Hybrid vehicle and method for heating combustion engine coolant

Abstract

Hybrid vehicle that includes the following: an internal combustion engine (14); an electric machine (18) designed to recharge a battery (20) by regenerative braking; an electric heating element (76) designed to heat an internal combustion engine coolant; and a controller (50) programmed to direct regenerative braking power to the electric heating element (76) in response to a temperature of the combustion engine coolant being less than a threshold, wherein the regenerative braking power directed to the electric heating element (76) is a portion of the total regenerative braking power that exceeds a limit of a charging rate of the battery (20), and the threshold corresponds to a coolant reserve temperature that exceeds a minimum coolant temperature required for an EV operating mode or a minimum coolant temperature required to meet interior heating requirements.

Description

FIELD OF INVENTION

[0001] The present disclosure relates to hybrid vehicles and methods for redirecting regenerative braking power to heat engine coolant. GENERAL STATE OF THE ART

[0002] Internal combustion engines operate more efficiently once the engine coolant and engine oil have reached optimal operating temperatures.

[0003] DE 10 2007 032 726 A1 already discloses a vehicle with an internal combustion engine and an electric motor, in which regenerative braking power is fed to an electric heating element. Further vehicles are known from DE 10 2009 028 326 A1, US Pat. No. 5,291,960 A, DE 10 2012 214 994 A1, and DE 10 2014 019 269 A1.

[0004] Based on this state of the art, it can be considered an objective task to improve the efficiency of a vehicle of this type.

[0005] According to the invention, this object is achieved by a vehicle according to claim 1 and by a method according to claim 6. Advantageous embodiments of the invention are specified in the dependent claims and the following description. BRIEF DESCRIPTION OF THE INVENTION

[0006] A vehicle is provided. The vehicle includes an internal combustion engine, an electric machine, an electric heating element, and a controller. The electric machine is configured to recharge a battery through regenerative braking. The electric heating element is configured to heat an internal combustion engine coolant. The controller is programmed to direct regenerative braking power to the electric heating element in response to an internal combustion engine coolant temperature being less than a threshold.

[0007] A method for heating engine coolant in a hybrid vehicle is provided. The method includes generating power with an electric machine via regenerative braking and directing power from the electric machine to an electric heating element to heat the engine coolant based on a temperature of the engine coolant being less than a threshold.

[0008] A vehicle is provided. The vehicle includes an internal combustion engine, an electric machine, an electric heating element, and a controller. The electric machine is configured to recharge a battery through regenerative braking. The electric heating element is configured to heat an internal combustion engine coolant. The controller is programmed to direct regenerative braking power to the electric heating element in response to an internal combustion engine oil temperature being less than a threshold. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of an exemplary powertrain of a hybrid electric vehicle; Fig. 2 is a schematic diagram of an exemplary cooling system of an internal combustion engine in a hybrid electric vehicle; and Fig. 3 is a method for utilizing regenerative braking power to operate an electric heating element to heat the engine coolant of a hybrid electric vehicle. DETAILED DESCRIPTION

[0009] With reference to Fig. 1: A schematic diagram of a hybrid electric vehicle (HEV) 10 is illustrated according to an embodiment of the present disclosure. Fig. 1 illustrates representative relationships between the components. The physical arrangement and orientation of the components within the vehicle may vary. The HEV 10 includes a powertrain 12. The powertrain 12 includes an internal combustion engine 14 that drives a transmission 16, which may be referred to as a modular hybrid transmission (MHT). As described in more detail below, the transmission 16 includes an electric machine, such as an electric motor / generator (M / G) 18, an associated traction battery (hereinafter also referred to as battery) 20, a torque converter 22, and a multi-speed automatic transmission (hereinafter also referred to as transmission) 24.

[0010] The engine 14 and the M / G 18 are both power sources for the HEV 10. The engine 14 generally represents a power source that may include an internal combustion engine, such as a gasoline, diesel, or natural gas-powered engine, or a fuel cell. The engine 14 generates engine power and corresponding engine torque, which is supplied to the M / G 18 when a disconnect clutch 26 between the engine 14 and the M / G 18 is at least partially engaged. The M / G 18 may be implemented by any of several types of electric machines. For example, the M / G 18 may be a permanent magnet synchronous motor. The power electronics condition direct current (DC) power provided by the battery 20 to the requirements of the M / G 18, as described below.For example, power electronics can provide three-phase alternating current (AC) to the M / G 18.

[0011] When the disconnect clutch 26 is at least partially engaged, power flow is possible from the engine 14 to the M / G 18 or from the M / G 18 to the engine 14. For example, the disconnect clutch 26 may be engaged, and the M / G 18 may operate as a generator to convert rotational energy provided by a crankshaft 28 and an M / G shaft (hereinafter also referred to as shaft) 30 into electrical energy for storage in the battery 20. The disconnect clutch 26 may also be disengaged to disconnect the engine 14 from the rest of the powertrain 12 so that the M / G 18 can function as the sole power source for the HEV 10. The shaft 30 extends through the M / G 18. The M / G 18 is continuously drivingly connected to the shaft 30, whereas the internal combustion engine 14 is only drivingly connected to the shaft 30 when the separating clutch 26 is at least partially engaged.

[0012] The M / G 18 is connected to the torque converter 22 via shaft 30. The torque converter 22 is therefore connected to the internal combustion engine 14 when the disconnect clutch 26 is at least partially engaged. The torque converter 22 includes an impeller fixedly attached to the M / G shaft 30 and a turbine fixedly attached to a transmission input shaft 32. The torque converter 22 thus provides a hydraulic coupling between the shaft 30 and the transmission input shaft 32. The torque converter 22 transfers power from the impeller to the turbine when the impeller rotates faster than the turbine. The magnitude of the turbine torque and the impeller torque generally depends on the relative speeds. If the ratio of impeller speed to turbine speed is sufficiently large, the turbine torque is many times the impeller torque.A torque converter bypass clutch (also known as a torque converter lock-up clutch) 34 may also be provided which, when engaged, frictionally or mechanically couples the impeller and turbine of the torque converter 22, allowing for more efficient power transfer. The torque converter bypass clutch 34 may operate as a launch clutch to provide smooth vehicle launch. Alternatively, or in combination, a launch clutch similar to the disconnect clutch 26 may be provided between the M / G 18 and the transmission 24 in applications that do not include a torque converter 22 or a torque converter bypass clutch 34. In some applications, the disconnect clutch 26 is generally referred to as an upstream clutch, and the launch clutch (which may be a torque converter bypass clutch 34) is generally referred to as a downstream clutch.

[0013] The transmission 24 may include gear sets (not shown) that are selectively placed into different gear ratios by selectively engaging friction elements, such as clutches and brakes (not shown), to establish the desired plurality of discrete or stepped drive ratios. The friction elements are controllable by a shift command that connects and disconnects certain elements of the gear sets to control the gear ratio between a transmission output shaft (hereafter also referred to as an output shaft) 36 and the transmission input shaft 32. The transmission 24 is automatically shifted from one gear ratio to another by an associated controller, such as a powertrain control unit (PCU), based on various vehicle and ambient operating conditions. The transmission 24 then provides driveline output torque to the output shaft 36.

[0014] It should be understood that the hydraulically controlled transmission 24 used with a torque converter 22 is merely one example of a transmission or transmission arrangement; any multi-speed transmission that receives input torque(s) from an internal combustion engine and / or an electric motor and then provides torque to an output shaft at the different ratios is acceptable for use with embodiments of the present disclosure. For example, the transmission 24 may be implemented by an automatic, mechanical (or manual) transmission (ASC) that includes one or more servomotors to translate / rotate shift forks along a shift rail to select a desired gear ratio. As is well known to those of ordinary skill in the art, an ASC may be used, for example, in applications with higher torque requirements.

[0015] As in the representative embodiment in Fig. 1, the output shaft 36 is connected to a differential 40. The differential 40 drives a pair of wheels 42 through respective axles 44 connected to the differential 40. The differential transmits approximately equal torque to each wheel 42, allowing for slight speed differences, such as when the vehicle is cornering. Different types of differentials or similar devices may be used to distribute torque from the driveline to one or more wheels. In some applications, the torque distribution may vary, for example, depending on the particular operating mode or condition.

[0016] The powertrain 12 further includes an associated controller 50, such as a powertrain control unit (PCU). Although illustrated as a controller, the controller 50 may be part of a larger control system and controlled by various other controllers present throughout the vehicle 10, such as a vehicle system controller (VSC). Therefore, it should be understood that the powertrain control unit and one or more other controllers may be collectively referred to as a "controller," which controls various actuators in response to signals from various sensors to control functions such as starting / stopping the engine 14, operating the M / G 18 to provide wheel torque or charge the battery 20, selecting or commanding transmission shifts, etc.The controller 50 may include a microprocessor or central processing unit (CPU) in communication with various types of computer-readable storage devices or media. Computer-readable storage devices or media may include, for example, volatile and non-volatile memory in read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM). KAM is permanent or non-volatile memory that can be used to store various operating variables while the CPU is powered down.Computer-readable storage devices or media may be implemented using any number of known storage devices, such as programmable read-only memories (PROMs), erasable PROMs (EPROMs), electrically erasable PROMs (EEPROMs), 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 controller to control the internal combustion engine or vehicle.

[0017] The controller communicates with various internal combustion engine / vehicle sensors and actuators via an input / output (I / O) interface, which may be implemented as a single integrated interface providing various raw data or signal conditioning, processing, and / or conversion, short-circuit protection, and the like. Alternatively, one or more dedicated hardware or firmware chips may be used to condition and process particular signals before they are fed to the CPU. As shown in the representative embodiment in Fig. 1, the controller 50 may communicate signals to and from the internal combustion engine 14, the disconnect clutch 26, the M / G 18, the battery 20, the launch clutch, the transmission 24, and the power electronics 56. Although not explicitly illustrated, one of ordinary skill in the art will recognize various functions or components that may be controlled by the controller 50, each within the subsystems identified above.Representative examples of parameters, systems, and / or components that are directly or indirectly actuated using control logic executed by the controller include fuel injection timing, amount, and duration, throttle position, spark plug timing (for spark ignition engines), intake / exhaust valve timing and duration, front-end accessory drive (FEAD) components such as an alternator, air conditioning compressor, battery charging and discharging (including determining maximum charging and discharging power limits), regenerative braking, M / G operation, clutch pressures for the disconnect clutch 26, the launch clutch, and the transmission 24, and the like.Sensors that communicate input variables via the I / O interface can be used to indicate, for example, turbocharger boost pressure, crankshaft position (PIP), engine speed (RPM), wheel speeds (WS1, WS2), vehicle speed (VSS), engine coolant temperature (ECT), intake manifold pressure (MAP), accelerator pedal position (PPS), ignition switch position (IGN), throttle position (TP), air temperature (TMP), exhaust gas oxygen content (EGO) or the concentrations or presence of other exhaust constituents, intake air flow (MAF), transmission gear, ratio or mode, transmission oil temperature (TOT), transmission turbine speed (TS), torque converter bypass clutch 34 (TCC) status, deceleration or shift mode (MDE), battery temperature, voltage, current or state of charge (SOC).

[0018] Control logic or functions performed by controller 50 may be illustrated by flowcharts or similar diagrams in one or more figures. These figures provide representative control strategies and / or logic that may be implemented using one or more processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Thus, various illustrated steps or functions may be performed in the order illustrated, 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 specific processing strategy used.Likewise, the order of processing is not necessarily required to achieve the features and advantages described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily in software executed by a microprocessor-based vehicle, internal combustion engine, and / or powertrain controller, such as controller 50. Of course, the control logic may be implemented as software, hardware, or a combination of software and hardware in one or more controllers, depending on the particular application. When implemented as software, the control logic may be provided in one or more computer-readable storage devices or media storing data representing code or instructions executed by a computer to control the vehicle or its subsystems.The computer-readable storage devices or media may include one or more of a variety of known physical devices utilizing electrical, magnetic, and / or optical storage to hold executable instructions and associated calibration information, operating variables, and the like.

[0019] An accelerator pedal 52 is used by the driver of the vehicle to provide a requested torque, power, or drive command to propel the vehicle. Generally, the depression and release of the accelerator pedal 52 generates an accelerator position signal that can be interpreted by the controller 50 as a request for more power or less power, respectively. Based on at least the input from the pedal, the controller 50 requests torque from the engine 14 and / or the M / G 18. The controller 50 also controls the timing of gear shifts in the transmission 24, as well as the engagement or disengagement of the disconnect clutch 26 and the torque converter bypass clutch 34. Like the disconnect clutch 26, the torque converter bypass clutch 34 can be modulated between the engaged and disengaged positions.This creates a variable slip in the torque converter 22 in addition to the variable slip created by the hydrodynamic coupling between the impeller and the turbine. Alternatively, the torque converter bypass clutch 34 can be operated locked or opened, depending on the particular application, without using a modulated mode of operation.

[0020] To drive the vehicle with the engine 14, the disconnect clutch 26 is at least partially engaged to transfer at least a portion of the engine torque through the disconnect clutch 26 to the M / G 18 and then from the M / G 18 through the torque converter 22 and the transmission 24. The M / G 18 may assist the engine 14 by providing additional power to rotate the shaft 30. This operating mode may be referred to as a "hybrid operating mode" or an "electric assist operating mode."

[0021] To drive the vehicle with the M / G 18 as the sole power source, the power flow remains the same except that the disconnect clutch 26 disconnects the engine 14 from the rest of the driveline 12. Combustion in the engine 14 may be disabled or otherwise OFF during this time to conserve fuel. The traction battery 20 transfers stored electrical energy via wires 54 to power electronics 56, which may include, for example, an inverter. The power electronics 56 converts DC voltage from the battery 20 to AC voltage for use by the M / G 18. The controller 50 commands the power electronics 56 to convert voltage from the battery 20 to an AC voltage, which is provided to the M / G 18 to provide positive or negative torque to the shaft 30. This mode of operation may be referred to as an "all-electric" mode of operation.

[0022] In any operating mode, the M / G 18 may function as an electric motor, providing motive power to the powertrain 12. Alternatively, the M / G 18 may function as a generator, converting kinetic energy from the powertrain 12 into electrical energy to be stored in the battery 20. For example, the M / G 18 may function as a generator while the internal combustion engine 14 provides motive power to the vehicle 10. During times of regenerative braking, where rotational energy from rotating wheels 42 is transferred back through the transmission 24 and converted into electrical energy for storage in the battery 20, the M / G 18 may additionally function as a generator.

[0023] It is understood that the Fig. The schematic illustrated in Figure 1 is merely exemplary and is not intended to be limiting. Other configurations are contemplated that utilize selective engagement of both an internal combustion engine and an electric motor for transmission. For example, the M / G 18 may be offset from the crankshaft 28, an additional electric motor may be provided to start the internal combustion engine 14, and / or the M / G 18 may be provided between the torque converter 22 and the transmission 24. Other configurations are contemplated without departing from the scope of the present disclosure.

[0024] With reference to Fig. 2: A schematic representation of a cooling system 58 of the internal combustion engine 14 is illustrated according to an embodiment of the present disclosure. The cooling system 58 further includes a series of cooling circuits 60. A coolant is circulated through the cooling circuits 60 to remove excess heat from the internal combustion engine 14. The cooling circuits 60 may include at least one heat exchanger configured to remove the excess heat from the coolant. For example, excess heat from the coolant may be transferred to the external environment of the HEV 10 as the coolant flows from the internal combustion engine 14 and through a first heat exchanger 62 (i.e., radiator). A fan 64 may be included to direct air to flow over the first heat exchanger 62 such that heat from the coolant flowing through the first heat exchanger 62 is transferred to the air.A pump 66 is used to circulate the coolant through the cooling circuits 60. A thermostat 68 may be included to cause the coolant to bypass the first heat exchanger 62 and to continuously circulate the coolant through the internal combustion engine 14 until an optimal operating coolant temperature is reached. A second heat exchanger 70 (i.e., cabin heater or heater core) may be used to transfer excess heat from the coolant to the air flowing into the cabin of the HEV 10. A fan blower (hereinafter also referred to as blower for short) 72 is included to direct the air flowing into the cabin to flow over the second heat exchanger 70 such that heat from the coolant flowing through the second heat exchanger 70 is transferred to the air.A control valve 74 may be used to throttle or shut off the coolant flowing through the second heat exchanger 70. The control valve 74 may be connected to a cabin climate control system and may be configured to open and close based on the climate requirements of a cabin occupant. The fan blower 72 may also be connected to the climate control system and may be configured to operate based on the climate requirements of the cabin occupant.

[0025] The cooling system 58 may also include an electric heating element 76 that can be used to transfer heat to the coolant flowing through the cooling circuits 60. The electric heating element 76 can be any type of electric heating element that can be used to transfer heat to a fluid, including resistive heating elements, rod heaters, and PTC (positive temperature coefficient) heaters. The electric heating element 76 can be in communication with the controller 50. The controller 50 can be configured to activate the electric heating element 76 under circumstances where it may be advantageous to transfer heat to the coolant flowing through the cooling circuits 60.

[0026] The electrical heating element 76 may receive power via electrical wiring from the traction battery 20, an accessory battery 78 (such as a 12V battery commonly found in automobiles), an alternator (not shown), the M / G 18, or any other power source that may be included in the HEV 10. The electrical heating element 76 may be configured to receive AC and / or DC electrical power. An AC-to-DC converter may be included if the electrical heating element 76 is configured to operate only with DC electrical power and the power source (e.g., the alternator or the M / G 18) is configured to generate AC electrical power. A DC-to-AC converter may be included if the electrical heating element 76 is configured to operate only with AC electrical power and the power source (e.g.,B. the battery) is designed to generate direct current electrical power.

[0027] The controller 50 may also be in communication with the traction battery 20, the accessory battery 78, the M / G 18, the alternator, or any other power source that may be used to power the electric heating element 76. The controller 50 may coordinate which power source will be used to power the electric heating element 76 when conditions exist under which it would be beneficial to transfer heat to the coolant in the cooling circuits 60.For example, the traction battery 20 may be used to power the electric heating element 76 if the traction battery 20 is sufficiently charged, the accessory battery 78 may be used to power the electric heating element 76 if the accessory battery 78 is sufficiently charged, the M / G 18 may be used to power the electric heating element 76 if the M / G 18 is operating as a generator, or the alternator may be used to power the electric heating element 76.

[0028] The controller 50 may also be in communication with a series of sensors configured to communicate certain conditions of the HEV 10 or the environment to the controller 50. At least one coolant temperature sensor may be configured to communicate the temperature of the coolant in the cooling circuits 60 to the controller 50. In the illustrated embodiment, a first coolant temperature sensor 80 is shown on the exhaust side of the internal combustion engine 14, and a second coolant temperature sensor 82 is shown on the intake side of the internal combustion engine 14. However, the disclosure should not be construed as limited to this configuration, but should be construed to include cooling systems having one or more coolant temperature sensors that may be located at any position in the cooling circuits 60.At least one engine oil temperature sensor 84 may be configured to communicate the temperature of the engine oil to the controller 50. The engine oil temperature sensor 84 may be located at any suitable location within the engine 14 capable of providing an accurate oil temperature reading. At least one ambient air temperature sensor 86 may be configured to communicate the ambient temperature to the controller 50.

[0029] The cooling system 58 is for illustrative purposes only and should not be interpreted as being based on the Fig. 2. For example, the order or location of the cooling circuits 60 (or the components located in the cooling circuits) may be restructured or rearranged; the cooling system 58 may include an overflow tank or degas bottle; the cooling system 58 may include additional cooling circuits used to cool other components of the HEV 10, such as the transmission 24, the torque converter 22, the power electronics 56 or the M / G 18, the catalytic converter (not shown), the turbocharger (if included), or any other vehicle component that may require cooling.

[0030] It may be beneficial to operate the electric heating element 76 to increase the coolant temperature under certain circumstances. Internal combustion engines (including engine 14) operate more efficiently once the engine temperature is at or above a temperature threshold. When an internal combustion engine operates at a temperature below the temperature threshold, internal friction losses within the engine may increase (including friction losses occurring at the piston-cylinder ring interfaces, various bearings, and valvetrain components). This is a function of local engine oil and metal temperatures, which are influenced by the engine coolant temperature.Fuel also tends to form a film on the internal surfaces of the engine's air intake components, disrupting the air-fuel ratio control system and resulting in increased emissions from the engine. The electric heating element 76 may be operated to increase the temperature of the coolant, which in turn will increase the temperature of the engine 14 when the engine 14 is operating below a temperature threshold. The temperature threshold of an engine may correspond to a minimum operating coolant temperature ranging between 180°F (82°C) and 220°F (104°C) for efficiency purposes. The temperature threshold of the engine may correspond to a minimum operating coolant temperature ranging between 110°F (43°C) and 140°F (60°C) for emissions purposes.

[0031] The internal combustion engine 14 may shut down under certain circumstances to conserve fuel and increase fuel efficiency. When the internal combustion engine 14 is shut down, the HEV 10 may be powered by the M / G 18, which draws electrical power from the traction battery 20. When the M / G 18 powers the HEV 10 alone, the HEV 10 operates in a mode that may be referred to as EV mode (i.e., electric vehicle mode). The period of time the HEV 10 can operate in EV mode is typically limited by the amount of charge in the traction battery 20. However, the period of time the HEV 10 can operate in EV mode may also be limited by the minimum operating temperature of the coolant to ensure that the internal combustion engine 14 is operating above the temperature threshold for emissions purposes.The electric heating element 76 may be operated to increase the temperature of the coolant to maximize the period of time the HEV 10 operates in EV mode. The electric heating element 76 may be operated in anticipation of an EV mode or during an EV mode. The minimum engine coolant temperature required to maximize the period of time the HEV 10 can be in an EV mode may coincide with the minimum operating coolant temperature for emissions purposes (which ranges between 110°F (43°C) - 140°F (60°C)), or it may coincide with the minimum operating coolant temperature for efficiency purposes (which ranges between 180°F (82°C) - 220°F (104°C)).Alternatively, the minimum engine coolant temperature required to maximize a period of time that the HEV 10 is in an EV mode may be a temperature reserve value that exceeds the minimum operating coolant temperature for emissions purposes by 5°F (-5°C) - 40°F (4°C), or it may be a temperature reserve value that exceeds the minimum operating coolant temperature for efficiency purposes by 5°F (-5°C) - 40°F (4°C).

[0032] The electric heating element 76 may also be operated to increase the temperature of the engine coolant during periods when the second heat exchanger 70 and the blower 72 are operating to heat air flowing into the interior of the HEV 10. The minimum engine coolant temperature required when the second heat exchanger 70 and the blower 72 are used may be the same as the minimum operating coolant temperature for efficiency purposes (which ranges between 180°F (82°C) - 220°F (104°C)), or it may be a temperature reserve value that exceeds the minimum operating coolant temperature for efficiency purposes. For example, the minimum engine coolant temperature required when using the second heat exchanger 70 and blower 72 may exceed the minimum operating coolant temperature for efficiency purposes by 5°F (-5°C) - 40°F (4°C).

[0033] The electric heating element 76 may also be operated to increase the temperature of the engine coolant in anticipation that the second heat exchanger 70 and the fan 72 will be used to heat the air flowing into the interior of the HEV 10. For example, if the ambient air temperature is below a threshold (ranging between 45°F (7°C) - 65°F (18°C)) and the engine coolant is operating below a desired operating temperature (ranging between 180°F (82°C) - 220°F (104°C)), it may be advantageous to operate the electric heating element 76 due to the likely use of the second heat exchanger 70 and the fan 72 to heat the air flowing into the interior of the HEV 10.

[0034] It may also be beneficial to operate the electric heating element 76 to increase the temperature of the internal combustion engine oil under certain circumstances. Internal combustion engines (including internal combustion engine 14) operate more efficiently once the temperature of the internal combustion engine oil is at or above an optimal temperature threshold. The internal combustion engine oil is more viscous at lower temperatures, which increases friction between moving parts of the internal combustion engine, resulting in a loss of efficiency. The electric heating element 76 may be operated to increase the temperature of the coolant, which in turn will increase the temperature of the internal combustion engine oil when the internal combustion engine oil is operating below the optimal temperature threshold. In an alternative embodiment, the electric heating element 76 may be configured to directly increase the temperature of the internal combustion engine oil.The optimal temperature threshold of combustion engine oil can range between 180 °F (82 °C) and 250 °F (121 °C).

[0035] With reference to Fig. 3: A method 100 for utilizing regenerative braking power to operate the electric heating element 76 to heat the engine coolant is illustrated. The method 100 is initiated at the start block 102. The method 100 may be initiated by placing a vehicle ignition in an "on" position, pressing a "start / run" button, placing the transmission of the HEV 10 in a specific gear selection, or by any other suitable condition in which the HEV 10 can potentially generate power via the M / G 18 through regenerative braking.

[0036] In step 104, it is determined whether the M / G 18 (electric machine) is generating electrical power via regenerative braking. If the M / G 18 is not generating electrical power via regenerative braking, the method 100 ends in step 106. If the M / G 18 is generating electrical power via regenerative braking, the method continues to step 108.

[0037] In step 108, it is determined whether the total regenerative braking power generated exceeds a traction battery 20 charging rate limit. The traction battery 20 charging rate limit may be dictated by several factors, including the traction battery 20's capacity to accept charge, the power electronics 56's capacity to transport electricity, the maximum power of the M / G 18, or the maximum torque of the M / G 18. If the total regenerative braking power does not exceed the traction battery 20 charging rate limit, the method 100 ends in step 106. If the total regenerative braking power exceeds the traction battery 20 charging rate limit, the method continues to step 110.

[0038] In step 110, it is determined whether the engine oil temperature is below a threshold. The engine oil temperature threshold may correspond to the optimal engine oil temperature threshold discussed above. If the engine oil temperature is not below a threshold, the method 100 ends in step 106. If the engine oil temperature is below a threshold, the method continues to step 112.

[0039] In step 112, it is determined whether the engine coolant temperature is below a threshold. The engine coolant temperature threshold may correspond to any of the coolant temperatures discussed above that are related to engine emissions, engine efficiency, maximizing the amount of time the HEV 10 operates in EV mode, heating air flowing into the cabin of the HEV 10, or anticipating heating air flowing into the cabin of the HEV 10. If the engine coolant temperature is not below a threshold, the method 100 ends in step 106. If the engine coolant temperature is below a threshold, the method continues to step 114.

[0040] In step 114, the electrical power generated by the M / G 18 through regenerative braking is directed to power the electrical heating element 76 to heat the engine coolant. The amount of regenerative braking power directed to power the electrical heating element 76 may correspond to a portion of the total regenerative braking power that exceeds the traction battery 20 charge rate threshold.

[0041] Method 100 should not be interpreted as limiting the illustration in Fig. 3, but should be interpreted to include variants in which one or more steps may be chronologically restructured or omitted.

[0042] It is understood that the hybrid vehicle configuration in Fig. 1 is merely exemplary and is not intended to be limiting. The scheme from Fig. 2 and the procedure from Fig.3 may be applicable to other hybrid vehicle configurations that should be construed as disclosed herein. Other hybrid vehicle configurations that should be construed as disclosed herein include series hybrid vehicles, parallel hybrid vehicles, series-parallel hybrid vehicles, power-split hybrid vehicles, plug-in hybrid electric vehicles (PHEVs), fuel cell hybrid vehicles, or any other hybrid vehicle configuration known to one of ordinary skill in the art. List of reference symbols 10 hybrid electric vehicles 12 Drivetrain 14 Internal combustion engine 16 gearboxes 18 Electric motor / generator (M / G) 20 traction battery 22 torque converter 24 automatic transmissions 26 Separating clutch 28 Crankshaft 30 M / G wave 32 Gearbox input shaft 34 Torque converter bypass clutch 36 Output shaft 40 Differential 42 wheels 44 Axis 50 Control 52 Accelerator pedal 54 Line 56 Power electronics 58 Cooling system 60 Cooling circuit 62 heat exchangers 64 blowers 66 Pump 68 Thermostat 70 heat exchangers 72 fan blowers 74 Control valve 76 Heating element 78 Accessory battery 80 first coolant temperature sensor 82 second coolant temperature sensor 84 Combustion engine oil temperature sensor 86 Ambient air temperature sensor 100 procedures 102 Start Block 104 steps 106 steps 108 steps 110 steps 112 steps 114 steps

Claims

[1] Hybrid vehicle comprising: an internal combustion engine (14); an electric machine (18) configured to recharge a battery (20) by regenerative braking; an electric heating element (76) configured to heat an internal combustion engine coolant; and a controller (50) programmed to direct regenerative braking power to the electric heating element (76) in response to a temperature of the engine coolant being less than a threshold, wherein the regenerative braking power diverted to the electric heating element (76) is a portion of the total regenerative braking power that exceeds a threshold of a charging rate of the battery (20), and the threshold corresponds to a coolant reserve temperature that exceeds a minimum coolant temperature required for an EV operating mode or a minimum coolant temperature required to meet cabin heating requirements. [2] The hybrid vehicle of claim 1, wherein the threshold corresponds to a minimum coolant temperature required to maximize efficiency of the internal combustion engine (14). [3] The hybrid vehicle of claim 1, wherein the threshold corresponds to a minimum coolant temperature required for an EV operating mode. [4] The hybrid vehicle of claim 1, wherein the threshold corresponds to a minimum coolant temperature required to meet interior heating requirements. [5] The hybrid vehicle of claim 1, wherein the controller is further programmed to direct the regenerative braking power to the electric heating element (76) in response to an oil temperature of the internal combustion engine (14) being less than a threshold. [6] A method for heating internal combustion engine coolant in a hybrid vehicle, comprising: to generate power with an electric machine (18) via regenerative braking; and direct the power from the electric machine (18) to an electric heating element (76) to heat the engine coolant based on a temperature of the engine coolant being less than a threshold, wherein the power directed to the electric heating element (76) is a portion of the total regenerative braking power that exceeds a threshold of a charging rate of a battery (20), and the threshold corresponds to a coolant reserve temperature that exceeds a minimum coolant temperature required for an EV operating mode or a minimum coolant temperature required to meet cabin heating requirements. [7] The method of claim 6, wherein the threshold corresponds to a minimum coolant temperature required to maximize internal combustion engine efficiency. [8] The method of claim 6, wherein the threshold corresponds to a minimum coolant temperature required for an EV operating mode. [9] The method of claim 6, wherein the threshold corresponds to a minimum coolant temperature required to meet interior heating requirements. [10] The method of claim 6, wherein the conducting is further performed based on an engine oil temperature being less than a threshold.

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