FR2736606A1 - Servomotor with supplementary valve for motor vehicle braking assistance system - Google Patents

Abstract

The servomotor has a piston with a low pressure source connected to one side and a high pressure source connected to the other. The piston is connected to the brake master cylinder piston to augment force applied by the driver. Communication between the high pressure side of the piston and the high pressure source is established when the force applied to the master cylinder piston exceeds a preset value. A valve (300) is fitted in the servo wall to provide passage from the high pressure source. A solenoid valve (90) is placed at the high pressure inlet of this valve to keep it closed till the solenoid valve is operated. The solenoid valve is controlled by a detector (E) responding to force applied (28) to the brake master cylinder piston.

Description

PNEUMATIC SERVOMOTOR
WITH ADDITIONAL VALVE
The present invention relates to pneumatic servomotors, of the type which are used to provide braking assistance for motor vehicles.

 Such servomotors have been known for a long time in the automotive technique.

Conventionally, they comprise an envelope, separated in leaktight manner by at least one movable partition structure in a front chamber permanently connected to a low pressure source, and a rear chamber selectively connected to the front chamber or to a source of high pressure by a valve actuated by a control rod capable of pressing, via the front face of a plunger, on the rear face of a thrust rod secured to a reaction disc when a pressure difference between the front and rear chambers, generated by the opening of the valve, is exerted on the movable partition and drives a pneumatic piston movable relative to the casing and carrying the valve.

 Although they have generally satisfactory operation, these servomotors nevertheless have some drawbacks. This is why during braking, the passage offered to atmospheric air, constituting for example the high pressure source, towards the rear chamber is reduced, which slows the movement of air towards the chamber. backward and increases the servo motor response time. Different compromises have been proposed so that this response time is acceptable for so-called normal braking or only a slowing down of the vehicle is desired. However, this response time is always much too long during vigorous braking, where the driver wishes to stop the vehicle immediately, and where rapid intervention of the braking assistance is necessary.

 The present invention therefore aims to provide a pneumatic booster of the type mentioned above, whose response time is as short as possible for vigorous braking, without otherwise altering the normal operation of the braking device, and by using means reliable and inexpensive.

For this purpose, according to the invention, communication between the rear chamber of the booster and the high pressure source is established when an input force applied to the control rod is greater than a predetermined value
According to a preferred embodiment, such communication is established by at least one additional valve.

 Advantageously, this additional valve can be disposed on a part of the casing of the booster delimiting the rear chamber, and comprise first and second valve seats formed in a housing and cooperating respectively with a first and a second valve, the l opening and closing are controlled by an axis.

Other objects, characteristics and advantages of the invention will emerge clearly from the description which is given below, for information and in no way limitative, with reference to the appended drawings in which
FIG. 1 is a sectional view of a pneumatic brake booster produced in accordance with the present invention, and
- Figures 2 to 6 are sectional views on a larger scale of the additional valve fitted to the booster of Figure 1, shown in several stages of operation.

 Figure 1 shows a section of a brake booster, designated as a whole by the reference 100, intended to be placed in the usual way between the brake pedal (not shown) of a vehicle and the master cylinder 200 controlling the hydraulic braking circuit (not shown) of this vehicle.

By convention, the part of the servomotor facing the master cylinder is called "front" of the booster and the part facing the brake pedal is the "rear" part of the booster. On the
Figure 1, The front is thus on the left and the rear on the right, and in Figures 2 to 6, The front is at the bottom and the rear at the top.

 Insofar as the invention relates only to an improvement made to pneumatic brake booster motors, and where the general construction and operation of the latter are well known to those skilled in the art, these servomotors will not be quickly described here only to allow a complete understanding of the improvement represented by the invention.

 The booster 100 itself comprises a rigid casing 10 separated into a front chamber 12 and a rear chamber 14, in leaktight manner, by a movable partition 16 comprising a membrane 18 and a rigid skirt 20 integral with a pneumatic piston 22 movable at inside the envelope 10.

 The front chamber 12, the front face of which is tightly closed by the master cylinder 200, is permanently connected to a source of vacuum (not shown) through a connector 24.

 The pressure in the rear chamber 14 is controlled by a valve 26, controlled by a control rod 28 connected at the rear to a brake pedal (not shown) and at the front to a plunger 30.

 When the control rod 28 is in the rest position, in this case urged backwards, the valve 26 allows communication between the two chambers 12 and 14 of the booster.

 The rear chamber 14 then being subjected to the same vacuum as the front chamber 12, the piston 22 is pushed back, in the rest position, by a spring 32.

 During braking, actuation of the control rod 28 forwards has the effect, firstly, of moving the valve 26 so that it isolates the chambers 12 from one another and 14 then, in a second step, to move this valve so that it opens the rear chamber 14 at atmospheric pressure.

 The pressure difference between the two chambers then felt by the membrane 18 exerts on the movable partition 16 a thrust which tends to move it forward and allow it to drive the piston 22 which in turn moves, the spring 32 compressing.

 The braking force exerted on the control rod 28, or "input force" and the braking assistance force, or "assistance force", resulting from the thrust of the movable partition 16, are then applied together along the axis XX 'of the control rod 28 on a reaction disc 34 integral with a push rod 36, and combine to constitute the actuating force of the primary piston 38 of the master cylinder 200.

 The rear chamber 14, which previously communicated with the front chamber 12 and was therefore under reduced pressure, therefore sucks air at atmospheric pressure through the valve passage of small section between the valve 26 and the valve seat formed at the rear end of the plunger 30. This therefore results in a significant obstacle to the passage of air, limited by the section of the valve passage 26-30 and by the environment of the valve 26, and this therefore results in a significant response time, which, if it is not very sensitive in braking where only the vehicle slowing down is desired, can become prohibitive during vigorous braking in an emergency.

 The present invention overcomes this drawback, by providing for admitting into the rear chamber 14 of the booster an amount of air additional to that which is normally admitted by opening the valve 26, when an energetic braking action is applied. initiated by the driver of the vehicle.

 As can be seen in FIG. 1, an additional valve 300 is installed on the rear part of the casing 10 of the booster, which delimits the rear chamber 14. It is for example placed in a housing 54 inserted in a sealed manner in an extension cylindrical 56 of the casing 10 directed towards the rear. This additional valve is shown on a larger scale in Figures 2 to 6 which will now be referred to.

 In Figure 2, we see the additional valve 300 in the position it occupies when the actuator 100 is in the rest position.

 The housing 54 is formed with two valve seats 58 and 60, directed respectively towards the front and towards the rear, and of the same diameter. The valve seat 58 is capable of cooperating with a valve 62 secured to a central axis 64, itself secured to a cup 66.

 A compression spring 68 is disposed between the cup 66 and the valve 62 to urge the latter backwards with respect to the axis 64. A compression spring 70 is disposed between a shoulder 72 of the housing 54 and the cup 66 for pull the latter forward. We can form the front part of the housing 54 with axial ribs 73 to guide the cup 68 in its movements and prevent it from off-center.

 A support 74 is capable of sliding on the axis 64, between a rear stop 76 and a front stop 78, a compression spring 80 being disposed between the front stop 78 and the support 74 to urge the latter backwards. The rear stop 78 is located, in this position, slightly behind the valve 62, so as to also form a stop for this valve.

 The support 74 is integral with a valve 82 capable of cooperating with the valve seat 60. An end piece 84 (Figure 1) is disposed at the rear of the housing 54, this end piece being connected to a two-way and two-way solenoid valve 90 positions, allowing or preventing communication with the high pressure source, in this case air at atmospheric pressure.

 Finally, a sensor 92, for example a strain gauge, is arranged on the control rod 28, to measure the input force to which it is subjected on the part of the driver of the vehicle. A simple electronic circuit E receives the signal from this strain gauge as an input, and outputs an excitation current from the solenoid valve 90 as a function of the signal present at its input.

 It is quite clear that an emergency braking situation always results in an input force, measured on the control rod, greater than a predetermined value. It is therefore easier to use a force sensor on this rod. However, the urgency of braking can be determined by other sensors. We can for example use a displacement speed sensor of this rod, or a pressure sensor on the brake pedal, or a signal provided by any suitable device such as an anti-collision radar. We can even use a combination of these different signals to obtain a signal truly representative of the emergency nature of braking.

 Whatever the sensor used, when the input force on the control rod 28 is less than a predetermined value, the solenoid valve 90 adopts, under the control of the circuit E, a position in which it prohibits communication between the 'end piece 84 and atmospheric air. The actuator then operates as described above. This is the situation corresponding to normal deceleration braking of the vehicle.

 On the other hand, when the input force is greater than this predetermined value, for which it is apparent that the driver brakes vigorously to obtain an emergency stop of his vehicle, the circuit E then commands the tilting of the solenoid valve 90 in the position shown in Figure 1, where it allows atmospheric air to reach the tip 84.

 The response times of the strain gauge 92, of the electronic circuit E and of the solenoid valve 90 can be estimated as negligible compared to that of the servomotor, and it can be considered that, depending on the intensity of the input force , the general design of the booster and the preload of the spring 32, the state of the booster at this time is identical to or very close to the rest position shown in FIG. 1.

 If the actuator is still in the rest position during the tilting of the solenoid valve 90 in its on state, the movable partition 16 is in the rear extreme position under the stress of the spring 32, the chamber 14 then having its minimum volume, and the movable partition 16 bears on the front end of the axis 64 which, via the cup 66, applies the valve 62 to its seat 58, against the action exerted by the springs 68 and 70, the sum of the prestresses at rest is less than that of the spring 32.

 The input force, applied to the control rod 28, controls the operation of the valve 26 so that it opens to the atmosphere, after a predetermined stroke, the rear chamber 14 of the servomotor, which was previously isolated from the front chamber 12. A pressure difference is installed in the chambers 12 and 14, and generates an assistance force on the rigid skirt 20, which then drives the pneumatic piston 22 forward.

 The valve 300 then takes the position shown in Figure 3, where we see that the movable assembly consisting of the axis 64, the support 74 and the valve 82, the cup 66 and the valve 62 has moved en bloc to follow the movable partition 16. The movable assembly moves under the effect of the spring 70, the spring 68 urging the valve 62 backwards until it comes to bear against the stop 78.

 It can therefore be seen that the valve passage 58-62 opens, while the valve passage 6082 is also open. Air at atmospheric pressure can therefore arrive directly in the rear chamber 14 by taking the path indicated by the arrow F in FIG. 3, this air being added to that which is admitted by the valve 26 of the booster. As a result, the pressure in the chamber 14 can then increase relatively rapidly, depending on the sections of the valve passages 60-82 and 58-62.

 The movement of the moving assembly continues until the valve 82 comes to bear on its seat 60, then interrupting the air supply to the rear chamber 14 by the additional valve 300. This is the situation shown in Figure 4.

 The closure of the valve passage 60-82 occurs after a stroke L of the moving assembly, defined mainly by the distance D between the stops 76 and 78 of the axis 64. This stroke L can be predetermined to obtain any influx of additional air desired in the rear chamber 14, so as to provide the driver with all possible assistance in emergency braking.

 On the other hand, for the reasons mentioned above, if the actuator was already no longer in its rest position when the solenoid valve 90 was tilted in its on state, that is to say if the movable partition 16 has already slightly advanced, the valve 300 then has at this time the position shown in Figure 3. Thus, as soon as the solenoid valve 90 is in its on state, air at atmospheric pressure is admitted into the rear chamber 14, coming add to that which is admitted by the valve 26. The valve 300 then operates in accordance with that which has just been described, when it was initially in its rest position.

 Then, the movable partition 16, continuing to advance, loses contact with the axis 64, and the movable assembly remains in the position shown in Figure 4, and the operation of the servomotor 100 is then in accordance with that which has was described above when the driver of the vehicle continues to press the brake pedal during normal deceleration of the vehicle.

 However, the pressure in the rear chamber 14 having increased much faster than if the valve 26 had been the only one to supply air at atmospheric pressure, the pressure in the master cylinder and in the braking circuit increased it too much faster, providing the driver with the braking effort he was looking for in an emergency.

 When the driver releases his force on the brake pedal, this results in a reduction in the input force, and correspondingly a reduction in the assistance force, by reduction in the pressure difference between the chambers 12 and 14.

 The movable partition 16 therefore returns back under the action of the spring 52 which has become preponderant, and it resumes contact with the axis 64, as shown in FIG. 5. By continuing its movement towards the rear, this axis 64 compresses, via the cup 66, the spring 68, until the valve 62 comes to bear on its seat 58.

 During this movement, the valve passage 60-82 remains closed. Indeed, the valve 82 remains supported on its seat 60, because it is subjected, on its rear face, to atmospheric pressure, and on its front face, to the low pressure prevailing in this operating phase in the rear chamber 14 , and the preload and stiffness of the spring 80 not being sufficient to overcome the force generated on the valve 82 by this pressure difference. The spring 80 thus compresses while the valve 62 comes to bear on its seat 58.

 At the end of the movement of return of the movable partition 16 in the rest position, the two valve passages 58-62 and 60-82 are therefore closed, and the valve occupies the position shown in Figure 6. The volume 84 located between the two valves 62 and 82 being always under reduced pressure, it is necessary to apply mechanical force to the valve 82 to cause it to reopen. This mechanical force is provided by the movable partition 16 which, at the end of the return stroke, continues to push back the axis 64, until the cup 66 comes to bear on the front face of the valve 62.

During this final movement, the stop 78 is distant from the rear face of the valve 62, it comes into contact with the support 74 and biases it towards the rear, thus forcing the reopening of the valve passage 60-82. The spring 80 can then return the support 74 and the valve 82 to their initial rest position, so that the valve 300 returns to the position shown on the
Figure 2.

 It can therefore be seen that the additional valve 300 allows an additional quantity of air to be admitted into the rear chamber of the booster when the solenoid valve 90 connects the nozzle 84 to atmospheric air, that is to say when it is controlled by circuit E having detected an emergency braking situation. It follows that the response time of the actuator can be reduced in significant proportions under these extreme conditions.

 In addition, the design of the valve 300 is particularly simple, which makes it reliable and inexpensive. Its operation is purely mechanical and automatic, the axis 64 playing the role of a position sensor of the movable partition 16 to control the operation of the valve. Similarly, the electronic circuit E is a simple threshold detection circuit, which we know how to manufacture at low cost, and the solenoid valve 90 is two-way and two-position, it works in all or nothing, and therefore comes out of '' a perfectly mastered technology.

 The valve 300, and in particular the diameters of the valve seats 58 and 60, may be given any dimension desired to determine the section offered for the passage of air in the direction of the rear chamber, which it is not possible to do with the valve 30 of the servomotor without prohibitively increasing the dimensions.

 Of course, the invention is not limited to the embodiment which has been described, but it is on the contrary liable to receive numerous modifications which will appear to those skilled in the art. Thus, for example, the invention can advantageously be applied to servo motors of the tandem type or with additional chamber, where the air volume of the rear chambers is greater than on the simple servomotor which has been described, and therefore where the response time in case of emergency braking is longer. It will also be possible to have several additional valves 300 on the rear casing of the booster, these additional valves all being connected to the same solenoid valve, or each to a particular solenoid valve, the solenoid valves being controlled in parallel by the electronic circuit E, or sequentially in function. the degree of emergency detected by different sensors. Alternatively, the additional valve and the solenoid valve may be combined in a single component.

Claims (10)

 1. Pneumatic brake booster (100), comprising a casing (10), leaktightly separated by at least one movable partition structure (16) in a front chamber (12) permanently connected to a bass source pressure, and a rear chamber (14) selectively connected to the front chamber (12) or to a high pressure source by a valve (26) actuated by a control rod (28) capable of being supported, via of the front face of a plunger (30), on the rear face of a push rod (36) secured to a reaction disc (34) when a pressure difference between the front (12) and rear chambers (14), generated by the opening of the valve (26), is exerted on the movable partition (16) and drives a pneumatic piston (22) movable relative to the casing (10) and carrying the valve (30) , characterized in that communication between the rear chamber (14) of the actuator (100) and the high pressure source is established l when an input force applied to the control rod (28) is greater than a predetermined value.  2 - Pneumatic booster according to claim 1, characterized in that the communication between the rear chamber (14) of the booster (100) and the high pressure source is established by at least one additional valve (300).  3 - Pneumatic booster according to claim 2, characterized in that the additional valve (300) is arranged on a part of the casing (10) of the booster (100) delimiting the rear chamber (14) and comprises a first (58) and a second (60) valve seats formed in a housing (54) and cooperating respectively with a first (62) and a second (82) valves whose opening and closing are controlled by an axis (64).  4 - Pneumatic booster according to claim 3, characterized in that the axial position of the axis (64) in the housing (54) is determined by the position of the movable partition (16) in the casing (10) of the booster (100), the axis (64) being formed with a first (78) and a second (76) stop between which fear sliding a support (74) integral with the second valve (82), the support (74) being biased towards the rear by a spring (80) bearing on the first stop (78).  5 - Pneumatic booster according to claim 4, characterized in that the axis (64) is integral with a cup (66) biased forward by a spring (70) bearing on the housing (54).  6 - Pneumatic booster according to claim 5, characterized in that a spring (68) bearing on the cup (66) biases the first valve (62) bearing on the first valve seat (58) or on the first stop (78).  7 - Pneumatic booster according to claim 4, characterized in that the closing of the second valve (82) is controlled by the axis (64) and maintained by a pressure difference exerted on its front and rear faces.  8 - Pneumatic booster according to claim 2, characterized in that a solenoid valve (90) is interposed between the additional valve (300) and the high pressure source.  9 - Pneumatic booster according to claim 8, characterized in that the solenoid valve (90) is controlled by a device (E, 92) sensitive to the force applied to the control rod (28).  10 - Pneumatic booster according to claim 9, characterized in that the positive say (E, 92) sensitive to the force applied to the control rod (28) comprises a sensor (92) disposed on the control rod (28) and a threshold detection circuit (E).