Vehicle and corresponding regenerative braking control system

Abstract

The invention provides a vehicle and a corresponding regenerative braking control system. A vehicle includes an electric machine, a friction brake, a brake pedal, and a controller. The controller is programmed to reduce a speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking in response to depression of the brake pedal to generate a first command to reduce the speed of the vehicle. The controller is further programmed to generate a second command to reduce the speed of the vehicle in response to (i) releasing the brake pedal after the first command, (ii) the speed of the vehicle being less than a threshold, and (iii) depressing the brake pedal after releasing the brake pedal, and reducing the speed of the vehicle via only friction braking.

Description

Technical Field

[0001] The present disclosure relates to a hybrid vehicle or an electric vehicle and a control system for the hybrid vehicle or the electric vehicle. Background Art

[0002] Hybrid and electric vehicles may include an electric machine configured to propel the vehicle or to decelerate the vehicle via regenerative braking. Summary of the invention

[0003] A vehicle includes an electric motor, a friction brake, a brake pedal, and a controller. The electric motor is configured to brake the vehicle via regenerative braking. The friction brake is configured to brake the vehicle via friction braking. The brake pedal is configured to generate a command to reduce the speed of the vehicle via regenerative braking or friction braking. The controller is programmed to generate a first command to reduce the speed of the vehicle in response to pressing the brake pedal and (i) reduce the speed of the vehicle via regenerative braking or (ii) reduce the speed of the vehicle via regenerative braking plus friction braking. The controller is also programmed to reduce the speed of the vehicle via friction braking only in response to (i) releasing the brake pedal after the first command, (ii) the speed of the vehicle is less than a threshold, and (iii) pressing the brake pedal after releasing the brake pedal to generate a second command to reduce the speed of the vehicle.

[0004] A vehicle includes an electric motor, a friction brake, and a controller. The electric motor is configured to brake the vehicle via regenerative braking. The friction brake is configured to brake the vehicle via friction braking. The controller is programmed to (i) reduce the speed of the vehicle via regenerative braking in response to a first command to reduce the speed of the vehicle. The controller is also programmed to limit the regenerative braking torque to the second negative value and reduce the speed of the vehicle (i) via friction braking or (ii) via friction braking plus regenerative braking in response to a second command to reduce the speed of the vehicle after the torque of the electric motor increases from the first negative value to the second negative value, (i) the torque of the electric motor increases from a first negative value during the first command to a second negative value after the first command, (ii) the speed of the vehicle is less than a threshold, and (iii) the speed of the vehicle is reduced after the torque of the electric motor increases from the first negative value to the second negative value.

[0005] A vehicle includes an electric motor, a friction brake, and a controller. The electric motor is configured to brake the vehicle via regenerative braking. The friction brake is configured to brake the vehicle via friction braking. The controller is programmed to (i) reduce the speed of the vehicle via regenerative braking in response to a first command to reduce the speed of the vehicle. The controller is also programmed to control the regenerative braking torque to zero and reduce the speed of the vehicle via friction braking only in response to a second command to reduce the speed of the vehicle after the torque of the electric motor increases from the negative value to zero or positive value, (ii) the speed of the vehicle is less than a threshold, and (iii) the speed of the vehicle is reduced after the torque of the electric motor increases from the negative value to zero or positive value. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of a representative powertrain system of an electric vehicle;

[0007] Figure 2 is a flow chart illustrating a method for controlling regenerative braking in an electric vehicle; and

[0008] Figure 3 is a flowchart showing a method for setting a low speed flag, the low speed flag being used as Figure 2 The input of the method shown in . DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples and that other embodiments may take different and alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show the details of a particular component. Therefore, the specific structural details and functional details disclosed herein should not be interpreted as limiting, but only as a representative basis for teaching those skilled in the art to adopt the embodiments in different ways. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any one of the drawings may be combined with the features shown in one or more other drawings to produce embodiments that are not explicitly shown or described. The combination of features shown provides representative embodiments for typical applications. However, for specific applications or embodiments, various combinations and modifications of features consistent with the teachings of the present disclosure may be desired.

[0010] refer to Figure 1 , showing a schematic diagram of an electric vehicle 10 according to an embodiment of the present disclosure. Figure 1Representative relationships between components are shown. The physical layout and orientation of the components within the vehicle may vary. The electric vehicle 10 includes a powertrain 12. The powertrain 12 includes an electric machine, such as an electric motor / generator (M / G) 14, which drives a transmission (or gearbox) 16. More specifically, the M / G 14 can be rotatably connected to an input shaft 18 of the transmission 16. The transmission 16 can be placed in PRNDSL (parking, reverse, neutral, driving, sports, low gear) via a transmission gear selector (not shown). The transmission 16 can have a fixed gear transmission relationship that provides a single gear ratio between the input shaft 18 and the output shaft 20 of the transmission 16. A torque converter (not shown) or a starting clutch (not shown) can be provided between the M / G 14 and the transmission 16. Alternatively, the transmission 16 can be a multi-speed ratio automatic transmission. The associated traction battery 22 is configured to deliver power to the M / G 14 or receive power from the M / G.

[0011] The M / G 14 is a drive source for the electric vehicle 10 configured to propel the electric vehicle 10. The M / G 14 may be implemented by any of a variety of types of electric machines. For example, the M / G 14 may be a permanent magnet synchronous motor. The power electronics 24 regulates the direct current (DC) power provided by the battery 22 as required by the M / G 14, as will be described below. For example, the power electronics 24 may provide three-phase alternating current (AC) to the M / G 14.

[0012] If the transmission 16 is a multi-ratio automatic transmission, the transmission 16 may include a gear set (not shown) that is selectively placed in different gear ratios by selectively engaging friction elements such as clutches and brakes (not shown) to establish a desired plurality of discrete or multi-ratio gear ratios. The friction elements may be controlled by a shift schedule that connects and disconnects certain elements of the gear set to control the gear ratio between the transmission output shaft 20 and the transmission input shaft 18. The transmission 16 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 environmental conditions. Power and torque from the M / G 14 may be delivered to and received by the transmission 16. The transmission 16 then provides the powertrain output power and torque to the output shaft 20.

[0013] It should be understood that the hydraulically controlled transmission 16, which may be coupled to a torque converter (not shown), is merely one example of a gearbox or transmission arrangement; any multi-ratio gearbox that accepts one or more input torques from a power source (e.g., M / G 14) and then provides torque to an output shaft (e.g., output shaft 20) at different gear ratios is acceptable for use with embodiments of the present disclosure. For example, the transmission 16 may be implemented by an automated mechanical (or manual) transmission (AMT) that includes one or more servomotors to translate / rotate a shift fork along a shift rail to select a desired gear ratio. As is generally understood by those of ordinary skill in the art, an AMT may be used, for example, in applications with higher torque requirements.

[0014] like Figure 1 As shown in the representative embodiment of FIG. 1 , the output shaft 20 is connected to a differential 26. The differential 26 drives a pair of drive wheels 28 via respective axles 30 connected to the differential 26. The differential 26 transmits substantially equal torque to each wheel 28, while allowing for slight speed differences, such as when the vehicle is turning. Different types of differentials or similar devices may be used to distribute torque from the drivetrain to one or more wheels. In some applications, the torque distribution may vary depending on, for example, a particular operating mode or operating condition.

[0015] The powertrain system 12 also includes an associated controller 32, such as a powertrain control unit (PCU). Although shown as one controller, the controller 32 may be part of a larger control system and may be controlled by various other controllers throughout the vehicle 10, such as a vehicle system controller (VSC). It should therefore be understood that the powertrain control unit 32 and one or more other controllers may be collectively referred to as a "controller" that controls various actuators in response to signals from various sensors to control functions such as operating the M / G 14 to provide wheel torque or charging the battery 22, selecting or scheduling transmission shifts, etc. The controller 32 may include a microprocessor or central processing unit (CPU) that communicates with various types of computer-readable storage devices or media. The computer-readable storage devices or media may include volatile and non-volatile storage devices such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operating variables when the CPU is powered off. The computer-readable storage device or medium may be implemented using any of several known memory devices, such as a PROM (programmable read-only memory), an EPROM (electrical PROM), an EEPROM (electrically erasable PROM), flash memory, or any other electrical, magnetic, optical, or combination memory device capable of storing data, some of which represents executable instructions used by the controller to control the vehicle.

[0016] The controller 32 communicates with various vehicle sensors and actuators via an input / output (I / O) interface (including input channels and output channels), which may be implemented as a single integrated interface that provides various raw data or signal conditioning, processing and / or conversion, short circuit protection, etc. Alternatively, one or more dedicated hardware or firmware chips may be used to condition and process specific signals before supplying them to the CPU. Figure 1 As generally shown in the representative embodiment of FIG. 1 , the controller 32 may transmit signals to the M / G 14, the battery 22, the transmission 16, the power electronics 24, and other components of the powertrain 12 that may include but are not described in detail. Figure 1 14 and transmission 16). Although not explicitly shown, one of ordinary skill in the art will recognize the various functions or components that may be controlled by the controller 32 within each of the subsystems identified above. Representative examples of parameters, systems, and / or components that may be actuated directly or indirectly using control logic and / or algorithms executed by the controller 32 include front end accessory drive (FEAD) components such as an alternator, an air conditioning compressor, battery charging or discharging, regenerative braking, M / G 14 operation, clutch pressure of the transmission gearbox 16, or any other clutch that is part of the powertrain 12, etc. For example, sensors transmitting input through the I / O interface can be used to indicate wheel speed (WS1, WS2), vehicle speed (VSS), coolant temperature (ECT), accelerator pedal position (PPS), ignition switch position (IGN), ambient air temperature (e.g., ambient air temperature sensor 33), transmission gear, gear ratio or mode, transmission oil temperature (TOT), transmission input and output speeds or shift pattern (MDE), battery temperature, voltage, current or state of charge (SOC).

[0017] The control logic or functions performed by the controller 32 may be represented by a flowchart or similar diagram in one or more of the accompanying drawings. These drawings provide representative control strategies and / or logic that can be implemented using one or more processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc.). Thus, the various steps or functions shown may be performed in the order shown, may be performed in parallel, or may be omitted in some cases. Although not always explicitly shown, it will be recognized by those of ordinary skill in the art that one or more of the steps or functions shown may be repeatedly performed depending on the specific processing strategy used. Similarly, the processing order 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 and / or powertrain controller (such as controller 32). Of course, depending on the specific application, the control logic may be implemented in software, hardware, or a combination of software and hardware in one or more controllers. When implemented in software, the control logic may be provided in one or more computer-readable storage devices or media, which store data representing codes or instructions executed by a computer to control a vehicle or a vehicle subsystem. The computer-readable storage device or medium may include one or more of several known physical devices that use electrical, magnetic, and / or optical storage to hold executable instructions and associated calibration information, operating variables, and the like.

[0018] The driver of the vehicle uses an accelerator pedal 34 to provide the desired torque, power or drive command for propelling the vehicle to the powertrain 12 (or more specifically, the M / G 14). Typically, depressing and releasing the accelerator pedal 34 generates an accelerator pedal position signal, which can be interpreted by the controller 32 as a need for increased power or reduced power, respectively. The brake pedal 36 is also used by the driver of the vehicle to provide the desired braking torque to decelerate the vehicle. Typically, depressing the brake pedal 36 generates a brake pedal position signal, which can be interpreted by the controller 32 as a need to reduce or lower the vehicle speed. Based on inputs from the accelerator pedal 34 and / or the brake pedal 36, the controller 32 commands torque and / or power to the M / G 14 and the friction brake 38. The friction brake 38 is configured to brake the vehicle 10 via friction braking (e.g., via brake pads engaging a brake disc or brake shoes engaging a drum). The controller 32 also controls the timing of shifting in the transmission 16.

[0019] A command to reduce or slow down the speed of the vehicle 10 (which may be generated via depression of the brake pedal 36) may include an A term corresponding to the amount of friction braking (i.e., braking via the friction brakes 38) and a B term corresponding to the amount of regenerative braking (e.g., braking via the M / G 14 operating as a generator to reduce the speed of the vehicle). The ratio of the A term to the B term may depend on the degree or rate at which the brake pedal is depressed, the capacity of the battery 22 to receive energy, etc. For example, the B term may be low or drop to zero if a large braking command is generated (e.g., full depression of the brake pedal 36 or rapid depression of the brake pedal 36), or if the capacity of the battery 22 to receive charge is low.

[0020] The M / G 14 can function as a motor and provide driving force for the powertrain 12. To drive the vehicle with the M / G 14, the traction battery 22 transmits stored electrical energy to the power electronics 24, which may include, for example, inverter and rectifier circuits, via the wiring 40. The inverter circuit of the power electronics 24 can convert the DC voltage from the battery 22 into an AC voltage to be used by the M / G 14. The rectifier circuit of the power electronics 24 can convert the AC voltage from the M / G 14 into a DC voltage to be stored by the battery 22. The controller 32 commands the power electronics 24 to convert the voltage from the battery 22 into an AC voltage provided to the M / G 14 to provide positive or negative torque to the input shaft 18.

[0021] The M / G 14 also functions as a generator and converts kinetic energy from the powertrain 12 into electrical energy for storage in the battery 22. More specifically, the M / G 14 may function as a generator during regenerative braking events, in which torque and rotational (or kinetic) energy from the spinning wheels 28 are transferred back through the transmission 16 and converted into electrical energy for storage in the battery 22. Regenerative braking refers to a scenario in which the M / G 14 operates as a generator to both brake the vehicle and recover kinetic energy, which may then be stored in the battery 22.

[0022] It should be understood that the vehicle configurations described herein are exemplary only and are not intended to be limiting. Other electric vehicle or hybrid electric vehicle configurations should be interpreted as disclosed herein. Other electric or hybrid vehicle configurations may include, but are not limited to, series hybrid vehicles, parallel hybrid vehicles, series-parallel hybrid vehicles, plug-in hybrid electric vehicles (PHEVs), fuel cell hybrid vehicles, battery-operated electric vehicles (BEVs), or any other vehicle configuration known to those of ordinary skill in the art.

[0023] In a hybrid configuration including an internal combustion engine such as a gasoline, diesel or natural gas powered engine or a fuel cell, the controller 32 may be configured to control various parameters of such an internal combustion engine. Representative examples of internal combustion parameters, systems and / or components that may be directly or indirectly actuated using control logic and / or algorithms executed by the controller 32 include fuel injection timing, rate and duration, throttle position, spark plug firing timing (for spark ignition engines), intake / exhaust valve timing and duration, etc. Sensors that transmit inputs from such an internal combustion engine to the controller 32 via an I / O interface may be used to indicate turbocharger boost pressure, crankshaft position (PIP), engine speed (RPM), intake manifold pressure (MAP), throttle position (TP), exhaust oxygen (EGO) or other exhaust constituent amounts or pressures, intake air flow (MAF), etc.

[0024] It should be understood that Figure 1 The schematic diagrams shown in are representative only and are not intended to be limiting. Other configurations are contemplated without departing from the scope of the present disclosure. For example, the vehicle powertrain 12 may be configured to deliver power and torque to one or both of the front wheels, rather than the rear wheels 28 shown.

[0025] refer to Figure 2 , a flow chart of a method 200 for controlling regenerative braking in a vehicle 10 is shown. The flow chart may correspond to a braking event of the vehicle 10. The method 200 may be stored as control logic and / or an algorithm within the controller 32. The controller 32 may implement the method 200 by controlling various components of the vehicle 10. The method begins at box 202, where it is determined whether the brake pedal 36 is on (e.g., whether the brake pedal 36 is depressed so that a braking command is generated by the controller 32). If the brake pedal 36 is not on (e.g., if the brake pedal 36 is not depressed so that a braking command is not generated), the method 200 proceeds to box 204, where any existing braking commands (e.g., friction braking commands to the friction brakes 38 and / or regenerative braking commands to the M / G 14) are canceled. Moreover, a regenerative braking command may be generated in response to the accelerator pedal 34 being in a sufficiently low position. The method 200 then returns to box 202.

[0026] Returning to frame 202, if the brake pedal 36 is on, the method 200 proceeds to frame 206, where it is determined whether a low vehicle speed flag has been set. The low vehicle speed flag may correspond to a vehicle speed less than a threshold or less than a threshold plus a hysteresis value, which will be discussed below with respect to Figure 3Further discussion. If the low vehicle speed flag has not been set, the method 200 proceeds to box 208, where a command is generated to brake the vehicle 10 and regenerative braking is not modified. More specifically, at box 208, (i) the M / G 14 may brake the vehicle 10 via regenerative braking only, (ii) the friction brakes 38 may brake the vehicle 10 via friction braking only, or (iii) the vehicle 10 may brake via a combination of regenerative braking via the M / G 14 and friction braking via the friction brakes 38, depending on the desired A and B terms. The method 200 then returns to box 202.

[0027] Returning to frame 206, if it is determined that the low vehicle speed flag has been set, the method 200 proceeds to frame 210, where it is determined whether regenerative braking is being delivered (e.g., whether the M / G 14 is braking the vehicle 10). If regenerative braking is not being delivered, the method 200 proceeds to frame 212, where the torque delivered by the powertrain 12 (e.g., the torque generated by the M / G 14) is maintained at a value greater than or equal to zero (i.e., a zero or positive torque value is maintained) to prevent a gap-through event within the powertrain 12 during the braking event. The friction brakes 38 will provide all braking force during the braking event, which ends at frame 212. The method 200 then returns to frame 202.

[0028] It should be noted that positive torque values ​​may correspond to the powertrain 12 outputting torque (e.g., the M / G 14 operating as a motor to generate torque to propel the vehicle 10), while negative torque values ​​may correspond to the powertrain 12 receiving or absorbing torque (e.g., the M / G 14 operating as a generator to perform regenerative braking operations to absorb kinetic energy to recharge the battery). Thus, an increase in regenerative braking torque may correspond to a decrease in the negative torque value, but an increase in the absolute torque value.

[0029] Returning to frame 210, if it is determined that regenerative braking is being delivered, the method 200 proceeds to frame 214, where it is determined whether the torque of the powertrain 12 is greater than a threshold. If the torque of the powertrain 12 is not greater than the threshold, the method 200 proceeds to frame 208. If it is determined that the torque delivered by the powertrain 12 (e.g., the torque generated or received by the M / G 14) is greater than the threshold, the powertrain is approaching a gap crossing event and the method 200 proceeds to frame 216, where the torque delivered by the powertrain 12 (e.g., the torque generated or received by the M / G 14) is prevented from being further negative during the braking event (e.g., the regenerative torque, because the absolute value is modified and cannot increase). The method 200 then returns to frame 202.

[0030] refer to Figure 3 , showing the Figure 2206 in the flowchart of the method 300 of setting the low speed flag at the box 206 in the controller 32. The method 300 can be stored in the controller 32 as control logic and / or algorithm. The controller 32 can implement the method 300 by controlling various components of the vehicle 10. The method 300 starts at box 302, where it is determined whether the speed of the vehicle 10 is less than a threshold. If the speed of the vehicle is less than the threshold, the method 300 proceeds to box 304, where the low speed flag is set, and then the method 300 returns to box 302. If the speed of the vehicle is not less than the threshold, the method 300 proceeds to box 306, where it is determined whether the speed of the vehicle 10 is greater than the threshold plus hysteresis (e.g., the threshold from box 302 plus the offset value). If the speed of the vehicle 10 is not greater than the threshold plus hysteresis, the method 300 returns to box 302. If the speed of the vehicle 10 is greater than the threshold plus hysteresis, the method 300 proceeds to box 308, where the low speed flag is cleared. Then, the method 300 returns to box 302.

[0031] The first use case scenario may correspond to the controller 32 generating a first command to reduce the speed of the vehicle 10 (e.g., via depressing the brake pedal 36) and generating a second command to reduce the speed of the vehicle 10 (e.g., via depressing the brake pedal 36) subsequent to the first command, wherein (i) the intermediate event interrupts the first command to reduce the speed of the vehicle 10, (ii) the intermediate event is subsequent to the first command to reduce the speed of the vehicle 10, and (iii) the intermediate event is prior to the second command to reduce the speed of the vehicle 10. In the first use case scenario, the first command to reduce the speed of the vehicle 10 results in an unmodified regenerative braking command at box 208, while the second command to reduce the speed of the vehicle 10 results in a modified regenerative braking command at box 216. The braking event resulting from the first command to reduce the speed of the vehicle 10 may include regenerative braking only or a combination of regenerative braking and friction braking.

[0032] The intermediate event in the first use case scenario may correspond to releasing the brake pedal 36 and / or the torque of the M / G 14 increasing from a first negative value during the first command to a second negative value after the first command, which may be caused by the introduction or increase of creep torque and / or a decrease in regenerative braking torque caused by releasing the brake pedal 36. The absolute value of the first negative value may be greater than the absolute value of the second negative value because the increase in the torque of the M / G 14 from the first negative value to the second negative value may correspond to a decrease in regenerative braking torque. Finally, in the first use case scenario, during the braking event generated by the second command to reduce the speed of the vehicle 10, the regenerative braking torque may be limited to the second negative value (e.g., the regenerative braking torque may be limited to a value between the second negative value and zero). More specifically, the braking event generated by the second command to reduce the speed of the vehicle 10 may include friction braking only or a combination of regenerative braking and friction braking, wherein the regenerative braking is limited to the second negative value.

[0033] The second use case scenario may correspond to the controller 32 generating a first command to reduce the speed of the vehicle 10 (e.g., via depressing the brake pedal 36) and generating a second command to reduce the speed of the vehicle 10 (e.g., via depressing the brake pedal 36) subsequent to the first command, wherein (i) the intermediate event interrupts the first command to reduce the speed of the vehicle 10, (ii) the intermediate event is subsequent to the first command to reduce the speed of the vehicle 10, and (iii) the intermediate event is prior to the second command to reduce the speed of the vehicle 10. In the second use case scenario, the first command to reduce the speed of the vehicle 10 results in an unmodified regenerative braking command at box 208, while the second command to reduce the speed of the vehicle 10 results in a modified regenerative braking command at box 216. The braking event resulting from the first command to reduce the speed of the vehicle 10 may include regenerative braking only or a combination of regenerative braking and friction braking.

[0034] The intermediate event in the second use case scenario may correspond to releasing the brake pedal 36 and / or the torque of the M / G 14 increasing from a negative value during the first command to a zero or positive value after the first command, which may be caused by the introduction or increase of creep torque and / or a decrease in regenerative braking torque due to the release of the brake pedal 36. Finally, in the second use case scenario, regenerative braking may control torque to zero (e.g., the torque of the M / G 14 may be zero or positive) to prevent gap crossing, and the speed of the vehicle 10 may be reduced via friction-only braking during the braking event resulting from the second command to reduce the speed of the vehicle 10.

[0035] Once the low vehicle speed flag has been set at box 206, and once the regenerative braking torque has been modified at box 216 or has been eliminated at box 212, the method 200 will proceed to box 212, where regenerative braking is not applied, or will proceed to box 216, where the torque delivered by the powertrain 12 (e.g., torque generated by the M / G 14) is prevented from being further negative (e.g., regenerative torque, because the absolute value is modified and cannot increase) until the low vehicle speed flag has been cleared. Clearing the low vehicle speed flag requires increasing the speed of the vehicle to greater than the threshold value plus the hysteresis value at box 306. Once the low vehicle speed flag has been set at box 206, and once the regenerative braking torque has been modified at box 216 or has been eliminated at box 212, the method 200 may be prevented from proceeding to box 208.

[0036] In the first use case scenario, the low speed flag may remain or may be cleared. If there is an increase in vehicle speed after the second command to reduce the speed of the vehicle 10 and after the third command to reduce the speed of the vehicle in the first use case scenario, the braking event generated by the third command to reduce the speed of the vehicle 10 may include friction braking only or a combination of regenerative braking and friction braking, wherein if the increase in vehicle speed after the second command does not clear the low speed flag (i.e., if the increase in vehicle speed is less than the threshold plus hysteresis), the regenerative braking is limited to the second negative value (e.g., preventing the method 200 from returning to box 208). In other words, if the increase in vehicle speed after the second command clears the low speed flag (i.e., if the increase in vehicle speed is greater than the threshold plus hysteresis), the braking event generated by the third command to reduce the speed of the vehicle in the first use case scenario may include regenerative braking or a combination of regenerative braking and friction braking (e.g., the method 200 may return to box 208).

[0037] In the second use case scenario, the low speed flag may remain or may be cleared. If there is an increase in vehicle speed after the second command to reduce the speed of the vehicle 10 and after the third command to reduce the speed of the vehicle in the second use case scenario, if the increase in vehicle speed after the second command does not clear the low speed flag (i.e., if the increase in vehicle speed is less than the threshold plus hysteresis), then the braking event generated by the third command to reduce the speed of the vehicle 10 may include friction braking only (e.g., preventing the method 200 from returning to box 208). In other words, if the increase in vehicle speed after the second command clears the low speed flag (i.e., if the increase in vehicle speed is greater than the threshold plus hysteresis), then the braking event generated by the third command to reduce the speed of the vehicle in the second use case scenario may include regenerative braking or a combination of regenerative braking and friction braking (e.g., the method 200 may return to box 208).

[0038] A third use case scenario may correspond to the controller 32 generating a single command to reduce the speed of the vehicle 10 (e.g., via depressing the brake pedal 36), where the intervening events do not interrupt the single command to reduce the speed of the vehicle 10 (e.g., the brake pedal 36 is not released or the torque is not increased to greater than the threshold at block 214). In the third use case scenario, the single command to reduce the speed of the vehicle 10 may result in an unmodified regenerative braking command at block 208, where regenerative braking is utilized to decelerate the vehicle to substantially zero speed. Such a scenario of utilizing regenerative braking to decelerate the vehicle to substantially zero speed may correspond to a situation where there is no release of the brake pedal 36. Substantially zero speed may refer to any incremental speed value between one mile per hour and zero miles per hour.

[0039] A fourth use case scenario may include: (i) an increase in vehicle speed greater than a threshold plus hysteresis resulting in a low speed flag being cleared (the low speed flag being cleared after a second command to reduce the speed of the vehicle 10 in either the first use case scenario or the second use case scenario), (ii) a brake pedal being depressed to generate a command to reduce the speed of the vehicle (e.g., the brake pedal being depressed to generate a third command after the low speed flag is cleared in either the first use case scenario or the second use case scenario), and (iii) a continued increase in vehicle speed due to the vehicle being positioned on an inclined surface during the third command. In the fourth use case scenario, the controller 32 may be programmed to reduce the rate at which regenerative braking is increased.

[0040] This solution described herein provides several advantages. For example, in contrast to current systems that eliminate regenerative braking at low speeds, allowing regenerative braking to be reduced to zero speed or near zero speed has significant efficiency and drivability advantages (e.g., recovering additional energy). When the driver changes his mind, the main disadvantage of performing regenerative braking at very low speeds without the hysteresis described herein is demonstrated. Leaving the brake pedal (i.e., releasing the brake pedal 36) at a speed low enough to obtain positive creep torque and stepping on it again (i.e., stepping on the brake pedal 36) may trigger two gap crossing events (e.g., the first gap crossing of the powertrain torque from negative torque to positive torque and the second gap crossing of the powertrain torque from positive torque to negative torque). In particular, when the driver re-steps on the brake pedal, the second gap crossing event may be problematic. At the moment when the powertrain response rate may not be able to perform such a fast response, a fast response time from the system is required. Similarly, the current system circumvents this situation by eliminating regenerative braking at low speeds. By using hysteresis, we can get all of the above benefits (e.g., regenerative braking reduced to zero speed or near zero speed) while avoiding the disadvantages associated with changing one's mind at low speeds (e.g., causing several gap crossing events that affect controllability and response time).

[0041] It should be understood that the first, second, third, fourth, etc. labels for any components, states or conditions described herein may be rearranged in the claims so that they are arranged in chronological order with respect to the claims. In addition, it should be understood that any components, states or conditions described herein without a numerical designation may be given a first, second, third, fourth, etc. designation in the claims if one or more specific components, states or conditions are claimed.

[0042] The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments can be combined to form additional embodiments that may not be explicitly described or shown. Although various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, it should be recognized by those of ordinary skill in the art that one or more features or characteristics may be compromised to achieve the desired overall system properties, depending on the specific application and implementation. To this end, embodiments that are described as being less desirable than other embodiments or prior art implementations with respect to one or more characteristics are within the scope of the present disclosure and may be desirable for a particular application.

[0043] According to the present invention, a vehicle is provided, comprising: a motor configured to brake the vehicle via regenerative braking; a friction brake configured to brake the vehicle via friction braking; a brake pedal configured to generate a command to reduce the speed of the vehicle via regenerative braking or friction braking; and a controller programmed to reduce the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking in response to pressing the brake pedal to generate a first command to reduce the speed of the vehicle, and to reduce the speed of the vehicle via friction braking only in response to (i) releasing the brake pedal after the first command, (ii) the speed of the vehicle being less than a threshold, and (iii) pressing the brake pedal after releasing the brake pedal to generate a second command to reduce the speed of the vehicle.

[0044] According to an embodiment, the controller is also programmed to reduce the speed of the vehicle via friction-only braking in response to (i) an increase in vehicle speed that is less than the threshold plus hysteresis after the second command and (ii) pressing the brake pedal after the vehicle speed increase to generate a third command to reduce the speed of the vehicle.

[0045] According to an embodiment, the controller is also programmed to respond to (i) an increase in vehicle speed greater than the threshold plus hysteresis after the second command and (ii) pressing the brake pedal after the vehicle speed increase to generate a third command to reduce the speed of the vehicle, thereby reducing the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking.

[0046] According to an embodiment, the controller is also programmed to limit the torque of the motor to greater than or equal to the second negative value during the second command in response to (i) pressing the brake pedal after releasing the brake pedal to generate the second command to reduce the speed of the vehicle and (ii) the torque of the motor increasing from a first negative value to a second negative value when the brake pedal is released.

[0047] According to an embodiment, the controller is also programmed to limit the torque of the motor to greater than or equal to zero during the second command in response to (i) the brake pedal being depressed after the brake pedal is released to generate the second command to reduce the speed of the vehicle and (ii) the torque of the motor increasing from a negative value to zero or a positive value when the brake pedal is released.

[0048] According to an embodiment, the controller is also programmed to reduce the rate at which regenerative braking is increased in response to (i) an increase in vehicle speed that is greater than the threshold plus hysteresis after the second command, (ii) depression of the brake pedal after the vehicle speed increase to generate a third command to reduce the speed of the vehicle, and (iii) a continued increase in vehicle speed due to the vehicle being positioned on an inclined surface during the third command.

[0049] According to the present invention, a vehicle is provided, comprising: an electric motor configured to brake the vehicle via regenerative braking; a friction brake configured to brake the vehicle via friction braking; and a controller programmed to (i) reduce the speed of the vehicle via regenerative braking in response to a first command to reduce the speed of the vehicle, and to limit the regenerative braking torque to the second negative value and reduce the speed of the vehicle (i) via friction braking or (ii) via friction braking plus regenerative braking in response to a second command to reduce the speed of the vehicle in which (i) the torque of the electric motor increases from a first negative value during the first command to a second negative value after the first command, (ii) the speed of the vehicle is less than a threshold, and (iii) the speed of the vehicle is reduced after the torque of the electric motor increases from the first negative value to the second negative value.

[0050] According to an embodiment, the controller is further programmed to control the regenerative braking torque to zero and reduce the speed of the vehicle via friction braking only in response to (i) the torque of the motor increases from the first negative value during the first command to zero or a positive value after the first command, (ii) the speed of the vehicle is less than the threshold, and (iii) a third command to reduce the speed of the vehicle after the torque of the motor increases from the first negative value to the zero or positive value.

[0051] According to an embodiment, the controller is also programmed to reduce the speed of the vehicle (i) via friction braking or (ii) via friction braking plus regenerative braking in response to (i) an increase in vehicle speed that is less than the threshold plus hysteresis after the second command and (ii) a third command to reduce the speed of the vehicle after the vehicle speed increase.

[0052] According to an embodiment, the controller is also programmed to reduce the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking in response to (i) an increase in vehicle speed that is greater than the threshold plus hysteresis after the second command and (ii) a third command to reduce the speed of the vehicle after the vehicle speed increase.

[0053] According to an embodiment, the absolute value of the first negative value is greater than the absolute value of the second negative value.

[0054] According to an embodiment, the controller is further programmed to reduce the rate at which regenerative braking is increased in response to (i) an increase in vehicle speed that is greater than the threshold plus hysteresis after the second command, (ii) a third command that reduces the speed of the vehicle after the vehicle speed increase, and (iii) a continued increase in vehicle speed due to the vehicle being positioned on an inclined surface during the third command.

[0055] According to an embodiment, the controller is further programmed to reduce the speed of the vehicle to substantially zero via regenerative braking during the first command without releasing the brake pedal.

[0056] According to the present invention, a vehicle is provided, comprising: a motor configured to brake the vehicle via regenerative braking; a friction brake configured to brake the vehicle via friction braking; and a controller programmed to (i) reduce the speed of the vehicle via regenerative braking in response to a first command to reduce the speed of the vehicle, and to control the regenerative braking torque to zero and reduce the speed of the vehicle via friction braking only in response to a second command to reduce the speed of the vehicle after the torque of the motor increases from the negative value to the zero or positive value, wherein the regenerative braking torque is controlled to zero.

[0057] According to an embodiment, the controller is further programmed to limit the regenerative braking torque to the second negative value and reduce the speed of the vehicle (i) via friction braking or (ii) via friction braking plus regenerative braking in response to (i) the torque of the motor increases from the negative value during the first command to a second negative value after the first command, (ii) the speed of the vehicle is less than the threshold, and (iii) a third command to reduce the speed of the vehicle after the torque of the motor increases from the negative value to the second negative value.

[0058] According to an embodiment, the absolute value of the negative value is greater than the absolute value of the second negative value.

[0059] According to an embodiment, the controller is also programmed to reduce the speed of the vehicle via friction-only braking in response to (i) an increase in vehicle speed that is less than the threshold plus hysteresis after the second command and (ii) a third command to reduce the speed of the vehicle after the vehicle speed increase.

[0060] According to an embodiment, the controller is also programmed to reduce the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking in response to (i) an increase in vehicle speed that is greater than the threshold plus hysteresis after the second command and (ii) a third command to reduce the speed of the vehicle after the vehicle speed increase.

[0061] According to an embodiment, the controller is further programmed to reduce the rate at which regenerative braking is increased in response to (i) an increase in vehicle speed that is greater than the threshold plus hysteresis after the second command, (ii) a third command that reduces the speed of the vehicle after the vehicle speed increase, and (iii) a continued increase in vehicle speed due to the vehicle being positioned on an inclined surface during the third command.

[0062] According to an embodiment, the controller is further programmed to reduce the speed of the vehicle to substantially zero via regenerative braking during the first command without releasing the brake pedal.

Claims

1. A vehicle comprising: an electric machine configured to brake the vehicle via regenerative braking; a friction brake configured to brake the vehicle via friction braking; a brake pedal configured to generate a command to reduce the speed of the vehicle via regenerative braking or friction braking; as well as A controller programmed to: generating a first command to reduce the speed of the vehicle in response to depression of the brake pedal, and reducing the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking, and The speed of the vehicle is reduced via friction-only braking in response to (i) releasing the brake pedal after the first command, (ii) the speed of the vehicle being less than a threshold, and (iii) depressing the brake pedal after releasing the brake pedal to generate a second command to reduce the speed of the vehicle.

2. A vehicle as described in claim 1, wherein the controller is further programmed to reduce the speed of the vehicle via friction braking only in response to (i) an increase in vehicle speed that is less than the threshold plus hysteresis after the second command and (ii) pressing the brake pedal after the vehicle speed increase to generate a third command to reduce the speed of the vehicle.

3. A vehicle as described in claim 1, wherein the controller is further programmed to respond to (i) an increase in vehicle speed greater than the threshold plus hysteresis after the second command and (ii) pressing the brake pedal after the vehicle speed increase to generate a third command to reduce the speed of the vehicle, thereby reducing the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking.

4. A vehicle as described in claim 1, wherein the controller is further programmed to limit the torque of the motor to greater than or equal to the second negative value during the second command in response to (i) the brake pedal being depressed after the brake pedal is released to generate the second command to reduce the speed of the vehicle and (ii) the torque of the motor increasing from a first negative value to a second negative value when the brake pedal is released.

5. The vehicle of claim 1 wherein the controller is further programmed to limit the torque of the motor to greater than or equal to zero during the second command in response to (i) the brake pedal being depressed after the brake pedal is released to generate the second command to reduce the speed of the vehicle and (ii) the torque of the motor increasing from a negative value to zero or a positive value when the brake pedal is released.

6. The vehicle of claim 1 wherein the controller is further programmed to reduce the rate at which regenerative braking is increased in response to (i) an increase in vehicle speed greater than the threshold plus hysteresis after the second command, (ii) depression of the brake pedal after the vehicle speed increase to generate a third command to reduce the speed of the vehicle, and (iii) a continued increase in vehicle speed due to the vehicle being positioned on an inclined surface during the third command.

7. A vehicle comprising: an electric machine configured to brake the vehicle via regenerative braking; a friction brake configured to brake the vehicle via friction braking; as well as A controller programmed to: (i) reducing the speed of the vehicle via regenerative braking in response to a first command to reduce the speed of the vehicle, and In response to (i) the torque of the motor increases from a first negative value during the first command to a second negative value after the first command, (ii) the speed of the vehicle is less than a threshold, and (iii) a second command to reduce the speed of the vehicle after the torque of the motor increases from the first negative value to the second negative value, the regenerative braking torque is limited to the second negative value and the speed of the vehicle is reduced (i) via friction braking or (ii) via friction braking plus regenerative braking.

8. The vehicle of claim 7, wherein the controller is further programmed to control the regenerative braking torque to zero and reduce the speed of the vehicle via friction braking only in response to (i) the torque of the motor increases from the first negative value during the first command to zero or a positive value after the first command, (ii) the speed of the vehicle is less than the threshold, and (iii) a third command to reduce the speed of the vehicle after the torque of the motor increases from the first negative value to the zero or positive value.

9. A vehicle as described in claim 7, wherein the controller is further programmed to reduce the speed of the vehicle (i) via friction braking or (ii) via friction braking plus regenerative braking in response to (i) an increase in vehicle speed less than the threshold plus hysteresis after the second command and (ii) a third command to reduce the speed of the vehicle after the vehicle speed increase.

10. The vehicle of claim 7 wherein the controller is further programmed to reduce the speed of the vehicle (i) via regenerative braking or (ii) via regenerative braking plus friction braking in response to (i) an increase in vehicle speed greater than the threshold plus hysteresis following the second command and (ii) a third command to reduce the speed of the vehicle following the increase in vehicle speed.

11. The vehicle of claim 7 wherein the controller is further programmed to reduce the rate at which regenerative braking is increased in response to (i) an increase in vehicle speed greater than the threshold plus hysteresis following the second command, (ii) a third command to reduce the speed of the vehicle following the increase in vehicle speed, and (iii) a continued increase in vehicle speed due to the vehicle being positioned on an inclined surface during the third command.

12. The vehicle of claim 7, wherein the controller is further programmed to reduce the speed of the vehicle to substantially zero via regenerative braking during the first command without releasing a brake pedal.

13. A vehicle comprising: an electric machine configured to brake the vehicle via regenerative braking; a friction brake configured to brake the vehicle via friction braking; as well as A controller programmed to: (i) reducing the speed of the vehicle via regenerative braking in response to a first command to reduce the speed of the vehicle, and In response to (i) the torque of the motor increases from a first negative value during the first command to zero or a positive value after the first command, (ii) the speed of the vehicle is less than a threshold, and (iii) a second command to reduce the speed of the vehicle after the torque of the motor increases from the negative value to the zero or positive value, the regenerative braking torque is controlled to zero and the speed of the vehicle is reduced via friction braking only.

14. The vehicle of claim 13, wherein the controller is further programmed to limit the regenerative braking torque to the second negative value and reduce the speed of the vehicle (i) via friction braking or (ii) via friction braking plus regenerative braking in response to (i) the torque of the motor increases from the negative value during the first command to a second negative value after the first command, (ii) the speed of the vehicle is less than the threshold, and (iii) a third command to reduce the speed of the vehicle after the torque of the motor increases from the negative value to the second negative value.

15. The vehicle of claim 13 wherein the controller is further programmed to reduce the speed of the vehicle via friction-only braking in response to (i) an increase in vehicle speed less than the threshold plus hysteresis following the second command and (ii) a third command to reduce the speed of the vehicle following the increase in vehicle speed, and In response to (i) an increase in vehicle speed that is greater than the threshold plus hysteresis after the second command and (ii) the third command to reduce the speed of the vehicle after the vehicle speed increase, the speed of the vehicle is reduced (i) via regenerative braking or (ii) via regenerative braking plus friction braking.

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