0001] The present disclosure generally relates to power transmissions for use in
automobiles and the like. In particular, the present disclosure relates to the fail safe operation of a
dual clutch transmission system having two clutches.
BACKGROUND
[0002] Dual Clutch Transmissions (DCT) is an Automated Manual Transmission (AMT)
system that involves two distinct clutches for transmission with each clutch being associated
with separate gear sets, which, for example, can be even and odd gear sets. The system provides
minimal power interruption by way of allowing only a respective clutch to change position when
a corresponding gear is needed. This is achieved by allowing one clutch to engage with a
respective shaft while disengaging the other clutch from the shaft. However, during the gear
shifting period, an overlap time exists where both clutches tend to have non-zero torques and
therefore may be in motion.
[0003] Due to the existence of this non-zero torque situation with the clutches during the
overlap time, software issues and hardware component issues associated with the Transmission
Control Unit (TCU) can cause the closure of the two clutches simultaneously which, in turn, can
result in excessive deceleration of the vehicle, eventually causing blockage of the wheels.
[0004] Attempts have been made in the prior art to realize solutions for effective and
efficient DCT systems that provide an improved safety systems in various fields. For example,
Japanese Patent document number JP6329189B2 discloses a DCT system including two clutches
with each clutch being associated with different gear set.The DCT system is configured to
disengage its clutches when an abnormality is detected. This patent document disclosure,
however, does not address/attempt to solve the situation of simultaneous closure of clutches
unwanted deceleration.
[0005] Another patent document number WO2004097266A1 also discloses a DCT system
including two clutches with each clutch being associated with different gear set.The DCT system
is switchable between a mode in which, during a shift between gears both clutches engage during
the shift and a mode where only one clutch engages at any time with provided benefits being a
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limp-home mode and improved AMT shift regime. This patent document disclosure, however,
does not address/attempt to solve the situation of simultaneous closure of clutches that can avoid
unwanted deceleration.
[0006] Yet another patent document number US8460155B2 discloses a control unit for a
DCT system that provides a seamless transition for the two clutches. This patent document
disclosure, however, does not address/attempt to solve the situation of simultaneous closure of
clutches that can avoid unwanted deceleration.
[0007] There is, therefore, a need to provide a simple and, efficient solution that
addressesthe situation of simultaneous closure of clutches that can avoid unwanted deceleration.
OBJECTS OF THE INVENTION
[0008] A general object of the present disclosure is to provide an efficient and effective
DCT system that provides an improved functional safety.
[0009] An object of the present disclosure is to provide an efficient and effective DCT
system that can provide an improved product liability aspect.
SUMMARY
[0010] Aspects of the present disclosure relate to power transmissions for use in automobiles
and the like. In particular, the present disclosure relates to the fail safe operation of a dual clutch
transmission system having two clutches. The present disclosure provides a solution to
inefficient DCT systems typically implemented in automobiles, while meeting all functional
requirements.
[0011] An aspect of the present disclosure relates to a method for fail-safe operation of a
dual clutch transmission (DCT) system in vehicle. The method comprises (i) actuating a first
clutch and a second clutch associated with the DCT system by a first clutch actuator and a
second clutch actuator respectively; (ii) monitoring continuously, clutch parameters associated
with the first clutch and the second clutch by a monitoring system; (iii) detecting abnormalities
associated with the clutch parameters by a detecting mechanism; and (iv) toggling, when an
abnormality is detected, a shutoff path associated with the DCT system where the first clutch and
the second clutch are disengaged from a respective shaft associated with the automobile.
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[0012] In an aspect, the clutch parameters include current associated with outputs of the first
clutch and the second clutch.
[0013] In an aspect, the abnormalities are further associated with a closure of the first clutch
and the second clutch simultaneously with respect to a shaft associated with the vehicle.
[0014] In an aspect, the clutch parameters further include vehicle speed, clutch speed,
acceleration.
[0015] In an aspect, actuating the first clutch and the second clutch further comprises
actuating before the toggling of the shutoff path; and wherein the method further comprises
identifying whether the first clutch or the second clutch is actuated based on current feedback.
[0016] In an aspect, actuating the first clutch and the second clutch further comprises
actuating after the toggling of the shutoff path; and wherein the method further comprises
ensuring whether the first clutch or the second clutch is not actuated based on current feedback.
[0017] In an aspect, the method further comprises disabling a respective clutch that is based
on current feedback.
[0018] In an aspect, the method further comprises disabling a respective clutch that is not
based on current feedback.
[0019] Another aspect of the present disclosure pertains to a fail-safe DCT system for use in
an automobile. The system includes a first clutch and a second clutch, both configured to
operatively connect with an automobile shaft to operate the shaft in an operational position, the
clutches being associated with different gear sets of the automobile. The system further includes
a first actuator and a second actuator, both configured to actuate the first clutch and the second
clutch respectively in an operational position. The system also includes a control unit configured
to monitor clutch parameters and detect abnormalities associated with the parameters, the unit
further configured to toggle a shutoff path phase during overlap time for the clutches if an
abnormality is detected.
[0020] In an aspect, during the shutoff path phase, the clutches are prevented by the control
unit from simultaneously engaging with the shaft.
[0021] Various objects, features, aspects and advantages of the inventive subject matter will
become apparent from the following detailed description of preferred embodiments, along with
the accompanying drawing figures in which like numerals represent like components.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings are included to provide a further understanding of the
present disclosure, and are incorporated in and constitute a part of this specification. The
drawings illustrate exemplary embodiments of the present disclosure and, together with the
description, serve to explain the principles of the present disclosure.
[0023] FIG. 1 shows an exemplary method for fail-safe operation of a DCT system in a
vehicle, in accordance with embodiments of the present disclosure.
[0024] FIG. 2 illustrates an exemplary safety monitoring pattern with respect to the
exemplary method, in accordance with embodiments of the present disclosure.
[0025] FIG. 3 shows an exemplary microcontroller associated with the control unit shown in
FIG. 2, in accordance with embodiments of the present disclosure.
[0026] FIG. 4 illustrates an exemplary clutch actuator power stage shutoff mechanism with
respect to the exemplary method, in accordance with embodiments of the present disclosure.
[0027] FIG. 5 shows an exemplary monitoring function architecture, in accordance with
embodiments of the present disclosure.
[0028] FIG. 6 shows an exemplary monitoring function flow diagram, in accordance with
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0029] The following is a detailed description of embodiments of the disclosure depicted in
the accompanying drawings. The embodiments are in such details as to clearly communicate the
disclosure. However, the amount of detail offered is not intended to limit the anticipated
variations of embodiments; on the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope of the present disclosure as
defined by the appended claims.
[0030] Embodiments explained herein relate to power transmissions for use in automobiles
and the like. In particular, the present disclosure relates to the failsafe operation of a dual clutch
transmission system having two clutches.
[0031] FIG. 1 shows an exemplary method 100 for fail-safe operation of a DCT system in a
vehicle, in accordance with embodiments of the present disclosure. The fail-safe DCT system is
associated typically with an automobile but can also be implemented in other vehicles. The
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system typically includes two clutches, a first clutch and a second clutch, and respectively
associated first clutch actuator and a second actuator for the actuating the clutches (all not
shown).
[0032] As shown in FIG. 2, the proposed system uses a 3-Level Safety Monitoring Pattern
(but not limited to) for the illustration of the fail-safe operation of abnormalities in the clutches,
which consists of 3 levels: actuation (function) level, monitoring level, and control level. The
function level can include subprograms& hardware components for carrying out the intended
functionality (i.e. clutch control strategy and actuation). The monitoring level is similar and
parallel to function level but includes checks for abnormalities in function level software and
takes the vehicle to a safe state upon abnormality detection. To be independent of common cause
failures, single point failure and latent point failure, all inputs heretofore explained are read
redundantly and processed independently. The control level software is the facilitator of safe
operating environment by securing memory and other hardware's where the monitoring level will
be operating.
[0033] Referring now to FIG. 1, at 102, the first clutch and the second clutch are both
configured to operatively connect with an automobile shaft to operate the shaft in an operational
position with the clutches being associated with different gear sets of the automobile. The first
actuator and the second actuator are both configured to actuate the first clutch and the second
clutch respectively in an operational position. At 104, parameters associated with the clutches are
monitored based on a monitoring system known in the art. Typically, it is based on continuous
clutch current monitoring. A current sensor as shown in FIG. 3, continuously measures the
current at the output of the clutch actuator power stage, which is acquired and processed by the
level 2monitoring software as shown. With reference to 106 and 108 in FIG. 1, any abnormality
in the clutch control is detected by the level 2 monitoring software and level 3 software in turn
activates the redundant shutoff path, which shuts off the power to the actuator power stage. For
the purposes of this document, the shutoff path and the safe mode both have similar
corresponding meanings where the clutches are disengaged and remain in that position when an
abnormality is detected as is herein explained.
[0034] Referring now to 106 in FIG. 1, the abnormalities are events associated with
parameters, which can lead to the engagement of both clutches’ closure on the shaft in the
operational position which results in unwanted deceleration and wheel blockage. Thus, they can
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include other parameters such as vehicle speed, clutch speed, acceleration, and other parameters
that may be appreciated by a person skilled in the art.
[0035] Referring to FIG. 4 in association with 104 from FIG. 1, the clutch actuator power
stage shut off mechanism is shown in FIG. 4. The microcontroller outputs the target clutch
current, which is given to the power stage, which drives the actuators. Two MOSFETS acting as
switches are connected in series to the power stage, each controlling the currents for each clutch
actuator. When the redundant shut off path is activated, the MOSFETS are switched off, thus
shutting off the power stage. The clutches being normally open type clutch, are released once the
power to the actuators is cut off, there by achieving the safe state. Due to the introduction of
these power stages and shut off paths, it becomes necessary to perform effectiveness on these
lines for its working, so as to be sure of shutting off the power stage when needed to avoid
hazard.
[0036] Referring again to FIG. 2, the control unit shown executes the following steps at
regular time periods in addition to conventional clutch control algorithm known in the art. All
inputs to be considered in the monitoring algorithm are plausibilized for errors and if error found,
safe state is achieved through shutoff path. With regards to clutch operating mode detection to
determine if the clutches are in the steady state or transition state including: vehicle speed and
clutch speed estimation from shaft speed sensor; shift map based target gear calculation from
accelerator pedal and vehicle speed; determining if target gear is not equal to current gear;
initiation of clutch transition from steady state; and determining if slip between clutch speed and
engine speed is less than threshold, which corresponds to steady state operation as provided
under FIG. 6.
[0037] FIG. 6 discloses aspects of clutch current acquisition and processing current sensors
in accordance with embodiments of the present disclosure. Here, when in steady state:
determining if the driven gear is even or odd (which typically is the case in DCT systems with
one clutch being associated with even gear set while the other being associated with the odd gear
set), thus determining the corresponding clutch which is in disengaged state; and continuous
monitoring of the disengaged clutch current to be equal to zero shutting off power to actuator
power stage, when disengaged clutch current becomes greater than zero for a de-bounce time.
Second, when in transition state: determining if both clutch currents are above a threshold – i.e.
enough current to transfer torque; determining if the absolute change in currents is below a
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threshold – clutch currents are expected to change continuously during the transition phase:
shutting off power to actuator power stage if the above condition remains true for a de-bounce
time.
[0038] Referring now to FIG. 5 which generally shows the monitoring function architecture,
the method 100 can include aspects of input acquisition and plausibility algorithms that may be
developed based on clauses from ISO26262 as is known in the art, with regards to common
cause failures, single point failures and latent point failures. For example, here (i) output shaft
speed sensors are verified by comparing values of two output shaft speed sensors.
(Generally, most of the vehicles are equipped with two sensors to determine the vehicle
movement direction). Scope is not limited as plausibility can also be done using wheel speed
sensors if present; (ii) vehicle speed information is calculated from these output shaft speed
sensors; (iii) gear position sensors are verified against and Vehicle speed/Engine speed ratio
(V/N). V/N ratio will be same for a selected gear. These ratios are calibrated in the software and
are verified periodically. (iv) engine speed can be verified using vehicle speed, gear and clutch
state information; (v) two accelerator pedal sensors values are used to verify correctness; (vi)
clutch current sensors are verified by using estimated clutch speed values and engine speed
values. All the above plausibility methods are mentioned here are examples and for explanation.
Scope is not limited in the way plausibility is executed.
[0039] The DCT system disclosed can also include the following aspect for the shutoff path.
With regards to the Shutoff Path Test, the following steps of algorithm can be executed during
initialization of control unit. The effectiveness of redundant shutoff path to control clutch
actuator power stage is verified at the initialization of control unit. Before the start of the driving
cycle, a positive test can be done by following steps: (i) no activation of redundant shutoff path;
(ii) clutch actuation; (iii) check if the corresponding clutch is actuated by taking feedback (Ex.
Feed back from power-stage status, sensor feedback). Before the start of driving cycle, a
negative test can also be done by following steps: (i) activation the redundant shutoff path; (ii)
clutch actuation; (iii) ensuring that corresponding clutch is not actuated by taking feedback (Ex.
feedback from power-stage status, sensor feedback). Failure in any of the above test is
considered as redundant shutoff path ineffectiveness. If redundant shutoff path is found
ineffective, then clutch actuation functionality is disabled and engine start is prohibited for the
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driving cycle and the user driver is informed about it and error storage is done for later
diagnostics.
[0040] Thus, the present disclosure providesa power transmission for use in automobiles and
the like. In particular, the present disclosure provides a fail safe operation of a dual clutch
transmission system having two clutches. The DCT system, through the implementation of a
continuous monitoring function, overcomes disadvantages associated with conventional DCT
systems.
[0041] While the foregoing describes various embodiments of the invention, other and
further embodiments of the invention may be devised without departing from the basic scope
thereof. The scope of the invention is determined by the claims that follow. The invention is not
limited to the described embodiments, versions or examples, which are included to enable a
person having ordinary skill in the art to make and use the invention when combined with
information and knowledge available to the person having ordinary skill in the art.
ADVANTAGES OF THE INVENTION
[0042] The present disclosure provides an efficient and effective DCT system that can
provide an improved functional safety system.
[0043] The present disclosure provides an efficient and effective DCT system that can
provide an improved product liability aspect.

We Claim:

1. A method (100) for fail-safe operation of a dual clutch transmission in a vehicle, the
method (100) comprising:
actuating a first clutch and a second clutch associated with the dual clutch
transmission system by a first clutch actuator and a second clutch actuator respectively;
monitoring continuously, clutch parameters associated with the first clutch and the
second clutch by a monitoring system;
detecting abnormalities associated with the clutch parameters by a detecting
mechanism; and
toggling, when an abnormality is detected, a shut off path associated with the dual
clutch transmission system where the first clutch and the second clutch are disengaged
from a respective shaft associated with the automobile; and
wherein the clutch parameters include current associated with outputs of the first clutch and
the second clutch; and
wherein the abnormalities are further associated with a closure of the first clutch and the
second clutch simultaneously with respect to a shaft associated with the vehicle.
2. The method (100) as claimed in claim 1, wherein the clutch parameters further include
vehicle speed, clutch speed, acceleration.
3. The method (100) as claimed in claim 2, wherein actuating the first clutch and the second
clutch further comprises actuating before the toggling of the shutoff path; and wherein the
method (100) further comprises identifying whether the first clutch or the second clutch is
actuated based on current feedback.
4. The method (100) as claimed in claim 2, wherein actuating the first clutch and the second
clutch further comprises actuating after the toggling of the shutoff path; and wherein the
method (100) further comprises ensuring whether the first clutch or the second clutch is not
actuated based on current feedback.
5. The method (100) as claimed in claim 3, wherein the method (100) further comprises
disabling a respective clutch that is based on current feedback.
6. The method (100) as claimed in claim 4, wherein the method (100) further comprises
disabling a respective clutch that is not based on current feedback.
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7. A fail-safe dual clutch transmission system for use in an automobile, the system
comprising:
a first clutch and a second clutch, both configured to operatively connect with an
automobile shaft to operate the shaft in an operational position, the clutches being
associated with different gear sets of the automobile;
a first actuator and a second actuator, both configured to actuate the first clutch and
the second clutch respectively in an operational position; and
a control unit configured to monitor clutch parameters and detect abnormalities
associated with the parameters, the unit further configured to toggle a shutoff path phase
during overlap time for the clutches if an abnormality is detected; and
wherein, during the shut off path phase, the clutches are prevented by the control unit from
simultaneously engaging with the shaft.