METHOD FOR OPERATING AN AUTOMATIC START / STOP SYSTEM IN A VEHICLE WITH A WET STARTING CLUTCH

Abstract

Vehicle (10), including: a motor (22); a gearbox (24); a starting device which includes a release clutch for selectively coupling the engine (22) and the transmission (24); and a control unit configured to disengage the release clutch in response to the engine (22) being switched off when a brake pedal is applied and the vehicle speed is above a first speed limit associated with the vehicle's idle speed (10), in order to decouple the engine (22) and the transmission (24).

Description

TECHNICAL FIELD

[0001] This disclosure relates to a method and system for operating an automatic start / stop system in a motor vehicle having an internal combustion engine, transmission, and wet launch device with an impeller clutch. GENERAL STATE OF THE ART

[0002] Many motor vehicles are equipped with an automatic start / stop system, which automatically shuts off and restarts the vehicle's engine to reduce fuel consumption under certain conditions. During operation, the automatic start / stop system allows the combustion engine to be automatically stopped—i.e., switched off—when no propulsion is required, such as when idling at a traffic light, and restarted when the driver demands more power.

[0003] DE 10 2013 104 516 A1 describes systems and methods for improving the operation of a hybrid vehicle. To improve vehicle torque response, for example, a driveline torque demand after a shift is predicted to determine whether it is desirable to start the engine early so that engine torque is available after the shift. Further prior art relating to the background of the invention is provided by DE 10 2011 007 716 A1, DE 10 2009 002 521 A1, DE 199 50 080 A1, DE 10 2013 219 276 A1, and DE 10 2011 053 972 A1.

[0004] One type of start / stop system is known as a coasting start / stop. A coasting start / stop system involves shutting down the internal combustion engine when the vehicle is coasting or decelerating. When engine power is needed, for example, when the driver no longer applies the brakes, the engine is automatically restarted. The engine can also be automatically restarted in response to other conditions, such as battery charge or loads in the electrical system. These automatic engine shutdowns can improve fuel economy and reduce emissions by reducing engine idling time and, consequently, fuel consumption during the driving cycle.However, a coasting start / stop in a vehicle with an automatic transmission connected to the powertrain via a conventional torque converter can result in unpleasant noise, vibration, and harshness (NVH) or unpleasant handling. One strategy to mitigate these effects is to automatically shift the transmission into neutral, although this requires a quick transition back to Drive when power is demanded and can result in a noticeable gear change, which may also be unpleasant for some occupants. SUMMARY

[0005] A system and method for operating an automatic start / stop system in a motor vehicle with an internal combustion engine, transmission, and wet launch device includes operating an impeller disconnect clutch during an automatic roll-stop event. Embodiments according to the present disclosure may be implemented in various applications for improving fuel economy.

[0006] According to one embodiment of the present disclosure, a vehicle includes an engine, a transmission, and a launch device. The launch device may include a disconnect clutch for selectively coupling the engine and the transmission. The vehicle may further include a controller configured to disengage the disconnect clutch to decouple the engine and the transmission in response to engine shutdown when a brake pedal is applied and a vehicle speed exceeds a first speed limit associated with the vehicle's idle speed. The controller may further be configured to disengage the disconnect clutch in response to engine shutdown at a vehicle speed below a second speed limit associated with a coast-to-stop threshold.

[0007] In another embodiment, a start / stop system for a vehicle having an engine, a transmission, and a launch device with a disconnect clutch is disclosed. The start / stop system may include a controller configured to control the disconnect clutch of the launch device to selectively couple the engine and transmission in response to an alternating shutdown and restart of the engine during an automatic roll-stop event. The controller may also be programmed to disengage the disconnect clutch to decouple the engine and transmission in response to the engine being shut down when a brake pressure exceeds a pressure limit and a vehicle speed exceeds a first speed limit but is below a second speed limit.

[0008] In yet another embodiment, a method of operating an automatic start and stop system in a vehicle having an engine, a transmission, and a launch device with a disconnect clutch for selectively coupling the engine and the transmission is disclosed. The method may include controlling the launch device to disengage the disconnect clutch to decouple the engine and the transmission in response to automatically shutting off the engine when a brake line pressure exceeds a pressure limit and a vehicle speed exceeds a first speed limit but is below a second speed limit. The first speed limit may be based on an idle speed of the vehicle, and the second speed limit may be based on a coast-to-stop speed limit.The method may further include controlling the launch device to maintain disengagement of the release clutch when a change in brake pressure is below a threshold value.

[0009] Embodiments according to the present disclosure may provide several advantages. For example, controlling an impeller clutch during a roll-stop / start may save fuel and reduce emissions associated with shorter engine operating time and lower engine drag torque while the vehicle is decelerating. Reduced NVH upon engine restart may increase customer satisfaction, making roll-stop / start operating modes more readily accepted and adopted by customers. Isolating the engine from the transmission using an impeller clutch may reduce wear on the engine, transmission, and interconnecting components. Additionally, the use of a wet launch clutch may provide axial space savings compared to a conventional torque converter.The foregoing and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a powertrain system of a vehicle according to an embodiment of the present disclosure; Fig. 2 is a schematic representation of a wet launch device with an impeller clutch according to one or more embodiments of the present disclosure; and Fig. 3 is a flowchart illustrating a method of operating an engine start / stop system using a wet launch device with an impeller disconnect clutch according to a representative embodiment of the present disclosure. DETAILED DESCRIPTION

[0010] Embodiments of the present disclosure are described herein. It should be understood, however, that the disclosed embodiments are merely exemplary in nature, and other embodiments may take different and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or reduced to illustrate details of particular components. Accordingly, 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 how to variously employ the embodiments.One of ordinary skill in the art will understand that various features illustrated and described with reference to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, different combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or embodiments.

[0011] Vehicles equipped with start / stop systems are powered by conventional internal combustion engines. A control unit can initiate automatic shutdown or startup under certain operating conditions. For example, the start / stop system can automatically shut down the engine when the vehicle is stopped or decelerating and the engine is not needed for propulsion or other purposes. At a later time, the start / stop system can restart the engine when it is needed for propulsion or other purposes, e.g., when the brake pedal is no longer applied and / or the accelerator pedal is depressed. By shutting down the engine whenever possible, overall fuel consumption is reduced.

[0012] One type of start / stop system is known as a rolling start / stop ("RSS"). An RSS system involves shutting down the internal combustion engine while the vehicle is moving. Specifically, a vehicle equipped with RSS technology is configured to shut down the engine below a predetermined vehicle speed limit when the driver applies the brakes. The predetermined vehicle speed at which an RSS strategy can be implemented depends on the vehicle application. One of the challenges regarding RSS technology in vehicles equipped with automatic transmissions is that the engine remains firmly connected to the driveline during the RSS event due to the use of a conventional torque converter.When the engine is automatically shut down after applying the brakes or while a vehicle is idling at a traffic light, a conventional torque converter still delivers fluid but performs no useful work, thereby reducing fuel economy. Accordingly, embodiments of the present disclosure provide systems and methods for implementing an RSS strategy in an automatic transmission vehicle that improves fuel economy through the use of a wet launch device with an impeller clutch without causing drivability impacts.

[0013] With reference to Fig. 1 is a schematic diagram of a powertrain of a vehicle 10 according to an embodiment of the present disclosure. Fig. Figure 1 illustrates representative relationships among the components. The physical arrangement and orientation of the components within the vehicle may vary. The powertrain of the vehicle 10 includes a vehicle control module (VSC) 12, which has appropriate logic / controls for implementing an engine start / stop system. The VSC 12 receives signals from an accelerator pedal position sensor (APPS) 14 and a brake pedal position sensor (BPPS) 16 to determine the vehicle's acceleration and deceleration requirements.

[0014] The powertrain of vehicle 10 includes an engine 22 that drives a transmission 24. An engine control unit (ECU) 18 is configured to control the engine 22, and a transmission control unit (TCU) 20 is configured to control the operation of the transmission 24 and a wet launch clutch 26. The VSC 12 communicates data between the TCU 20 and ECU 18 and also connects to various vehicle sensors. The engine 22 generates mechanical power by converting chemical energy stored in a fuel source. The transmission 24 adjusts the speed and torque of the mechanical power generated by the engine 22 to the current needs of the vehicle. The mechanical power from the transmission 24 is transmitted to the wheels 28 through the differential 30.

[0015] The transmission 24 may include gear sets (not shown) that are selectively arranged in different gear ratios to achieve the desired drive ratios by selectively engaging friction elements, such as clutches and brakes (not shown). The transmission 24 is automatically shifted from one ratio to another based on varying vehicle and environmental operating conditions by an associated control unit, such as the TCU 20. The transmission 24 then provides output torque to the output shaft 44.

[0016] The wet launch clutch 26 transfers the power and torque from the crankshaft of the engine 40 to the transmission input shaft 42 of the transmission 24. The wet launch clutch 26 may include an impeller clutch 32, an impeller 34, and a turbine 36. The impeller clutch 32 of the wet launch clutch 26 may be controlled to selectively couple the engine 22 to the impeller 34 and the transmission 24. A bypass clutch 38 may also be provided, which, when engaged, frictionally or positively couples the impeller 34 to the turbine 36 of the wet launch clutch 26. The bypass clutch 38 for the wet start clutch 26 can be selectively engaged to provide a mechanical connection between the impeller side and the turbine side of the wet start clutch 26 to transfer torque directly from the crankshaft of the engine 40 to the transmission input shaft 42.

[0017] In general, the control system for the powertrain of the vehicle 10 may include any number of control units, such as the VSC 12, ECU 18, and TCU 20, and may be integrated into a single control unit or comprise different modules. Some or all of the control units may be connected via a Controller Area Network (CAN) or other system. The control system may be configured to control the operation of various components of the transmission 24, the wet launch clutch 26, and the engine under any number of different conditions, including an engine start / stop system. The control system, including the VSC 12, ECU 18, and TCU 20, may implement an engine start / stop system by shutting down the engine 22 at appropriate times by stopping the fuel supply and restarting the engine 22 when propulsion is needed.

[0018] The control system controls various actuators in response to signals from various sensors to control functions such as engine 22 starting / shutting down, actuating the impeller clutch 32 of the wet launch clutch 26 to selectively disengage the impeller 34 from drive, selecting or scheduling gear changes, etc. The control system may include a microprocessor or central processing unit (CPU) connected to various types of computer-readable storage devices or media. Computer-readable storage devices or media may include volatile and non-volatile memory, such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is persistent or non-volatile memory that may be used to store various operating variables while the CPU is powered down.Computer-readable storage devices or media may be implemented using any of a variety of known storage devices, such as PROM (programmable read-only memory), EPROM (electronic PROM), EEPROM (electronic erasable PROM), flash memory, or any other electronic, magnetic, optical, or combination storage devices capable of storing data, some of which may be executable instructions used by the control unit to control the engine or vehicle.

[0019] Fig. 2 schematically illustrates a wet launch clutch 200 according to one or more embodiments of the present disclosure. The wet launch clutch resembles a torque converter without a stator and therefore cannot increase engine torque. Because the wet launch clutch does not have a stator, it offers an axial space savings compared to a conventional torque converter. The wet clutch is designed to be engaged only during low-speed maneuvers, such as walking speed and in parking lots, and initially during a launch event. The wet launch clutch has the same idler disengagement capability at idle speed and allows the idler to slip for a shorter acceleration time during launch. The method for controlling the idler and lock-up clutches can be controlled to achieve the desired vehicle performance.This is achieved by controlling the amount of torque on these clutches. The smaller axial footprint of the wet start clutch allows for the addition of additional gear sets in the transmission, further increasing the gear ratio range. With a wider gear ratio range, the need for torque increase decreases, making the wet start clutch an improvement for vehicle drivetrains.

[0020] The wet launch clutch 200 provides two parallel power flow paths from the crankshaft of the engine 202 to the transmission input shaft 204. One hydrodynamic power flow path includes the impeller clutch 206, the impeller 208, and the turbine 210. The impeller 208 is selectively coupled to the crankshaft of the engine 202 by the impeller clutch 206. An impeller clutch 206 is an actively controlled friction clutch that selectively couples an impeller 208 of the wet launch clutch 200 to the crankshaft of the engine 202. The impeller clutch 206 enables the engine and transmission to be decoupled from the driveline during certain vehicle events, such as during an RSS event. The turbine 210 is fixedly coupled to the transmission input shaft 204. The crankshaft of the engine 202 is selectively coupled to the transmission input shaft 204 by the bypass clutch 212, creating a second power flow path.

[0021] During a launch condition, the pressure in the wet launch clutch 200 increases to engage the impeller clutch 206, while the bypass clutch 212 remains disengaged. The impeller clutch 206 is engaged to connect the impeller 208 to the vehicle's engine, so that the torque received from the crankshaft of the engine 202 is transferred through the turbine 210 to the transmission input shaft 204. The impeller 208 directs the fluid into the turbine 210 and into the transmission input shaft 204 to propel the vehicle. After the initial launch, the pressure in the wet launch clutch 200 increases to a level sufficient to engage the bypass clutch 212. By engaging the bypass or lock-up clutch 212, the fluid circuit is bridged so that the torque is transmitted directly from the crankshaft of the engine 40 to the transmission input shaft 204.Whereas during vehicle stop or RSS event, the impeller clutch 206 and the bypass clutch 212 may be disengaged so that the impeller does not rotate and fuel economy may be improved.

[0022] Both the impeller clutch 206 and the bypass clutch 212 are actively controlled friction clutches with torque capacities that respond to changes in fluid pressure in hydraulic circuits. The hydraulic circuits may be dedicated circuits whose sole function is to control the clutch. Alternatively, the hydraulic circuits may also be used for other functions, such as supplying fluid to the torus of the wet launch clutch.

[0023] The control logic or control functions described above may be illustrated by flowcharts or similar diagrams in one or more figures. These figures provide representative control strategies and / or representative control logic that may be implemented using one or more processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various illustrated steps or functions may be performed in the illustrated order, in parallel, or in some cases omitted. Although not always explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be performed repeatedly, depending on the particular processing strategy employed.

[0024] With reference to Fig. 3, a control algorithm 300 is described which illustrates a method for operating an engine start / stop system using a wet launch clutch with an impeller release clutch. The control algorithm begins at block 302. A set of input conditions is then evaluated in blocks 304-312. At decision block 306, a first brake pressure P brk1 with a first pressure limit P thd1 compared. The first pressure limit P thd1 is a value associated with the driver's intention to initiate an automatic roll-stop event. When the first brake pressure P brk1 at decision block 306 below the first pressure limit P thd1 , the control algorithm returns to the starting point to re-evaluate the input conditions at block 304. If the first brake pressure P brk1 at decision block 306 greater than or equal to the first pressure limit P thd1the control algorithm compares at block 308 a vehicle speed V sp with a lower speed limit V sp_low . The lower speed limit V sp_low can be a value associated with the idle speed of the vehicle.

[0025] If the vehicle speed V sp at decision block 308 below the lower speed limit V sp low , the control algorithm returns to the starting point to re-evaluate the input conditions at block 304. If the vehicle speed V sp at decision block 308 greater than the lower speed limit V sp_low the control algorithm compares the vehicle speed V sp with an upper speed limit V sp_high . The upper speed limit V sp_high is a value associated with a maximum vehicle speed at which a roll start / stop mode can be executed. If the vehicle speed V spat decision block 310 above the upper speed limit V sp_high , the control algorithm returns to the starting point to re-evaluate the input conditions at block 304. If the vehicle speed V sp at decision block 310 below the upper speed limit V sp_high , the control algorithm evaluates other vehicle conditions to determine whether the engine can be shut down. Other vehicle conditions may include battery charge level, electronic system loads, catalyst temperature, etc.

[0026] If other vehicle conditions indicate that the engine should not be shut down at this time, the control algorithm returns to the starting point to re-evaluate the input conditions at block 304. In contrast, if it is determined at decision block 312, after evaluating other vehicle conditions, that the engine can be shut down, a rolling start / stop strategy ("RSS") is implemented at block 314. During the implementation of the RSS mode, the engine is automatically shut down and the impeller clutch of the wet launch clutch is requested to disengage to decouple the impeller and the engine (i.e., driveline is open). The control algorithm then determines a current brake pedal pressure P brk2 at block 316 and then calculates a difference ΔP at block 318 brk between the current brake pedal pressure P brk2 and the first brake pedal pressure P brk1 .

[0027] The change or difference ΔP brk between the current brake pedal pressure P brk2 and the first brake pedal pressure P brk1 is then compared at decision block 320 with a corresponding pressure limit P thd2 The corresponding pressure limit P thd2 is a value associated with the driver's intention to exit the automatic roll-stop event. If the change in brake line pressure exceeds ΔP brk the corresponding pressure limit P thd2 , this indicates the driver's intention to exit the automatic roll-stop event, and the control algorithm subsequently exits the RSS strategy at block 324. The engine is then restarted and the drivetrain is closed, i.e., the impeller clutch is engaged to couple the impeller and the engine. If the change in brake line pressure falls below ΔP brkat block 320 the corresponding pressure limit P thd2 , this indicates that the vehicle operator intends to continue the automatic roll-stop event, and the control algorithm then evaluates at decision block 322 whether other vehicle conditions require the engine to be restarted.

[0028] Other vehicle conditions may include the battery state of charge, loads in the electronic system, catalyst temperature, etc. For example, the control module may determine whether the vehicle's power demand exceeds a currently available electrical power, where the vehicle's power demand is based on the amount of electrical energy required to power the vehicle's additional loads and subsystems. If this is the case, the engine may need to be restarted to meet the vehicle's power demand. Similarly, the control module may determine that the engine should be restarted in response to a battery voltage that meets a threshold.

[0029] If other vehicle conditions require restarting the engine at decision block 322, the control algorithm exits the RSS strategy at block 324, restarts the engine, and the impeller clutch is engaged to close the driveline and couple the wet launch clutch impeller to the engine. If other vehicle conditions do not require restarting the engine at decision block 322, the control algorithm returns to block 316 to determine the current brake pedal pressure P brk2 and any subsequent change in the brake line pressure ΔP brk to be further evaluated. The control strategy ends at block 326.

[0030] While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. The terms used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. In addition, the features of various embodiments may be combined to form further embodiments of the invention.

Claims

[1] Vehicle (10), including: an engine (22); a gearbox (24); a starting device including a clutch for selectively coupling the engine (22) and the transmission (24); and a controller configured to disengage the disconnect clutch to decouple the engine (22) and the transmission (24) in response to the engine (22) being shut down upon actuation of a brake pedal and a vehicle speed above a first speed limit associated with the idle speed of the vehicle (10). [2] The vehicle (10) of claim 1, wherein the controller is further configured to disengage the disconnect clutch in response to the engine (22) shutting down at a vehicle speed below a second speed limit associated with a roll-stop limit. [3] The vehicle (10) of claim 1, wherein the controller is further configured to engage the disconnect clutch in response to restarting the engine (22) when a change in brake line pressure exceeds a threshold. [4] The vehicle (10) of claim 1, wherein the controller is further configured to maintain disengagement of the disconnect clutch when a change in brake line pressure is below a threshold. [5] The vehicle (10) of claim 1, wherein the controller is further configured to engage the disconnect clutch in response to restarting the engine (22) when at least one of the following applies: a power demand of the vehicle (10) exceeds a currently available electrical power and an accelerator pedal is applied. [6] The vehicle (10) of claim 5, wherein the power demand of the vehicle (10) is based on an amount of electrical energy required to power additional loads and subsystems of the vehicle (10).

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