Antiskid control with surface friction compensation

• US 4,666,218 A
• Filed: 08/08/1984
• Issued: 05/19/1987
• Est. Priority Date: 08/09/1983
• Status: Expired due to Term

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation), Jidosha Kabushiki Kaisha
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Asami, Ken, Sakai, Kazunori, Tamura, Kimio, Masaki, Syouichi, Nakashima, Noriyuki, Wakao, Teruyoshi
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): OBERLEY, ALVIN E
• Application Number:
  US06/638,717
• Time in Patent Office: 1,014 Days
• Field of Search: 303/103, 303/105, 303/106, 303/107, 303/109, 303/96, 303/97, 303/110, 188/181 A, 188/181 C, 364/426, 364/565
• US Class Current: 303/150
• CPC Class Codes: B60T 2270/415 Short-circuit, open circuit failure
• CPC Class Codes: B60T 2270/416 Wheel speed sensor failure
• CPC Class Codes: B60T 8/17616 Microprocessor-based systems
• CPC Class Codes: B60T 8/885 using electrical circuitry

Abstract

In an antiskid control system for the hydraulic braking system of a wheeled vehicle, the rotational speed of a vehicle wheel and the acceleration of the wheel are detected and levels of road surface friction are determined on the basis of the wheel speed and acceleration to give a first indication that the road has a high value of friction or a second indication that the road has a low value of friction. The wheel speed and acceleration are analyzed to detect a down-pressure mode to decrease the fluid pressure of the braking system and an up-pressure mode to increase the pressure. In response to the presence of the first indication, the down-pressure mode is effected at a lower rate and then at a higher rate. In response to the occurrence of the second indication, the down-pressure mode is effected at the higher rate.

Claims

1. An antiskid control system for a hydraulic braking system of a wheeled vehicle having means for lowering the fluid pressure of the braking system at a variable rate comprising:

means for detecting a speed of a vehicle wheel; and

data processing means for;

(a) detecting a rate of variation of said detected wheel speed;

(b) detecting when said wheel speed variation rate becomes higher than high acceleration threshold to produce a first indication that the surface friction of the road is high, and for detecting when said wheel speed becomes lower than a low speed threshold to produce a second indication that said surface friction is low;

(c) if said first indication is given, detecting a gradual down-pressure mode when said wheel speed is higher than a high speed threshold and said wheel speed variation rate is simultaneously lower than a low acceleration threshold and operating said pressure lowering means at a lower rate during said detected gradual down-pressure mode;

(d) if said first indication is given, detecting a rapid down-pressure mode when said wheel speed is lower that said high speed threshold and said wheel speed variation rate is simultaneously lower than a medium acceleration threshold and operating said pressure lowering means at a higher rate which is higher than said lower rate in response to said detected rapid down pressure mode;

(e) if said second indication is given, detecting said rapid down-pressure mode when one of;

(a) said wheel speed is higher than said high speed threshold and said wheel speed variation rate is simultaneously lower than said low acceleration threshold and (b) when said wheel speed is lower than said high speed threshold and said wheel speed variation rate is simultaneously lower than said medium acceleration threshold, and operating said pressure lowering means at said higher rate in response to the last-mentioned rapid down-pressure mode; and

(f) detecting an up-pressure mode when one of (a) said wheel speed is higher than said high speed threshold and said wheel speed variation rate is simultaneously higher than said low acceleration threshold and (b) when the wheel speed variation rate is higher than said medium acceleration threshold, and disabling said pressure lowering means in response to said detected up-pressure mode.

2. A method for controlling the fluid pressure of a hydraulic braking system of a wheeled vehicle, the steps of:

(a) detecting the speed of a vehicle wheel;

(b) detecting the acceleration of the wheel;

(c) detecting when said wheel acceleration becomes higher than a higher acceleration threshold for giving a first indication that the surface friction of the road is high and detecting when said wheel speed becomes lower than a lower speed threshold for giving a second indication that said surface friction is low;

(d) if said first indication is given, detecting a gradual down-pressure mode when the wheel speed is higher than a higher speed threshold and the wheel acceleration is simultaneously lower than a lower acceleration threshold;

(e) operating said pressure decreasing means at a lower rate during the detected gradual down-pressure mode;

(f) if said first indication is given, detecting a rapid down-pressure mode when the wheel speed is lower than said higher speed threshold and the wheel acceleration is simultaneously lower than a medium acceleration threshold;

(g) if said second indication is given, detecting said rapid down-pressure mode when the wheel speed is higher than said higher speed threshold and the wheel acceleration is simultaneously lower than said lower acceleration threshold or when the wheel speed is lower than said higher speed threshold and the wheel acceleration is simultaneously lower than said medium acceleration threshold;

(h) operating said pressure decreasing means at a higher rate which is higher than said lower rate during the rapid down-pressure mode detected by either the step (f) or step (g);

(i) detecting an up-pressure mode when the wheel speed is higher than said higher speed threshold and the wheel acceleration is simultaneously higher than a lower acceleration threshold or when the wheel acceleration is higher than said medium acceleration threshold; and

(j) disabling said pressure decreasing means during the detected up-pressure mode.

3. An antiskid control system for a hydraulic braking system of a wheeled vehicle having means for lowering the fluid pressure of the braking system at a variable rate, said variable rate operable at a higher rate and a lower rate, comprising:

(a) speed detector means for detecting a speed of a vehicle wheel;

(b) rate variation detector means responsive to a rate of variation of the detected wheel speed for detecting when said wheel is under one of positive and negative acceleration;

(c) vehicle speed detector means for detecting the speed of said vehicle;

(d) friction detector means responsive to said detected vehicle speed for deriving a reference wheel speed and generating a high friction signal in response to said detecting of said negative acceleration until said wheel speed reaches said reference wheel speed and generating a low friction signal when said wheel speed becomes lower than said reference wheel speed;

(e) control means responsive to the detection of said negative acceleration for controlling said pressure lowering means for a period of time to decrease said braking pressure at said higher and lower rates and responsive to said detection of the positive acceleration for controlling said pressure lowering means to increase said braking pressure and terminate said period;

(f) correcting means responsive to said high friction signal for controlling said pressure lowering means during a portion of said period during which the pressure of said braking system is decreased by said control means at said lower rate which is lower than said higher rate during said portion; and

(f) disabling means responsive to the low friction signal for disabling said correcting means.

4. An antiskid control system as claimed in claim 3, wherein said correcting means includes means for alternately operating and releasing said pressure lowering means at time intervals that correspond to said portion of said period to reduce said rate in response to said high friction signal and said detection of said negative acceleration.

5. An antiskid control system as claimed in claim 3, wherein said correcting means includes means for gradually operating said pressure lowering means for said portion of said period in response to said high friction signal and said detection of the negative acceleration.

6. An antiskid control system for a hydraulic braking system of a wheeled vehicle having means for lowering the fluid pressure of the braking system at a variable rate, said variable rate operable at a higher rate and a lower rate, comprising:

speed detector means for detecting a speed of a vehicle wheel;

rate variation detector means responsive to a rate of variation of the detected wheel speed for detecting when said wheel is under positive or negative acceleration;

vehicle speed detector means for detecting the speed of said vehicle;

friction detector means responsive to said detected vehicle speed for deriving a reference wheel speed and generating a high friction signal in response to said detecting of said negative acceleration until said wheel speed reaches said reference wheel speed and generating a low friction signal when said wheel speed becomes lower than said reference wheel speed; and

control means responsive to the detection of the negative acceleration for controlling said pressure lowering means for a period of time to decrease the braking pressure at said higher and lower rates and responsive to said detecting of said positive acceleration for controlling said pressure lowering means to increase said braking pressure and terminate said period and further responsive to said high friction signal for controlling said pressure lowering means at said lower rate which is lower than said higher rate for a portion of said period during which said pressure is decreased.

7. An antiskid control system as claimed in claim 6, wherein said control means includes means for alternately operating and releasing said pressure lowering means at intervals that correspond to said portion of said period to reduce said rate exclusively in response to said high friction signal and the detection of said negative acceleration.

8. An antiskid control system as claimed in claim 6, wherein said control means includes means for gradually operating said pressure lowering means for said portion of said period exclusively in response to said friction signal and the detection of the negative acceleration.

9. An antiskid control system for a hydraulic braking system of a wheeled vehicle having means for lowering the fluid pressure of the braking system at a variable rate comprising:

means for detecting a speed of a vehicle wheel; and

data processing means for;

(a) detecting a rate of variation of said detected wheel speed;

(b) detecting when said wheel speed variation rate becomes higher than a high acceleration threshold for giving a first indication that the surface friction of the road is high and detecting when said wheel speed becomes lower than a low speed threshold for giving a second indication that said surface friction is low;

(c) if said first indication is given, detecting a gradual down-pressure mode when said wheel speed is higher than a high speed threshold and the wheel speed variation rate is simultaneously lower than a low acceleration threshold;

(d) operating said pressure lowering means at a lower rate in response to the detection of said gradual down-pressure mode;

(e) measuring an elapse of time from the initiation of the operation of said pressure lowering means at said higher rate;

(f) disabling said pressure lowring means when said measured time reaches a preset value;

(g) if said first indication is given, detecting a rapid down-pressure mode when the wheel speed is lower than said high speed threshold and the wheel speed variation rate is simultaneously lower than a medium acceleration threshold and operating said pressure lowring means at a higher rate which is higher than said lower rate in response to said detected rapid down-pressure mode;

(h) if said second indication is given, detecting one of (a) said rapid down-pressure mode when the wheel speed is higher than said high speed threshold and said wheel speed variation rate is simultaneously lower than said low acceleration threshold, and (b) when the wheel speed is lower than said high speed threshold and the wheel speed variation rate is simultaneously lower than said low acceleration threshold and operating said pressure lowering means at said higher rate in response to the last mentioned rapid down-pressure mode and

(i) detecting an up-pressure mode when one of (a) said wheel speed is higher than said high speed threshold and the wheel speed variation rate is simultaneously higher than said low acceleration threshold and (b) when the wheel speed variation rate is higher than said medium acceleration threshold and disabling said pressure lowering means in response to such detection.