Patent Application
20110077830
The present invention relates to the shift control of a transmission having neutral idle functionality in a vehicle having an engine start-stop powertrain.
Vehicle transmissions are designed to transmit torque from an engine to a set of drive wheels in order to propel the vehicle in a range of output speeds. The engine output shaft may be selectively connected to a transmission input shaft when engine propulsion is required. In a manual transmission, a clutch pedal may be depressed to allow a driver to shift gears and/or to place the transmission into a neutral state. In an automatic transmission, a hydrodynamic torque converter automatically provides this engine/transmission connection.
A torque converter includes an impeller/pump, a turbine, and a stator. The torque converter is filled with oil. The pump, which may be bolted to a rotating engine flywheel to continuously rotate at engine speed, discharges the oil into the turbine. The turbine is connected to the transmission input shaft, and therefore rotation of the turbine ultimately causes a rotation of the coupled transmission input shaft. A stator redirects oil discharged from the turbine back into the pump. The use of a torque converter thus enables a variable fluid coupling effect to automatically occur between the engine and the transmission, thereby allowing the vehicle to slow to a stop without stalling, while also allowing required torque multiplication to occur at low vehicle output speeds.
This variable slip capability allows the engine to continue to rotate when the vehicle is idling in certain transmission states or modes, e.g., in park (P), neutral (N), or in a drive state, i.e., a forward drive mode (D) or a reverse mode (R). In some transmission designs operating in a neutral (N) state during a drive detent position, i.e., when the vehicle reaches zero output speed at a standstill or when idling and the engine remains running, the transmission may be automatically shifted to a hydraulic neutral state referred to as neutral idle (NI).
Certain vehicle powertrains such as hybrid electric vehicle (HEV) powertrains are able to selectively utilize different energy sources to optimize fuel efficiency. An HEV having a full hybrid powertrain can use either or both of an internal combustion engine and a high-voltage energy storage system (ESS) for propulsion. That is, a typical full HEV powertrain can be electrically-propelled immediately upon starting the HEV and during vehicle speeds up to a relatively low threshold speed. One or more high-voltage motor/generator units (MGU) may alternately draw power from and deliver power to the ESS as needed. Above the threshold speed, the engine can be restarted and engaged with the transmission to provide the required propulsive torque.
The powertrain of a mild HEV lacks the capability of propelling the HEV via purely electrical means, but nevertheless retains certain key design features of the full hybrid powertrain, e.g., the capability of selectively shutting down or powering off the engine at idle. The capability of any HEV to selectively shut off and restart its engine when the vehicle is at a standstill, and/or when operating in a stabilized low-speed drive mode, is of particular fuel-saving benefit relative to conventional vehicle designs.
Accordingly, a method and apparatus are provided herein for controlling a neutral idle (NI) clutch shift operation to allow a vehicle with automatic engine start-stop functionality to utilize the NI state as a transitional shift state. By using the NI state as a transitional shift state, either upon or prior to engine shutdown as well as upon restart of the engine, the vehicle driveline is decoupled to minimize driveline disturbances, and torque multiplication may be prevented upon engine restart. Shutting down an engine reduces fuel consumption, as noted above, however doing so may result in a temporary loss of oil pressure to the various clutches and gears of a transmission gear box. Some amount of oil pressure is required for optimal transmission control upon engine restart and vehicle launch, and therefore an auxiliary device, e.g., an auxiliary pump or a surge accumulator, may be used for this purpose without departing from the intended scope of the invention.
Maintaining oil pressure with an auxiliary device allows the transmission to remain in 1st gear in a conventional powertrain. However, a starter motor must crank against a stationary turbine and a locked gearbox, a situation which may produce cranking and combustion-related torsional transients along the driveline during engine restart. The present method and apparatus therefore enable the engine to shut down and restart in an unloaded or a partially-loaded state as set forth herein, depending on the particular auxiliary device that is used.
Execution of the algorithm embodying the method by an onboard controller unloads the engine upon shutdown, and unloads or partially loads the engine as a designated NI clutch reapplies during an engine restart event. The vehicle includes a multi-speed automatic transmission, e.g., a 6-speed or an 8-speed transmission of the type disclosed herein, having a plurality of torque transfer mechanisms or clutches. One of these clutches may be designated as the NI clutch. This designated NI clutch may be selectively actuated to enter the NI state, and may also be used to launch the vehicle in 1st gear.
As the NI state is entered, the unloaded engine shuts down. The algorithm commands a clutch pressure, which is either zero or a pre-learned return spring pressure depending on the particular oil-assist type or auxiliary device, if used, e.g., an auxiliary pump, a surge accumulator. Upon engine restart, the NI clutch may be held at a pre-learned return spring pressure or commanded via a fill pulse, again depending on the oil-assist type. Clutch reapply for vehicle launch begins at a predetermined point in the engine restart event. As the vehicle begins to move during launch, reapply of the NI clutch, which is also configured as the 1st gear clutch, continues until the NI clutch is locked and the vehicle moves. When a partially-loaded state is used, the NI clutch may begin slipping and pulling down turbine speed earlier in the process.
In particular, a vehicle is provided that includes an engine, a plurality of clutches that are selectively engageable, alone or in combination with each other, to establish a plurality of forward drive modes, with one of these clutches being designated as the NI clutch. The engine is adapted to shut down at idle or when the vehicle is stationary to conserve idle fuel consumption. A controller includes an algorithm adapted for shifting the transmission into the NI state to at least partially unload the engine prior to the engine shut down and during the subsequent restart maneuver.
A method is also provided for shifting a transmission of a vehicle into the NI state during an engine shut down and restart event, the transmission having a plurality of clutches that are selectively engageable, alone or in combination with each other, to establish a plurality of forward drive modes. The method includes determining the presence of a commanded engine shut down event using a controller, actuating a designated one of the clutches as an NI clutch using the controller to thereby enter the NI state prior to shutting down the engine to thereby at least partially unload the engine, and determining the presence of a commanded engine restart event using the controller. The method also includes starting the engine while the engine remains at least partially unloaded, and then actuating the NI clutch to thereby launch the vehicle.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, the vehicle 10 shown in
The engine 12 is controlled to provide start-stop functionality, also known as autostop/autostart capability, wherein the engine is selectively turned off at idle or at zero speed to conserve fuel as noted above. A starter motor 11 may be used to crank and restart the engine 12. The engine 12 is selectively coupled to an automatic transmission (T) 14 via a hydrodynamic torque converter 16. An output shaft 13 of the engine 12 rotates at an engine speed (NE), and an input shaft 15 of the transmission 14 rotates at a turbine speed (NT). Transfer of an input torque (Ti) to the transmission 14 thus occurs at a variable rate through the torque converter 16.
The transmission 14 also includes an output shaft 18 connected to a set of road wheels 24. The output shaft 18 ultimately carries a transmission output torque (To) from various clutch and gear sets 17 of the transmission 14, including a designated NI clutch as noted below with reference to
The clutch and gear sets 17 may be selectively actuated using electro-hydraulic controls powered by fluid from a main transmission pump (P) 33 at a line pressure (PL). The pump 33 may be configured to draw fluid 37 from a sump 35, with the fluid having a temperature (TSump). However, other non-fluidic actuating means or devices may also be used within the scope of the invention. Additionally, an optional auxiliary device (AUX) 33A, e.g., an electrically-operated auxiliary fluid pump or a surge accumulator adapted for temporarily directing oil to the clutch and gear sets 17 when the engine 12 is restarted, may be used to ensure delivery of sufficient oil pressure to the transmission 14 during an engine-off state and upon engine restart.
Still referring to
In a neutral idle (NI) state, the transmission 14 may be placed in a drive (D) mode while electro-hydraulic clutch pressure regulation valves (not shown) reduce the pressure on a designated NI clutch, thereby placing the transmission into a partially-loaded “hydraulic neutral” state as noted above. Data used by the algorithm 100 may reside within or may be accessible by the controller 26, and may be sampled or processed thereby during other transmission states such as neutral (N) and park (P).
Vehicle data that may be sampled in order to determine appropriate NI state entry conditions may include, but are not necessarily limited to: vehicle output speed (NO), a value which may be measured by one or more sensors 39 shown separately in
Still referring to
The controller 26 is adapted for receiving, reading and/or measuring, calculating, and recording or storing various required measurements, values, or figures including any required readings fully describing the engine speed (NE), turbine speed (NT), and the transmission output speed (NO), such as via one or more speed sensors 39 having an output speed or speeds labeled generically as (NX). The speed signals (NE), (NO) may be transmitted electrically via conductive wiring, although other transmitting means are also usable within the scope of the invention, for example radio frequency (RF) transmitters and receivers.
The torque converter 16 includes a stator 30 between an impeller or pump 32 and a turbine 34. An optional lockup torque converter clutch (TCC) 31 may also be used to selectively lock the pump 32 and turbine 34 above a threshold lockup speed. The pump 32 may be bolted or otherwise directly connected to the output shaft 13 to thereby rotate at engine speed (NE). Within the torque converter 16, the turbine 34 is driven by fluid 37 and is connected to the input shaft 15 of transmission 14. Thus, a rotation of turbine 34 ultimately rotates the input shaft 15 at a turbine speed (NT) less than or equal to engine speed (NE). Viscous drag or friction losses occurring within the transmission 14 may reduce the turbine speed (NT) to a level slightly less than engine speed (NE) as shown in
Referring to
In the 6-speed embodiment of
The first gear set 140 may include nodes 142, 144, and 146, which in one possible embodiment may be a ring gear (R1), a carrier member (PC1), and a sun gear (S1), respectively. The input shaft 15 may be directly connected to node 142, and to an input side of clutch C456, i.e., clutch 51. Node 144 may be connected to an input side of clutch C1234, i.e., clutch 138, and to an input side of clutch C35R, i.e., clutch 53. Node 146 is grounded to the stationary member 28. As will be understood by those of ordinary skill in the art, as used in
Second gear set 150 includes nodes 152, 154, 156, and 157, which may be respectively embodied as a sun gear (S2), a ring gear (R2), a carrier gear (PC2), and another sun gear (s2A), respectively. Node 154 is directly connected to the transmission output shaft 18 and rotates at output speed (Tout). Node 156 is connected to an input side of clutch CBR1, i.e., clutch 136, which is also connected to stationary member 28.
As noted above, either of clutches 136 and 138 may be utilized as the designated NI clutch without departing from the intended scope of the invention. When using clutch 138, an optional free-wheeling mechanism (F1) 19 may be connected between stationary member 28 and node 156 to allow rotation with respect to node 156 in only one rotational direction. When using clutch 136 as the NI clutch, the free-wheeling mechanism 19 may be omitted.
Referring to
In the 6-speed embodiment of
First gear set 240 may include nodes 242, 244, and 246, which in one possible embodiment may be a ring gear (R1), a carrier gear (PC1), and a sun gear (S1), respectively. The input shaft 15 may be selectively connected to nodes 244 and 246 via clutches 251 and 253, respectively. Node 242 is directly connected to node 264 of the third gear set 260.
Second gear set 250 includes nodes 254, 256, and 257, which in one possible embodiment may be configured as a ring gear (R2), a carrier gear (PC2), and a sun gear (S2), respectively. Node 257 is directly connected to the transmission input shaft 15. Node 254 is connected to node 244 of the first gear set 240. Free-wheeling element (F1) 19 connects to stationary member 28 to allow rotation with respect to node 254 in only one rotational direction.
Third gear set 260 includes nodes 262, 264, and 266, which may be embodied as a ring gear (R3), a carrier gear (PC3), and a sun gear (S3), respectively. Node 266 is selectively connected to stationary member 28 via a clutch CB1234, i.e., clutch 238. Node 264 is connected to node 242 of the first gear set 240, and to the output shaft 18 of transmission 14. Node 262 is directly connected to node 256 of the second gear set 250.
Clutch 238, i.e., CB1234, may be utilized as the NI clutch in this particular embodiment as noted above. When using clutch 238, free-wheeling mechanism (F1) 19 may be connected between nodes 244 and 254 of gear sets 240 and 250, respectively, to allow rotation with respect to node 254 in only one rotational direction. Clutch 236, i.e., CBR1 can be used as the NI clutch if F1 is omitted.
Referring to
In the 8-speed embodiment of
The first gear set 40 may include nodes 42, 44, and 46, which may be a sun gear (S1), a carrier (PC1), and a ring gear (R1), respectively. Node 46 maybe selectively connected to stationary member 28 via a clutch CB12345R, i.e., clutch 41. Node 42 may be selectively connected to stationary member 28 via a clutch CB1278R, i.e., clutch 36. Node 42 is also connected to a node 52 of second gear set 50. Node 54 of gear set 50 is connected to an input side of a rotating clutch C13567, i.e., clutch 38, as is the transmission input shaft 15 with input torque (Tin). Node 56 is connected to a third gear set 60 as explained below.
The second gear set 50 may include nodes 52, 54, and 56, which may be a sun gear (S2), carrier (PC2), and ring gear (R2), respectively. Node 52 maybe directly connected to node 42 of gear set 40. Node 54 may be directly connected to the transmission input shaft 15.
The third gear set 60 may include nodes 62, 64, and 66, which may be a sun gear (S3), carrier (PC3), and ring gear (R3), respectively. Node 66 may be directly connected to node 56 of the second gear set 50, and selectively connected to node 54 by a clutch C23468, i.e., clutch 58, and a clutch C13567, i.e., clutch 38.
The fourth gear set 70 may include nodes 72, 74, and 76, which may be a sun gear (S4), a carrier gear (PC4), and a ring gear (R4), respectively. Node 76 is directly connected to node 44 via a member 45. Node 74 is directly connected to the transmission output shaft 18, and directly connected to node 64 of the third gear set 60 via a member 47. Node 72 is selectively connected to node 62 via a clutch C45678R, i.e., clutch 48.
Referring to
Algorithm 100 begins with step 102, wherein the auxiliary system 33A, if one is used, is turned on or made ready, and wherein a set of conditions (X) is examined to determine if the engine shutdown process may proceed.
Conditions (X) may include, without being limited to, a determination that an NI state has commenced during engine shut down at approximately point 80 on the engine speed trace, i.e., line 82 of
At step 104, clutch pressure to the designated NI clutch, e.g., clutch 1234 of
At step 106, the engine 12 is automatically shut down. Engine run flag 85 may be set to zero at approximately point 91 of line 82 to indicate that engine shutdown has been completed. The brake pedal 29B of
At step 108, the algorithm 100 commands NI clutch pressure to a predetermined level, represented as PX in
At step 110, another set of conditions (Y) is examined to determine if a subsequent restart of the engine 12 may commence. For example, conditions (Y) may include a driver taking a foot off of the brake pedal 29B of
At step 112, the engine 12 is cranked and started, e.g., using the starter motor 11, or using a belt alternator starter (BAS) system if so equipped. The turbine 34 of the torque converter 16 begins to rotate in conjunction with the engine output shaft 13. If equipped with a surge accumulator or no oil-assist mechanism at all other than the pump 33, a fill pulse may be optionally commanded to the designated NI clutch. Otherwise, the return spring pressure (PRS) of line 88 may be commanded to begin to fill the NI clutch, which is also configured as the 1st gear clutch. If equipped with an auxiliary pump, the auxiliary pump could be commanded on so that a hydraulic or other clutch control system (not shown) ultimately fed by the pump 33 may command the return spring pressure (PRS) of line 88 while the engine is off, and holding the return spring pressure (PRS) during engine crank, until the main pump 33 takes over. Algorithm 100 proceeds to step 114.
At step 114, another set of conditions (Z) is examined to determine if the NI clutch may be actuated. For example, conditions (Z) may include passing a calibrated engine speed threshold, or an event in which the engine run flag 85 transitions from a value of 0 to a value of 1, i.e., when engine speed reaches approximately point 81. The algorithm 100 proceeds to step 116 if conditions (Z) are satisfied, otherwise the algorithm proceeds to step 118.
At step 116, NI clutch control is executed to prevent turbine speed (NT) represented by line 84 of
At step 118, an alternate or default shift sequence may be executed when conditions (Z) of step 114 are not satisfied. For example, a state other than NI may be entered for launch of the vehicle 10, such as a command to maximum holding pressure resulting in a loaded start. The algorithm then proceeds to step 120.
At step 120, the designated NI clutch is commanded to full pressure, i.e., rising from the level of point 92 to a maximum holding pressure level of line 94. When using clutch C1234 of
Accordingly, execution of the algorithm 100 using the controller 26 allows the engine 12 to shut down and restart in an unloaded or a partially loaded state by using the NI state as a transitional shift state. Execution of the algorithm 100 may provide an optimal driveline feel during engine restart and shutdown, and may provide a reduced rate of idle fuel consumption, e.g., zero when the engine 12 is off, in city driving or in other stop-and-go traffic conditions conducive to engine start-stop cycling.
While the best modes for carrying out the invention have been described in detail, 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.
