Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
1999-01-08
2001-02-27
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S582000, C060S591000
Reexamination Certificate
active
06192685
ABSTRACT:
The present invention relates to a master cylinder intended in particular to equip a motor vehicle electro-hydraulic braking installation.
BACKGROUND OF THE INVENTION
Electro-hydraulic braking installations conventionally comprise a service braking system using an external energy source and an emergency braking system using muscle power as its source, these two braking systems being controlled by a brake master cylinder, the actuating pedal of which is situated in the cockpit of the vehicle.
The braking system with an external energy source comprises a generator of brake fluid at high pressure, comprising a hydraulic pump associated with a hydraulic pressure accumulator. Upon a braking action performed by this system, the pressure supplied by the hydraulic pressure accumulator is communicated to the wheel brake cylinders via at least one solenoid valve so that the pressure leaving this solenoid valve has a value which is a function of the travel of the brake pedal and of the force with which this pedal is actuated, or a function of the force with which a handbrake lever is actuated, or alternatively a function of the brake fluid pressure produced using the footbrake pedal or the handbrake lever.
In such operation in service braking mode, the master cylinder is normally isolated from the braking installation of the vehicle by means of a shut-off solenoid valve. This then means that brake fluid cannot flow back from the master cylinder towards the wheel brake cylinders and that its piston cannot move or can move only by a minimum travel. However, for the brake pedal or handbrake lever to have a normal actuating travel, depending on the force with which they are actuated, a device which simulates the brake actuation travel is used.
Such a device that simulates the brake actuation travel is known, for example, from document U.S. Pat. No. 4,462,642. The known brake actuation travel simulator comprises a simulator cylinder with a simulator piston which can move in this cylinder when it is acted upon by the pressure of the brake fluid from the master cylinder, against the action of a spring and which can move inside this cylinder.
In the event of failure of the braking system with an external energy source, for service braking mode, the shut-off solenoid valve is switched to allow the master cylinder to actuate the wheel brake cylinders itself, for an emergency braking operating mode using as its energy source muscle power provided by the driver of the vehicle.
The brake actuation travel simulator device according to the aforementioned document is hydraulically connected to the master cylinder and to the shut-off solenoid valve and communicates, even in emergency braking mode, with the brake master cylinder. The known brake-actuating simulator therefore has the drawback of absorbing a certain amount of brake fluid in emergency braking mode using muscle power, and this needlessly increases the brake pedal travel and detracts from the effectiveness in emergency braking.
SUMMARY OF THE INVENTION
The present invention falls within this context in that it proposes, in the known way, a master cylinder for a vehicle hydraulic braking installation, the installation comprising a service braking system using external energy, and an emergency braking system using muscle power for actuating wheel brake cylinders, it being possible for the master cylinder to be isolated from the wheel brake cylinders by at least one shut-off valve for service braking using external energy, the master cylinder being associated with a simulator simulating the brake actuation travel and comprising a simulator piston defining a simulation chamber which can receive brake fluid from the brake master cylinder, an elastic simulator element urging simulator piston against the action of the pressure of the brake fluid in the simulation chamber, the master cylinder being of the tandem type and comprising a bore in which a primary piston and a secondary piston are mounted so that they can slide from respective positions of rest and therein delimit a primary working chamber and a secondary working chamber, respectively.
In this context, the object of the present invention is to propose a master cylinder, associated with a brake actuation travel simulation device for a motor vehicle electro-hydraulic braking installation which allows an emergency braking mode using muscle power, in which all of this muscle power is used for the emergency braking without this power being dissipated into other devices, it being necessary for this master cylinder to be reliable under all circumstances, easy to manufacture and low in cost.
To this end, the master cylinder of the invention, which in other respects is in accordance with the above preamble, is essentially characterized in that the simulation chamber has an inlet orifice opening into the bore, and in that means of selective communication connect the simulation chamber to the primary working chamber when the secondary piston is in its position of rest, and isolate the simulation chamber from the primary working chamber when the secondary piston is moved away from its position of rest.
According to a first embodiment of the invention, the means of selective communication comprise a peripheral groove formed in the bore and a sealing element borne by the secondary piston and capable selectively of shutting off the bore some distance from the peripheral groove, the peripheral groove being arranged in the bore between the primary piston and the inlet orifice of the simulation chamber, and the sealing element being located selectively facing the peripheral groove when the secondary piston is in its position of rest.
According to a second possible embodiment of the invention, the means of selective communication comprise: an axial hole made in the secondary piston and having an inlet opening into the primary working chamber; a radial hole made in the secondary piston and having an outlet permanently communicating with the simulation chamber and selectively placed in communication with the inlet of the axial hole; and an elongate plunger which is stationary with respect to the bore, mounted so that it can slide in the axial hole and interacting at least with the axial hole of the secondary piston to form a hydraulic valve which selectively isolates the outlet of the radial hole from the inlet of the axial hole when the secondary piston is moved from its position of rest.
In this second embodiment, the plunger rests, for example, on a pin passing across the bore.
According to a first possible alternative form of the second embodiment of the invention, the plunger has a blind axial hole and a radial passage communicating with the blind axial hole, the radial passage forming a first seat for the hydraulic valve, being arranged selectively facing the radial hole of the secondary piston when this secondary piston is in its position of rest, and being shut off by the axial hole of the secondary piston which itself forms a second seat for the hydraulic valve, when this secondary piston is moved away from its position of rest.
According to a second possible alternative form of the second embodiment of the invention, the inlet of the axial hole in the secondary piston bears an annular seal which forms a first seat for the hydraulic valve and which is selectively shut off by the plunger, which itself forms a second seat for the hydraulic valve, when the secondary piston is moved away from its position of rest.
In this second embodiment, the plunger rests, for example, on a pin passing across the bore.
Other objects, features and advantages of the present invention will emerge more clearly from the description which follows of one embodiment given by way of an illustration with reference to the appended drawings in which:
REFERENCES:
patent: 4812777 (1989-03-01), Shirai
patent: 5887432 (1999-03-01), Clauss et al.
Bourlon Philippe
Levrai Roland
Quirant Werner
Comstock Warren
Lazo Thomas E.
Lopez F. Daniel
McCormick Jr. Leo H.
Robert & Bosch GmbH
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