DE3912234A1 - HYDRAULIC BRAKE SYSTEM - Google Patents

Abstract

A hydraulic brake system comprising a master cylinder 1 having working pistons 5 and 6 and working chambers 7 and 8 is provided with solenoid valves 22 in pressure fluid lines 20, 21 between the working chambers 7, 8 and a supply reservoir 14 and a switch for sensing the rest position of a brake pedal energises the valves 22 to establish a short term pressure fluid connection to replenish the reservoir 14 and relieve system pressure when the brake pedal is at or near to its rest position. In this manner, the hydraulic connection of the reservoir 14 to the working chambers 7, 8 is constituted solely via electromagnetically controllable connections, thereby obviating the need for a breather bore or central valve. In a modification the valves 22 are omitted and the replenishment of the reservoir is effected through the inlet and outlet valves 12, 15 which latter are switched open. Expansion of the brake fluid can be detected by a temperature, pressure or noise sensor and causes opening of the valves 22 or 15. The system is particularly suitable for anti-skid and traction-slip control. <IMAGE>

Description

The invention relates to a hydraulic brake location according to the preamble of claim 1.

A hydraulic brake system usually consists of a master brake cylinder and wheel connected to it brake cylinder. The cylinders and brake lines are filled with brake fluid. When the head is not activated brake cylinder becomes a connector for the following reasons extension of the brake circuits to a reservoir.

Firstly, it must be ensured that the brake circuits are always completely filled with pressure medium, otherwise Air bubbles in the brake when the brake system is actuated circles arise due to their compressibility a direct transmission of the pedal force to the wheel brakes prevent. The second is thermal expansion of the brake note liquid. Would it be the brake circuit would be closed systems, the expansion would brake fluid to apply force to the Wheel brakes cause the vehicle to be undesirable Way is delayed.

So far, two paths have been taken to connect the brake circuits to the reservoir when not actuated to implement the brake. The simplest solution is in that the brake circuits over a so-called. Sniffer hole (Cross hole in the master cylinder housing) that with the  Storage container is connected and immediately in front the working piston of the master brake cylinder in the working Chamber of the master brake cylinder opens to fill. At the When the brake is actuated, the working pistons are moved, which is the sniffer hole assigned to them run over so that when the brake is applied a closed Brake circuit system is created. The driver releases his foot from the Pedal, so the working pistons by return springs pushed back into its basic position so that the verbin between the working chamber and the storage container is restored via the sniffer hole. As long as such a brake system does not control the brake is used, the brake is refilled circles with sniffing holes without any problems.

In the case of hydraulic anti-lock braking systems, Re adjustment of the wheel brake pressure from an external energy source Pressure medium filled in the brake circuits. This has to Consequence that a residual pressure in the brake circuits and thus in Master brake cylinder is present when the working piston the sniffer holes of the master brake cylinder. Due to the pressure in the brake circuits, the Dichtman gently press the working piston into the sniffer holes and destroyed by it. With hydraulic anti-lock protection braking systems has therefore gone over to the Sniffing holes through so-called. To replace central valves. These valves that are in the working pistons of the master cylinder are usually made up of a valve ball by a plunger attached to a housing Pin rests in the basic position of the working piston in the  Distance to the valve seat is kept. When pressing the Brake, i.e. when moving the working piston, can the valve balls sit on their valve seat, whereby the brake circuits are locked hydraulically. So easy this measure appears to be in practice significant problems. Add to that the central valves are much more expensive than the sniff hole construction tion, and assembly is difficult.

Both methods also lead to a considerable extension master cylinder, since the working pistons too at least once again show the length of the work area must.

Another disadvantage is that both sy steme have an empty path due to the design. Before pressure can be built up in the master brake cylinder, must first run over the sniffer holes or the Central valves are closed. This empty path expresses when braking, that in the first phase of Pedal actuation no braking effect is achieved.

Furthermore, when installing the master brake cylinder a precise adjustment of the working pistons is done so the empty paths don't get too big. Particularly complicated becomes the situation when the master cylinder of one Amplifier is operated. The booster piston must also be precisely adjusted so that the basic position of the Ar Beitskolben and booster piston exactly matched must be voted.  

The invention is therefore based on the object to create a refill system that goes beyond that leads to the construction of the master brake cylinder considerably can be simplified. In addition, the main one Build the brake cylinder as short as possible and easy to install be animals.

The task is solved by means of the features that are known in the drawing part of claim 1 are mentioned.

The idea that is pursued can also be how characterize follows. While in the known state of the Technology the hydraulic system is open as long as none The brake is applied and is only closed when the master cylinder is actuated sees the invention a system that ge even when the brake is not applied is closed. This eliminates the above mentioned parts. For example, the system no longer has an empty path. It only becomes an electromagnetically switchable pressure provided middle way, which only under well-defined kri terien is opened for a short time. E.g. can be provided who the one that opens the pressure medium path after each braking to reduce the pedal pressure in the system. The invent System according to the invention also has the advantage that the brake system, which is usually closed, is easier in the rear leakage is to be monitored.

The pressure medium path with the electromagnetic valve can then advantageously at a certain distance from  Basic position of the working piston in the master cylinder open the working room. This eliminates coordination problems with the pedal mechanism and possibly the master cylinder switched amplifier. Pedal mechanism and amplifier show also stops on the basic position of the pedal and define the booster piston. They have to go with them the basic position of the working piston must be coordinated with it when the pedal is not pressed, the sniffer hole in the Work area opens or the central valve is open. These problems are eliminated in the system according to the invention.

In principle, it is possible to use the front according to the invention impact even with conventional, i.e. when not hatching controlled brake systems. The additional However, costs for the electromagnetic valves come into play competition to the cost of a central valve or Sniffer hole.

The invention can therefore be particularly advantageous use slip-controlled braking systems, since these systems already have solenoid valves that are changed by means of a control for the refilling of pressure medium in the Brake circuits can be used.

A brake system is known from DE-OS 36 35 846, in which the working chamber of the master brake cylinder by means of Central valve are connected to the reservoir. In the connecting line between the working chamber of the Master brake cylinder and the reservoir is between Storage tank and central valve each an electromagnetic valve  til switched that is open when de-energized. To Regulation of the drive slip is by means of pressure medium a pump in the brake lines, so that unab depending on pedal actuation, a pressure in the wheel brake can be built. The reflux to the reservoir ter must be prevented. This will be there achieved by that during traction control the solenoid valves mentioned between the reservoir and the central valves are closed.

In application of the inventive idea and in continuation the brake system according to the laid-open specification use the solenoid valves mentioned as a refill valve. These are then advantageously closed, as soon as possible the solenoids are de-energized. The brake circuits are therefore normally locked hydraulically, so that at Brake actuation a pressure can be built up. The Ven Tiles are then briefly ge according to certain criteria opens so that in the brake circuits when not actuated no pressure can build up on the pedal.

With this type of brake system, the pressure medium can be away between the master cylinder and the reservoir represent ter as the housing bore in the master cylinder housing. The pump line for the delivery of pressure medium during a slip control opens into this housing bore.

It is also conceivable for the valve to be closed when de-energized the connection of the wheel brake to the reservoir as after fill valve to use. The valve effort is still reduced  ger. The pressure medium connection then exists over the Brake line and the relief line.

The signal to open the refill valve can now open generated in different ways. The basic requirement is in any case, that the pedal is in its basic position. This can easily be determined by a pedal switch that is coupled to the pedal. So that can be ensured that at least at the end of a Braking the refill valve is opened briefly.

The signals of a pressure sensor can be used as further criteria sors or a temperature meter. Builds up a pressure in the master brake cylinder when the pedal is not pressed the refill valve is opened briefly. Poss liche, it is already sufficient, at a tem temperature increase to open the valve. It is also possible, possible grinding noises of the pads on the brake disc or to record on the brake drum and whenever when on because of the grinding noises it can be concluded that the Brake is applied in an undesired manner, the after open the filling valve.

To compensate for pressure loss due to small leaks Chen, a warning switch can be provided with which Help when pedaling over a threshold hi pump delivery is triggered.

Another switch on the pedal is used to control the pressure medium pump delivery during a slip control  check. The pressure medium delivery is affected flows that the pedal during a regulation in a be agreed position is brought. By switching on and off the pump drive or by brief opening impulses for the valves in the refill line, the pressure amount of medium that is conveyed into the brake lines, be be influenced.

The idea of the invention will be explained in more detail with the aid of two exemplary embodiments, some of which are shown as sectional views or as hydraulic circuits in FIGS. 1 to 3.

The brake system consists of a master brake cylinder 1 , which is preceded by a vacuum booster 2 . In a bore 3 of the master cylinder housing 4 , two working pistons 5 and 6 are sealingly guided. The push rod piston 6 is dalkraft under the direct influence of the amplified Pe, while the floating piston 5 is exposed to the hydraulic pressure in the working chamber. 8 By means of the pistons 5 and 6 , two Ar beitskammern 7 and 8 are formed in the master cylinder housing 4, each device via a Bremslei device 9 , 10 to the wheel brakes 11 in connection. In the brake lines 9 , 10 and in the branch lines to the wheel brakes 11 , an inlet valve 12 is switched on. The inlet valve 12 is controlled electromagnetically, where it is switched to the open position when the solenoids are not energized. It is abbreviated to a "normally open" valve.

The wheel brakes 11 are still connected via a relief line 13 to the reservoir 14 . To the branch lines of the relief line 13 to the wheel brakes 11 , an outlet valve 15 is switched, which is controlled electromagnetically and which is switched in its locked position when the coils are not flowing through current. One also speaks of a "normally closed" valve.

The brake system also has two pumps 16 , 17 which are driven by a common electric motor M. The pumps deliver from the reservoir 14 into the working chambers 7 and 8 of the master brake cylinder. The pressure lines 18 , 19 of the pumps open after the game Ausführungsbei of Fig. 3 in the brake lines 9 and 10 , directly below the master cylinder.

According to FIG. 1, about absorbed. Follow-up lines 20 , 21 a direct connection of the working chambers 7 , 8 to the storage container 14 . In the follow-up lines 20 , 21 is a so-called. Refill valve 22 turned on. The refill valves 22 are controlled electromagnetically. As long as the solenoids are de-energized, the valves are in their locked position. The pressure lines of the pumps 16 , 17 open into the follow-up lines 20 , 21 , namely between the working chamber 7 or 8 and the refill valve 22 .

In Fig. 2, a possi ble execution of the hydraulic circuit shown in FIG. 1 is shown in a sectional view. The trailing lines 20 , 21 are shown as channels or housing bores in the master cylinder housing 4 , which extend from the working chambers 7 , 8 to the connecting pieces 23 , 24 for the reservoir 14 .

In the right part of Fig. 2, a side view of the braking device is shown. A receiving bore 25 for a solenoid valve 22 can be seen . The pressure port 26 for the pump is on the opposite side. The associated check valve is integrated in port 26 .

Important safety functions are represented by three switches A , B , C , which detect the pedal position. In Fig. 3, these switches are shown symbolically and who operated the directly from the pedal. The switch actuation can of course take place in an equivalent manner by another part of the system, as long as its movement is uniquely linked to the pedal position. Such parts are the push rod piston 6 or the movable wall of the booster.

The switch A has the task of determining whether the pedal is in its basic position. Switch B is required to regulate the delivery rate of the pump and thus to position the pedal. Leakage losses are to be recorded using switch C.

The operation of the brake system will be explained below. The driver operates the brake by depressing the (symbolically represented) pedal. As a result, the push rod piston 6 and, as a result, also the floating piston 5 are displaced. Pressure medium comes from the working spaces 7 and 8 to the wheel brakes 11 , whereby the brakes are applied and the vehicle is decelerated. The advantage over the systems known from the prior art is that the pressure is built up without loss of travel, since the brake circuits are hydraulically closed from the outset. In the prior art, loss paths occur because the sniffer hole is first run over or the central valve has to be closed.

If sensors that monitor the turning behavior of the wheels determine that one of the wheels is about to lock, the system switches to the anti-lock mode. This means that the pump drive M is switched on and the pumps are pumped into the working chambers. By switching the inlet and outlet valves, the pressure in the wheel brakes can be reduced or increased depending on the rotational behavior of the corresponding wheel, so that blocking of the wheel is prevented and at the same time an optimal slip value is set. This is a known method, so that no further explanations need to be given here.

The pump pressure is now regulated using switch B. The brake slip control continuously removes pressure medium from the working chambers of the master brake cylinder. This has the consequence that the push rod piston 6 is displaced more and more into the master cylinder, and the pedal follows this movement. The pedal falls through. When the pedal reaches a position which is characterized by switch B , the pump drive M is switched on. The delivery rate of the pumps is generally greater than the amount of pumps that are extracted from the working chambers by the control unit. Since the pistons 5 and 6 are reset, ie pushed out of the master cylinder. The pedal is reset, causing switch B to return to its home position. The pump drive is switched off. In this way it is caused that a pressure proportional to the foot force prevails in the brake circuits and the pedal is fixed to a certain position, which is given by the switch B before. The pump flow rate can be controlled not only by switching the pump drive on and off, but also by hydraulically short-circuiting the pump. This is done with the help of the refill valves 22 , which bring about a brief feedback of the pump pressure side with the suction side.

The brake system is also easy to traction success. With traction control who which the driven wheels with a brake pressure strikes so that an excessive driving torque re so far that the remaining moment is induced by the friction forces between the tire and the road surface can. The wheels should spin when starting be prevented this way. For traction control pressure fluid must be introduced into the wheel brakes. The This pressure medium is supplied by the pump and into the  Brake circuits promoted. In the state of the art not actuated pedal a pressure medium connection of the Ar working rooms to the storage container. This must first ge be closed. Since according to the proposed invention Work rooms are hydraulically locked from the outset, this step is omitted, so that an immediate Druckbe wheel brakes driven wheels can.

Since there is no permanent connection between the reservoir and the working spaces of the master cylinder in the proposal according to the invention when the brake is not actuated, some additional switches are to be provided. The most important switch is switch A , which responds as soon as the pedal is pressed.

As soon as braking is ended and the switch A is reset, a short-term connection between the working spaces of the master brake cylinder and the reservoir 14 is established. In this way, the residual pressure that may be present in the wheel brakes can be built down. This happens either in that the Ven tile 22 according to FIG. 1 is briefly activated or else the normally closed valves 15 according to FIG. 3. In the first case there is a connection via the follow-up lines 20 , 21 , in the second case via the brake lines 9 , 10 and the relief line 13 .

Thermal expansions of the brake fluid when the brake is not actuated can either be determined using a pressure switch, which is not shown, or else using a temperature sensor (also not shown). It would also be conceivable to record grinding noises of the brake linings that are applied due to the thermal expansion of the brake fluid. As soon as one of the sensors responds, the valves 22 or 15 are briefly actuated. In this way it is ensured that the system according to the Invention remains depressurized as long as the pedal is not operated and no traction control is provided.

The constant pressure medium connection of the brake system in the prior art when the brake is not actuated also has the purpose of compensating for pressure medium losses due to small leaks. In order to be able to implement this in the system according to the invention, the switch C is provided. The pedal travel will gradually increase in the event of a loss of pressure medium, so that the switch C responds to a specific loss of pressure medium. If this is the case, the pumps are switched on and pressure medium is pumped into the working chambers.

The main idea of the invention can be formu as follows be lated. The abandonment of the sniffer holes or the central valve can the working pistons of the main Brake cylinders are built much shorter, so that the Master cylinder becomes shorter overall, at the same time one achieves a shortening of the pedal travel, since the loss paths to drive over the sniffer holes or to Closing the central valves can be avoided. The task ben the sniffer hole and the central valve  can be taken over by a pedal travel monitoring, being an electromagnetic valve under certain conditions is switched in any connection line between the master brake cylinder and the reservoir is arranged.  

Reference symbol list:

1 master brake cylinder
2 vacuum brake boosters
3 longitudinal bore
4 master cylinder housings
5 floating pistons
6 push rod pistons
7 working chamber
8 working chamber
9 brake line
10 brake line
11 wheel brakes
12 normally open valves
13 discharge line
14 storage containers
15 normally closed valves
16 pressure pump
17 pressure medium pump
18 pressure line
19 pressure line
20 refill line
21 refill line
22 refill valve
23 tank connection
24 tank connection
25 valve mounting hole
26 Pressure connection with check valve

Claims (14)

1. Hydraulic brake system, in particular for brake and / or traction control, with a pedal-operated master brake cylinder ( 1 ) and attached wheel brake cylinders ( 11 ), and a pressure medium reservoir ( 14 ), with the piston ( 5 , 6 ) in the basic position the master brake cylinder ( 1 ) there is a pressure medium path between the working chambers ( 7 , 8 ) of the master brake cylinder ( 1 ) and the pressure medium reservoir ( 14 ), which has at least one electromagnetically actuated valve ( 22 , 12 , 15 ), characterized in that a sensor ( A ) is provided for pedal actuation and that when the pedal is not actuated, the electromagnetically actuated valve ( 22 , 12 , 15 ) is switched at least temporarily into a position that opens the pressure medium path. 2. Brake system according to claim 1, characterized in that the pressure medium path ( 20 , 21 , 9 , 13 ) opens at a distance from the basic position of the working piston ( 5 , 6 ) of the master brake cylinder ( 1 ) into the working chamber ( 7 , 8 ) , so that regardless of the position of the working piston ( 5 , 6 ) the mouth is always open. 3. Brake system according to claim 1, characterized in that the electromagnetic valve ( 22 , 12 , 15 ) is a 2/2-way valve. 4. Brake system according to claim 1, characterized in that a pressure sensor detects the pressure in the master cylinder ( 1 ), and that the solenoid valve ( 22 , 12 , 15 ) is open when the pedal is not actuated and the pressure sensor responds. 5. Brake system according to claim 1, characterized records that a temperature measurement of the Brake fluid takes place. 6. Brake system according to claim 1, characterized records that a noise sensor grinding noises of the brake pads on the brake disc detected. 7. Brake system according to claim 1, characterized in that from the working chamber ( 7 , 8 ) of the master brake cylinder ( 1 ) a brake line ( 9 , 10 ) to the wheel brake cylinders and a refill line ( 20 , 21 ) to the pressure medium reservoir ( 14 ) branches, the electromagnetic valve (refill valve 22 ) being inserted into the refill line ( 20 , 21 ). 8. Brake system according to claim 7, characterized in that the refill valve ( 22 ) is closed during regulation of the drive slip. 9. Brake system according to claim 7, characterized in that the refill line ( 22 ) through a housing bore in the master cylinder housing is Darge. 10. Brake system according to claim 9, characterized in that the pump pressure line ( 18 , 19 ) opens via a check valve in the housing bore. 11. Brake system according to claim 10, characterized in that the master cylinder housing has receiving bores ( 25 ) for the refill valve ( 22 ). 12. Brake system according to claim 1, with a normally open solenoid valve ( 12 ) in the brake line ( 9 ) between the master cylinder ( 1 ) and the Radbrem sen ( 11 ) and a normally closed valve ( 15 ) in the relief line ( 13 ) between the Wheel brake ( 11 ) and the reservoir ( 14 ), characterized in that the normally closed valve ( 15 ) is addressed by the evaluation electronics as a refill valve. 13. Brake system according to claim 1, characterized in that the pedal movement can be determined beyond a setpoint (switch B) and when the pedal is moved beyond a setpoint, brake pressure medium is conveyed into the brake lines ( 9 , 10 ). 14. Brake system according to one of the preceding claims, characterized in that the after filling container ( 14 ) is arranged spatially separate from the master brake cylinder.