Hybrid electric vehicle and method for smooth engine operation with fixed throttle position

Abstract

Method for controlling a hybrid electric vehicle with a power unit (16) having a throttle valve and a battery-powered traction motor (46), comprising the following: Operating the engine (16) with a fixed throttle position while the vehicle is stationary or decelerating to generate excess engine torque relative to a requested engine torque; Charging the battery (12) using the excess engine torque; and Shutting off the fuel supply to the engine (16) when the requested engine torque is less than a threshold torque, wherein operating the engine (16) with a fixed throttle position includes: Setting a misfire torque limit associated with a minimum torque for stable combustion to provide a set misfire torque limit corresponding to an engine torque calculated on the basis of the fuel supply to all engine cylinders and the airflow associated with the fixed throttle position, with the requested engine torque being set to the set misfire torque limit when the requested engine torque is less than the set misfire torque limit and greater than the threshold torque.

Description

[0001] The present invention relates to a method of operating an engine of a hybrid electric vehicle (HEV) such that partial fuel shutoff of the engine does not occur while it is in a fixed throttle position.

[0002] An internal combustion engine must receive at least a minimum amount of airflow to operate with stable combustion. This engine operating point can be referred to as the combustion stability limit. The combustion stability limit can be defined in terms of airflow, which translates into an engine braking torque value. Consequently, a minimum engine torque can be specified to ensure stable combustion. This torque value, sometimes referred to as the misfire limit, is the lower bound on engine torque production.

[0003] The engine air intake system may include a throttle valve to regulate intake airflow and indirectly control the charge (fuel and air) combusted during each combustion cycle. The throttle valve position may be electronically controlled by the engine control unit in response to various engine and ambient operating conditions. One or more operating parameters, such as fuel injection quantity and fuel injection timing, may be scheduled and / or adjusted based on the throttle position and the corresponding amount of airflow entering the engine. As such, engine performance may be varied depending on the throttle position.

[0004] When the engine is operating at a specific throttle position and operating conditions change such that reduced engine torque is requested (e.g., a rapid release of an accelerator pedal), under some conditions the throttle may remain fixed in that position, causing the engine to produce more torque than requested by the vehicle system control unit. In this case, partial fuel injector deactivation may occur to reduce engine torque to the desired torque target. However, partial fuel injector deactivation can cause undesirable noise, vibration, and harshness (NVH).

[0005] DE 10 2004 013 812 A1 discloses a method for operating a hybrid motor vehicle having an internal combustion engine and at least one electric machine, wherein during the transition from a first operating state with a first drive torque to a second operating state with a lower second drive torque, before switching to the second operating state, a drive torque of the internal combustion engine is reduced by reducing a cylinder charge and / or closing a throttle valve.

[0006] The object of the present invention is to provide an improved method for operating a hybrid electric vehicle.

[0007] This object is solved by the subject matter of independent claim 1. Preferred embodiments are the subject matter of the subclaims.

[0008] In one embodiment, a method for operating a hybrid vehicle having an engine, a battery, and a generator includes setting or adjusting a misfire torque limit to the estimated or expected torque resulting from engine operation with a fixed throttle position to prevent fuel injector shutoff. An engine torque request greater than the misfire limit results in no engine fuel shutoff. An engine torque request less than both the misfire limit and a minimum torque loss value results in complete fuel shutoff for all engine cylinders.The method may also include setting an engine torque request that is less than the misfire limit and greater than the magnitude of the minimum torque loss level to greater than the misfire limit and controlling the engine using the set engine torque request. Any resulting excess engine torque may be used to charge the battery.

[0009] A method for operating a hybrid vehicle with an engine and a battery, according to one embodiment, includes establishing a misfire limit corresponding to an expected engine torque resulting from fixed throttle operation in response to detecting fixed throttle position operation. The method may include receiving an engine torque request while the engine is operating at a fixed throttle position, operating the engine using the torque request when the engine torque request is greater than the misfire limit such that no fuel cutoff is indicated, and shutting off all fuel when the engine torque request is less than a minimum torque loss level.This method further includes setting the engine torque request to be greater than the misfire limit when the engine torque request is less than the misfire limit and greater than the magnitude of the minimum torque loss level, and outputting the set engine torque request to the engine such that no fuel is shut off to the engine.

[0010] In one embodiment, a system operates with an engine and a controller for setting a misfire limit to an expected engine torque resulting from fixed throttle operation to provide smooth engine operation when operating at a fixed throttle position. The controller is configured such that an engine torque request greater than the misfire limit results in no fuel cutoff for the engine. An engine torque request less than both the misfire limit and the magnitude of a minimum torque loss level results in a full fuel cutoff for the engine.The controller is further configured to set an engine torque request that is less than the misfire limit and greater than the magnitude of the minimum torque loss level to greater than the misfire limit and output the set engine torque request to the engine. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a hybrid electric vehicle (HEV) powertrain illustrating the operation of a system or method according to various embodiments of the present invention; and Fig. 2 is a flowchart illustrating operation of a system or method for operating an HEV to provide smooth engine operation in response to a fixed throttle position, according to various embodiments of the present invention. DETAILED DESCRIPTION

[0011] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show the details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0012] As stated above, under certain operating conditions with a fixed throttle position, a vehicle's engine produces more torque than required by the vehicle system controller when the vehicle is stationary or decelerating. Instead of enabling partial fuel injector shutdown to reduce engine torque to the desired torque target, various embodiments of the present disclosure continue to operate the engine with the fixed throttle position and use the excess torque to charge the battery, or provide complete fuel injector shutdown to reduce or eliminate undesirable NVH.

[0013] Embodiments of the present invention solve the problem associated with partial fuel cutoffs during fixed-throttle operation by exploiting the fact that, in an HEV, excess engine power not absorbed by the traction wheels can be diverted to recharge the HEV's traction battery, such as when the HEV is stopped or decelerating. Consequently, rather than initiating a partial fuel cutoff to reduce engine power to a level the traction wheels can absorb, the engine can be fully fueled and continue to operate with a fixed throttle position, with the traction battery absorbing any excess engine power for subsequent use. The resulting battery recharge can be used to extend the HEV's range and performance.

[0014] With reference to Fig. 1, a schematic representation of an HEV powertrain capable of embodying the present invention is shown. The powertrain includes two power sources connected to the driveline: 1) an internal combustion engine 16 and a generator 50, interconnected via a planetary gear arrangement 20; and 2) an electric drive system including a battery 12, an electric motor 46, and a generator 50. The battery 12 is an energy storage system for the motor 46 and the generator 50.

[0015] A vehicle system control unit (VSC) 10 is configured to send control signals to and receive sensor feedback information from one or more of the battery 12, the engine 16, the motor 46, and the generator 50 to control the power delivered to the vehicle traction wheels 40 and propel the vehicle to meet driver demand. The control unit 10 controls the power source split between the battery 12 and the engine 16 to provide power to propel the vehicle, thereby controlling the state of charge (SOC) of the battery 12. The control unit 10 may communicate with one or more other control units via a control unit area network (CAN) and provide status and control messages and commands. Other control units or control modules may include an engine control module (ECM), a powertrain control module (PCM), a battery control module (BCM), and the like.Various control units may include a microprocessor in communication with a memory management unit (MMU), which controls the movement of data and instructions between the microprocessor and various computer-readable storage media. The computer-readable storage media may include volatile and non-volatile or persistent memory, for example, in read-only memory (ROM), random access memory (RAM), and hold memory (KAM). The KAM may be used to store various operating variables while the control unit is powered off. The computer-readable storage media may be implemented using any of a number of known storage devices, such as:PROMs (Programmable Read-Only Memory), EPROMs (Electrical PROM), EEPROMs (Electrically Erasable PROM), Flash memory, or any other electrical, magnetic, optical, or combination storage devices capable of storing data, some of which are executable instructions used by the microprocessor to control the vehicle.

[0016] In one embodiment, the computer-readable storage media includes stored data or stored code representing instructions executable by a microprocessor within the VSC 10 to control an HEV, as described with reference to Fig. 1 and Fig. 2. The code includes instructions that control operation of the engine 16 at a fixed throttle position to manage NVH while controlling the torque delivered to the vehicle wheels 40, as described in more detail herein. The code may also include instructions that continue to operate the engine 16 at a fixed throttle position while the vehicle is stationary or decelerating by controlling the generator 50 and the motor 46 to charge the battery 12.

[0017] The transmission 14 includes a planetary assembly 20 including a ring gear 22, a sun gear 24, and a carrier assembly 26. The ring gear 22 distributes torque to step ratio gears having intermeshing gear elements 28, 30, 32, 34, and 36. A torque output shaft 38 of the transmission 14 is drivably connected to the gears 40 through a differential and axle mechanism 42.

[0018] Gears 30, 32, and 34 are mounted on a countershaft 31, with gear 32 meshing with a motor-driven gear 44. The motor 46 drives gear 44. Gear 44 acts as the torque input for countershaft 31.

[0019] The engine 16 distributes torque through the input shaft 18 to the transmission 14. The battery 12 supplies electrical power to the motor 46 through the power flow path 48. The generator 50 is electrically connected to the battery 12 and to the motor 46, as shown at 52.

[0020] While the battery 12 acts as the sole power source when the engine 16 is off, the input shaft 18 and the carrier assembly 26 are braked by an overrunning clutch (i.e., a one-way clutch (OWC)) 53. A mechanical brake 55 anchors the rotor of the generator 50 and the sun gear 24 when the engine 16 is on and the powertrain is in a parallel drive mode, with the sun gear 24 acting as a reaction member.

[0021] The control unit 10 receives a PRND (Park, Reverse, Neutral, Drive) signal from a transmission range selector 63, which is distributed to the transmission control module (TCM) 67 along with a desired wheel torque, a desired engine speed, and a generator brake command, as shown at 71. A battery switch 73 is closed after the vehicle "power-on" start. The engine 16 may be a throttle-controlled internal combustion engine. As generally understood by those skilled in the art, a throttle-controlled engine includes an intake with a throttle valve that controls airflow into the engine 16. The throttle valve position is feedback-controlled by the control unit 10 using a small motor to move the throttle valve and a throttle valve position sensor to provide a feedback signal indicative of the actual throttle valve position.Control unit 10 generates an engine torque request for engine 16 based at least in part on a signal from an accelerator pedal position sensor (APPS) 65 and current engine, vehicle, and / or ambient operating conditions. The engine torque request is used to generate a corresponding signal for an engine electronic throttle control (ETC) module 69, which provides feedback position control of the throttle plate to control airflow and resulting engine torque.

[0022] A brake pedal position sensor (BPPS) provides a wheel brake signal to control unit 10, as shown at 61. A brake system control module (not shown) can issue a regenerative braking command based on information from the BPPS. The TCM 67 outputs a generator brake control signal to generator brake 55. The TCM 67 also distributes a generator control signal to generator 50.

[0023] In the representative embodiment of a HEV, which is Fig. 1, the HEV is a plug-in hybrid electric vehicle (PHEV), such that the battery 12 is rechargeable from an external electrical power source (e.g., an external electrical utility grid or generator). The battery 12 periodically receives AC electrical energy from the grid via a charging port 76 that connects to the grid. An onboard charging device 78 receives the AC electrical energy from the charging port 76. The charging device 78 is an AC / DC converter that converts the received AC electrical energy to DC electrical energy suitable for charging the battery 12. The charging device 78, in turn, supplies the DC electrical energy to the battery 12 to charge the battery 12 during the recharging process (i.e., a charging event).

[0024] As previously described, the HEV includes an engine 16 and a motor 46, which function as complementary power sources for developing vehicle traction power. The first power source comprises a combination of the engine 16 with the planetary assembly 20 for distributing power through separate flow paths. The second power source is an electric drive system including the battery 12, the motor 46, and the generator 50. The battery 12 acts as an energy storage medium for the motor 46 and the generator 50. The generator 50 supplies electrical power to the motor 46, which provides motive power to the traction wheels 40 through the planetary assembly 20. When the powertrain is operating using the first power source, the engine power is divided between the two paths by controlling the speed of the generator 50.

[0025] When the engine 16 and the generator 50 are connected by the planetary assembly 20, the generator 50 can act as a generator to provide power to charge the battery 12, which operates the motor 46, or the generator 50 can operate as a motor to provide a torque input to the planetary assembly 20. The generator 50 can be used to control the speed of the engine 16 when the generator 50 is connected to a torque reaction element of the planetary assembly 20. Both the motor 46 and the generator 50 can act as motors using power from the battery 12 to provide the desired traction wheel torque. Alternatively, both the motor 46 and the generator 50 can act as generators to provide electrical power to the battery 12 through the high-voltage bus 48, which electrically couples the battery 12, the motor 46, and the generator 50.

[0026] The engine 16 may operate in a torque control mode or an engine speed control mode. In either operating mode, excess torque generated by the engine 16 may drive the motor 46 and / or generator 50 to develop charging current for the battery 12. Consequently, excess engine power not delivered to the wheels 40 may be used to charge the battery 12, such as when the vehicle is stopped or decelerating and the engine 16 is operating at a fixed throttle position.

[0027] With reference to Fig. 2, a flowchart 80 illustrates the operation of a system or method for managing NVH in an HEV powertrain when the engine is operated at a fixed throttle position, according to embodiments of the present disclosure. In particular, as indicated above, according to the method, the engine is operated such that the fuel supply to the engine is either fully maintained (e.g., no fuel shutoff) or fully shut off (i.e., a full fuel shutoff) in response to the fixed throttle position, depending on certain engine, vehicle, and / or ambient operating conditions. The operation of the method, as set forth in flowchart 80, will be described with reference to the Fig. 1. As one skilled in the art will understand, the functions represented by the flowchart blocks may be performed by software and / or hardware associated with one or more control units or control modules, such as VSC 10, TCM 67, and BCM / Battery 12. Depending on the particular processing strategy, such as event-driven, interrupt-driven, etc., the various functions may be performed in a different order or sequence than in Fig. 2. Likewise, one or more steps or functions may be performed repeatedly, although not explicitly depicted. In one embodiment, the depicted functions are implemented primarily by software, instructions, or code stored in a persistent or non-transitory computer-readable storage medium and executed by a computer or microprocessor-based control unit to control the operation of the vehicle.

[0028] Operation of the system or method begins by determining whether the engine 16 is operating at a fixed throttle position, as indicated in decision block 82. The throttle may be determined to be at a fixed throttle position after the throttle position does not change for a given predetermined period of time. The predetermined period of time may vary based on engine, vehicle, or ambient operating conditions. Block 82 may also determine whether the HEV is stationary or decelerating, for example, based on wheel speed sensors or transmission output shaft speed.As previously described, when the engine 16 continues to operate in a particular fixed throttle position while the vehicle is stationary or decelerating, the engine 16 may produce more torque than is required to drive the traction wheels 40 for an associated driver requested torque or power based on the APPS 65.

[0029] If block 82 determines that the throttle is not at a fixed throttle position, or if a fixed throttle position is indicated but the vehicle is not stationary or decelerating, then the engine 16 operates normally with respect to the misfire limit, which is set to the lowest engine torque for stable combustion under current engine and ambient operating conditions, as represented by block 83. As previously described, the misfire limit corresponds to the minimum engine torque required to operate the engine with stable combustion. As described in more detail below, the misfire limit may be temporarily set to a higher engine torque when operating with a fixed throttle to prevent partial fuel cutoff and associated NVH.

[0030] If the throttle is at a fixed throttle position, then the engine 16 is operated with the torque and power resulting from the fixed throttle position, as indicated in block 84. Again, block 84 may be implemented when a fixed throttle position exists and the HEV is either stationary or decelerating.

[0031] Operation of the method proceeds from block 84 to block 86. In block 86, control unit 10 sets the misfire limit to the expected engine torque resulting from fixed throttle operation. That is, control unit 10 changes the misfire limit from the ordinary misfire limit to a modified misfire limit. The modified misfire limit, or "fixed throttle misfire limit," is equal to the expected engine torque produced by the engine as a result of operation at the fixed throttle position according to block 84. The expected engine torque at the fixed throttle position is generally greater than the minimum engine torque required for stable combustion.As such, in block 86, the misfire limit is effectively increased from the usual misfire limit, corresponding to the minimum engine torque required for stable combustion, to the fixed-throttle misfire limit, which corresponds to the expected engine torque resulting from fixed-throttle operation. Control unit 10 calculates the engine torque and engine power resulting from fixed-throttle operation and uses this engine torque as the engine torque request, which now becomes the fixed-throttle misfire limit.

[0032] The control unit 10 stores the fixed throttle misfire limit for use as lower and upper limits for the requested engine torque, as represented by block 88 and described in more detail below. Previous control strategies associated with conventional engine-powered vehicles (i.e., non-hybrid vehicles) adapted fixed throttle operation using partial fuel cut-off to reduce the engine torque produced by the engine 16. However, this resulted in undesirable NVH. The present disclosure recognizes that HEV implementations provide the ability to adapt fixed throttle engine operation in an alternative manner. As such, the system and method described in the embodiments of Fig. 1 and Fig. 2, an alternative torque management strategy to avoid partial fuel cut-off and associated NVH.Although partial fuel cut-off may be used under various other operating conditions, fixed throttle operation according to embodiments of the present disclosure avoids partial fuel cut-off when any of the following three conditions are met: (i) the engine torque request is greater than the fixed throttle misfire limit; (ii) the engine torque request is less than the fixed throttle misfire limit and is greater than the torque level associated with full fuel cut-off, but the engine torque request is set to be at or above the fixed throttle misfire limit; or (iii) the engine torque request is less than the torque level that results in full fuel cut-off.In cases (i) and (ii), there is no fuel cutoff and the engine is fully fueled. In case (iii), there is a complete fuel cutoff and the engine is not receiving any fuel. In all cases (i), (ii), and (iii), there is no partial fuel cutoff per se.

[0033] Blocks 90-98 of Fig. 2 implement a control strategy to ensure that at least one of cases (i), (ii), and (iii) exists at any given time. In particular, blocks 90-98 result in case (ii) when appropriate, so that an engine torque request that is less than the fixed-throttle misfire limit and greater than the torque level that results in full fuel cutoff is set at or above the misfire limit. Consequently, there is no partial fuel cutoff that would otherwise occur if the engine torque request were not set at or above the fixed-throttle misfire limit. Any engine torque not required to drive the traction wheels 40 is then used to charge the battery 12. As such, the control strategy determined by blocks 90-98 of Fig. 2 to fuel the engine in response to a fixed throttle position rather than a demanded torque associated with an accelerator pedal position while charging the battery, to utilize any engine torque produced above the demanded torque while the demanded torque exceeds a threshold (tqe-los), as represented by blocks 90, 92, 94, and 96, and otherwise to shut off fuel to all cylinders, as represented by block 98.

[0034] In decision block 90, the engine torque request is compared to the fixed-throttle misfire limit. If the engine torque request is greater than the fixed-throttle misfire limit, then no fuel shutoff occurs, as indicated in block 92. In this case, the engine 16 operates without fuel shutoffs, and all cylinders of the engine 16 are fueled. As such, there is no adjustment to the engine torque request and no partial fuel shutoff occurs.

[0035] If the engine torque request is less than the fixed-throttle misfire limit, then operation of the method continues from decision block 90 to decision block 94. In decision block 94, the engine torque request is again compared to the fixed-throttle misfire limit and the torque loss level. System losses such as friction losses and pumping losses, for example, are generally represented by a negative torque loss term ("tqe_los"). If the engine torque request is less than the torque required to overcome the system losses, as determined by block 94, then all fuel is shut off, as represented by block 98.If the engine torque request is less than the fixed throttle misfire limit and greater than the magnitude of the torque loss level, then the engine torque request is adjusted to be equal to or greater than the fixed throttle misfire limit, as indicated in block 96. In this case, as in block 92, the engine 16 is operated without fuel cuts and all cylinders of the engine 16 are fueled. Adjusting the engine torque request may include limiting the engine torque request to be at or above the fixed throttle misfire limit. As indicated above, without this engine torque request adjustment, a partial fuel cut would occur.Consequently, partial fuel cutoff is avoided by setting the engine torque request to be at or above the fixed throttle misfire limit, thus maintaining full fuel supply.

[0036] Operation controlled according to blocks 92 and 96 continues to operate the engine with the fixed throttle position and corresponding fueling so that the engine produces more torque than required to drive the traction wheels. The VSC 10, battery / BCM 12, and TCM 67 operate to control the generator 50 and motor 46 to charge the battery using any excess engine torque until the requested torque is less than the torque loss term, shutting off all fuel to the engine cylinders. In other words, various embodiments according to the present disclosure supply fuel to the engine in response to the fixed throttle position rather than the requested torque until the requested torque is less than a corresponding threshold representing the system loss torque.If the requested torque is less than the threshold (tqu_los), all fuel is shut off, so the engine no longer produces torque. This enables smooth engine operation between full fueling and full shutdown by maintaining or continuing engine operation with the fixed throttle position, using the excess engine torque to recharge the vehicle battery until engine torque is no longer required, avoiding partial fuel shutoff and associated NVH as a torque management strategy.

[0037] As demonstrated by the representative embodiments described above, various embodiments according to the present disclosure provide an alternative torque management strategy for an HEV with an engine operating at a fixed throttle position to better manage NVH. While the engine is operating at a fixed throttle position and the vehicle is stationary or decelerating, the engine produces more torque than required by the vehicle system controller. Instead of enabling partial fuel injector deactivation to reduce engine torque to the desired torque target, such asperformed in conventional engine control, various embodiments of the present disclosure continue to operate the engine at a fixed throttle position and use the excess engine torque to charge the battery until the requested torque is below an appropriate level to provide full fuel injector shutdown to reduce or eliminate undesirable NVH associated with partial fuel shutdown.

[0038] Although embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. The words used in the specification are words of description rather than limitation, and it is to be understood that various changes may be made without departing from the spirit and scope of the invention. Furthermore, the features of various implementations may be combined to form further embodiments of the invention. Key to symbols

[0039] Fig. 1 12 Battery / BCM 78 On-board charging device AC Power Alternating current power 76 Charging port

[0040] Fig. 2 82 In fixed throttle position? 83 Operate engine normally with misfire limit set to lowest engine torque for stable combustion 84 Operate the engine with the torque and power resulting from the fixed throttle position 86 Set misfire limit equal to expected engine torque resulting from fixed throttle operation 88 Route misfire limit to VSC to act as lower and upper limit for engine torque request (torque request) 90 Torque demand > misfire limit? 94 Torque request < misfire limit and > - tqe_los? 92 No fuel is shut off when the engine torque request is greater than the misfire limit 96 Set engine torque request at or above the misfire limit so that no fuel is shut off 98 All fuel is shut off when the engine torque request is less than the torque loss level that results in a full fuel shutoff

Claims

[1] A method for controlling a hybrid electric vehicle having a prime mover (16) with a throttle valve and a battery-powered traction motor (46), comprising: Operating the engine (16) at a fixed throttle position while the vehicle is stationary or decelerating to produce excess engine torque relative to a requested engine torque; Charging the battery (12) using the excess engine torque; and Shutting off fuel to the engine (16) when the requested engine torque is less than a threshold torque, wherein operating the engine (16) with a fixed throttle position comprises: Setting a misfire torque limit associated with a minimum stable combustion torque to provide a set misfire torque limit corresponding to an engine torque calculated based on fueling of all engine cylinders and airflow associated with the fixed throttle position, wherein the requested engine torque is set to the set misfire torque limit when the requested engine torque is less than the set misfire torque limit and greater than the threshold torque. [2] The method of claim 1, wherein the requested engine torque is set to the set misfire torque limit only when the requested engine torque is less than the set misfire torque limit. [3] The method of claim 1, wherein the threshold torque corresponds to the torque required to overcome system losses. [4] The method of claim 1, wherein the threshold torque corresponds to estimated engine torque losses.

Images