WO2006017905A1

WO2006017905A1 - Multi-ratio automatic transmission with independent rate of engagement and/or disengagement control of friction elements

Info

Publication number: WO2006017905A1
Application number: PCT/AU2005/001246
Authority: WO
Inventors: Robert Krupic; Ling Qiu; Frank Bauer; Sandi Prizmic; Kent Jian Liu; John Morey; Simon Smith; Paul Anthony Donnelly; Darren Lee Firth; Stephen Tapper; Richard Terrence Tamba
Original assignee: Drivetrain Systems International Pty Ltd
Priority date: 2004-08-20
Filing date: 2005-08-19
Publication date: 2006-02-23
Also published as: KR20070083577A; MY149206A; TW200610666A; TWI375628B; CN101133266B; CN101133266A; HK1117585A1

Abstract

A multi-ratio automatic transmission (10) for a vehicle, the transmission (10) having at least one planetary gear set (16, 18), a plurality of friction elements (C1, C2, C3, B1, B2) for coupling components of the planetary gear set (16, 18) between an input and an output of the transmission in different configurations so as to achieve a plurality of drive ratios, and a control system (26) for selectively engaging/disengaging the friction elements (C1, C2, C3, B1, B2) in different combinations to effect selection of the ratios, wherein rate of engagement and/or disengagement of one or more of the friction elements (C1, C2, C3, B1, B2) is controlled independently of the or each of the other friction element(s) (C1, C2, C3, B1, B2).

Description

TRANSMISSION

Field of the Invention

The present invention relates to a transmission, and more particularly, but not exclusively, to a multi-gear automatic transmission for an automobile.

Background of the Invention

Automatic transmissions for automobiles are widely used in modern vehicles, and are recognised for their convenience and ease of use. It is a trend in the development of such automatic transmissions for them to be produced with more forward ratios to provide better acceleration and fuel economy. Early automatic transmissions had 2 forward ratios and provided limited acceleration and fuel economy as an engine coupled to the transmission was forced to rev relatively high in first gear owing to the spacing between the ratios being wide in order to achieve acceptable top-speed capabilities. However, more recently, automatic transmissions for automobiles have been developed with 3, 4, 5 and 6 forward ratios. By having more forward ratios, the ratios can be spaced closer together while still achieving good top-speed capabilities such that an engine can operate within a narrow optimum operating band to improve fuel economy and/or performance.

However, such multi-ratio automatic transmissions typically rely upon several friction elements in order to operate between the various ratios. In particular, it is common for multi-ratio automatic transmissions to engage at least two friction elements in each ratio. The friction elements are normally in the form of clutches and brake bands which, owing to the frictional nature of their operation, generate heat (thus wasting energy) and are subject to wear.

One particular multi-ratio automatic transmission has 6 forward ratios which are operated by engaging/disengaging 5 friction elements, consisting of 3 clutches and 2 brake bands.

However, each of the forward ratios requires 2 of the 5 friction elements to be engaged. The applicant has determined that it is inefficient for a transmission of this type to make such high use of friction elements for controlling operation between the ratios of the transmission, and that it would be advantageous for a multi-ratio automatic transmission to make less use of friction elements.

Summary of the Invention

In accordance with one aspect, there is provided a multi-ratio automatic transmission for a vehicle, the transmission having at least one planetary gear set, a plurality of friction elements for coupling components of the planetary gear set between an input and an output of the transmission in different configurations so as to achieve a plurality of drive ratios, and a control system for selectively engaging/disengaging the friction elements in different combinations to effect selection of the ratios, wherein rate of engagement and/or disengagement of one or more of the friction elements is controlled independently of the or each of the other friction element(s).

Advantageously, such independent control of rate of engagement and/or disengagement enables adaptive control of said one or more of the friction elements. Such adaptive control may be, for example, for achieving smoother transition between transmission gear states, for achieving shift feel and/or shift performance tailored to suit vehicle conditions and driver inputs, for adjusting to wear or leakages that develop during the life of the transmission, etc.

Preferably, each ratio corresponds to at least one discrete gear state of the transmission, and at least one gear state driving power flow is routed through a one-way clutch arranged to transmit drive in only one direction, such that rotation of the one-way clutch prevents the transmission from providing braking from input to output, and in other gear states that clutch is bypassed to permit braking from input to output. Preferably, the one-way clutch is a sprag type one-way clutch. Alternatively, the one-way clutch may be a roller clutch, mechanical diode, or the like. More preferably, the transmission has at least one gear state of a given ratio in which braking from input to output is permitted, and an alternative gear state of the same ratio in which the one-way clutch is able to operate to prevent braking from the input of the transmission to the output of the transmission.

Preferably, the transmission has an automatic mode in which change of ratios is selected automatically and a manual mode in which change of ratios is selected manually, wherein said gear state is used for accessing said given ratio in the manual mode and said alternative gear state is used for accessing said given ratio in the automatic mode. In an alternative form, said gear state is used for accessing the given ratio in the automatic mode and the alternative gear state is used for accessing tfye given ratio in the manual mode.

Preferably, the transmission has at least two planetary gear sets, and the plurality of friction elements are operable for coupling components of the planetary gear sets in series between the input and the output in different configurations so as to achieve the plurality of drive ratios.

In one example, the transmission has 6 forward ratios and control between all 6 of the forward ratios is effected by engagement/disengagement of 5 friction elements. More preferably, the 5 friction elements include 3 clutches and 2 brake bands. More preferably still, each of the 3 clutches has an apply piston which is substantially centrifugally balanced. At least one of the brake bands may have a position sensor for detecting a position of the brake band during engagement/disengagement of the brake band for use by a control system. Preferably, when the transmission is in the alternative gear, only one of the friction elements of the transmission is engaged.

Preferably, the transmission has first, second and third clutches (eg. Cl, C2 & C3), and first and second brake bands (eg. Bl & B2). More preferably, in the first gear, the second clutch is engaged, the second brake band is engaged, and the other friction elements are disengaged. Preferably, in the alternative first gear state, the second clutch is engaged, and the other friction elements are disengaged. In the alternative first gear state, the one-way clutch is employed so as to prevent braking from the input to the output of the transmission. Preferably, for a second ratio of the transmission, the second clutch is engaged, the first brake band is engaged, and the other friction elements are disengaged. Preferably, for a third ratio of the transmission, the second clutch is engaged, the third clutch is engaged, and the other friction elements are disengaged. Preferably, for a fourth ratio of the transmission, the second clutch is engaged, the first clutch is engaged, and the other friction elements are disengaged. Preferably, for a fifth ratio of the transmission, the first and third clutches are engaged, and the other friction elements are disengaged. Preferably, for a sixth ratio of the transmission, the first clutch is engaged, the first brake band is engaged, and the other friction elements are disengaged. Preferably, for a reverse ratio of the transmission, the third clutch is engaged, the second brake band is engaged, and the other friction elements are disengaged.

In accordance with another aspect, there is provided a multi-ratio automatic transmission for a vehicle, the transmission having at least one planetary gear set, a plurality of friction elements for coupling components of the planetary gear set between an input and an output of the transmission in different configurations so as to achieve a plurality of drive ratios, and a control system for selectively engaging/disengaging the friction elements in different combinations to effect selection of the ratios, the control system including an electrohydraulic system having a plurality of solenoid operated valves, wherein when the vehicle travels at or below a predetermined relatively low velocity, by selective operation of the solenoid operated valves to disengage one or more of the friction elements a neutral- in-drive condition of the transmission is automatically effected whereby the output of the transmission is disengaged from being driven by the input of the transmission.

In accordance with another aspect, there is provided a multi-ratio automatic transmission for a vehicle, the transmission having a plurality of forward ratios, wherein selection of the forward ratios is effected by engaging/disengaging friction elements, said engagement/disengagement being actuated by way of a control system having at least one solenoid operated valve, wherein the solenoid operated valve is isolated from exposure to fluid pressure when not being used in a given state of the transmission.

By reducing hydraulic leakage in this way, it is possible to achieve a desired hydraulic pressure in the system with reduced energy consumption by a hydraulic pump.

In accordance with another aspect, there is provided a multi-ratio automatic transmission for a vehicle, the transmission having at least one planetary gear set, a plurality of friction elements for coupling components of the planetary gear set between an input and an output of the transmission in different configurations so as to achieve a plurality of drive ratios, and a one-way clutch, wherein each ratio corresponds to at least one discrete gear state of the transmission, and wherein in at least one gear state driving power flow is routed through the one-way clutch arranged to transmit drive in only one direction, such that rotation of the one-way clutch prevents the transmission from providing braking from input to output, and in other gear states that clutch is bypassed to permit braking from input to output.

A multi-ratio automatic transmission module having a first planetary gear set, friction elements controlling the gear set to provide a plurality of forward ratios, and selectively either: a further friction element for controlling the gear set to provide 4 forward ratios; or a further planetary gear set in series with the first planetary gear set and downstream thereof in the direction of power transmission from input to output, and means for controlling the second planetary gear set to act in conjunction with the first planetary gear set to provide at least 5 forward ratios.

Further components may also be used to provide further drive ratios and/or to adapt the transmission for use in specific applications such as, for example, front wheel-drive applications, hybrid drive applications, etc.

In accordance with another aspect, there is provided a method of converting an automatic transmission having at least three friction elements, including the steps of: removing a friction element; providing a planetary gear set in place of the friction element; and providing a ^' control system to operate the remaining friction elements independently of one another.

In accordance with another aspect, there is provided an automatic transmission having 6 forward ratios, wherein the transmission is configured such that mechanical hardware is able be omitted in order to provide an automatic transmission having 4 forward ratios.

Brief Description of the Drawings

The invention is described, by way of non-limiting example, with reference to the accompanying drawings in which:

Figure IA is a diagrammatic sectional representation of a transmission, also showing a diagrammatic representation of an electro-hydraulic control system of the transmission;

Figure IB is the diagrammatic sectional representation of Figure IA, showing additional reference numerals;

Figure 1C is the diagrammatic sectional representation of Figures IA and IB, showing additional reference numerals;

Figure 2 A is a sectional diagram of the transmission of Figure 1 ;

Figure 2B is a sectional diagram of a transmission arranged for use in a front-wheel drive configuration;

Figure 3 is a table showing shift- elements used in various gears offered by the transmission of Figures 1 and 2; Figure 4 is a power flow diagram of the transmission of Figures 1 and 2, showing a neutral state of the transmission;

Figure 5 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a first gear state of the transmission;

Figure 6 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a manual first state of the transmission;

Figure 7 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a second gear state of the transmission;

Figure 8 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a third gear state of the transmission;

Figure 9 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a fourth gear state of the transmission;

Figure 10 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a fifth gear state of the transmission;

Figure 11 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a sixth gear state of the transmission;

Figure 12 is a power flow diagram of the transmission of Figures 1 and 2, showing power flow in a reverse gear state of the transmission;

Figure 13 is a diagrammatic graph of pressure versus current for a normally high variable bleed solenoid of the electro-hydraulic control system shown in Figure 1 ;

Figure 14 is a diagrammatic graph of pressure versus current for a normally low variable bleed solenoid of the electro-hydraulic control system of Figure 1;

Figure 15 is a diagrammatic graph of pressure versus current for a normally low O/I solenoid of the electro-hydraulic control system of Figure 1;

Figure 16 is a diagrammatic graph of force/torque applied versus damper displacement for a damper of a lock-up clutch of a torque converter of the transmission of Figures 1 and 2; and

Figure 17 is a sectional diagram of a transmission arranged for use in a hybrid drive;

Detailed Description

Introduction

With reference to Figures IA, IB, 1C and 2 A, an automatic transmission 10, particularly for use in a rear- wheel drive vehicle, has a bell housing 12 which houses a torque converter 14, three friction clutches Cl, C2 and C3, two brake bands Bl and B2, a first, simple planetary gear set 16, a second, Ravigneux-type planetary gear set 18 and a one-way clutch 20. As each of the clutches Cl₅ C2 and C3 and brake bands Bl and B2 is a friction element (ie. for selectively holding one part relative to another by friction), the transmission 10 thus has five friction elements in total. The transmission 10 uses these mechanical components to transmit power from an input 22 of the transmission 10 to an output 24 of the transmission 10, at a variety of ratios. The example transmission shown in the drawings provides six forward gear ratios for forward propulsion of the vehicle, as well as a reverse gear ratio for propelling the vehicle in reverse, and a neutral condition.

Figure 2B shows an alternative configuration using a similar transmission 10, in a form suitable for use in a front- wheel-drive application. The layout of the main features of the transmission itself is similar to that shown in Figures IA, IB, 1C and 2A, and comparable features have been labelled with like reference numerals. As can be seen, the main difference lies in that, in Figure 2B, the torque converter 14 and its bell housing are located to the side of the transmission, such that the torque converter rotates about an axis spaced from the axis of the transmission, so as to accommodate space constraints imposed by typical front-wheel-drive configurations.

As well as these mechanical components which perform the power transmission, the transmission 10 also includes an electro-hydraulic control system 26, as shown diagrammatically in the lower part of Figure 1. The electro-hydraulic control system 26 has a sump 28 which holds a reservoir of hydraulic fluid 30 which is drawn through a filter 32 and into a network of hydraulic lines, indicated generally by reference numeral 34. The network of hydraulic lines 34 has a pump 36 for providing the hydraulic fluid with pressure so that it can flow through the network of hydraulic lines 34, a cooler 38 for cooling the hydraulic fluid 30, a manual valve 40 operable in response to movement of a gear mode selector of the vehicle by a driver of the vehicle, and various valves and solenoids throughout which control flow of the hydraulic fluid through the network 34 so as to operate the clutches Cl, C2 and C3, the brake bands Bl and B2, and the torque converter 14, and to provide lubrication to the transmission 10. The solenoids are controlled by way of an electronic control system (not shown) which may form part of a CAN (Control Area Network) in which information is shared from other electronic control units (for example an engine control unit, traction control unit, anti-lock braking system control unit, air bag control unit etc.).

Mechanical overview

In a typical mounting of the transmission 10 within a vehicle, an engine of the vehicle is bolted to the torque converter 14 by way of a flywheel of the engine being bolted to bolt anchor 42. As such, rotation of the flywheel is transmitted to a housing 44 of the torque converter 14. By way of hydraulic fluid 30 inside of the torque converter housing 44 forming a fluid coupling, power is transmitted from the housing 44 to a turbine 46 of the torque converter 14 by way of the fluid coupling. More particularly, fins on the inside of the housing 44 rotating in the hydraulic fluid 30 cause the hydraulic fluid to enter blades of the turbine 46, thus causing the turbine 46 to rotate. Power is transmitted from the turbine to an input shaft 48, which in turn transmits power to a ring gear 50 of the simple planetary gear set 16, via hub 52.

The ring gear 50 has teeth formed on its inside which mesh with teeth of a pinion gear 54 which is mounted for rotation about a carrier 56. The pinion 54 also meshes with a sun gear 58. The carrier 56 is connected to and transmits power to component 60 which also forms an input to clutch C2.

The input shaft 48 is also connected via hub 52 to an input 62 of clutch Cl. Clutch Cl has five clutch plates 64 which are able to be brought into driving engagement by way of piston 66 being driven against compression spring 68 by hydraulic fluid being allowed into volume 70. As hydraulic fluid 30 enters volume 70, the piston 66 moves away from hub 52 such that volume 70 expands. This movement of the piston 66 causes an outer edge 72 of the piston 66 to clamp the clutch plates 64 into driving engagement.

The piston 66 is centrifugally balanced by hydraulic fluid in chamber 74 which prevents self-apply of the piston 66 owing to hydraulic fluid 30 being driven outwardly as rotation of the clutch Cl accelerates. As chamber 74 has a similar outward extent to volume 70, the effects of centrifugal force acting on the hydraulic fluid 30 are largely negated by the centrifugal force acting on the hydraulic fluid in the chamber 74. Each of the other clutches C2 and C3 also has a similar centrifugally balanced apply piston.

The clutch plates 64 are attached to and transmit power to component 76 which, in turn, transmits power to shaft 78 by way of spline 80. Shaft 78 transmits rotation to carrier 82 which carries short pinion 84 and long pinion 86 of the Ravigneux planetary gear set 18, by way of spline 88.

Clutch C2 has six clutch plates 90 which are able to be brought into driving engagement in response to movement of piston 92 against compression spring 94 as hydraulic fluid 30 is allowed into volume 96. The clutch plates 90 are attached to and transmit power to component 98 which, in turn, transmits power to shaft 99 by way of spline 100. Shaft 99 transmits power to a forward sun 102 of the Ravigneux planetary gear set 18.

Component 60 which also forms the input to clutch C2, is connected to and transmits power to five clutch plates 104 of clutch C3. The clutch plates 104 are able to be brought into driving engagement with an output 106 of clutch C3 under force from piston 108 as it is moved against compression spring 110 as a result of hydraulic fluid entering volume 112. The output 106 of clutch C3 is able to be held still relative to the bell housing 12 by way of brake band Bl. The output 106 is also connected to reverse sun 114 of the Ravigneux planetary gear set 18 by way of spline 116.

Brake band Bl has a quick-apply piston 117 within a large force piston 119, with an integrated position sensor 120 which senses a position of a push rod 122 during a gearshift to an accuracy of 0.1mm.

Both the reverse sun 114 and the forward sun 102 are in driving engagement with the long pinion 86, the forward sun 102 being in driving engagement with the long pinion 86 via the short pinion 84. The long pinion is meshed with a ring gear 118, which, in turn drives the output shaft 24 of the transmission 10. The carrier 82 about which the short and long pinions 84, 86 rotate is held relative to the bell housing 12 by the one-way clutch 20. In particular, a Sprag-type one-way clutch allows rotation of the carrier 82 in only one direction relative to the bell housing 12. The carrier 82 is also able to be held stationary from rotation in either direction relative to the bell housing 12 by brake band B2.

A B2 brake band servo 124 is connected to the rear brake band B2 via a lever 126 that amplifies the apply force from a piston 128 of the servo 124 to the brake band B2.

In the example of the transmission 10 shown, the one-way clutch 20 is a sprag type one¬ way clutch 20. However, in alternative examples, the sprag type one-way clutch 20 could be replaced by a roller clutch, a mechanical diode or the like. Hydraulic overview

The electro-hydraulic control system 26 has a suction line 200 through which hydraulic fluid 30 is drawn from sump 28, through filter 32 to pump 36. The pump 36 is of a Parachoidal type, and is shown in its actual location in the sectional view of the transmission 10, between the torque converter 14 and the simple planetary gear set 16. The pump 36 is driven by the housing 44 of the torque converter 14 and pumps hydraulic fluid 30 through hydraulic line 202 which feeds the pressurised hydraulic fluid to a primary regulator valve 204, a solenoid supply valve 206, a line relief valve 208, and the manual valve 40. The manual valve 40 is operable in response to changes in the position of a gear mode selector, as made by a user of the vehicle to which the transmission 10 is fitted, for example by moving a T-bar gear mode selector, column shift, drive-by-wire control, push button selector, etc. as is the case in the particular vehicle.

The primary regulator valve 204 regulates pressure of hydraulic fluid in line 202 by way of feedback line 210. As pressure in the feedback line 210 increases, the piston 212 of the primary regulator valve 204 is caused to move to the right (as depicted in Figure IA) against the force exerted by compression spring 214 and the pressure of the fluid in hydraulic line 202 such that surplus pressure is used to feed hydraulic fluid to controls of the torque converter 14 along line 216 and to lubrication of the transmission 10. If further surplus pressure is present, the piston 212 moves further such that surplus pressure is dumped into suction line 200. The feedback line 210 is provided with a flow restricting orifice or baffle 217, the size of which is tuned so that the primary regulator valve 204 operates to a desired extent in response to pressure of the hydraulic fluid.

Various exhaust lines 218 are provided throughout the network of hydraulic lines 34 such that hydraulic fluid 30 can be released through these exhaust lines 218 to drain back into the sump 28.

Hydraulic fluid 30 is fed from the primary regulator valve 204 to an apply limit regulator 220 through line 222, and to a release limit regulator 224 through line 216. The apply limit regulator 220 has a feedback line 226 (with flow-restricting orifice 227) and compression spring 228 which operate in a manner similar to the feedback described previously in relation to the primary regulator valve 204 so that hydraulic fluid in line 230 is at a known pressure. The release limit regulator 224 similarly has a feedback line 232 (with flow- restricting orifice 233) and compression spring 234 so that hydraulic fluid in line 236 is at a known pressure.

Hydraulic fluid from the apply limit regulator 220 is fed through line 230 to a torque converter regulator valve 238. Hydraulic fluid from the release limit regulator 224 is fed through line 236 to the torque converter regulator valve 238 (through line branch 240), and is also fed to a cooler/lube control regulator 242 (through line branch 244).

The torque converter regulator valve 238 has a piston 246 which operates in response to pressure from the hydraulic fluid fed through lines 230 and 240, pressure from hydraulic fluid fed through feedback lines 248 and 250, force from compression spring 252, and pressure from hydraulic fluid in line 254. In response to these inputs, hydraulic fluid is fed at varying rates along torque converter apply line 256 and torque converter release line 258. Hydraulic fluid fed through the torque converter apply line 256 causes flow of hydraulic fluid through the inside of the torque converter 14 which results in the torque converter being brought into a locked condition wherein the turbine 46 is locked by friction of lock-up clutch 47 (provided within the torque converter housing 44) against the front wall 45 of the torque converter housing 44. Conversely, hydraulic fluid fed through the torque converter release line 258 causes flow of hydraulic fluid through channel 260 between front wall 45 and the lock-up clutch 47 to release the lock-up clutch 47 from its frictional engagement against the torque converter housing 44.

Hydraulic fluid fed through line 254 to the torque converter regulator valve 238 is supplied from hydraulic line 202 through the manual valve 40, along hydraulic drive line 304 through the converter shift valve 390 to a variable bleed solenoid (VBS) 262 via line 264. Converter shift valve 390 is controlled via an ON/OFF (O/I) solenoid 348, which is provided by flow of hydraulic fluid through the solenoid supply valve 206. The solenoid supply valve 206 is provided with a feedback line 284 (having a flow-limiting orifice 285) and compression spring 286. Line 264 has a thimble filter 266 for filtering the hydraulic fluid (eg. for metal particles), as well as a flow-restricting orifice 268 for reducing amplitude of pressure fluctuations caused by the pump 36, and an accumulator 270 which further reduces pressure fluctuations and prevents hammer. The VBS 262 is controlled by an electronic control system in response to which it provides a controlled bleed of hydraulic fluid so as to control pressure of hydraulic fluid in line 254 which is fed to the torque converter regulator valve 238 as mentioned above. As such, VBS 262 is a lock-up pressure solenoid. VBS 262 is of a normally low (NL) type such that, in the absence of power supplied to the VBS 262, it will default to a condition wherein the output of hydraulic fluid is at low pressure. A graph of pressure versus current for a NL VBS is provided in Figure 14.

Line 202 also feeds hydraulic fluid along line 272 leading to VBS 274 by which flow of hydraulic fluid through line 275 is controlled. The VBS 274 is fitted in series with a thimble filter 276, a flow-restricting orifice 278 and an accumulator 280 in an arrangement similar to that described above for VBS 262. Hydraulic fluid fed through line 275 is received by the primary regulator valve 204 as a further input used to adjust the position of piston 212. As such, VBS 274 is a line pressure control solenoid. VBS 274 is of a normally high (NH) type such that, in the absence of power supplied to the VBS 274, it will default to a condition wherein the output of hydraulic fluid is at high pressure. A graph of pressure versus current for a NH VBS is provided in Figure 13.

Provision for an additional VBS 282 is shown in broken lines. It is foreseen that such an additional VBS 282 may be used, for example, to control operation of a two-ratio decoupler unit used in combination with the 6 forward ratio transmission so as to provide a total of 7 forward ratios.

Flow of hydraulic fluid through the cooler 38 and for lubrication of the transmission 10 is provided by line 236, either via the torque converter regulator valve 238 and line 287, or via line branch 244 and cooler/lube control regulator 242. Line 287 is provided with an anti-drain back valve 286 to enable only one way flow of hydraulic fluid along the line 287. Line 244 is split into two line branches 288 and 290 which are both fed as inputs to the cooler/lube control regulator 242. Pressure from hydraulic fluid in these branches 288 290, together with pressure from hydraulic fluid in feedback line 296 dictate movement of a piston 294 of the cooler/lube control regulator 242 to determine distribution of hydraulic fluid through a cooler line 296 and a cooler bypass line 298. Hydraulic fluid leaving the cooler 38 rejoins hydraulic fluid in the cooler bypass line 298 at line junction 300, from where it is distributed to parts of the transmission 10 along line 302 as lubricant.

Each of the clutches Cl, C2 and C3 is controlled by a similar electro-hydraulic control setup having an on/off (O/I) solenoid which operates a shift valve for controlling flow of hydraulic fluid to a VBS. The VBS controls flow of hydraulic fluid to a clutch regulator valve which, in turn, controls flow of hydraulic fluid to the clutch piston to engage/disengage the clutch.

More particularly, control of clutch Cl is achieved by way of hydraulic fluid fed from hydraulic line 202 through manual valve 40 (when manual valve 40 is in a Drive mode position) along drive hydraulic line 304 and line 306 to Cl shift valve 308. Cl shift valve 308 is operated by an O/I solenoid 310 which receives hydraulic fluid from the solenoid supply valve 206 along line 312. Line 312 includes a thimble filter 314 just upstream of the O/I solenoid 310. The O/I solenoid 310 is of a normally low (NL) type such that in the absence of power supplied to the O/I solenoid 310 it defaults to a low pressure state, as illustrated in Figure 15. The Cl shift valve 308 controls feed of hydraulic fluid to VBS 316 the output of which is fed to Cl regulator valve 318. Line 320 to which the VBS 316 is fitted is also provided with a thimble filter 322, an accumulator 324, and an orifice 326, 328 on either side of the VBS 316. A piston 330 of the Cl regulator valve 318 moves in response to pressure from hydraulic fluid in lines 320, 332 and feedback line 334. The output of the Cl regulator valve 318 is fed through line 336 to the volume 70 of clutch Cl so as to move piston 66. VBS 316 is a normally high VBS.

Clutch C2 is controlled by a similar setup comprising O/I solenoid 338, C2 shift valve 340, VBS 342, and C2 regulator valve 344 which controls flow of hydraulic fluid to volume 96 via line 346 to control movement of piston 92. VBS 342 is a normally high VBS.

Clutch C3 is also controlled by a similar setup comprising O/I solenoid 348, C3 shift valve 350, VBS 352, and C3 regulator valve 354 which controls flow of hydraulic fluid to volume 112 via line 356 to control movement of piston 108. VBS 352 is a normally low VBS.

Front servo 360 for engaging brake band Bl is also controlled by an arrangement similar to that used for the clutches Cl, C2 and C3. More particularly, the arrangement comprises O/I solenoid 362, Bl shift valve 364, VBS 366, and Bl regulator valve 368 which controls flow of hydraulic fluid to volume 370 via line 372 to control movement of piston 117 (and thus push rod 122). VBS 366 is a normally low VBS.

Rear servo 124 for engaging brake band B2 is also controlled by an arrangement similar to that used for the clutches Cl, C2, C3 and the brake band Bl. However B2 shares O/I solenoid 310 to control B2 shift valve 392. In addition, B2 also utilises VBS 352 which controls flow of hydraulic fluid to volume 128 and 394 via line 378 to control movement of piston 396.

When the transmission 10 is in reverse gear, the rear servo 124 is actuated by way of hydraulic fluid fed through reverse hydraulic line 374, and lines 376 and 378. A ball check valve 380 is provided at the end of line 376 and prevents unwanted back-flow from line 376 into line 382, or vice-versa.

In the example shown the manual valve 40 has four mode position valve movement (ie. P (park), R (reverse), N (neutral) and D (drive)). The manual valve may also be configured to have seven mode position valve movement (for example, to include gears 4, 2 and 1). Of course, it should also be understood that the manual valve may also have a different number (ie. other than 4 or 7) of mode positions of valve movement. So, the hydraulic control system in the transmission described has four On/Off (O/I) solenoids 310, 338, 348, 362 and six Variable Bleed Solenoids (VBS) 262, 274, 316, 342, 352, 366 (plus proposed additional VBS 282). It should be understood that any of these solenoids could be substituted with solenoid types having equivalent function, for example, Pulse Width Modulated type (PWM), Variable Pressure/Force Type (VPS/VFS), bleed solenoids etc.

Each friction element in this transmission 10 design, be it a clutch Cl, C2 or C3 or brake band Bl or B2, is able to be individually electro-hydraulically controlled during gearshifts, thus providing the calibration/application engineer with full range control of gearshift quality and also enabling the control system itself to adjust to wear or leakages that develop during the life of the transmission 10. Because the control system has full range control over any of the friction elements, it is possible to also effect a neutral condition when the transmission 10 is in Drive or Reverse, for example when the vehicle is stopped at traffic lights, and/or when it reaches a predetermined relatively low velocity (for example, when the vehicle is about to stop). This results in improved fuel economy as the transmission 10 will not load the engine and/or torque converter when idling for extended periods, for example in traffic. This "Neutral-in-Drive" feature would happen without the knowledge of the driver.

The control system consists of key features that enable various control methodologies to be employed when engaging or disengaging the clutches Cl, C2 and C3 and brake bands Bl and B2, and by virtue of the ability to bypass VBSs not being used (eg. by isolating the VBSs from exposure to fluid pressure), has the ability to reduce leakage of pressure of hydraulic fluid and thus fuel consumption. Line pressure can be controlled by way of VBS 274 to any level within the design limits and can hence also be used for clutch/brake band engagement control or to effect abuse protection. The line pressure system is a line- priority system, which maintains line pressure under low oil conditions and sacrifices other circuit demands like cooler flow to maintain this pressure. Although the pump 36 shown is a Parachoidal type, this could be substituted with any other suitable pump such as a Gerotor, Crescent, or Vane pump. The torque converter lock-up circuit comprising the apply limit regulator 220, release limit regulator 224, torque converter regulator valve 238 and lock-up pressure regulator solenoid 262 is designed in such a way so as effect control over pressure on both sides of the lock- up clutch 47, thus enabling controlled slip of the lock-up clutch 47 against the front wall 45 of the torque converter housing 44.

The torque converter regulator valve 238 is a unique design that has two feedback areas 248, 250 — one for the apply pressure and one for the release pressure. The design of the torque converter regulator valve 238 and its sizing is done in such a way that the valve 238 will always act to achieve a certain differential pressure between these two circuits. In order to successfully control these two pressures, the torque converter regulator valve 238 requires a known supply pressure source. This is achieved by feeding the torque converter regulator valve 238 with two separate regulators, the apply limit regulator 220 and the release limit regulator 224. These two regulators 220, 224 are set to a fixed pressure that enables the source oil to the torque converter regulator valve 238 to be preset. Based on a third input from the lock-up pressure regulator VBS 262 into the torque converter regulator valve 238, the torque converter regulator valve 238 will apply or release the lock-up clutch 47 while maintaining a preset pressure differential across the lock-up clutch 47.

The lubrication circuit is designed so that if the cooler 38 becomes blocked, or flow is limited during very low temperature operation, the lubrication oil can bypass the cooler 38 and pass directly into the lube distribution line 302.

The transmission 10 is also fitted with an input shaft speed sensor and an output shaft speed sensor. The input speed sensor provides a speed signal, whilst the output speed sensor provides both a speed and rotation direction signal. This rotation direction is important for certain clutch and band apply strategies, especially in the case of a Neutral- Drive or Neutral-Reverse selection where the vehicle direction of movement is important to maximise effective shift control. The combination of these two speed sensors enables closed loop or adaptive control strategies along with transmission slip diagnostics to be performed.

The hydraulic circuit 26 is arranged in such a way so that in the event of total electrical power loss to the transmission solenoids (ie. O/I solenoids and VBSs) the transmission 10 is still able to maintain Park, Reverse, Neutral and Drive (4^th) whilst maintaining cooler flow, maximum line pressure and lubrication flow.

Operation of the Transmission

Operation of the transmission through the various gear states (including First and Manual First Gears, Reverse and Neutral) is described below.

1. First Gear

Hydraulically, first gear is engaged by the operator first moving the T-Bar or Column Shift or other gear mode direction command mechanism into the drive position. This then causes the manual valve 40 in the transmission 10 to move into the drive position; this movement can be executed using a lever, cable, actuator or solenoid. Once in the drive position, the manual valve 40 allows oil to flow to the relevant drive circuits of the valve body and pump cover thus energising the clutch and brake band shift valves with hydraulic pressure. These shift valves are electro-hydraulically controlled and will not allow oil pressure into the clutch or brake band engagement circuits until commanded by the electronic control unit. Once these valves have been pressurised, a Neutral-Drive shift can be executed by electro-hydraulically commanding the C2 shift valve 340 to toggle (using the O/I solenoid 338, VBS, PWM or similar) into a position where it allows oil pressure and flow to pass through it into the feed to the regulator valve circuit. At the same time, oil is fed to the regulator valve pressure control solenoid (which can be a PWM, VFS, VPS, VBS 342 or similar). The clutch engagement can now be executed by electro-hydraulically ramping the C2 clutch on using the regulator valve 344 in combination with the pressure control solenoid. Thus, the shift feel of the N-D shift can be controlled by the electronic controller and can be tailored/calibrated to suit a variety of vehicle conditions and driver inputs. Abuse protection is also effected by de-energising the clutch to protect the driveline if an abuse protection software algorithm has been initiated. By only feeding oil to the individual pressure control solenoids when the shift valves are actuated allows the leakage associated with these types of solenoids to be limited to conditions only where the solenoid needs to be used. When the solenoid is not required, oil is not fed to it and hence no leakage is demanded from the hydraulic circuit and the pump size can then be optimised resulting in maximum fuel economy benefits. As an alternative control method for the engagement of the C2 clutch, the clutch regulator valve 344 can be set to maximum pressure during the N-D process, this would normally result in a harsh shift shock, however, to alleviate this, the line pressure control solenoid 274 can be used to ramp the line pressure or source oil on slowly, thus resulting in a smooth engagement.

Power flow for first gear is shown diagrammatically in Figure 5.

Mechanically, the input comes from the torque converter 14 and through the front reduction gear set, in the form of planetary gear set 16. The clutch C2 is engaged, providing the input to the rear planetary gear set 18, and power flow is routed through the 1-2 sprag-type one-way clutch 20 so that the carrier reaction torque is taken by the one¬ way clutch 20. There is no engine braking, therefore the vehicle can coast.

More particularly, under acceleration, only the one-way clutch 20 is used to hold the carrier stationary in the negative direction (ie. opposite to engine rotation). Under a coasting condition, the one-way clutch 20 cannot hold the carrier in the positive direction and hence power flow cannot continue and engine braking is not possible.

Mechanical lock-up is not provided through the lock-up clutch 47 in the torque converter 14 as this is prevented in the electro-hydraulic control system 26. With this arrangement, it can be seen that first gear can be achieved with only one friction element (C2) being engaged by an electro-hydraulically controlled hydraulic piston 66. Although identified as a 1-2 sprag-type one-way clutch, a learned person can identify that this same function could be achieved with a similar device, for example a roller clutch, mechanical diode or the like.

2. Manual First Gear

Power flow for manual first gear is shown diagrammatically in Figure 6, with one diagram showing power flow during coasting and another diagram showing power flow during driving.

Manual first gear is similar to first gear, except that the B2 brake band is also applied such that the one-way clutch 20 is not capable of preventing braking from the input of the transmission to the output of the transmission. Accordingly, engine braking is able to be effected in manual first gear.

More particularly, in manual first gear, the B2 brake band and the one-way clutch 20 are used to prevent the carrier of the planetary gear set from rotating in the negative rotation (ie. opposite to engine rotation). Since the B2 brake band does not have the capacity to hold the carrier under heavy accelerations (ie. during a driving condition), the one-way clutch 20 and the B2 brake band share the torque applied via the carrier. In contrast, during a coasting condition, the reverse occurs in which the carrier tries to spin in the positive direction and hence applies a torque in the opposite direction when compared to the driving condition. By definition, the one-way clutch 20 can only prevent rotation in one direction and, as a result, the carrier is held only by the B2 brake band. Since the carrier is stationary, the power flow continues through the gear set and to the engine such that engine braking is provided. .

This may be of benefit in particular driving situations such as, for example, when engine braking is desirable when a vehicle in which the transmission is fitted is travelling around a corner and/or down a hill. Control of the transmission may be arranged such that manual first gear can be selected either automatically by the control system and/or manually by the driver. For example, in one form, the transmission has a selector movable between an automatic (eg. "Drive") mode in which first gear is selected automatically when the first ratio is appropriate, and a manual mode in which the driver selects gear changes manually by movement of the selector and in which manual first gear is used when the driver selects the first ratio.

In manual first gear, the input comes from the torque converter 14 and through the front reduction gear set 16. Clutch C2 is on, providing the input to the rear gear set 18. Brake band B2 locks the carrier assembly 82 and takes the reaction, hence, engine braking is provided in manual first with only one clutch and the B2 brake band being engaged. Mechanical lock-up is not provided through the lock-up clutch 47 in the torque converter 14, the electro-hydraulic control system 26 having an override valve that prevents lock-up from occurring.

Hydraulically, the circuit is the same as for first gear except that the B2 brake band is also electro-hydraulically engaged and can be ramped on or off during engagement or disengagement. As soon as the transmission 10 is shifted into second gear, the first gear bias valve 349 toggles and robs the B2 circuit (via line 347) of oil supply, thus preventing the B2 brake band staying on and causing tie-up.

3. Second Gear

Power flow for second gear is shown diagrammatically in Figure 7.

Second gear is obtained by keeping clutch C2 energised in the first gear state and then by engaging brake band Bl. This locks the reverse sun gear 102 and the carrier assembly 82 thereby causing the rear planetary gear set 18 to overrun the 1-2 mechanical sprag-type one-way clutch 20. Mechanical lock-up is provided through the lock-up clutch 47 in the torque converter 14. This lock-up clutch 47 would normally be fitted with a damper assembly to dampen out engine-induced vibrations and the lock-up clutch 47 can also employ pressure differential controlled slip to further alleviate torsional vibrations. The pressure differential controlled slip is achieved by virtue of control of pressure on either side of the lock-up clutch 47 by the torque converter regulator valve 238 in combination with the apply limit regulator 220 and the release limit regulator 224. This enables precise control of engagement of the lock-up clutch 47 against the front wall 45 of the housing 44 of the torque converter 14. This results in the engine speed at which lock-up is introduced to be lowered over conventional damper-only systems thus maximising fuel economy benefits. This applies to all gear states where lock-up is activated.

A multi-stage (for example a three-stage) damper may be provided by fitting the lock-up clutch 47 with dampers of different rates in series such that the damper displacement is staged against force/torque applied, as shown in Figure 16. Such multi-staging of the damper enables improved suppression of vibrations at a range of frequencies.

Hydraulically, at the start of the shift, line pressure is increased to a level higher than that required for the shift event. Then, the relevant Bl shift valve 364 is electro-hydraulically actuated and will not allow oil pressure into the Bl brake band engagement circuit (ie. to Bl regulator valve 368) until commanded by the electronic control unit. Once this valve 364 has been energised, oil is supplied to the Bl regulator valve 368 and VBS 366 and a 1- 2 shift can be executed by electro-hydraulically commanding the Bl regulator valve pressure control solenoid 366 to increase the pressure in the Bl band apply piston circuit. The Bl engagement can be now be executed by electro-hydraulically ramping the Bl brake band on using the regulator valve 368 in combination with the pressure control solenoid 366. Thus, the shift feel of the 1-2 shift can be controlled by the electronic controller and can be tailored/calibrated to suit a variety of vehicle conditions and driver inputs.

As an additional input to the electronic controller, a band push rod position sensor 120 is included in the front servo push rod and cover. This sensor 120 informs the controller of the position of the engagement of the brake band Bl so that different control methodologies can be applied. These can include, rapid uptake of brake band Bl clearance followed by slow controlled apply, or slow torque reduction followed by rapid disengagement. Abuse protection is also effected by de-energising the brake band to protect the driveline if the abuse protection software algorithm has been initiated. 4. Third Gear

Power flow for third gear is shown diagrammatically in Figure 8.

Third gear is achieved by engaging clutches C2 and C3. This locks the rear gear set 18 together in a 1:1 ratio. The total transmission output ratio is then equal to the ratio of the front gear set 16. Mechanical lock-up is provided through the lock-up clutch 47 in the torque converter 14.

Hydraulically, at the start of the shift, line pressure is increased to a level higher than that required for the shift event. Then, the relevant C3 shift valve 350 is electro-hydraulically actuated and will not allow oil pressure into the C3 engagement circuit until commanded by the electronic control unit. Once this valve 350 has been energised, oil is supplied to the C3 regulator valve 354 and VBS 352 and a 2-3 shift can be executed by electro- hydraulically commanding the Bl regulator valve pressure control solenoid 366 to decrease the pressure in the Bl band apply piston circuit and at the same time, commanding the C3 regulator valve pressure control solenoid 352 to ramp pressure on, in effect swapping the Bl circuit with the C3 circuit. Once the Bl circuit has lost torque carrying capacity, the C3 circuit can now finish the shift event off by electro-hydraulically finishing ramping the C3 clutch on using the regulator valve 354 in combination with the pressure control solenoid 352. Thus, the shift feel of the 2-3 shift can be controlled by the electronic controller and can be tailored/calibrated to suit a variety of vehicle conditions and driver inputs.

5. Fourth Gear

Power flow for fourth gear is shown diagrammatically in Figure 9.

Fourth gear is obtained by having two inputs to the rear gear set 18. One input is from the front reduction gear set 16 and clutch C2, and the other is directly from the input shaft 48 (via clutch Cl). The Cl clutch links the carrier assembly 82 of the rear gear set 18 to the input shaft 48 while the forward sun gear 102 is driven from the output of the front gear set 16 through the C2 clutch. Mechanical lock-up is provided through the lock-up clutch 47 in the torque converter 14.

Hydraulically, the 3-4 shift is effected in the same way as the 2-3 shift except that the C3 circuit is ramped off while the Cl circuit is ramped on.

6. Fifth Gear

Power flow for fifth gear is shown diagrammatically in Figure 10.

Fifth gear is obtained by having two inputs to the rear gear set 18. One input is from the front reduction gear set 16, and the other is directly from the input shaft 48 (via clutch Cl). The Cl clutch links the carrier assembly 82 of the rear gear set 18 to the input shaft 48 while the reverse sun gear 114 is driven from the output of the front gear set 16 through the C3 clutch. Mechanical lock-up is provided through the lock-up clutch in the torque converter 14.

Hydraulically, the 4-5 shift is effected in the same way as the 3-4 shift except that the C2 circuit is ramped off while the C3 circuit is ramped on.

7. Sixth Gear

Power flow for sixth gear is shown diagrammatically in Figure 11.

Sixth gear is obtained by locking the reverse sun gear 114 to the transmission casing 12 using the Bl brake band and then driving directly into the rear gear set carrier assembly 82 from the input shaft 48 with the Cl clutch. Mechanical lock-up is provided through the lock-up clutch 47 in the torque converter 14. Hydraulically, the 5-6 shift is effected in the same way as the 4-5 shift except that the C3 circuit is ramped off while the Bl circuit is ramped on.

8. Reverse Gear

Reverse is obtained by driving through the front gear set 16 through the C3 clutch and by locking the rear gear set carrier assembly 82 to the transmission casing 12 using the B2 brake band. Mechanical lock-up is not provided through the lock-up clutch 47 in the torque converter and is hydraulically prevented via the electro-hydraulic control circuit.

Hydraulically, reverse is engaged by the operator first moving the T-Bar or Column Shift or other gear mode direction command mechanism into the reverse position. This then causes the manual valve 40 in the transmission 10 to move into the reverse position; this movement can be executed using a lever, cable, actuator or solenoid. Once in the reverse position, the manual valve 40 allows oil to flow to the relevant reverse circuits of the valve body and pump cover thus energising the clutch and brake band shift valves with hydraulic pressure. The B2 brake band is energised substantially immediately as the reverse position is selected on the manual valve 40. Its apply rate can be controlled using line pressure, but the bias valve 349 used for drive applications is bypassed in the reverse gear. Once the B2 brake band is on, clutch C3 is engaged by electro-hydraulically commanding the C3 shift valve 350 to toggle (using an O/I 348, VBS, PWM or similar) into a position where it allows oil pressure and flow to pass through it into the feed to the regulator valve circuit (ie. to C3 regulator valve 354). At the same time, oil is fed to the regulator valve pressure control solenoid (which can be a PWM, VFS, VPS, VBS 352 or similar). The clutch engagement can be now be executed by electro-hydraulically ramping the C3 clutch on using the regulator valve 354 in combination with the pressure control solenoid 352. Thus, the shift feel of the N-R shift can be controlled by the electronic controller and can be tailored/calibrated to suit a variety of vehicle conditions and driver inputs. Abuse protection is also effected by de-energising the clutch to protect the driveline if the abuse protection software algorithm has been initiated. By only feeding oil to the individual pressure control solenoids when the shift valves are actuated allows the leakage associated with these types of solenoids to be limited to conditions only where the solenoid needs to be used. When the solenoid 352 is not required, oil is not fed to it and hence no leakage is demanded from the hydraulic circuit and the pump size can then be optimised resulting in maximum fuel economy benefits. As an alternative control method for the engagement of the C3 clutch, the clutch regulator valve 354 can be set to maximum pressure during the N- R process. This would normally result in a harsh shift shock, however, to alleviate this, the line pressure control solenoid 274 can be used to ramp the line pressure or source oil on slowly, thus resulting in a smoother engagement.

9. Neutral

The neutral condition of the transmission 10 is achieved by disengaging all three clutches Cl, C2 and C3, and also by disengaging brake bands Bl and B2. Accordingly, the neutral condition is an unbraked neutral wherein the input and the output of the transmission are free to rotate relative to the housing of the transmission.

Development

The 6 forward ratio (ie. "6 speed") transmission was developed so that it could be manufactured using an existing production line already used for manufacturing 4 forward ratio (ie. "4 speed") transmissions, and is able to be manufactured on the same production line and at the same time as 4 speed transmissions. Over 70% of the original 4 speed transmission parts and tooling are also used for the 6. speed transmission, such that a basic module which is common to both 4 and 6 speed variants can be produced. The basic module may include, for example, the transmission housing and/or an insert for the transmission housing. Different parts may be added to the basic module according to which variant is to be made.

The design of the existing 4 speed automatic transmission was converted to suit the 6 forward ratio transmission by removing a friction element from the design of the 4 speed transmission, providing a planetary gear set in place of the removed friction element, and providing a control system to operate remaining friction elements independently of one another.

The 6 speed automatic transmission is configured such that mechanical hardware (including the additional planetary gear set) is able to be omitted in order to provide an automatic transmission having 4 forward ratios.

Features

The transmission 10 of the example described above features the following:

• A single input shaft driving the transmission;

• A full neutral function in neutral (unbraked neutral);

• The use of 3 clutches, 2 brake bands and 1 one-way clutch to achieve 6 forward ratios; • The use of 17 valves to achieve total electro-hydraulic control of the transmission;

• The inclusion of a locking clutch in the torque converter;

• The ability to achieve a first ratio with the engagement of only one friction element;

• Individual controllability of all friction clutches and brake bands from zero pressure to maximum pressure using individual solenoid combinations; • The use of non-linked friction elements (ie. no common pressure or hydraulic areas between elements);

• The use of an input shaft speed sensor for control decisions;

• The use of a quadrature output speed sensor for control decisions;

• The use of an analogue front brake band pushrod position sensor for control decisions; • The use of direct clutch and brake band controls to enable abuse protection of the vehicle driveline;

• The use of direct clutch and brake band controls to enable smooth engagement of forward and reverse gear conditions from neutral using electro-hydraulic control;

• Packaging to enable the 6 forward ratio transmission hardware to fit within the original package space confines of a 4 forward ratio transmission;

• Mechanical hook-up that allows a 4 forward ratio transmission to be built by omitting mechanical hardware, still using the 6 forward ratio control system;

• Mechanical hook-up that allows the 6 forward ratio transmission to be built using existing manufacturing tooling and facilities;

• The use of combined closed loop and adaptive control strategies to ensure smooth gearshift control;

• The use of a pressure differential electro-hydraulic controls for the lock-up clutch in the torque converter that enables the use of slip control strategy to achieve lower locked engine speeds and to reduce NVH (Noise Vibration Harshness) in 2nd, 3rd, 4th, 5th and 6th gears; • The use of a full range variable line pressure control that is independent of other transmission functions;

• A hydraulic control system that still allows for "limp-home" function of Park, Reverse, Neutral and Drive 4th gears in the event of electronic failure;

• A hydraulic control system that hydraulically prevents torque converter lock-up from occurring in Park, Neutral, Drive first and Reverse gears;

• A hydraulic control system having a cooler bypass circuit that protects the transmission from cooler blockage or freezing;

• The use of a fixed displacement pump;

• The use of a quick-apply feature in the front brake band piston assembly; • The use of line priority pressure feed from the pump supply;

• The use of a combination of On/Off solenoids, Variable Bleed Solenoids, Shift Valves and Pressure Regulator Valves to achieve electro-hydraulic clutch and brake band controls;

• Valve arrangement that disconnects the solenoids and minimises solenoid leakages when the solenoids are not required;

• Modular design capabilities to incorporate driveline system variations such as: 4 speed, 5 speed, 6 speed, 7 speed, hybrid transmissions and front wheel drive.

Hybrid

It will be understood by those people skilled in the art that a transmission in accordance with the present invention may also be used in a hybrid drive arrangement, such as the arrangement shown in Figure 17. For example, the transmission may be provided with a further, upstream planetary gear set 401 which couples the transmission to both an internal combustion engine (not shown) and an electric motor 400.

Many modifications and variations may be made to the transmission without departing from the spirit and scope of the invention. For example, the transmission may be provided with an electric oil pump which operates independently of the rotational speed of the input to the transmission so as to provide oil pressure as required (ie. "pressure on demand"), particularly in circumstances where the mechanical oil pump of the transmission is unable to provide sufficient pressure (such as, for example, when a vehicle to which the transmission is fitted is travelling slowly or is stopped).

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A multi-ratio automatic transmission for a vehicle, the transmission having at least one planetary gear set, a plurality of friction elements for coupling components of the planetary gear set between an input and an output of the transmission in different configurations so as to achieve a plurality of drive ratios, and a control system for selectively engaging/disengaging the friction elements in different combinations to effect selection of the ratios, wherein rate of engagement and/or disengagement of one or more of the friction elements is controlled independently of the or each of the other friction element(s).

2. A transmission as claimed in claim 1, wherein the control system includes an electrohydraulic system having a plurality of solenoid operated valves.

3. A transmission as claimed in claim 2, wherein one or more of the friction elements is controlled by a dedicated solenoid operated valve.

4. A transmission as claimed in claim 2 or claim 3, wherein when the vehicle travels at or below a predetermined relatively low velocity, by selective operation of the solenoid operated valves to disengage one or more of the friction elements a neutral-in-drive condition of the transmission is automatically effected whereby the output of the transmission is disengaged from being driven by the input of the transmission.

5. A multi-ratio automatic transmission for a vehicle, the transmission having at least one planetary gear set, a plurality of friction elements for coupling components of the planetary gear set between an input and an output of the transmission in

_. different configurations so as to achieve a plurality of drive ratios, and a control system for selectively engaging/disengaging the friction elements in. different combinations to effect selection of the ratios, the control system including an electrohydraulic system having a plurality of solenoid operated valves, wherein when the vehicle travels at or below a predetermined relatively low velocity, by selective operation of the solenoid operated valves to disengage one or more of the friction elements a neutral-in-drive condition of the transmission is automatically effected whereby the output of the transmission is disengaged from being driven by the input of the transmission.

6. A transmission as claimed in any one of claims 2 to 5, having isolating means for isolating one or more of the solenoid operated valves, not being used in any given state of the transmission, from exposure to fluid pressure.

7. A transmission as claimed in claim 4 or claim 5, or claim 6 when dependent on claim 4 or claim 5, wherein said neutral-in-drive condition is an unbraked neutral condition, wherein both the input and the output of the transmission are free to rotate relative to a housing of the transmission.

8. A transmission as claimed in any one of the preceding claims, wherein each ratio corresponds to at least one discrete gear state of the transmission, and wherein in at least one gear state driving power flow is routed through a one-way clutch arranged to transmit drive in only one direction, such that rotation of the one-way clutch prevents the transmission from providing braking from input to output, and in other gear states that clutch is bypassed to permit braking from input to output.

9. A transmission as claimed in claim 8, wherein the transmission has at least one gear state of a given ratio in which braking from input to output is permitted, and an alternative gear state of the same ratio in which the one-way clutch is able to operate to prevent braking from the input of the transmission to the output of the transmission.

10. A transmission as claimed in claim 9, wherein said given ratio is a lowest forward ratio provided by the transmission.

11. A transmission as claimed in claim 9 or claim 10, the transmission having an automatic mode in which change of ratios is selected automatically and a manual mode in which change of ratios is selected manually, wherein said gear state is used for accessing said given ratio in the manual mode and said alternative gear state is used for accessing said given ratio in the automatic mode.

12. A transmission as claimed in any one of claims 9 to 11, wherein, when the transmission is in the alternative gear state, only one of the friction elements of the transmission is engaged.

13. A transmission as claimed in any one of claims 8 to 12, wherein the one-way clutch is a sprag type one-way clutch.

14. A transmission as claimed in any one of the preceding claims, wherein the transmission has at least two planetary gear sets, and the plurality of friction elements are operable for coupling components of the planetary gear sets in series between the input and the output in different configurations so as to achieve the plurality of drive ratios.

15. A transmission as claimed in any one of the preceding claims, wherein each of the friction elements is operable independently of the other friction elements.

16. A transmission as claimed in any one of the preceding claims, wherein the transmission has 6 forward ratios and control between all 6 of the forward ratios is effected by engagement/disengagement of 5 friction elements.

17. A transmission as claimed in claim 16, wherein the 5 friction elements include 3 friction clutches and 2 brake bands.

18. A transmission as claimed in claim 17, wherein the transmission has first, second and third clutches, and first and second brake bands, and wherein, when in a first gear state of a first ratio, the second clutch is engaged, the second brake band is engaged, and the other friction elements are disengaged.

19. A transmission as claimed in claim 18, wherein in an alternative gear state of the first ratio, the second clutch is engaged, and the other friction elements are disengaged.

20. A transmission as claimed in claim 19, wherein for a second ratio of the transmission, the second clutch is engaged, the first brake band is engaged, and the other friction elements are disengaged.

21. A transmission as claimed in claim 20, wherein for a third ratio of the transmission, the second and third clutches are engaged, and the other friction elements are disengaged.

22. A transmission as claimed in claim 21, wherein for a fourth ratio of the transmission, the first and second clutches are engaged, and the other friction elements are disengaged.

23. A transmission as claimed in claim 22, wherein for a fifth ratio of the transmission, the first and third clutches are engaged, and the other friction elements are disengaged.

24. A transmission as claimed in claim 23, wherein for a sixth ratio of the transmission, the first clutch is engaged, the first brake band is engaged, and the other friction elements are disengaged.

25. A transmission as claimed in claim 24, wherein for a reverse ratio of the transmission, the third clutch is engaged, the second brake band is engaged, and the other friction elements are disengaged.

26. A transmission as claimed in claim 25, wherein for a selected neutral condition of the transmission, none of the friction elements are engaged.

27. A multi-ratio automatic transmission for a vehicle, the transmission having a plurality of forward ratios, wherein selection of the forward ratios is effected by engaging/disengaging friction elements, said engagement/disengagement being actuated by way of a control system having at least one solenoid operated valve, wherein the solenoid operated valve is isolated from exposure to fluid pressure when not being used in a given state of the transmission.

28. A multi-ratio automatic transmission for a vehicle, the transmission having at least one planetary gear set, a plurality of friction elements for coupling components of the planetary gear set between an input and an output of the transmission in different configurations so as to achieve a plurality of drive ratios, and a one-way clutch, wherein each ratio corresponds to at least one discrete gear state of the transmission, and wherein in at least one gear state driving power flow is routed through the one-way clutch arranged to transmit drive in only one direction, such that rotation of the one-way clutch prevents the transmission from providing braking from input to output, and in other gear states that clutch is bypassed to permit braking from input to output.

29. A transmission as claimed in claim 28, wherein the transmission has at least one gear state of a given ratio in which braking from input to output is permitted, and an alternative gear state of the same ratio in which the one-way clutch is able to operate to prevent braking from the input of the transmission to the output of the transmission.

30. A transmission as claimed in claim 29, wherein said given ratio is a lowest forward ratio provided by the transmission.

31. A multi-ratio automatic transmission module having a first planetary gear set, friction elements controlling the gear set to provide a plurality of forward ratios, and selectively either: a further friction element for controlling the gear set to provide 4 forward ratios; or a further planetary gear set in series with the first planetary gear set and downstream thereof in the direction of power transmission from input to output, and means for controlling the second planetary gear set to act in conjunction with the first planetary gear set to provide at least 5 forward ratios.