Abstract:
A detection scheme for diagnosing failure of clutch control components in a hydraulic control module of a power transmission utilizes pressure switch sensors to detect the position of each of the valves associated with the clutch control mechanization. The mechanization of these sensors with the valves provides the ability to clearly define the position of each of the valves, while also enabling the transmission electro-hydraulic control module (TEHCM) to diagnose the state of health of each pressure switch. The detection scheme may then differentiate between a failed switch and a failed (e.g., “stuck” or “out of position”) valve, while preventing unexpected and undesired shift sequencing within the transmission.

Description:
CLAIM OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/042,451, filed on Apr. 4, 2008, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to motorized vehicle powertrains, and more specifically to hydraulic control modules for vehicle transmissions, and diagnostic detection methodologies for the same. 
     BACKGROUND OF THE INVENTION 
     In general, motorized vehicles, such as the conventional automobile, include a powertrain that is comprised of an engine in power flow communication with a final drive system (e.g., rear differential and wheels) via a multi-speed power transmission. Hybrid type powertrains generally employ an internal combustion engine (ICE) and one or more motor/generator units that operate either individually or in concert to propel the vehicle. That is, power output from the engine and motor/generators are transferred through planetary gearing in the multi-speed transmission for communication to the vehicle&#39;s final drive system. The primary function of the transmission is to regulate speed and torque to meet operator demands for vehicle speed and acceleration. 
     Most automatic transmissions include a number of gear elements, generally in the nature of one or more epicyclic planetary gear sets, for coupling the transmission&#39;s input and output shafts. Traditionally, a related number of hydraulically actuated torque establishing devices, such as clutches and brakes (the term “torque transmitting device” often used to refer to both clutches and brakes), are selectively engageable to activate the aforementioned gear elements for establishing desired forward and reverse speed ratios between the transmission&#39;s input and output shafts. Engine torque and speed are converted by the transmission, for example, in response to the tractive-power demands of the motor vehicle. 
     Shifting from one speed ratio to another is performed in response to engine throttle and vehicle speed, and generally involves releasing one or more “off-going” clutches associated with the current or attained speed ratio, and applying one or more “on-coming” clutches associated with the desired or commanded speed ratio. To perform a “downshift”, a shift is made from a low speed ratio to a high speed ratio. That is, the downshift is accomplished by disengaging a clutch associated with the lower speed ratio, and engaging a clutch associated with the higher speed ratio, to thereby reconfigure the gear set(s) to operate at the higher speed ratio. Shifts performed in the above manner are termed clutch-to-clutch shifts, and require precise timing in order to achieve high quality shifting. 
     To operate properly, most power transmissions require a supply of pressurized fluid, such as conventional transmission oil. The pressurized fluid may be used for such functions as cooling and lubrication. The lubricating and cooling capabilities of transmission oil systems greatly impact the reliability and durability of the transmission. Additionally, multi-speed power transmissions require pressurized fluid for controlled engagement and disengagement, on a desired schedule, of the various torque transmitting mechanisms that operate to establish the speed ratios within the internal gear arrangement. 
     Transmissions are traditionally supplied with hydraulic fluid by a wet sump (i.e., internal reservoir) oil system, which is separate from the engine&#39;s oil system. The fluid is typically stored in a main reservoir or main sump volume where it is introduced to a pickup or inlet tube for communication to one or more hydraulic pumps. In hybrid-type transmissions, it is conventional practice to have one hydraulic pump assembly that is driven by the engine (e.g., via the engine crankshaft) for supplying hydraulic pressure to the transmission control system. It is also conventional practice to have an additional pump which is driven from alternate power sources so that pressure is available when the engine is not running and the vehicle is in motion. 
     The various hydraulic subsystems of a power transmission are typically controlled through operation of a hydraulic circuit, also known as a hydraulic control module. The hydraulic control module, in collaboration with an electronic control unit, regulates the flow of pressurized fluid for cooling and lubricating the transmission components, and the selective pressurization of the various torque-transmitting mechanisms to enable transmission shifting and vehicle braking. The hydraulic control module traditionally engages (actuates) or disengages (deactivates) the various transmission subsystems through the manipulation of hydraulic pressure generated within the transmission oil pump assembly with a plurality of valves. The valves used in a conventional hydraulic control circuit commonly comprise electro-hydraulic devices (e.g., solenoids), spring-biased accumulators, spring-biased spool valves, and ball check valves. 
     SUMMARY OF THE INVENTION 
     The present invention provides advanced hardware diagnostic detection for the clutch control components in a hydraulic control module of a multi-mode hybrid transmission. The detection scheme utilizes pressure switch sensors to detect the position of each of the valves associated with the clutch control mechanization. The mechanization of these sensors with the valves provides the ability to clearly define the position of each of the valves, while also enabling the transmission electro-hydraulic control module (TEHCM) to diagnose the state of health of each pressure switch. This will allow the diagnostics to differentiate between a failed switch and a failed (e.g., “stuck” or “out of position”) valve. 
     One of the primary benefits of this invention is the ability to safely diagnose the clutch control components in a power transmission. That is, a TEHCM operating in accordance with the present invention can systematically identify the position and state of health of each of the clutch control valves and, from that, determine what clutches are available to ensure that any undesired clutches are locked out and unable to apply during vehicle operation. The detection scheme of the present invention prevents unexpected and undesired shift sequencing within the transmission. 
     In accordance with one embodiment of the present invention, a hydraulic control module for a vehicle transmission is provided. The transmission has a plurality of torque transmitting devices and a hydraulic fluid reservoir. The hydraulic control module includes a controller, two trim valves, two pressure switches, and a blocking valve. 
     The first of the trim valves is in fluid communication with both the hydraulic fluid reservoir and a first of the plurality of torque transmitting devices. The first trim valve is configured to selectively actuate the first torque transmitting device. The second of the trim valves is in fluid communication with both the hydraulic fluid reservoir and a second of the plurality of torque transmitting devices. The second trim valve is configured to selectively actuate the second torque transmitting device. 
     The first of the pressure switches is in fluid communication with the first trim valve, and in operative communication with the transmission controller. The first pressure switch is configured to monitor or detect whether the first trim valve is in an engaged or disengaged state, and transmit signals indicative thereof to the controller. In a similar respect, the second of the pressure switches is in fluid communication with the second trim valve and in operative communication with the controller. The second pressure switch is configured to monitor or detect whether the second trim valve is in an engaged or disengaged state, and transmit signals indicative thereof to the controller. 
     The first blocking valve is in fluid communication with the first and second trim valves and the first and second pressure switches. The first blocking valve is preferably configured to selectively simultaneously reverse the hydraulic polarity (e.g., switch from fill to exhaust, or from exhaust to fill) of the first and second pressure switches. The controller is operable to detect if either or both of the pressure switches unintentionally toggles, and to shift the transmission to a safe operating mode in response to either of the pressure switches unintentionally toggling. 
     In accordance with one aspect of this particular embodiment, shifting the transmission to a safe operating mode includes disabling any/all of the trim valves that are in operative communication with a pressure switch that unintentionally toggles. 
     According to yet another aspect, the hydraulic control module also includes two more trim valves, another two pressure switches, and a second blocking valve. The third of the trim valves is in fluid communication with the hydraulic fluid reservoir and a third of the plurality of torque transmitting devices. The third trim valve is configured to selectively actuate the third torque transmitting device. The fourth of the trim valves is in fluid communication with both the hydraulic fluid reservoir and a fourth of the plurality of torque transmitting devices. The fourth trim valve is configured to selectively actuate the fourth torque transmitting device. 
     The third of the pressure switches is in fluid communication with the third trim valve and in operative communication with the controller. The third pressure switch is configured to monitor or detect whether the third trim valve is in an engaged or disengaged state, and transmit signals indicative thereof to the controller. Similarly, the fourth of the pressure switches is in fluid communication with the fourth trim valve and in operative communication with the controller. The fourth pressure switch is configured to monitor or detect whether the fourth trim valve is in an engaged or disengaged state, and transmit signals indicative thereof to the controller. 
     The second blocking valve is in fluid communication with the third and fourth trim valves and the third and fourth pressure switches. The second blocking valve is preferably configured to selectively simultaneously reverse the hydraulic polarity of the third and fourth pressure switches. In this instance, the controller is further operable to detect if either or both of the third and fourth pressure switches unintentionally toggles, and to shift the transmission to a safe operating mode in response to either of the third and fourth pressure switches unintentionally toggling. 
     According to another aspect of this embodiment, the controller is further operable to identify which clutch control component has failed in response to any of the pressure switches unintentionally toggling. In this particular instance, the controller then determines any undesirable transmission operating modes that require use of the failed clutch control component(s), and commands the transmission to operate in a transmission operating mode other than the undesirable operating modes. 
     According to yet another aspect, determining or identifying the failed clutch control component includes, in any order: determining if the pressure switch or switches that unintentionally toggled have failed; if not, determining if the respective trim valve attached to that pressure switch has failed (e.g., is stuck or inadvertently shifts); and, if not, determining if the blocking valve has failed. One way of determining if a pressure switch has failed includes toggling the blocking valve, and detecting if the pressure switches fails to toggle. In a similar regard, determining if one or both of the trim valves has failed may include toggling the respective blocking valve, and detecting if the corresponding pressure switches toggles. Finally, one manner of determining if the blocking valve has failed includes toggling the blocking valve, and detecting if both of the pressure switches in fluid communication therewith fail to toggle. 
     According to yet another aspect of this embodiment, the first trim valve is in direct fluid communication with the first pressure switch, and the second trim valve is in direct fluid communication with the second pressure switch. Contrastingly, the first trim valve is preferably characterized by a lack of a direct fluid communication with the second pressure switch, whereas the second trim valve is characterized by a lack of a direct fluid communication with the first pressure switch. Ideally, the various trim valves and blocking valves are all spool-type valve assemblies. 
     According to another embodiment of the present invention, a method of diagnosing failure of clutch control components in a hydraulic control module of a power transmission is provided. The clutch control components include a first trim valve in operative communication with a first pressure switch, a second trim valve in operative communication with a second pressure switch, and a blocking valve in fluid communication with the first and second trim valves and the first and second pressure switches. The blocking valve is preferably configured to selectively simultaneously reverse the hydraulic polarity of the first and second pressure switches. The first and second pressure switches toggle in response to toggling of a respective trim valve. 
     The method includes the steps of: detecting if either or both of the first or second pressure switches unintentionally toggles; shifting the transmission to a safe operating mode in response to either pressure switch unintentionally toggling; determining or identifying a failed clutch control component if either of the pressure switches unintentionally toggles; determining undesirable transmission operating modes that require use of the failed clutch control component; and operating the transmission in a transmission operating mode other than the undesirable operating modes. 
     According to one aspect of this embodiment, shifting the transmission to a safe operating mode includes disabling any/all trim valves that are in operative communication with a pressure switch that unintentionally toggles. 
     According to another aspect, determining a failed clutch control component includes, in any order: determining if the pressure switch that unintentionally toggled has failed; if it didn&#39;t, determining if the respective trim valve that is in operative communication with the pressure switch that unintentionally toggled has failed; and, if not, determining if the blocking valve has failed. In this instance, determining if either of the pressure switches has failed preferably includes toggling the blocking valve, and detecting if one of the pressure switches fails to toggle. Moreover, determining if a trim valve failed preferably includes toggling the blocking valve, and detecting if its respective pressure switch toggles (or fails to toggle). Finally, determining if the blocking valve has failed ideally includes toggling the blocking valve, and detecting if both of the first and second pressure switches fail to toggle. 
     In accordance with another aspect of this embodiment, the method further comprises determining if the first and second pressure switches are operating and positioned properly at vehicle start-up. To this regard, determining if the pressure switches are operating properly at vehicle start-up preferably includes toggling the first trim valve and detecting if the first pressure switch toggles contemporaneously therewith, and toggling the second trim valve and detecting if the second pressure switch toggles contemporaneously therewith. 
     In accordance with yet another aspect, the method further comprises determining if the first and second trim valves are operating and positioned properly at vehicle start-up. Determining if the trim valves are operating and positioned properly at vehicle start-up respectively includes toggling the blocking valve, and detecting if both the first and second pressure switches toggle. 
     According to yet another aspect, the first pressure switch is operable to monitor whether the first trim valve is in one of an active state and an inactive state. Likewise, the second pressure switch is preferably operable to monitor whether the second trim valve is in one of an active state and an inactive state. 
     The above features and advantages, and other features and advantages of the present invention, will be readily apparent from the following detailed description of the preferred embodiments and best modes for carrying out the invention when taken in connection with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary vehicle powertrain arrangement for implementation and practice of the present invention; 
         FIG. 2A  is a schematic representation of an exemplary hydraulic control module and electronic control unit for carrying out the control of the present invention, illustrating the blocking valves in inactive states; 
         FIG. 2B  is a schematic representation of the hydraulic control module and electronic control unit of  FIG. 2A , illustrating the blocking valves in active states; 
         FIG. 3  is a table mapping the expected mechanization sequence of the first and third pressure switches of  FIGS. 2A and 2B  corresponding to the engagement of certain torque-transmitting devices in the transmission of  FIG. 1 ; 
         FIG. 4  is a table mapping the expected mechanization sequence of the second and fourth pressure switches of  FIGS. 2A and 2B  corresponding to the engagement of certain torque-transmitting devices in the transmission of  FIG. 1 ; and 
         FIG. 5  is a table illustrating the state of the blocking valves of  FIGS. 2A and 2B  corresponding to the various operating modes of the vehicle powertrain of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is described herein in the context of the multi-mode hybrid-type powertrain having a multi-speed power transmission shown in  FIG. 1 . The hybrid powertrain illustrated in  FIG. 1  has been greatly simplified, it being understood that further information regarding the standard operation of a hybrid power transmission (or a hybrid-type vehicle for that matter) may be found in the prior art. Furthermore, it should be readily understood that  FIG. 1  merely offers a representative application by which the present invention may be incorporated and practiced. As such, the present invention is by no means limited to the particular arrangement illustrated in  FIG. 1 . 
     Referring to the drawings, wherein like reference numbers refer to like components throughout the several views, there is shown in  FIG. 1  a schematic depiction of an exemplary vehicle powertrain system, identified generally as  10 , having a restartable engine  14  drivingly connected to, or in power flow communication with, a final drive system  16  via a hybrid-type power transmission  12 . The engine  14  transfers power, preferably by way of torque, to the transmission  12  by an engine output shaft or crankshaft  18 . The transmission  12 , in turn, distributes torque via a transmission output shaft  26  to drive the final drive system  16 , represented herein by a rear differential  20  and wheels  22 , and thereby propel the hybrid vehicle (not specifically identified herein). In the embodiment depicted in  FIG. 1 , the engine  14  may be any engine, such as, but not limited to, a 2-stroke diesel engine or a 4-stroke gasoline engine, which is readily adapted to provide its available power output typically at a number of revolutions per minute (RPM). Although not illustrated in  FIG. 1 , it should be appreciated that the final drive system  16  may comprise any known configuration, such as front wheel drive (FWD), rear wheel drive (RWD), four-wheel drive (4WD), or all-wheel drive (AWD). 
     The transmission  12  is adapted to manipulate and distribute power from the engine  14  to the final drive system  16 . Specifically, engagement of one or more torque transmitting devices included in the transmission  12  (e.g., a clutch or brake) interconnects one or more epicyclic gear arrangements, preferably in the nature of interconnected planetary gear sets (not shown) to transfer power from the engine  14  at varying ratios to the transmission output shaft  26 . The transmission  12  may utilize one or more planetary gear sets in collaboration with, or independent of, one or more clutches and brakes to provide input split, compound split, and fixed ratio modes of operation. 
       FIG. 1  displays certain selected components of the transmission  12 , including a main housing  13  configured to encase and protect first and second electric motor/generator assemblies A and B, respectively. The first and second motor/generators A, B are indirectly journaled onto a main shaft of the transmission  12 , shown hidden at  24 , preferably through the above noted series of planetary gear sets. The motor/generators A, B operate, in conjunction with the planetary gear sets and selectively engageable torque transmitting mechanisms, to rotate the transmission output shaft  26 . The main housing  13  covers the inner most components of the transmission  12 , such as the motor/generators A, B, planetary gear arrangements, main shaft  24 , and torque transmitting devices. The motor/generator assemblies A, B are preferably configured to selectively operate as a motor and a generator. That is, the motor/generator assemblies A, B are capable of converting electrical energy to mechanical energy (e.g., during vehicle propulsion), and converting mechanical energy to electrical energy (e.g., during regenerative braking). 
     An oil pan or sump volume  28  (also referred to herein as “hydraulic fluid reservoir”) is located on the base of the main housing  13 , and is configured to stow or store hydraulic fluid, such as transmission oil (shown hidden in  FIG. 1  at  30 ) for the transmission  12  and its various components. Additionally, an auxiliary (or secondary) transmission pump  32  is mounted to the transmission main housing  13 . The auxiliary oil pump  32  is in fluid communication (e.g., via hydraulic circuitry) with the transmission  12  to provide pressurized fluid to the transmission  12  during specific operating conditions, such as engine-off mode and transitionary phases thereto and therefrom. 
     The various hydraulically actuated components of the transmission  12  are controlled by a transmission electro-hydraulic control module (TEHCM), an exemplary embodiment of which is illustrated schematically in  FIGS. 2A and 2B  and designated generally by reference numeral  40  therein. The electronic portion of the TEHCM  40  is primarily defined by a transmission control module (TCM)  36 , which is depicted in  FIG. 1  in a representative embodiment as a microprocessor-based electronic control unit of conventional architecture. The TCM  36  is in operative communication with the transmission  12  and the various constituent parts of the TEHCM  40 , and operable, at least in part, to control the individual and cooperative operation thereof. The TCM  36  controls the operation of the transmission  12  based on a number of inputs to achieve a desired transmission speed ratio. Such inputs may include, but are not limited to, signals representing the transmission input speed (TIS), a driver torque command (TQ), the transmission output speed (TOS), and the hydraulic fluid temperature (TSUMP). Those skilled in the art will recognize and understand that the means of communication utilized by the TCM  36  is not restricted to the use of electric cables (“by wire”), but may be, for example, by radio frequency and other wireless technology, fiber optic cabling, etc. 
     The hydraulic portion of the TEHCM  40  is in fluid communication with one or more pump assemblies, such as auxiliary pump  32  ( FIG. 1 ), and various pressure regulators and solenoid-operated fluid control valves (not shown) to develop a regulated pressure line. According to the embodiment of  FIG. 2 , the hydraulic portion of the TEHCM  40  also includes a plurality of clutch control valves, such as first, second, third, and fourth trim valves T 1  through T 4 , respectively. Recognizably, the numbering of the trim valves T 1 -T 4  (i.e., first, second, third, fourth) may be modified without departing from the scope and spirit of the present invention, and therefore should not be considered limiting. Each clutch trim valve T 1 -T 4  is operable to actuate at least one of the torque transmitting devices in the transmission  12 . Specifically, each trim valve is actuated or stroked (e.g., using a solenoid), directing line pressure supply directly to a respective clutch or brake, which allows the clutch to close and transmit torque. When the trim valve destrokes, the clutch cavity is exhausted, disabling the clutch. For example, the first of the trim valves T 1  is in fluid communication with both the hydraulic fluid reservoir  28  and a first of the plurality of torque transmitting devices, namely clutch C 1 . The first trim valve T 1  is configured to selectively actuate clutch C 1 . In a similar respect, the second, third and fourth trim valves T 2 -T 4  are each in fluid communication with a respective torque transmitting device, namely second, third and fourth clutches C 2 -C 4 , and the hydraulic fluid reservoir  28 . Moreover, each trim valve T 2 -T 4  is configured to selectively actuate its respective clutch C 2 -C 4 . 
     First and second blocking valves, identified in  FIGS. 2A-2B  as X and Y, respectively, combine to selectively block the line pressure feed to the trim valves T 1 -T 4 , preferably in accordance with the mechanization schedule defined in the table of  FIG. 5 . Specifically, the first blocking valve X is in direct fluid communication with both the first and third trim valves T 1 , T 3 . In a similar regard, the second blocking valve Y is in direct fluid communication with both the second and fourth trim valves T 2 , T 4 , as well as the first blocking valve X. The supply of hydraulic fluid to the first clutch C 1  may be impeded in this arrangement by deactivating or destroking the first blocking valve X (shown destroked in  FIG. 2A ), and activating or stroking the second blocking valve Y (shown stroked in  FIG. 2B ). Likewise, the supply of hydraulic fluid to the second clutch C 2  may be prevented by activating the first blocking valve X (shown stroked in  FIG. 2B ), and deactivating the second blocking valve Y (shown destroked in  FIG. 2A ). As a final example, the supply of hydraulic fluid distributed to the third clutch C 3  may be prevented by deactivating both the first and second blocking valves X, Y, as specified in the fourth row of the table in  FIG. 5 . 
     Each trim valve T 1 -T 4  has a dedicated pressure switch, denoted S 1  through S 4 , respectively, which determines the position of that particular trim valve. For example, as seen in  FIGS. 2A and 2B , the first of the pressure switches S 1  is in fluid communication with the first trim valve T 1 , and in operative communication with the TCM  36 . The first pressure switch S 1  is configured to monitor whether the first trim valve T 1  is in an engaged (stroked) or disengaged (destroked) state, and transmit signals indicative thereof to the TCM  36 . That is, when the first trim valve T 1  is in one position (e.g., stroked), the first switch track  42  may be pressurized to open the first pressure switch S 1 , which will communicate this information to the TCM  36 . When the first trim valve T 1  changes position (e.g., destrokes), the first switch track  42  may exhaust to close the first pressure switch S 1 . In a similar respect, the second, third and fourth pressure switches S 2 , S 3 , S 4  are each in fluid communication with a respective trim valve T 2 , T 3 , T 4 , and in operative communication with the TCM  36 . The second, third and fourth pressure switches S 2 , S 3  and S 4  are configured to monitor whether their respective trim valve T 2 , T 3 , T 4  is in an engaged (stroked) or disengaged (destroked) state, and transmit signals indicative thereof to the TCM  36 . Similar to the first pressure switch S 1 , when the second, third or fourth trim valve T 2 , T 3 , T 4  are in one position, a respective switch track  44 ,  46 , and  48  will be pressurized to open the pressure switch S 2 , S 3 , S 4 . When one of the trim valves T 2 , T 3 , T 4  changes position, its respective switch track  44 ,  46 ,  48  will exhaust to close the pressure switch S 2 , S 3 , S 4 . 
     The first and second blocking valves X and Y also operate to selectively reverse the hydraulic polarity of the pressure switches S 1 -S 4 —i.e., change from fill to exhaust, or from exhaust to fill. Specifically, the first blocking valve X, as seen in  FIG. 2A , is in fluid communication with the first and third pressure switches S 1 , S 3 , and configured to selectively simultaneously reverse the hydraulic polarity of the same. The second blocking valve Y is in fluid communication with the second and fourth pressure switches S 2 , S 4 , and configured to selectively simultaneously reverse the hydraulic polarity of the same. The changes in hydraulic polarity may be seen when comparing the hydraulic connections of the various pressure switches S 1 -S 4  in  FIG. 2A , where the first and second blocking valves X, Y are destroked, to the hydraulic connections to the pressure switches S 1 -S 4  in  FIG. 2B , where the blocking valves X, Y are stroked. For example, in  FIG. 2A , a first exhaust path  50  is being communicated to the first pressure switch S 1  through trim valve T 1  when the first blocking valve X is deactivated, whereas a first fill path  52  is communicated with the third pressure switch S 3  through trim valve T 3 . Contrastingly, the respective hydraulic polarities of the first and third pressure switches swap, as seen in  FIG. 2B , when the first blocking valve X is activated or stroked, such that the first fill path  52  is now being communicated with the first pressure switch S 1 , whereas a second exhaust path  54  is now being communicated to the third pressure switch S 3 . The same comparison can be made for the second and fourth pressure switches S 2 , S 4  and trim valves T 2 , T 4 , and accompanying communication with third and fourth exhaust paths  60  and  64 , respectively, or second fill path  62  via second blocking valve Y when comparing  FIGS. 2A and 2B . 
     The TCM  36  has a suitable amount of programmable memory  38  that is programmed to include, among other things, a diagnostic detection methodology for TEHCM  40 , namely a method of diagnosing failure of clutch control components in a hydraulic control module, as will be discussed in further detail below. The clutch control components include at least two trim valves, each in operative communication with a respective pressure switch, and a blocking valve in fluid communication with the two trim valves and pressure switches. The present invention is described herein with respect to the arrangement illustrated in FIGS.  1  and  2 A- 2 B as an exemplary application by which the methods of the present invention may be practiced. The present invention, however, may also be employed in other powertrain and transmission assemblies without departing from the intended scope of the present invention. 
     The TCM  36  operates to continuously monitor and detect if any of the pressure switches in the TEHCM  40  unintentionally toggles (i.e., switches position). As noted above, any commanded change in position of a given trim valve T 1 -T 4 , should result in a change of state of that valves designated pressure switch S 1 -S 4 . In a similar regard, for a commanded change in position of a blocking valve X or Y, two pressure switches S 1  and S 3  or S 2  and S 4 , respectively, should contemporaneously change state. Thus, a single pressure switch unexpectedly changing state (i.e., inadvertently toggling) indicates an unexpected or inadvertent change in position of a trim valve. The TCM  36  responds to a pressure switch unintentionally toggling by shifting the transmission  12  to a safe operating mode. Shifting the transmission  12  to a safe operating mode includes disabling the respective trim valve T 1 -T 4  and, thus, associated clutch C 1 -C 4 , that is in operative communication with the pressure switch S 1 -S 4  that unintentionally toggled. By changing the position of the associated blocking valve X or Y to lock out the given clutch C 1 -C 3 , the TCM  36  is given the opportunity to determine if the trim valve actually changed position, or the pressure switch connected thereto has failed. 
     Next, the TCM  36  determines or identifies which of the clutch control components failed. According to preferred practice, the TCM  36  identifies the failed clutch control component by: determining if the pressure switch that unintentionally toggled has failed; if it didn&#39;t, determining if the respective trim valve that is in operative communication with the pressure switch that unintentionally toggled has failed; and determining if the blocking valve has failed if the respective trim valve has not failed. Notably, the order of these steps may be varied, and may be assessed simultaneously. 
     The mechanization above provides the ability to safely determine if the pressure switch has failed by toggling the blocking valve in communication therewith, and detecting if one of the pressure switches fails to toggle. By way of example, if the first pressure switch S 1  unintentionally toggles, the TCM  36  can determine if switch S 1  is the failed clutch control component by toggling the first blocking valve X, and detecting if only the third pressure switch S 3  toggles, which can be seen by comparing row  2  and row  6  of the table in  FIG. 3 . If the first pressure switch S 1  responds properly, the TCM  36  will determine that the first trim valve T 1  has failed (e.g., is stuck). That is, by toggling the first blocking valve X, and detecting that the first pressure switch S 1  toggles, one can deduce from the relationship described above that the first trim valve T 1  is the failed clutch control component. Finally, if the first blocking valve X is toggled, and the TCM  36  detects that neither of the first and second pressure switches S 1  or S 3  toggles, the TCM  36  will identify the first blocking valve X as the failed component. 
     Once the failed clutch control component is identified, the TCM  36  can determine any undesirable transmission operating modes that require use of the failed clutch control component, and operate the transmission  12  in an operating mode other than the undesirable operating modes. Referring to  FIG. 5 , the mode operations M 1  through M 4  for the hybrid transmission  12  are when two clutches (e.g., C 1  and C 2 , or C 3  and C 4 ) are applied, and the transmission is effectively operating as an electrically-variable transmission (EVT), where the speed of the first and second motor/generator assemblies A, B are used to vary the ratio between the speed of engine  14 , and the transmission output speed. The gear operations G 1 -G 3  are instances where three of the clutches C 1 -C 4  are applied, and there is a fixed ratio between engine speed and transmission output speed—e.g., the transmission  12  is operating like a traditional step ratio automatic transmission. As the vehicle operator commands higher and lower output speed/torque, the TCM  36  can navigate through the various modes M 1 -M 4  and gears G 1 -G 3  to produce the desired results. The mode-mode, gear-mode, gear-gear shifts are simply the type of shift being executed. For example, in a mode  1  to gear  1  (M 1 /G 1 ) shift, the transmission  12  transitions or shifts from operating in M 1  with the first and third clutches C 1 , C 3  applied, to gear  1  G 1  by adding the fourth clutch C 4 . The TCM  36  can also execute mode-mode and gear-gear shifts by commanding double clutch transitions. By identifying which of the mode-mode, gear-gear, and mode-gear states require use of the failed clutch component, the TCM  36  can operate in an alternate state without compromising operator feel or the integrity of the TEHCM  40 . 
     The TCM  36  is preferably also configured to determine if the pressure switches S 1 -S 4  are operating properly at vehicle start-up. To this regard, determining if the pressure switches are operating properly at vehicle start-up preferably includes toggling the each of the trim valves T 1 -T 4 , and detecting or monitoring to see if each respective pressure switch S 1 -S 4  toggles contemporaneously therewith. In a similar respect, the TCM  36  can determine if each of the trim valves T 1 -T 4  is operating properly at vehicle start-up, for example, by toggling the each blocking valve X and Y, and monitoring to see that both the pressure switches in communication therewith contemporaneously toggle. 
     The methods of the present invention preferably include at least those steps identified above. Nevertheless, it is within the scope and spirit of the claimed invention to omit steps, include additional steps, and/or modify the order presented herein. It should be further noted that the method described above represents a single diagnostic cycle. However, it is contemplated that the method be applied in a systematic manner on a “real-time” basis. 
     The present invention allows for complete diagnoses of the clutch control system in the multi-mode hybrid-type transmission  12 . Always knowing the position of each of the clutch control valves allows the software to know the available clutches and maintain safe operation of the hybrid system by blocking undesired mode-mode, mode-gear, gear-gear shifts. The mechanization of the switches allows the system to utilize an existing TEHCM containing only four switches which reduces cost and validation associated with designing a new TEHCM. The mechanization provides for continuous diagnostic on the position of the valves, but also the state of health of the switches. 
     While the best modes for carrying out the present invention have been described in detail hereinabove, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.