Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
1998-11-25
2001-03-27
Nguyen, Hoang (Department: 3748)
Power plants
Pressure fluid source and motor
Pulsator
C060S585000
Reexamination Certificate
active
06205783
ABSTRACT:
This invention relates to reservoir assemblies for vehicle hydraulic braking systems.
There is a problem of overfilling reservoir assemblies with the attendant risk that overflow may occur which is not only messy but represents a fire hazard. This may occur simply by filling to the top, above the marked “max” level. In braking systems in which the reservoir assembly contains a volume of fluid for supplying a pump, which in turn charges an accumulator, if the reservoir is overfilled whilst the accumulator is charged, subsequent discharge from the accumulator could cause overflow with the inherent problems discussed above.
In addition, in vehicle hydraulic braking systems of the kind in which a wheel brake is adapted to be applied by a first power circuit comprising a source of hydraulic fluid under pressure under the control of the control valve, and a second back-up hydrostatic circuit capable of actuating the brake hydrostatically from a pedal-operated master cylinder upon failure of the first circuit, each circuit is supplied with hydraulic fluid from a dedicated reservoir. Typically such a braking system may be of the brake-by-wire electro-hydraulic type (EMB) in which the control valve comprises a solenoid-operated valve which is operated by an energising current from an electronic control unit and of which the magnitude is determined by operation of a brake-pedal. The source of hydraulic fluid under pressure may be provided by a gas-charged hydraulic accumulator.
In such known hydraulic braking systems it is desirable to separate the fluid in the hydrostatic circuit from that in the first power circuit. However certain faults in the system will cause fluid from the reservoir of one circuit to be transferred to the reservoir of the other circuit. Such fluid transfer could take place in either direction. The fault will, ultimately, be detected by a fluid level warning indicator (FLWI) with which each reservoir is incorporated. One FLWI will be actuated by reduced fluid level in its associated chamber, but it may not be possible for the system to diagnose accurately the original cause. In such systems a service engineer may change a wrong major component of a particular circuit.
Faults which may cause fluid to transfer from one reservoir to the other may comprise:
a) leakage of a seal which separates the back-up hydrostatic circuit from return to reservoir line of the first power circuit; and/or
b) blocking of a return line from a solenoid-operated valve to the reservoir.
Unless the fault is diagnosed correctly a complete solenoid-operated valve may be replaced unnecessarily when all that has occurred is blockage of a return line.
If fluid in a reservoir is simply replenished, without identifying and fixing the real fault, a warning lamp of the FLWI might be extinguished but over flow will eventually occur without warning, at the other reservoir. Not only is this messy but, more importantly, represents a fire hazard, as discussed above.
Of course the problem can be overcome by the provision of two separate reservoirs, each provided with an individual filling point. However it is preferable for the two reservoirs to have a single, common, filling point. The most convenient way to achieve this would be to combine the two reservoirs into a common tank containing two chambers separated by a baffle in a manner similar to known reservoirs fitted to pedal-operated master cylinders of the tandem type. Such a combined tank will neatly avoid the risk of over flow from a reservoir, but will neutralise attempts to detect those faults causing fluid transfer. Excess fluid in one chamber of the tank will spill over into the other chamber, so that the levels will not change. It would, of course, be a simple matter to arrange for the baffle height to exceed the normal maximum level for one of the two chambers, but this would only allow transfer detection in one sense. Such transfer cannot take place in an opposite direction from the chamber of the first power circuit to the chamber of the second back-up hydrostatic circuit because after filling the tank, the fluid level in the chamber for the second back-up hydrostatic circuit will always be level with the top of the baffle. Any additional fluid introduced, for example to compensate for leakage due to a blocked return line as described above, will merely flow over the baffle and back into the chamber supplying the first power circuit.
According to one aspect of our invention, in a reservoir assembly for a vehicle hydraulic braking system and including at least one chamber for the storage of hydraulic fluid, the reservoir assembly is provided with means for increasing the effective volume of the chamber.
This enables a volume of fluid to be accommodated in a chamber of increased volume, thereby substantiously eliminating the possibility of volume in excess of a given volume from overflowing from the chamber.
Conveniently means for increasing the effective volume of the chamber is operative automatically with fitting of a filling cap onto the reservoir assembly to seal a filler opening for that chamber.
According to another aspect of our invention in a reservoir assembly for a vehicle hydraulic braking system comprising a common tank for hydraulic fluid which is divided internally into first and second chambers by means of an imperforate baffle and the tank has a single filler opening through which one of the chambers can be filled directly with the other chamber being filled indirectly to a given level by spillage over the baffle, the said one chamber is provided with means for increasing its effective volume automatically with fitting of a filling cap onto the tank to seal the filler opening.
Increasing the effective volume of the said one chamber ensures that the fluid level in that chamber is reduced below baffle height sufficiently to prevent fluid from that chamber from spilling over the baffle and into the other chamber. This is achieved by accommodating a given volume of fluid in a chamber of which the effective volume has been increased.
When the reservoir is installed in the vehicle hydraulic braking system of the known type described above, the said one chamber supplies fluid to the second back-up hydrostatic circuit and the other chamber supplies fluid to the first power circuit. This enables any transfer of fluid, for example because of seal leakage, from the power circuit to the hydrostatic circuit to be detected as a result of change in the level of fluid in the said one chamber. Unless the original level is below baffle height it will merely spill over.
The means for increasing the effective volume of the said chamber comprises a hollow member housed within the chamber and moveable from the first position, in which it defines within the chamber a first given volume, into a second position, in which the effective volume of the chamber is increased to a second given volume, and in which the volume of fluid which can then be accommodated within the chamber lies below the baffle height.
The hollow member may comprise a bellows which is located in the fully extended position when the chamber is filled with fluid and in which the chamber is of a first given volume but which is contracted by co-operation with the filler cap to increase the effective volume of the chamber to the second given volume. The bellows is sealed from the interior of the chamber so that no fluid enters the bellows.
The interior of the bellows may be exhausted to atmosphere. Alternatively it may be connected by a pipe into the reservoir above the fluid level. Not only does this ensure that no vacuum is created within the interior of the bellows, but it also enables any fluid permeating through the wall of the bellows to be returned to the reservoir, rather than be lost to the system.
In another construction the hollow member may comprise a hollow bucket which is displaced downwardly into the chamber as the filler cap is fitted onto the tank, initial movement of the bucket acting to displace the fluid over the baffle into the other chamber and reduce the effecti
Harris Alan Leslie
Holding Keith Lawrence
Mortimer Ivan
Uzzell Robert George
Lucas Industries Public Limited Company
MacMillan Sobanski & Todd LLC
Nguyen Hoang
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