Power plants – Pressure fluid source and motor – Pulsator
Patent
1993-07-27
1995-05-16
Look, Edward K.
Power plants
Pressure fluid source and motor
Pulsator
60581, B60T 1120, F15B 700
Patent
active
054149983
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hydraulic tandem master cylinder comprising: end-cap; fashion, from a rest position in which these pistons are furthest away from the end-cap as far as at least an actuation position in which these pistons are moved closer to the end-cap; secondary pistons, this chamber containing first elastic means having a predetermined stiffness and exerting a first elastic force between the pistons in a direction which tends to move these pistons apart; and the end-cap, this chamber containing second elastic means having a predetermined stiffness and exerting a second elastic force between the secondary piston and the end-cap in a direction which tends to move this piston away from the end-cap, rest position to said actuation position, from respective low values to respective high values, the low value of the second force being greater than that of the first force, whereas the high value of the second force is less than that of the first force.
Master cylinders of this type have been used for very many years in dual braking circuits for motor vehicles, and Patent GB 2,169,368 provides a relatively recent example of this.
One problem which conventionally arises in tandem master cylinders is to make the pressure in the secondary chamber as close as possible to that which prevails in the primary chamber for as short a stroke of the primary piston as possible.
The difficulty to be overcome in order to solve this problem lies in the fact that the primary spring has, a priori, to be as stiff as possible so that the actuation of the primary piston rapidly drives that of the secondary piston by compressing the secondary spring, whereas the secondary spring has nevertheless to be quite stiff in order to enable the secondary piston, in the absence of actuation, to return to its rest position.
This problem is conventionally solved, as Patent GB 2,169,368 shows, by compressing at least the primary spring in a cage which can be deformed in compression but the maximum length of which is adjusted and predetermined as a function of the maximum distance between the primary and secondary pistons.
The object of the present invention is to provide means which make it possible to dispense with the use of such cages and with the fitting and adjustment operations which they require.
This object itself gives rise to two new difficulties connected with the absence of adjustment, the first stemming from the fact that the stiffness of the springs, in the absence of measurement, is only known with a relatively large uncertainty, and the stemming from the mechanical tolerances of the manufactured components and which themselves lead to a degree of uncertainty in the length of the springs, in the maximum distance between the pistons, etc.
In order to overcome these difficulties, the tandem master cylinder of the invention is essentially characterized in that the first elastic means essentially comprise: position of the pistons, at least the greatest part of the low value of the first force, this first prestressed spring having a stiffness at least equal to that of the second elastic means, and actuating the pistons, a force which is added to that of the prestressed spring and which is several times greater than that which this additional spring develops for the rest position of the pistons.
The second elastic means may then quite simply comprise a second prestressed spring, of lower stiffness than that of the first prestressed spring.
The first prestressed spring and the additional spring are advantageously arranged one inside the other, the second preferably being inside the first.
Furthermore, it is advantageous for these springs to be coiled in opposite directions so as to prevent any catching of one on the other.
Other characteristics and advantages of the invention will clearly emerge from the description which is made of it hereinbelow, by way of indication and by no means of limitation, with reference to the accompanying drawings in which:
FIG. 1 is a sectional view of a tandem master cylinder in accordanc
REFERENCES:
patent: 3421321 (1969-01-01), Lewis
patent: 4779422 (1988-10-01), Brown
patent: 5036751 (1991-08-01), Seip et al.
patent: 5050382 (1991-09-01), Burgdorf et al.
patent: 5179834 (1993-01-01), Rauschenbach
Manzo Vincenzo
Tristano Nicola
Bendix Altecna S.p.A.
Look Edward K.
McCormick Jr. Leo H.
Nguyen Hoang
Palguta Larry J.
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