Fluid-pressure and analogous brake systems – Speed-controlled – Regenerative brakes
Reexamination Certificate
1998-07-28
2001-05-15
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Regenerative brakes
C303S003000
Reexamination Certificate
active
06231134
ABSTRACT:
This application is based on Japanese Patent Application No. 9-250546 filed Sep. 16, 1997, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a braking system for a motor vehicle, which includes both of a frictional braking device and a regenerative braking device.
2. Discussion of the Related Art
An example of a vehicle braking system of the type indicated above is disclosed in JP-A-6-171489. The frictional braking device is arranged to apply a frictional braking torque to each of a plurality of wheels of the vehicle, by frictional engagement of a friction member with a rotor which rotates with the wheel. On the other hand, the regenerative braking device is arranged to apply a regenerative braking torque to at least one drive wheel of the vehicle, by regenerative braking by at least one electric motor connected to the above-indicated at least one drive wheel. In the vehicle braking system including both of these frictional and regenerative braking devices, each of the wheels is braked with a total braking torque which includes at least one of the frictional braking torque and the regenerative braking torque. When the total braking torque of a given wheel has exceeded an upper limit corresponding to a friction coefficient of a road surface, the frictional braking device for that wheel is controlled in an anti-lock fashion, so that the frictional braking torque is controlled so as to hold the wheel in a substantially optimum slipping state, while the regenerative braking torque is held zero.
In the vehicle braking system disclosed in the above-identified publication, the anti-lock control of the frictional braking device for the drive wheel has a problem such as insufficiency of the total braking torque due to zeroing of the regenerative braking torque.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a braking system for a motor vehicle, which includes a frictional braking device and a regenerative braking device and which is adapted to reduce an influence of the zeroing of the regenerative braking torque during an anti-lock control of the frictional braking device.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and may refer back to the other mode or modes, as needed, so as to indicate possible combinations of elements or features in preferred forms of the present invention.
(1) A braking system for a motor vehicle having a plurality of wheels which include at least one drive wheel, comprising: a frictional braking device for forcing a friction member onto a rotor rotating with each of the wheels, to thereby apply a frictional braking torque to the each wheel; a regenerative braking device including at least one electric motor which is connected to the above-indicated at least one drive wheel, to apply a regenerative braking torque to the above-indicated at least one drive wheel; and total braking torque control means for controlling a total braking torque including at least one of the regenerative braking torque and the frictional braking torque which are applied to each of the plurality of wheels, the total braking torque control means operating, when the total braking torque applied to each of at least one of the plurality of wheels has exceeded an upper limit corresponding to a friction coefficient of a road surface on which the vehicle is running, for zeroing the regenerative braking torque of each of the above-indicated at least one wheel and controlling the frictional braking torque of each of the above-indicated at least one wheel while reducing an influence of the zeroing of the regenerative braking torque.
In the vehicle braking system according to this mode of the present invention, the regenerative braking torque applied to each drive wheel whose total braking torque has exceeded the upper limit is zeroed, and the frictional braking torque of that wheel is controlled so as to reduce the influence of the zeroing of the regenerative braking torque. The influence caused by the zeroing of the regenerative braking torque includes insufficiency of the total braking torque of the drive wheel where an anti-lock control of the frictional braking device is effected for the drive wheel, and an abrupt increase of the frictional braking torque for the non-anti-lock-controlled wheel which is not subjected to the anti-lock control. The total braking torque control means is operated to reduce these kinds of influence of the zeroing of the regenerative braking torque.
The insufficiency of the total braking torque of the drive wheel can be reduced by reducing the amount of decrease of the frictional braking torque or increasing the rate or gradient of increase of the frictional braking torque during the anti-lock control of the frictional braking device, as compared with that in an anti-lock brake control in a vehicle braking system which does not include a regenerative braking device, or as compared with that in a normal anti-lock control of the frictional braking device which is effected when the regenerative braking torques of all of the wheels are zero. Since the total braking torque of the drive wheel is reduced by the zeroing of the regenerative braking torque, it is desirable to control the frictional braking torque such that the frictional braking torque is larger than in the normal anti-lock control, so that the drive wheel is held in a substantially optimum slipping state. In this arrangement wherein the frictional braking torque of the drive wheel during the anti-lock control is controlled to be relatively large, the total braking torque control means is considered to include the anti-lock control means adapted to reduce or limit the braking torque or anti-lock control means adapted to effect an anti-lock control for the drive wheel.
(2) A braking system according to the above mode (1), wherein the frictional braking device includes (a) a common controller for commonly controlling the frictional braking torques of the plurality of wheels, and (b) independent controllers for controlling the frictional braking torques of the plurality of wheels, respectively, independently of each other, and the total braking torque control means includes (c) cooperative control means for controlling the common controller such that a sum of the frictional braking torque and the regenerative braking torque coincides with a desired braking torque value desired by an operator df the motor vehicle, and (d) anti-lock control means for controlling the independent controllers such that the frictional braking torque of each wheel controlled by a corresponding one of the independent controllers permits each wheel to be held in a substantially optimum slipping state.
In the above mode (2) of the present invention, the frictional braking torques of all of the plurality of wheels are increased when the regenerative driving torque is zeroed when the total braking torque applied to at least one of the wheels has exceeded the upper limit. Further, the frictional braking torque of each wheel whose total braking torque has exceeded the upper limit is controlled by the anti-lock control means. Accordingly, the total braking torque of the non-anti-lock-controlled wheel or wheels whose frictional braking torque is not controlled by the anti-lock control means is abruptly or rapidly increased. Where the non-anti-lock-controlled wheel is the non-drive wheel, the frictional braking torque of that non-drive wheel to which the regenerative braking torque has not been applied is rapidly increased by the common controller and the cooperative control means, by an amount equal to the regenerative braking torque which has been applied to the drive wheel. As a result, the running stability of the vehicle is deteriorated, or the anti-lock control of the frictional braking device is initiated for the non-anti-lock-controlled wheel, at an earlier point of time than required. On the ot
Asada Hiroki
Enomoto Naoyasu
Fukasawa Tsukasa
Sakai Akira
Sakai Toshiyuki
King Bradley
Oberleitner Robert J.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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