Abstract:
A vehicle includes an engine, transmission, engine control module (ECM), and transmission control module (TCM). The transmission includes an input member and an input clutch which selectively connects a crankshaft of the engine to the input member. The TCM identifies a target clutch torque of the input clutch during a creep maneuver of the vehicle, and communicates the identified target clutch torque to the ECM. The ECM maintains engine idle speed at a threshold level through the creep maneuver and a requested launch using the target clutch torque as a feed-forward term. A method includes identifying a target clutch torque of the input clutch during a creep maneuver, and communicating the identified target clutch torque to the ECM. The idle speed is maintained at a threshold level by the ECM through the creep maneuver and a detected launch using the target clutch torque as a feed-forward idle speed control term.

Description:
TECHNICAL FIELD 
     The present disclosure relates to engine idle speed control. 
     BACKGROUND 
     A dual clutch transmission (DCT), which combines features of a manual and an automatic transmission, has oddly-numbered and evenly-numbered gears. A first input clutch is applied to engage any oddly-numbered gears such as 1 st , 3 th , or 5 th  gear. A second input clutch is similarly applied to engage any evenly-numbered gears. One of these input clutches is also engaged when entering reverse. A controller predicts the next gear to be selected using various available control inputs such as engine acceleration and braking levels, and then stages the next gear ahead of the impending shift. This dual input clutch design and advance staging functionality can result in relatively fast gear shifts. 
     When idling in a vehicle having a DCT, a driver can remove pressure from a brake pedal to allow the vehicle to slowly move or “creep” forward at a threshold rate of speed. Sufficient throttle request added before or during creep results in launch of the vehicle. In order to creep or launch in a vehicle having a DCT, as well as in a vehicle having a manual or an automatic manual transmission (AMT), an input clutch is applied as a designated launch clutch while the engine is idling. Control of clutch pressure during creep/launch is automatically modulated via a controller in the DCT and AMT designs, while a driver&#39;s manually-applied clutch apply pressure serves the same function in a manual transmission. 
     SUMMARY 
     A vehicle is disclosed herein. The vehicle includes an internal combustion engine, a transmission, an engine control module (ECM), and a transmission control module (TCM). The transmission includes an input member and a launch clutch. The TCM, which is in communication with the ECM, is programmed to execute a control method in conjunction with the ECM during launch or creep maneuvers of the vehicle. Execution of the method is intended to optimize the overall quality and feel of the launch/creep maneuver. 
     It is recognized herein that application of a launch clutch may impart a significant load on the crankshaft of the engine. In response, engine idle speed can momentarily sag at the start of the creep or launch maneuver. Sag in engine speed, if sufficiently pronounced, can stall the engine at launch. The present invention is intended to address such potential engine sag during the creep and launch maneuvers, specifically by using feed-forward compensation from the TCM to the ECM. In the disclosed approach, the TCM identifies the clutch load and communicates the identified clutch load to the ECM. The ECM then uses the communicated clutch load to maintain engine idle speed at a threshold level through the duration of the creep or launch maneuver. 
     In particular, a vehicle is disclosed herein having the engine, transmission, ECM, and TCM noted above. The engine includes a crankshaft and has an idle speed. The transmission includes an input member and one or more input clutches that selectively connect the crankshaft to the input member. The TCM is programmed to identify a target clutch torque, with the target clutch torque being the torque capacity required of the input clutch during a creep maneuver of the vehicle. This identified target clutch torque is communicated to the ECM. The ECM is programmed to maintain the idle speed of the engine at a threshold level through the creep maneuver using the identified target clutch torque as a feed-forward engine idle speed control term. 
     The transmission may be optionally embodied as a dual clutch transmission having, as the input clutch, a first and a second input clutch. 
     The vehicle may include a brake pedal, the depression of which generates a braking signal. The ECM may detect a threshold braking event via processing of the braking signal, and decrease or ramp down the target clutch torque at a calibrated rate in response to such a threshold braking event. 
     The vehicle may also include an accelerator pedal, the depression of which generates a throttle request signal. The ECM may detect a launch maneuver of the vehicle via the throttle request signal, and increase or ramp up the target clutch torque at a calibrated rate in response to the detected launch maneuver. The calibrated rate may include multiple calibrated rates, each corresponding to a different threshold throttle request. 
     Additionally, the TCM may calculate an amount of slip across the input clutch during the launch maneuver. One of the calibrated rates in this instance may correspond to a determined slip across the input clutch that exceeds a calibrated threshold, with this rate being applied when such a threshold slip event occurs. The TCM may decrease the target clutch torque at another of the calibrated rates upon detection by the ECM of a throttle tip-out event. 
     A system for the above described vehicle includes the transmission and TCM. 
     A method for controlling the idle speed of the engine is also disclosed. The method includes identifying, via a transmission control module (TCM), a target clutch torque of an input clutch of the vehicle during a creep maneuver, and then communicating the identified target clutch torque to an engine control module (ECM). The method additionally includes maintaining the idle speed of the engine at a threshold level through the creep maneuver using the identified target clutch torque as a feed-forward idle speed control term. 
     The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the invention, as defined in the appended claims, when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example vehicle having a transmission that is controlled during a creep or launch maneuver using the control method set forth herein. 
         FIG. 2  is a time plot describing a set of parameters of the vehicle shown in  FIG. 1 , with amplitude and time depicted on the respective vertical and horizontal axes. 
         FIG. 3  is another time plot showing feed-forward clutch torque as used in the present control method. 
         FIG. 4  is a flow chart describing an example embodiment of a feed-forward idle speed compensation control method usable with the vehicle shown in  FIG. 1  or other vehicles having an input clutch. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components throughout the several Figures, a vehicle  10  is shown schematically in  FIG. 1 . The vehicle  10  includes an internal combustion engine  12  and a transmission  14 . The transmission  14  is shown in  FIG. 1  as an example dual clutch transmission (DCT) having a pair of input clutches C1 and C2. Other transmission designs having an input clutch as a designated launch clutch, such as manual or automated manual transmissions, may also be used within the scope of the present invention. For illustrative consistency, the example DCT of  FIG. 1  will be used hereinafter without limiting the transmission  14  to a DCT configuration. 
     The vehicle  10  of  FIG. 1  includes a control system having a transmission control module (TCM)  20  and an engine control module (ECM)  30 . Although omitted from  FIG. 1  for simplicity, other control modules may be included as needed. The TCM  20  and the ECM  30  communicate with each other, e.g., over a controller area network (CAN) bus or other suitable network path. The TCM  20  and the ECM  30  are configured, i.e., programmed in software and equipped in hardware, to execute a feed-forward engine idle speed compensation control method  100 , an example of which is described below with reference to  FIG. 4 . Execution of the method  100  is intended to optimize the overall quality and feel of creep and launch maneuvers relative to conventional transmission designs. The method  100  prevents a perceptible sag in engine speed upon application of a launch/creep clutch, such as either of the input clutches C1 or C2 of the example transmission  14  of  FIG. 1 . The effect of the present method  100  on various vehicle parameters during creep and launch is described in greater detail below with reference to  FIGS. 2-4 . 
     The engine  12 , which is shown schematically in  FIG. 1 , is responsive to a received throttle request (arrow Th%). Throttle request (arrow Th%) may be commanded by a driver of the vehicle  10  as a force or a percentage of travel of an accelerator pedal  11 A to indicate a relative level of requested engine torque. Such force/travel may be detected via a throttle sensor (not shown) in the conventional manner. In response to receipt of the throttle request (arrow Th%) by the ECM  30 , the engine  12  delivers input torque (arrow T I ) to an engine crankshaft  15 . The input torque (arrow T I ) is ultimately transmitted to the transmission  14 . Similar force/travel of a brake pedal  11 B may be captured as a braking signal (arrow B X ) and input to the ECM  30  for use in execution of the method  100 , as a release of the brake pedal  11 B may signal the start of the creep maneuver, and may also coincide with a requested launch of the vehicle  10 . 
     As is well understood in the art, a DCT of the type shown in  FIG. 1  includes a gearbox  13  containing two independently-operated input clutches, i.e., the respective first and second input clutches C1 and C2 of the example vehicle  10 . Either input clutch C1 or C2 may be applied as a launch clutch when launching the vehicle  10 , for instance applying input clutch C1 when launching from 1 st  gear. While omitted from  FIG. 1  for illustrative simplicity, each input clutch C1 and C2 may also include a center plate containing any number of friction discs, friction plates, or other suitable friction materials. 
     The input clutches C1 and C2 may be lubricated/wet or dry. If lubricated, fluid (arrow F) may be circulated by an engine-driven fluid pump  31  to the input clutches C1, C2, or the fluid (arrow F) may be circulated only to the gearbox  13  in a dry DCT embodiment. Associated electronic and hydraulic clutch control devices (not shown) ultimately control the shift operation and vehicle launch in response to instructions from various onboard controllers as explained in detail below. 
     In the example transmission  14  of  FIG. 1 , the first input clutch C1 controls the oddly-numbered gear sets  24  (GS O ) of the DCT assembly  14 , for instance first, third, fifth, and seventh gears in an example 7-speed transmission, while the second input clutch C2 controls any evenly-numbered gear sets  124  (GS E ), e.g., second, fourth, and sixth in the same example 7-speed transmission. Within each of the gear sets  24 ,  124 , additional clutches, typically hydraulic piston-actuated rotating or braking clutches, may be engaged or disengaged as needed to establish the desired gear states. The reverse gear state may be part of the oddly-numbered gear set  24  and controlled via the first input clutch C1. Using this gear arrangement, the transmission  14  can be rapidly shifted through its available range of gears without completely interrupting the power flow from the engine  12 . 
     In the example vehicle  10  of  FIG. 1 , the transmission  14  also includes an output shaft  21  that is connected to a set of drive wheels (not shown). The output shaft  21  ultimately transmits transmission output torque (arrow T O ) to the drive wheels (not shown) to propel the vehicle  10 . The transmission  14  may include a first shaft  25  connected to the first input clutch C1, a second shaft  27  connected to the second input clutch C2, and the respective odd and even gear sets  24 ,  124  (GS O , GS E ) located within the gearbox  13 , both of which may be cooled and lubricated via circulation of transmission fluid from a sump  35  via an engine-driven main pump  31 , e.g., via a pump shaft  37 , or alternatively via an auxiliary pump (not shown). 
     Within the transmission  14 , the first shaft  25  is connected to and drives only the oddly-numbered gear sets  24  (GS O ). The second shaft  27  is connected to and drives only the evenly-numbered gear sets  124  (GSE), including a reverse gear set. The transmission  14 , when constructed as a DCT as shown, further includes upper and lower main shafts  17  and  19 , respectively, which are connected to final drive (F/D) gear sets  34 ,  134 . The final drive gear sets  34  and  134  in turn are connected to the output shaft  21  of the transmission  14 , and are configured to provide any required final gear reduction. 
     Still referring to  FIG. 1 , the TCM  20  and the ECM  30  may be configured as microprocessor-based computer devices having associated hardware elements such as processors  22 ,  32  and memory  23 ,  33 . The memory  22 ,  33  may include, but is not necessarily limited to, tangible, non-transitory computer-readable media such as read only memory (ROM), optical memory, solid state flash memory, and the like, as well as random access memory (RAM), electrically-erasable programmable read-only memory (EEPROM), flash memory, etc. The TCM  20  and the ECM  30  may also include circuitry including but not limited to a high-speed clock, analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, a digital signal processor or DSP, transceivers  26 ,  36 , and the necessary input/output (I/O) devices and other signal conditioning and/or buffer circuitry needed for executing the method  100 , which will now be described with reference to the remaining Figures. All associated steps of the method  100  may be programmed into the memory  23  and/or  33  and executed therefrom via the processors  22  and/or  32  as needed. Thus, the term “configured to” as used herein refers to programming and/or otherwise constructing or equipping the TCM  20  and ECM  30  to perform their required functions without further modification. 
     Referring to  FIG. 2 , a time plot  50  describes changing amplitudes (A) of a set of parameters of the vehicle  10  shown in  FIG. 1 , with the amplitudes plotted on the vertical axis and time (t) plotted on the horizontal axis. Prior to t 0 , the vehicle  10  of  FIG. 1  is at a standstill with the brake pedal  11 B of  FIG. 1  fully applied and the accelerator pedal  11 A fully released. At t 0 , the driver releases the brake pedal  11 B and, as a result, the associated braking signal B X  drops to zero, thereby signaling the start of a creep maneuver and a possible launch. That is, absent a threshold amount of the throttle request (arrow Th%) shown in  FIG. 1 , the vehicle  10  would only creep forward at a calibrated creep speed, governed via a calibrated maximum creep torque, without launching. 
     In either case, one of the input clutches C1 or C2 of  FIG. 1  is fully applied as a launch clutch. Absent use of the present method  100 , this action might result in an immediate sag in engine speed of a magnitude ΔN E , as indicated by the trajectory of trace N E *. The sag in engine speed would be sustained until engine torque (trace T E *) rises sufficiently to increase the shaft torque (T S ) acting on the transmission  14  of  FIG. 1 , e.g., on the shaft  17  when launching in first gear. Therefore, between t 1  and t 2  engine speed (N E *) would rise to its target level N E,TGT . However, the transient engine sag occurring between t 0  and t 2  may be perceptible to a driver. The present method  100  seeks to reduce the amplitude and duration of this sag via a specific communication between the TCM  20  and ECM  30  of  FIG. 1  using a feed-forward clutch load compensation approach. 
     Specifically, the TCM  20  shown in  FIG. 1  determines the target clutch load (T C ) for the designated input clutch as described below with reference to  FIG. 3 . The target clutch load (T C ) is a required torque capacity of the launch clutch, which once again in the example of  FIG. 1  is either of the input clutches C1 or C2 depending on the design, with the target clutch load (T C ) value communicated by the TCM  20  to the ECM  30 . 
     The ECM  30 , upon receipt of the communicated target clutch load (T C ), controls idle speed at launch/creep using the received clutch load (T C ) as a control parameter. This control action results in a trajectory shown by trace N E . Engine torque (trace T E ) is thus effectively smoothed between t 0  and t 2  as shown relative to engine torque (trace T E *) determined absent execution of the method  100 . The TCM  20  outputs the target clutch load (T C ) with a smooth trajectory. In the event of threshold hard braking event while the vehicle  10  is actively creeping, which occurs at t 3  in  FIG. 2 , the TCM  20  takes the additional step of ramping down the target clutch torque (T C ) at t 4 , as indicated by arrow R. This in turn reduces the rate of the sag in engine speed N E . 
     Referring to  FIG. 3 , the target clutch torque (T C ) is described in further detail. As with  FIG. 2 , when the engine  12  of  FIG. 1  is idling, the brake pedal  11 B is fully applied and the accelerator pedal  11 A is fully released. This occurs between t 0  and t 1  of  FIG. 3 . In  FIG. 3 , all ramp rates between t 1  and t 5  are based on the level of force/travel of the accelerator pedal  11 A, i.e., the level of throttle request, and may be calibrated ahead of time using different threshold force/travel values. The target clutch torque (T C ) may be provided with different ramp rates depending on the stage of the launch. 
     A first rate is shown between t 1  and t 2 , which corresponds to the initial acceleration phase of the launch maneuver. This continues from a first level T1 until a second level T2 is later reached. Here, the first level T1 may be region of 0% or negligible apply to the accelerator pedal  11 A of  FIG. 1 . If in creep mode, the level of T1 may be a calibrated creep torque, i.e., an engine torque value that results in a threshold creep speed, typically less than about 5 kph. Otherwise, the first level T1 may be 0 NM. 
     At t 1 , engine speed (N E ) begins to rise toward a target level, which is the second level T2, with this target level being equal to a requested axle torque less a calibrated offset. Slightly later, and shortly before t 3 , the input shaft speed (N 15 ) ramps up quickly in response to the feed-forward term, i.e., the clutch torque (T C ) provided from the TCM  20 . A third level T3 is then reached at t 3 , with the third level T3 being a calibrated holding axle torque. 
     The period t 2  to t 3  represents another phase of the launch maneuver wherein the target clutch torque (T C ) is held at a near constant level or increased at a slight ramp rate upward to the third level T3 as shown. As the input shaft speed (N 15 ) rises, the slip across the designated launch clutch rises. The TCM  20  commands another relatively fast ramp when the slip exceeds a calibrated slip threshold. A fourth level T4 is then reached, with level T4 being an amount of steady-state torque needed for a threshold non-negligible but minimal amount of slip across the launch clutch, e.g., slip of less than 1-2 RPM. Upon throttle tip-out at t 4 , the TCM  20  then drops the target clutch torque (T C ) back to the first level T1, doing so at a calibrated ramp rate so as to prevent any abrupt changes in output torque (arrow T O  of  FIG. 1 ). 
     Referring to  FIG. 4 , an example embodiment of the method  100  begins with step  102 , where the TCM  20  of  FIG. 1  determines whether certain conditions exist for executing a creep maneuver of the vehicle  10 . Step  102  may entail processing the braking signals (B X ) and the throttle request (Th%). If these signals indicate that creep of the vehicle  10  is requested, the method  100  proceeds to step  104 . Otherwise, step  102  is repeated. 
     At step  104 , the TCM  20  of  FIG. 1  next computes the target clutch torque (T C ) as the desired clutch capacity for the creep maneuver. By way of example, the target clutch torque (T C ) may be calculated as a function of the position of the accelerator pedal  11 A, i.e., the driver-requested axle torque. The method  100  proceeds to step  106  once the target clutch torque (T C ) is known. 
     Step  106  entails communicating the target clutch torque (T C ) to the ECM  30 , such as by transmitting the value of the target clutch torque (T C ) to the ECM  30  over the CAN bus of  FIG. 1  or any other suitable network path. Once the ECM  30  has received the target clutch torque (T C ), the method  100  proceeds to step  108 . 
     At step  108 , the ECM  30  of  FIG. 1  may set the engine speed target at a level sufficient to creep the vehicle  10  while also maintaining the target clutch torque (T C ) previously communicated at step  106 . The ECM  30  uses the received target clutch torque (T C ) as a feed-forward term, e.g., as part of a proportional-integral-derivative (PID) control loop as understood in the art, to maintain a target idle speed during creep. The method  100  then proceeds to step  110 . 
     At step  110 , the TCM  20  and ECM  30  of  FIG. 1  together determine whether launch of the vehicle  10  is requested, i.e., by processing the received throttle request (Th%). If so, the method  100  proceeds to step  112 . Step  108  is otherwise repeated. 
     Step  112  entails increasing engine speed, which is indicated as trace N E  in  FIG. 3 , while adding in the target clutch torque (T C ) to compensate for this additional clutch load. The method  100  proceeds to step  114 . 
     At step  114 , the method  100  includes determining if the vehicle launch maneuver requested at step  110  is complete. Part of step  114  may include, for example, detecting a threshold hard braking event of the type shown at t 3  in  FIG. 2 , such as by processing the braking levels (arrow B X  of  FIG. 1 ) and comparing these levels, as well as changing vehicle speed, to a calibrated hard braking threshold. If so, the method  100  proceeds to step  116 . Otherwise, step  112  is repeated. 
     Step  116  may include ramping out the target clutch torque (T C ) at a calibrated rate. This controlled ramp out rate, which is indicated by arrow R in  FIG. 2 , helps to prevent a perceptible sag in engine speed, which is an overarching goal of the present method  100 . The method  100  is finished after execution of step  116 , and may repeat anew starting at step  102 . 
     The underlying logic of the method  100  may be included in any transmission design having an input clutch that is used as a creep/launch clutch. Use of a target input clutch torque capacity or load as a feed-forward term in a PID-based engine idle control scheme, as set forth in detail above, may ultimately reduce or eliminate a perceptible sag in engine speed, specifically during a launch or creep maneuver. These and other potential benefits may be realized, with variations of the example embodiments shown in the various Figures being possible without departing from the intended inventive scope. 
     The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is intended to be defined solely by the claims. While the best mode, if known, and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.