GB2252371A

GB2252371A - Hydraulic master cylinder

Info

Publication number: GB2252371A
Application number: GB9102030A
Authority: GB
Inventors: Denis Bryan Saunders
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1991-01-30
Filing date: 1991-01-30
Publication date: 1992-08-05
Also published as: GB9102030D0

Abstract

A brakes hydraulic master cylinder has a piston (15) having a through passage (33) with a controlling valve member (34), the valve member (34) being connected by a pin (45) to a spring end cap (39A), located at one end of a spring (25) whose other end sits on a second end cap (39B) located on the piston and the valve member (34) screws on the pin (45) to form an abutment for the second end cap, for adjusting the maximum spacing between the two spring caps. Each spring cap has an end wall with a coaxial hole therein to accommodate the stem of the pin, the hole connecting into an enlarged aperture to permit the head of the pin to be inserted into the cap. <IMAGE>

Description

A TANDEM MASTER CYLINDER This invention relates to tandem master cylinders for hydraulic brake systems in particular for automobiles.

The present qeneration of master cylinders are generally ulanuEacured with pistons having centre valves located in a passageway extending through the piston and which allow fluid to feed an unpressurised supply chamber to a pressure chamber.

With tandem brake systems, in order to synchronise the opssration of the pistons, it is necessary to accurately locate the two pistons with respect to the master cylinder bore and to each other. In order that the lost travel is reduced to a minimum it is known to have a tolerance compensating mechanism acting between the pistons to accurately position the two pistons relative to each other.

The present invention provides a compensating mechanism for a tandem master cylinder which is easy to assemble.

According to the invention there is provided a piston spring assembly for a brakes hydraulic master cylinder, said piston assembly in use being sealingly slidable in a master cylinder bore in a master cylinder housing to generate pressure in a pressure chamber of the bore, the assembly comprising a spring, a piston having a through passage therein which in use connects the pressure chamber with a feed chamber of the master cylinder when said piston is in an inoperative position, the passageway having a valve therein to open and close the passageway, wherein one end of the spring is seated on a first spring seat associated with a spring cap, and the other end of the spring is seated in a second spring seat associated with second piston, the spring cap being connected to the valve so that expansion of the spring beyond a determined limit can open the valve, and compression of the spring to permit the valve to close, a piston spring assembly for a brakes hydraulic master cylinder, said piston assembly in use being sealingly slidable in a master cylinder bore in a master cylinder housing to generate pressure in a pressure chamber of the bore, the assembly comprising a spring, a piston having a through passage therein which in use connects the pressure chamber with a feed chamber of the master cylinder when said piston is in an inoperative position, the passageway having a valve therein to open and close the passageway, wherein one end of the spring is seated on a first spring seat associated with a spring cap, and the other end of the spring is seated a second spring cap associated with second piston, the sprinq cap being connected to the valve so that expansion, of the spring beyond a determined limit can open the valve, and compression of the spring permits the valve to close and the two spring caps are biased apart by the return spring, and have a connector there between to limit the maximum spacing therebetween, and the valve is mounted on the connector to form an abutment for the second end cap, the connector having a co-axial stem with a screw threaded portion at the end adjacent the second spring cap and the valve is adjustibly mounted on the screw threaded portion of the pin to adjust the maximum spacing between the two spring caps.

Preferably the master cylinder is for a hydraulic braking system and has a housing, a piston sealingly slidable in a master cylinder bore in the housing to generate pressure in a pressure chamber of the bore, said piston being returned to an inoperative position by a return spring wherein said return spring and piston or part of a piston/spring assembly as disclosed above.

More preferably the master cylinder is a tandem master cylinder and further comprises a second piston sealingly slideable in the bore and which is returned to an inoperative position by a second return spring, wherein said second piston and second return spring are a piston/spring assembly as disclosed above.

The invention will be described by way of example and with reference to the accompanying drawings in which: Fig 1 is a longitudinal section through a master cylinder according to the invention, with a direct acting booster fitted thereon.

Fig 2 is an end view of the master cylinder housing of Fig 1 showing an anti tamper device.

Fig 3 is an enlarge detail of Figure 1.

Fig 4 is a plan view of string cap.

Fig 5 is a detailed section of the connector pin and spring cap before assembly to a piston.

With reference to Fig 1 there is illustrated a tandem master cylinder for a vehicle hydraulic brake system, and which is compatible with brake systems associated with anti skid systems. The master cylinder is shown in assembly with a brake booster B which forms no part of the present invention and will not be described in any further detail. The master cylinder 1(3 comprises a housing 11 having a master cylinder bore 12 with two pistons 14, and 15 sealingly slideable therein. The master cylinder bore 12 is supplied with hydraulic fluid from a reservoir 15 via passageways 17 and 18 which feed into supply chambers 19 and 21 respectively disposed behind the primary seals 22 and 23 of the pistons 14 and 15 respectively. Each piston 14 and 15 is biased into an inoperative position by a return spring 24 and 25.

The return spring reacts against the housing 24 at the closed end of the bore, and the return spring 25 biases the piston 15 against a retaining clip 28 at the mouth end of the bore 12 and the position of the piston 14 is determined by load balance between the return springs 24 and 25. The clip 28 could be omitted and the piston 15 allowed to rest on the servomotor pus'trod 4(3.

The piston 14 located in the closed end of the master cylinder bore 12 (will hereinafter be referred to as the second piston 14) has a piston seal 22 at its end portion adjacent the closed end of the bore 12 with a coaxial stepped diameter passageway 33 providing a connection between the supply chamber 19 and the pressure chamber 26 side of the second piston 14, when the second piston 14 is biased into an inoperative position by the return spring 24 (hereinafter referred to as the second return spring) housed in the closed end of the bore 12.

The supply chamber 19 is sealed from the pressure chamber 36 of the other piston 15 (hereinafter called the first piston) by a secondary seal 27. The second piston 14 has a smaller diameter end portion 29 extending toward the open end of the bore 12 which has a coaxial blind bore 3X therein. The supply chamber 21 oE the first piston 15 is sealed from the atmosphere by a secondary seal 31. The first piston 15 has its primary seal 22 located between its supply chamber 21 and its pressure chamber 36. A co-axial stepped diameter passageway 33 in the first piston 15 interconnects the two chambers 21 and 36.

The passageway 33 of both pistons 14 and 15 are opened and closed by a valve 34. Since the basic mechanism for controlling the valve 34 is the same for each piston only one such mechanism will be described. Therefore with reference to the first piston 15 adjacent the mouth of the bore 12, the stepped diameter passageway 33 has a larger diameter portion 33a which opens into the pressure chamber 36 and which accommodates a valve 34. The valve 34 has a seal 35 in its end face to seat against the shoulder 38 in the stepped diameter passageway 33 to cut off the connection between the two chambers 21 and 36.

The valve 34 is biased into a open position by the respective piston return spring 25. rach piston 14 or 15 and its respective return spring 24 and 25 form a piston/spring assembly. Each return spring 14 and 15 is contained between a pair of spring end caps 39. The valve 34 is biased to its closed position by a coaxial lighter valve spring 4(3 which rests between the valve itself and its respective adjacent end cap 39.

Each end cap 39 comprises a cylindrical wall 41 having an outwardly projecting annular flange 42 at one end thereof and an end wall 43 at the other end. The end wall 43 has a coaxial hole 44 therein which is of sufficient size to accommodate the stem 45 of a screw threaded pin 45 but not to allow the head 47 of the pin to pass through. The coaxial hole 44 is connected to a enlarged aperture 48 in the end cap to allow the pin head 47 to be inserted into the cap without passing the stem 45 of the pin through the hole 48. In Fig 4, the enlarged aperture is shown as being in the end wall, but a key-hole shaped aperture in the sidewall 41 which is connected to the coaxial hole 44 by a radial slot would be preferred.The flange 42 on each end cap 39 provides spring seat for the end of the spring 25 and the cylindrical wall 41 sits within the hollow centre of the spring 25.

The first spring end cap 39a at the end of the spring 25 remote from the first piston 15 is connected to the valve 34 by the pin 46 whose head 47 provides an abutment for the respective end cap 39a. The other end of the spring 25 reacts against the first piston 15, and seats on a second end cap 39b. The stem 45 of the pin pass through the coaxial hole 44 in the end cap 39h which is retained on the pin 44 by the valve 34 which form an abutment to limit the spacing between the end caps 39 under the bias of the spring 25.

The valve 34 is screwed onto the threaded end portion of the stem 45 to facilitate setting the maximum axial distance D1 between the end caps to a predetermined dimension. The valve spring 4 is a light spring which biases pin 46 and the valve 34 to the closed position only when the spring 25 is compressed to releive the load exerted on the pin 44.

The first piston 15 has a smaller diameter end portion 5(3 at its end adjacent the second piston 14. This end portion 5(3 locates within the cylindrical side wall 41 of the end cap 39b, and the end face 43 of the end cap is in abutment with the end face of the first piston 15. Simarlaly the smaller diameter end portion 29 of the second piston also locates within its adjacent end cap 39A, the head 47 of the pin 46 being accomodated by the bore 3(3.

The distance between the two pistons 14 and 15 in the inoperative condition is set by the distance D1 between the end cap 39, at which distance to the valve 34 is held clear of the shoulder 38 so that the pressure chamber 36 and feed chamber 21 are in communication.

The piston/spring valve assembly for the second piston 14 is identical except that the respective first end cap 39a sits directly onto the blind end of the master cylinder bore 12.

The two return springs 24 and 25 may have the same spring rating or as is more usual, the first return spring 25 may be a stiEfer spring that the second return spring 24.

The whole assembly within the master cylinder bore 12 is contained between the inner surface 61 of the blind end of the master cylinder housing 11 and which the spring cap 39A seats and the the retaining clip 28 at the mouth of the bore 12. This distance is D2. By forming the blind end of the master cylinder bore on a separate plug 62 which is screwed into the end of the bore 12 then the end plug 62 can be screwed into the housing so that all dimensional tolerances relating to the dimensions of the pistons 14,15, spring, master cylinder etc. which go to male up the distance D2 can be compensated for by screwing the plug 61 into the housing 11 until there is no play in the internal assemblies at which point the spring 24, and 25 resist inwards movement of the plug 62.

The end plug is then locked in position by a tamper-proof cover 65 which is staked over the end of the master cylinder housing 11.

With the master cylinder in the conditions shown as Fig 1, both pistons 14 and 15 are biased the retaining clip 28, and position of the pistons 14 is determined by the postion of the piston 15 against which it reacts. The respective centre valves are open to supply Eluid to the respective supply chambers 19 and 21. When the operating load is applied to the first piston 15 both pistons move into the bore 12, compressing the return springs 24 and 25 closing the valves, allowing a pressure build up in the pressure chantSers for operation of the brakes. The sequence of closing of the valves can be altered as desired by arranging for the retrun springs 24 and 25 to have the same, or different spring ratings, as is desired.

Claims

1. A piston spring assembly for a brakes hydraulic master cylinder, said piston assembly in use being sealingly slidable in a master cylinder bore in a master cylinder housing to generate pressure in a pressure chamber of the bore, the assembly comprising a spring, a piston having a through passage therein which in use connects the pressure chamber with a feed chamber of the master cylinder when said piston is in an inoperative position, the passageway having a valve therein to open and close the passageway, wherein one end of the spring is seated on a first spring seat associated with a spring cap, and the other end of the spring is seated a second spring cap associated with second piston, the spring cap being connected to the valve so that expansion of the spring beyond a determined limit can open the valve, and compression of the spring permits the valve to close and the two spring caps are biased apart by the return spring, and have a connector there between to limit the maximum spacing therebetween, and the valve is mounted on the connector to form an abutment for the second end cap, the connector having a co-axial stem with a screw threaded portion at the end adjacent the second spring cap and the valve is adjustibly mounted on the screw threaded portion of the pin to adjust the maximum spacing between the two spring caps.

2. A piston/spring assembly as claimed in claim 1 wherein the connector is a pin having a stem with a head at one end and screw threaded portion at the other end, the stem of the pin passing through coaxial apertures in the two spring caps so that the spring caps are axially movable along the pin with the head of the pin providing an abutment for the first spring cap.

3. A piston spring assembly as claimed in Claim 2 wherein each spring cap comprises a substantially cylindrical body which locates within the spring, a radially outwardly projecting flange at one end thereof which forms a spring seat, and an end wall at the other end thereof having a coaxial hole to accomodate the stem of the pin, the coaxial hole being connected to an enlarged aperture in the top to allow the pin head within the cap without passing the stem of the pin through to be inserted.

4. A piston spring assembly as claimed in Claim 3 wherein the enlarged aperture is a key hole slot in the cylindrical body of the cap connected to the coaxial hole by a second slot.

5. A master cylinder for a hydraulic brake system having a housing, a piston sealingly slidable in a master cylinder bore in the housing to generate pressure in a pressure chamber of the bore, said piston being returned to an inoperative position by a return spring wherein said return spring and piston form part of a piston/spring assembly as claimed in any one of Claims 2 to 4.

6. A master cylinder as claimed in Claim 5, being a tandem master cylinder and further comprising a second piston sealingly slideable in the bore and which is returned to an inoperative position by a second return spring, wherein said second piston and second return spring are a piston/spring assembly as claimed in any one of Claims 1 to 4.

7. A tandem master cylinder as claimed in claim 6, wherein the first piston is adjacent the mouth of the bore and the second piston is adjacent the closed end of the bore, and the first piston return spring acts between the first piston and the second piston, and the second piston return spring acts between the closed end of the bore and the second piston, and the closed end of the bore is Eormed on an end plug which is adjustably mounted in the mas-ter cylinder housing.

8. A tandem master cylinder as claimed in Claim 7 wherein the end cap is screw threaded into the housing and is positioned axially in the bore to remove substatially axial all axial play between the components assembled in the bore, between the end plug and the retention means at the mouth of the bore.

9. A tandem master cylinder as claimed in Claim 7 or Claim 8 wherein the end plug is secured in position by a tamper-proof shield after it has been located in its axial position.