GB2313652A

GB2313652A - Hydraulic transmission unit

Info

Publication number: GB2313652A
Application number: GB9611342A
Authority: GB
Inventors: Raymond Simms
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-05-31
Filing date: 1996-05-31
Publication date: 1997-12-03
Also published as: GB9611342D0

Abstract

A transmission unit comprises a housing (102, 105) rotatably mounting an input shaft (110) and an output shaft (112), the input shaft being coupled to cam plates (123, 124,..) arranged to cause reciprocation of at least one pumping piston (133) in a respective cylinder (132) of a hub (125) connected to the output shaft. With the hub and output shaft held fast to the housing by a brake (155, 158, 160, 162), hydraulic fluid is pumped by the piston or pistons round a circuit comprising inlet and outlet valves (137, 136) and a flow path (141-144, 152, 145-148, 150) having a selectively operable valve (151). Closure of the valve (151) causes a build-up of pressure in the passage (142) resulting in the pressurisation of an annular cylinder (161) and the release of the brake. The release of the brake allows the cam plates to cooperate with the piston(s) to drive the hub and the output shaft. The embodiment shown has radially acting pistons, but in a further embodiment a single piston co-axial with the shafts and operated by an axial cam is provided.

Description

TRANSMISSION UNIT This invention relates to a transmission unit. In particular it is concerned with a unit for controlled coupling between a driving shaft and a driven one. A conventional unit for this purpose in the automotive field is provided by a dry plate friction clutch in which one or more plates are pressed into frictional engagement by a strong spring, to couple the shafts, the spring pressure being reduced progressively by mechanical means to disengage the plates, to separate the shafts. Such a clutch predominates in motor vehicles making use of manually selected transmission gears. Despite being simple in design and cheap the use of a dry plate clutch can have disadvantages. Typically in most vehicle applications such a clutch requires considerable physical effort in operation. Such a clutch can be abused by the vehicle driver leading to progressive deterioration in function to the point of failure and the possibility of damage to other parts of the transmission system. Apart from user abuse the commonest forms of clutch failure arise from contamination of the friction plates by liquids, such as oil or hydraulic fluid, and from wear arising from rubbing contact between the plates. Dry plate clutches have for a long time been in widespread use for cars having a manual transmission and the associated disadvantages have been accepted. The clutch is used to interrupt the transmission of torque from a driving shaft to a gearbox input shaft permitting the user to select a different gear ratio after which the clutch is re-engaged allowing continued power flow to the driven car wheels by way of the new gear ratio.

Attempts have been made to automate a dry plate clutch to allow automatic operation so that coordinated transmission gear selection and clutch operation could be undertaken without the need for the driver to simultaneously operate clutch and transmission gear mechanisms. Such attempts at automation have not been widely accepted and are a relatively expensive way of eliminating a clutch operating pedal.

There has been an increasing use of semi-automatic and automatic transmissions where the coupling of the driving shaft to the driven shaft is achieved, for example, by way of hydraulic, centrifugal or magnetic couplings whose operation is not necessarily governed directly by a driver but by way of a control system which takes into account a number of factors, such as engine speed, road speed, transmitted torque and direction of travel, when responding to driver input.

For automatic transmission systems for a vehicle widespread use is made of a hydraulic coupling, referred to as a torque converter, between driving and driven shafts. The torque converter comprises a driving impeller co-axial with a driven rotor. The impeller and rotor are provided with complementary surface configurations by means of which flows of hydraulic fluid are established to so as to 'lock-up' the driving impeller to the driven rotor to provide for synchronous rotation with little torque transmission loss. By providing an automatic gear selection system with a torque converter rather than a dry plate clutch gear ratio changes can be undertaken swiftly and more rapidly than would be possible with a manually regulated transmission and a conventional dry plate clutch. A hydraulic torque converter readily accommodates transient changes in transmitted torque and in relative shaft speeds so providing for a rapid and jerk free change of gear ratio to occur between the driving and the driven shafts. However conventional torque converters are more expensive to manufacture than a dry plate clutch, they do not provide positive drive characteristics and although gear selection is fast their overall gear change time is slow.

According to a first aspect of the present invention there is provided a transmission unit having: a housing an input shaft to the housing; an output shaft from the housing at least one hydraulic pump in the housing including a piston member, a cylinder member and a hydraulic fluid inlet to, and a hydraulic fluid outlet from, the cylinder member; interactable cam surfaces linking the input shaft and the pump whereby the input shaft can displace the piston member or the cylinder member to cause pressurisation of an internal volume of the pump; a first hydraulic circuit extending internally of the pump from the fluid inlet to the fluid outlet; a second hydraulic circuit extending externally of the pump from the fluid outlet to the fluid inlet; a valve in the second hydraulic circuit operable between a closed position where the valve inhibits the passage of fluid along the second hydraulic circuit and an open position where the valve does not inhibit the passage of fluid as aforesaid; the pump being disposed in the housing relative to the input shaft and the output shaft such that with the input shaft rotating and with the valve in the closed position the second hydraulic circuit is maintained pressurised such that the input shaft causes the displacement of the, or each, pump and the displacement of the pump is transmitted to the output member by way of the piston or cylinder and a mechanical link to provide for synchronous rotation between input shaft and output shaft.

According to a first preferred version of the first aspect of the present invention the unit incorporates a brake acting to inhibit rotation of the output shaft relative to the housing when the valve is in the open position.

According to a second preferred version of the first aspect of the present invention or the first preferred version thereof the input shaft and the output shaft are co axial.

According to a third preferred version of the present invention or any preceding preferred version thereof the piston and cylinder are disposed co-axially relative to the input shaft.

According to a fourth preferred version of the first aspect of the present invention or of the first or second preferred versions thereof the, or each, piston and cylinder are disposed radially relative to the input shaft.

According to a second aspect of the present invention there is provided a vehicle equipped with a transmission unit according to the first aspect for the purpose of controllably isolating an output shaft of a prime mover of the vehicle from a device driven by way of the output shaft.

Exemplary embodiments of the invention will now be described with reference to the accompanying drawing which are sectional elevations of transmission units providing for controlled separation of torque transmitting shafts of which: Figure 1 is a section of a first embodiment; Figure 2 is of a second embodiment; and Figure 3 is a perspective view of compotnets of Figure 1.

Figure 1 COMPONENTS AND LAYOUT Transmission unit 11 is contained in a housing made up of an output end casing 13 with integral outer flange 13A and inner flange 13B and an input end casing 14 with integral outer flange 14A and inner flange 14B. The inner flanges 13B, 14B are secured together by way of bolts, typically bolt 17. A gasket 18 provides for the joint between the secured flanges 13B, 14B to be liquid tight.

Input shaft 19 is rotatable about axis 19A. Output shaft 20 is rotatable about axis 20A and serves to transmit torque received by way of the input shaft 19 in a manner described hereafter. In this case the axis 19A and 20A are coaxial.

Input shaft 19 is located by bearing 21 in aperture 22 in input end casing 14..

Rotary seal 23 provides for a liquid tight seal between the casing 14 and the input shaft 19.

Output shaft 20 is located by bearing 24 in aperture 25 in output end casing 13.

Rotary seal 26 provides for a liquid tight seal between the casing 13 and the output shaft 20.

Input shaft 19 has a cam profiled inner end 27A which complements a matching cam profile 27B on the left hand side of end flange 29 of hollow cylinder 28. The cylinder 28 forms part of a hydraulic pump which is used to power operation of the unit 11 as will be described hereafter. Cylinder 28 contains a bore 30 providing a fluid tight rotary and sliding fit for section 31 of output shaft 20. The cylinder 28 has towards its left hand end 32 a bore 33 of reduced diameter in which is located a capsule 34 containing a suction valve 35. The capsule 34 serves to define a left hand boundary of a working chamber 36 for the pump. A right hand boundary for the working chamber 36 is provided by inner end face 37 of output shaft 20.

The cylinder 28 is capable of axial displacement, and also rotary displacement, relative to axis 19A.

The right hand face of end flange 29 of cylinder 28 is resiliently loaded by compression spring 38 so that given no hydraulic pressure differential across the cylinder 28 the cylinder 28 is biassed to the left as viewed in the drawing so tending to maintain the cam profile 27B of the cylinder 28 in contact with cam profile 27A of the input shaft 19.

Output shaft 20 has a blind ended bore 40 extending from end face 37 to cross bore 41. Open end 42 of the bore 40 is closed by a pressure valve 43. The cross bore 41 opens into a annular chamber 44 in end web 45 of output end casing 13.

A discharge duct 46 extends from chamber 44 to an outlet port 47 on outer perimeter 48 of end casing 13. A corresponding inlet port 49 is provided on the end casing from which an inlet duct 50 in the output end casing 13 leads to a matching duct 51 in input end casing 14. Duct 51 opens by way of outlet 52 into plenum 53. Input shaft 19 is provided with ports 54, 55 and cylinder 28 with ports 56, 57 to enable fluid in the plenum 53 to pass freely into recess 58 at the left hand end of the cylinder 28.

Control valve 59 provides a path 60 for hydraulic fluid passing from outlet port 47 and inlet port 49. The valve 59 can be switched by means of solenoid 59A between two positions: an open position in which the valve allows the flow of hydraulic fluid along path 60; and a closed position in which the valve inhibits such a flow.

The unit 11 provides two distinct hydraulic circuits: a first path extending through working chamber 36 from suction valve 35 to pressure valve 43; and a second path outside working chamber 36 from pressure valve 43, bore 40, cross bore 41, annular chamber 44, discharge duct 46, port 47, path 60, inlet port 49, inlet duct 50, duct 51, outlet 52, plenum 53, recess 58 and suction valve 35.

A reaction brake 63 is provided to prevent rotation of output shaft 20 in the event valve 59 is not closed. The brake 63 normally engages wear ring 61 located in a recess 62 in end web 45. The brake 63 is coupled to the output shaft 20 by a castellated ring 64. The brake 61 is regulated by way of a piston 65 which is adopted for axial displacement relative to axis 20A by way of annular hydraulic cylinder 66 Compression spring 67 acts to drive the piston 65 to the right as shown in Figure 1 maintaining the brake 63 engaged with the wear ring 61 which is forced into the recess 62. In this position the output shaft 20 is prevented from rotating. In the event pressure in discharge duct 46 rises (as will be considered later) the pressure change is transmitted by way of bore 68 into annular cylinder 66 resulting in the displacement of the piston 65 to the left. This results in brake 63 being left to rotate unhindered by compression spring 67. The castellated ring 64 is in constant engagement with complementary slots 69 in end flange 29 of cylinder 28.

FUNCTION In use with rotation of the input shaft 19 and with the control valve 59 in its open position cam profiled ends 27A of the shaft 19 engages with the matching profile 27B of the cylinder 28. As the cylinder 28 cannot rotate it is displaced axially to the right against the resilient loading provided by compression spring 38. As a result of the consequent reduction in the volume of working chamber 36 hydraulic fluid in the chamber is forced through pressure valve 43 into the blind ended bore 40 and flows around the second path of the two hydraulic circuits described above. The flowing fluid passes around the circuit to enter the plenum 53.

Continuing rotation of the input shaft 19 results in the interaction between cam profiles 27A, 28A allowing the cylinder 28 to be driven back to its original leftwards position by the action of compression spring 38. As a result the volume of working chamber 36 increase resulting in a relative vacuum being formed in a chamber leading to the closure of pressure valve 43 and the opening of suction valve 35 allowing a flow of fluid into the chamber 36 from the plenum 53 by way of ports 54-57 and recess 58.

This cycle of fluid circulation around the two hydraulic circuits will continue for as long as the input shaft rotates and the control valve 59 is left open. Output shaft 20 will be prevented against inadvertent turning by way of brake 63.

In the event the unit 11 is to provide for rotation of output shaft 20 by way of input shaft 19 the control valve 59 is closed by operation of solenoid 59A. The continuing interaction of the cam profiles 27A, 27B will result in an increase in pressure in the part of the second hydraulic circuit made up of blind ended bore 40, cross bore 41, annulus 44, discharge duct 46 and outlet port 47. The pressure rise will be applied to annular hydraulic cylinder 66 with a consequent displacement of piston 65 against the action of spring 67 so releasing reaction brake 63 from engagement with wear ring 61. Slots 69 on flange 29 of cylinder 28 are constantly engaged castellated ring 64 on output shaft 20 so providing for the rotating input shaft 19 to drive output shaft 20 for as long as the control valve 59 remains closed inhibiting the flow of hydraulic fluid around the second fluid circuit.

Figure 3 shows the axial relationship of brake 63, castellated ring 64 and end flange 29.

The pumping action provided by way of working chamber 36 does not occur while the unit is providing for rotation of output shaft 20 by way of input shaft 19.

The embodiment incorporates an anti-reaction brake 63. However it is envisaged that in some applications the provision of such a brake will not be necessary.

The embodiment described in connection with Figure 1 has a pump including cylinder 28 to provide a pumping action. This is conveniently described as an axial arrangement since the pumping action is provided by motion of cylinder 28 along an axis co-axial with the axis of rotation of the inlet (and outlet) shafts. This configuration is appropriate for transmitting powers of the order of 8hp at up to 3000 rpm typically for use for electric traction. However for use with, say, internal combustion engines providing power outputs of between 60 and 180 bhp at up to 6000 rpm another configuration could be used where the pump arrangement is a radial one. An example of this configuration will now be described in connection with Figure 2.

Figure 2 COMPONENTS AND LAYOUT Transmission unit 101 is contained in a housing made up of an output end casing 102 with integral outer flange 103 and inner flange 104; and an input end casing 105 with integral outer flange 106 and inner flange 107. The inner flanges 104, 107 are secured together by way of bolts, typically bolt 108. A gasket 109 provides for the joint between the secured flanges 104, 107 to be liquid tight.

Input shaft 110 is rotatable about axis 111. Output shaft 112 is rotatable about axis 113 and serves to transmit torque received by way of the input shaft 110 in a manner described hereafter. In this case the axis 111 and 113 are themselves coaxial.

Input shaft 110 is located by bearing 114 in aperture 115 in input end casing 105.

Rotary seal 116 provides for for a liquid tight seal between the casing 105 and the input shaft 110.

Output shaft 112 is located by bearing 119 in aperture 120 in output end casing 102. Rotary seal 121 provides for for a liquid tight seal between the casing 102 and the output shaft 112.

Input shaft 110 has concentrically mounted on it, and keyed to it, a wheel 122 carrying three angularly equi-spaced cam plates of which only plate 123 and 124 are shown. Only cam plate 123 will hereafter be described in further detail but the remaining two plates are similar in form and function.

Output shaft 112 has an integrally formed end in the form of a hub 125 mounted by way of bearings 126, 127. Bearing 126 is mounted in a recess 128 in wheel 122.

Bearing 127 is mounted in recess 129 in web 130 of casing 102. The hub 125 contains three recesses (of which only recess 131 is shown) angularly spaced to correspond with the spacing of cam plates 123, 124 and the hidden plate. Since the recesses and their associated components are similar in form and function only recess 131 and items associated therewith will be described in further detail.

Recess 131 houses a cylinder 132 in which is located a piston 133 reciprocable on axis 134 radial to input axis 111 (and to output axis 113). Cylinder 132 and piston 133 serve to define a working chamber 135 (shown here at minimum volume).

Hydraulic fluid under pressure in working chamber 135 is expelled from the chamber 135 by way of pressure valve 136. When suction is created in working chamber 135 is low hydraulic fluid is drawn into the chamber 135 by way of suction valve 137. The hydraulic circuits relating to the working chamber 135 and valves 136, 137 will be described hereafter.

Valve 136 enables hydraulic fluid to pass by way of bore 138 into blind ended bore 139 common to the output of the working chambers corresponding to chamber 135 in the other two cylinders. Bore 139 is closed at its left hand end (as viewed in Figure 2) by a bolt 140. Bore 141 links bore 139 to radial passage 142.

The passage 142 extends to an outlet port 143 on outer periphery 144 of output end casing 102.

A corresponding inlet port 145 is provided on the input end casing 102 from which an inlet duct 146 in the input end casing 105 extends into plenum 147.

Wheel 122 is provided with apertures, typically apertures 148, 149 to enable fluid in the plenum 147 to pass freely into recess 150 immediately upstream of suction valve 137 and the corresponding suction valves of the other two cylinders.

Control valve 151 provides a path 152 for hydraulic fluid passing from outlet port 143 to inlet port 145. The valve 151 can be switched by means of solenoid 153 between two positions: an open position in which the valve allows the flow of hydraulic fluid along path 152 and a closed position in which the valve inhibits such flow.

In the first position a variable flow control valve may be used to modulate flow along path 152.

The transmission unit 101 provides two distinct hydraulic circuits: a first circuit extending through the working chamber 135 from suction valve 137 to pressure valve 136; and a second circuit external to the working chamber 135 from pressure valve 136, bore 138, blind ended bore 139, bore 141, radial bore 142, outlet port 143, path 152, inlet port 145, inlet duct 146, plenum 147, apertures 148, 149, recess 150 and suction valve 137.

A reaction brake 158 is provided to prevent rotation of output shaft 112 in the event valve 151 is not closed. The brake 158 normally engages wear ring 155 which is located in a recess 156 in web 157 in output end casing 102. The brake 158 is coupld to the hub 125 and to the remainder of output shaft 112, by a flange 159. The brake 158 is regulated by way of a piston 160 which is adopted for axial displacement relative to axis 113 by way of annular hydraulic cylinder 161.

Conical spring washer 162 acts to drive the piston 160 to the right as shown in Figure 2 maintaining the brake 158 engaged with wear ring 155. In this configuration the output shaft 112 is prevented from rotating. In the event pressure in radial bore 142 rises (as will be discussed later) the pressure change is transmitted by way of bore 163 into annular cylinder 161 resulting in the displacement of the piston 160 to the left. This frees the hub 125 resulting in the output shaft 112 being driven to rotate synchronously with input shaft 110 as will be described hereafter.

FUNCTION In use with rotation of the input shaft 110 and with the control valve 151 in its open position wheel 122 rotates causing cam plates 123, 124 to act on the piston 133 in cylinder 132 and the corresponding pistons in the other two cylinders in recesses equally spaced around the hub 125 resulting in the pistons being driven periodically down their respective cylinders to reduce the size of the working chamber 135. Hydraulic fluid in working chamber 135 is consequently periodically forced through pressure valve 136 by way of bore 138 into blind ended bore 139 and so around the second of the two hydraulic circuits described above. The flowing fluid passes into the plenum 147.

Continuing rotation of the input shaft 110 and wheel 122 results in the interaction between cam plates 123, 124 and the unshown one of the set allowing their respective pistons to be driven outwardly by the action, such as in the case of piston 133, of compression spring 133A. As a result the volume of working chamber 135 increases resulting in a relative vacuum being formed in the working chamber 135 leading to the closure of pressure valve 136 and the opening of suction valve 137. This provides for a flow of hydraulic fluid into the chamber 135 from the plenum 147 by way of apertures 148, 149 and recess 150.

This cycle of fluid circulation around the two hydraulic circuits will continue for as long as the input shaft 110 rotates and the control valve 151 remains open allowing flow through path 152. Output shaft 112 will be prevented against inadvertent turning by way of reaction brake 158.

When the unit 101 is to provide for rotation of output shaft 112 by way of input shaft 110 the control valve 151 is closed by operation of solenoid 153. The continuing interaction of the cam plates 123, 124 will result in an increase in pressure in the down stream part of the second hydraulic circuit form blind ended bore 139 to outlet port 143 but no further once the valve 151 is closed.

The pressure rise will be applied to annular hydraulic cylinder 161 via bore 163 with a consequent displacement of piston 160 against the action of spring 162 so driving reaction brake 158 out of engagement with wear ring 155 situated in recess 156. At the same time pistons 133 and the other two pistons spaced around hub 125 will lock up so causing them to remain engaged with a cam plate resulting in the wheel 122 and the hub 125 being driven as one by the input shaft 110.

Rotation of input shaft 110 will cause output shaft 112 to be driven for as long as the control valve 151 remains closed inhibiting the flow of hydraulic fluid around the second fluid circuit.

The transmission units described in connection with the two embodiments provide a simple selfcontained hydraulic unit comprising a fully immersed, positive displacement (piston) pump of either axial or radial design. The pump assembly incorporates pistons and cylinders forming a part of the link between the input and output shafts. Each embodiment includes a spring loaded hydraulically released anti-reaction brake to prevent rotation of the pump assembly while displacing fluid. In the embodiment of Figure 2 this feature can provide protection against over-revving. In both embodiments pumping action does not occur while the unit is transmitting power.

The embodiments are made up of assemblies enclosed in a light metal casing filled with hydraulic fluid to provide a reservoir. preferably the casing incorporates a pressure relief valve together with provision for supplementary service connections, a pressure switch transducer and a speed sensor. A low cost non-contact torque transducer can be fitted.

The control valves (59, 151) and their solenoid units (59A, 153) are located on the outside of their respective units. In alternative embodiments operation can be by way of mechanical, hydraulic or electrical devices depending on the type of control required.

The embodiments provide for a low cost, low friction device that would carry out the function of a clutch while requiring less physical effort than the conventional type. The device is capable of use for an automatic transmission without modification or additional components. The devices are dimensionally reconcilable with a conventional clutch, provide for a long service life and absorb virtually no engine power. The device further provides for the elimination of clutch abuse, contamination, maladjustment and misalignment associated with conventional clutches.

A unit can be used in fully automatic vehicles to replace a conventional torque converter and producing positive drive characteristics but at lower cost when compared with existing products.

A unit can be used to carry out other functions in vehicles such as replacing a viscous coupling to provide a positive, controllable four wheel drive.

Claims

1A transmission unit having: a housing an input shaft to the housing; an output shaft from the housing at least one hydraulic pump in the housing including a piston member, a cylinder member and a hydraulic fluid inlet to, and a hydraulic fluid outlet from, the cylinder member; interactable cam surfaces linking the input shaft and the pump whereby the input shaft can displace the piston member or the cylinder member to cause pressurisation of an internal volume of the pump; a first hydraulic circuit extending internally of the pump from the fluid inlet to the fluid outlet; a second hydraulic circuit extending externally of the pump from the fluid outlet to the fluid inlet; a valve in the second hydraulic circuit operable between a closed position where the valve inhibits the passage of fluid along the second hydraulic circuit and an open position where the valve does not inhibit the passage of fluid as aforesaid; the pump being disposed in the housing relative to the input shaft and the output shaft such that with the input shaft rotating and with the valve in the closed position the second hydraulic circuit is maintained pressurised such that the input shaft causes the displacement of the, or each, pump and the displacement of the pump is transmitted to the output member by way of the piston or cylinder and a mechanical link to provide for synchronous rotation between input shaft and output shaft.

2 A transmission unit as claimed in Claim 1 including a brake acting to inhibit rotation of the output shaft relative to the housing when the valve is in the open position.

3 A transmission unit as claimed in any preceding claim wherein the input and the output shafts are co-axial.

4 A transmission unit as claimed in any preceding claim wherein the piston and cylinder are disposed co-axially relative to the input shaft.

5 A transmission unit as claimed in Claim 1, Claim 2 or Claim 3 wherein the, or each, piston and cylinder are disposed radially relative to the input shaft.

6 A transmission unit as hereinbefore described with reference to and as illustrated in Figure 1 or Figure 2.

7 A vehicle equipped with a transmission unit as claimed in any preceding claim for the purpose of controllably isolating an output shaft of a prime mover of the vehicle from a device driven by way of the output shaft.

A transmission unit having: a housing an input shaft to the housing; an output shaft from the housing at least one hydraulic pump in the housing including a piston member, a cylinder member and a hydraulic fluid inlet to, and a hydraulic fluid outlet from, the cylinder member, interactable cam surfaces linking the input shaft and the pump whereby the input shaft can displace the piston member or the cylinder member to cause pressurisation of an internal volume of the pump; a first hydraulic circuit extending internally of the pump from the fluid inlet to the fluid outlet; a second hydraulic circuit extending externally of the pump from the fluid outlet to the fluid inlet; a valve in the second hydraulic circuit operable between a closed position where the valve inhibits the passage of fluid along the second hydraulic circuit and an open position where the valve does not inhibit the passage of fluid as aforesaid; the pump being disposed in the housing relative to the input shaft and the output shaft such that with the input shaft rotating and with the valve in the closed position the first or second hydraulic circuits or both provide for the input shaft to engage and displace the, or each, pump; the displacement of the pump being transmitted to the output member by way of the piston or cylinder and a mechanical link to provide for synchronous rotation between input shaft and output shaft.