FR2638789A1 - Device for controlling a booster, particularly for a motor vehicle braking system - Google Patents

Abstract

In order to increase the effectiveness of a booster 10 the back chamber 18 of which contains an auxiliary motor member 28 including a pressure chamber 30 connected to a pressure source 34 through a control device 36, the latter includes a valve 38 which is normally closed, through which the source 34 may communicate with the pressure chamber 30, and means 40 for actuating this valve, which means automatically command the latter to open when the pressure in the back chamber 18 exceeds the pressure in the front chamber 16 of the booster by a given value. Such an assembly may in particular be used on a motor vehicle braking system.

Description

DEVICE FOR CONTROLLING A SERVOMOTOR, IN PARTICULAR
FOR MOTOR VEHICLE BRAKING SYSTEM.

 The invention relates to a control device intended to be associated with an assistance booster, and in particular with a booster fitted to the braking system of a motor vehicle.

 More specifically, the invention relates to a control device intended to be used on an assistance booster such as that described in the document FR-A-2 334 862 (US-A-4 117 769). In this document, there is described a booster usually comprising a housing in which is housed a driving piston forming inside the housing a front chamber and a rear chamber. The actuation of the brake pedal moves an actuator input control member, which acts on a control valve having the effect of creating a pressure difference between the rear chamber and the front chamber. This pressure difference results in the application of an assistance force which is added to the mechanical force exerted on the input control member.

 In this document, the booster further comprises, inside the rear chamber, an auxiliary motor member comprising a pressure chamber capable of being connected to an external pressure source by means of a control device. When the control device is actuated, the auxiliary motor member thus exerts on the actuating piston of the booster an assistance force induced by the actuation of the brake pedal. In document FR-A-2 334 862, this auxiliary assistance force is used completely independently of the normal braking system of the vehicle, to allow the addition to the latter of an automatic assisted braking system, without it it is necessary to use an additional servomotor.

 The present invention relates to a completely different application of the booster equipped with an auxiliary motor member as described in document FR-A-2 334 862, the auxiliary motor member no longer being used to enable the brakes to be actuated. of the vehicle by an automatic system independent of the vehicle braking system, but on the contrary to improve the efficiency of the latter system under certain braking conditions.

 More specifically, the subject of the invention is a device for controlling a booster of the aforementioned type, designed to automatically exert an additional booster force on the drive piston of the booster, during a strong actuation and extended by the brake pedal, which makes it possible to reduce the diametrical size of the booster for a given assistance force or, on the contrary, to increase the assistance force for an unchanged size.

 According to the invention, this result is obtained by means of a device for controlling an assistance booster comprising a housing, in which a driving piston separating a front chamber from a rear chamber can move during actuation. an input control member establishing a pressure difference between the rear chamber and the front chamber, an auxiliary motor member comprising a pressure chamber being placed in the rear chamber of the actuator, the control device being placed between the pressure chamber of the actuator and a pressure source, and being characterized in that it comprises a normally closed valve, through which the pressure chamber communicates with the pressure source, and means for actuating said valve , sensitive to the pressure difference between the rear chamber and the front chamber to automatically open the valve when this difference exceeds a predetermined threshold .

 Advantageously, the control device according to the invention comprises a body in which are formed a pressurized fluid inlet chamber communicating with the pressure source, a pressurized fluid outlet chamber, communicating with the pressure chamber, a first control chamber communicating with the front chamber and a second control chamber communicating with the rear chamber, said inlet and outlet chambers forming between them a first valve seat against which a valve is normally held in sealed support by a first elastic means, the first and second control chambers being separated in leaktight manner by means forming a piston axially aligned with the valve seat and an extension of which carries a second valve seat capable of coming into sealing contact with the valve and of displacing this last away from the first seat, a second elastic means normally maintaining the second valve seat away from the valve.

 According to another embodiment, the control device comprises a hollow body in which are formed a pressurized fluid inlet chamber communicating with the pressure source, a pressurized fluid outlet chamber, communicating with the pressure chamber , a first control chamber communicating with the front chamber and a second control chamber communicating with the rear chamber, the inlet and outlet chambers forming between them a first valve seat against which a first valve is normally held in sealed support by a first elastic means, the first and second control chambers being separated in leaktight manner by a means forming a piston axially aligned with the first valve seat and an extension of which forms a second valve capable of coming to seal against a second seat of valve integral with the first valve, so as to initially close a communication between the ch pressure fluid outlet amber and the front chamber when a pressure difference is established between the control chambers, and, in a second step, to move the first valve away from the first seat, a second elastic means now normally the second valve away from the second seat.

Two preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which
FIG. 1 schematically represents part of a braking system comprising a booster with which a control device according to the invention is associated, this device as well as the booster being shown in longitudinal section, and
- Figure 2 schematically shows another embodiment of the control device according to the invention.

 In FIG. 1, the reference 10 generally designates a brake booster of the vacuum pneumatic type. This booster is similar to that which is described in document FR-A-2 334 862. For a detailed description, reference will therefore be made to this document.

 For a good understanding of the invention, it will be recalled here that the booster 10 comprises a housing 12 whose internal volume is divided into two parts by a driving piston 14.

Given the location of the booster on the vehicle, these two parts of the interior volume of the housing 12 constitute a front chamber 16 and a rear chamber 18. A nozzle 20 mounted on the housing 12 allows the chamber to communicate by an appropriate circuit. front 16 with a vacuum source 63 installed on the vehicle.

 The servomotor 10 further comprises an input control member constituted by a push rod 22 whose movement is controlled by actuation of the brake pedal (not shown) of the vehicle. The end of the push rod 22 placed in the driving piston 14 actuates a three-way valve (not shown), making it possible to communicate the rear chamber 18 either with the front chamber 16 or with the external atmosphere, depending on the position relative between the push rod 22 and the engine piston 14.

 When the push rod 22 is not actuated, the aforementioned three-way valve communicates the rear chamber 18 with the front chamber 16 by passages passing through the piston 14. The latter is then maintained in its rear rest position illustrated on the Figure by a compression spring 24 placed in the front chamber 16 and interposed between the housing 12 and the piston 14.

 When the driver of the vehicle actuates the brake pedal, the displacement of the push rod 22 which results therefrom switches the aforementioned three-way valve, so that the communication between the chambers 16 and 18 is interrupted and the rear chamber 18 communicates with the external atmosphere through passages also formed in the driving piston 14. Under the effect of the resulting pressure difference between the chambers 18 and 16, an assistance force is exerted forward on the piston engine 14 against the spring 24. This force is transmitted to an output member constituted by a rod 26 usually connected to the master cylinder (not shown) equipping the vehicle's braking circuit.

 In the booster shown in Figure 1, an auxiliary drive member 28 is also placed in the rear chamber 18. In the illustrated embodiment, this drive member 28 is constituted by an annular enclosure whose outer and inner peripheral walls are formed by an elastomeric diaphragm with bellows and the end walls of which are flat and respectively supported on a rear plate of the housing 12 and on the drive piston 14. The auxiliary drive member 28 thus internally delimits a pressure chamber 30 completely sealed by compared to the rear chamber 18.

 This pressure chamber 30 is connected by a pipe 32 passing through the housing 12 to a source of pressurized fluid 34 located outside the booster 10, through a control device 36 produced in accordance with the invention.

 The control device 36 according to an embodiment of the invention essentially consists of a valve 38, normally closed, placed in the pipe 32 between the chamber 30 and the source 34, and actuation means 40 which are sensitive permanently at the pressure difference between the front 16 and rear 18 chambers of the actuator, for automatically controlling the opening of the valve 38 when the pressure in the rear chamber 18 exceeds the pressure in the front chamber 16 by a predetermined valve .

 More specifically, the control device 36 comprises a hollow body 42, produced in several parts, so as to successively form inside the body 42 and from one end to the other thereof a chamber annular inlet 44 for pressurized fluid, an outlet chamber 46 for pressurized fluid, a first control chamber 48 and a second control chamber 30.

 The inlet chamber 44 for pressurized fluid communicates with the source 34 through a passage 52 formed in the body 42 and to which a part of the pipe 32 located upstream of the device 36 is connected. The outlet chamber 46 communicates with respect to it with the pressure chamber 30 through a passage 54 also formed in the body 42 and to which the part of the pipe 32 situated downstream of the device 36 is connected.

 The valve 38 is placed between the chambers 44 and 46 so as to normally interrupt any communication between these chambers.

To this end, an annular valve 56 internally delimiting the inlet chamber 44, and on which a compression spring 58 is supported, is normally in sealed support against a valve seat 60 formed in an axial passage through which the chambers 44 and 46 can communicate. The compression spring 58 is also placed in the chamber 44 and its ends bear respectively on an end wall of the housing 42 and on the valve 56.

 Beyond this end wall of the housing 42, the latter extends in the form of a tube 42a delimiting an exhaust chamber 106 whose communication with the external atmosphere is controlled by a unidirectional valve 100 authorizing the exhaust to the atmosphere of the fluid contained in the chamber 106.

 The annular valve 38 slides in leaktight manner in the tube 42a, by means of a seal 62 isolating the chambers 44 and 106 relative to one another.

 The first control chamber 48 of the device 36 permanently communicates either directly with the vacuum source 63, or with the front chamber 16 of the booster as shown, by a pipe 64 connected to a passage 66 formed in the body 42. In a comparable manner , the second control chamber 50 communicates permanently with the rear chamber 18 of the booster by a pipe 68 connected to a passage 70 also formed in the body 42.

 The actuating means 40 of the valve 38 comprise a piston 72 which is mounted in a floating manner inside the body 42, to seal the first and second control chambers 48 and 50 in leaktight manner. This piston 72 is disposed approximately along the same axis as the valve 38 and it has an extension 72a which passes through a partition 74 belonging to the body 42 and separating, inside the latter, the outlet chamber 46 from the first chamber 48. This extension 72a crosses the outlet chamber 46 and its end is received inside the annular valve 38. Inside the chamber 46, the extension 72a supports a thrust washer 76. Under the action of a compression spring 78 placed in the first chamber 48 and the ends of which bear respectively on the partition 74 and on the piston 72, the latter normally occupies at rest a position in which the thrust washer 76 is in abutment against the partition 74, c as illustrated in the single Figure.

 In this rest position of the piston 72, the outlet chamber 46 communicates permanently with the chamber 106 by axial 104 and radial 102 passages formed in the end of the extension 72a. Between the thrust washer 76 and the radial passages 102, the extension 72a comprises an annular seat 110 capable of coming to bear sealingly on the valve 38.

 In the embodiment shown, the axial passage 104 is extended to the opposite end of the piston 72 by an axial passage 80 opening into the chamber 50 and comprising a restriction 108. In the rest position of the piston 72, the chamber 46 then communicates with the second control chamber 50 via this axial passage 80 and the radial passages 102. Under these conditions, the rear chamber 18 of the booster continuously communicates with the pressure chamber 30 of the auxiliary motor member 28. Consequently , the behavior of the booster is then completely identical to that of a conventional booster having no auxiliary motor member.

 In an alternative embodiment not shown, the passage 80 does not exist. The chamber 30 then remains at atmospheric pressure as long as the piston 72 is at rest.

The floating mounting of the piston 72 inside the body 42 is ensured, between the control chambers 48 and 50, by a first waterproof membrane 82 and, between the extension 72a and the partition 74 by a second waterproof membrane 84. These membranes 82 and 84 allow the piston 72 to be centered approximately inside the body 42 of the control device, while allowing a slight clearance making it possible to guarantee the tightness of the contact between the seat 110 and the valve 56, when the piston 72 is move to the left considering the
Figure 1, as will be described later.

 At rest, the various elements of the control device 36 occupy the positions illustrated in the Figure, that is to say that the inlet chambers 44 and outlet 46 are isolated from each other by the support sealed valve 56 on the valve seat 60 under the action of spring 58. The pressure chamber 30 of the auxiliary motor member of the booster is therefore isolated from the pressure source 34. On the contrary, the front chamber 46 can communicate with the second control chamber 50 through the passage 80 as previously mentioned. In this case, the pressure prevailing in the chamber 30 is therefore identical to the pressure prevailing in the rear chamber 18 of the booster.

 When the driver of the vehicle actuates the brake pedal, the control device 36 remains in the rest position illustrated in the Figure as long as the pressure difference between the control chambers 50 and 48 is less than a predetermined threshold corresponding to the preload. stored in the spring 78. Since the control chambers 48 and 50 communicate respectively with the front chamber 16 and the rear chamber 18 of the booster, the position of the piston member 70 therefore remains unchanged as long as the pressure prevailing in the rear chamber 18 does not exceed by a value corresponding to said predetermined threshold the pressure prevailing in the front chamber 16 of the booster. Before this threshold is reached when the passage 80 exists, the pressure in the chamber 30 of the auxiliary motor member 28 It therefore gradually increases at the same time as the pressure in the rear chamber 18.

The assistance force applied to the drive piston 14 of the booster is then identical to that of a conventional booster at the start of the braking phase.

 When the braking phase extends beyond this initial phase, which in practice corresponds to emergency braking, the pressure difference between the rear chamber 18 and the front chamber 16, which corresponds to the pressure difference between the control chambers 50 and 48, exceeds the threshold corresponding to the preload stored in the spring 78. The piston member 72 then moves to the left considering Figure 1, so that the seat 110 carried by the extension 72a comes into sealing contact with the valve 56 and moves the latter away from the seat 60 against the spring 58. The outlet chamber 46 is thus, initially, isolated from the control chamber 50 and from the chamber 106, then put into communication with the inlet chamber 44. As a result, the chamber 30 of the auxiliary motor member 28, which was previously at the same pressure as the rear chamber 18 of the booster, sees its pressure n increase rapidly under the effect of its communication with the pressure source 34. An assistance force generated by the booster itself is thus applied to the drive piston 14, so that the force exerted on the output rod 26 of the servomotor increases more rapidly than on a conventional servomotor.

 Of course, as soon as the driver of the vehicle releases, even momentarily the brake pedal, the pressure difference between the rear chambers 18 and front 16 of the booster drops to a value lower than that of the setting of the spring 78, so that the means forming piston 72 returns to its initial position shown in the Figure. The pressure in the chamber 30 of the auxiliary motor member then becomes equal to the pressure in the rear chamber 18 of the booster, by escaping through the passage 80, when the latter exists.

In the absence of this passage 80, the pressure in the chamber 30 remains equal to atmospheric pressure.

 Figure 2 shows another embodiment of a control device 36 according to the invention.

 Referring now to this FIG. 2, the body 42 is pierced with four passages 54, 52, 66, 70 respectively connected to the pressure chamber 30, to a source of pressurized fluid 34, for example of compressed air, to the front chamber 16 of the actuator and to the rear chamber 18 of the actuator. The passage 54 communicates with an outlet chamber 46, while the passage 52 communicates with an annular inlet chamber 44. The passages 66 and 70 communicate respectively with the control chambers 48 and 50 separated in a sealed manner by a means of actuation 40 constituted by a piston 72 and a sealing membrane 82. This actuation means 40 moves as a function of the difference between the pressures prevailing in the control chambers 48.50, against a helical spring 78 arranged in one of them.

 The end 72a of the piston 72 constitutes a valve capable of coming to bear on a valve seat 110 formed in a hollow cylinder 120, partially around which the annular inlet chamber 44 is formed.

 An aunnular shoulder 60 in the body 48 constitutes another valve seat separating the inlet chamber 44 from the outlet chamber 46. An annular valve 56 is normally supported on this seat 60 by means of a helical spring 58 disposed in the chamber outlet 46.

 At rest of the system, that is to say in the absence of braking, as shown in the Figure, the valve 56 closes the communication between the inlet chamber 44 and the outlet chamber 46. Variations in the pressure of the fluid under pressure in the inlet chamber 44 then have no effect on the system, the walls of the annular inlet chamber 44 balancing the assembly.

 It is known that at rest, the front 16 and rear 18 chambers of the booster are under vacuum at the same pressure. It is the same for the pressure chamber 30 which then communicates with the front chamber 16 via the outlet chamber 46, the hollow cylinder 120, the valve 110, 72a, the control chamber 48 and the passage 66 .

 During braking, the pressure in the rear chamber. 18 increases, while that in the front chamber 16 remains very low. The actuating means 40 sensitive to this difference between the pressures prevailing in the control chambers 48 and 50 where we find the difference in pressures between the front and rear chambers, therefore moves, against the spring 78 and , firstly, the valve 72a bears on the valve seat 110. It is understood that this cuts off the communication between the pressure chamber 30 and the front chamber 16. The valve 56 which is integral with the hollow tube 120 remains in support on its seat 60 under the effect of spring 58, the preload of which will determine the opening threshold of this valve when the difference between the pressures prevailing in the control chambers 48.50 will further increase. therefore a second step, the valve 56 moves away from its seat 60 and the inlet 44 and outlet 46 chambers communicate. The source of pressurized fluid 34 is then directly connected to the pressure chamber 30, which increases the force applied by the booster in a corresponding manner.

 The reaction of the fluid under pressure on the valve 56 tends to push the latter on its seat 60 and balances the opposite force determined by the action of the difference between the pressures prevailing in the chambers 48.50 on the actuating means 40 .

 When the driver of the vehicle releases the brake, the control device operates in reverse, that is to say that the valve 56 first returns to bear on the seat 60 to close the communication between the pressure source 34 and the chamber pressure 30, then, when the brake is fully released, the valve 72a moves away from its seat 110 again putting the pressure chamber 30 in communication with the front chamber 16 of the booster. The device then resumes its rest position shown.

 Thanks to the control device 36 according to the invention, it is therefore possible without modifying the booster to automatically increase its efficiency when the pressure difference between the rear and front chambers of the latter exceeds a predetermined threshold. For a given dimensioning of the actuator, its efficiency is therefore increased. Conversely, an efficiency comparable to that of a conventional servomotor is obtained for a reduced diametral size.

 Of course, the invention is not limited to the embodiments which have just been described by way of examples, but covers all the variants thereof. Firstly, instead of being completely pneumatic as has just been described, the control device according to the invention can consist of an electromagnetic valve whose movements are controlled in response to electrical signals generated by a computer receiving signals representative of the pressure prevailing in the rear and front chambers of the booster respectively. Furthermore, the embodiment of the pneumatically controlled device which has been described may undergo various modifications taking into account the usual knowledge of those skilled in the art, without departing from the scope of the invention.

Claims (16)

 1. Control device for an assistance servomotor (10) comprising a housing (12), in which a motor piston (14) separating a front chamber (16) from a rear chamber (18) can move during actuation of an input control member (22) establishing a pressure difference between the rear chamber and the front chamber, an auxiliary drive member (28) comprising a pressure chamber (30) being placed in the rear chamber (18) of the actuator, the control device (36) being placed between the pressure chamber of the actuator and a pressure source (34), and being characterized in that it comprises a valve (38) normally closed, at through which the pressure chamber communicates with the pressure source, and actuation means (40) of said valve, sensitive to the pressure difference between the rear chamber and the front chamber to automatically open the valve when this difference exceeds a threshold pr determined.  2. Device according to claim 1, characterized in that it comprises a hollow body (42) in which are formed an inlet chamber (44) of pressurized fluid communicating with the pressure source (34), a chamber outlet (46) for pressurized fluid, communicating with the pressure chamber (30), a first control chamber (48) communicating with the front chamber (16) and a second control chamber (50) communicating with the rear chamber (18), said inlet and outlet chambers forming between them a first valve seat (60) against which a valve (56) is normally held in sealed abutment by a first elastic means (58), the first and second chambers control elements being separated in leaktight fashion by means of piston (72) axially aligned with the valve seat and an extension (72a) of which carries a second valve seat (110) capable of coming to bear sealingly against the valve (56) and move it away from the first seat (60), a second elastic means (78) normally holding the second valve seat away from the valve.  3. Device according to claim 2, characterized in that said threshold is determined by the value of the prestressed emanagized in the second elastic means (78).  4. Device according to any one of claims 2 and 3, characterized in that the valve (56) is an annular valve internally delimiting an exhaust chamber (106) isolated from the inlet chamber (44) and communicating with the atmosphere by a non-return valve (100), said exhaust chamber communicating with the outlet chamber (46) when the second valve seat (110) is not in contact with the valve (38).  5. Device according to any one of claims 2 to 4, characterized in that said extension (72a) passes in leaktight manner a partition (74) of the hollow body, separating the outlet chamber (46) from the first chamber control (48).  6. Device according to claim 5, characterized in that said piston means (72) is axially traversed by a passage (80) through which the outlet chamber (46) communicates normally with the second control chamber (50), this passage being closed when the second valve seat (110) is in contact with the valve.  7. Device according to claim 6, characterized in that the passage (80) has a restriction (108).  8. Device according to any one of claims 5 to 7, characterized in that the extension (72a) of the piston means (72) supports a stop (76) placed in the outlet chamber (46) and normally maintained in support on said partition by the second elastic means (78).  9. Device according to any one of claims 2 to 8, characterized in that the second elastic means comprises at least one compression spring (78) placed in the first control chamber (48).  10. Device according to any one of claims 2 to 9, characterized in that the second elastic means comprises at least one compression spring (58) placed in the inlet chamber (44).  11. Device according to any one of claims 2 to 10, characterized in that the piston-forming means (72) is floatingly mounted inside the hollow body (42).  12. Device according to claim 1, characterized in that it comprises a hollow body (42) in which are formed an inlet chamber (44) of pressurized fluid (34), an outlet chamber (46) of fluid under pressure, communicating with the pressure chamber (30), a first control chamber (48) communicating with the front chamber (16) and a second control chamber (50) communicating with the rear chamber (18), said chambers inlet and outlet forming between them a first valve seat (60) against which a first valve (56) is normally held in leaktight support by a first elastic means (58), the first and second control chambers being separated from sealingly by means of a piston (72) axially aligned with the first valve seat and an extension (72a) of which forms a second valve and capable of coming into sealing contact with a second valve seat (110) integral with the first valve ( 56) so that firstly closing a communication between said outlet chamber (46) of pressurized fluid and said front chamber (16) when a pressure difference is established between said control chambers (48.50), and in a second time, to move said first valve (56) away from said first seat (60), a second elastic means (78) normally keeping said second valve away from said second seat (110).  13. Device according to claim 12, characterized by the fact that said inlet chamber (44) is an annular chamber, said first valve (56) being annular and being integral with a hollow cylinder (120) carrying the second valve seat (110), said outlet chamber (46) communicating with said front chamber (16) via said hollow cylinder (120) when said second valve is not supported on said second valve seat (110).  14. Device according to claim 12 or 13, characterized in that the prestressed stored in said first elastic means (58) determines said determined threshold.  15. Device according to any one of claims 12 to 14, characterized in that said first elastic means (58) consists of a compression spring arranged in said outlet chamber (46) and pressing against said first valve (56).  16. Device according to any one of claims 129 15, characterized in that said second elastic means (78) consists of a spring disposed in one (48) of said control chambers.