Tandem master cylinder with electromagnetic position sensors for each piston

• US 4,914,916 A
• Filed: 04/04/1988
• Issued: 04/10/1990
• Est. Priority Date: 04/04/1988
• Status: Expired due to Fees

• Current Assignee: Automotive Products PLC A British Company of Tachbrook
• Original Assignee: Automotive Products PLC (Whitnash Plc)
• Inventors: Leigh-Monstevens, Keith V., Mabee, Brian D.
• Primary Examiner(s): Garrett, Robert E.
• Assistant Examiner(s): Kapsalas, George
• Application Number:
  US07/177,312
• Time in Patent Office: 736 Days
• Field of Search: 60/534, 60/535, 60/538, 60/545, 60/562, 60/582, 303/84.2, 91/1, 200/82 D, 338/32 H, 324/208, 324/251, 324/235, 92/5 R
• US Class Current: 60/534
• CPC Class Codes: B60T 11/20 Tandem, side-by-side, or other multiple master cylinder units
• CPC Class Codes: B60T 17/226 using devices being responsive to the difference between the fluid pressions in conduits of multiple braking systems

Abstract

A brake failure warning system for a dual hydraulic master cylinder for use with a motor vehicle. The warning system employs a pair of Hall Effect magnetic sensors which are positioned on the exterior of a plastic cylinder in association with the two pistons mounted within the bore of the cylinder. The pistons have ferrous frustoconical portions which coact with the respective sensors to generate position signals that vary as the pistons move in the bore past the respective sensors. The two position signals are fed to a logic board which compares the signals and generates an error or warning signal in the event that the difference between the two signals exceeds a predetermined amount indicative of failure of one of the two braking systems of the vehicle.

Claims

1. A hydraulic master cylinder assembly comprising:

(A) a cylinder formed of a nonferrous material and defining an axial bore;

(B) first and second pistons, each including a portion formed of a ferrous material, mounted for stroking reciprocal joint axial movement in said bore an coacting with said cylinder to define first and second pressure chambers in said cylinder;

(C) first and second discharge ports in said cylinder communicating respectively with said first and second pressure chambers so that pressurized fluid is delivered through said first and second discharge ports in response to stroking axial movement of said pistons in said bore; and

(D) sensing means including a magnetic sensor associated with each piston, operative to continuously sense the individual instantaneous axial positions of each piston in said bore as the pistons undergo reciprocal stroking movement in said bore and to continuously generate first and second signals respectively and continuously representing the instantaneous sensed position of said first and second pistons in said bore.

2. A master cylinder assembly according to claim 1 wherein said sensing means is further operative in response to a predetermined sensed differential movement between said pistons as said pistons move in said bore to generate a warning signal.

3. A master cylinder assembly according to claim 1 wherein:

(E) said magnetic sensors are Hall Effect sensors.

4. A master cylinder assembly according to claim 1 wherein:

(E) said sensing means comprises a first sensor associated with said first piston and operative to generate an electrical signal that varies in magnitude in proportion to the axial position of said first piston in said bore and a second sensor associated with said second piston and operative to generate an electrical signal that varies in magnitude in proportion to the axial position of said second piston in said bore.

5. A master cylinder assembly according to claim 4 wherein:

(F) said sensors are operative to generate electrical signals that remain substantially identical to each other in response to substantially identical joint movement of said pistons in said bore but vary from each other in response to differential movement of said pistons in said bore; and

(G) said sensing means is operative to generate a warning signal in response to signals from said first ans second sensors that vary from each other by a predetermined amount.

6. A master cylinder according to claim 5 wherein said sensing means further includes:

(H) a first comparator receiving the output signal from said first and second sensors and operative to generate an output signal including an error signal representing any variations between said sensor output signals.

7. A hydraulic master cylinder assembly comprising:

(A) a cylindrical defining an axial bore;

(B) first and second pistons mounted for stroking reciprocal joint axial movement in said bore and coacting with said cylindrical to define first and second pressure chambers in said cylinder;

(C) first and second discharge ports in said cylinder communicating respectively with said first and second pressure chambers so that pressurized fluid is delivered through said first and second discharge ports in response to stroking axial movement of said pistons in said bore; and

(D) sensing means operative to sense the individual axial positions of each piston in said bore as the pistons move linearly in said bore;

(E) said cylinder being formed of a non-ferrous material;

(F) said pistons each including a portion formed o ferrous material;

(G) said sensing means including a magnetic sensor associated with each piston;

(H) said magnetic sensors being mounted on said cylinder in axially spaced relation with each sensor adjacent said ferrous portion of a respective piston; and

(I) said ferrous portion of each piston having a cross-sectional configuration that varies along the axis of said ferrous portion so that the signal generated by the respective sensor varies as the respective piston moves axially in said bore.

8. A master cylinder assembly according to claim 7 wherein:

(J) said ferrous portion of each piston has a frustoconical configuration.

9. A master cylinder assembly according to claim 8 wherein:

(K) each piston further includes first and second cylindrical land portions at the opposite ends of the frustoconical ferrous portion.

10. A master cylinder assembly according to claim 9 wherein:

(L) at least one of said land portions of each piston is formed of a non-ferrous material.

11. A master cylinder assembly according to claim 10 wherein:

(M) said ferrous portions of said pistons are formed of steel and said non-ferrous portions are formed of aluminum.

12. A hydraulic master cylinder assembly comprising:

(A) a cylinder defining an axial bore;

(B) first and second pistons mounted for stroking reciprocal joint axial movement in said bore and coacting with said cylinder to define first and second pressure chambers in said cylinder;

(C) first and second discharge ports in said cylinder communicating respectively with said first and second communicating respectively with said first and second pressure chambers so that pressurized fluid is delivered through said first and second discharge ports in response to stroking axial movement of said pistons in said bore; and

(D) sensing means operative to sense the individual axial positions of each piston in said bore as the pistons move linearly in said bore;

(E) said sensing means comprising a first sensor associated with said first piston and operative to generate an electrical signal that varies in magnitude in proportion to the axial position of said first piston in said bore and a second sensor associated with said second piston and operative to generate an electrical signal that varies in magnitude in proportion to the axial position of said second piston in said bore;

(F) said sensors being operative to generate electrical signals that remain substantially identical to each other in response to substantially identical joint movement of said pistons in said bore but vary from each other in response to differential movement of said pistons in said bore;

(G) said sensing means being operative to generate a warning signal in response to signals from said first and second sensors that vary from each other by a predetermined amount;

(H) said sensing means further including a first comparator receiving the output signal from said first and second sensors and operative to generate an output signal inlcuding an error signal representing any variations between said sensor output signals, a second comparator receiving the output signal from said first comparator and operative to generate a warning output signal when the received signal exceeds a predetermined maximum threshold signal level and a third comparator and operative to generate a warning output signal when the received signal is less than a predetermined minimum threshold signal level.

13. A hydraulic master cylinder assembly comprising:

(A) a cylinder formed of a non-ferrous material and defining an axial bore;

(B) first and second pistons mounted for stroking reciprocal joint axial movement in said bore, each including a ferrous portion of varying cross-sectional configuration measured along the axis thereof, and respectively coacting with said cylinder to define first and second pressure chambers in said cylinder;

(C) first and second discharge ports in said cylinder communication respectively with said first and second pressure chambers so that pressurized fluid is delivered through said first and second discharge ports in response to stroking axial movement of said pistons in said bore;

(D) a first magnetic sensor mounted on said cylinder exteriorly of said bore proximate the ferrous portion of said first piston and operative to establish a magnetic field extending through the non-ferrous material of said cylinder and into said bore for coaction with said varying cross-sectional configuration of said first piston ferrous portion to generate a first position signal that varies with variations in the axial position of said first piston in said bore; and

(E) a second magnetic sensor mounted on said cylinder exteriorly of said bore proximate the ferrous portion of said second piston and operative to establish a magnetic field extending through the non-ferrous material of said cylinder and into said bore for coaction with said varying cross-sectional configuration of said second piston ferrous portion to generate a second position signal that varies with variations in the axial position of said second piston in said bore.

14. A hydraulic master cylinder assembly according to claim 13 and further including:

(F) control means receiving said first and second pisition signals and operative in response to a predetermined difference in said position signals to generate a warning signal indicating excessive relative movement between said first and second pistons.

15. A hydraulic cylinder assembly comprising:

(A) a cylinder formed of a non-ferrous material and having a cylinder wall defining an axial bore;

(B) a piston mounted for reciprocal axial movement in said bore and having an axially extending portion forming the outer peripheral surface of the piston, formed of a ferrous material, and having a cross-section configuration that varies along the axis of the piston; and

(C) a magnetic sensor mounted exteriorly of said cylinder proximate said piston portion with a portion of said cylinder wall interposed between the radially inner end of said sensor and said piston with said varying cross-section piston portion, said magnetic sensor coacting with said varying cross-section configuration of said piston portion to generate a signal that varies in relation to the linear position of said piston in said bore.

16. A hydraulic cylinder assembly according to claim 15 wherein:

(D) said magnetic sensor is a Hall Effect sensor.

17. A hydraulic cylinder assembly according to claim 15 wherein:

(D) said piston portion has a frustoconical configuration.

18. A hydraulic cylinder assembly according to claim 17 wherein:

(E) said piston further includes first and second cylindrical land portions at the opposite ends of said frustoconical portion.

19. A hydraulic cylinder assembly according to claim 18 wherein:

(F) at least one of said cylindrical land portions is formed of a non-ferrous material.