BRAKE BOOSTER

Abstract: The invention provides a brake booster (7) including in a preferred embodiment a housing (50), first and second annular flexible diaphragms (41,42) spaced from one another forming a sealed second chamber (57) within the housing and a sealed first chamber (58) between the first diaphragm and a first end (51) of the housing, a generally annular shaped power piston (16) for connection with a master cylinder (90) piston (91), a valve seat sealing surface (12) separating the first and second chambers, an inlet valve (11) slidably mounted within the power piston, and a control valve (8) spring biased away from the power piston and connected with the pedal linkage (5) and being slidably and sealably mounted within first end of the housing.

Description: This invention relates to a brake booster for vehicle hydraulic braking systems. It is known in the art to provide a brake booster for increasing the force exerted on the piston of a vehicle hydraulic brake master cylinder. Most brake boosters utilize the vacuum supplied by the internal combustion engine of the vehicle. Vacuum supplied power boosters tend to be large. In smaller vehicles, space constraints underneath the hood can make the use of vacuum brake boosters very difficult to fit in the space available. Also, due to the size of vacuum boosters it is virtually impossible to place them within the passenger compartment of the vehicle. Meeting the challenge of vehicle emission standards and the use of turbo chargers has reduced the amount of vacuum which is available for use with the brake booster. Furthermore, on mid-sized trucks the amount of vacuum available is often borderline for full activation of the braking system, thereby making the provision of an alternative booster advantageous. An alternative to the vacuum brake booster is a hydraulic brake booster. Typically the hydraulic brake booster offers greater capacity, however, most hydraulic brake boosters require the addition of an electro-hydraulic pump or are parasitic off of the power steering system pump, thus requiring the hydraulic system supporting the brake booster to have an accumulator for additional capacity. The cost of the hydraulic system is one of the main factors discouraging the use of hydraulic brake boosters. A further alternative, as specified in the preamble of claim 1, is disclosed in DE-C-1426459. To overcome the disadvantages of many prior vacuum or hydraulic brake boosters the present invention is brought forth. To this end, a brake booster in accordance with the present invention is characterised over DE-C-1426459 by the features specified in the characterising portion of claim 1. The present invention provides a brake booster which can use any pressurized fluid. The present inventive brake booster in its preferred embodiment provides a brake booster having a wide range of application in a very small size that can be utilized in cars as well as mid-sized trucks. The new brake booster has a very low hysteresis because of its low friction and has no requirement for sliding seals. The present inventive brake booster has opposed rolling diaphragms. The rolling diaphragms are advantageous in that with the combination of a check valve the brake booster has its own air reservoir providing braking power after failure of any air supply system for a limited amount of powered braking. Additionally, the inventive brake booster offers a more desirable response than that previously available therefore providing a firmer brake pedal action and faster activation. It is an object of the present invention to provide a pressurized fluid vehicle brake booster for connection between a brake pedal linkage and a piston of a master cylinder, the brake booster including a housing having means of connection with the vehicle and the master cylinder, the housing also having a fluid inlet, a first end being generally sealed, and a second end having a vent, first and second annular flexible diaphragms spaced from one another forming a sealed second chamber within the housing and a sealed first chamber between the first diaphragm and the first end of the housing, the second chamber being in fluid communication with the fluid inlet, a generally annular shaped power piston for connection with the piston of the master cylinder, the power piston being spring biased in a first direction and the power piston exterior being connected with both of the diaphragms, and the power piston having a first fluid passage connecting the second chamber with the power piston interior and a second fluid passage from the interior of the power piston to an area in the second end of the housing, a valve seat sealing surface separating the first and second chambers, a spring biased annular inlet valve slidably mounted within the power piston with a fluid passage between an exterior of the inlet valve and an interior of the inlet valve, the inlet valve having a valving surface of a first diameter in contact with the valve seat sealing surface preventing fluid communication between the first fluid passage and the first chamber, and having a first exterior sliding surface at the same first diameter of the valving surface, and the inlet valve having a second exterior sliding surface at a second diameter which differs from the first diameter of the first exterior sliding surface and the inlet valve having an exhaust valve seat, and a control valve spring biased away from the power piston and connected with the brake pedal linkage and being slidably and sealably mounted within the first end of the housing at the second diameter, the control valve having a valving surface at the second diameter for contacting the exhaust valve seat, whereby movement of the control valve by the brake pedal linkage causes the control valve valving surface to contact the exhaust valve seat to seal off the interior of the inlet valve from the vent and further movement of the control valve against the spring biasing of the inlet valve causes the valving surface to be removed from the valve seat sealing surface allowing fluid from the second chamber to pass to the first chamber to urge the power piston against the piston of the master cylinder and whereby in the activated position the inlet valve and the control valve are pressure balanced by the fluid. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevational view of a preferred embodiment of brake booster according to the present invention; and Figure 2 is a view along line 2-2 of Figure 1. Referring to Figures 1 and 2, a brake booster 7 is shown which is a servomechanism designed to multiply the manual pedal force provided by the driver of a vehicle to operate the vehicle brake system via a piston 91 of a master cylinder 90. The brake booster 7 is connected between a brake pedal linkage 5 and the piston 91 of the master cylinder 90. Pressurized air is the energy transfer medium described below, however, other mediums (for example, hydraulic fluid) may be used with minor modifications. Figure 1 shows the brake booster 7 in the normal position prior to brake application. The brake booster 7 has a housing 50. The housing 50 has a first end 51 and a second end 52. First end 51 is generally sealed and second end 52 is open to the atmosphere through a vent 53. First end 51 also has an inlet 56. Within the housing 50 are two annular flexible diaphragms 41, 42 which are spaced from one another forming a sealed air storage second chamber 57 or air reservoir. The second chamber 57 is in fluid communication with the inlet 56. Between the first flexible diaphragm 41 and the housing first end 51 is a sealed first chamber 58. Sealingly connected with the first 41 and second 42 diaphragms along its exterior is an annular shaped power piston 16. The power piston 16 has an inner ring 61, front ring 62, intermediate ring 63 and rearward ring 64. The rearward ring 64 mounts first and second diaphragms 41 and 42 respectively. Intermediate ring 63 forms a support for second diaphragm 42. Front ring 62 is threaded to inner ring 61 and holds intermediate and rearward rings 63 and 64 in place. The power piston 16 has a first fluid passage 32 connecting the second chamber 57 with the interior of the power piston. First fluid passage 32 is comprised of passage 2 in rearward ring 64 and passage 3 in inner ring 61. The power piston 16 is biased in a first direction away from the master cylinder 90 by a spring 46. The power piston 16 has a second fluid passage 66 from its interior to an area of the housing second end 52 formed by slots 68 and 69 in front and inner rings 62 and 61 respectively. A valve seat insert 67 separating the first 58 and second 57 fluid chambers is threadably connected to the inner ring 61. Valve seat insert 67 has a valve seat sealing surface 12 made of a compressible material. A control valve 8 has a passage 15 connecting the second 57 and first 58 fluid chambers. Slidably mounted within power piston 16 is an inlet valve 11. The inlet valve 11 is biased by spring 75. The inlet valve 11 has a modulated fluid passage 24 between its interior and exterior. The inlet valve 11 also has, at a first larger diameter, a valving surface 10 for contact with the valve seat sealing surface 12 to prevent fluid communication between the first fluid passage 32 and the first chamber 58. The inlet valve 11 also has a first exterior sliding surface 71 at the first diameter sealed by an O-ring 29. At a second diameter, differing from the first diameter (by being smaller) the inlet valve 11 has a second exterior sealing surface 73 and is sealed by O-ring 26. At the second diameter the inlet valve 11 has an exhaust valve seat 9. The control valve 8 is connected with the piston 91 of the master cylinder 90 and the brake pedal linkage 5. The control valve 8 is biased by a spring 6 away from power piston 16. The control valve 8 is slidably and sealably connected in the first end 51 of the housing 50 and is sealed by a lip (or other type seal) seal 30 at the second diameter. At the second diameter the control valve 8 has a valving surface 37 for mating with the exhaust valve seat 9 at the second diameter. Movement of the control valve 8 by the brake pedal (via brake pedal linkage 5) causes the valving surface 37 to contact the exhaust valve seat 9 to seal off the interior of the inlet valve 11 from the vent 53. Pressurized air from a supply source 47 passes through a check valve 45. The air then passes into the second chamber 57. Connecting passages 2 and 3 form a power piston first fluid passage to admit supply pressurized air to annulus 4. All other areas of the brake booster 7 are at atmospheric pressure. When force is applied at the brake pedal linkage 5, sufficient to overcome spring 6, the valving surface 37 of the control valve 8 is moved into contact with the exhaust valve seat 9, closing annulus 13 from the atmosphere. Further motion (of control valve 8) moves the valving surface 10 of the inlet valve 11 away from contact with the valve seat sealing surface 12 admitting the supply pressure from second chamber 57 to annulus 13. From annulus 13, supply pressure is admitted to first chamber 58 through passage 15 (formed by a milled slot in control valve 8). The imbalance of pressure behind power piston 16 causes a force in the direction of the brake pedal linkage 5 force (towards the master cylinder 90). The rolling first and second diaphragms 41 and 42 allow the power piston 16 to move in the direction of the push rod force and to push against a reaction support 18 through a reaction ring 19, through a reaction disc 20, through a master cylinder piston guide 21, and finally against the piston 91 of the conventional hydraulic master cylinder 90, to apply the brakes of the vehicle. Since the reaction disc 20 is a relatively soft elastomer, the force applied to it tends to displace a portion of its volume through a slidable reaction piston 23 to the end of the control valve 8 and hence through the brake pedal linkage 5 and on to the brake pedal where a force proportional to the area of master cylinder piston guide 21 and the reaction piston 23 and the lever ratio of the pedal is transmitted to the foot of the driver. The above-noted mechanism, by providing a force directly proportional to that applied to the piston 91, provides the driver with the "feel" necessary to a controlled vehicle stop. Using this feedback mechanism, the driver is able to meter the supply pressure from second chamber 57 to first chamber 58 and is in full control of the modulated pressure in second chamber 58. During brake supply the modulated or variable pressure also exits in the annulus 13. Modulated fluid passage 24 admits modulated air into an annulus 25. Since the diameter at the inside of o-ring 26 is equal to that of the valving surface 37 of the control valve 8, and the pressure on both areas is modulated pressure, it follows that the inlet valve 11 is balanced for any value of modulated pressure. Modulated air in annulus 13 is admitted to first chamber 58 through passage 15. Since the diameter at the inside of lip seal 30 is equal to that of the valving surface 37 of the control valve 8 and the pressure on both areas is modulated pressure, it follows that the control valve 8 is balanced for any value of modulated pressure. The above together with the balancing of the inlet valve 11 (described later) provides for a controlled force between valving surface 37 of the control valve 8 and the face of the exhaust valve seat 9 which is unaffected by modulated pressure. Supply air in annulus 4 is admitted to an annulus 27 through a clearance 28 between the inlet valve 11 and the power piston 16. Since the diameter at the inside of o-ring 29 is equal to that of the valving surface 10 of the inlet valve 11 and the pressure on both areas is supply pressure, the inlet valve 11 is balanced for any value of supply pressure. The above provides for a controlled force between valving surface 10 of the inlet valve 11, and the valve seat sealing surface 12, which is unaffected by supply pressure. Without the various balancing arrangements described above, the device would tend to self-apply, self-release, or create variable forces for different pressure values dependent on the magnitude and/or direction of the area imbalance. When the force on the brake pedal is reduced, the reaction forces urge the control valve 8 in a direction to allow the valving surface 10 of the inlet valve 11 to again contact the valve seat sealing surface 12, annulus 13 from supply pressure and maintaining the brake apply force as is. This is known as "poise" position. Further reduction of pedal force moves the valving surface 37 of the control valve 8 away from the exhaust valve seat 9 and opens annulus 13 to atmospheric pressure. If the valving surface 37 remains out of contact with exhaust valve seat 9, all modulated pressure will be lost and the vehicle brakes will be released. The concept of using two opposed rolling diaphragms 41,42 to admit pressurized fluid to the valving area from a stationary housing has the advantage of providing a low friction leak-proof means of transferring pressurized fluid from the stationary housing 50. Also the diaphragms 41,42 in combination with check valve 45 serve as a fluid reservoir for emergency stops when a compressible medium is employed. The exterior bolting arrangement provides a of transmitting brake loads from the master cylinder 90 to the support area of the vehicle fire wall 80. The above construction eliminates the necessity for heavy booster housing structures to support the brake transmitted loads. Four bolts 70 are shown in the present design. However three-bolt or two-bolt configurations are feasible. Other designs utilize bolts for carrying master cylinder loads, however, prior boosters use bolts that pierce the housing walls necessitating expensive seals with additional friction at several points on each bolt. The design of the present brake booster 7 uses fully exterior bolts 70 that require no seals of any kind. The present invention provides a method of boosting the force exerted by a vehicle occupant on a brake pedal against the piston 91 of a master cylinder 90 the method in combination comprising: 1. Connecting with the vehicle a housing 50 having a first end 51 being generally sealed and a second end 52 being vented 53 and having an inlet 56 for admittance of pressurized fluid; 2. Connecting with the housing 50 first 41 and second 42 annular flexible diaphragms to form a second sealed chamber 57 between the diaphragms and a first sealed chamber 58 between the first diaphragm 41 and the first end 51 of the housing; 3. Connecting with the first 41 and second 42 diaphragms and the piston 91 an annular power piston 16 having first fluid passage 32 between the second chamber 57 and the power piston 16 interior; 4. Spring 46 biasing the power piston 16 away from the piston 91; 5. Separating the first 57 and second chambers 58 with a valve seat sealing surface 12; 6. Slidably mounting and spring biasing an inlet valve 11 within the power piston 16, the inlet valve 11 having a modulated fluid passage 24 between the exterior of the inlet valve 11 and the interior of the inlet valve 11, the inlet valve 11 having a valving surface 10 at a first diameter and a first exterior sliding surface 71 at the first diameter and an exhausted valve seat 9 at a second diameter and a second exterior sliding surface 73 at the second diameter, the second diameter differing from the first diameter; 7. Spring biasing away from the power piston 16 a control valve 8 which is slidably and sealably mounted within the first end 51 of the housing 50 along the second diameter, the control valve 8 having a valving surface 37 at the second diameter for contacting the exhaust valve seat 9; and 8. Moving the control valve 8 whereby the valving surface 37 contacts the exhaust valve seat 9 and displaces the inlet valve 11 away from the valve seat sealing surface 12 whereby fluid is allowed to flow from the second chamber 57 into the first chamber 58 to move the power piston 16 against the piston 91 and whereby the inlet valve 11 and the control valve 8 are pressure balanced by the pressurized fluid.

Claims: A brake booster (7) for connection between a brake pedal linkage (5) and a piston (91) of a master cylinder (90), the brake booster (7) comprising a housing (50), the housing (50) also having a fluid inlet (56), a first end (51) being substantially sealed, and a second end (52); first (41) and second (42) annular flexible diaphragms spaced from one another forming a sealed second chamber (57) within the housing (50) and a sealed first chamber (58) between the first diaphragm (41) and the first end (51) of the housing (50), the second chamber (57) being in fluid communication with the fluid inlet (56); a substantially annular shaped power piston (16) for connection with the piston (91) of the master cylinder (90), the power piston (16) being spring (46) biased in a first direction and the power piston exterior being connected with one of the diaphragms (41,42), the power piston (16) having a first fluid passage (32) connecting the second chamber (57) with the power piston interior; a valve seat sealing surface (12) separating the first (58) and second (57) chambers; a spring (75) biased annular inlet valve (11) slidably mounted within the power piston (16) with a fluid passage (24) between an exterior of the inlet valve (11) and an interior of the inlet valve (11), the inlet valve (11) having a valving surface (10) of a first diameter in contact with the valve seat sealing surface (12) preventing fluid communication between the first fluid passage (32) and the first chamber (58) and having a first exterior sliding surface (71), and the inlet valve (11) having an exhaust valve seat (9); and a control valve (8) spring (6) biased away from the power piston (16) and connected with the brake pedal linkage (5) and being slidably and sealably mounted within the first end (51) of the housing (50); characterised in that the housing has means (70) of connection with the vehicle and the master cylinder (90); in that the second end (52) has a vent (53); in that the power piston exterior is also connected with the other of the diaphragms (41,42); in that the power piston has a second fluid passage (66) from the interior of the power piston to an area in the second end (52) of the housing; in that the first exterior sliding surface (71) is at the same first diameter of the valving surface (10); in that the inlet valve (11) has a second exterior sliding surface (73) at a second diameter which differs from said first diameter of the first exterior sliding surface (71); in that the control valve (8) is slidably and sealably mounted within the first end (51) at the second diameter; and in that the control valve (8) has a valving surface (37) at the second diameter for contacting the exhaust valve seat (9), whereby movement of the control valve (8) by the brake pedal linkage (5) causes the control valve (8) valving surface (37) to contact the exhaust valve seat (9) to seal off the interior of the inlet valve (11) from the vent (53) and further movement of the control valve (8) against the spring (75) biasing of the inlet valve (11) causes the valving surface (10) to be removed from the valve seat sealing surface (12) allowing fluid from the second chamber (57) to pass to the first chamber (58) to urge the power piston (16) against the piston (91) of the master cylinder (90) and whereby in the activated position the inlet valve (11) and the control valve (8) are pressured balanced by the fluid. A brake booster as claimed in claim 1, wherein the fluid is air. A brake booster as claimed in claim 1 or claim 2, wherein the valve seat sealing surface (12) is connected with the power piston (16). A brake booster as claimed in any one of claims 1 to 3, wherein the housing (50) is connected together with the master cylinder (90) and the vehicle by exterior bolts (70). A brake booster as claimed in any one of claims 1 to 4, having mechanical feedback means (20) exerting back a proportion of the force exerted upon the piston (91) of the master cylinder (90) back to the control valve (8). A brake booster as claimed in any one of claims 1 to 5, wherein the sealed second chamber (57) is formed within the housing (50) between the diaphragms (41,42); wherein the power piston (16) is spring biased away from the master cylinder (90); wherein the inlet valve (11) is spring biased away from the master cylinder (90); and wherein the second diameter is less than the first diameter. A method of boosting the force exerted by a vehicle occupant on a brake pedal linkage (5) against the piston (91) of a master cylinder (90) by use of a brake booster as claimed in any one of claims 1 to 6, characterised by the step of moving the control valve (8) whereby the valving surface (37) contacts the exhaust valve seat (9) and displaces the inlet valve (11) away from the valve seat sealing surface (12) whereby fluid is allowed to flow from the second chamber (57) into the first chamber (58) to move the power piston (16) against the piston (91) of the master cylinder (90) and whereby the inlet valve (11) and the control valve (8) are pressure balanced by the pressurized fluid.

Inventors: DEHOFF, EDWARD J., MILLER, JON E., SCHENK, DONALD E.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1989
Main classification: B60T13
IPC codes: B60T13