METHOD FOR STABILIZING THE SELECTION OF OPERATING STATES USING AN ENERGY-BASED STABILIZATION STRATEGY FOR HYBRID DRIVETRAIN SYSTEMS

Abstract

Method for stabilizing the choice between a plurality of operating range states of an electromechanical multi-mode transmission (10) configured to transmit torque under a power machine (14), at least one electric machine (60, 62) and a final drive (90), the method comprising: Requesting the execution of a switch from a first operating range state to a second operating range state, wherein the first operating range state comprises a current operating range state and the second operating range state comprises a desired operating range state selected from a plurality of available operating range states; and Monitoring costs associated with operating the gearbox (10) in each of the plurality of operating range states, which include the first and second operating range states; characterized by Determining a corresponding energy difference between each of the available operating range states and the first operating range state based on the monitored costs; Monitoring of respective integration thresholds, each assigned to one of the energy differences between the first operating range state and each of the available operating range states; Select the available operating range state that corresponds to the respective energy difference that first reaches the respective integration threshold as the desired operating range state, wherein, in the case that at least two available operating range states reach the respective integration threshold simultaneously, the operating range state to which a normalized cost difference with a highest gradient is assigned is selected as the desired operating range state; and Switching from the first operating range state to the second operating range state is only performed if the energy difference reaches the integration threshold value that is assigned to the energy difference between the first operating range state and the available operating range state that is selected as the desired operating range state.

Description

TECHNICAL AREA

[0001] This invention relates to a method according to the preamble of claim 1 for stabilizing the choice between a plurality of operating range states of an electromechanical multi-mode transmission, as is known essentially from EP 2 070 792 A2. BACKGROUND

[0002] Powertrain systems can be designed to transmit torque from multiple torque-generating devices through a torque transmission device to an output element, which may be coupled to a final drive. Such powertrain systems include hybrid powertrain systems and extended-range electric vehicle systems. Control systems for operating such powertrain systems operate the torque-generating devices and employ torque transmission components in the transmission to transfer torque in response to operator-commanded output torque requests, taking into account fuel economy, emissions, drivability, and other factors. Exemplary torque-generating devices include internal combustion engines and non-combustion-based electric machines.Non-combustion electric machines can include electric machines that operate as motors or generators to produce a torque input to the transmission independently of a torque input from the internal combustion engine. These electric machines can convert the vehicle's kinetic energy, transferred through the final drive, into electrical energy in a process known as recuperation, which can then be stored in an electrical energy storage device.A control system monitors various inputs from the vehicle and the operator and provides functional control of the hybrid powertrain, which includes controlling the transmission operating state and gear shifting, controlling the torque-generating devices, and regulating the electrical power exchange between the electrical energy storage device and the electric machines to manage transmission outputs that include torque and speed.

[0003] Known transmission systems employ torque transmission clutches to transfer torque between the engine, electric motors, and final drive. Operating a drivetrain system involves engaging and disengaging the clutches to achieve operation in selected operating conditions.

[0004] The invention is based on the objective of providing a method for operating an electromechanical multi-mode gearbox, with which the selection of the operating range states of the gearbox can be stabilized. SUMMARY

[0005] This problem is solved by a method having the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Now, one or more embodiments will be described by way of example with reference to the accompanying drawings, in which: Fig. 1 a multi-mode powertrain system comprising an internal combustion engine, a transmission, a final drive and a controller, as illustrated in the present disclosure; Fig. 2 an analytical framework for determining powertrain system operating costs for an exemplary power cost function 500, which refers to the multi-mode powertrain system 100, which is in Fig.1 is described, is described, is illustrated according to the present revelation; Fig. 3 illustrates a flowchart for stabilizing the choice of operating range states using an energy-based stabilization strategy according to the present disclosure; Fig. 4 an exemplary graphical representation 410 describing monitored costs of the first and second operating range states, an exemplary graphical representation 420 describing an energy difference between the first and second operating range states, and an exemplary graphical representation 430 illustrating the choice between the first and second operating range states, according to the present disclosure; and Fig.5 an exemplary graphical representation 510, which describes the monitored costs of a current and two available operating range states, an exemplary graphical representation 520, which describes a first energy difference between the current and one of the available operating range states and a second energy difference between the current and the other of the available operating range states, and an exemplary graphical representation 530, which describes the choice between the available operating range states, as illustrated in the present disclosure. DETAILED DESCRIPTION

[0007] Now, with reference to the drawings, the illustrations of which are provided solely for the purpose of illustrating certain exemplary embodiments, it is stated that Fig.Figure 1 represents a non-restrictive powertrain system 100 comprising an internal combustion engine (power engine) 12, an electromechanical multi-mode transmission (transmission) 10, a high-voltage electrical system 80, a final drive 90, and a control module 5. The transmission 10 is mechanically coupled to the power engine 12 and the first and second electric machines 60 and 62, respectively, and is configured to transmit torque between the power engine 12, the electric machines 60 and 62, and the final drive 90. As illustrated, the first and second electric machines 60 and 62 are electric motors / generators.

[0008] The high-voltage electrical system 80 comprises an electrical energy storage device (ESD) 85, which is electrically coupled to a geared power converter control module (TPIM) 82 via a high-voltage electrical bus 84, and is equipped with suitable devices for monitoring the electrical power flow, including devices and systems for monitoring the electrical current and voltage. The ESD 85 can be any suitable high-voltage electrical energy storage device, e.g., a high-voltage battery, and preferably includes a monitoring system that provides a measure of the electrical power supplied to the high-voltage electrical bus 84, comprising voltage and current.

[0009] The power unit 12 can be any suitable internal combustion engine and comprises a multi-cylinder internal combustion engine that can be selectively operated in different states to transmit torque to the transmission 10 via an input element 14. It can be either a spark-ignition or a compression-ignition engine. The power unit 12 includes a crankshaft coupled to the input element 14 of the transmission 10. A speed sensor 11 monitors the crank angle and speed of the input element 14. The power output of the power unit 12, i.e., speed multiplied by the power unit torque, can differ from the input speed and torque to the transmission 10 due to the placement of torque-consuming components at the input element 14 between the power unit 12 and the transmission 10, e.g., a torque management device.The power unit 12 is designed to perform auto-stop and auto-start operations during continuous powertrain operation in response to operating conditions. The control module 5 is designed to control actuators of the power unit 12 and thus control combustion parameters, including controlling the intake air flow rate, ignition timing, injected fuel quantity, fuel injection timing, EGR valve position for controlling the flow of recirculated exhaust gases, and intake and / or exhaust valve timing and phase positions on power units so equipped. Thus, the power unit speed can be controlled by controlling combustion parameters, including air flow torque and ignition spark-induced torque. The power unit speed can also be controlled by controlling the motor torques of the first and second electric machines 60 and 60, respectively.62 The reaction torque is controlled at the input element 14.

[0010] The illustrated transmission 10 is an electromechanical four-mode transmission 10 with combined power splitting, comprising three planetary gear sets 20, 30, and 40 and five engageable torque-transmitting devices, i.e., clutches C1 52, C2 54, C3 56, C4 58, and C5 50. Other embodiments of the transmission are considered. The transmission 10 is coupled to a first and second electric machine 60 and 62, respectively. The transmission 10 is configured to transmit torque between the power machine 12, the electric machines 60 and 62, and the output element 92 in response to an output torque request. In one embodiment, the first and second electric machines 60 and 62 are motors / generators that use electrical energy to generate and counteract torque. The planetary gear set 20 comprises a sun gear element 22, a ring gear element 26 and planet gears 24, which are coupled to a carrier element 25.The carrier element 25 rotatably mounts the planet gears 24, which are arranged in a meshing relationship with both the sun gear element 22 and the ring gear element 26, and is coupled to a rotatable shaft element 16. The planet gear set 30 comprises a sun gear element 32, a ring gear element 36, and planet gears 34, which are coupled to a carrier element 35. The planet gears 34 are arranged in a meshing relationship with both the sun gear element 32 and the ring gear element 36. The carrier element 35 is coupled to the rotatable shaft element 16. The planet gear set 40 comprises a sun gear element 42, a ring gear element 46, and planet gears 44, which are coupled to a carrier element 45. As shown, a first and second set of planet gears 44 are coupled to the carrier element 45. Thus, the planetary gear set 40 is a compound sun gear element-pinion gear-pinion gear-ring gear set.The carrier element 45 is rotatably coupled between couplings C1 52 and C2 54. The sun gear element 42 is rotatably coupled to the rotatable shaft element 16. The ring gear element 46 is rotatably coupled to the output element 92.

[0011] As used herein, couplings refer to torque transmission devices that can be selectively engaged in response to a control signal and that can be any suitable devices, including, for example, single or compound plate couplings or packs, one-way couplings, band couplings, and brakes. A hydraulic circuit 72 is designed to control the engagement states of each of the couplings with hydraulic pressurized fluid supplied by an electrically driven hydraulic pump 70, which is functionally controlled by the control module 5. Couplings C2 54 and C4 58 are hydraulically engaged rotary friction couplings. Couplings C1 52, C3 56, and C5 50 are hydraulically controlled brake devices that can be fixed to a gearbox 55.In this embodiment, each of the clutches C1 52, C2 54, C3 56, and C4 58 is hydraulically engaged using hydraulic pressure fluid supplied by the hydraulic control circuit 72. The hydraulic circuit 72 is functionally controlled by the control module 5 to activate and deactivate the aforementioned clutches, to supply hydraulic fluid for cooling and lubricating transmission components, and to supply hydraulic fluid for cooling the first and second electric motors 60 and 62. The hydraulic pressure in the hydraulic circuit 72 can be determined by measurement using a pressure sensor(s), by estimation using onboard routines, or by other suitable methods.

[0012] The first and second electric machines 60 and 62 are three-phase AC motor / generator machines, each comprising a stator, a rotor, and a resolver. The motor stator for each of the electric machines 60 and 62 is fixed to an outer section of the gearbox 55 and comprises a stator core with helical electrical windings extending from it.

[0013] The rotor for the first electric machine 60 is supported on a hub-plate gear, which is mechanically attached to a hollow shaft 18 coupled to the first planetary gear set 20. The rotor for the second electric machine 62 is fixed to a hollow shaft hub 19, which is mechanically attached to the second planetary gear set 30. Each resolver is connected to the transmission power converter control module (TPIM) 82 both signal-wise and functionally, and each detects and monitors the rotational position of the resolver rotor relative to the resolver stator, thereby monitoring the rotational position of the first and second electric machines 60 and 62, respectively. Additionally, the signals output by the resolvers can be used to determine the rotational speeds of the first and second electric machines 60 and 62, respectively.

[0014] The output element 92 of the transmission 10 is rotatably connected to the final drive 90 to supply output power to the final drive 90, which is transmitted to one or more vehicle wheels via a differential or transaxle assembly or other suitable device. The output power at the output element 92 is characterized in terms of output speed and output torque. A transmission output speed sensor 93 monitors the speed and direction of rotation of the output element 92. Each of the vehicle wheels is preferably equipped with a sensor configured to monitor the wheel speed and thus determine the vehicle speed and absolute and relative wheel speeds for brake control, traction control, and vehicle acceleration management.

[0015] The input torque from the power machine 12 and the motor torques from the first and second electric machines 60 and 62, respectively, are generated as a result of energy conversion from fuel or electrical potential stored in the electrical energy storage device ESD 85. The ESD 85 is coupled to the TPIM 82 via the high-voltage DC bus 84, which preferably includes a contactor that allows or prohibits the flow of electrical current between the ESD 85 and the TPIM 82. The TPIM 82 preferably comprises a pair of power converters and respective motor control modules configured to receive torque commands and control the converter states accordingly, thus providing motor drive or recuperation functionality to comply with the motor torque commands.The power converters comprise complementary three-phase power electronics, each including a plurality of insulated-gate bipolar transistors for converting DC power from the ESD 85 into AC power to drive the first and second electric machines 60 and 62, respectively, by high-frequency switching. The insulated-gate bipolar transistors form a switching power supply configured to receive control commands. There is one pair of insulated-gate bipolar transistors for each phase of each of the three-phase electric machines. The states of the insulated-gate bipolar transistors are controlled to provide mechanical motor drive power generation or electrical energy recuperation functionality.The three-phase converters receive or supply direct current (DC) electrical energy via DC transmission conductors 27 and convert it into or from three-phase alternating current (AC) energy, which is then routed to or from the first and second electric machines 60 and 62, respectively, for operation as motors or generators, via transmission conductors. The TPIM 82 transmits electrical power to and from the first and second electric machines 60 and 62, respectively, through the power converters and the respective motor control modules in response to the motor torque commands. Electrical current is transmitted to and from the ESD 85 via the high-voltage electrical bus 84 to charge and discharge the ESD 85.

[0016] The control module 5 is linked to various actuators and sensors in the powertrain system via a communication link 15, both signal-wise and functionally, to monitor and control the operation of the powertrain system. This includes synthesizing information and inputs and executing routines to control actuators in order to achieve control objectives related to fuel economy, emissions, performance, drivability, and the protection of components, including the batteries of the ESD 85 and the first and second electric machines 60 and 62, respectively. The control module 5 is a component of the vehicle's overall control architecture and provides coordinated system control of the powertrain system.The control module 5 can comprise a distributed control module system containing individual control modules, including a monitoring control module, a power unit control module, a transmission control module, a battery pack control module, and the TPIM 82. A user interface 13 is preferably connected via signaling to a plurality of devices through which a vehicle operator controls and directs the operation of the powertrain system. The devices preferably include an accelerator pedal 112, an operator brake pedal 113, a transmission range selector 114 (PRNDL), and a vehicle speed control system 116.The transmission range selector 114 can have a discrete number of operator-selectable positions, which include specifying the direction of the vehicle's intended movement and thus the preferred direction of rotation of the output element 92, either forward or reverse. It should be noted that a vehicle may still move in a direction other than the specified direction of movement intended by the operator due to rollback caused by the vehicle's position, e.g., on a hill. The user interface 13 can comprise a single device, as shown, or alternatively, it can comprise multiple user interface devices directly connected to individual control modules.

[0017] The aforementioned control modules communicate with other control modules, sensors, and actuators via communication link 15, which enables structured communication between the various control modules. The specific communication protocol is application-specific. Communication link 15 and suitable protocols ensure robust message transmission and interfaces for multiple control modules between the aforementioned control modules and other control modules that provide functionality such as anti-lock braking, traction control, and vehicle stability. Multiple communication buses can be used to improve communication speed and provide a degree of signal redundancy and integrity, including direct connections and serial peripheral interface (SPI) buses.Communication between individual control modules can also be achieved using a wireless connection, e.g., a short-range wireless communication bus. Individual devices can also be directly connected.

[0018] Control module, module, control, controller, control unit, processor and similar terms mean any of or various combinations of one or more of an application-specific integrated circuit(s) (ASIC), an electronic circuit, a central processing unit (preferably a microprocessor), and associated memory and storage (read-only memory, programmable read-only memory, random access memory, hard disk memory, etc.).The controller includes one or more software or firmware programs or routines, a combinational logic circuit, an input / output circuit and input / output devices, suitable signal conditioning and buffering circuitry, and other components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms, and similar terms mean any set of instructions executable by a controller, including calibrations and lookup tables. The control module has a set of control routines that are executed to provide the desired functions.Routines are executed, for example by a central processing unit, to monitor inputs from sensors and other networked control modules and to perform control and diagnostic routines to manage the operation of actuators. Routines can be executed at regular intervals, for example every 3, 125, 6, 25, 12.5, 25, and 100 milliseconds, during continuous operation of power machines and vehicles. Alternatively, routines can be executed in response to the occurrence of an event.

[0019] The powertrain 100 is designed to operate in one of a plurality of powertrain states, encompassing a plurality of transmission ranges and engine states, to generate torque and transmit it to the final drive 90. The engine states include an on state, an off state, and a fuel cut-off state. When the engine is in the off state, it is not supplied with fuel, does not ignite, and does not rotate. When the engine is in the on state, it is supplied with fuel, ignites, and rotates. When the engine is in the fuel cut-off state, it rotates but is not supplied with fuel and does not ignite.The transmission ranges comprise a plurality of ranges from neutral, fixed gear, variable mode (EVT mode), electric vehicle (EV#), and transition (EV transition state # and pseudo-gear #), which are achieved by selectively activating clutches C1 150, C2 152, C3 154, C4 156, and C5 158. A pseudo-gear range is a variable mode transmission range in which the torque delivered by the transmission 10 equals the input torque from the power unit 12, taking into account torque losses associated with torque-consuming components at the input element 14. The pseudo-gear ranges are primarily used as intermediate gear ranges during shifts between the EVT mode ranges. Table 1 shows a plurality of transmission ranges and power unit states for operating the powertrain 100. Table 1 Area Power machine condition C1 C2 C3 C4 C5 Neutral 1 on off Neutral 2 on off x Neutral 3 on off x Pseudogang 1 on off x Pseudogang 2 on off x Neutral out of x EVT mode 1 on off x x EVT mode 2 on off x x EVT mode 3 on off x x EVT mode 4 on off x x EV transition state 1 out of x x EV transition state 2 out of x x Gear 1 a x x x Gear 2 a x x x Gear 3 a x x x EV1 out of x x x EV2 out of x x x EV3 out of x x x EV4 out of x x x EV transition state 3 out of x x x Neutral on off x x Pseudogang 3 on off x x Neutral out of x x Neutral out of x x

[0020] Fig.Figure 2 schematically illustrates an analytical framework for determining powertrain system operating costs for an exemplary power cost function 500, which is described with reference to the multi-mode powertrain system 100, which is described with reference to Fig.1 is described. Powertrain elements include power machine 120, transmission 200, (a) non-combustion electric machine(s) 400, battery 520, power converter 540, wheel brakes 98, final drive 90 and a fuel storage system 8. Pseudo-elements include an inertial load 17, which is an element designed to account for system inertias, and a high-voltage electrical load 560, which is an element designed to account for high-voltage loads in the vehicle outside of the load used for the powertrain system 100.Power flow paths comprise a first power flow path 9 from the fuel storage system 8 to transfer fuel energy to the power engine 120, a second power flow path 19 between the power engine 120 and the gearbox 200, a third power flow path 53 between the battery 520 and the converter 540, a fourth power flow path 57 between the converter 540 and the high-voltage electrical load 560, a fifth power flow path 59 between the converter 540 and the non-combustion electric machine(s) 400, a sixth power flow path 23 between the non-combustion electric machine(s) 400 and the gearbox 20, a seventh power flow path 25 between the inertial load 17 and the gearbox 200, an eighth power flow path 88 between the gearbox 200 and the wheel brakes 98, and a ninth power flow path 99 between the Wheel brakes and the final drive 90.Power losses include engine power losses 11, battery power losses 55, mechanical power losses 87, electric motor losses 89, and brake power losses 97. Total power costs can be the sum of engine power losses 11, battery power losses 55, mechanical power losses 87, electric motor losses 89, and brake power losses 97. The power cost inputs to the power cost function 500 are determined based on factors related to vehicle drivability, fuel economy, emissions, and battery usage. Power costs are allocated and assigned to fuel consumption and electrical energy consumption and are associated with specific operating points of the multi-mode powertrain.Lower operating costs can be attributed to lower fuel consumption at high conversion efficiencies, lower battery energy use, and lower emissions for each speed / load operating point of the power machine, taking into account the candidate operating state of the power machine 14. Power costs can include the power machine power losses 11, electric motor power losses 89, battery power losses 55, brake power losses 97, and mechanical power losses 87, which are attributed to operating the multi-mode powertrain at specific operating points for the power machine 100 and the non-combustion-based electric machine(s) 400. Subjective costs, including but not limited to torque request costs, battery state-of-charge costs, and output speed costs, can be monitored.The power cost function 500 can be applied to determine the total cost of operation at a chosen operating point of the power machine over the range of power machine operation. Accordingly, total costs can include the sum of the subjective costs, power machine power losses 11, battery power losses 55, mechanical power losses 87, electric motor losses 89, and brake power losses 97 in any given operating range condition.

[0021] Fig. Figure 3 illustrates an exemplary flowchart 300 for stabilizing the selection between a plurality of operating range states of a multi-mode transmission according to the present disclosure. Stabilizing the selection between operating range states reduces shift frequency, thereby increasing drivability and fuel economy. The flowchart 300 is illustrated with reference to the one in Fig.Figure 1 illustrates the multi-mode powertrain system 100. The flowchart 300 can be implemented within the control module 5. Table 2 serves as a key for Fig. 3 is specified, where the numbered blocks and the corresponding functions are executed as follows. Table 2 BLOCK BLOCK CONTENTS 302 Requesting the execution of a switch from a first operating range state to a second operating range state 304 Monitoring costs associated with operating the gearbox in each of a plurality of operating range conditions, including the first and second operating range conditions. 305 Determining an energy difference between the first and second operating range states based on the monitored power losses. 306 Does the energy difference exceed an integration threshold? 308 Switching from the first operating range state to the second operating range state should only be performed if the energy difference exceeds the integration threshold.

[0022] Flowchart 300 begins at block 302. In a first embodiment, block 302 requests the execution of a switch from a first operating range state to a second operating range state. The requested execution of the switch from the first operating range state to the second operating range state can occur in response to a torque request by the operator, e.g., an operator input to the accelerator pedal 112, and can be monitored by the user interface 13 and the control module 5 via the communication link 15. However, the request for the execution of the switch is not limited to torque requests by the operator. The first operating range state can include a current operating range state, and the second operating range state can include an available operating range state that is determined to be a desired operating range state.The second operating range state is associated with lower transmission operating costs than the first operating range state. Referring to Table 1, the first and second operating range states each comprise one of a neutral range state, a pseudo-gear state, a fixed-gear range state (gears 1-3), a variable-mode range state (EVT modes 1-4), and an electric vehicle range state (EV 1-4).

[0023] In a second embodiment, block 302 detects a potential switch from a current operating range state to one of a plurality of available operating range states. Available operating range states that have a lower cost than a current operating range state can be referred to as preferred operating range states.

[0024] Referring to block 304, flowchart 300 monitors costs associated with operating the transmission in each of a plurality of operating range states, including the first and second operating range states. In the second embodiment, block 304 monitors costs associated with operating the transmission in each of the current and available operating range states. The monitored costs may include total costs, encompassing the monitoring of a sum of subjective costs, power losses 11 of the engine, power losses 55 of the battery, mechanical power losses 87, electric motor losses 89, and brake power losses 97, associated with operating the transmission 10 in the first (e.g., the current) operating range state.Likewise, the monitored costs can include a total loss, which comprises the sum of subjective costs, power losses 11 of the engine, power losses 55 of the battery, mechanical power losses 87, electric motor losses 89 and power losses 97 of the brake, which are attributed to operating the transmission 10 in the second (e.g. the desired) operating range state.

[0025] Referring to Block 305, Flowchart 300 determines an energy difference between the first and second operating range states based on the monitored costs. Block 305 initially uses a cost difference between the monitored costs of the first operating range state and the monitored costs of the second operating range state. In the first embodiment, the cost difference is calculated based on the difference between the monitored costs of the first operating range state and the monitored costs of the second operating range state. In the second embodiment, a cost difference between the current operating range state and each of the available operating range states is determined. The energy difference between the first and second operating range states is determined by integrating the cost difference.Similarly, the respective cost differences between the current operating state and each of the available operating states can be expressed as a cost difference over time. Integrating this cost difference can be expressed according to the following relationship. Edif=∫Pdifdt where E dif the energy difference is, and P dif The cost difference is...

[0026] Therefore, the energy difference is the cost difference between the first (e.g., the current) and the second (e.g., the desired) operating range state over time. In a non-restrictive embodiment, the P dif expressed in kilowatts (kW), and the E dif is expressed in kilowatt-seconds (kW*s). Flowchart 300 proceeds to decision block 306 as soon as the energy difference, E dif , has been determined.

[0027] Decision block 306 determines whether the energy difference in the first embodiment reaches an integration threshold. The energy difference is thus compared to an integration threshold. The integration threshold relates to the switching from the first operating range state to the second operating range state. Furthermore, the integration threshold can be used to normalize the cost difference between the first and second operating range states. An "O" indicates that the energy difference does not exceed the integration threshold, and flowchart 300 returns to block 304. A "1" indicates that the energy difference exceeds the integration threshold, and flowchart 300 proceeds to block 308.

[0028] In the second embodiment, decision block 306 first monitors integration thresholds, each of which is assigned to a corresponding cost difference between the current operating state and each of the available operating range states. Each cost difference is normalized based on its respective integration threshold. More precisely, each cost difference is divided by its respective integration threshold, and each of the normalized cost differences is determined based on this division. Subsequently, decision block 306 determines whether a normalized cost difference over time is assigned to one of the available operating range states and reaches a normalized threshold. It should be noted that the normalized thresholds represent the normalization of each of the corresponding integration thresholds and can include a value of 1.A "0" indicates that none of the available operating range states has a normalized cost difference over time assigned to it that reaches the normalized threshold. Flowchart 300 then returns to block 304. A "1" indicates that one of the available operating range states has a normalized cost difference over time assigned to it that reaches the normalized threshold, and flowchart 300 proceeds to block 308. Accordingly, a "1" designates the one of the available operating range states to which the normalized cost difference over time assigned is the first to reach the normalized threshold as the desired operating range state. In a scenario where at least two available operating range states with normalized cost differences over time assigned to them reach the normalized threshold simultaneously (e.g.,(at the same moment), one of the at least two available operating range states, to which the normalized cost difference with a highest gradient is assigned, is determined as the desired operating range state.

[0029] Referring to block 308, the switching from the first operating range state to the second operating range state is performed in the first embodiment. More precisely, the switching from the first operating range state to the second operating range state is only performed if the energy difference reaches the integration threshold. Similarly, the operation of the drive train system 100 continues in the first operating range state if the energy difference does not exceed the integration threshold. In the second embodiment, block 308 commands the execution of the switching from the current operating range state to the desired operating range state.More precisely, the switching from the current operating range state to the desired operating range state is only executed if the normalized cost difference over time, which is assigned to the cost difference between the current operating range state and the available operating range state (i.e., when the desired operating range state is determined in decision block 306), has reached the normalized threshold. In other words, the transmission continues to operate in the current operating range unless either of the cost differences over time reaches the normalized threshold.

[0030] Remaining in the operating range state, unless the energy difference reaches the integration threshold, reduces the switching frequency that would otherwise result each time a potential switch from a current operating range state to an available operating range state is detected. Similarly, overstabilization in the current operating range state is avoided by commanding the execution of the switch to the desired operating range state when the energy difference reaches the integration threshold. Known methods execute switches to the available operating range state only when a cost difference exceeds a power threshold, and thus overstabilization can occur if a relatively small cost difference between the current and desired operating range states persists over a long period.It can be observed that small cost differences occurring over a long period of time can undesirably increase costs.

[0031] Fig.Figure 4 illustrates an exemplary graphical representation 410, which describes the monitored costs of a first and second operating range state; an exemplary graphical representation 420, which describes an energy difference between the first and second operating range states; and an exemplary graphical representation 430, which describes a choice between the first and second operating range states, according to the present disclosure. The graphical representations 410, 420, and 430 contain experimental and derived data for stabilizing the choice between a plurality of operating range states when the execution of a switch from a first operating range state to a second operating range state is requested. The graphical representations 410, 420, and 430 are presented with reference to the multi-mode powertrain system 100, which is based on Fig. 1 is described, and the flowchart, which is based on Fig.As described in section 3, the horizontal axis in all three graphical representations 410, 420, 430 represents time in seconds. Each dashed vertical line 401, 402, 403, 404, 405, 406, extending through each of the graphical representations 410, 420, 430, represents a specific point in time during the operation of the powertrain system 100.

[0032] Referring to graph 410, the vertical axis represents costs corresponding to power output in kilowatts (kW). The monitored costs associated with operating the gearbox in the first operating range state are represented by a first cost profile 440. The monitored costs associated with operating the gearbox in the second operating range state are represented by a second cost profile 450. As mentioned above, block 304 of flowchart 300 monitors costs associated with operating the gearbox in each of the first and second operating range states. The cost difference at any given time can be determined based on the difference between the first and second cost profiles 440 and 450, respectively. Area 412 represents a cost difference over time between the dashed vertical lines 401 and 402.Area 414 represents a cost difference over time between dashed vertical lines 403 and 404. Area 416 represents a cost difference over time between dashed vertical lines 405 and 406.

[0033] Referring to graph 420, the vertical axis represents energy in kilowatt-seconds (kW*s). An energy difference between the first and second operating range states is represented by the energy difference profile 411, which extends from the dashed vertical line 401 beyond the dashed vertical line 406. The energy difference between the first and second operating range states based on the monitored costs is determined in block 305 of flowchart 300. More precisely, the cost difference can be integrated to determine the energy difference between the first and second operating range states using equation [1].Accordingly, the area 412 shown in graphical representation 410 between the dashed vertical lines 401 and 402 is expressed as an energy difference corresponding to the first quantity 421 of energy consumed between the first and second operating states at dashed vertical line 402. The area 414 shown in graphical representation 410 between the dashed vertical lines 403 and 404 is expressed as an energy difference corresponding to the second quantity 422 of energy consumed between the first and second operating states at dashed vertical line 404. The area 416 shown in graphical representation 410 between the dashed vertical lines 405 and 406 is expressed as an energy difference corresponding to the second quantity 422 of energy consumed between the first and second operating states at dashed vertical line 406.

[0034] With reference to graphical representation 420, the segmented horizontal line 425 denotes an integration threshold. As mentioned above, decision block 406 compares the energy difference (e.g., the energy difference profile 411) with the integration threshold 425. In an exemplary embodiment, a value for the integration threshold is chosen based on the second operating range state. It can be observed that the energy difference profile 411 reaches only the first quantity 421 of consumed energy at the dashed vertical line 402 and therefore does not reach the integration threshold 425. However, the energy difference profile 411 reaches the integration threshold at each of the dashed vertical lines 404 and 406.

[0035] Referring to graphical representation 430, a choice between the first and second operating range states 440 and 450, respectively, is shown to avoid overstabilization due to the energy difference between these two states. Overstabilization is used to describe a transmission that remains in a current operating range state, incurring relatively low costs over a long period, which leads to accumulated power losses or costs. The vertical axis denotes the first and second operating range states 440 and 450, respectively. The solid profile line 470 represents a selected operating range state 440 or 450. The dashed profile line 480 represents an available operating range state 440 or 450.

[0036] Between the dashed vertical lines 401 and 402, the second operating range state 450 is available, as represented by the dashed profile line 480. In other words, a switch from the first operating range state to the second operating range state would have been performed if no integration had been carried out. The second operating range state 450 is available as a preferred operating range state between lines 401 and 402 because the monitored costs of the second operating range state 450 are lower than the monitored costs of the first operating range state 440, as shown in the graphical representation 410 between the dashed vertical lines 401 and 402. However, the operation of the drive train system 100 continues in the first operating range state because the energy difference (e.g.,The difference in energy costs over time between the first and second operating range states does not exceed the integration threshold, as represented by the first quantity 421 of energy consumed, which does not reach the integration threshold 425 in the graphical representation 420 at the dashed vertical line 402. It can be observed that switching frequency between lines 401 and 402 is avoided, even though the second operating range state 450 has lower costs. Between the dashed vertical lines 401 and 402, decision block 306 determines a "0", indicating that the energy difference at line 402 does not reach the integration threshold, and flowchart 300 returns to block 304.

[0037] Between the dashed vertical lines 403 and 404, the second operating range state 450 is available as a preferred operating range state, as represented by the dashed profile line 480. However, operation of the powertrain system 100 continues in the operating range state between lines 403 and 404 because the graphic representation 420 shows that the energy difference profile 411 (e.g., cost difference over time) between the first and second operating range states never reaches the integration threshold 425 up to the dashed vertical line 404. Thus, switching frequency, which affects drivability, is avoided up to the dashed vertical line 404.

[0038] At the dashed vertical line 404, the switching from the first operating range state to the second operating range state is performed. As shown in the graphical representation 420, the energy difference profile 411 with the second quantity 422 of consumed energy reaches the integration threshold 425 at the dashed vertical line 404. Therefore, at the dashed vertical line 404, the decision block 306 determines a "1", indicating that the energy difference at line 404 reaches the integration threshold, and the flowchart 300 proceeds to block 306, where the switching to the operating range state is performed.

[0039] The powertrain system 100 has selected and is operating in the second operating range state between the dashed vertical lines 404 and 405. The area 419 between the dashed vertical lines 404 and 405, shown in graphic 410, correlates with energy savings that would otherwise have resulted in overstabilization costs if switching to the second operating range state had not been selected. In other words, because the cost difference between the first and second operating range states is relatively small and remains constant, switching between the dashed vertical lines 403 and 405 should not be performed if the switching were based solely on the monitored cost difference.However, the energy difference reaches the integration threshold at the dashed vertical line 404, which necessitates the execution of switching, and therefore energy savings occur between the dashed vertical lines 404 and 405.

[0040] In the exemplary embodiment, the energy difference profile 411 is reset at the dashed vertical lines 402 and 404 as soon as it reaches the integration threshold 425. However, other exemplary embodiments may include negative integration or “counting down” of the energy difference profile 411 should the cost of the first operating range state 440 subsequently become lower than the cost of the second operating range state 450.

[0041] Between the dashed vertical lines 405 and 406, a switch from the second operating range state to the first operating range state has been requested while integration is being performed. Operation of the drive train system 100 will continue in the second operating range state unless the energy difference (e.g., cost difference over time) between the first and second operating range states reaches the integration threshold. It should be noted that if the cost difference between the first and second operating range states 440 and 450 were to immediately exceed the integration threshold, the switching would occur immediately.At vertical line 406, the energy difference reaches the integration threshold, as represented by the second quantity 422 of consumed energy, which exceeds the integration threshold 425 in graphical representation 420 at the dashed vertical line 402. Thus, the switch from the second operating range state 450 to the first operating range state 440 is executed at the dashed vertical line 406. Accordingly, stabilization is introduced between lines 405 and 406 while the drive train remains in the second operating range state until the energy difference exceeds the integration threshold at line 406, at which point the switch to operating range state 440 is executed to avoid overstabilization.

[0042] Fig.Figure 5 illustrates an exemplary graphical representation 510, which describes the monitored costs of a current operating range state and a first and second available operating range state; an exemplary graphical representation 520, which describes a first energy difference between the current and the first available operating range state and a second energy difference between the current and the second available operating range state; and an exemplary graphical representation 530, which describes the choice between the first and second available operating range states, according to the present disclosure. The graphical representations 510, 520, and 530 contain experimental and derived data for a stabilization selection between a plurality of operating range states when switching from a first operating range state to a second operating range state is requested.Graphical representations 510, 520, 530 are presented with reference to the multi-mode powertrain system 100, which is based on . Fig. 1 is described and the flowchart 300, which is based on Fig. As described in section 3, the horizontal axis in all three graphical representations 510, 520, 530 represents time in seconds. Each dashed vertical line 501, 502, 503, extending through each of the graphical representations 510, 520, 530, represents a specific point in time during the operation of the powertrain system 100.

[0043] With reference to graphical representation 510, the vertical axis denotes the power in kilowatts (kW). The monitored costs associated with operating the gearbox in the current operating range state are designated by current cost profile 540. The monitored costs associated with operating the gearbox in the first and second available operating range states are designated by current cost profiles 550 and 560, respectively. This disclosure is not limited to two available operating range states and may include any number of available operating range states. As mentioned above, block 304 (e.g., second embodiment) of flowchart 300 monitors the costs associated with operating the gearbox in each of a plurality of operating range states.The cost difference at any given point in time can be determined based on the difference between the current and the first available operating range state 450 or 550, and the difference between the current and the second available operating range state 540 or 560. Area 512 represents a cost difference between the current and the first available operating range state 540 or 550 over time between the dashed vertical lines 501 and 503. Area 514 represents a cost difference over time between the current and the second available operating range state 540 or 550 between the dashed vertical lines 502 and 503. It should be understood that the cost profile 550 represents a "preferred" operating range state once the costs are lower than the current cost profile 540, i.e., after the dashed vertical line 501.It is to be understood that cost profile 560 denotes a “preferred” operating condition once the costs are lower than the current cost profile 540, i.e., after the dashed vertical line 504.

[0044] In an exemplary embodiment, integration thresholds are monitored, each corresponding to the cost difference between the current operating state 540 and each of the available operating states 550 or 560. Thus, a first integration threshold refers to the cost difference between the current and the first available operating state 540 or 550. Similarly, a second integration threshold refers to the cost difference between the current and the second available operating state 540 or 560. Each cost difference can be normalized based on its respective integration threshold. For example, the cost difference between the current and the first available operating state 540 or 550 can be divided by the first integration threshold to obtain a first normalized cost difference.Similarly, the cost difference between the current and the second available operating state 540 or 560 can be divided by the second integration threshold to determine a second normalized cost difference.

[0045] Referring to graph 520, the vertical axis denotes energy in kilowatt-seconds (kW-s). An energy difference between the current and first available operating range states is denoted by energy difference profile 513, which extends from the dashed vertical line 501 to the dashed vertical line 503. In an exemplary embodiment, energy difference profile 513 represents the first normalized cost difference over time. More precisely, the first normalized cost difference over time can be determined by summing the first normalized cost difference with respect to first normalized cost differences from each preceding iteration. An energy difference between the current and second available operating range states is denoted by energy difference profile 515, which extends from the dashed vertical line 502 to the dashed vertical line 503.In an exemplary embodiment, the energy difference profile 515 represents the second normalized cost difference over time. More precisely, the second normalized cost difference over time can be determined by summing the second normalized cost difference with the respective second normalized cost differences from each preceding iteration. Accordingly, the area 512 between the dashed vertical lines 501 and 503, shown in graphical representation 510, is expressed as the first normalized cost difference over time (i.e., profile 513 in graphical representation 520), and the area 514 between the dashed vertical lines 502 and 503, shown in graphical representation 510, is expressed as the second normalized cost difference over time (i.e., profile 515 in graphical representation 520).

[0046] Referring further to graphical representation 520, the horizontal line 522 denotes a normalized threshold. As mentioned above, decision block 306 compares the energy difference with the integration threshold. Accordingly, if a plurality of available operating range states have lower costs than a current operating range state, a normalized threshold can be determined. More precisely, the normalized threshold can have a magnitude of 1 if each cost difference between the current operating range state and each of the available operating range states is normalized based on one of the respective integration thresholds. In other words, cost differences over time that reach the corresponding integration thresholds correspond to normalized cost differences that reach the normalized threshold with a magnitude of 1.

[0047] Referring to graphical representation 530, a selection is shown between the current operating range state 540 and the first and second available operating range states 550 and 560, respectively. The vertical axis denotes the current operating range state 540 and the first and second available operating range states 550 and 560, respectively. The dashed profile line represents an available operating range state, and the solid profile line represents a selected operating range state.

[0048] Between the dashed vertical lines 501 and 503, the first available operating range state 550 is available. In other words, a potential switch from the current operating range state 540 to the first available operating range state 550 is detected. The first available operating range state 550 is available as a preferred operating range state between lines 501 and 503 because the monitored costs of the first available operating range state 550 are lower than the monitored costs of the current operating range state 540, as shown in the graphical representation 510 between the dashed vertical lines 501 and 503. In an exemplary embodiment, the transmission continues to operate in the current operating range state 540 unless one of the cost differences over time (e.g.,Energy difference profiles 513 and 515) reach the normalized threshold 520 in graph 520. Therefore, the gearbox continues to operate in the current operating range state 540 up to the dashed vertical line 503, because neither the first nor the second normalized cost difference over time 513 or 515 reaches the normalized threshold 522, as shown in graph 520. It should be noted that switching frequency between the dashed vertical lines 501 and 503 is avoided, although the first available operating range state 550 is preferred at the dashed vertical line 501. Up to the dashed vertical line 503, decision block 306 determines a "0", indicating that the first normalized cost difference over time 513 has not reached the normalized threshold 522.

[0049] Between the dashed vertical lines 502 and 503, the second available operating range state 560 is available as a preferred operating range state. In other words, a potential switch from the current operating range state 540 to the second available operating range state 560 is detected. The second available operating range state 560 is available as a preferred operating range state between lines 502 and 503 because the monitored costs of the second available operating range state 560 are lower than the monitored costs of the current operating range state 540, as shown in graph 510 between the dashed vertical lines 502 and 503.It can be observed that switching frequency is avoided between the dashed vertical lines 502 and 503, although the second available operating range state 560 is preferred at the dashed vertical line 502. Up to the dashed vertical line 503, decision block 306 determines a "0", indicating that the second normalized cost difference over time 515 has not reached the normalized threshold 522.

[0050] In an exemplary embodiment, one of the first and second available operating range states, which is associated with the normalized cost difference over time that first reaches the normalized threshold 522, is designated as the desired operating range state. The first and second normalized cost differences over time 513 and 515, respectively, each reach the normalized threshold 522 at time 503, the time indicated by the dashed vertical line. As mentioned above in Block 306, if at least two normalized cost differences over time reach the normalized threshold simultaneously, the normalized cost difference with the steeper gradient is selected as the desired operating range state. Accordingly, the second available operating range state, which is associated with the second normalized cost difference over time 515, is selected as the desired operating range state.Thus, the execution of the switching from the current operating range state 540 to the second available operating range state 560 (i.e., the desired operating range state) is commanded, and the second available operating range state 560 is selected at the dashed vertical line 503.

[0051] Fig.Figure 5 demonstrates that if there are multiple available operating range states, the available operating range state to which the normalized cost difference over time is assigned that first reaches the normalized threshold is determined to be the desired operating range state. If at least two available operating range states reach the normalized threshold simultaneously, the available operating range state to which the normalized threshold over time is assigned that exhibits the highest gradient is determined to be the desired operating range state.Thus, the available operating range state that has the lowest cost among the majority of available operating range states can be designated as the desired operating range state; however, a different operating range that does not have the lowest cost among the majority of available operating range states can be designated as the desired operating range state, as long as the cost difference reaches the normalized threshold first over time.

Claims

[1] A method for stabilizing the selection between a plurality of operating range states of an electromechanical multi-mode transmission (10) configured to transmit torque among a prime mover (14), at least one electric machine (60, 62), and a driveline (90), the method comprising: Requesting an execution of a switch from a first operating range state to a second operating range state, wherein the first operating range state comprises a current operating range state and the second operating range state comprises a desired operating range state selected from a plurality of available operating range states; and monitoring costs associated with operating the transmission (10) in each of the plurality of operating range states including the first and second operating range states; characterized by Determining a corresponding energy difference between each of the available operating range states and the first operating range state based on the monitored costs; monitoring respective integration thresholds associated with a respective one of the energy differences between the first operating range state and each of the available operating range states; Selecting the available operating range state corresponding to the respective energy difference that reaches the respective integration threshold first as the desired operating range state, wherein, in the event that at least two available operating range states simultaneously reach the respective integration threshold, the operating range state associated with a normalized cost difference having a highest gradient is selected as the desired operating range state; and performing the switching from the first operating range state to the second operating range state only when the energy difference reaches the integration threshold associated with the energy difference between the first operating range state and that available operating range state selected as the desired operating range state. [2] The method of claim 1, wherein performing the switching from the first operating range state to the second operating range state only when the energy difference reaches the integration threshold further comprises: Continuing operation of the transmission (10) in the first operating range state if the energy difference does not reach the integration threshold. [3] The method of claim 1, wherein the current operating range state is associated with a higher cost of operating the transmission (10) than the available operating range states. [4] The method of claim 1, wherein the second operating range state comprises an operating range state associated with the lowest cost of operating the transmission (10) among a plurality of available operating range states. [5] The method of claim 1, wherein the first and second operating range states each comprise one of a neutral range state, a pseudo-gear state, a fixed gear range state, a variable mode range state, and an electric vehicle range state. [6] The method of claim 1, wherein the cost difference is normalized based on the predetermined integration threshold. [7] The method of claim 1, wherein the predetermined integration threshold relates to switching from the first operating range state to the second operating range state.

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