GB2025534A - Diaphragm suction pump - Google Patents

Abstract

The invention relates to a diaphragm suction pump, particularly for actuating a device in a motor vehicle, for example a brake servo booster, the pump being of the kind with a reciprocating diaphragm driven by a connecting rod working on an eccentric, and with an air chamber, at the connecting rod side of the diaphragm, which is adapted to be pressurized. The invention is characterised in that the air chamber, at the connecting rod side of the diaphragm, communicates with the external atmosphere through at least one sniffer valve arranged to admit air into the chamber from the external atmosphere but preventing air from escaping from the chamber. <IMAGE>

Description

SPECIFICATION Diaphragm suction pump The invention relates to a diaphragm suction pump, particularly for actuating a device in a motor vehicle, for example a brake servo booster, with a reciprocating diaphragm driven by a connecting rod working on an eccentric.

Suction pumps of the diaphragm type are often used in motor vehicles for actuating various auxiliaries. In particular, in a vehicle equipped with a fuel-injection engine, or a diesel engine, a diaphragm suction pump is often used for actuating the brake servo booster because engine inlet suction is inadequate for this purpose, particularly at low engine speeds. But the known suction pumps of this type have the disadvantage that the air trapped in the air chamber under the diaphragm, that is at the connecting rod side of the diaphragm, leaks out and consequently during the delivery stroke of the pump the diaphragm flops inside out, reversing the direction of its curvature and increasing the unswept volume of the suction chamber, a highly undesired result.

To prevent this, what is required is to maintain sufficient positive pressure in the air chamber under the diaphragm to stabilize the diaphragm and prevent it from flopping inside out. A solution of this kind is described in the German Gebrauchsmuster 66 08 311. The air chamber under the diaphragm, that is at its connecting rod side, is sealed air-tight against the surrounding atmosphere so that all through the delivery stroke the air chamber contains a positive air pressure, for stabilizing the diaphragm. Nevertheless, some air unavoi dably leaks out through seals of the air chamber and in the course of time positive pressure is lost in the air chamber, at least during the upper portion of the stroke, degrading the stability of the diaphragm.

The intention in the present invention is to provide a pump in which leakage from the air chamber, for example due to worn out seals, does not degrade the stability of the diaphragm, changing the unswept volume of the suction chamber.

Starting from a pump of the kind mentioned at the beginning, the problem is solved, according to the invention, in that the air chamber, at the connecting rod side of the diaphragm, communicates with the external atmosphere through at least one sniffer valve arranged to admit air into the chamber from the external atmosphere but preventing air from escaping from the chamber. This ensures that the air chamber always contains a positive pressure, all through the delivery stroke of the pump, so that the diaphragm does not flop inside out.

To prevent damage to the diaphragm, or other parts of the pump, the sniffer valve can be equipped with an air filter, to prevent particles of grit or the like from being sucked in with the air.

The invention will now be described in greater detail on the basis of the example represented in the drawing.

The drawing shows a diaphragm suction pump intended, in particular, for actuating a device in a motor vehicle, such as a brake servo booster. When the diaphragm 1 moves downwards from top dead centre towards bottom dead centre a positive pressure, that is to say a pressure above atmospheric, builds up in the air-tight chamber 2 under the diaphragm 1, the positive pressure stabilizing the diaphragm, that is keeping it upwards-convex in shape, as represented in the drawing. The pressure in chamber 2 is prevented from falling substantially below atmospheric pressure at any time by a sniffer valve 3 which opens as soon as the least suction develops in chamber 2, admitting air from the external atmosphere into chamber 2. Thus even near top dead centre the pressure in chamber 2 is at least equal to the surrounding atmospheric pressure.As soon as the diaphragm 1 moves downwards the sniffer valve 3 closes and a positive pressure builds up in chamber 2, stabilizing the upwards-convex shape of the diaphragm all through the subsequent movements of the diaphragm. The sniffer valve 3 compensates any outward leakage of air from chamber 2, which consequently never contains suction.

The pump is driven, in the conventional manner, by a connecting rod 4, an eccentric shaft 5 and a pulley wheel 6. The sniffer valve 3 can, if desired, by equipped with an air filter 7.

The sniffer valve 3 is conveniently constituted by a resilient flap which permits oneway flow of atmospheric air through an orifice normally covered by the flap.

1. A diaphragm suction pump, particularly for actuating a device in a motor vehicle, for example a brake servo booster with a reciprocating diaphragm driven by a connecting rod working on an eccentric, and with an air chamber, at the connecting rod side of the diaphragm, which is adapted to be pressurized, characterised in that the air chamber, at the connecting rod side of the diaphragm, communicates with the external atmosphere through at least one sniffer valve arranged to admit air into the chamber from the external atmosphere but preventing air from escaping from the chamber.

2. A diaphragm suction pump according to claim 1, characterised in that the sniffer valve is equipped with an air filter.

3. A pump according to either of claims 1 or 2, wherein the sniffer valve is a one-way

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Diaphragm suction pump The invention relates to a diaphragm suction pump, particularly for actuating a device in a motor vehicle, for example a brake servo booster, with a reciprocating diaphragm driven by a connecting rod working on an eccentric. Suction pumps of the diaphragm type are often used in motor vehicles for actuating various auxiliaries. In particular, in a vehicle equipped with a fuel-injection engine, or a diesel engine, a diaphragm suction pump is often used for actuating the brake servo booster because engine inlet suction is inadequate for this purpose, particularly at low engine speeds. But the known suction pumps of this type have the disadvantage that the air trapped in the air chamber under the diaphragm, that is at the connecting rod side of the diaphragm, leaks out and consequently during the delivery stroke of the pump the diaphragm flops inside out, reversing the direction of its curvature and increasing the unswept volume of the suction chamber, a highly undesired result. To prevent this, what is required is to maintain sufficient positive pressure in the air chamber under the diaphragm to stabilize the diaphragm and prevent it from flopping inside out. A solution of this kind is described in the German Gebrauchsmuster 66 08 311. The air chamber under the diaphragm, that is at its connecting rod side, is sealed air-tight against the surrounding atmosphere so that all through the delivery stroke the air chamber contains a positive air pressure, for stabilizing the diaphragm. Nevertheless, some air unavoi dably leaks out through seals of the air chamber and in the course of time positive pressure is lost in the air chamber, at least during the upper portion of the stroke, degrading the stability of the diaphragm. The intention in the present invention is to provide a pump in which leakage from the air chamber, for example due to worn out seals, does not degrade the stability of the diaphragm, changing the unswept volume of the suction chamber. Starting from a pump of the kind mentioned at the beginning, the problem is solved, according to the invention, in that the air chamber, at the connecting rod side of the diaphragm, communicates with the external atmosphere through at least one sniffer valve arranged to admit air into the chamber from the external atmosphere but preventing air from escaping from the chamber. This ensures that the air chamber always contains a positive pressure, all through the delivery stroke of the pump, so that the diaphragm does not flop inside out. To prevent damage to the diaphragm, or other parts of the pump, the sniffer valve can be equipped with an air filter, to prevent particles of grit or the like from being sucked in with the air. The invention will now be described in greater detail on the basis of the example represented in the drawing. The drawing shows a diaphragm suction pump intended, in particular, for actuating a device in a motor vehicle, such as a brake servo booster. When the diaphragm 1 moves downwards from top dead centre towards bottom dead centre a positive pressure, that is to say a pressure above atmospheric, builds up in the air-tight chamber 2 under the diaphragm 1, the positive pressure stabilizing the diaphragm, that is keeping it upwards-convex in shape, as represented in the drawing. The pressure in chamber 2 is prevented from falling substantially below atmospheric pressure at any time by a sniffer valve 3 which opens as soon as the least suction develops in chamber 2, admitting air from the external atmosphere into chamber 2. Thus even near top dead centre the pressure in chamber 2 is at least equal to the surrounding atmospheric pressure.As soon as the diaphragm 1 moves downwards the sniffer valve 3 closes and a positive pressure builds up in chamber 2, stabilizing the upwards-convex shape of the diaphragm all through the subsequent movements of the diaphragm. The sniffer valve 3 compensates any outward leakage of air from chamber 2, which consequently never contains suction. The pump is driven, in the conventional manner, by a connecting rod 4, an eccentric shaft 5 and a pulley wheel 6. The sniffer valve 3 can, if desired, by equipped with an air filter 7. The sniffer valve 3 is conveniently constituted by a resilient flap which permits oneway flow of atmospheric air through an orifice normally covered by the flap. CLAIMS

1. A diaphragm suction pump, particularly for actuating a device in a motor vehicle, for example a brake servo booster with a reciprocating diaphragm driven by a connecting rod working on an eccentric, and with an air chamber, at the connecting rod side of the diaphragm, which is adapted to be pressurized, characterised in that the air chamber, at the connecting rod side of the diaphragm, communicates with the external atmosphere through at least one sniffer valve arranged to admit air into the chamber from the external atmosphere but preventing air from escaping from the chamber.

2. A diaphragm suction pump according to claim 1, characterised in that the sniffer valve is equipped with an air filter.

3. A pump according to either of claims 1 or 2, wherein the sniffer valve is a one-way flap valve.

4. A diaphragm suction pump substantially as hereinbefore described with reference to the accompanying drawing.