DE3629564A1 - Brake system with slip control - Google Patents

Abstract

In a brake system with slip control comprising a pedal-operated, power-assisted brake pressure sensor (1), to which the wheel brakes (31 to 34) are connected by pressure medium lines, a hydraulic servo pressure supply system with a hydraulic pump (26), with a pressure medium reservoir (20) and with a servo pressure control valve (25), and wheel sensors (51 to 54) and electronic control circuits (28) for detection of the wheels' rotational behaviour and for generating electrical brake pressure control signals, by means of which solenoid-operatable pressure medium inlet valves (29, 30 and 43, 44) and outlet valves (35, 36), inserted into the pressure medium lines, can be controlled for controlling the slip, a switch (58) is inserted into the pressure line (55) of the auxiliary power source which, once a predetermined hydraulic pressure is attained, sends an electrical signal to the signal processing and logic circuit (28), which for a test cycle causes the motor (M) of the pump (26) to be switched on or off, and which then indicates to the driver of the vehicle, by way of a visual or audible signal, that the motor-pump unit is functional. <IMAGE>

Description

The invention relates to a brake system with slip control, consisting essentially of a pedal-operated, preferred as auxiliary power-assisted brake pressure sensor to the Pressure fluid lines connected to the wheel brakes a hydraulic auxiliary pressure supply system with one Hydraulic pump, with a pressure compensation and pressure medium storage tank and with an auxiliary pressure supply system, as well as from wheel sensors and electronic switching circles to determine the wheel turning behavior and to generate supply of electrical brake pressure control signals with which inserted into the pressure medium lines for slip control Electromagnetically actuated pressure fluid inlet valves and exhaust valves are controllable.

In known brake systems of this type (DE-OS 30 40 561, DE-OS 30 40 562) a brake master cylinder with upstream hydraulic brake booster used.  The auxiliary pressure supply system contains a hydraulic pump and a hydraulic accumulator from which with brake application With the help of a control valve, an aid proportional to the foot force pressure is initiated. This dynamic pressure becomes one on the master cylinder to the on the master cylinder closed static brake circuits. On the other hand are attached to the pressure chamber in which the foot force is proportional Pressure is introduced via the control valve, the wheel brakes an axle, preferably connected directly to the rear axle sen. For slip control are also both in the stati circuits as well as in the dynamic circuit intake valves inserted, which are normally switched to pass and with which the pressure is impending when a wheel is imminent medium flow to the wheel brake in question are blocked can. There are also exhaust valves through which if necessary, pressure medium from the wheel brake to the Pressure expansion tank can be derived. When on the slip control is set via a so-called head valve the amplifier room, in which the from the auxiliary pressure Ver regulated pressure prevails, with connected to the static brake circuits of the master cylinder the amount of pressure medium withdrawn via the outlet valves again to be able to feed into the static circles. The one to produce generation, storage and control of the hydraulic auxiliary pressure, for dynamic flow into the static circles and for Ensuring the brake functions in the event of individual failure Circles required design effort is considerable.

The control signals for the intake and exhaust valves are in brake systems of this type with the help of electronic Circuits generated, the inputs of which with wheel sensors, e.g. inductive transducers, and are connected  to a change in the wheel turning behavior, the risk of locking indicates by keeping constant, dismantling and restarting again build the pressure on the corresponding wheel can react.

A disadvantage of known brake systems with slip control be is now that a suitably equipped vehicle Experience has shown that it takes a long time, especially during the warm season, can be used without the Driver of the vehicle can be seen that the engine for the Pump of the auxiliary pressure source or the pump itself between have become defective in time, so that in the event of one after unexpectedly difficult braking maneuvers with blocking wheels then the slip control (e.g. on the first snowfall of the year) failed unexpectedly.

The invention has for its object the brake system train that periodically a functional check of the Auxiliary pressure source takes place. The braking system should be simple to be constructed and inexpensive to manufacture.

According to the invention, this is done by a in the pressure line Auxiliary source switched switch reached after Reaching a predetermined hydraulic pressure switches and thus an electrical signal to the signal processor processing and logic circuit there, which in the case of Test cycle the power supply to the drive motor of the pump like which interrupts after a timer or the Start the vehicle engine, switch on the electric motor had caused.

Preferably, the pressure line of the auxiliary source is connected on the one hand to a pressure control valve and on the other hand to a pressure limiting valve, the pressure control valve being connected to the pressure chambers of the master cylinder via signal lines and wherein an electrical switch is switched on in the pressure line, which switch is reached when a fixed pressure is reached a signal to the signal processing and logic circuit, which causes the motor ( M ) of the pump ( 26 ) of the auxiliary pressure source to be switched on and off for a test cycle.

Other features, advantages and possible uses of the Invention go from the dependent claims and from the following Description of an embodiment using the Figure out, in simplified form, part wise in section, partly the most important in purely schematic form Components of a slip-controlled brake system according to an off type of management of the invention shows.

In the illustrated embodiment, he has the inventive brake system as a brake pressure sensor 1, we sentlichen consisting of a tandem master cylinder 2 and an upstream vacuum booster 3 existing hydraulic unit. Via a push rod 4 , the pedal force F exerted on a brake pedal 5 is transmitted to the vacuum booster 3 and assisted by this on the working pistons 6 and 7 of the tandem master cylinder 2 in a known manner.

In the illustrated release position of the brake, the pressure chambers are 8, 9 of the master cylinder 2 through an open central valves 10, 11, via connecting channels 12, 13 in the interior of the piston 6, 7 and finally through annular chambers 14,15, holes through terminal 16, 17 and connected via hydraulic lines 18 , 19 to a pressure compensation and pressure medium reservoir 20 .

At the two pressure chambers 8 , 9 of the tandem master cylinder 2 , the control inputs 21 , 22 and via this the control chambers 23 , 24 of a pressure control valve 25 are connected. About pistons 49 , 50 inside the pressure control valve 25 , the control pressure is transferred to a ball seat valve 51 which is hydraulically connected to the pressure side of a hydraulic pump 26 and the valve 53 and on the other hand to the Bremsdrucklei device 52 . The suction side of the pump 26 is also connected to the container 20 . It is an electric motor (motor M ) driven hydraulic pump. The electrical connections "m" and "ground" are also symbolically indicated if.

The pressure relief valve 53 is provided with a ball seat valve 54 via which the pump pressure line 55 can be connected to the pressure medium reservoir 20 , the valve body of the ball seat valve 54 being acted upon by the pressure of the brake pressure line 52 or a spring 56 with piston 57 .

The two brake circuits I, II of the master cylinder 2 are operated via electromagnetically actuated valves which are switched to passage in the basic position, namely so-called isolating or intake valves 29 , 30 , each with two wheel brakes 31 , 32 ; 33 , 34 connected. The wheel brakes 31 , 32 and 33 , 34 connected in parallel can, for example, as shown here, each be assigned to the wheels of an axle (rear wheels HR, HL, front wheels VR, VL) or the diagonals.

The wheel brakes are connected to electromagnetically actuated, in the basic position blocked outlet valves 35 , 36 , which are connected to the pressure compensating tank 20 via a hydraulic return line 37 .

The brake circuits I, II are also each connected via a flow valve 43 , 44 and a check valve 38 , 39 and via a brake pressure line 52 to the auxiliary pressure supply system or to the hydraulic pump 26 and to the auxiliary pressure control valve 25 . The check valves 38 , 39 open as soon as the auxiliary pressure rises by a certain minimum value above the pressure currently prevailing in the brake circuits I, II and as soon as the inflow valves 43 , 44 are switched to passage.

The vehicle wheels are equipped with inductive sensors S ₁ to S ₄ , which interact with a toothed disc that synchronizes with the wheel rotation and generate electrical signals that indicate the wheel turning behavior, ie the wheel speeds and changes. These signals are fed via inputs s ₁ to s _{4 to} an electronic signal processing and logic circuit 28 which generates brake pressure control signals with which the inflow, isolating and exhaust valves 29 , 30 , 35 , 36 , 43 are detected when a tendency to block is detected , 44 temporarily switched, thereby keeping the brake pressure constant, reducing it and increasing it again at the appropriate time. For this purpose, the actuating magnets of the intake and exhaust valves are controlled via the outputs A ₁ to A ₄ ; the electrical connecting lines between the connections A ₁ to A ₄ and the windings of the valves 29 , 30 , 35 , 36 , 43 , 44 are not shown for the sake of clarity.

The circuit 28 can be realized in a known manner by wired circuits or by programmable electronic components, such as microcomputers or microcontrollers.

The switch-on signal for starting up the drive motor M of the hydraulic pump 26 , which only runs during a slip control, is applied to the motor M via the connection m .

An electrical switch 58 is connected to the pump pressure line 55 and , when a predetermined pressure is reached, for example 30/35 bar, gives a corresponding signal to the signal processing and logic circuit 28 .

The brake system works as follows:

When the brake is actuated, the pedal force F , supported by the negative pressure in the booster 3 , is transmitted to the master cylinder pistons 6 , 7 . The central valves 10 , 11 close, so that now in the pressure chambers 8 , 9 and thus in the brakes I, II brake pressure can arise, which reaches the wheel brakes 31 , 32 and 33 , 34 via the valves 29 , 30 .

The pressures in the chambers 8 and 9 are passed to the Steuerein gears 21 , 22 of the control valve 25 and act there via the pistons 49 , 50 and the plunger 59 on the ball seat valve 51 . However, this remains without effect as long as the hydraulic pump 26 is not yet in operation.

Is now detected with the help of sensors S ₁ to S ₄ and the scarf device 28 a tendency to lock on one or more wheels, the slip control begins. The drive motor M of the pump 26 turns on, so that now in the auxiliary pressure supply system and on the supply or brake pressure line 52 a proportional to the pressure in the pressure chambers 8 , 9 and thus to the pedal force F can arise.

A signal from the circuit 28 leads to the switching of the electromagnetically actuated valves 29 , 30 and thus to block the brake circuits I, II. A further displacement of the master cylinder piston 6 , 7 in the direction of the pedal force F and an emptying of the pressure chambers 8 , 9 is prevented . As soon as a sufficient pressure is reached, the auxiliary pressure supply system takes over the function of the brake pressure transmitter 1 via the supply line 52 and the check valves 38 , 39 that are now opening. Pressure medium flows dynamically into the brake circuits I, II via the check valves 38 , 39 and the inflow valves 43 , 44 . The actual brake pressure curve in the wheel brakes 31 to 34 is determined by the inlet and exhaust valves 29 , 30 , 35 , 36 , which are fed via lines A ₁ to A ₄ slip-regulating brake pressure control signals.

From the comparison of the pressures in the pressure chambers 8 , 9 of the master cylinder 2 and the signal lines 60 , 61 leading to the control valve 25 with the instantaneous auxiliary pressure provided by the pump 26 and the control valve 53 , taking into account the operating state, ie normal braking or If the slip control is activated, defects of various types can be reliably identified with the aid of a device (not shown in more detail). With uncontrolled braking, pressure must be created in the pressure chambers 8 , 9 , but not in the auxiliary pressure supply system. In the event of a failure or a fault in the pump 26 , the valves 25 , 53 , in the event of a fault in the switch-on travel of the motor M or the like, an overpressure in the pressure chambers 8 , 9 relative to the supply line 52 is maintained even after the slip control has been inserted. By logically linking these and other states with the aid of circuit 28 , errors can thus be identified and signaled. Depending on the type of error, the circuit 28 will then automatically switch off the slip control completely or partially, ie limited to some wheel brakes, so that effective braking is still possible via the intact brake circuit.

As can be seen from the drawing, the inlet and separation valves 29 , 30 are still secured by parallel check valves 41 , 42 . These check valves 41 , 42 enable the brake pressure control to be terminated or the wheel brakes to be released in special cases since, with the separating valves 29 , 30 still closed, a small amount of pressure medium can flow back from the wheel brakes into the pressure chambers 8 , 9 .

A particular advantage of the brake system shown is that the inflow valves 43 , 44 can be designed dimmed, that is to say that their flow cross-sections can be dimensioned such that the pressure medium conveyed by the pump 26 cannot flow into the wheel brakes too suddenly in the case of brake pressure control. In contrast, the inlet or separating valves 29 , 30 are more generously dimensioned with regard to their passage cross sections, as a result of which a "spongy" pedal feeling can be avoided.

Furthermore, there is a great advantage of the brake system described that, in the case of brake pressure control, the noise generated by the brake system is reduced to a minimum in that a low pressure gradient can be maintained. If, for example, a pressure of 100 bar is reached at the outlet of the pump 26 and the inflow valves 43 , 44 are then opened suddenly, then the pressure at the pump outlet or in the supply line drops comparatively slowly, since the flow cross sections in this branch the braking system can be designed to be relatively small.

To check the power supply, voltage is applied to the test circuit 62 so that the pump 26 starts. Now a pressure at the level of the limiter pressure is built up in the dynamic circuit (eg 40 bar). This pressure is present up to regulator 25 . With the pressure switch 58 the presence of the pressure is determined. The test cycle only lasts a few hundred milliseconds. At the same time, the electric motor can still be checked electrically.

If the brake pedal 5 is actuated and a wheel comes into slip, the pump 26 is switched on. The pump 26 provides a basic pressure. Controlled by the tandem master cylinder, the controller 25 ensures a regulated pressure. This pressure can be changed from zero to max. If the pressure in the tandem master cylinder 2 is greater than 40 bar, for example, the control line from the regulated pressure to the limiter ensures that the limiter pressure is continuously raised. The pressure limiter is normally about 40 bar above the regulated pressure. Behind the regulator, the dynamic pressure branches into the circles to the wheel cylinders via two check valves and SO valves. Here the wheel cylinder pressure is built up and dismantled. If the brake pedal is released, the regulator pressure is reduced. Excess volume is reduced from the wheel cylinders via the check valves into the tandem master cylinder. When the brake control has ended, the pump 26 is stopped.

The test cycle can e.g. every time the vehicle is started motors. Then, for example, at every tenth brake application.  

• List of items 1 brake pressure transmitter
  2 tandem master cylinders
  3 vacuum boosters
  4 push rod
  5 brake pedal
  6 and 7 working pistons
  8 and 9 pressure chamber
  10 and 11 central valve
  12 and 13 connection channel
  14 and 15 ring chamber
  16 and 17 connection hole
  18 and 19 hydraulic line
  20 pressure compensation and pressure medium storage tanks
  21 control input
  22 control input
  23 control chamber
  24 control chamber
  25 Pressure control valve, pressure switching valve
  26 hydraulic pump
  27 hydraulic line
  28 Signal processing and logic circuit
  29 and 30 inlet valve, isolation valve
  31 to 34 wheel brake
  35 and 36 exhaust valve
  37 return line
  38 and 39 check valve
  41 and 42 check valve
  43 and 44 inlet valve
  45 room
  46 room
  47 and 48 valve compartment
  49 and 50 pistons
  51 Ball seat valve
  52 Brake pressure line, supply line
  53 pressure relief valve
  54 ball seat valve
  55 Pump pressure line, delivery rate
  57 pistons
  58 electrical switches
  59 plungers
  60 and 61 signal line
  62 test circuit
  63 valve passage
  64 chamber
  65 test lamp

Claims (6)

1.Brake system with slip control, consisting essentially of a pedal-operated, preferably auxiliary power-assisted brake pressure sensor, to which the wheel brakes are connected via pressure medium lines, from a hydraulic auxiliary pressure supply system with a hydraulic pump, with a pressure compensation and pressure medium reservoir and with one Auxiliary pressure control valve, as well as from wheel sensors and electronic circuits for determining the wheel turning behavior and for generating electrical brake pressure control signals with which, for slip control, electromagnetically actuated pressure medium inlet valves and outlet valves inserted into the pressure medium lines can be controlled, characterized by one in the Pressure line ( 55 ) of the auxiliary power source, a switched switch ( 58 ) which switches after reaching a predetermined hydraulic pressure and thus gives an electrical signal to the signal processing and logic circuit ( 28 ), which is for a The test cycle switches the motor ( M ) of the pump ( 26 ) on and off and can thus signal the operational readiness of the motor-pump unit ( 26 , M ) to the vehicle driver via an optical or acoustic display. 2.Brake system with slip control, consisting essentially of a pedal-operated, preferably auxiliary power-assisted brake pressure sensor, to which the wheel brakes are connected via pressure medium lines, from a hydraulic auxiliary pressure supply system with a hydraulic pump, with a pressure compensation and pressure medium reservoir and with one Auxiliary pressure control valve, as well as from wheel sensors and electronic circuits for determining the wheel turning behavior and for generating electrical brake pressure control signals with which, for slip control, electromagnetically actuated pressure medium inlet valves and outlet valves inserted in the pressure medium lines can be controlled, characterized in that the pressure line ( 55 ) of the auxiliary pressure source is connected on the one hand to a pressure control valve ( 25 ) and on the other hand to a pressure limiting valve ( 53 ), the pressure control valve ( 25 ) via signal lines ( 60 , 61 ) to the pressure chambers ( 8 , 9 ) of the Master cylinder ( 2 ) are connected and in the pressure line ( 55 ) an elec trical switch ( 58 ) is switched on, which gives a signal to the signal processing and logic circuit ( 28 ) when a fixed pressure is reached, for a test cycle switching the motor ( M ) of the pump ( 26 ) of the auxiliary pressure source on or off. 3. Brake system according to claims 1 or 2, characterized in that the control valve ( 25 ) has two pistons ( 49 , 50 ) arranged one behind the other in a longitudinal bore of the housing, the space ( 24 ) between the two pistons ( 49 , 50 ) and the space ( 23 ) in front of the first piston ( 49 ) is connected via a signal line ( 60 , 61 ) to a respective pressure chamber ( 8 , 9 ) of the master cylinder ( 2 ), and the second piston ( 50 ) to the closing member Valve, for example a ball seat valve ( 51 ), and the space ( 45 ) in front of the closing element corresponds to the supply line ( 52 ) for the regulated pressure and the space ( 46 ) behind the closing element corresponds to the pump pressure line ( 55 ). 4. Brake system according to one of the preceding claims, characterized in that the pressure limiting valve ( 53 ) has two valve spaces ( 47 , 48 ), the space ( 47 ) before the valve passage ( 63 ) to the pump pressure line ( 55 ) and the space ( 48 ) behind the valve passage ( 63 ) is connected to the pressure medium reservoir ( 20 ) and wherein a piston ( 57 ) acts on the valve body controlling the pressure medium passage, which plunges into a chamber ( 64 ) which connects to the from the regulated pressure supply line ( 52 ) is connected. 5. Braking system according to one or more of the preceding claims, characterized in that the pump ( 26 ) of the auxiliary pressure source driving motor ( M ) is connected to an electrical test circuit ( 62 ) which allows a test lamp ( 65 ) to light up as long as the motor ( M ) is subjected to electrical current. 6. Brake system according to one or more of the preceding claims, characterized in that the motor ( M ) driving the pump ( 26 ) of the auxiliary pressure source is switched into the circuit of an electrical test circuit which gives an acoustic or optical signal when the switch ( 58 ) after the engine ( M ) has not registered the set switching pressure.