Method and apparatus for executing a shift in a powertrain system

This disclosure is related to vehicle powertrain systems and shift execution.

The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art

Powertrain systems including hybrid powertrain systems, electric-only powertrain systems, and extended-range electric powertrain systems are configured to operate in a plurality of operating modes. Such powertrain systems use torque generators, clutches and transmissions to transfer torque to a driveline. Executing a shift from a first operating mode to a second operating mode may include executing a direct shift process that includes deactivating an off-going clutch and activating an oncoming clutch. Propulsion torque during shift execution may be maintained by slipping either an oncoming clutch or an off-going clutch while synchronizing speeds of clutch elements of the oncoming clutch before fully applying the oncoming clutch, with an applied clutch that is common for the first and second states being continuously applied during the shift execution. Synchronizing the speeds of the clutch elements includes controlling operation of one of the torque generators to achieve a synchronization speed. Other powertrain control permutations to maintain output torque during a shift execution are known.

Known issues associated with executing a direct shift process include driveline power loss and energy loss during clutch slippage. The power loss during clutch slippage may be discernible by a vehicle operator.

A method to shift a powertrain system from a first operating mode to a second operating mode wherein a common clutch is activated to effect operation in both the first and second operating modes includes, in sequence, deactivating the common clutch, activating an oncoming clutch associated with the second operating mode and deactivating an off-going clutch associated with the first operating mode, and activating the common clutch.

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary powertrain system including an internal combustion engine, first and second torque machines, and planetary gear set coupled to a driveline in accordance with the disclosure;

FIG. 2 is a control scheme in flowchart form, including sequentially executed steps to effect a shift from a first operating mode to a second operating mode in accordance with the disclosure;

FIGS. 3-1 through 3 - 5 depict progression of a first shift sequence for a powertrain system using the control scheme of FIG. 2 in accordance with the disclosure; and

FIGS. 4-1 through 4 - 5 depict progression of a second shift sequence for a powertrain system using the control scheme of FIG. 2 in accordance with the disclosure.

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIG. 1 is a schematic diagram of an exemplary powertrain system 5 including an internal combustion engine 10 and a transmission 25 including first and second torque machines 20 and 30 , respectively, and a planetary gear set 40 . The powertrain system 5 is coupled to a driveline 50 to transfer tractive torque thereto. The internal combustion engine 10 and the first and second torque machines 20 , 30 are any suitable machines. In one embodiment, the first and second torque machines 20 , 30 are multiphase electric motor/generator devices that electrically connect to a high-voltage power source via an electric power inverter. A control module 15 is configured to control operation of the powertrain system 5 . The powertrain system 5 as shown is configured for use in an extended range electric vehicle (EREV) configuration, with the concepts described herein applicable to other powertrain and vehicle configurations. The powertrain system 5 is meant to be illustrative and not limiting.

The internal combustion engine 10 is configured to execute an autostop event and an autostart event during ongoing powertrain operation. As is appreciated, an autostop event occurs when engine operation is discontinued and the internal combustion engine 10 is in an OFF state and is not rotating during ongoing powertrain operation to conserve fuel. As is appreciated, an autostart event is executed subsequent to executing an autostop event to start or restart engine operation during ongoing powertrain operation. As is appreciated, the engine 10 may be started to transfer tractive torque to the driveline 50 and/or to provide power to the first torque machine 20 to generate energy that may be used to generate tractive torque by one or both the first and second torque machines 20 , 30 .

The powertrain system 5 includes first, second, and third torque-transfer devices C 1 32 , C 2 34 , and C 3 36 , respectively, which may be any suitable clutch elements, e.g., friction clutch packs, brakes, band clutches, and one-way clutches. All torque transfer devices are simply referred to herein as clutches. The first clutch C 1 32 is a brake element that is configured to couple a ring gear element 46 of the planetary gear set 40 to a transmission case ground 38 when applied. The second clutch C 2 34 is configured to couple the ring gear element 46 of the planetary gear set 40 to an output member 24 of the first torque machine 20 when applied. The third clutch C 3 36 is configured to couple an input member 22 of the first torque machine 20 to an output member 12 of the engine 10 when applied. An input member 28 of the second torque machine 30 couples to a sun gear element 42 of the planetary gear set 40 . An output member 45 coupled to a planet gear assembly 44 of the planetary gear set 40 couples to the driveline 50 .

Table 1 describes clutch activations associated with specific operating modes of the powertrain system of FIG. 1 . The term ‘x’ indicates that the specific clutch is activated when in the corresponding operating mode. Each of the operating modes is indicated by the activated clutch(es), if any.

Specific ones of the powertrain elements, e.g., the internal combustion engine 10 and the first and second torque machines 20 , 30 , are controlled to generate tractive torque, if any, in the various operating modes in response to load demands including an operator torque request. “EV” indicates electric vehicle operation, i.e., tractive torque being generated by one or both of the first and second torque machines 20 , 30 . The engine 10 is preferably in the OFF state during the electric vehicle operation, although such operation is not required.

The first neutral mode (Neutral 1 ) indicates that no tractive torque is being generated, and it is accomplished with the first, second, and third torque-transfer clutches C 1 32 , C 2 34 , and C 3 36 , respectively, being deactivated.

The second neutral mode (Neutral 2 ) indicates that no tractive torque is being generated, and it is accomplished with the first and second torque-transfer clutches C 1 32 and C 2 34 being deactivated. The third torque-transfer clutch C 3 36 is activated, permitting torque transfer between the engine 10 and the first torque machine 20 . This may include electric power generation, i.e., power flow from the engine 10 to the first torque machine 20 , or engine starting, i.e., power flow from the first torque machine 20 to the engine 10 .

Mode 1 (1 motor EV) is an electric vehicle mode wherein tractive torque is generated by torque machine 30 . In this embodiment, the second torque machine 30 generates tractive torque and the engine 10 and the first torque machine 20 are decoupled from the driveline 50 by deactivation of the second and third torque-transfer clutches C 2 34 and C 3 36 . The first torque-transfer clutch C 1 32 is activated to ground the ring gear 46 to transfer torque and speed of the second torque machine 30 to the driveline 50 .

Mode 2 (2 motor EV) is an electric vehicle mode wherein tractive torque is generated by both the first and second torque machines 20 , 30 . The engine 10 is decoupled from the driveline 50 by deactivation of the third torque-transfer clutch C 3 36 . The second torque-transfer clutch C 2 34 is activated to combine and transfer torque and speed from the first and second torque machines 20 , 30 through the planetary gear set 40 to the driveline 50 .

Mode 3 (Series) is a series-hybrid mode wherein tractive torque is generated by the second torque machine 30 and the engine 10 is coupled to the first torque machine 20 by activation of the third torque-transfer clutch C 3 36 to generate electric power that is preferably used by the second torque machine 30 . The engine 10 is decoupled from the driveline 50 by deactivation of the second torque-transfer clutch C 2 34 . The first torque-transfer clutch C 1 32 is activated to ground the ring gear 46 to transfer torque and speed of the second torque machine 30 to the driveline 50 .

Mode 4 (Load Share) is an engine-on load share mode wherein tractive torque is generated by both the first second torque machines 20 , 30 , and the engine 10 by activation of the second torque-transfer clutch C 2 34 and the third torque-transfer clutch C 3 36 . The first torque-transfer clutch C 1 32 is deactivated. The second torque-transfer clutch C 2 34 and the third torque-transfer clutch C 3 36 are activated to combine and transfer torque and speed from the engine 10 and the first and second torque machines 20 , 30 through the planetary gear set 40 to the driveline 50 .

The Transition Mode is an operating mode that is preferably utilized exclusively during mid-shift between Mode 3 (series-hybrid mode) and Mode 4 (load share mode), and between Mode 1 (1 Motor EV mode) and Mode 2 (2 Motor EV mode). The Transition Mode includes the first torque-transfer clutch C 1 32 activated, the second torque-transfer clutch C 2 34 activated and the third torque-transfer clutch C 3 36 deactivated.

FIG. 2 illustrates a control scheme 200 that includes steps that are sequentially executed to effect a shift from a first operating mode to a second operating mode. The control scheme 200 is described with reference to the illustrated powertrain system 5 of FIG. 1 to effect a shift between a first of the operating modes described in Table 1 to a second of the operating modes described in Table 1 during ongoing operation. It is preferred to control torque output to the driveline 50 so that a shift is imperceptible to a vehicle operator. It is appreciated that a synchronous shift is preferred to minimize clutch slippage affecting power losses. The control scheme 200 is particularly suited to effecting a shift between operating modes wherein the oncoming operating mode and the off-going operating mode have an activated clutch in common. By way of example, the powertrain system 5 illustrated with reference to FIG. 1 includes Mode 3 (Series) with clutches C 1 32 and C 3 36 activated and Mode 4 (Load Share) with clutches C 2 34 and C 3 36 activated. Clutch C 3 36 is a commonly activated clutch, enabling the engine 10 to provide torque for either electric power generation (Mode 3 ) or torque and electric power generation (Mode 4 ).

The control scheme 200 is implemented as one or a plurality of algorithms that are executed in the control module 15 . Control module, module, control, controller, control unit, processor and similar terms mean any one or various combinations of one or more of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms and similar terms mean any controller executable instruction sets including calibrations and look-up tables. The control module has a set of control routines executed to provide the desired functions. Routines are executed, such as by a central processing unit, and are operable to monitor inputs from sensing devices and other networked control modules, and execute control and diagnostic routines to control operation of actuators. Routines may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines may be executed in response to occurrence of an event. Table 2 is provided as a key to FIG. 2 wherein the numerically labeled blocks and the corresponding functions are set forth as follows.

During ongoing operation, a shift is commanded ( 202 ). The commanded shift may be a shift between Mode 3 (Series) and Mode 4 (Load Share), either from Mode 3 to Mode 4 or from Mode 4 to Mode 3 . The commanded shift may be a shift between Mode 1 (1 Motor EV mode) and Mode 2 (2 Motor EV mode), either from Mode 1 to Mode 2 or from Mode 2 to Mode 1 . It is appreciated that shifts between other operating modes may instead be commanded, but are outside the scope of the control scheme 200 .

The commanded shift described with reference to the control scheme 200 of FIG. 2 is a shift between Mode 3 (Series) and Mode 4 (Load Share). The commanded shift includes a sequence of events that includes deactivating the common clutch, e.g., C 3 36 , during an interim period as described herein. As such, the control system offloads torque from the common clutch by coordinating the magnitude of torque produced by the engine 10 with the magnitude of torque produced by the first torque machine 20 to neutralize torque across clutch C 3 36 ( 204 ). In one example, this includes increasing power output from the first torque machine 20 and/or decreasing power output from the engine 10 to neutralize torque across clutch C 3 36 .

When the torque across common clutch C 3 36 is neutralized, clutch C 3 36 is deactivated ( 206 ). The powertrain system 5 then operates in one of the powertrain operating modes, e.g., Mode 1 or Mode 2 in accordance with the still activated clutch C 1 32 or C 2 34 , respectively, to synchronize speeds of elements of the oncoming clutch ( 208 ).

When shifting to Mode 4 (Load Share), clutch C 1 32 is still activated during this period in the shift process and the powertrain operating mode is presently Mode 1 (1 motor EV). The speed of the first torque machine 20 is controlled to synchronize the oncoming clutch C 2 34 with the speed of the ring gear 46 of the planetary gear set 40 . When shifting to Mode 3 (Series), clutch C 2 34 is still activated during this period in the shift process and the powertrain operating mode is presently Mode 2 (2 motor EV). The speeds of the first and second torque machines 20 and 30 are controlled to synchronize the speed of the ring gear 46 of the planetary gear set 40 with the transmission case ground 38 , i.e., the speeds of the first and second torque machines 20 and 30 are suitably controlled to stop rotation of the ring gear 46 and thus synchronize the speed of clutch C 1 32 with the transmission case ground 38 .

When the speeds of elements of the oncoming clutch are synchronized, the oncoming clutch is activated ( 210 ), and the powertrain system 5 operates in the Transition Mode with clutches C 1 32 and C 2 34 activated. By synchronizing the speeds of the elements of the oncoming clutch prior to activation, the oncoming clutch may be activated without slipping, i.e., is synchronously activated. The powertrain system 5 then operates in the Transition Mode to offload torque from the off-going clutch ( 212 ).

When shifting to Mode 4 (Load Share), clutch C 1 32 is the off-going clutch and the torques of the first and second torque machines 20 and 30 are controlled to offload torque thereacross. When shifting to Mode 3 (Series), clutch C 2 34 is the off-going clutch, and the speeds of the first and second torque machines 20 and 30 are controlled to offload torque across clutch C 2 34 .

When torque across the off-going clutch is offloaded, the off-going clutch is deactivated ( 214 ). The powertrain system 5 operates in one of the powertrain operating modes Mode 1 or Mode 2 in accordance with the still activated clutch C 1 32 or C 2 34 , respectively, to control the first and/or second torque machines 20 and 30 and control operation of the engine 10 to synchronize the speeds of the elements of the common clutch, i.e., clutch C 3 36 ( 216 ).

When shifting to Mode 4 (Load Share), clutch C 2 34 is the still activated clutch, and the powertrain operating mode is presently Mode 2 (2 motor EV). The speeds of the engine 10 and the first and second torque machines 20 and 30 are controlled to synchronize the speeds of the elements of the oncoming clutch C 3 36 without affecting the output torque to the output member 45 coupled to the driveline 50 .

When shifting to Mode 3 (Series), clutch C 1 32 is the still activated clutch, and the powertrain operating mode is presently Mode 1 (1 motor EV). The speeds of the engine 10 and the first torque machine 20 are controlled to synchronize the speeds of the elements of the oncoming clutch C 3 36 . The output torque to the output member 45 coupled to the driveline 50 is maintained by the second torque machine 30 .

When the speeds of the elements of the common clutch, i.e., clutch C 3 36 are synchronized, clutch C 3 36 is activated ( 218 ). The shift is complete, and the powertrain system 5 operates in the second operating mode.

FIGS. 3-1 through 3 - 5 depict progression of an exemplary first shift sequence from Mode 3 (Series) to Mode 4 (Load Share) for the powertrain system 5 using the sequentially executed control scheme 200 depicted with reference to FIG. 2 . FIGS. 3-1 through 3 - 5 each shows the powertrain system 5 of FIG. 1 with selected ones of the first, second and third clutches C 1 32 , C 2 34 , and C 3 36 activated or deactivated, with activation indicated by broken line ovals.

FIG. 3-1 shows initial operation in Mode 3 (Series) with clutches C 1 32 and C 3 36 activated. FIG. 3-2 shows operation in Mode 1 (1 motor EV) with clutch C 1 32 activated after the common clutch C 3 36 is deactivated. FIG. 3-3 shows operation in the Transition Mode with clutches C 1 32 and C 2 34 activated after clutch C 2 34 has been activated. FIG. 3-4 shows operation in Mode 2 (2 motor EV) with clutch C 2 34 activated after clutch C 1 32 is deactivated. FIG. 3-5 shows operation in Mode 4 (Load Share) with clutches C 2 34 and common clutch C 3 36 activated, after common clutch C 3 36 is activated to end the shift sequence.

FIGS. 4-1 through 4 - 5 depict progression of a second exemplary shift sequence from Mode 4 (Load Share) to Mode 3 (Series) for the powertrain system 5 using the sequentially executed control scheme 200 depicted with reference to FIG. 2 . FIGS. 4-1 through 4 - 5 each shows the powertrain system 5 of FIG. 1 with selected ones of the first, second and third clutches C 1 32 , C 2 34 , and C 3 36 activated or deactivated, with activation indicated by broken line ovals.

FIG. 4-1 shows initial operation in Mode 4 (Load Share) with clutches C 2 34 and clutch C 3 36 activated. FIG. 4-2 shows operation in Mode 2 (2 motor EV) with clutch C 2 34 activated after clutch C 3 36 is deactivated. FIG. 4-3 shows operation in the Transition Mode with clutches C 1 32 and C 2 34 activated after clutch C 1 32 has been activated. FIG. 4-4 shows operation in Mode 1 (1 motor EV) with clutch C 1 32 activated after the clutch C 2 34 is deactivated. FIG. 4-5 shows final operation in Mode 3 (Series) with clutches C 1 32 and common clutch C 3 36 activated, after common clutch C 3 36 is activated to end the shift sequence.

The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.