Fluid-pressure and analogous brake systems – Speed-controlled – Regenerative brakes
Patent
1996-09-19
1998-07-07
Poon, Peter M.
Fluid-pressure and analogous brake systems
Speed-controlled
Regenerative brakes
303 3, 303122, 30312211, B60L 710
Patent
active
057757844
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an electric automobile which runs by driving wheels with an electric motor, and especially to a braking control system for an electric automobile so that braking of a vehicle is controlled relying upon regenerative braking by a motor.
BACKGROUND ART
In recent years, electric automobiles each of which drives wheels by an electric motor instead of an internal combustion engine have attracted an increasing interest from the viewpoint of prevention of air pollution and reduction of vehicle noise.
These electric automobiles easily allow so-called regenerative braking. This regenerative braking can be performed by limiting a supply of electric power to a drive motor and converting the motor into a power-generating state. At this time, a load is applied to each drive wheel so that, while braking the drive wheel, rotational energy of the drive wheel can be recovered as electric energy.
Incidentally, regenerative braking in such electric automobiles is controlled so that a regenerative torque has such characteristics as shown in FIG. 4. Described specifically, at a low motor rotational speed, application of a regenerative torque causes a vehicle to move backward after the vehicle is brought to halt subsequent to a deceleration. A large electric current is also required for inducing the regeneration so that the motor produces more heat, although recoverable electric power is small, leading to a negative effect from the standpoint of energy. To avoid these problems, control is therefore performed so that no regenerative torque is produced at a certain rotational speed (for example, N.sub.0) or lower.
Techniques for producing a regenerative torque even at a low motor rotational speed have been proposed to date. For example, the technique disclosed in Japanese Patent Application Laid-Open (Kokai) No. SHO 62-95903 performs PI (proportional and integral) control so that the rotational speed of a motor becomes 0 even when the motor is in a near-stop range (low-speed range).
As a consequence, it is possible to produce a regenerative torque even at a low speed while preventing a vehicle from moving backward subsequent to stopping of the vehicle. This however results in a negative effect from the standpoint of energy because at such a low speed, electric power consumed for inducing regeneration becomes greater than recoverable electric power as mentioned above.
If regenerative braking is always applied as described above, an inconvenience therefore arises in that the coverable distance of an electric automobile is reduced. Further, production of heat by the motor also becomes a problem.
Upon applying brakes at a normal time in an electric automobile, mechanical brakes such as foot brakes are operated as in ordinary automobiles of the internal combustion type, and like an engine brake in the automobiles of the internal combustion engines, regenerative braking is applied further in addition to the mechanical brakes.
To stop a conventional electric automobile which is running at such a low speed that the rotational speed of its motor is equal to or lower than a predetermined value (for example, N.sub.0), only the above-mentioned mechanical brakes are usually relied upon since it is not desired to produce a regenerative torque.
If the mechanical brakes fail, no braking force is therefore applied when the motor is at a low speed. Although it is of course possible to provide the mechanical brakes themselves with a fail-safe function, it is desired to make it possible to appropriately use regenerative braking of the electric automobile in the event of a failure in the mechanical brakes because the regenerative braking can produce a substantially large regenerative torque even at a low speed.
With the foregoing problems in view, the present invention has as an object thereof the provision of a braking control system for an electric automobile so that regenerative braking is appropriately used in the event of a failure in mechanical brakes to ensure stopping of a vehicle while making it p
REFERENCES:
patent: 3924902 (1975-12-01), Engle
patent: 5378053 (1995-01-01), Patient et al.
patent: 5573312 (1996-11-01), Muller et al.
Furukawa Nobuya
Kato Masaaki
Kawamura Nobuyuki
Koga Hisamitsu
Kumagai Naotake
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Poon Peter M.
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