FR2727370A1 - Braking system with hydraulic servo assisted unit for vehicle - Google Patents

Abstract

The pneumatic brake servo unit (300) comprises a front vacuum chamber (26) and a rear working chamber (28), separated by a moving sealed partition (30) rigidly fixed to an activating rod (32) which activates a pressure transmitter (400). The operation is regulated by a control unit (100) which has a valve (22) activated by a controlling rod (10) to open channels between a primary chamber (18) and either a secondary chamber (20) or a source of high pressure (A).Two pipelines (36,38)communicate respectively the primary and secondary chambers of the control unit with the working and vacuum chambers of the servo unit respectively. An electro-valve (500) is arranged in one of these two pipelines linking the control unit to the servo unit.

Description

ASSISTED HYDRAULIC BRAKING SYSTEM
The present invention relates to hydraulic assisted braking systems, consisting of pneumatic booster motors and master cylinders, of the type which are used for motor vehicles.

 Such systems conventionally comprise a pneumatic booster, the envelope of which is fixed by its rear part to a wall isolating the passenger compartment from the engine compartment of a vehicle, and separated in leaktight manner by a movable wall structure in a front chamber. permanently connected to a vacuum source and a rear chamber selectively connected to the front chamber or to a high pressure source by a valve means actuated by a control rod capable of being supported, via the front face a plunger on the rear face of a reaction disc integral with a thrust rod coaxial with the control rod. A master cylinder is usually fixed on the front part of the casing of the booster, so that the actuator push rod cooperates with the master cylinder piston when actuating the actuator control rod, which passes through an opening of the bulkhead and which is actuated by a brake pedal in the passenger compartment.

 However, there are cases in which it is not possible to place the actuator directly between the brake pedal and the master cylinder. Such a situation arises, for example, on certain vehicles whose driving position is located to the right of the vehicle, and where the diametrical size of the booster makes such installation in the engine compartment impossible.

 The documents EP-A-0 326 965 or GB-A-2 200 419 have provided a solution to this problem, by providing for dissociating the pneumatic booster from the master cylinder. In this design, only a servomotor control module and the master cylinder are placed in the extension of the control rod actuated by the brake pedal, the servomotor itself being able to be placed at any location in the engine compartment.

The control module comprises a valve which selectively places a first chamber in communication with a second chamber permanently connected to a vacuum source or to a high pressure source, in this case the atmosphere. Two pipes connect the chambers of the control module to the chambers of the actuator, which actuates a simple cylinder master, connected to an assistance chamber of the control module, so that the input force exerted by the control rod is amplified by this assistance effort to act on the push rod actuating the master cylinder connected to the brake motors.

 These braking systems are quite complex, and above all they do not make it easy to perform the functions which are today required of most braking systems, such as traction control under acceleration or automatic braking functions, c 'is to say controlled electrically.

The present invention therefore aims to provide an assisted hydraulic braking system, which is simple in design, and which can easily be controlled independently of the will of the driver of the vehicle, for traction control or automatic braking operation.
To this end, the present invention provides an assisted hydraulic braking system, comprising a pneumatic booster comprising a front vacuum chamber and a rear working chamber separated by a movable watertight partition secured to an actuating rod, a pressure transmitter actuated by the actuating rod, pneumatic actuator control means comprising a valve element actuated by a control rod and selectively placing a first chamber in communication with a second chamber or with a high pressure source, the control rod supported by a reaction disc on a push rod actuating a master cylinder connected to at least one brake motor, a first pipe communicating the first chamber of the control means with the working chamber of the servomotor, a second pipe communicating the second chamber of the control means with the ch amber vacuum of the booster, the control means comprising a piston sliding in a bore and defining therein the first and second chambers and an assistance chamber connected to the pressure transmitter.

According to the invention, an electrovalve is placed on one of the pipes connecting the chambers of the control means to the chambers of the booster. Advantageously,
The solenoid valve can be placed on the first pipe connecting the first chamber of the control means with the working chamber of the booster, and the solenoid valve is preferably of the three-way and two-position type. In this case, the solenoid valve allows, in a first position, the communication between the first chamber of the control means and the working chamber of the booster, and, in a second position, prohibits this communication and connects the working chamber of the booster. at the high pressure source.

 Also advantageously, the solenoid valve can be arranged on the second pipe connecting the second chamber of the control means with the vacuum chamber of the booster, and the solenoid valve is preferably of the three-way and two-position type. In this case, the solenoid valve allows, in a first position, the communication between the second chamber of the control means and the vacuum chamber of the booster, and, in a second position, prohibits this communication and connects the second chamber of the means of high pressure source control.

Other objects, characteristics and advantages of the present invention will emerge more clearly from the following description of an exemplary embodiment given by way of illustration, with reference to the appended drawings in which:
FIG. 1 represents a sectional view of an assisted hydraulic braking system, produced in accordance with the present invention, and
- Figure 2 shows a vivid section of a variant of the embodiment of the
Figure 1.

 Figure 1 shows a sectional view of a braking system, known for example from the above documents, and which will therefore be described succinctly. It consists of a control module, designated as a whole by the reference 100, a master cylinder 200, a pneumatic servomotor 300 and a pressure transmitter 400, a simple master cylinder in the example shown.

 By convention, the direction in which the moving parts move when they are actuated is called "before". and "back" the direction in which they move to return to their rest position. In the Figures, the front is thus on the left and the rear on the right.

 The control module 100 is actuated by a control rod 10 connected to a brake pedal (not shown) located in the passenger compartment of the vehicle. The module 100 comprises a body 12 formed with a stepped bore 14 in which slides in leaktight manner a stepped piston 16. The piston 16 internally divides the bore 14 into a first chamber 18 formed at the rear of the bore and a second chamber 20 formed at the front, and permanently connected to a source of vacuum V.

 The first chamber is selectively placed in communication with the second chamber or with a high pressure source A, the atmosphere for example, by a conventional three-way valve element 22, placed in a housing of the piston 16, and actuated by a plunger 23 secured to the control rod 10.

 The pneumatic booster 300 is formed of a casing 24, internally divided into a front chamber 26 permanently connected to the vacuum source V and a rear chamber 28 by a movable watertight partition j0. The partition 30 is integral with an actuation 32 and cooperates with the piston 34 of the pressure transmitter 400, fixed to the front wall of the casing 24.

 The rear chamber 28 of the actuator 300 is connected to the first chamber 18 of the control module 100 by a pneumatic line 36. Likewise, the front chamber 26 of the actuator 300 is connected to the second chamber 20 of the control module 100 by a line pneumatic 38. The outlet of the pressure transmitter 400 is connected by a hydraulic line 40 to an annular actuation chamber 42 formed in the body 12 of the control module 100 between the shoulders of the stepped bore 14 and the stepped piston 16.

 The operation of this braking system is also known. At rest, all the moving parts occupy their rear position shown in Figure 1. In this position, the valve 22 allows communication between the first and second chambers 18 and 20 of the control module 100, and prohibits communication between the first chamber 18 and the high pressure source A. The chambers 18 and 20 are therefore at the pressure of the vacuum source V, as are the front and rear chambers 26 and 28 of the servomotor 300 with which they communicate via the pipes 36 and 38 .

When the driver of the vehicle actuates the brake pedal, the control rod 10 moves forward. The plunger 23 then controls the movement of the valve 22 so that it first isolates the chambers 18 and 20 from each other, then places the first chamber 18 in communication with the high pressure source A. this results in an increase in pressure in the chamber 18, transmitted by the line 36 to the rear chamber 28 of the booster 100, the front chamber 26 of which is permanently connected to the source of vacuum
V.

 This pressure difference is exerted on the two faces of the movable partition 30 and tends to move it forward, so that the actuating rod 32 moves the piston 34 of the pressure transmitter 400 and causes an increase. pressure in line 40, transmitted to assistance chamber 42.

 The pressure in the annular chamber 42 is exerted on the piston 16 and thus tends to make it advance. The piston 16 has an annular face surrounding the front face of the plunger 23, these two faces being supported on a reaction disc 44 secured to a push rod 46. The reaction disc 44 therefore simultaneously receives the input force transmitted by the plunger 23 and the assistance force transmitted by the piston 16 on which the pressure in the chamber 42 is exerted.

The reaction disc 44 and the push rod 46 transmit the sum of these two forces to the piston 48 of the master cylinder 200, which then generates an increase in pressure in the brake motors 50, which does indeed cause the braking action. assistance required by the driver of the vehicle.

 In accordance with the present invention, provision is very simply made to obtain a braking action independent of the will of the driver of the vehicle, for example to obtain traction control or automatic braking operation.

 In the embodiment shown in Figure 1, it can be seen that an electrovalve 500 has been placed on the pipe connecting the first chamber 18 of the control module 100 to the rear chamber 28 of the booster. The solenoid valve 500 is of the three-way, two-position type. In its rest position shown, it allows communication between these two chambers, and therefore an operation of the braking system as described above.

The vehicle is also equipped with various sensors (not shown) and a computer (not shown). When the computer detects, for example, a speed of rotation of the driving wheels of the vehicle that is too high compared to the speed of rotation of the non-driving wheels, it then controls the excitation of the solenoid valve 500. Proximity sensors can also detect the presence an obstacle or too high a relative speed with the vehicle in front
When the solenoid valve is energized, it switches to its second position, where it isolates the two chambers from one another, and puts the rear chamber 28 of the actuator in communication with the atmosphere A. This therefore results in an increase pressure in the chamber 28, since it was previously subjected to the pressure of the vacuum source V, and a pressure difference with the front chamber of the booster where the pressure of the vacuum source V prevails.

This pressure difference is exerted on the two faces of the movable partition 30 and tends to move it forward, and to control the operation of the pressure transmitter 400. This therefore results in an increase in pressure in the chamber annular 42, which is exerted on the piston 16 and creates on the reaction disc 44 and the push rod 46 a force actuating the master cylinder 200, and consequently the brake motors 50. brakes, controlled by the vehicle's on-board computer, to brake the drive wheels and prevent them from slipping during acceleration, or to brake the vehicle if an obstacle is deemed too close
As soon as the traction control situation or the presence of an obstacle has disappeared, the computer controls the de-excitation of the electrovalve 500, which then returns to its rest position shown. The rear chamber 28 of the servomotor 300 is then put back into communication, via the pipe 36, with the first chamber 18 of the control module 100, where the pressure of the vacuum source V prevails. The pressure in the rear chamber 28 can thus s 'to lower.

 The first chamber 18 communicating permanently with the vacuum source V, the pressure difference between the chambers 26 and 28 of the booster is canceled, so that the movable partition 30 can return to its rear position of rest under the effect of 'a return spring 52 disposed in the front chamber 26 of the booster. The piston 34 of the pressure transmitter 400 is thus itself recalled backwards, whence there results a decrease in pressure in the pipe 40 and in the assistance chamber 42.

The piston 16 is then also returned to its rear rest position by a return spring 54 located in the bore 14, bringing the push rod 46 and the piston 48 of the master cylinder 200 backwards. The pressure in the brake motor 50 can therefore lower and return to its initial value, thus putting an end to the period of operation in anti-skid or automatic braking
In addition, during periods of traction control or automatic braking, if the computer detects that the braking thus obtained is too intense, it can command the return of the solenoid valve to its rest position, then a new excitation, so as to obtain the desired braking effect, that is to say the desired pressure in the brake motors 50, that is to say also the desired pressure in the rear chamber 28 of the booster. In this way, by modulating the excitation current of the solenoid valve, for example by modulating the width of the pulses or their duty cycle, it is thus possible to obtain exactly the desired braking action as a function of the external conditions.

It can therefore be seen that the traction control or automatic braking functions for an assisted hydraulic braking system have been obtained in a very simple, efficient and reliable manner. Indeed, the solenoid valve used being of the two-position type, it is particularly simple, reliable and inexpensive. In addition, it is the only additional component necessary to fulfill this function
In addition, in the anti-skid or automatic braking operating phase, the pressure build-up in the rear chamber 28 of the booster occurs very quickly, since the air entering this chamber encounters practically no obstacle in its path, if the the solenoid valve 500 is placed in the immediate vicinity of the rear chamber 28 and if it is suitably sized.

Similarly, when the solenoid valve 500 returns to its rest position, the pressure balance in the two chambers of the booster is very quickly restored, so that the braking system quickly returns to its initial configuration, allowing the driver of the vehicle to take back the braking initiative
In order to obtain a finer modulation of the braking, and to avoid causing the spool of the solenoid valve 500 to beat too quickly, which could generate vibrations and noises, it is possible to use a proportional solenoid valve, that is to say in which the position of the drawer controlling the communications between the three channels depends on the intensity of the current flowing in the winding of the solenoid valve.

 It will also be understood that the pressure in the rear chamber 28 can be controlled with the solenoid valve 500 as long as this pressure is less than atmospheric pressure. Thus, during a braking action, where the pressure in the chamber 28 is between the pressures of sources A and V, and depending on the sensors installed on the vehicle, it will be possible to control the solenoid valve 500 to increase the pressure in chamber 28 and at the same time the intensity of braking.

 There is shown in Figure 2 a variant of the embodiment which has just been described, where the same components are assigned the same reference sign. According to this variant, it can be seen that the solenoid valve 500 ′ is placed on the pipe 38 connecting the front chamber 26 of the booster 300 to the second chamber 20 of the control module 100.

 When the solenoid valve 500 ′ is in the rest position shown in FIG. 2, it allows the braking system to operate under the action of the control rod 10 identical to that which has been described above for controlling the braking by the driver of the vehicle.

When the solenoid valve 500 'is energized, it prohibits communication between on the one hand the chambers 26 and 20 between them and on the other hand between the chamber 20 and the vacuum source
V, and it places the chamber 20 in communication with the high pressure source A. The resulting pressure increase in the chamber 20 is transmitted to the chamber 18, communicating at rest with the chamber 18, and via the pipe 36 to the rear chamber 28 of the booster. As a result, as described above in connection with FIG. 1, this results in actuation of the vehicle brakes for traction control or automatic braking operation.

 When the solenoid valve 500 'is de-energized and returns to its rest position, the chamber 20 is connected again to the vacuum source V, which has the effect of decreasing the pressure in this chamber, as well as in the chambers 18 and 28. This results in a return to the rest position of the entire braking system, as described above, and the cessation of braking for a traction control or automatic braking phase.

 In this embodiment, it is also possible to use a proportional solenoid valve 500 ′.

 Of course, the invention is not limited to the embodiments which have been described, but it is on the contrary liable to receive numerous modifications which will appear to a person skilled in the art and which fall within the scope of the appended claims.

Claims (9)

 1 - Hydraulic assisted braking system, comprising a pneumatic servomotor (300) comprising a front vacuum chamber (26) and a rear working chamber (28) separated by a mobile watertight bulkhead (30) secured to an actuating rod (32), a pressure transmitter (400) actuated by the actuating rod (32), control means (100) of the pneumatic actuator (300) comprising a valve element (22) actuated by a control rod ( 10) and selectively placing a first chamber (18) in communication with a second chamber (20) or with a high pressure source (A), the control rod (10) being supported by means of a disc reaction (44) on a push rod (46) actuating a master cylinder (200) connected to at least one brake motor (50), a first pipe (36) making the first chamber (18) of the control means communicate (100) with the working chamber (28) of the actuator (300), a second ca nalisation (38) communicating the second chamber (20) of the control means (100) with the vacuum chamber (26) of the actuator (300), the control means (100) comprising a piston (16) sliding in a bore (14) and defining therein the first (18) and second (20) chambers and an assistance chamber (42) connected to the pressure transmitter (400), characterized in that a solenoid valve (500) is arranged on one of the pipes (36,38) connecting the chambers (18,20) of the control means (100) to the chambers (28,26) of the servomotor (300).  2 - Hydraulic assisted braking system according to claim 1, characterized in that the solenoid valve (500) is arranged on the first pipe (36) connecting the first chamber (18) of the control means (100) with the working chamber (28) of the servomotor (300).  3 - Hydraulic assisted braking system according to claim 2, characterized in that the solenoid valve (500) is proportional.  4 - Hydraulic assisted braking system according to claim 2, characterized in that the solenoid valve (500) is of the three-way and two-position type.  5 - Hydraulic assisted braking system according to claim 3 or claim 4, characterized in that, in a first position, the solenoid valve (500) allows communication between the first chamber (18) of the control means (100) and the working chamber (28) of the booster (300), and in a second position, prohibits this communication and connects the working chamber (18) of the booster (300) to the high pressure source (A).  6 - Hydraulic assisted braking system according to claim 1, characterized in that the solenoid valve (500) is disposed on the second pipe (3S) connecting the second chamber (20) of the control means (100) with the vacuum chamber (26 ) of the servomotor (300).  7 - Hydraulic assisted braking system according to claim 6, characterized in that the solenoid valve (500) is proportional  8 - Hydraulic assisted braking system according to claim 6, characterized in that the solenoid valve (500) is of the three-way and two-position type.  9 - Assisted hydraulic braking system according to claim 7 or claim 8, characterized in that, in a first position, the solenoid valve (500) allows communication between the second chamber (20) of the control means (100) and the vacuum chamber (26) of the booster (300), and in a second position, prohibits this communication and connects the second chamber (20) of the control means (100) to the high pressure source (A).