Brakes – With condition indicator – Wear
Reexamination Certificate
2000-04-21
2001-11-06
Graham, Matthew C. (Department: 3613)
Brakes
With condition indicator
Wear
C188S00111E
Reexamination Certificate
active
06311804
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system for electrically detecting piston positions in a hydraulic system, and more specifically to a system for electrically detecting piston positions in a hydraulic brake system for improved control of response to changes within the brake system.
BACKGROUND OF THE INVENTION
It is known to use pressure switch assemblies actuatable in response to fluid pressure for detecting a predetermined condition within a hydraulic system. For example, U.S. Pat. No. 4,454,393 discloses an electronic warning device for signaling an error condition in a hydraulic system employing three pistons which are spatially arranged so that when predetermined spatial relations are established therebetween in response to fluid pressure, electronic signals are issued by switching elements to indicate an error condition.
It is also known to employ stroke switch assemblies for detecting a predetermined condition within a brake system. For example, U.S. Pat. No. 5,388,894 discloses a brake fluid distribution system for use in antilocking brake systems (ABS) which employs a switch in communication with low pressure accumulator for activating pumps that evacuate the brake fluid from the low pressure accumulator. The accumulator has an indicator piston which indicates the amount of brake fluid within the accumulator. When the amount of brake fluid within the accumulator reaches a preselected level, the indicator piston causes a switch piston to turn on the switch for activating pumps that evacuate the brake fluid.
Like the >894 patent, U.S. Pat. No. 4,799,048 discloses an accumulator disposed in fluid supply tube system of a hydraulically operated device (e.g., automotive hydraulic anti-skid braking system) which employs a switch mechanism, e.g., a reed switch, to indicate when there is excessive fluid pressure in the accumulator.
The prior art pressure switch or stroke switch assemblies in hydraulic systems, especially hydraulic brake systems, pose a significant disadvantage because they do not indicate different positions of the brake-applying/brake-releasing piston. This drawback will be further illustrated with respect to spring apply, hydraulic release (SAHR) brake systems for vehicles. SAHR brakes, as known, generally operate in the following manner: a spring normally biases a piston which applies the brakes; normal operation of a brake release actuator causes pressurized hydraulic fluid to move the piston against spring bias to release the brakes.
If the movement of the piston to release the brakes in the SAHR brake system is partially blocked so that brakes are not fully released, the prior art pressure switch assemblies may still indicate that the brakes are fully released if the amount of hydraulic fluid pressure measured within the system exceeds a certain preset threshold. This may result in significant damage to the components of the brake system if an operator of the vehicle operates the vehicle believing that the brakes are fully released. Also, stroke switch assemblies, such as used in the >048 and >894 patents, are not very useful for controlling brake operations since the stroke switch assemblies only detect one position of the piston.
Therefore, what is desired is a system for a hydraulic system which will accurately, electrically indicate brake positions by detecting piston positions so that braking operations can be controlled to respond to changes in the hydraulic system.
SUMMARY OF THE INVENTION
Accordingly, it is one object of the invention to provide a system for electrically detecting piston positions of a moveable piston within a piston housing of a hydraulic system.
Another object of the invention is to provide a system for electrically detecting piston positions in a spring apply, hydraulic release (SAHR) brake system.
A further object of the invention is to provide a system for electrically detecting piston positions in a brake system which uses electrically conductive areas along the path of movement of the piston so that there are no moving wires.
Still another object of the invention is to provide a system for electrically detecting piston positions in a brake system which uses an electrical conductor attached to the piston so that there are no moving wires.
Yet another object of the invention is to provide a system for electrically detecting piston positions and for controlling a pump which governs the movement of the piston in accordance with the piston position detected.
A further object of the invention is to provide a system for electrically detecting piston positions by employing conductive areas along the path of movement of the piston having different resistance values.
These and other objects of the invention are achieved by a system for electrically detecting different positions of a movable piston within a piston housing of a hydraulic system. The system includes at least two electrically conductive pads mounted on the piston housing at different locations along the path of movement of the piston, an electrically conductive segment mounted on the piston housing along the path of movement of the piston adjacent the conductive pads, and an electrical coupler, such as a spring-loaded conductor, attached for movement with the piston to provide an electrical connection between each conductive pad and the conductive segment as the piston moves along within the piston housing. The system also includes an electronic control unit, which may be a microprocessor, coupled to each conductive pad and the conductive segment to detect electrical connection between each conductive pad and the conductive segment. Each electrical connection corresponds to a specific position of the piston. Depending upon the electrical connection detected, the electronic control unit causes the hydraulic system to respond in a predetermined manner (for example, causing a hydraulic pump of the hydraulic system to turn off or a solenoid valve to close so that no more hydraulic fluid enters the piston housing).
In another embodiment of the present invention, conductive pads having different preselected resistance values are used and the electronic control unit is designed to measure the different preselected resistance values.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
REFERENCES:
patent: 2914630 (1959-11-01), Ralston
patent: 3776329 (1973-12-01), Hope et al.
patent: 4642603 (1987-02-01), Martinez, Jr.
patent: 4883150 (1989-11-01), Arai
patent: 5358075 (1994-10-01), Jarzombek
patent: 5967266 (1999-10-01), Carnegie
patent: 466604 (1992-01-01), None
patent: 1512003 (1978-05-01), None
Baalmann Joseph G.
Hanaway Roger D.
McMullen Robert J.
Graham Matthew C.
Haldex Brake Corporation
St. Onge Steward Johnston & Reens LLC
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