GB1590685A - Method of bleeding a hydraulic system - Google Patents

Description

(54) METHOD OF BLEEDING A HYDRAULIC SYSTEM (71) We, REVERSE INJECTION COMPANY (PROPRIETARY) LIMITED, a Company incorporated with limited liability in accordance with the laws of the Republic of South Africa, of Midmacor House, Booy sens Road, Selby, Transvaal Province, Republic of South Africa, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of bleed - ing an hydraulic system.It relates in par ticular to a method of bleeding an hydraulic system which comprises a master cylinder and piston assembly, a slave cylinder and piston assembly, and an hydraulic line con necting the master cylinder to the slave cylin der for operatively conducting fluid between them. The method therefore finds particular use in bleeding the hydraulic brake systems of motor vehicles.

Divisional applications have been filed for the bleed nipple and for the apparatus described herein.

By the term "bleeding" is to be under stood the removal of air, dirt, or other con taminants from the hydraulic system, or charging, purging, or flushing the system with clear, uncontaminated hydraulic fluid, i.e.

hydraulic fluid which is free of substances which can impair the proper operation of the system, e.g. dirt, air, water vapour, or the like.

In conventional hydraulic brake systems known to the applicant, closable bleed open ings are provided at high points in the sys tems, i.e. at the upper regions of the slave cylinders. Closability is provided by screw threaded bleed nipples adapted to screw into screw-threaded sockets to close off the bleed openings.

Bleeding of such systems takes place by opening the bleed opening, unscrewing the bleed nipple, and by pumping hydraulic fluid by means of the piston in the master cylinder, thereby expelling air from the slave cylinder.

The bleed opening is then closed by screwing the bleed nipple home. A disadvantage of this system of bleeding is that one person is needed to operate the master piston to pump hydraulic fluid from the master cylinder through to the slave cylinder, and another person is required to watch the bleed opening and to close it off as soon as air stops issuing from it. The master cylinder then has to be charged again with hydraulic fluid to the appropriate level. Bleeding carried out in this fashion is often not fully effective, because it is not always possible to bleed all the air out of such systems in this fashion.

It is an object of this invention to provide a method of bleeding hydraulic systems which is more effective than the method presently known to the applicant.

According to the invention, a method of bleeding an hydraulic system which comprises a master cylinder and piston assembly, a slave cylinder and piston assembly, an hydraulic line conecting the master cylinder to the slave cylinder for operatively conducting hydraulic fluid between the cylinders, and a master cylinder reservoir which is in fluid flow communication with the master cylinder, includes the steps of withdrawing hydraulic fluid from the master cylinder reservoir; and of introducing hydraulic fluid into the system of the slave cylinder to cause flow of hydraulic fluid from the slave cylinder and along the hydraulic line to the master cylinder.

The use of the term 'bleeding' is not perhaps strictly its conventional usage, because no actual bleeding takes place at the slave cylinder. However, its use in the context is felt to he justified because introduction of hydraulic fluid at the slave cylinder leads to an air free hydraulic system.

The hydraulic fluid may be withdrawn from the reservoir of the master cylinder while maintaining the hydraulic fluid in the master cylinder reservoir at a predetermined level.

Liquid withdrawn from the master cylinder may be introduced again at the slave cylinder.

The introduction of hydraulic fluid may take place for a period and the method may include the further step, at the end of said period, of applying a suction at the slave cylinder to cause reverse flow out of the slave cylinder.

The introduction of hydraulic fluid at the slave cylinder may be preceded by a step of applying a suction for a period of short duration at the slave cylinder. The duration of the suction period may be ten seconds at the most. The period during which hydraulic fluid is introduced into the cylinder may be of adjustable duration. The step of introducing hydraulic fluid into the system and the step of applying suction may take place in cyclic sequence automatically. The suction step and step of introducing hydraulic fluid into the slave cylinder may take place via separate flow paths communicating at the slave cylinder.

Apparatus for carrying out the method as described comprises hydraulic fluid suction means adapted for drawing hydraulic fluid from the master cylinder reservoir, and hydraulic fluid supply means adapted to supply hydraulic fluid under pressure to the slave cylinder.

The hydraulic fluid suction means may include a tube having a suction opening submersible in the hydraulic fluid at a predetermined level above the floor of the master cylinder reservoir. The volumetric flow rate of the hydraulic fluid suction means may be about 1f to 2 litres per minute and may exceed that of the hydraulic fluid supply means by about 50%. There may be provided an hydraulic fluid flow connection between the hydraulic fluid suction means and the hydrau lic fluid supply means.

The apparatus may include valve means, and valve operating means for operating the valve means, for closing off the hydraulic fluid supply under pressure to the slave cylinder, and for applying suction to the slave cylinder.

The apparatus may include valve operating means and hydraulic fluid supply and suction means for each of a plurality of slave cylinders, the several valve operating means for the plurality of slave cylinders being operable discretely in succession.

The hydraulic fluid supply means may include a clean hydraulic fluid reservoir and a pressure pump having its suction connected to the clean hydraulic fluid reservoir. The hydraulic fluid suction means may include a spent fluid reservoir and a suction pump having its delivery connected to the spent fluid reservoir; and theremay be provided at least one electric motor for driving the pumps.

line apparatus may further include an hydraulic connector for connecting the hydraulic fluid supply means to the slave cylinder, the hydraulic connector incorporating a valve closure member urged to the closed position, the said closure member being adapted to become unseated when the hydraulic connector engages with a bleed nipple in the slave cylinder.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings.

In the drawings: Figure 1 shows an hydraulic and electrical circuit diagram of apparatus for carrying out the method according to the invention, the apparatus being shown connected to the hydraulic brake system of a motor vehicle; Figure 2 shows an hydraulic circuit diagram of an alternative form of apparatus; Figure 3 shows an hydraulic circuit diagram of another alternative form of apparatus; Figure 4 shows diagrammatically a diagram of hydraulic fluid flow in another embodiment of the apparatus; Figure 5 shows a schematic diagram of the electric circuitry of apparatus of Figure 4; Figure 6 shows a side view of the transportable trolley incorporating apparatus for carrying out the method according to the invention; Figure 7 shows a bird's eye view of the control panel of the trolley shown in Figure 6; Figure 8 shows a bleed nipple forming part of the assembly of Figure 4;; Figure 9 shows an hydraulic flow line diagram of yet another embodiment of apparatus for carrying out the method according to the invention; Figure 10 shows an axial section of an hydraulic connector with connected conduits as used in the embodiment of Figure 9; Figure 11 shows a cross section of the conduits at XI-XI in Figure 10; Figure 12 shows an electrical circuit diagram (including cams and valves) of the embodiment of Figure 9; Figure 13 shows an oblique view of a cam shaft with a few cams mounted thereon; Figure 14 shows a timing diagram of the operation of various parts and of flow along the various passages through valves operated by the various cams; and Figure 15 shows diagrammatically a sectional elevation of a slave cylinder and bleed nipple assembly for a disc brake.

A 'bleed' nipple is referred to above and hereinafter. This term must be understood to have a meaning corresponding to the term 'bleeding' as hereinbefore defined. Thus while no actual bleeding takes place at the nipple, yet by feeding in hydraulic fluid at the nipple, air is 'bled' from the hydraulic system as a whole.

In Figure 1, reference numeral 10 generally indicates an apparatus having hydraulic fluid supply means and hydraulic fluid suction means in the form of pressure and suction pumps for use in bleeding the hydraulic brake system of a motor vehicle. Reference numeral 12 indicates part of a vehicle's brake system.

The brake system includes a master cylinder and piston assembly 14, a brake pedal 16 for operating the piston of the assembly 14, and a master cylinder reservoir 18. When the pedal is released, the reservoir 18 is - in fluid flow communication with the cylinder 14. The reservoir has a filler opening 20.

The brake system further includes a brake slave cylinder and piston assembly 22 on each (say) of the four wheels (only one of which is shown at 24) of the vehicle. The master cylinder of the master cylinder and piston assembly 14 is connected to the slave cylinder of the slave cylinder and piston assembly 22 by means of connector 25 and an hydraulic line 26.

The apparatus 10 includes a trolley which can be moved around by hand. It comprises hydraulic fluid supply means in the form of a delivery pump 28. The pump 28 is a self timing, pressure regulated vane pump having a suction inlet 28.22, a delivery outlet 28.21 and a pressure relief connection 28.1.

The pump 28 is driven by a 12 volt electric motor 30. The apparatus further comprises hydraulic fluid suction means in the form of a suction pump which is a peristaltic pump 32 having a suction inlet 32.1 and a delivery outlet 32.2. The pump 32 is driven by a 12 volt electric motor 34 via a reduction gearbox 36. Still further, the apparatus comprises a spent hydraulic fluid reservoir 38 and a clean hydraulic fluid reservoir 40.

A suction conduit 42 for withdrawing hydraulic fluid from the master cylinder reservoir 18, and a delivery conduit 44 for introducing hydraulic fluid into the slave cylinder 22 are also provided. The suction conduit 42 comprises a length of flexible tubing 42.1 having at its end a suction connection in the form of a hooked piece of rigid tubing 42.2.

The tubing 42.2 is connected to the tubing 42.1 via a stop cock 46. An opening in the tubing 42.2 is arranged to lie at a certain level in the master cylinder reservoir to maintain a certain level of fluid therein.

The delivery conduit also comprises a length of flexible tubing 44.1 having at its end a delivery connection in the form of a length of rigid tubing 44.2. The rigid tubing 44.2 is connected to the flexible tubing via a stop cock 48. The rigid tubing 44.2 can be connected to the slave cylinder 22 by means of a screw-on coupling 50. For this purpose, the slave cylinder is provided with a nipple (See Figure 8) having a passage in which there is a non-return valve permitting flow of hydraulic fluid into the slave cylinder.

The suction conduit 42 leads to the suction inlet 32.1 of the peristaltic pump 32.

The delivery outlet 32.2 of the peristaltic pump 32 is connected to a bi-directional valve 52 whereby the delivery of the pump 32 can be connected either to the spent fluid reservoir 38 via conduit 54, or to the clean fluid reservoir 40 via conduit 56.

The delivery outlet 28.21 of the pump 28 is connected to the delivery connection 44 via a regulating valve 58. Downstream of the valve 58 there is provided a pressure gauge 60.

The suction inlet 28.22 of the pump 28 is connected via a filter 62 to the clean fluid reservoir 40.

The pressure relief connection 28.1 is con nected to the clean fluid reservoir 40 via a T-junction in the conduit 56.

Each reservoir 38, 40 is provided with an overflow 64, 66 respectively. In addition, the spent fluid reservoir 38 is provided with a drainage outlet 68 having a stop cock 70.

The clean fluid reservoir 40 is provided in addition with a breather 41 which is connected to atmosphere via a silica gel filter 41.1.

The unit 10 also comprises a chargeable 12 volt battery 72 and a battery charger 74 for charging the battery from a 220 volt ac mains supply. The battery 72 is connected via a switch 76 to the two motors 30, 34. A voltmeter 78 is provided to indicate the condition of the battery.

In use, the hooked end 42.2 of the suction conduit is hooked into the filler opening 20 of the vehicle's master cylinder reservoir and the stop cock 46 is opened. Also, the delivery conduit 44.2 is connected to the slave cylinder of one of the wheels of the vehicles by means of the screw-on connection 50 and the valve 48 is opened.

The bi-directional valve 52 is positioned for delivery into the spent fluid reservoir 38 and the unit is then switched on by means of the switch 76 which sets the motors 30 and 34 in operation.

Hydraulic fluid is pumped from the clean fluid reservoir 40 by means of the pump 28 via the conduit 44 into the hydraulic system 12. The hydraulic fluid thus pumped into the system displaces contaminated hydraulic fluid already in the system. Such contaminated hydraulic fluid is hereinafter referred to as spent hydraulic fluid, and may be contami nated by air bubbles, dirt, water vapour and other impurities. The flow of fluid takes place via the line 26 in the direction 80 to the master cylinder and thence into the master cylinder reservoir 18.

At the same time, spent hydraulic fluid is drawn from the master cylinder reservoir 18 via the connection 42 by means of the peristaltic pump 32. This fluid is pumped via the bi-directional valve 52 and the conduit 54 into the spent fluid reservoir 38.

This process is continued for approximately half a minute, or until clear hydraulic fluid appears in the master cylinder reservoir 18.

Spent hydraulic fluid in that part of the sys tem has now been replaced by new hydraulic fluid. However, there may still be some air bubbles in that part of the system. Hence introduction of hydraulic fluid into the system is continued, to purge the system of such air.

Then after a while when the line 42 has been cleared of spent fluid, the valve 52 is posi tioned to deliver into conduit 56 whereupon hydraulic fluid drawn from the master cylin der reservoir 18 will be pumped towards the clean fluid reservoir 40 via the conduit 56.

This is to avoid wasting new hydraulic fluid while air is being removed. The pumps are now allowed to run for approximately one minute, or until no more air bubbles appear in the master cylinder reservoir 18.

The rate of flow of hydraulic fluid pumped into the system is controlled by adjusting the regulating valve 58.

After having run for a minute or so, the pump is stopped, the stop cock 48 closed and the connector 44.2 unscrewed from the slave cylinder 22. Thereafter, the other wheels of the vehicle are each treated in the same manner to complete the bleeding of the brake system.

When the bleeding has been completed, the connector 44.2 is unscrewed and the tube 42.2 taken out of the master cylinder reservoir after the valves 48 and 46 have been closed.

The pipes 42 and 44 are then stowed away on the trolley.

In the variation shown in Figure 2, the delivery pump 28 is dispensed with by placing the clean fluid reservoir at a high level to be able to make use of the static head.

Thereby the necessary pressure head is obtained to cause introduction of fluid into the hydraulic system. This may be of use in permanent installations such as at assembly plants.

In Figure 2 the same reference numerals as in Figure 1 are used for the same parts.

In the variation shown in Figure 3, the suction pump 32 is dispensed with by placing the clean fluid reservoir at a low level, i.e.

lower than the level of the master cylinder reservoir. Thereby, hydraulic fluid can be withdrawn from the master cylinder reservoir by a siphoning action. In Figure 3 the same reference numerals as in Figure 1 are used for the same parts.

By way of modification, the apparatus illustrated in Figure 1 may be provided with a solenoid operated cross-over valve 82 shown in dotted lines in Figure 1. The valve will be connected in the suction conduit 42 and in the delivery 28.21 of the pump 28 downstream of the regulating valve 58, as shown in dotted lines at 84 and 86 respectively. In its de-energised condition the cross-over valve 82 will then permit bleeding to take place as described above. When the valve 82 is energised, however, the conduit 44 is connected to the suction pump 32 and the conduit 42 to the delivery of the delivery pump 28.

The valve 82 is provided to permit the reverse flow of hydraulic fluid out of the slave cylinder for a short while at the end of a bleeding operation at each wheel. The applicants have found that, in certain makes of vehicle, air which may be present in the slave cylinders themselves is not all removed by bleeding according to the method described above. By reversing the flow for a short while at the end of a bleeding operation, this air is removed.

The switch 76 will then be replaced by a double pole double throw, centre off switch (not shown) whereby the solenoid may be energised by switching the switch to one of its positions.

By way of development the apparatus may be provided with jump connections 88 fed from the pressure pump 28 via valves 90.

These connections 88 are adapted for connection to jump conduits for bleeding an hydraulic system other than an hydraulic brake system.

Referring now to Figure 4 of the drawings, reference numeral 10.4 indicates generally the hydraulic fluid flowline of another embodiment of apparatus according to the invention. It is a more developed form of the apparatus shown in Figures 1 to 3. Like numbers refer to like parts. In the following description reference will only be made to the differences between the embodiments of Figures 1 to 3 on the one hand and the embodiment of Figures 4 to 9 on the other hand.

The present embodiment comprises an hydraulic fluid supply line 44 to which is connected a pressure gauge 60 and which has a connection 44.11 to which a manifold 45 is connected having as many branch supply lines 45.1 as there are slave cylinders of a vehicle to be served. Usually, the number will be four only. Each of the supply lines 45.1 will be provided with a valve 48 and delivery pipe 44.2 whereby flow along any supply line 45.1 can be controlled. Each supply line 45.1 is provided with a connection 45.3 to which flexible conduits 45.4 are connectable via connections 45.5. Each flexible conduit 45.4 also has a connection 45.6 for connection to a bleed nipple 21 of a slave cylinder 22. The slave cylinder 22 has a connection 25 to which is connected a hydraulic line 26 which is fed from a master cylinder 14 having a reservoir 18. The master cylinder 14 has a piston 14.1 which is connected to a pedal 16.

The connections 45.3 and 45.5 may each have valves incorporated in them so that when connections are made both valves become unseated. This is to ensure that hydraulic fluid contained in the various conduits does not drain when the conduits are disconnected.

Likewise, the connections 45.6 and the bleed nipples 21 have valves which are unseated when connection is made between a con nection 45.6 and a bleed nipple 21. See in this connection the description with reference to Figures 8 and 10 of the drawings.

The apparatus also comprises a hydraulic fluid withdrawal line 42.1 having a connecting device 43 to which is connectable a flexible withdrawal line 42 having a connecting device 43.1 adapted to connect with the connecting device 43. Each of the connecting devices 43.1 and 43 has a valve incorporated therein.

Both such valves become unseated when connection is made between the connecting devices 43 and 43.1. See in this connection also the description with reference to Figures 8 and 10 of the drawings.

The suction end of the withdrawal line 42 has a relatively stiff tube 42.2 which has a longitudinal slot 42.3 near its end. A slidable sleeve 42.4 is provided over the end of the tube 42.2. The end of the tube 42.2 is insertable into the reservoir 18 of the master cylinder 14. By adjusting the height of the sleeve 42.4 relative to the end of the tube 42.2.and allowing the end of the tube 42.2 to rest on the bottom of the reservoir, the hydraulic fluid can be maintained at a desired level 18.1 in operation while hydraulic fluid is being fed into the hydraulic system via the slave cylinder 22, and while hydraulic fluid is being withdrawn from the hydraulic system via the slot 42.3 in the end of the tube 42.2. The arrangement is such that hydraulic fluid is withdrawn from the reservoir as long as the hydraulic fluid covers the exposed portion of the slot 42.3 completely.

As soon as the level of the hydraulic fluid drops below the sleeve 42.4 then a portion of the slot 42.3 becomes exposed, thereby permitting air to enter the suction tube 42.2 and thereby preventing the level of the hydrau lic fluid dropping below the level 18.1. In this way, hydraulic fluid which would otherwise have gone to waste by overflowing the reservoir 18, is now recovered and does not go to waste.

Flow of hydraulic fluid along the hydraulic supply line 44 and the suction line 42.1 is conveniently controlled by a control valve 59.

A suction filter or strainer, or both, 51 is connected in the suction line 42.1 so as to remove such impurities as could damage or affect the operation of the suction pump 32.

The suction line 42.1, or the delivery line 32.2, incorporates a transparent portion so that the purity of the hydraulic fluid therethrough can be judged. Depending upon the nature of the fluid, the position of the valve 52 can be regulated. For clean fluid, the valve 52 will be connected to the line 56. However, when the fluid is dirty the valve 52 will be positioned to deliver into the line 54.

Referring now to Figure 5 of the drawings, reference numeral 100 indicates generally the electric circuit diagram of the apparatus according to Figure 4. It comprises a suction pump motor 34, a pressure pump motor 30 fed via lines 106 from a battery 72. Voltage supplied by the battery is indicated by volt meter 78. The illumination for the volt meter 78 is supplied by the light 112. The illumination for the pressure gauges 60 and 75 are provided by the lights 114 and 116 respectively. The various parts of the circuit are energised via lines 106 from the battery 72 via the double-pole double-throw switch 118.

When the pole 118.1 is making contact with the contact 118.2, then the circuit is energised.

When the pole 118.3 contacts the contact 118.4, then the relay coil 120 is energised.

The coil 120 being energised, opens contacts 122 and prevents the battery charger 74 being energised while current is being drawn from the battery 72. The battery charger 74 is energised via lines 126 from ordinary AC supply. The high voltage AC circuit is protected by a fuse 128. The battery charger has a pilot light 130 to indicate when it is energised. The battery charger itself comprises a transformer rectifier unit, details of which are not shown. The output of the battery charger is connected via lines 132 and fuse 134 to the battery 72. The contacts 122 are normally closed unoperated and only open when the coil 120 is energised.

If the battery 72 has become discharged and does not have sufficient charge to operate the various motors, then an emergency supply can be connected to terminals 140 which are connected via fuse 142 and leads 144 to the leads 106 via the pole 118.1 when it makes contact with contact 144.1.

The electrical and hydraulic equipment and piping are all incorporated and brought together in a console from which the various operations to bleed a hydraulic system, may be controlled. Thus, the battery, the battery charger, the motors for the suction and pressure pumps, and the suction and pressure pumps themselves, and the associated piping and valves, filters and clean fluid reservoir 40 and spent fluid reservoir 38, are all brought together. For convenience, they are brought together in a push-type trolley having a control panel at its upper end. In this connection reference is made to Figures 6 and 7 of the drawings. It comprises an upright console indicated generally by reference numeral 150.

It has a pair of wheels 152 and legs 154. It can be pushed around by means of handles 156. The trolley 150 has a control panel 158 on which the various controls are assembled.

Referring now to Figure 7 of the drawings, there are shown details of the control panel as well as of the various connecting lines.

Referring to Figure 8 of the drawings, reference numeral 21 refers generally to a bleed nipple suitable for use with apparatus as described. It has a hexagon formation 180 for engagement by a spanner, a screw thread 182 adapted to screw into a threaded socket in a slave cylinder. It has a seat 184 adapted to engage sealingly with a non-return valve, generally indicated by reference numeral 186, engaging with the screw-threaded bore 188.

The non-return valve 186 is of substantially similar construction to that used for pneumatic tyres and tubes. However, there is this difference that the seal 186.1 of the non-return valve as well as the seat 186.2 of the valve are of a resilient material which is resistant to attack by hydraulic fluid. The nipple is provided further with a screw thread or other suitable connection 190 for engaging with the connection 45.6 of the flexible supply lines 45.4 . The closure member 186.3 of the non-return valve 186 becomes unseated when the connection 45.6 engages with the screw thread 190 (see Figure 10). The valve closure member 45.61 abuts against the end 186.31 of the closure member 186.3, resulting in both closure members being unseated. A removeable dust cap 192 engaging wtih the screw thread 190 is also provided.

In operation, for the bleeding of the hydraulic brake system of a vehicle, the trolley 150 is pushed so that it is near to the vehicle. Thereupon, four conduits 45.4 are connected to the connections 45.3 and 50 of the various wheels. There will therefore be four conduits 45.4 interconnecting the con sole 150 to the four wheels of the vehicle.

Upon making the connections 45.6 and 21, the non-return valves built into the connection pieces, become unseated. The passages in them are thereby placed in communication with each other. The flexible conduits 45.4 may form more or less a permanent part of the apparatus but may be disconnected at 45.5 from the connections 45.3.

Thereupon the piping 42.2 is inserted into the reservoir 18 of the master cylinder 14.

The sleeve 42.4 is adjusted to a position to ensure that when hydraulic fluid is pumped into the system, it will be drawn off at a sufficient rate by the suction pump so that the level will not rise above a reasonable level in the reservoir, e.g. at level 18.1 as indicated in Figure 4 of the drawings. Thereupon the motors for the suction and pressure pumps are energised by closing the switch 118. This causes clean hydraulic fluid to be forced along the supply line 44 and into the manifold 45.

The appropriate valve 48 is opened and the fluid then flows into the slave cylinder 22 via the flexible conduit 45.4. Hydraulic fluid in the slave cylinder 22 thereby becomes dis placed into the reservoir 18 of the master cylinder 14. However, hydraulic fluid is being withdrawn from the master cylinder via the tube 42.2, the level of fluid in the master cylinder not dropping below the level 18.1 because of the position of the sleeve 42.4 over the slot 42.3 in the tube 42.2.

The capacity of the suction pump is greater than that of the supply pump, therefore the level of hydraulic fluid in the master cylinder will not rise above the level 18.1 and will therefore not spill over at the master cylinder.

As previously mentioned the reservoir 40 may be provided with a breather 41 which is in turn connected to atmosphere via a silica gel filter 41.1. This is to ensure that the air which enters into the reservoir 40 is dry and that water vapour does not eventually condense in the reservoir and cause problems in charging hydraulic fluid lines.

A reservoir capacity of about 5 liters has been found to be adequate for a portable apparatus. However, if a permanent installation is contemplated then a clean fluid reservoir 40 may have many times that capacity.

While the fluid flowing in the suction line 42.1 and in the suction pump delivery line 32.2 is dirty, then the valve 52 is in such a position that the dirty fluid is discharged along the line 54 to the spent fluid reservoir 38 or directly to drain via line 68. However, as soon as the fluid is seen to be clean in the transparent flowline, the position of the valve 52 is changed so that the clean fluid is returned via line 56 to the clean fluid reservoir 40.

The slave cylinder 22 shown in Figure 4, is shown as used conventionally in hydraulic brake systems. In other words, the bleed connection 21 is provided at the top of the cylinder. It has been found with such slave cylinders that it is still possible to have a small bubble of air entrapped as at 22.1 (see Figure 4) even after clean hydraulic fluid has been flowing through the slave cylinder.

In such circumstances it has been found that the bubble 22.1 can be withdrawn from the slave cylinder by merely causing hydraulic fluid to flow in a return direction along the conduits 45.4. This is done by changing the position of the four-way valve 59, so that suction is applied at the connection 21 for a few seconds merely.

As the bleeding of the slave cylinder 24 is completed, so the apropriate valve 48 is closed and the next valve 48 for the next slave cylinder is opened. In this way the various slave cylinders may be bled in succession by operating the appropriate valves in the appropriate sequence.

By way of development, a more sophisticated arrangement may be made by having the various valves 48 of the push-button type arrangement, operable by a cam or cams on a spindle so that in different positions of the cam about its axis, different valves 48 will be closed and only a single valve will be open at any one time. In this regard reference is made to Figures 9 to 14 of the drawings.

Reference numeral 200 refers generally to another embodiment of apparatus for carrying out the method in accordance with the invention. The apparatus has four sets of twin conduits 45.41, 45.42 terminating in four hydraulic connectors 45.6 (see Figures 10 and 11 for details). For purposes of identification the connectors 45.6 are marked A,B,CD. A connector is provided for each wheel of a vehicle. The twin conduits are connected via connectors 45.3 to pairs of valves arranged in two banks 48.1 and 48.2.

The bank of valves 48.1 are connected in parallel to the delivery 44 of the pressure pump 28. The bank of valves 48.2 are connected in parallel to the suction conduit 42.1 of the suction pump 32.

The banks of valves 48.1 and 48.2 are cam operated and will be more fully explained hereafter. The flow of fluid along conduit 42 from the master cylinder reservoir is controlled by a manually operable valve 43.1, and by a valve controlled by a clean fluid sensor 43.21, and by a cam operated valve 43.3. The clean fluid sensor may be in the form of a photo-electric cell responsive to light rays of sufficient intensity being able to pass through the fluid.

The bank of valves 48.1 controls the flow of hydraulic fluid along conduits 1A, 2B, 3C, and 4D. Likewise the bank of valves 48.2 control the suction in conduits Aa, Bb, Cc, Dd.

The electrical circuitry and cams of the apparatus are shown in Figure 12. Details of cams are shown in Figure 13, and the timing of the operation of various parts is shown in Figure 14.

The embodiment 200 has terminals 201 for energizing from a battery, say the battery of the vehicle whose brakes are being bled.

Alternatively, the apparatus may be energised via AC terminals 202 and via switch 202.1 and transformer 203 and fullwave rectifier 204. The apparatus also includes a trickle charger 205 for trickle charging a battery.

The apparatus comprises a six pole three position selector switch 206. In Figure 12 it is shown in the off position. When in the upward position it is in the 'automatic position 'Au' and when down, it is in the 'manual' position 'Ma'. The circuit also has a nain switch 207, and is protected by a fuse 208.

Besides including solenoid valves 90.1 serving the purpose of valves 90 in Figures 1 and 4 of the drawings, the circuit also includes the pressure and suction pump motors 30 and 34.

The circuit also includes a cam motor 209 controlled by variable speed control 209.1 and gearbox 210 driving a camshaft 211 on which is mounted a series of cams, CI, CII to CX. The cam CI has four lobes and operates valve 43.3 (see also Figures 9, 13 and 14).

Cam II operates cycle termination switch 212 which stops operation of the machine when it is operating on automatic. The cams CII I, CV, CVII and CIX each have two lobes and are adapted to open the suction lines Aa, Bb, Cc, Dd at the beginning and end of a bleeding cycle for each of wheels WI, WII, WIII and WIV (see Figures 9, 13 and 14) in succession. These cams operate the bank of valves 48.2. The cams CIV, CVI, CVIII and CX each have one lobe and are adapted to open the pressure lines 1A, 2B, 3C, 4D (Figures 9 and 14) at the same time that the suction line through valve 43.3 is open (see Figures 9 and 14).

The circuit further comprises a push button start switch 213, a relay coil 214 adapted to hold itself energised over lower contacts 214.1. In Figure 12 contacts 214.1 are shown in the unoperated position. The circuit also includes a cycle termination indicator in the form of a light 215.

When the selector switch is in the manual position 'Ma' (see Figure 12) the main switch is switched on and the push button switch 213 is closed. The relay coil 214 becomes energised and holds itself energised over the lower contacts 214.1. At the same time the pressure and suction pump motors 30 and 34 are energised as well as the two solenoid valves 90.1. The apparatus can then be used for bleeding any other hydraulic system by making use of jump connections 88 (see Figures 1 and 4 above). On manual, the cam motor 209 is not energised.

For automatic operation the various connectors 45.6 are connected to the nipples 21 at A,B,C,D of the four wheels WI, WII, WIII and WIV. (See Figures 9, 10 and 11).

When the selector switch 206 is on automatic 'Au' then the cam motor becomes energised when the main switch 207 and start switch 213 are closed. In addition those portions of the apparatus which were energised under 'Manual' are also energised. The cycle of operations is started by holding the start button 213 for a few seconds to ensure that cam CII is no longer operating the cycle termination switch 212 and that switch 212 is in its unoperated closed position shown in Figure 12.

The cam shaft 211 starts rotating and the pressure and suction pumps 28 and 32 are connected in timed sequence via the valve 43.3 and the banks of valves 48.1, and 48.2 for the various wheels forming part of the system to be bled. The connections take place according to the timing and sequence as shown in Figure 14.

Further details are set out in the table below.

Wheel Wheel Wheel Wheel WI WII WIII WIV Energized A B C D Phase 1 Closed 1-4 1-4 1-4 1-4 Open a b c d Closed bcd acd abd abc Closed 43.3 43.3 43.3 43.3 Phase 2 Open 1 2 3 4 Closed 234 134 124 123 Closed abcd abcd abcd abcd Open 43.3 433 43.3 43.3 Phase 3 Closed 1-4 1-4 1-4 1-4 Open a b c d Closed bed acd abd abc Closed 43.3 43.3 43.3 43.3 One revolution of the cam shaft constitutes one complete cycle. At the end of the cycle cam CII operates the cycle termination switch 212 thereby de-energising the apparatus including relay coil 214. The contacts 214.1 return to their unoperated upper position thereby energizing cycle termination indicator light 215.This indicates that bleeding on a particular vehicle has been completed and that the hydraulic connector 45.6 at A,B,C,D may be disconnected, and reconnected to the next vehicle for the next cycle of operations.

The initial short suction phase applied to the conduit in phase 1 for a few seconds, is intended to remove dust or other dirt at the bleed nipple inlet. This is to prevent such dust or dirt being charged into the hydraulic system. Then follows phase 2, introducing hydraulic fluid into the slave cylinder for about a minute or more. Finally there is another short suction phase for a few seconds.

The duration of the cycle is chosen such that with the pump capacities of the apparatus an hydraulic system can be adequately bled. For large systems the length of cycle can be increased by slowing the cam motor down by means of control 209.1.

The method of bleeding according to the invention can be carried out particularly successfully where the line leading from the slave cylinder to the master cylinder is at a higher level than the level at which introduction of the hydraulic fluid into the slave cylinder takes place. Reference is now made to Figure 15 in which there is shown a slave cylinder assembly 220 suitable for bleeding in accordance with the invention.

This assembly comprises a pair of slave cylinders 222 and 224 interconnected via a channel 226. The cylinders have pistons 228 and 230 arranged on either side of a disc 232. In accordance with conventional practice, the master cylinder hydraulic line connects with the cylinder 224 at about the line 224.1; and a bleed screw nipple is provided at the end of the branch passage 226.1. In the assembly (shown in Figure 15) however, the master cylinder hydraulic line connects with the branch passage 226.1, and bleed screws or bleed nipples 21 are provided at a low level in each of the cylinders 222 and 224.

Hence, in accordance with this invention, it is better to have the bleed nipple of a slave cylinder at a low level rather than at a high level as has been the practice heretofore.

Accordingly, the slave cylinder has means for connecting it operatively to a master cylinder, and has a bleed nipple at a low level leading into the slave cylinder, the bleed nipple having means for connection to a hydraulic fluid supply capable of causing flow of hydraulic fluid through the slave cylinder to the master cylinder. The slave cylinder connection leading to the master cylinder may be at a high level.

Attention is directed to our copending applications 17323/78 [Serial No. 1,590,686] 4520/80 [Serial No. 1,590,687] and 223/80 [Serial No. 1,590,688] which respectively claim the above-described bleed nipple, the non-return valve of the nipple and apparatus for carrying out the method of this invention.

WHAT WE CLAIM IS:- 1. A method of bleeding an hydraulic system which comprises a master cylinder and piston assembly, a slave cylinder and piston assembly, an hydraulic line connecting the master cylinder to the slave cylinder for operatively conducting hydraulic fluid between the cylinders, and a master cylinder reservoir which is in fluid flow communication with the master cylinder, and which includes the steps of withdrawing hydraulic fluid from the master cylinder reservoir; and of introducing

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

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. Wheel Wheel Wheel Wheel WI WII WIII WIV Energized A B C D Phase 1 Closed 1-4 1-4 1-4 1-4 Open a b c d Closed bcd acd abd abc Closed 43.3 43.3 43.3 43.3 Phase 2 Open 1 2 3 4 Closed 234 134 124 123 Closed abcd abcd abcd abcd Open 43.3 433 43.3 43.3 Phase 3 Closed 1-4 1-4 1-4 1-4 Open a b c d Closed bed acd abd abc Closed 43.3 43.3 43.3 43.3 One revolution of the cam shaft constitutes one complete cycle. At the end of the cycle cam CII operates the cycle termination switch 212 thereby de-energising the apparatus including relay coil 214. The contacts 214.1 return to their unoperated upper position thereby energizing cycle termination indicator light 215.This indicates that bleeding on a particular vehicle has been completed and that the hydraulic connector 45.6 at A,B,C,D may be disconnected, and reconnected to the next vehicle for the next cycle of operations. The initial short suction phase applied to the conduit in phase 1 for a few seconds, is intended to remove dust or other dirt at the bleed nipple inlet. This is to prevent such dust or dirt being charged into the hydraulic system. Then follows phase 2, introducing hydraulic fluid into the slave cylinder for about a minute or more. Finally there is another short suction phase for a few seconds. The duration of the cycle is chosen such that with the pump capacities of the apparatus an hydraulic system can be adequately bled. For large systems the length of cycle can be increased by slowing the cam motor down by means of control 209.1. The method of bleeding according to the invention can be carried out particularly successfully where the line leading from the slave cylinder to the master cylinder is at a higher level than the level at which introduction of the hydraulic fluid into the slave cylinder takes place. Reference is now made to Figure 15 in which there is shown a slave cylinder assembly 220 suitable for bleeding in accordance with the invention. This assembly comprises a pair of slave cylinders 222 and 224 interconnected via a channel 226. The cylinders have pistons 228 and 230 arranged on either side of a disc 232. In accordance with conventional practice, the master cylinder hydraulic line connects with the cylinder 224 at about the line 224.1; and a bleed screw nipple is provided at the end of the branch passage 226.1. In the assembly (shown in Figure 15) however, the master cylinder hydraulic line connects with the branch passage 226.1, and bleed screws or bleed nipples 21 are provided at a low level in each of the cylinders 222 and 224. Hence, in accordance with this invention, it is better to have the bleed nipple of a slave cylinder at a low level rather than at a high level as has been the practice heretofore. Accordingly, the slave cylinder has means for connecting it operatively to a master cylinder, and has a bleed nipple at a low level leading into the slave cylinder, the bleed nipple having means for connection to a hydraulic fluid supply capable of causing flow of hydraulic fluid through the slave cylinder to the master cylinder. The slave cylinder connection leading to the master cylinder may be at a high level. Attention is directed to our copending applications 17323/78 [Serial No. 1,590,686] 4520/80 [Serial No. 1,590,687] and 223/80 [Serial No. 1,590,688] which respectively claim the above-described bleed nipple, the non-return valve of the nipple and apparatus for carrying out the method of this invention. WHAT WE CLAIM IS:-

1. A method of bleeding an hydraulic system which comprises a master cylinder and piston assembly, a slave cylinder and piston assembly, an hydraulic line connecting the master cylinder to the slave cylinder for operatively conducting hydraulic fluid between the cylinders, and a master cylinder reservoir which is in fluid flow communication with the master cylinder, and which includes the steps of withdrawing hydraulic fluid from the master cylinder reservoir; and of introducing

hydraulic fluid into the system at the slave cylinder to cause flow of hydraulic fluid from the slave cylinder and along the hydraulic line to the master cylinder.

2. A method as claimed in claim 1, in which the hydraulic fluid is withdrawn from the reservoir of the master cylinder while maintaining the hydraulic fluid in the master cylinder reservoir at a predetermined level.

3. A method as claimed in claim 1 or claim 2 in which liquid withdrawn from the master cylinder is introduced again at the slave cylinder.

4. A method as claimed in any one of the preceding claims, in which the introduction of hydraulic fluid takes place for a period and which includes the further step, at the end of said period, of applying a suction at the slave cylinder to cause reverse flow out of the slave cylinder.

5. A method as claimed in any one of the preceding claims, in which the introduction of hydraulic fluid at the slave cylinder is preceded by a step of applying a suction for a period of short duration at the slave cylinder.

6. A method as claimed in claim 4 or claim 5, in which the duration of the suction period is ten seconds at the most.

7. A method as claimed in any one of the claims 4 to 6 inclusive, in which the suction step and step of introducing hydraulic fluid into the slave cylinder take place via separate flow paths communicating at the slave cylinder.

8. A method as claimed in any one of the claims 4 to 7 inclusive, in which the step of introducing hydraulic fluid into the system and the step of applying suction take place in cyclic sequence.

9. A method as claimed in claim 8, in which the steps are arranged to take place automatically.

10. A method as claimed in claim 8 or claim 9, in which the period during which hydraulic fluid is introduced into the cylinder is of adjustable duration.

11. A method of bleeding an hydraulic system substantially as described and illustrated herein.