FR2753949A1 - HYDRAULIC BRAKING SYSTEM FOR A MOTOR VEHICLE EQUIPPED WITH A BRAKE ACTUATION SIMULATOR - Google Patents

Abstract

The invention relates to a hydraulic braking system (10) for a motor vehicle, comprising an external energy service braking system and a muscle energy emergency braking system, a master cylinder (34) connected to a driving simulator. brake actuator (40) provided with a piston (44) which can be biased by fluid from the master cylinder (34) and move against the force of a spring (60). In order to obtain a progressive pedal characteristic, the invention proposes to use a second simulator (40) whose spring (68) keeps the piston (44) prestressed in the rest position. Thus, the second piston (44) only moves when the liquid pressure reaches a value which corresponds to the spring preload and the pedal force. To increase the progression, the invention proposes to use springs (60, 68) with progressive characteristics.

Description

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  State of the art The invention relates to a hydraulic braking system for a motor vehicle comprising a service braking system with external energy, an emergency braking system with muscle or auxiliary energy, a brake master cylinder which can be isolated from the wheel brake cylinders by means of a stop valve as well as a brake actuation simulator which is connected to the master -brake cylinder and has a simulator piston biased by brake fluid from the brake master cylinder and an elastic simulator element which biases the simulator piston

  against brake fluid pressure.

  Braking systems of this type include a hydraulic pump for the purpose of generating brake fluid pressure in a hydraulic accumulator. For external energy braking, this so-called accumulator pressure is lowered by means of a valve controlled to a braking pressure depending on the stroke and the force with which a foot brake pedal is depressed or a lever hand brake is pulled, or the brake fluid pressure that is produced using the foot brake pedal or using the hand brake lever. Wheel brake cylinders

  the vehicle's brake system receives the reduced brake pressure.

  The brake pressure adjustment valve is usually controlled by a single master cylinder which, in service braking mode, is hydraulically isolated from the vehicle's braking system by means of a valve d 'stop. In the event of a failure, for example, of the hydraulic pump, the shut-off valve opens and braking by muscular energy with

  emergency braking is possible.

  Since the brake master cylinder in service braking mode is hydraulically isolated from the wheel brakes of the vehicle brake system, the brake fluid cannot flow back from the master cylinder

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  towards the wheel brakes and its piston cannot move or can only move a minimum stroke. However, during braking, the normal movement of the pedal or lever with a stronger pedal force or lever force must be accompanied by a greater pedal stroke or lever stroke. For this, an actuation simulator of

brake is required.

  Such a brake actuation simulator is known for example from document US-A-4,462,642. The known brake actuation simulator comprises a simulator cylinder with a simulator piston which is subjected to the action of a spring and can move inside said cylinder. The brake actuation simulator is hydraulically connected between the master cylinder and the stop valve and even communicates in emergency braking mode with the brake master cylinder. The disadvantage of the known brake actuation simulator has a linear dependence between the pedal force and

the pedal stroke.

  Advantages of the invention The brake actuation simulator according to the invention comprises an elastic element endowed with a progressive characteristic, so that the pedal force increases in proportion to the increase in the pedal stroke. . The pedal force can increase continuously over the entire length of the pedal stroke, that is to say without discontinuity ("inflections"). It can also include discontinuities, the pedal force increasing linearly or gradually

  in sectors of the pedal travel between two discontinuities.

  The brake actuation simulator according to the invention has the advantage that the braking force can be dosed in a fine manner up to an average range of braking force in which the braking actions normally take place in urban traffic. Beyond this range, the pedal force, and with it the braking force which depends on the pedal force increases suddenly. Thus, it is possible to quickly initiate braking with a high braking force or braking at full intensity. A

  another advantage is that a volume of brake fluid from the master

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  brake cylinder and absorbed by the brake actuation simulator increases proportionally less than the increase in pedal travel; in other words, the more the pedal stroke increases, the more the volume of brake fluid admitted in addition by the brake actuation simulator decreases. The advantages presented are valid both for braking

  service only for emergency braking.

  Advantageous refinements and improvements can be

  brought to the present invention.

  Provision may be made for two brake actuation simulators to be connected to the two braking circuits of a dual circuit vehicle braking installation. In this arrangement of the invention, progressiveness is obtained by the fact that a piston of a brake actuation simulator is held with pretension in a rest position by the elastic element of the associated simulator, while the another simulator piston moves as soon as the brake master cylinder is applied. As soon as one of the simulator pistons leaves its rest position, hardening appears on the brake pedal and the pedal force increases more strongly than the pedal stroke. Additional hardening can be achieved when the simulator piston which was first moved reaches a limit position

  and no longer moves even if you continue to depress the brake pedal.

  Besides the fact that it makes it possible to obtain a pedal force which increases progressively with the pedal stroke, this arrangement has the advantage that the two brake actuation simulators, with the exception of the elements

  elastic of simulator, have an identical construction.

  The progressive brake pedal characteristic can be obtained with two brake actuation simulators, by using two elastic simulator elements with different stiffnesses or also by using elastic simulator elements of different length or by placing a spacer under the one of the two elastic simulator elements, the simulator piston biased by the longest elastic element or by the elastic element provided with a spacer being then held with prestress in

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  its rest position, until the appearance of a corresponding adapted braking pressure. Preferably, the brake actuation simulator is arranged in the form of a screwed cartridge, that is to say that it comprises on a front face a standardized thread of brake pipe by means of which it is screwed so tight in a complementary thread of brake line of the brake master cylinder, instead of a main brake line. On its opposite front face, the screwed cartridge has a thread which corresponds to the brake line thread of the brake master cylinder and to which a main brake line is normally directly screwed. If necessary, one of the fittings can be fitted with a thread of different diameter. This arrangement of the invention has the advantage that the brake actuation simulator can be mounted directly on the brake master cylinder without loss of space. Another advantage is its simple mechanical fixing, which does not require any additional fixing element. Added to this is the advantage that there is no need to make modifications to the vehicle's braking system. Only the brake lines are connected to the brake master cylinder via the brake actuation simulator instead of being connected directly. Depending on the case, the main brake line must

  be shortened by the length of the brake actuation simulator.

  Drawings The invention will now be described in detail with the aid of an example embodiment shown in the drawings. These show: FIG. 1, a hydraulic braking installation according to the invention and FIG. 2, a pedal force / pedal stroke curve drawn diagrammatically for the vehicle braking installation shown in FIG. 1.

  Description of the exemplary embodiment

  The vehicle braking installation shown in FIG. 1, and designated as a whole by the reference 10, is arranged in the form of an external energy braking installation and a muscular energy emergency braking installation. It has two circuits

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  braking I, II independent which act as well in braking mode of

  service only in emergency braking mode.

  In FIG. 1, one I of the two braking circuits is represented in a simplified manner by symbols of hydraulic circuits: the braking circuit I comprises as an external source of energy for service braking a hydraulic pump 12, the suction is connected to a reservoir 14 for supplying hydraulic fluid. The hydraulic pump 12 is driven by an electric motor 16 which also drives a hydraulic pump not shown for the braking circuit II. The discharge side of the hydraulic pump 12 is connected to a hydraulic accumulator 18 which delivers pressurized brake fluid for service braking, as well as to a pressure limiting valve 20 which leads to the suction of the hydraulic pump 12 and to the supply tank 14 and limits the maximum pressure

  discharge side of the hydraulic pump 12.

  Wheel brake cylinders 24, only one of which is shown in the drawing, are connected to the discharge of the hydraulic pump 12 and to the hydraulic accumulator 18 by means of a common inlet valve 22 or each by a clean inlet valve. The inlet valve 22 is here

  a 2/2 continuous action solenoid valve which is closed in its rest position.

  To lower a brake pressure in the wheel brake cylinder 24, there is provided a common outlet valve 26 or a clean outlet valve for each wheel brake cylinder, which communicates said wheel brake cylinder with the -power tank 14. The outlet valve 26 is here

  a 2/2 continuous action solenoid valve which is closed in its rest position.

  Any wheel brake pressure can be set in the brake cylinder.

  wheel brake 24 using the inlet valve 24 and the outlet valve 26.

  The braking circuit II not shown is arranged in the same way

  that the braking circuit I and works in the same way as this one.

  The inlet valve 22 and the outlet valve 26 for adjusting the pressure in the wheel brake cylinder 24 are controlled using an electronic control unit 28 which also controls the pump motor 16 and receives a wheel brake pressure dependent signal issued by a

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  wheel pressure sensor 30 associated with the wheel brake cylinder 24. For the muscular energy emergency braking, the braking circuits I and II are connected independently of one another, each via a shut-off valve 32, to a tandem master cylinder 34 known per se on which the supply reservoir 14 is mounted and with which the brake master cylinder 34 communicates directly. The shut-off valve 32 is a 2/2 solenoid valve which is open in the rest position and is controlled by the electronic control unit 28. During external energy service braking, the valve

  32 is closed, i.e. hydraulically the master

  brake cylinder 34 is isolated from the vehicle's brake system. During service braking, the brake master cylinder 34 serves as a setpoint transmitter for the wheel brake pressure to be adjusted by

  the electronic control device 10 in said wheel brake cylinder 24.

  For this purpose, a master cylinder pressure sensor 36 is connected to a braking circuit I of the brake master cylinder, which sensor provides a

  signal for the electronic control unit 28.

  The vehicle braking system 10 according to the invention is actuated in a manner known per se using a foot brake pedal (not

  shown), via which a piston rod 38 of the master

  brake cylinder 34 can be biased towards the inside of the brake master cylinder. In order to transmit to a driver, during an external energy service braking, during which the stop valve 32 is closed and consequently no brake fluid is discharged from the brake master cylinder 34 in the circuits brake I and II, the usual pedal characteristic with a pedal stroke in relation to the force with which the brake pedal is depressed, a brake actuation simulator 40 is connected to each of the brake circuits I, II of the brake master cylinder 34; these simulators will be described below with reference to the brake actuation simulator 40

  shown in the right part of the drawing.

  The brake actuation simulator 40 includes a simulator body 42 which forms a cylinder for a simulator piston 44 sliding inside said cylinder. The body 42 is arranged in the form of a screw-in cartridge provided, on one of its front faces, with a standardized thread 46 of brake pipe by which it is screwed, in the same way as

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  brake line, on the brake master cylinder 34 and is thus hydraulically connected to said brake master cylinder 34. A front face of the simulator body 42 remote from the brake master cylinder 34 is closed by a cap screw 48 provided with a standardized thread 50 for brake line corresponding to that of the brake master cylinder 34. By this thread 50, a brake line leading to the relevant braking circuit I, II is connected to the brake master cylinder 34. The two braking circuits I, II are hydraulically connected to the brake master cylinder 34 via

  brake actuation simulators 40.

  The simulator piston 44 is produced in the form of a hollow cylinder in the bore 52 from which penetrates a section of tube 54 which forms a one-piece assembly with the screw cap 48. An O-ring 56 provides sealing between the piston simulator 44 and the tube section 54. The screw cap 48 is provided with a through hole 58 which passes through its tube section 54 and opens into the brake pipe thread 50. The braking circuits I, It communicate with the brake master cylinder 34 via the bore 52 in the simulator piston 44 and the through hole 58 in the screw cap 48 and, in emergency braking mode, the stop valve 32 being

  open, can be supplied with pressure by actuation of the master

  brake cylinder 34. A helical compression spring 60 mounted as an elastic element in the simulator body 42 is supported on the screw cap 48 and pushes the simulator piston 44 into a rest position at one end of the simulator 42, towards the master cylinder of

brake.

  When the brake master cylinder 34 is actuated, an annular front surface 62 of the simulator piston 44 facing the master cylinder is biased by brake fluid coming from the brake master cylinder 34; the simulator piston 44 is pushed against the force of the compression coil spring 60 so that, even when the stop valve 32 is closed, brake fluid can be pumped out of the brake master cylinder 34. The piston rod 38 can be inserted into the master cylinder of

  brake 34 using the brake pedal not shown, a master pressure

  brake cylinder which is a function of the force of the compression helical spring 60 being thus generated, which pressure is transformed into a

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  electrical signal by the brake master cylinder pressure sensor 36 which is transmitted to the electronic control unit 28 which closes the stop valve 32 for service braking and controls, as described above, a brake pressure wheel in the wheel brake cylinder 24. For emergency braking, the stop valve 32 remains open and the brake cylinder

  wheel 24 receives the pressure generated by the brake master cylinder 34.

  In order to obtain a progressive spring characteristic, the helical compression spring 60 is wound tighter in its middle part 64 than in the region of its ends. The fact of providing closer turns in the central region 64 of the spring 60 has the advantage of reducing the risk of buckling in the presence of stress. The brake master cylinder pressure and the pedal force therefore increase proportionally greater than the stroke. The stroke of the simulator piston 44 is limited by the screw cap 48 which thus forms a stop for said simulator piston 44. The volume of brake fluid that can be admitted by the brake actuation simulator 40 is therefore limited. The volume of brake fluid which can be admitted by the brake actuation simulator 40 is adapted to a delivery volume of the brake master cylinder 34 so as to obtain a sufficient brake pressure for braking at full intensity in mode. emergency braking, during which brake fluid is discharged from the

  brake master cylinder 34 in the brake system 10.

  To ensure that the front face 62 of the piston is supplied with brake fluid when the simulator piston 44 is in its rest position, at the front end of the simulator body 42, the front face of the piston

  simulator 44 is provided with radial grooves 66.

  To obtain a progressive elastic characteristic, the elastic element 60 can also be formed from several helical compression springs which, mechanically, are arranged one behind the other or in parallel (not shown). For parallel mounting, for example two or more helical compression springs having different lengths can be placed one inside the other. Due to the difference in length, only the longest spring is first compressed

  until the length of the spring coming immediately after is reached.

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  The two coil springs are then deformed simultaneously, resulting in

  results in an increase in the stiffness of an elastic element thus formed.

  The two brake actuation simulators 40 of the vehicle braking system 10 according to the invention are identical, with the exception of their elastic elements 60, 68, and operate in the same way. The elastic element 68 of the brake actuation simulator 40 shown on the left in the drawing is also produced in the form of a helical compression spring with more closely spaced turns in its middle part, this in order to obtain a progressive characteristic. . This spring 68 may have a stiffness different from that of the spring 60 of the brake actuation simulator 40 shown on the right of the drawing. The spring 68 of the left brake actuation simulator 40 is longer so that it pushes the simulator piston 44 back into its rest position. As a result, this simulator piston 44 leaves its rest position shown only when the other simulator piston 44 has traveled a certain stroke and a brake fluid pressure has been established. The elastic element 68 of the brake actuation simulator 40 shown on the left therefore only comes into action when the brake fluid pressure produced with the brake master cylinder 34 generates a pressure which corresponds to the preload of the spring. helical compression 68. This gives a discontinuity in the relationship between the pedal force proportional to the brake master cylinder pressure and the stroke of the brake pedal not shown; the pedal force increases more rapidly with the pedal force from the moment the second piston of

  simulator 44 left its rest position.

  Another increase in the pedal force is obtained which is proportional to the pedal stroke as soon as the simulator piston 44 of the brake actuation simulator 40 shown on the right comes into abutment against the screw cap 48 and can no longer be move. From this moment, only the stiffer compression coil spring 68 of the

  brake actuation simulator 40 on the left is active.

  The relationship between the pedal force F and the pedal stroke s is shown schematically in Figure 2. Between the origin and the point Y of the curve only is active - the helical compression spring 60 of the

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  brake actuation simulator 40 shown on the right of FIG. 1 which acts with its progressive characteristic, which spring is not or is only slightly prestressed. From point Y, the piston 44 of the brake actuation simulator 40 shown on the left in FIG. 1 also begins to move from its rest position; the curve has a discontinuity ("inflection" in Y) and a steeper slope. Between the points Y and Z, the two helical compression springs 60, 68 are active with their progressive characteristics. At point Z, the piston 44 of the brake actuation simulator 40 shown on the right of FIG. 1 which is not or is only slightly prestressed comes into abutment on the screw cap 48 so that beyond from point Z only the steepest spring 68 continues to act. There follows a new discontinuity at point Z and a further increase in

  the slope of the characteristic curve of the pedal force.

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Claims (10)

  1. Hydraulic vehicle brake system comprising an external energy service braking system and a muscular energy or auxiliary energy emergency braking system, a brake master cylinder which can be isolated from wheel brake cylinders with using a stop valve as well as a brake actuation simulator which is connected to the brake master cylinder and has a simulator piston urged by brake fluid from the brake master cylinder and a elastic simulator element which biases the simulator piston against a brake fluid pressure, characterized in that the elastic simulator element (60, 68) has a progressive characteristic.   2. Vehicle braking installation according to claim 1, characterized in that the braking installation (10) of the vehicle is produced in the form of a dual circuit braking installation with a tandem master cylinder (34) and by the fact that it has a brake actuation simulator (40)   for each braking circuit I, II.   3. Vehicle braking installation according to claim 2, characterized in that the brake actuation simulator (40) comprises a stop for   stroke limitation for its simulator piston (44).   4. Vehicle braking installation according to claim 2 or 3, characterized in that the elastic elements (60, 68) of the simulator of the two brake actuation simulators (40) have different stiffnesses.   5. Vehicle braking installation according to one of claims 2 to 4,   characterized in that the elastic element (68) of the simulator of the two brake actuation simulators (40) pushes back the piston   simulator (44) in a rest position.   6. Vehicle braking installation according to one of claims 1 to 5,   characterized in that the brake actuation simulator (40) is in the form of a screw-in cartridge which is screwed into a thread -12- 2753949   from the brake master cylinder (34) and has a thread (50) to which is connected a brake line leading from the brake master cylinder (34)   to the wheel brake cylinders (24).   7. Vehicle braking installation according to one of claims   above, characterized in that the elastic element (68) of the simulator comprises a helical compression spring (60, 68) with distances between variable turns.   8. Vehicle braking installation according to claim 7, characterized in that the distances between turns are shorter in a central region of the   compression helical spring (60, 68).   9. Vehicle braking installation according to one of claims   above, characterized in that the elastic element (60, 68) of   simulator has several helical compression springs.   10. Vehicle braking installation according to one of claims   previous, characterized in that the simulator piston (44) is shaped like a hollow cylinder.