Motor vehicles – Power – Electric
Reexamination Certificate
2001-07-24
2004-04-13
Vanaman, Frank (Department: 3618)
Motor vehicles
Power
Electric
Reexamination Certificate
active
06719076
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a vehicle that may be braked with a motor as well as with a mechanical brake utilizing frictional force, and also to a method of controlling such a vehicle. More specifically the present invention pertains to a vehicle that is braked with a motor to attain an arbitrarily adjustable speed reduction rate, as well as to a controlling method to actualize such braking.
BACKGROUND ART
A hybrid vehicle with both an engine and a motor as the power source has been proposed as one form of transportation. For example, a hybrid vehicle disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 9-37407 additionally has a motor placed in series between an engine and a transmission in a power system of an ordinary vehicle where an output shaft of the engine is connected with a drive shaft via the transmission. This arrangement enables the hybrid vehicle to be driven by means of both the engine and the motor as the power source. The engine generally has poor fuel consumption at a time of starting the vehicle. In order to avoid driving having poor fuel consumption, the hybrid vehicle makes a start by utilizing the power of the motor. After the speed of the vehicle reaches a predetermined level, the hybrid vehicle starts its engine and is subsequently driven by utilizing the power of the engine. The hybrid vehicle accordingly improves the fuel consumption at the time of starting. The hybrid vehicle causes the motor to regenerate the rotations of the drive shaft as electric power, which is used for braking (hereinafter such braking is referred to as the regenerative braking). The hybrid vehicle carries out the regenerative braking and thereby enables the kinetic energy to be used without significant waste. These characteristics desirably improve the fuel consumption of the hybrid vehicle.
There are two different types of braking in the vehicle. One braking process presses a brake pad against the drive shaft in response to actuation of a brake pedal, so as to apply frictional force to the axle (hereinafter referred to as the wheel braking). The other braking process causes the power source to apply a load to the drive shaft, like engine brake (hereinafter referred to as the power source braking). The hybrid vehicle utilizes, as the power source braking, engine brake based on a pumping loss of the engine and regenerative braking due to a regenerative load of the motor. The power source braking does not require the driver to change the foot position from the accelerator pedal to the brake pedal for the purpose of braking. In order to enhance the effectiveness of the power source braking, it is desirable to arbitrarily set a speed reduction rate required by the driver.
The engine brake results in a substantially fixed speed reduction rate according to the engine speed, unless the open and close timings of an intake valve and an exhaust valve are changed. In order to attain a desired speed reduction rate by engine brake, the driver is required to operate a gearshift level to vary the gear ratio of the transmission and thereby change the ratio of the torque of the power source to the torque output to the drive shaft. The advantage of the regenerative braking of the motor is, on the other hand, relatively easy control of the regenerative load, which leads to relatively easy control of the speed reduction rate. From this point of view, the hybrid vehicle disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 9-37407 controls the regenerative speed reduction rate of the motor, in order to attain the desired speed reduction rate set by the driver.
The prior art hybrid vehicle, however, requires specific operations to change the setting of the speed reduction rate. The power source braking does not readily attain the driver's desired speed reduction rate and is thus not utilized effectively enough. The required speed reduction rate frequently varies according to the driving state of the vehicle. In the prior art hybrid vehicle, the change of the actual speed reduction rate does not sufficiently follow the variation in required speed reduction rate. Namely the prior art hybrid vehicle has difficulties in subtle adjustment of the speed reduction rate.
In the prior art hybrid vehicle, the speed reduction rate can be set only in a changeable range of the regenerative load of the motor. In some cases, the hybrid vehicle can not sufficiently attain the speed reduction rate required by the driver. The insufficient speed reduction rate occurs especially in the course of high-speed driving of the vehicle.
Utilizing the wheel braking to compensate for the insufficiency of the speed reduction rate damages the advantage of the power source braking that effects the braking without any change of the foot position. The wheel braking causes the kinetic energy of the vehicle to be consumed in the form of thermal energy and accordingly damages the advantage of the hybrid vehicle that is the effective use of energy.
In the prior art hybrid vehicle, a large speed reduction rate may be attained by operating the gearshift lever to change the gear ratio of the transmission. In this case, however, the speed reduction rate drastically varies with the operation of the gearshift lever, which results in a poor ride.
The problems discussed above arise not only in the hybrid vehicle with both the engine and the motor as the power source but in any vehicle that is braked with the torque of the motor. The problems are also found in vehicles with a motor that is not used as the power source during a drive but is mounted for the purpose of regenerative braking.
DISCLOSURE OF THE INVENTION
One object of the present invention is thus to provide a vehicle that readily regulates the speed reduction rate in the process of braking with the torque of a motor by a compatible operation, which does not make the driver feel uneasy, as well as a method of controlling such a vehicle. Another object of the present invention is to provide a vehicle that enables smooth regulation of the speed reduction rate in a wide possible range of setting in response to a driver's instruction, and a controlling method to attain such braking.
The present invention adopts the following arrangement, in order to attain at least part of the above and the other related objects.
The present invention is thus directed to a vehicle that is driven while regulating power output from a power source to a drive shaft through an operation of an accelerator unit. The vehicle includes: a motor that is capable of applying a braking force to the drive shaft; a detection unit that measures an operating amount of the accelerator unit; a target speed reduction rate setting unit that, when the observed operating amount of the accelerator unit is not greater than a predetermined level, sets a target speed reduction rate of the vehicle corresponding to the observed operating amount, based on a preset relationship between operating amount and speed reduction rate; a motor driving state specification unit that specifies a target driving state of the motor to apply a required braking force to the drive shaft, in order to attain the setting of the target speed reduction rate; and a control unit that controls the motor to be driven in the target driving state, so as to brake the vehicle.
The target driving state of the motor is specified with a diversity of driving state-related parameters, for example, a target torque, a quantity of electric power regenerated by the motor, and a value of electric current flowing through the motor.
In the vehicle of the present invention, the target speed reduction rate is set corresponding to the observed operating amount of the accelerator unit. The vehicle is under braking control with the setting of the target speed reduction rate. The accelerator unit is manipulated to specify a required magnitude of the power to be output from the power source. The accelerator unit generally has a margin of manipulation called play. When the operating amount of the accelerator unit is sufficiently small to be within a range of
Amano Masaya
Nakamura Seiji
Tabata Atsushi
Taga Yutaka
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Vanaman Frank
LandOfFree
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