Pressure control actuator for a brake control system

• US 5,433,514 A
• Filed: 03/11/1994
• Issued: 07/18/1995
• Est. Priority Date: 03/16/1993
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Watanabe, Takayuki, Tsukamoto, Masahiro
• Primary Examiner(s): Graham, Matthew C.
• Application Number:
  US08/208,711
• Time in Patent Office: 494 Days
• Field of Search: 303/115.2, 303/113.1, 303/113.2, 180/197
• US Class Current: 303/113.2
• CPC Class Codes: B60T 2270/203 hydraulic system components
• CPC Class Codes: B60T 8/175 Brake regulation specially adapted to prevent excessive wheel spin during vehicle acceleration, e.g. for traction control safety devices for propulsion unit control responsive to, or preventing, skidding of wheels B60K28/16
• CPC Class Codes: B60T 8/17616 Microprocessor-based systems
• CPC Class Codes: B60T 8/348 4 Channel systems B60T8/345 takes precedence
• CPC Class Codes: B60T 8/4266 having an electro-mechanically actuated expansion unit, e.g. solenoid, electric motor, piezo stack
• CPC Class Codes: B60T 8/4863 closed systems B60T8/4845, B60T8/489 take precedence

Abstract

A pressure control actuator suitable for an automotive brake control system comprises a pressure-regulation cylinder slidably enclosing a piston and cooperative with the piston for defining therein a variable-volume pressure chamber which is fluidly connected to a wheel cylinder, a shut-off valve through which the variable-volume chamber is connected to a master cylinder, a motor-driven thrust generator drivingly connected to the piston for producing a thrust, and a heavily pre-loaded return spring for biasing the piston in a first direction opposite to a second direction in which the piston is pushed by the master-cylinder pressure shut-up in the chamber, when the piston is displaced apart from its neutral position in the second direction so that the volume of the chamber is enlarged. A pre-load of the spring is set to balance with a force acting on the piston by a maximum master-cylinder pressure introduced into the chamber. In the absence of thrust acting on the piston after termination of the ABS pressure-reduction control, the piston quickly and precisely returns to the neutral position. Zero-thrust ensures a quick recovery of the piston to the neutral position at the aid of light braking action after termination of the TCS pressure-intensifying control.

Claims

1. A pressure control actuator fluidly disposed in a fluid-pressure line, comprising:

a shut-off valve fluidly disposed in said fluid-pressure line, said shut-off valve being responsive to a valve-open signal for establishing a fluid communication between upstream and downstream lines of said valve, and responsive to a valve-closing signal for blocking said fluid communication and for shutting a fluid pressure in said downstream line;

a pressure-regulation cylinder slidably accommodating therein a piston having a piston rod and cooperative with said piston for defining therein a variable-volume pressure chamber which is fluidly connected to said downstream line;

a thrust generator drivingly connected to said piston for producing a thrust acting on said piston; and

spring means for biasing said piston in a first axial direction when said piston is shifted apart from its neutral position in a second axial direction opposite to said first axial direction under a fluid pressure introduced into said chamber so that a volume of said chamber is enlarged,

wherein a pre-load of said spring means is set to balance with a force acting on said piston by a maximum fluid pressure introduced into said chamber; and

wherein said piston rod comprises a stepped piston rod, and said spring means includes a return spring and a movable annular spring seat formed separate from said stepped piston rod and having an outside diameter greater than an inside diameter of a radially inwardly projecting annular shoulder formed on an inner wall of said cylinder so that said spring seat is spring-loaded against said annular shoulder by said pre-load of said spring, and an outside diameter of a larger diameter section of said piston rod is dimensioned to be greater than an inside diameter of said annular spring seat so that said piston is positioned in the neutral position by abutment between said larger diameter section of said stepped piston rod and said spring seat abutting with said shoulder.

2. The pressure control actuator as set forth in claim 1, wherein said shut-off valve comprises an electromagnetic solenoid-type two-port two-position, normally-open valve, and said thrust generator comprises a motor-driven thrust generator which produces both a thrust acting in said first axial direction and a thrust acting in said second axial direction and has a drive shaft rigidly connected to a piston rod of said piston.

3. The pressure control actuator as set forth in claim 2, wherein said piston, said stepped piston rod, said movable spring seat, said spring, and said drive shaft are axially aligned to each other.

4. An automotive brake control system comprising:

a master cylinder generating a master-cylinder pressure depending on a depression of a brake pedal;

a wheel cylinder attached to each of road wheels, for converting said master-cylinder pressure to a brake force;

a slip-rate detection means for detecting a slip rate of the road wheel;

a motor-driven pressure control actuator, said actuator including;

an electromagnetic solenoid-type shut-off valve fluidly disposed in a brake-fluid line, said shut-off valve having a first port communicating with said master cylinder via an upstream line and a second port communicating with said wheel cylinder via a downstream line, and said shut-off valve being responsive to a valve-open signal for establishing a fluid communication between the two ports, and responsive to a valve-closing signal for blocking said fluid communication and for shutting said master-cylinder pressure in said downstream line;

a pressure-regulation cylinder slidably accommodating therein a piston having a piston rod and cooperative with said piston for defining therein a variable-volume pressure chamber which is fluidly connected to said downstream line;

a reversible motor-driven thrust generator drivingly connected to said piston for producing a thrust acting on said piston; and

spring means for biasing said piston in a first axial direction when said piston is shifted apart from its neutral position in a second axial direction opposite to said first axial direction under said master-cylinder pressure introduced into said chamber so that a volume of said chamber is enlarged, a pre-load of said spring means being set to balance with a force acting on said piston by a maximum master-cylinder pressure introduced into said chamber;

a brake controller responsive to a driving condition of a vehicle, for controlling the valve position of said valve and a direction and a magnitude of said thrust produced by said thrust generator;

wherein said brake controller generates said valve closing signal to shift said valve to the valve-closed position when the detected slip rate exceeds a predetermined first threshold, and generates said valve-open signal when the detected slip rate is less than a predetermined second threshold preset at a smaller value than said first threshold; and

wherein said piston rod comprises a stepped piston rod, and said spring means includes a return spring and a movable annular spring seat formed separate from said stepped piston rod and having an outside diameter greater than an inside diameter of a radially inwardly projecting annular shoulder formed on an inner wall of said cylinder so that said spring seat is spring-loaded against said annular shoulder by said pre-load of said spring, and an outside diameter of a larger diameter section of said piston rod is dimensioned to be greater than an inside diameter of said annular spring seat so that said piston is positioned in the neutral position by abutment between said larger diameter section of said stepped piston rod and said spring seat abutting with said shoulder.

5. The automotive brake control system as set forth in claim 4, wherein when the detected slip rate exceeds said first threshold, in addition to shifting to the valve-closing position, said controller controls said thrust generator to produce a thrust acting on said piston in said second axial direction so that said wheel-cylinder pressure is reduced according to an increase in the volume of said chamber.

6. The automotive brake control system as set forth in claim 5, wherein when the detected slip rate exceeds said first threshold, in addition to shifting to the valve-closing position, said controller controls said thrust generator to produce a thrust acting on said piston in said first axial direction so that said wheel-cylinder pressure is increased according to a decrease in the volume of said chamber.