Abstract:
A system for decelerating a hybrid vehicle, the system includes a continuously variable transmission (CVT), a brake pedal, an accelerator pedal, a sensor for detecting a vehicle deceleration, a memory for storing a target deceleration corresponding to a coasting deceleration of the vehicle, and a processor. When the brake pedal and the accelerator pedal are released, the vehicle coasts. If the vehicle deceleration does not match the target deceleration, the processor adjusts the torque output by the CVT so that the vehicle deceleration substantially matches the target deceleration.

Description:
BACKGROUND 
     1. Field 
     The present application relates to systems and methods for controlling deceleration of continuously variable transmission (CVT) vehicles. 
     2. Description of the Related Art 
     CVT vehicles do not have set gear ratios as in conventional transmissions. When a CVT vehicle coasts or travels with the accelerator and brake pedals released, the CVT vehicle does not decelerate like a conventional or step transmission vehicle. Rather, CVT vehicles often have logic which aids a driver decelerate the vehicle. For example, a hybrid vehicle may have a sequential mode that creates virtual torque steps. The hybrid vehicle may activate the virtual torque steps when going downhill while the brake pedal is depressed. However, it may be difficult for a driver to smoothly decelerate while moving downhill. The driver may also prefer to coast downhill rather than manage the braking and drive mode of the vehicle. 
     Thus, there is a need for CVT control logic which enhances driver experience by smoothly decelerating the vehicle. 
     SUMMARY 
     The present application relates to CVT vehicles which uses feedback to control the vehicle&#39;s deceleration regardless of a road grade. In one implementation, a system for controlling deceleration of a vehicle comprises a continuously variable transmission (CVT), a brake pedal, an accelerator pedal, a sensor for detecting a vehicle deceleration, a memory for storing a target deceleration corresponding to a coasting deceleration of the vehicle, and a processor configured to adjust a torque output by the CVT so that the vehicle deceleration substantially matches the target deceleration when the brake pedal and the accelerator pedal are released. The brake pedal and the accelerator pedal may each have an applied or depressed position or state and a released or unapplied position or state. 
     In another implementation, a system for controlling deceleration of a vehicle comprises a continuously variable transmission (CVT), a brake pedal, an accelerator pedal, an accelerometer for detecting a vehicle deceleration, a speed sensor for detecting a vehicle speed, a memory for storing a target deceleration corresponding to a coasting deceleration of the vehicle, and a processor configured to adjust a torque output by the CVT so that the vehicle deceleration substantially matches the target deceleration when the brake pedal and the accelerator pedal are released and the vehicle speed is within a predetermined range. 
     In yet another implementation, the present application provides a method for controlling deceleration of a vehicle comprising detecting a vehicle deceleration, determining a target deceleration corresponding to a coasting deceleration of the vehicle, comparing the vehicle deceleration with the target deceleration, determining a target torque to substantially match the vehicle deceleration with the target deceleration, and applying the target torque. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, obstacles, and advantages of the present application will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein: 
         FIG. 1  is a diagram of a hybrid vehicle including an engine and a transmission according to an implementation of the present application; 
         FIG. 2  is a conceptual block diagram of a deceleration control system according to an implementation of the present application; 
         FIG. 3  is a map illustrating torque limits according to an implementation of the present application; and 
         FIG. 4  is a flowchart of deceleration control logic according to an implementation of the present application. 
     
    
    
     DETAILED DESCRIPTION 
     Apparatus, systems and methods that implement the implementations of the various features of the present application will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate some implementations of the present application and not to limit the scope of the present application. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. 
     In one implementation, the present application includes a hybrid vehicle  100  as shown in  FIG. 1 . The hybrid vehicle  100  can include a drive force unit  105  and wheels  170 . The drive force unit  105  further includes an engine  110 , a first electric motor-generator  191 , a second electric motor-generator  192 , a battery unit  195 , an inverter box  197 , a brake pedal  140 , a brake pedal sensor  145 , an accelerator pedal  130 , an accelerator pedal sensor  135 , a transmission  120 , a processor  150 , a memory  160 , a button  180 , a speed sensor  182 , and an accelerometer  184 . In one implementation, the brake pedal  140  has an applied or depressed position or state and a released or unapplied position or state as determined by the brake pedal sensor  145 . In one implementation, the accelerator pedal  130  has an applied or depressed position or state and a released or unapplied position or state as determined by the accelerator pedal sensor  135 . 
     The engine  110  primarily drives the wheels  170 . The engine  110  can be an internal combustion engine. The internal combustion engine can combust fuel, such as gasoline, ethanol, diesel, biofuel, or other types of fuels which are suitable for combustion. The accelerator pedal sensor  135  can detect a pressure applied to the accelerator pedal  130  or a position of the accelerator pedal  130 , which can adjust the power and torque provided by the engine  110  and/or the first and second motor-generators  191  and  192 . The torque output by the engine  110  is received by the transmission  120 . The first and second motor-generators  191  and  192  can also output torque to the transmission  120 . The engine  110  and the first and second motor-generators  191  and  192  may be coupled through a planetary gear (not shown in  FIG. 1 ). The transmission  120  delivers an applied torque to the wheels  170 . The torque output by the engine  110  does not directly translate into the applied torque to the wheels  170 . 
     The first and second motor-generators  191  and  192  can serve as motors which output torque in a drive mode, and can serve as generators to recharge the battery unit  195  in a regeneration mode. The electric power delivered from or to the first and second motor-generators  191  and  192  passes through inverter box  197  to the battery unit  195 . The brake pedal sensor  145  can detect pressure applied to the brake pedal  140  or a position of the brake pedal  140 , which may further affect the applied torque to the wheels  170 . The speed sensor  182  is connected to an output shaft of the transmission  120  to detect a speed input which is converted into a vehicle speed by the processor  150 . The accelerometer  184  is connected to the body or engine of the hybrid vehicle  100  to detect the actual acceleration or deceleration of the hybrid vehicle  100 . 
     The button  180  may be a button on an instrument panel (not shown in  FIG. 1 ) of the hybrid vehicle  100 , or may be located elsewhere within the driver&#39;s reach, such as on or near a steering wheel, or on the dash. The button  180  may be a switch or other similar device having an on state and an off state, and capable of sending a signal indicating the on state or the off state. Alternatively, the button  180  may be a touch-sensitive area capable of sending signals which may be interpreted as on or off, or may be part of a touch-screen interface capable of sending on and off signals. The processor  150  may detect a signal from the button  180  to activate or deactivate the deceleration control logic. In other implementations, the deceleration control logic may activated and deactivated automatically and thus may not need to be activated by the driver, obviating the need for the button  180 . 
     The transmission  120  is a transmission suitable for a hybrid vehicle. The transmission  120  can be an ECVT, which is coupled to the engine  110  as well as the first and second motor-generators  191  and  192 . The transmission  120  can deliver torque output from a combination of the engine  110  and the first and second motor-generators  191  and  192 . The processor  150  controls the transmission  120 , utilizing data stored in the memory  160  to determine the applied torque delivered to the wheels  170 . For example, the processor  150  may determine that at a certain vehicle speed, the engine  110  should provide a fraction of the applied torque to the wheels  170  while the first motor-generator  191  and/or the second motor-generator  192  provides most of the applied torque. The processor  150  and the transmission  120  can control an engine speed of the engine  110  independently from the vehicle speed. 
       FIG. 2  presents a block diagram of a deceleration control system  200  according to one implementation of the present application. The deceleration control system  200  is a feedback system adjusting torque for deceleration. A hybrid vehicle (HV) system  210  provides a current vehicle speed, current gear position, and current vehicle acceleration (Gx), which is a longitudinal acceleration. The speed of the vehicle may be determined from the speed sensor  182 . The acceleration of the vehicle may be determined from the accelerometer  184 . The gear position may be available from the transmission  120  or other related component, such as the processor  150 . The HV system  210  controls a propeller shaft torque Tp. 
     A target deceleration logic  230  uses the speed and the gear position to determine a target deceleration (target G). The target deceleration corresponds to a coasting deceleration of the vehicle. The coasting deceleration may correspond to the deceleration of the vehicle with the accelerator pedal and brake pedal released under normal driving circumstances, such as on a level road at or near sea level. 
     A deceleration control  220  receives the current vehicle acceleration Gx and the target deceleration (target G) to determine what propeller shaft torque (Tp OUT) must be added or subtracted to achieve the target deceleration. The torque Tp OUT is applied until Gx matches or substantially matches target G. The torque may be varied by changing the speeds of the engine and/or the motors-generators. The additional torque may be added to or subtracted from the current propeller shaft torque Tp. 
     When Gx matches or substantially matches target G, the vehicle decelerates as if it was coasting. For example, the vehicle  100  may be travelling downhill on a long, shallow downgrade. The driver may not wish to actively manage deceleration and may choose to release the accelerator pedal  130  and the brake pedal  140  to coast. However, the vehicle  100  decelerates slower when travelling down a long, shallow downgrade than on a flat, level road. Applying Tp OUT changes the deceleration of the vehicle  100  to more closely match the coasting deceleration on a level road. 
     At a feedback loop  250 , the torque Tp OUT is added to the current torque Tp, which is then detected by the HV system  210  to continue this feedback loop. For example, the Tp may have incrementally adjusted the current vehicle acceleration closer to the target deceleration. Based on the new current vehicle acceleration, the target deceleration logic  230  may calculate a new target deceleration and the deceleration control logic  220  may then calculate a new Tp OUT. 
       FIG. 3  illustrates a map  300  of torque limits based on engine speed and torque. A vehicle road load curve  310  corresponds to a road load, which is a load put on by a vehicle due to its weight, bearings, gears, aerodynamic drag, etc. The road load may be measured by the torque produced when the vehicle is driving in neutral. The road load curve  310  corresponds to the expected road load when the vehicle is driving in normal conditions, such as on a level road. 
     The map  300  further shows torque limits at various accelerator pedal applications. The maximum torque limit curve  330  corresponds to 100% accelerator pedal application. The map  300  shows curves corresponding to 100%, 50%, and 20%, but in other implementations other applications may be used, such as every 10%. For a given pedal application, such as 100%, the corresponding curve, such as the maximum torque limit curve  330 , may be used. For pedal applications without a corresponding curve, a curve is interpolated between the two nearest curves. For example, a 95% pedal application is interpolated from the 90% and 100% curves. 
     At 0% pedal application, the torque limits may vary by gear. A deceleration torque limit curve  320  may correspond to the first gear. The map  300  corresponds to a normal or default map. When the vehicle is, for example, travelling down a long, shallow downgrade, the actual torque produced varies from the map  300 . 
     The deceleration control logic attempts to restore the vehicle&#39;s movement to follow the torque limits of the map  300 . For example, the target deceleration and target torque may be determined as the torque needed to return to a given torque curve. In other words, the deceleration control logic changes the 0% application curve. Because the vehicle interpolates pedal application between two curves, changing the 0% curve requires additional considerations when reverting to a normal logic. For example, the deceleration control logic may store a previously used 0% curve or target deceleration for use as the 0% curve when the deceleration control logic is canceled. 
     Alternatively, the target deceleration may be determined by calculating a gap between the road load and the torque curve. As the engine RPM increases, the vehicle road load curve  310  increases, for instance due to additional aerodynamic drag and other forces. The gap between the vehicle road load curve  310  and a torque curve increases, signifying more deceleration when coasting at higher RPMs than at lower RPMs. However, when the vehicle coasts downhill, the road load does not similarly increase, for example because of the effects of gravity. The target deceleration may be determined based on restoring this gap to its expected value. 
     In certain implementations, the driver may manually modify or adjust the deceleration adjustment. For example, a user interface in the vehicle  100  may allow the driver to increase or decrease the amount of adjustment (e.g., 5%, 10%, etc.). The interface may store user settings as part of a user profile, for instance. 
       FIG. 4  presents a flowchart  400  of deceleration control logic according to an implementation of the present application. The deceleration control logic may wait until there is a 0% pedal application on the accelerator pedal, such as the accelerator pedal  130 . The deceleration control logic may have a delay after the pedal application reaches 0%, for a smoother transition. The deceleration control logic may further wait until the vehicle is decelerating outside of a defined range. For example, the difference between a target deceleration and a current deceleration may be greater than a deceleration threshold. The deceleration control logic may also wait until the vehicle is traveling within a predetermined speed range, such as between 20 mph to 70 mph. The deceleration control logic may cancel out if either the accelerator pedal or the brake pedal is applied. 
     At  410 , the current deceleration is detected. For example, the HV system  210  detects the current deceleration through the accelerometer  184  or other suitable sensors, such as vehicle speed sensors, wheel speed sensors, or propeller shaft sensors. However, if the accelerometer  184  or other suitable sensors fails, the deceleration control logic may gracefully exit by reverting to a normal torque and a normal logic. The HV system  210  may further store the current deceleration for use in the next iteration. When the deceleration control logic is canceled out, the current deceleration may be used as a 0% pedal application value in order to interpolate between the 0% application and 10% application curves. 
     At  420 , the target deceleration is determined. The target deceleration logic  230  determines the target deceleration based on the vehicle&#39;s current speed and gear position. The target deceleration may correspond to a coasting deceleration of the vehicle and may be determined by a torque map, such as the map  300 . At any given vehicle speed and gear position, the coasting deceleration may be a stored value based on factory testing, or may be based on historical coasting data from the vehicle itself. 
     At  430 , the current deceleration is compared with the target deceleration. At  440 , the target torque is determined. The target torque is determined based on adjusting the current deceleration until the target deceleration is achieved. 
     At  450 , the target torque is applied. For example, the processor  150  may control the transmission  120 , the engine  110 , and/or the first and second motor-generators  191  and  192  to apply the target torque to the propeller shaft. The deceleration control logic may follow or perform several iterations until the target deceleration is achieved. 
     Those of ordinary skill would appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Furthermore, the present application can also be embodied on a machine readable medium causing a processor or computer to perform or execute certain functions. 
     To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosed apparatus and methods. 
     The various illustrative logical blocks, units, modules, and circuits described in connection with the examples disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm described in connection with the examples disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The steps of the method or algorithm may also be performed in an alternate order from those provided in the examples. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an Application Specific Integrated Circuit (ASIC). The ASIC may reside in a wireless modem. In the alternative, the processor and the storage medium may reside as discrete components in the wireless modem. 
     The previous description of the disclosed examples is provided to enable any person of ordinary skill in the art to make or use the disclosed methods and apparatus. Various modifications to these examples will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other examples without departing from the spirit or scope of the disclosed method and apparatus. The described implementations are to be considered in all respects only as illustrative and not restrictive and the scope of the application is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.