WO2010100280A1

WO2010100280A1 - Multi clutch transmissions

Info

Publication number: WO2010100280A1
Application number: PCT/EP2010/052898
Authority: WO
Inventors: Simon Shepherd; Joern Behrenroth
Original assignee: Ricardo Uk Ltd
Priority date: 2009-03-06
Filing date: 2010-03-08
Publication date: 2010-09-10
Also published as: GB201115359D0; GB2480206A; GB0903870D0; GB2480206B

Abstract

A multi clutch transmission for a vehicle has a control system configured to regulate the operation of two clutches during the torque phase of a gear shift. The control system is programmed with one or more predetermined handover functions, which define a set torque profile for each clutch during the torque phase. The control system shifts the set torque profiles for the two clutches to take account of changes in the total torque demand, whereby both clutches carry a percentage of any change during the gear shift. The control system generates values indicative of the total clutch torque demand during the gearshift, e.g. based on slip or engine speed data, and apportions any change in accordance with the respective predetermined handover function.

Description

Multi clutch transmissions

The present invention relates to multi clutch transmissions, more particularly, but not exclusively, to control systems for multi clutch transmissions, and methods for controlling multi clutch transmissions during gear shift operations.

Dual clutch transmissions (DCT 's) are well known and include two clutches arranged so that the transmission has the ability to transfer drive from one gear ratio to another without interrupting the torque transmitted to the output drive.

In use, the clutch through which drive is being transferred is referred to as the 'active' clutch, and the other clutch is referred to as the 'inactive' clutch. The process of switching from the active clutch to the inactive clutch is referred to as the "torque handover" or "torque phase", wherein the active clutch becomes "off-going" and the inactive clutch becomes "on-coming".

An existing method for controlling the torque phase in a DCT is known from US5,890,392. In this method, the off-going clutch is regulated through feedback control to maintain micro slip (e.g. in the region of 10-20 rpm) throughout the duration of the torque phase, and the on-coming clutch is operated under a predetermined open loop ramp (i.e. at a predetermined apply rate with no feedback control) until it has taken over 100% of the total torque demand (e.g. the torque demand derived from the vehicle engine).

According to the method described in US5, 890,392, if there is a sudden increase in engine torque, the on-coming clutch will take longer to meet the increased torque demand than if the engine torque had remained constant, thereby extending the duration of the torque phase. Likewise, the torque phase will complete sooner if there is a sudden reduction in engine torque. However, variations in torque phase duration for a particular gear shift are undesired, as they may be perceived by the driver of the vehicle as in indicator of poor vehicle performance. Moreover, it is known that clutches are difficult to control in low torque regions (e.g. less than 30Nm), because their torque characteristics may become non-linear. However, according to the method described in US5, 890,392, the off-going clutch is required to react to changes in engine torque, even when the torque carried by the off- going clutch is much lower than the torque carried by the on-coming clutch. This may also lead to undesirable inconsistencies in vehicle performance.

In view of the above, it is clear that there is a need for an improved control system for a dual clutch transmission and so it is an object of the present invention to address one or more of the problems described above.

According to the present invention, there is provided a multi clutch transmission for a vehicle, preferably a dual clutch transmission, the transmission having multiple gear ratios and at least a first clutch and second clutch for realising a shift from a first of said gear ratios to a second of said gear ratios, wherein the transmission includes a control system configured to regulate the operation of said first and second clutches during the torque phase of a gear shift, so that each of said first and second clutches carries a proportion of any change in total torque demand experienced during said torque phase

Advantageously, if the total torque demand that the clutches are required to carry changes during a gear shift, e.g. due to a sudden change in vehicle engine torque or as a result of a control function of the transmission, both clutches are able to react to the change, with each carrying a percentage of the change. By controlling the torque phase in this way (i.e. through regulation of both clutches throughout the torque phase), changes in the total clutch torque demand will not affect the progress of the torque phase.

In this manner, the control system ensures that the torque phase always ends (i.e. with the oncoming clutch at 100% of the total torque demand) in a predetermined time period. The result is a consistent torque handover between the clutches during gear shifts. This allows for more repeatable acceleration profiles during gearshifts with an associated improvement in shift quality. The control system is preferably configured such that the regulation of both clutches during the control mode occurs substantially in real time, i.e. in order to account for real time changes in the total torque demand.

In a preferred embodiment, the control system operates a predetermined torque handover function, which defines a set torque profile for each of the two clutches during the torque phase. The control mode is preferably configured to adjust the set torque profile of the two clutches by a magnitude in accordance with the change in total torque demand (increase or decrease).

Preferably, the control system is configured to operate a closed loop control calculation for generating a value indicative of the total torque demand during the gearshift, and is configured to adjust the torque profile of the two clutches by a magnitude in accordance with any change in total torque demand as indicated by the closed loop control calculation.

In preferred embodiments, the closed loop control calculation is based on clutch slip or engine speed.

In preferred embodiments, the first clutch is arranged for transferring drive from a torque source (e.g. the vehicle engine or a motor) to a first transmission input shaft, and the second clutch arranged for transferring drive from a torque source (e.g. the vehicle engine or a motor) to a second transmission input shaft.

According to another aspect of the present invention, there is provided a control system for controlling the operation of two clutches in a transmission, preferably a dual clutch transmission, wherein the control system includes a control mode for regulating the operation of both clutches during the torque phase of a gear shift, such that a proportion of a change in total torque demand is carried by each clutch.

According to a still further aspect of the invention, there is provided a method of controlling the operation of two clutches in a transmission during a gear shift, preferably in a dual clutch transmission, the method including the step of regulating the operation of both clutches during the torque phase of a gear shift, so that a proportion of a change in total torque demand is carried by each clutch.

Although described herein with respect to dual clutch transmissions, the invention is also applicable to any 'multi' clutch transmission, i.e. a transmission having more than one clutch, which requires a torque handover between a first clutch which is off-going and a second clutch which is on-coming during a gearshift; the control system is configured for regulating the operation of the off-going and on-coming clutches throughout the torque phase.

Other aspects and preferred features of the invention will be apparent from the claims and following description of preferred embodiments, which is made by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic block diagram showing a dual clutch transmission for a vehicle incorporating a control system for use during gear shifts;

Figure 2 is a schematic illustration of a preferred control system for use in the dual clutch transmission of Figure 1;

Figure 3 is an illustration showing a number of possible handover functions for the shift control system in Figure 1; and

Figure 4 is similar to Figure 2 and shows a further preferred control system for use in the dual clutch transmission of Figure 1.

Referring firstly to Figure 1 , a dual clutch transmission for a vehicle is in indicated generally at 100. The transmission 100 includes a first clutch 102 arranged for transferring drive from a vehicle torque source 104 (e.g. the vehicle engine) to a first transmission input shaft 106 in communication with a first set of gear ratios 108 (e.g. the odd gear ratios in a 6-speed transmission), and a second clutch 110 arranged for transferring drive from the torque source 104 to a second transmission input shaft 112 in communication with a second set of gear ratios 114 (e.g. the even gear ratios in a 6- speed transmission). Each clutch 102, 110 has a respective actuation system 116, 118, e.g. operable to open or close the clutch 102, 110. Although not shown, the outputs of the two set of gear ratios are coupled to a common output shaft.

When driving in gear, the clutch through which drive is being transferred is referred to as the 'active' clutch, and the other clutch is referred to as the 'inactive' clutch. The process of switching from the active clutch to the inactive clutch during gear shift is referred to as the "torque handover" or "torque phase", wherein the active clutch is referred to as "off-going" and the inactive clutch is referred to as "on-coming". This process is controlled by a control system indicated generally at 120.

A preferred embodiment of a control system 120 for use with the transmission 100 is shown in more detail in Figure 2. In this embodiment, the control system 120 includes a priority module 122, which is programmed to provide output signals 124, 126 for simultaneous operation of clutches 102, 110 (e.g. via the actuation systems 116, 118) during a gear shift. The priority module 122 is programmed with one or more predetermined handover functions, which define a set torque profile for each clutch 102, 110 during the torque phase. Examples of suitable handover functions (in terms of torque against time) are illustrated in Figure 3, in which:

i) is indicative of a single phase linear handover function, incorporating a single linear ramp for each clutch; ii) is indicative of a two phase linear handover function, incorporating an initial ramp of a low gradient (e.g. to allow for bite point variations), followed by a second ramp of steeper gradient (e.g. to reduce the overall torque phase duration); iii) is indicative of an x² handover function having a gradually increasing gradient; and iv) is indicative of a d²T/dt² handover function, incorporating a generally s-shaped curve where the magnitude of the second differential of the torque handover is constant. The control system 120 preferably includes a control module 128 arranged to provide an output signal 130 to said priority module 122 indicative of the total torque demand of the vehicle during the gearshift.

In accordance with a preferred control mode of the control system 120, the output signal 130 from the control module 128 is communicated to the priority module 122. In response, the priority module 124 is programmed to shift the set torque profiles for the two clutches 102, 110, to take account of changes in the total torque demand experienced during the torque phase. Hence, the control system ensures that both of the clutches 102, 110 carry a percentage of any change in the total torque demand during the gear shift. By controlling the torque phase in this way (i.e. through regulation of both clutches during the gear shift), changes in the total torque demand should not affect the progress of the torque phase.

The control system 120 is preferably configured such that the regulation of the clutches 102, 110 during the control mode occurs substantially in real time.

In preferred embodiments, the control system 120 may operate the clutches 102, 110 in a permanent state of micro slip (e.g. in the region of 10-20 rpm) and the control module 128 may rely on slip data as an indicator of the real time total torque demand of the vehicle. Conventional methods and mechanisms for monitoring clutch slip may be utilised and are incorporated herein by reference.

In one embodiment, the control module 128 includes a slip controller (not shown) in communication with the off-going clutch for monitoring the level of slip in the off- going clutch. The slip controller monitors the actual slip against a target level of micro slip for the off-going clutch, and the output signal 130 from the control module 128 to the priority module will change dependent on the change required to maintain the target slip in the off-going clutch. Hence, for this embodiment the operation of the two clutches 102, 110 is regulated in response to data from the off-going clutch only.

It will be understood that for certain driving conditions (e.g. power on or power off) and shift patterns (e.g. up shift or down shift), it may be preferable for the clutches to be regulated in response to changes in slip experienced by the oncoming rather than the off going clutch. For a power off downshift, it will be preferred for the control module to monitor the slip in the off going clutch, whereas for a power on downshift, the objective slip information during the torque phase will preferably be from the oncoming clutch. Similarly, for a power off upshift the oncoming clutch will preferably provide the objective slip information, whereas the off going clutch will be preferred for a power on upshift.

A separate slip controller may be provided for each clutch 102, 110, with each slip controller having a target slip for its respective clutch. At any one time, it is preferred if only one slip controller will be active to affect changes to the output signal 130 for regulation of both clutches 102, 110. However, it may also be possible to have both controllers active, such that the clutches are regulated in response to the output from both controllers.

A slip controller for use in the control system of the invention may be of PIFF-type having three main components:

a) a feed- forward (FF) or open loop component, which will attempt to track the engine torque demand without any feedback element.

Where:

d θ — is the target difference in engine speed gradient and shaft speed dt² gradient.

J_E is the total inertia of the components on the engine side of the clutch; and

T_E is the indicated engine torque. b) a proportional term (P), which calculates the measured slip and its variation from the target slip value (known as the system error ) and multiplies the error by a proportional gain constant. This term will aim to control to the target slip by increasing or reducing torque (above or below the feed- forward level) with a magnitude, which is proportional to the variance from the desired slip.

T_p = K_p(AN_rgt - (N_E - N_s)) Where:

K_p is the proportional gain coefficient,

ΔN_Tgt is the target clutch slip magnitude N_E is the measured engine speed and N _s is the measured shaft speed.

c) an integral term (I), which integrates the slip error (variance of actual slip from the target clutch slip) with respect to time. This is a slower acting control element, which will indicate the calculated system torque error when the clutch has reached the required steady state operating point (the target micro slip).

T₁ = K₁](AN^ - (N_E - N_s))dt

Where:

Ki is the integral gain coefficient.

In an alternative embodiment, the control module 128 may be configured to monitor engine speed, in order to derive a signal 130 for the priority module 124. For example, an assessment of the engine speed and the off-going clutch shaft speed may be used, as an indicator of the torque balance. Any change in the predicted total torque demand is then communicated to the two clutches 102, 110 by the priority module 124, in accordance with the predetermined handover function, as described above.

A further preferred embodiment is shown in Figure 4, in which separate control modules 128', 128" for each clutch 102, 110 are intended to be active during the torque phase, each with a respective slip or engine speed target and each providing a respective output signal 130', 130" to the priority module 124. Changes in the individual output from each control module 128', 128" are then communicated to the two clutches 102, 110, in accordance with the predetermined handover function, as described above.

It will be understood that, when driving, the total torque demand that the clutches are required to carry may be influenced by a number of factors including changes in driver demand (e.g. related to accelerator position, resulting in changes in the torque delivered from the vehicle torque source), road load disturbances through the vehicle wheels or the vehicle torque source, and also system errors/control functions related to objective slip/engine speed calculations. However, for each embodiment of the invention, the control system ensures that the off-going and on-coming clutches are able to react to changes in the total torque demand occurring during a gearshift. Both clutches are regulated during the torque phase, preferably with each clutch following a set torque profile. This ensures that the torque phase always ends (i.e. with the oncoming clutch at 100% of the total torque demand) in a predetermined time period. The result is a consistent torque handover between the clutches during gear shifts, whereby the driver of the vehicle should experience little or no variation in the duration of the torque phase for particular gear shift operations.

The invention is further advantageous in that it facilitates a relatively simple reversal of the torque phase, since the torque profiles for each clutch can be readily reversed from the point at which a request for reversal is made.

Although described above with respect to dual clutch transmissions, the invention is also applicable to other multi clutch transmissions including a first clutch which is off- going and a second clutch is on-coming during the torque phase of a gearshift.

Claims

1. A multi clutch transmission for a vehicle, the transmission having multiple gear ratios and at least a first clutch and second clutch for realising a shift from a first of said gear ratios to a second of said gear ratios, wherein the transmission includes a control system configured to regulate the operation of said first and second clutches during the torque phase of a gear shift, so that each of said first and second clutches carries a proportion of any change in total torque demand experienced during said torque phase.

2. A transmission according to claim 1 wherein the control system is programmed with one or more predetermined handover functions, which define a set torque profile for each of said first and second clutches during the torque phase, and wherein the control system provides for simultaneous operation of said first and second clutches in accordance with one of said predetermined handover functions throughout the duration of the torque phase of the gear shift.

3. A transmission according to claim 2 wherein the control system is configured to apportion any change in the total clutch torque demand experienced during the torque phase between said first and second clutches in accordance with the respective predetermined handover function.

4. A transmission according to claim 3 wherein the control system is programmed to generate a value indicative of the total torque demand during the gearshift, in order to monitor and apportion any change in the total torque demand experienced during the torque phase between said first and second clutches in accordance with the respective predetermined handover function.

5. A transmission according to claim 3 or claim 4 wherein the control system is programmed to shift the set torque profiles for the first and second clutches to take account of changes in the total torque demand, whereby both of said first and second clutches carry a percentage of any change in the total torque demand during the gear shift.

6. A transmission according to any of claims 2 to 5 wherein the control system includes a control module configured to operate a closed loop control calculation for generating a value indicative of the total clutch torque demand during the gearshift, and further includes a priority module which receives the value from the control module and is configured to control the actuation of both of the first and second clutches throughout the duration of the torque phase of the gear shift and apportion any change in the total clutch torque demand during the torque phase between said first and second clutches in accordance with the respective predetermined handover function.

7. A transmission according to claim 6 wherein the closed loop control calculation is based on clutch slip or engine speed.

8. A transmission according to claim 6 or claim 7 wherein the priority module is configured to operate both of said first and second clutches simultaneously in accordance with a set torque profile for each clutch during the torque phase, and the priority module adjusts the torque profile of both of said first and second clutches by a magnitude in accordance with any change in total clutch torque demand as indicated by said control module.

9. A transmission according to any of claims 6 to 8 wherein the priority module is programmed to shift the set torque profiles for the first and second clutches to take account of changes in the total torque demand, whereby both of said first and second clutches carry a percentage of any change in the total torque demand during the gear shift.

10 . A transmission according to any of claims 1 to 9 wherein the control system is configured such that the regulation of both of said first and second clutches during the control mode occurs substantially in real time.

11. A transmission according to any of claims 1 to 10 wherein the control system includes a slip controller configured to indicate the total torque demand in real time, whereby both of said first and second clutches are regulated to carry a percentage of any change in the total torque demand with a magnitude in accordance with a predetermined handover function for said clutches, the handover function defining a set torque profile for each of said first and second clutches for the duration of the torque handover.

12. A method for controlling the operation of two clutches during a gear shift, the method including the step of regulating the operation of both clutches during the torque phase of a gear shift, so that a proportion of any change in the total torque demand experienced during the torque phase is carried by each clutch.

13. A method according to claim 12 wherein each clutch is operated to follow a set torque profile during the torque phase, and wherein the set torque profile of both clutches is adjusted by a magnitude in accordance with the experienced changes in total torque demand.

14. A method according to claim 13 wherein a closed loop control calculation is made to generate values indicative of the total clutch torque demand during the gearshift, and wherein both clutches are regulated in accordance with any real time changes in the total torque demand.

15. A method according to claim 13 or 14 wherein a slip controller indicates the total torque demand in real time, and wherein both clutches are regulated to carry a percentage of any change in the total torque demand with a magnitude in accordance with a predetermined handover function for said clutches, the handover function defining a set torque profile for each clutch for the duration of the torque handover.