Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2001-01-04
2003-08-26
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S581000, C188S354000, C303S009610
Reexamination Certificate
active
06609370
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to dual hydraulic booster assemblies for vehicle hydraulic braking systems of the kind comprising a pair of pedal-operated hydraulic boosters which are adapted to be operated simultaneously for applying brakes on wheels on opposite sides of a vehicle for vehicle retardation and independently for applying a brake on a wheel on one side of the vehicle to facilitate steering.
Dual hydraulic booster assemblies have application to braking systems for vehicles where it is desirable to achieve braking on front and rear wheels for normal service braking but to restrict braking to one rear wheel on one side only of the vehicle for steering purposes and in particular, but not exclusively, agricultural vehicles such as tractors which may tow trailers.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a dual hydraulic booster assembly which can be used for such application.
It is a preferred object of the present invention to provide a dual hydraulic booster assembly in which the fluid pressure obtained when both boosters are operated simultaneously is increased for braking on both sides of the vehicle.
According to one aspect of the present invention there is provided a dual hydraulic booster assembly for a vehicle braking system incorporating a logic valve responsive to booster pressures to control the supply of pressure fluid for braking on one side of a vehicle when one booster is operated on its own in a first mode of operation, and for braking on both sides of a vehicle when both boosters are operated simultaneously in a second mode of operation.
By this invention, the logic valve controls the supply of pressure fluid so that, in the first mode of operation, when one booster is operated, the supply of pressure fluid causes braking of one rear wheel on one side of the vehicle associated with that booster to facilitate steering and, in the second mode of operation, when both boosters are operated simultaneously, the supply of pressure fluid causes braking of the wheels on both sides of the vehicle for normal service braking.
More particularly, the logic valve controls the supply of fluid pressure in the second mode of operation when both boosters are operated to cause braking of the front wheels of the vehicle and a trailer (where provided) with the boosters causing braking of the rear wheels of the vehicle. In this way, all wheels are braked in the second mode of operation. By contrast, the logic valve isolates the supply of fluid pressure from the brakes for the front wheels and trailer (where provided) in the first mode of operation when only one booster is operated so that only the rear wheel associated with that booster is braked.
The dual hydraulic booster assembly of the present invention has the advantage that the logic valve is common to both boosters in an integrated unit that avoids the requirement for auxiliary logic heads and valves separate from the booster assembly. As a result, the number of parts and associated pipework and fittings are reduced to a minimum thereby facilitating installation and simplifying repair/maintenance.
Preferably, each booster comprises a boost piston working in a bore in a body adapted to generate an output force for operating a hydraulic master cylinder coupled to the rear brakes on one side of the vehicle in response to pressure in a boost chamber which is applied to a proportional power pressure chamber under the control of a control valve, in turn responsive to an input force from the pedal.
Advantageously, each booster and associated master cylinder are combined and both booster and master cylinder assemblies are integrated in a common housing with the outputs from the master cylinders arranged to operate the rear brakes on opposite sides of the vehicle. For example, each master cylinder may operate one rear brake such that a braking force may be applied to the rear wheel on that respective side only to facilitate steering.
In one construction the logic valve comprises inner and outer pressure-responsive telescopic pistons working in a bore in the body and responsive to pressure applied to the outer ends by the associated booster to control the supply of pressure fluid in the first and second modes of operation.
Preferably, the pistons are held in a passive condition of the logic valve by a first spring acting between the pistons, and by a second spring acting on the outer piston only with respective pre-loads of the springs being chosen to withstand the collective threshold forces of seals on each piston to ensure full return of each piston to the passive condition upon release of the pressure applied to the outer end.
Advantageously, when both boosters are actuated simultaneously in the second mode of operation, displacement of both pistons relative to each other allows flow through passages leading from the boosters to a pressure chamber defined between the pistons to activate a braking system for the front wheels on both sides of the vehicle and trailer brakes (where provided), with the passages being isolated from the pressure chamber in both the passive condition and when either booster is operated on its own in the first mode of operation.
More particularly, relative displacement of the pistons provides flow paths through the pressure chamber for the supply of pressure fluid to a common outlet port in the second mode of operation to activate the braking system for the front wheels and trailer brakes (where provided), and to isolate the outlet port in the first mode of operation.
In this way, the front brakes/trailer brakes are only applied when both boosters are actuated and, when either booster is operated on its own, the front brakes/trailer brakes are isolated so as to apply only the respective rear brake coupled to that booster.
Preferably, the logic valve is also provided with oppositely acting one-way return valves which are normally open in the passive condition and are closed to prevent fluid flowing from the pressure chamber back to the boosters when the pressure chamber is pressurised and which open again to return fluid to a reservoir upon release of the boost pressure at the end of the braking cycle.
Advantageously, the pistons are displaced by the full boost pressure from the associated booster which acts to close the one-way valves and, when both boosters are operated together, the pressure chamber is connected to the proportional pressure in the proportional power pressure chambers of both boosters which never exceeds the full boost pressure to ensure the one-way valves remain closed.
At the knee-point of the booster assembly, when the proportional pressure equals the full boost pressure, the logic valve is held in equilibrium and the springs urge the pistons into the passive position, but with full boost pressure applied through the pressure chamber.
The performance of the dual hydraulic booster assembly with logic valve is satisfactory for most applications but there can be situations for normal service braking when the front and rear braking requirement is such that a higher fluid pressure is required than the pressure conventionally available on the vehicle.
Accordingly, in a preferred arrangement, when both boosters are operated simultaneously, the pressure of the pressure fluid is increased by the provision of a pressure amplifier valve to enable higher fluid pressures to be obtained for the braking requirements under normal service braking.
The pressure amplifier valve may be provided separate from the booster assembly so as to receive the pressure fluid from the booster assembly via the logic valve in the second mode of operation. This adds to the overall cost of the braking system, in particular, the installation and maintenance costs for providing a separate pressure amplifier valve.
More preferably, however, the pressure amplifier valve is incorporated into the booster assembly to produce a single integrated unit. In this way, installation and maintenance is simplified compared to the provision of a separate pressure amplifier v
ArvinMeritor, Inc.
Carlson & Gaskey & Olds
Lopez F. Daniel
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