pulleys for axially displacing the half sheaves of that pulley one with respect to the other, and biasing means associated with the second pulley for biasing the half sheaves of that pulley axially towards each other to maintain the transmission member under tension and accommodate radial displacement of the transmission member resulting from operation of the control means during a variation in the ratio at which rotational speed is transmitted between the pulleys.Such a speed control device will hereinafter be referred to as of "the kind specifed".

Speed control devices of the kind specified are well known in the art as, for example, disclosed in our U.K. Patent Specification No.

1,426,351, and conveniently, but not essentially serve to control the speed of rotation of an output pulley to maintain that speed substantially constant by appropriate control of the axial displacement of the half sheaves of the pulleys when the speed of rotation of the input or driving pulley attains a predetermined value, which value may be variable within a predetermined range of the device. By relatively displacing the half sheaves of the respective pulleys the endless transmission member which, in conventional devices of the kind specified, is a V-belt, is displaced radially relative to the pulleys to vary the ratio at which rotational speed is transmitted from one pulley to the other. It has hitherto been proposed for example in our aforementioned U.K.

Specification for the control means to be in the form of a centrifugally operated governor which is responsive to the speed of rotation of one of the pulleys and reacts to adjust the relative axial displacement between the half sheaves of that pulley for varying the transmission ratio. The displacement of a pulley half sheave in this manner has necessitated in the use of centrifugal governors which are sufficiently large and heavily loaded to displace the half sheave with a smooth operation at the appropriate rotational speed of the pulley and it is an object of the present invention to provide a speed control device of the kind specified and having improved control means which can alleviate the require ment for relatively large and heavy centrifugal governors as aforementioned whilst providing smooth operation to half sheave displacement as required.

According to the present invention there is provided a speed control device of the kind specified in which the control means com prises a chamber which is expansible under fluid pressure and a variation in volume of which chamber controls relative axial displace ment between the half sheaves of the first pulley.

Further according to the present invention there is provided a system which includes a speed control device as specified in the immediately preceding paragraph.

Preferably the control means is responsive to the speed of rotation of one of the two pulleys, usually that of the first pulley, to control the fluid pressure in the expansible chamber in accordance with the speed of rotation of the pulley to which it responds.

The chamber may be formed as a piston and cylinder device which is appropriately linked or coupled to the, or one of the, axially displaceable half sheave of the first pulley so that such half sheave will be displaced axially relative to the other half sheave during operation of the piston and cylinder device by variations of fluid pressure in its chamber. In a more compact and preferred arrangement however the chamber can be formed integral with the half sheave which is intended to be axially displaced on the first pulley and in a convenient and compact construction that half sheave of the first pulley is axially slidable on a shaft for the pulley within a cylinder formed by a casing which is carried by the shaft and secured against axial displacement relative thereto, the chamber being formed between the said displaceable half sheave and the casing.

In a simple form of construction the chamber in the device of the invention may be in constant communication with a port through which the device is intended to be coupled to a source of fluid under pressure from which the fluid pressure is variable A system which includes such a simple construction may have a pump the fluid pressure output from which is variable in accordance with the speed of the pump and the pump output is in constant communication with the chamber by way of the aforementioned port and is also in constant communication by way of a restrictor with exhaust. Such a pump will be driven at variable speeds to vary the fluid pressure in the chamber and displace the half sheave of the first pulley to vary the speed transmission ration of the device as required.Desirably the pump is driven at a speed so that its fluid pressure output is proportional to the speed of rotation of the first pulley (conveniently the pump is driven directly from the first pulley or from a shaft which is rotatable with that pulley).

In a more preferred construction in which the chamber can be subjected to fluid pressure from a source which provides either a variable fluid pressure output or a substantially constant fluid pressure output (preferably the latter) the control means in the device of the present invention comprises a valve for determining the flow of fluid under pressure from said source to the chamber. The operation of this valve can be controlled automatically for its adjustment in accordance with variations in the rotational speed of either the first or the second pulley (preferably the first pulley) to which the control means is responsive.A speed sensitive electrical switch or similar device may be used to control operation of the valve but it is preferred that such operation in controlled by a centrifugal governor which reacts in accordance with the rotational speed of the pulley to which the control means is responsive. It is here to be noted that the centrifugal governor is required merely for the purposes of valve adjustment and not as in the proposal of our U.K. Specification No. 1,426,351, for the purpose of directly determining axial displacement of the half sheave of the first pulley and consequently the centrifugal governor as used in the present invention may be considerably smaller and less heavily loaded than that in the previous proposal.Conveniently the valve is in the form of a spool which controls the opening and closing of the port means to the chamber through which port means the chamber is intended to communicate with fluid under pressure or exhaust and which spool is biased by spring or other means in one sense of its displacement while the centrifugal governor is arranged, in use, to displace the spool against such spring biasing. For a compact construction in which the control means is responsive to the speed of rotation of the first pulley, the spool may be axially displaceable in a spool cylinder in a shaft of the first pulley and with which shaft both the centrifugal governor and the first pulley are rotatable.

As aforementioned devices of the kind specified are usually applied for maintaining the speed of rotation of one pulley substantially constant when the speed of rotation of the other pulley attains a predetermined value which value may be varied within a predetermined range and in the present invention it is preferred that the first pulley is intended to be driven through the transmission member from the second pulley and the control means determines fluid pressure in the chamber to control the expansion and contraction thereof and vary the speed transmission ratio between the pulleys to maintain the speed of rotation of the first pulley substantially constant over the intended range of the device.

The term "fluid" is intended to include expansion of the chamber either hydraulically or pneumatically and consequently when such chamber is open to communication with exhaust it is intended that hydraulic fluid within the chamber is open to communication with an appropriate reservoir.

One embodiment of a speed control device of the kind specified and constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings in which: Figure 1 shows the device in sectional side elevation, and Figure 2 shows, in schematic form, a modification for part of the device in Fig. 1.

The control device has a sealed housing 1 within which an input shaft 2 is mounted for rotation about an axis 3 by roller bearings 4 and a ball race 5. Mounted on the shaft 2 is a V-pulley 6 having half sheaves 7 and 8 with axially opposed frusto concial drive faces 9.

The half sheave 7 is keyed for rotation with, and axially secured relative to, the shaft 2 while the half sheave 8 is axially displaceable along the shaft 2 on a bearing sleeve 1 0. The half sheave 8 engages with the half sheave 7 through peg and socket devices 11 which ensure that both half sheaves rotate in unison with the shaft 2 irrespective of axial displacement of the half sheave 8. The half sheave 8 is biased axially towards the half sheave 7 by a helical spring 1 2 which reacts between the half sheave 8 and the flange 1 3 of a plate which is keyed for rotation with the shaft 2 and is secured axially with respect to that shaft.

Also mounted in the housing 1 in a ball race 14 and needle bearings 1 5 for rotation about an axis 1 6 (which is parallel with axis 3) is an output shaft 1 7. The output shaft 1 7 carries a second V-pulley 1 8 having half sheaves 1 9 and 20 with axially opposed frusto conical drive faces 21.The half sheave 1 9 is keyed for rotation with and secured axially relative to the shaft 1 7 while the half sheave 20 is axially displaceable in sealed manner along the shaft 1 7. Peg and socket connecting devices 22 are provided between the half sheaves 1 9 and 20 to ensure that they rotate in unison with the shaft 1 7 while the half sheave 20 is capable of axial displacement along the shaft.

The pulleys 6 and 1 8 are drivingly connected together by an endless transmission member 23 which can be in the form of a conventional V-belt or can be in a form suitable for traction drive in the manner which is the subject of our co-pending U.K. Patent Application No. (Ref: FJW/GDG/244; with the aforementioned traction drive the member 23 may be in the form of an annular steel ring or a steel chain which drivingly engages the drive faces 9 and 21 through a film of traction fluid such as the material sold under the Trade Mark "Santotrac" and which fluid is contained in the sealed housing 1.

The displaceable half sheave 20 is in the form of a piston which is in sealed and sliding engagement with a cylinder 24 of an annular casing 25 which is sealed to, and rotatable with, the shaft 17. Formed between the half sheave 20 and the casing 25 is a fluid chamber 26. In the absence of fluid pressure in the chamber 26 the biasing effect of spring 1 2 on pulley 6 will cause the transmission member 23 to be displaced from the position illustrated to a condition in which the radius R1 at which the transmission member 23 engages the drive faces 9 is at a maximum while the radius R2 at which the transmission member 23 engages the drive faces 21 is at a minimum (since the half sheaves 1 9 and 20 will have been displaced axially away from each other to their maximum spacing by the axial force exerted on those half sheaves from the biasing effect of spring 1 2 through the transmission member 23). With R1 at a maximum and R2 at a minimum the speed ratio at which drive will be transmitted from pulley 6 to pulley 1 8 will be at a maximum while the mechanical advantage of the device will be at a minimum (and consequently the shaft 1 7 will rotate at considerably higher speed than the shaft 2).If now the chamber 26 is subjected to fluid pressue to an extent which is sufficient to overcome the biasing effect of spring 1 2 through the transmission member 23, the half sheave 20 of pulley 1 8 will be displaced axially towards the half sheave 1 9 so causing the transmission member 23 to be displaced radially in a sense to increase the radius R2 while radius R1 is correspondingly decreased. By this latter effect the speed transmission ratio is progressively decreased (while the mechanical advantage of the device increases accordingly) until the position illustrated is attained where R2 and R1 are at a maximum and minimum respectively and the rotational speed at which the output shaft 1 7 is driven from the shaft 2 will be considerably less than the rotational speed of the shaft 2.

Fluid pressure in the chamber 26 is controlled by a valve 27 which is responsive to a centrifugal governor 28 which is in turn responsive to the speed of rotation.of the shaft 1 7. The valve 27 comprises a spool 29 which is axially slidable in a spool cylinder 30 formed by a co-axial blind bore in the end of the shaft 1 7. The spool 29 has an annular recess 31 which is in constant communication by way of a port 32 in the wall of the shaft 1 7 with the chamber 26. The spool 29 is able by its axial displacement to open communication between the annular recess 31 and either a port 33 or a port 34. The port 33 is in constant communication by way of a passage 35 in the shaft 1 7 and a chamber 36 with an exhaust port 37.The port 34 is in constant communication by way of a passage 38 in the shaft 1 7 and an annular recess 39 on the shaft 1 7 with a pressure port 40. Pressurisation of the chamber 26 can be effected hydraulically or pneumatically and in the present example the pressure port 40 communicates with the output from a constant delivery pump 41 which draws hydraulic fluid from a reservoir 42 while the exhaust port 37 communicates through a return line 43 with the reservoir 42.

The governor 28 has a flange or cage 44 which is connected through a rod 45 with the spool 29. Captured between the cage 44 and a ramp surface 46 on the end face of the shaft 1 7 in the chamber 36 are balls 47. The ramp surface 46 is frusto conical and co-axial with the axis 1 6. The cage 44, balls 47 and spool 29 rotate with the shaft 1 7 and abutting the cage 44 along the axis 1 6 is a mushroom button 48 which is biased by a spring 49 relative to a closure cap 50 of the chamber 36 and into engagement with the cage 44.The biasing effect of spring 49 on the cage 44 is to urge the balls 47 over the ramp surface 46 to a position in which they are at a minimum radius from the axis 1 7 and which position corresponds to the spool 29 being located at a condition substantially as drawn where the port 33 communicates with the recess 31 and thereby the chamber 26 communicates through the exhaust port 37 with the reservoir; consequently in the condition as drawn the chamber 26 will be contracting as the transmission member 23 is displaced radially under the biasing effect of spring 12 on pulley 6 to cause R1 to increase to its maximum and R2 to decrease to its minimum.When port 34 is closed by the spool to communication with the recess 31 as drawn it will be apparent that the output from the pump 41 is closed; to alleviate unnecessary strain on the pump 41 an hydraulic accummulator can be included between the pump and the port 40 or alternatively, and more preferably, the valve 27 can include appropriate porting to direct the output from the pump 41 back to the reservoir 42.

In use of the device in, for example, a motor vehicle in which the input shaft 2 may be driven at varying speeds (say from the crank shaft of the vehicle engine through a belt drive to a V-pulley 51 on the shaft 2) while the output shaft 1 7 may be used to drive auxilliary equipment of the vehicle (such as a water pump or generator again by belt drive from a V-pulley 52 of the shaft 17), if it is assumed that the pulley sheaves have been respectively displaced so that R1 is at a maximum and R2 is at a minimum, upon initial rotation of the shaft 2 the rotational speed of the output shaft 1 7 is considerably greater than that of the shaft 2.If the rotational speed of the shaft 1 7 attains a predetermined value upon its initial' rotation from the shaft 2 or attains such value as the speed of rotation of the shaft 2 progressively increases, the centrifugal governor 28 reacts by the balls 47 being displaced radially outwardly of the axis 1 6 and over the ramp surface 46 to cause the cage 44 and spool 29 to be displaced rightwardly in the drawing against the biasing effect of spring 49. Such displacement of the spool 29 closes communication between the port 33 and recess 31 and opens communication between the recess 31 and the port 34. The effect of this latter movement is to open communication between the chamber 26 and hydraulic fluid under pressure by way of port 32, recess 31, port 34, passage 38, annular recess 39 and port 40.

The chamber 26 is thus pressurised to bias the half sheave 20 axially towards the half sheave 1 9. When sufficient pressure is available in the chamber 26 the half sheave 20 will be displaced axially towards the half sheave 1 9 thereby causing the transmission member 23 to be displaced radially and the half sheaves 8 and 7 to be displaced axially against the biasing of spring 1 2 to progressively increase R2 and decrease R1 to provide a decrease in the ratio at which speed is transmitted from pulley 6 to pulley 1 8 and the rotational speed of shaft 1 8 decreases in comparison with the relatively increasing rotational speed of shaft 2.By appropriate selection of the characterics for the governor 28, the biasing spring 49, the pressurised area of the half sheave 20 in the chamber 26 and the spring 12, the automatic adjustment in the axial spacing of the half sheaves 1 9 and 20 can be controlled so that the rotational speed of the output shaft 1 7 is maintained substantially constant for a given speed of rotation of the input shaft 2 which given speed may be variable within a predetermined range.It will be apparent that, in the event of the rotational speed of the output shaft 1 7 falling below a predetermined value, the biasing effect of spring 49 will displace the balls 47 of the governor radially inwardly so permitting the spool 29 to close communication between the port 34 and the recess 31 and open communication between the port 33 and recess 31 with the effect that the chamber 26 communicates with the exhaust port 37 and R2 decreases accordingly while R1 increases to step up the ratio at which rotational speed is transmitted from the pulley 6 to the pulley 1 8 (thereby causing an increase in rotational speed of the output shaft 1 7 in an attempt to maintain that rotational speed substantially constant).

In the modification of the device shown in Fig. 2 the valve 27 and centrifugal governor 28 have been omitted while the chamber 26 is in constant communication by way of passage 51 with the output from a variable delivery pump 52 drawing fluid from the reservoir 42. In addition the output from the variable delivery pump 52 communicates by way of branch passage 53 and a temperature compensated restrictor 54 directly with the reservoir 42. The pump 52 is driven so that its output is in proportion with the speed of rotation of the shaft 1 7 (conveniently the variable delivery pump 52 is driven by appropriate connection from the output shaft 17).

By this arrangement when the shaft 1 7 is stationary its chamber 26 will be contracted through the biasing force exerted on the half sheave 20 through the transmission member 23 by the spring 1 2 (fluid from the chamber 26 passing to the reservoir by way of the restrictor 54), so that R1 will be at a maximum and R2 at a minimum. Upon rotation of the shaft 2 the output shaft 1 7 will have a considerably greater rotational speed than that of the input shaft and upon the speed attaining a predetermined value the output from the variable delivery pump 52 (as determined by the rotational speed of the shaft 17) pressurises the chamber 26 to an extent which causes the half sheave 20 to be displaced axially towards the half sheave 1 9 and a corresponding adjustment in the speed transmission ratio through the device. By this arrangement and appropriate selection of the restrictor 54 in the hydraulic system and the pressurised area of the half sheave 20 in the chamber 26 the rotational speed of the output shaft 1 7 can be maintained substantially constant irrespective of the speed of rotation of the input shaft 2 within a given range.

Claims (21)

1. A speed control device of the kind specified in which the control means comprises a chamber which is expansible under fluid pressure and a variation in volume of which chamber controls relative axial displacement between the half sheaves of the first pulley.

2. A device as claimed in claim 1 in which the control means is responsive to the speed of rotation of one of the two pulleys to control fluid pressure in the chamber in accordance with the speed of rotation of the pulley to which it is responsive.

3. A device as claimed in claim 2 in which the control means is responsive to the speed of rotation of the first pulley.

4. A device as claimed in any one of the preceding claims in which the control means comprises a valve for determining the flow of fluid under pressure from the source of such pressure to the chamber.

5. A device as claimed in claim 4 in which adjustment of the valve is determined by a speed sensitive device which is responsive to and adjusts the valve in accordance with variations in the speed of rotation of the pulley to which the control means is responsive.

6. A device as claimed in claim 5 in which the speed sensitive device is a centrifugal governor.

7. A device as claimed in either claim 5 or claim 6 in which the valve comprises a spool which is displaceable to control the opening and closing of port means to the chamber through which port means the chamber is intended to communicate with fluid under pressure or exhaust, said spool being biased in one sense of its displacement and the speed sensitive device being arranged to displace the spool against its biasing.

8. A device as claimed in claim 7 when appendant to claim 6 in which the spool is axially displaceable in a spool cylinder in a rotatable shaft of the first pulley and to the rotation of which shaft the centrifugal governor is responsive.

9. A device as claimed in claim 8 in which the centrifugal governor comprises caged balls which, during rotation of the shaft are displaceable radially outwardly against spring biasing and relative to the shaft over a ramp surface to impart axial displacement to the spool against said biasing.

10. A device as claimed in any one of claims 4 to 9 wherein the valve is biased to a condition in which it opens communication between the chamber and a port which is intended to be connected to exhaust and is displaceable against said biasing to close such communication and open communication between the chamber and a further port which is intended to be connected to a source of fluid under pressure.

11. A device as claimed in any one of the preceding claims in which the first pulley is driven through the transmission member from the second pulley.

1 2. A device as claimed in claim 11 in which the control means determines fluid pressure in the chamber to control the expansion and contraction thereof for maintaining the speed of rotation of the first pulley substantially constant when the speed of rotation of the second pulley attains a predetermined value which value is variable within a predetermined range.

1 3. A device as claimed in any one of the preceding claims in which the chamber is formed between the or an axially displaceable half sheave of the first pulley and a casing which is secured for rotation with said first pulley and against axial displacement with respect to that pulley.

14. A device as claimed in claim 1 3 in which the casing is carried for rotation with and secured against axial displacement relative to the, or a, shaft which is rotatable with the first pulley.

1 5. A speed control device of the kind specified and substantially as herein described with reference to Fig. 1 of the accompanying illustrative drawing.

1 6. A device as claimed in claim 1 5 and having the modification substantially as herein described with reference to Fig. 2 of the accompanying illustrative drawings.

1 7. A system which includes a speed control device as claimed in any one of the preceding claims.

18. A system as claimed in claim 1 7 when appendant to claim 4 in which first port means of the valve is in communication with a source of fluid under substantially constant pressure and second port means of the valve is in communication with exhaust, said valve being operable to open communication between the chamber and either said first port means or second port means to permit expansion or contraction of the chamber and corresponding displacement between the respective half sheaves of the first pulley.

1 9. A system as claimed in claim 1 7 in which the chamber is in constant communication with a source of fluid pressure which provides a variable pressure output which output is in constant communication with exhaust by way of a restrictor.

20. A system as claimed in claim 1 9 in which the source of fluid pressure provides an output the pressure of which increases and decreases in proportion to an increase and decrease respectively in the rotational speed of one of the pulleys.

21. A system as claimed in claim 20 in which fluid pressure is derived from a variable speed pump which is responsive to the speed of rotation of the first pulley so that the output of said pump is proportional to that speed of rotation and wherein the pump is coupled to be driven from said first pulley.