Fluid-pressure and analogous brake systems – Speed-controlled – Regenerative brakes
Reexamination Certificate
1999-04-30
2001-05-15
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Regenerative brakes
C060S574000, C060S592000
Reexamination Certificate
active
06231135
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to braking systems for electric vehicles or hybrid electric vehicles, and in particular to braking systems which comprise a regenerative braking system in conjunction with a conventional, mechanical friction braking system. As the term is used herein, “electric” vehicles are those which are propelled solely by an electric motor which receives energy from an on-board storage battery; “hybrid electric” vehicles are those which may be propelled, generally at different times, by either an electric motor, which receives energy from either an on-board storage battery or from a generator operatively coupled to an internal combustion engine (a “series hybrid electric vehicle”), or by an internal combustion engine selectively operatively coupled to the ground-engaging wheels (a “parallel hybrid electric vehicle”). Thus, while both electric and hybrid electric vehicles comprise a rechargeable on-board storage battery, electric vehicles are propelled by an electric motor alone, whereas hybrid electric vehicles are propelled by an electric motor and also comprise an internal combustion engine which is also used for propulsion or, alternatively, for generating electrical power via a generator to recharge the battery.
Generally, electrical power is connected to the motor only when driving propulsion is demanded by the operator (e.g., by pressing on the accelerator or “gas” pedal). At other times (during coasting or braking) the power feeding the motor is disconnected. The inertia of the moving vehicle, however, continues to rotate the rotor of the motor, which is coupled to a ground-engaging wheel of the vehicle. Regenerative braking systems use the rotating motor as a generator which works against an electrical load placed in communication with the motor/generator upon actuation of a vehicle braking control device, such as a brake pedal. The electrical load comprises the partially-depleted battery, which is at least partially recharged by the motor acting as a generator powered by the still-moving vehicle's inertia. The electrical load on the motor/generator slows the rotational speed thereof, thereby braking the vehicle.
Previous electric or hybrid electric vehicles have employed hybrid brake systems comprising both an electrical, regenerative brake system and a conventional, mechanical friction braking system. Generally, such vehicles couple the two brake systems so that they work together, with the regenerative braking system being first actuated upon initial depression of the brake pedal to slow the vehicle and provide a charge to the battery. Further depression of the brake pedal then additionally actuates, or completely switches to, the conventional mechanical braking system for stopping the vehicle. A problem encountered with prior hybrid brake systems, however, is that the transition from only regenerative braking to mechanical braking, alone or in combination with regenerative braking, has been abrupt, resulting in poor brake pedal “feel” and impairing the driveability the vehicle.
For example, some prior vehicles employing hybrid braking systems used only regenerative braking until the brake pedal was depressed a considerable distance toward the floorboard. Drivers operating these vehicles felt very little pedal resistance and encountered sluggish transition from regenerative braking to conventional braking because there was little or no pressure in the brake lines. Drivers of these vehicles overcorrected by stomping on the brakes, abruptly applying the conventional mechanical brake system, thereby causing erratic handling of the vehicle.
A means for providing a smooth transition between regenerative and conventional braking in an electric or hybrid electric vehicle is desired.
SUMMARY OF THE INVENTION
The present invention addresses the shortcomings of prior hybrid braking systems in electric or hybrid electric vehicles by providing a smooth transition between regenerative and conventional friction braking.
The present invention provides a hybrid brake system for a vehicle propelled at least by a rotating electric motor powered by a storage battery and in communication with at least one ground-engaging wheel, and includes an electrical brake system comprising the electric motor and the battery, and a vehicle braking control device. The battery provides an electrical load on the motor during times when the vehicle braking control device is actuated, the rotation of the motor during actuation of the vehicle braking control device providing electrical power to the battery, whereby the battery receives an electrical charge. The motor rotation slowed by the electrical load and the vehicle is thus braked by the motor. The hybrid brake system of the present invention also includes a mechanical brake system comprising a hydraulic cylinder with a piston sealably and slidably disposed therein. One side of the piston and the hydraulic cylinder partially define a chamber of variable volume, the pressure of the fluid therein varying with movement of the piston in the cylinder. A mechanical brake arrangement is in fluid communication with the chamber and is operatively coupled to at least one ground-engaging wheel for slowing the rotation thereof. The mechanical brake arrangement is variably actuated in response to changes in the pressure of the fluid during times when the vehicle braking control device is actuated, whereby the vehicle is braked by the mechanical brake system. The inventive hybrid brake system further includes means for deferring substantial actuation of the mechanical brake arrangement during actuation of the vehicle braking control device until after the electrical brake system has been actuated. The deferring means includes means for expanding the chamber volume in response to an increase in pressure of the fluid in the chamber.
In certain embodiments of the present invention, the above-described means for deferring substantial actuation of the mechanical brake arrangement includes partially defining the chamber with a displaceable wall which moves between a first position and second position. The wall is biased into the first position and is urged toward the second position by an increase in the pressure of the fluid in the chamber below a threshold pressure. Substantial application of the mechanical brake system during actuation of the vehicle brake control device is deferred until the threshold pressure is reached.
The present invention also provides a method for braking a vehicle propelled at least by a rotating electric motor powered by a battery, which includes the steps of: actuating a vehicle braking control device; placing the motor in mechanical communication with a rotating ground-engaging wheel and an electrical load comprising the battery; generating electrical energy with the motor; absorbing at least a portion of the electrical energy generated by the motor with the battery, thereby slowing the rotation of the motor, whereby the motor slows the vehicle; increasing the pressure of a fluid in a chamber between a first pressure and a threshold pressure during actuation of the vehicle braking control device, during which time the motor is slowing the vehicle; delaying application of a substantial fluid pressure to a mechanical brake arrangement in fluid communication with the chamber and in operative communication with a rotating ground-engaging wheel during actuation of the vehicle braking control device, until after the pressure of the fluid in the chamber has been increased to at least the threshold pressure; and applying a substantial fluid pressure above the threshold pressure to the mechanical brake arrangement during actuation of the vehicle braking control device, during which time the rotation of the ground-engaging wheel is slowed, whereby the mechanical brake arrangement further slows the vehicle.
The herein-described hybrid brake system and method has proven to be simple, and the results provided thereby closely approximate the feel of conventional braking alone. The present design can b
Bower Glenn R.
Koplin Michael D.
Baker & Daniels
Butler Douglas C.
Siconolfi Robert A.
Wisconsin Alumni Research Foundation
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