BACKGROUND OF INVENTION
1. Field of the Invention
The present invention generally relates to a method and an apparatus for determining whether a vehicle has been regeneratively braked and for frictionally braking the vehicle in the event that the vehicle has not been regeneratively braked and to a vehicle which incorporates the method and apparatus and more particularly, to a method and apparatus which measures and/or senses the speed of a vehicle after a regenerative braking assembly has been activated, effective to determine whether the vehicle has been regeneratively braked and, based upon the measured or sensed speed, activates a frictional brake assembly, effective to brake the vehicle.
2. Background of the Invention.
A vehicle may be braked or selectively decelerated or slowed by the use of several techniques or strategies. For example, a hybrid type vehicle may be regeneratively braked by selectively coupling the torque emanating from the transmission or powertrain assembly to an energy storage device (e.g., a flywheel assembly), thereby conserving energy while slowing or decelerating the vehicle. Some regenerative strategies require that the torque be converted into electrical energy, by a motor, and then stored within a battery.
While such regeneration does desirably slow a vehicle's velocity or speed, it does not typically provide sufficient deceleration to actually stop the vehicle. Hence, these regenerative braking strategies must normally be used in combination with traditional braking strategies which require the use of a frictional brake assembly on each of the wheels. Particularly, a frictional brake assembly selectively engages the wheel on which it is operatively disposed and, in this manner, these frictional brake assemblies selectively and cooperatively decelerate and stop a vehicle.
There exist a number of unique strategies which utilize such frictional braking assemblies and which seek to dynamically distribute the amount of braking between braking assemblies located at the rear of the vehicle (i.e., behind the driver) and the front of the vehicle in order to maintain overall vehicular stability. Typically, the vehicle is initially regeneratively braked in order to maximize the amount of energy which may be regeneratively stored and concomitantly decrease the use of the frictional brakes which wear over time and must be replaced or serviced.
- SUMMARY OF INVENTION
It is desirable to confirm whether regenerative deceleration of the vehicle has occurred and/or to confirm that the regenerative braking system is operable in order to avoid a relatively sudden application of the frictional brakes which is necessary in order to achieve the desired vehicular braking. Particularly, such a sudden application of the frictional brakes both reduces the operating life of these brakes, provides discomfort and annoyance to the passengers of the vehicle, and oftentimes prevents a desired brake distribution to occur. The present method and apparatus provides this confirmation benefit and provides a strategy which eliminates or reduces the need to suddenly and fictionally brake a vehicle due to a failure of the regenerative braking system to supply the desired braking.
A method and an apparatus is provided for braking a vehicle which overcomes some or all of the previously delineated drawbacks of prior braking systems and strategies.
In accordance with the present invention, an assembly is provided having a selectively energizable frictional braking assembly, a sensor which determines whether a certain amount of regenerative braking has been applied to a vehicle and which generates a signal in the absence of the sensed application of the certain amount of regenerative braking to the vehicle, and a controller assembly which is coupled to the selectively energizable frictional braking assembly and to the sensor, which receives the signal from the sensor and, in response to the receipt of the first signal from the sensor, selectively activates the frictional braking assembly, effective to provide braking to the vehicle.
In accordance with another aspect of the present invention, a vehicle is provided having at least one wheel which will be selectively braked, a frictional brake assembly which is selectively coupled to the at least one wheel; a regenerative braking assembly, a sensor which measures a speed of the vehicle and which produces a first signal which is indicative of the measured speed, a brake request member which selectively generates a second signal which represents a certain amount of desired vehicular deceleration, and a controller which is coupled to the brake request member, to the frictional brake assembly, and to the speed sensor, the controller receiving the second signal and, in response to the receipt of the second signal attempts to decelerate the vehicle by use of the regenerative braking assembly, the controller further receiving the first signal and uses the first and second signals to determine whether the vehicle has been decelerated and, based upon the determination, selectively brakes the at least one wheel by use of the frictional brake assembly.
In accordance with yet another aspect of the invention, a method for braking a vehicle is provided having the steps of initially attempting to regeneratively brake the vehicle; determining whether the vehicle has been regeneratively braked; and automatically causing the vehicle to be frictionally braked if the vehicle has failed to be regeneratively braked.
BRIEF DESCRIPTION OF DRAWINGS
These and other features and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.
FIG. 1 is a block diagram of a vehicle incorporating the apparatus of the preferred embodiment of the invention.
Referring now to FIG. 1, there is shown a vehicle 10 which includes a regenerative braking confirmation assembly 12 which is made in accordance with the teachings of the preferred embodiment of the invention.
Particularly, vehicle 10 includes a torque generator 14, such as but not limited to an internal combustion engine or fuel cell assembly, and a transmission assembly 16 which is physically coupled to the torque generator 14 by a powertrain member 18. Vehicle 10 further includes a regenerative brake assembly 20 which comprises a motor 22, a clutch 24, and a battery 26. Particularly, the clutch 24 is physically coupled to the transmission 16 by the output shaft 76, and to the motor 22. The motor 22 is electrically coupled to the battery 26 and the battery 26 may comprise a conventional vehicular battery.
Further, the vehicle 10 includes a differential assembly 30 which is physically coupled to the clutch 24 by a powertrain member 32. Moreover, vehicle 10 includes a pair of rear axles or halfshafts 36, 38 which are each coupled to the differential assembly 30 and to a respective rear wheel 40, 42. The vehicle 10 also includes a front axle 46 which is coupled to a pair of front wheels 48, 50, and frame members 54, 56 which are coupled to the front axle 46. Frame member 54 is further coupled to the rear axle 38 while the frame member 56 is coupled to the rear axle 36.
Vehicle 10 further includes frictional brake assemblies 60, 62, 64, and 66 which respectively reside upon or in close proximity to wheels 40, 42, 48, and 50 and which selectively and frictionally brake these respective wheels 40, 42, 48, and 50, effective to slow or stop the vehicle 10 (e.g., to brake the vehicle 10), and a controller 70 which is operable under stored program control and which is physically and communicatively coupled to the clutch 24 and to the frictional brake assemblies 60-66. Vehicle 10 also includes a selectively depressible brake request member or brake pedal 73 which is coupled to the controller 70. That is, controller 70, in one embodiment, forms part of the regenerative braking confirmation assembly 12 and also provides other vehicular functions which are set forth below. In other non-limiting embodiment, a separate controller may be used to provide the regenerative braking confirmation function of the preferred embodiment of the invention.
It should be realized that only the relevant portions of vehicle 10 are shown within FIG. 1 and described above and that while the vehicle 10 discloses a rear wheel drive vehicle, the present invention is applicable to a wide variety of vehicular architectures, including but not limited to a front wheel drive vehicle, an all wheel drive vehicle, and/or an on demand drive vehicle and that nothing in this description is meant to limit the applicability of the present invention only to the type of vehicle which is shown in FIG. 1.
In conventional operation, torque is produced by the torque generator 14 and is communicated to the transmission 16 by the drivetrain member 18. The transmission 16 then outputs at least a portion of the received torque by the use of the output shaft or member 76 which is coupled to the clutch 24 and to the transmission 16. Typically, the controller 70 controllably causes the clutch 24 to communicate the torque which is output from the transmission 16 (i.e., from the shaft 76) to the differential 30, by the use of powertrain member 32. The differential 30 then communicates the torque to the axles 36, 38, effective to allow the wheels 40, 42 to rotate and to allow the vehicle 10 to be driven.
When the controller 70 senses a depression of the member 73, the controller 70 controllably causes the clutch 24 to communicate the torque emanating from the output member 76 to the motor 22. The received torque causes the motor 22 to function as a generator and to communicate the generated electrical energy into the battery 26, thereby conserving energy (e.g., transforming the received kinetic energy into electrical energy) while braking or decelerating the vehicle 10 (e.g., regeneratively braking the vehicle 10). When the maximum allowable amount of regenerative braking has been achieved and additional amounts of braking have been requested, the controller 70 activates the frictional braking assemblies 60-66. It should be realized that a wide variety of frictional braking assemblies 60-66 may be employed such as those which are hydraulically or pneumatically activated and those which are of the anti-lock type. Moreover, it should be appreciated that a wide variety of regenerative braking assemblies may be used to replace the assembly 20, including but not limited to those including a flywheel which receives torque from the clutch 24, and that nothing in this description is meant to limit the present invention to use with a certain type of regenerative braking assembly or frictional braking assembly.
Regenerative braking confirmation assembly 12 includes or makes use of the controller 70. In other non-limiting embodiments, one or more controllers may be used to perform the functionality and methodology of the preferred embodiment of the invention. Nothing in this application is meant to limit the use of the present invention to a certain type of controller architecture. Assembly 12 further includes at least one speed sensor 80 which is coupled to the controller 70 and which is adapted to sense the speed of the wheel 40 and to communicate the sensed speed to the controller 70. While a single sensor 80 is shown in FIG. 1, it should be appreciated that additional numbers of sensors may be employed in other non-limiting embodiments of the invention on any or all of the other wheels 42, 48 and 50.
Hence, according to the teachings of the preferred embodiment of the invention, when controller 70 causes the clutch 24 to regeneratively brake the vehicle 10, the controller 70 communicates with the at least one speed sensor 80 in order to ascertain whether the vehicle 10 is decelerating (i.e., whether the vehicle 10 is being regeneratively braked). If, after some predetermined period of time, vehicular deceleration is not sensed (or, in one non-limiting embodiment of the invention, if a certain predetermined amount of vehicular deceleration is not sensed), the controller 70 automatically (i.e., without intervention by the user or operator of the vehicle) causes the frictional braking assemblies 60-66 to decelerate the vehicle 10, and may provide status or other types of information to the user/driver indicating that the desired regenerative braking has not occurred or is not occurring. In one non-limiting embodiment of the invention, the vehicle deceleration may be calculated by conventional slip control equations which utilize the wheel speed which is provided by the at least one sensor 80. Such a calculation may occur within controller 70. If additional wheel sensors are utilized, these equations are sequentially and separately applied to the respective wheel speed data emanating from these other sensors and the controller 70 only activates the frictional braking assemblies 60-66 if all of the data (for each wheel 40, 42, 48, 50) shows a lack of deceleration. The use of such slip control equations is explained within the paper entitled Comparison of Control Methods for Electric Vehicle Antilock Braking/Traction Control Systems, which is authored by P. Khatum, C. M. Bimgham, and P. H. Mellor, which is published by the Society of Automotive Engines (2001-01-0596) and which is fully and completely incorporated herein by reference, word for word and paragraph for paragraph. In another non-limiting embodiment, discrete positions of the member 73 are calibrated to ascertain the amount of deceleration which is respectively requested by each position. This calibrated data (along with the data associated with the current position of the member 73) is stored within the controller 70 and is used, by the controller 70, in combination with the data emanating from the at least one speed sensor 80 to not only ascertain whether the vehicle 10 is being decelerated, but to determine whether the requested amount of deceleration has been achieved. In an alternate embodiment of the invention, the frictional braking is not applied until it is determined that the full amount of the requested regenerative braking has not been applied to the vehicle 10.
In an alternate embodiment, torque generator 14 may comprise a reservoir of fluid in combination with a hydraulic pump which is communicatively coupled to the reservoir and controllably coupled to the controller 70. In this alternate embodiment, powertrain member 18 may be replaced by at least one hydraulic conduit and transmission 16 may be replaced by an assembly which rotates in response to the receipt of fluid. In operation, upon receipt of certain signals from the controller 70, the pump in cooperation with the reservoir will selectively couple the fluid to the transmission which causes the transmission to hydraulically provide positive or negative torque to accelerate or decelerate the vehicle 10.
It is to be understood that the invention is not limited to the exact construction and method which has been described above, but that various changes and modifications may be made without departing from the spirit and the scope of the inventions as are set forth in the following claims.