FR3095629A1 - VARIABLE FILTERED AIR INTAKE VALVE FOR PNEUMATIC AMPLIFIER - Google Patents

Abstract

The present invention relates mainly to an air inlet valve (12) for a pneumatic brake amplifier, said air inlet valve (12) comprising: - a first filter (21) with low permeability having a high quality of filtering and a low air flow rate, - a cup (23) for limiting the maximum deformation of said first filter (21), - a second highly permeable filter (22) having a high air flow rate and a low filtering quality, - said air inlet valve (12) being configured such that when an air flow through the air inlet valve (12) increases, the first filter (21) is capable of deforming until it comes all or part in abutment on the cup (23), so as to free an air passage section at the outer periphery of said first filter (21). Figure 6a

Description

VARIABLE FILTERING AIR INLET VALVE FOR PNEUMATIC AMPLIFIER

The present invention relates to a variable filtering air inlet valve for a pneumatic amplifier. The invention finds a particularly advantageous, but not exclusive, application with ABS (Anti-Blocking System) or ESP (Electronic Stability Program) type braking systems for motor vehicles.

In a manner known per se, a braking system comprises a master cylinder and hydraulic circuits coupled to the output of the master cylinder. Each hydraulic circuit comprises an inlet branch having an inlet solenoid valve and a discharge branch having a discharge solenoid valve and a discharge pump. Brake calipers are coupled to the hydraulic circuits. A computer controls the inlet solenoid valves, the outlet solenoid valves and the outlet pumps, so as to allow the circulation of a hydraulic fluid in the inlet and outlet branches of the hydraulic circuit.

Pressing the brake pedal produces, via a pneumatic brake amplifier, pressurization of the hydraulic fluid in an actuator. This actuator, positioned in a disc brake caliper, comprises a pressurized control piston housed in a control chamber. This piston creates a movement of the pads positioned in this brake caliper which grip the disc and which, by mutual friction, ensure the braking of the vehicle.

The pneumatic brake booster, commonly called "isovac", assists or amplifies the muscular effort delivered by the driver on the brake pedal. The basic principle of this pneumatic amplifier lies in the effort generated by an air pressure differential on either side of a piston supporting the muscular effort delivered by the driver, so that the master cylinder generates a pressure in the hydraulic circuit proportional to the muscular effort added to the pneumatic effort.

For proper operation of the pneumatic amplifier, it is necessary to have air free of impurities (particle pollution). For this purpose, as shown in Figure 1, an air inlet valve 1 is used provided with a filter 2 located around a control rod 3 intended to be connected to the brake pedal.

However, the filter chosen for its filtering qualities harms the passage of air. As can be seen in Figure 2, for current braking, operated at low dynamics (deceleration Dec of the vehicle less than 10m/s ³ ), the air flow passing through the filter is sufficient and the braking is of good quality. . On the other hand, for braking that is certainly less frequent but more dynamic, the air flow becomes insufficient to ensure good braking assistance performance, which has the effect of requiring more effort from the driver Eff_ped to produce the same deceleration to the motor vehicle.

The invention aims to overcome this drawback in particular by proposing an air inlet valve for a pneumatic brake amplifier, said air inlet valve comprising:
- a first low-permeability filter with high filtering quality and a low air flow rate,
- a maximum deformation limiting cup of said first filter,
- a second highly permeable filter with a high air flow rate and low filtering quality,
- said air inlet valve being configured in such a way that when an air flow passing through the air inlet valve increases, the first filter is capable of deforming until it comes fully or partially into abutment on the cup, so as to release an air passage section at the outer periphery of said first filter.

The invention thus makes it possible, thanks to the use of the two filters and the cup, to increase the flow of air that can penetrate the air inlet valve during dynamic braking. The braking assistance performance is then nominal over the entire useful range of braking dynamics. No parasitic increase in pedal effort will be felt by the driver during dynamic braking.

According to one embodiment, the first filter and the second filter are made from a foam material.

According to one embodiment, the first filter has a greater density than the second filter.

According to one embodiment, the cup is partially perforated so as to present a non-zero air passage section.

According to one embodiment, the cup comprises a plurality of petals spaced from one another by air passage spaces.

According to one embodiment, the cup is made of a material perforated with holes.

According to one embodiment, the holes are in particular of circular shape.

According to one embodiment, the cup is made of a material of the mesh type.

The invention also relates to a pneumatic brake amplifier comprising an air inlet valve as previously defined.

The invention further relates to a braking system comprising a pneumatic braking amplifier as previously defined.

The invention will be better understood on reading the following description and on examining the accompanying figures. These figures are given only by way of illustration but in no way limit the invention.

FIG. 1, already described, is a schematic representation of an air inlet valve for a pneumatic brake amplifier according to the state of the art;

FIG. 2, already described, is a graphic representation of the deceleration of a motor vehicle as a function of a pressing force on the brake pedal for an air inlet valve according to the state of the art;

Figure 3 is a schematic representation of a pneumatic brake amplifier comprising an air inlet valve according to the invention;

FIG. 4a illustrates the state of the pneumatic brake amplifier of FIG. 3 during a braking phase;

Figure 4b illustrates the state of the pneumatic brake amplifier of Figure 3 after the braking phase;

FIG. 5 is a schematic representation of an air inlet valve for a pneumatic brake amplifier according to the present invention;

FIG. 6a illustrates the state of the air inlet valve according to the invention during low dynamic pressure on the brake pedal;

FIG. 6b illustrates the state of the air inlet valve according to the invention during high dynamic pressure on the brake pedal;

FIG. 7 is a graphic representation of the deceleration of a motor vehicle as a function of a pressing force on the brake pedal for an air intake valve according to the present invention;

FIGS. 8a, 8b, 8c illustrate different variant embodiments of a cup for limiting deformation of the low permeability filter belonging to the air inlet valve according to the invention;

FIGS. 8a, 8b, 8c illustrate different variant embodiments of a cup for limiting deformation of the low permeability filter belonging to the air inlet valve according to the invention;

FIGS. 8a, 8b, 8c illustrate different variant embodiments of a cup for limiting deformation of the low-permeability filter belonging to the air inlet valve according to the invention.

In FIGS. 3 et seq., identical, similar or analogous elements retain the same reference from one figure to another.

FIG. 3 shows a schematic representation of a pneumatic brake amplifier 10 comprising a control rod 11 intended to be connected to the brake pedal, an air inlet valve 12, and a piston 13 consisting of a rigid plate and a deformable sealing membrane. A front chamber 15 has a volume delimited by a front half-shell 15' and the piston 13. A rear chamber 16 has a volume delimited by a rear half-shell 16' and the piston 13. A pneumatic tapping 18 could possibly be associated to a non-return valve. A vacuum source (not shown) is intended to be connected to tapping 18.

A push rod 19 is connected to the master cylinder. The push rod 19 provides an output force Fs which corresponds to the input force Fe delivered to the brake pedal which is increased by the force delivered by the pressure differential which is exerted on the piston 13.

In FIG. 3, the piston 13 is in the rest position, that is to say excluding braking (the forces Fe and Fs are zero). In this case, the front chamber 15 and the rear chamber 16 are physically in communication thanks to the valve mechanism 12 and therefore at the same pressure. The air pressure is lower than atmospheric pressure, thanks to the vacuum source connected to tapping 18.

FIG. 4a represents the pneumatic amplifier 10 during a braking phase. The forces Fe and Fs are now non-zero. Piston 13 has moved a marked distance ΔL. The communication between the two chambers 15 and 16 is closed by means of the valve 12. Air at atmospheric pressure has been admitted along the arrow A into the front chamber 15 thanks to the valve 12, which has the effect of increasing the air pressure of this chamber 15. There is therefore a pressure differential between the front chamber 15 and the rear chamber 16, which makes it possible to generate the pneumatic assistance force.

Figure 4b shows the pneumatic amplifier 10 after braking. The forces Fe and Fs are again zero. The piston 13 has returned to the rest position. The communication between the front chamber 15 and the rear chamber 16 is again opened via the valve 12 (cf. arrow A), so that the two chambers 15, 16 are then at the same pressure. The vacuum source connected to tapping 18 restores the pressure in pneumatic amplifier 10 before the next braking.

The source of vacuum can take several forms, including the natural aspiration of the heat engine, a vacuum pump mechanically driven by the camshaft of the heat engine, or an electrically driven vacuum pump.

As can be seen in Figure 5, the air inlet valve 12 comprises a first low-permeability filter 21 having a high filtering quality and a low air flow rate, and a second highly permeable filter 22 having a high flow rate of air passage and a low quality of filtering. The relative terms of the "low" permeable/"highly" permeable type are understood relatively by comparison between the characteristics of the first filter 21 and of the second filter 22. Thus, the first "low" permeable filter 21 is less permeable than the second filter 22 "very" permeable. The same is true for the notions of "low" air passage rate and "high" air passage rate. The first filter 21 therefore has a lower air flow rate than the second filter 22. In addition, it is also understood that the first filter 21 has better filtering quality than the second filter 22.

According to a particular embodiment, the first filter 21 and the second filter 22 are made from a foam material. The first filter 21 has a higher density than the second filter 22.

In addition, the valve 12 includes a cup 23 for limiting the maximum deformation of the first filter 21. The cup 23 is interposed between the first filter 21 and the second filter 22. The cup 23 may be curved in the direction of passage of the air. The first filter 21, the second filter 22, as well as the cup 23 are mounted around the control rod 11 carrying a stop 24 against which the second filter 22 can come to rest.

Figure 6a shows the behavior of the air inlet valve 12 in the case of low pedal pressure dynamics. The flow of air q penetrating inside the valve 12 is low and successively passes through the first filter 21 and the second filter 22.

FIG. 6b represents the behavior of the air inlet valve 12 in the case of high pedal pressure dynamics with a high air flow Q. The air flow passing through the filter increasing, the first filter 21 deforms until it comes all or in part to rest on the cup 23. This has the effect of releasing an air passage section at the outer periphery of the first filter 21. Thus, the flow of air that can penetrate the air inlet valve 12 during dynamic braking, this air passing at least through the second filter 22 for its filtration.

As emerges from FIG. 7, the braking assistance performance is then nominal over the entire useful dynamic range of braking, whatever the evolution over time of the deceleration Dec. No parasitic increase in pedal force Eff_ped will be felt by the driver.

Advantageously, the cup 23 is partially perforated so as to present a non-zero air passage section. As illustrated by FIG. 8a, the dish 23 seen from the front comprises a plurality of petals 26 spaced apart from one another by spaces 27 for the passage of air. The petals 26 may have a radial orientation with respect to an axis X of the cup 23. As illustrated by FIG. 8b, the cup 23 may be made of a material perforated with holes 28, in particular of circular shape. As illustrated by FIG. 8c, the cup 23 could also be made of a material of the mesh type.

The valve 12 also includes other components known to those skilled in the art which make it possible to generate the pneumatic assistance force. These components have not been shown, because they do not relate to the object of the present invention relating to the function of filtering the air passing through the valve 12.

Claims (10)

Air inlet valve (12) for pneumatic brake amplifier (10), characterized in that said air inlet valve (12) comprises:
- a first low-permeability filter (21) having a high filtering quality and a low air flow rate,
- a cup (23) for limiting the maximum deformation of said first filter (21),
- a second highly permeable filter (22) having a high air flow rate and low filtering quality,
- said air inlet valve (12) being configured such that when an air flow passing through the air inlet valve (12) increases, the first filter (21) is able to deform until all or part comes to rest on the cupel (23), so as to release an air passage section at the outer periphery of said first filter (21). Air inlet valve according to Claim 1, characterized in that the first filter (21) and the second filter (22) are made from a foam material. Air inlet valve according to Claim 2, characterized in that the first filter (21) has a greater density than the second filter (22). Air inlet valve according to any one of Claims 1 to 3, characterized in that the cup (23) is partially perforated so as to present a non-zero air passage section. Air inlet valve according to Claim 4, characterized in that the cup (23) comprises a plurality of petals (26) spaced from one another by air passage spaces (27). Air inlet valve according to Claim 4, characterized in that the cup (23) is made of a material perforated with holes (28). Air inlet valve according to Claim 6, characterized in that the holes (28) are in particular of circular shape. Air inlet valve according to Claim 4, characterized in that the cup (23) is made of a material of the mesh type. Pneumatic braking amplifier (10) comprising an air inlet valve (12) as defined according to any one of the preceding claims. Braking system comprising a pneumatic brake amplifier as defined according to the preceding claim.