Hydraulic brake system for motor vehicles

PRIOR ART

The invention is based on a brake system for motor vehicles.

One such brake system has been proposed in German Patent Disclosure 196 19 985 A1, published on May 28, 1997, after the priority filing date of the present application; in this reference, the self-aspirating charge pump, for instance in the event of traction control, supplies the high-pressure pump with brake fluid from the brake fluid supply container of a master cylinder, so that the brake fluid can generate brake pressure for pumping to the wheel brake in accelerated fashion.

A hydraulic brake system of this generic type is also known from European Patent Disclosure EP 0 482 367 A1; it has a charge pump with which, in traction control, brake fluid from a supply container of a master cylinder can be pumped both to the intake side of a high-pressure pump and directly into a brake line to which wheel brakes are connected. In such a brake system, it must be assured that no air will enter the system along the way via the charge pump. This could happen from an inadequate filling of the brake fluid supply container, or if the intake line is severed, not mounted, or comes loose.

In a self-aspirating hydropump with a defective intake line, it is therefore known from German Patent Disclosure DE 40 11 668 Al for a short-circuit connection between the suction chamber and the pressure chamber of the pump to be broken. In this defective state, the pump is incapable of building up pressure, so that no air can be fed into the system.

ADVANTAGES OF THE INVENTION

The brake system according to the invention has the advantage over the prior art that in the event of a defect, pumping of air through the charge pump into the system is avoided even if the intake line is properly connected to the charge pump. That is, as soon as the liquid level in the intake line reaches the siphon, su(h a large quantity of air is aspirated by the charge pump that this abruptly ceases any further pumping.

By the provisions recited herein advantageous refinements of and improvements to the brake system.

Thus the advantageous characteristic defined can be attained in a simple way by suitably laying the intake line, or by means of a hose shaped according to the invention or a bentor curved tube.

The advantageous feature of the invention disclosed moreover provides freedom from the aforementioned mounting requirements for the intake line, because the siphon is embodied entirely directly on the pump, in the housing thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Two exemplary embodiments of the invention are shown in simplified form in the drawing and described in further detail in the ensuing description.

FIG. 1

shows a circuit diagram of the brake system with a siphon in the intake line of a charge pump, as the first exemplary embodiment;

FIG. 2

is a longitudinal section through a charge pump with a siphon embodied in its housing, as the second exemplary embodiment; and

FIG. 3

is a section through the housing of the charge pump, taken along the line III—III of FIG.

2

.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A hydraulic brake system

10

for motor vehicles, schematically shown in

FIG. 1

, has a dual-circuit, pedal-actuatable master cylinder

11

with a supply container

12

for brake fluid. A first brake circuit I assigned to the wheel brakes

13

,

14

of a front axle of the vehicle is connected to the master cylinder

11

; a second brake circuit II of the master cylinder

11

communicates with wheel brakes

15

,

16

of the rear axle of the vehicle. Elements of the brake system

10

, which in accordance with the circuit diagram shown in

FIG. 1

are disposed between the master cylinder

11

and the wheel brakes

13

-

16

in the brake circuits I and II, are combined in a hydraulic unit

17

.

As will be described below in terms of brake circuit I, these elements include a shutoff valve

18

with a pressure limiting function; a charge valve

19

; a high-pressure pump

20

; and pressure buildup valves

21

,

22

and pressure reduction valves

23

,

24

of pressure modulating devices

25

and

26

that are assigned to the wheel brakes

13

and

14

. While the shutoff valve

18

and the pressure buildup valves

21

and

22

are located in brake lines

27

and

28

that lead from the master cylinder

11

to the wheel brakes

13

and

14

, the pressure reduction valves

23

and

24

are disposed in line branches

29

and

30

of a return line

31

, in which the high-pressure pump

20

is provided. The line branches

29

and

30

lead away from the brake lines

27

and

28

between the pressure buildup valves

21

and

22

and the wheel brakes

13

and

14

; conversely, on the outlet side of the high-pressure pump

20

, the return line

31

is connected to the brake line

27

between the shutoff valve

18

and the two pressure buildup valves

21

and

22

. The charge valve

19

is located in a charge line

32

, which leads away from the brake line

27

between the master cylinder

11

and the shutoff valve

18

and discharges into the return line

31

on the intake side of the high-pressure pump

20

. The brake circuit II is equipped correspondingly.

The brake system

10

also includes a charge unit

35

, which comprises a charge pump

36

, a check valve

37

, and a pressure sensor

38

. The charge pump

36

is connected by an intake line

39

to the brake fluid supply container

12

of the master cylinder

11

. The intake line

39

is embodied as a hose or tube that is resistant to brake fluid. A siphon

40

is located in the intake line

39

on the inlet side of the charge pump

36

. As shown in the first example in

FIG. 1

, this siphon is embodied outside the charge unit

35

in the intake line

39

. A pressure line

41

extends from the charge pump

36

and is connected to the brake line

27

between the master cylinder

11

and the shutoff valve

18

of brake circuit I. The check valve

37

is located in the pressure line. If the brake system

10

is to be equipped for automatic brakes for the sake of stabilizing the vehicle during cornering, then further sensors, such as steering wheel angle sensors, yaw speed sensors and transverse acceleration sensors, are a part of the equipment of the brake system

10

as well.

The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.

The mode of operation of such a brake system

10

is described in German Patent Application 196 19 985 A1 mentioned at the outset.

Both the high-pressure pumps

20

assigned to the two brake circuits I and II, and the charge pump

36

can be driven by an electric motor. The high-pressure pumps

20

are reciprocating piston pumps; conversely, the charge pump

36

is a self-aspirating recirculating positive displacement pump, for instance a toothed ring pump known by the tradename “GEROTOR”. While the charge pump

36

is capable of generating only relatively slight pressures, the high-pressure pumps

20

are designed to furnish pressures up to approximately 200 bar. The purpose of the charge pump

36

is, in the event of traction control and in automatic braking, to supply the high-pressure pumps

20

with brake fluid faster, in order to shorten the response time of the brake system

10

, especially if the brake fluid has a higher viscosity at low ambient temperatures than when the vehicle is at operating temperature. To that end, the charge pump

36

aspirates brake fluid from the supply container

12

and pumps it into the brake circuit I, which can be actuated by the rod piston of the master cylinder

11

. Internal resistances of the master cylinder

11

prevent the charge pressure of the charge pump

36

from decreasing toward the supply container

12

; instead, by displacement of brake fluid through the charge line

32

to the intake side of the high-pressure pump

20

, the charge pressure becomes operative. Because of the dividing piston located between the brake circuits I and II in the master cylinder

11

, the charge pressure likewise becomes operative in the brake circuit II and supplies the high-pressure pump

20

there with brake fluid in an equally accelerated manner.

As a result of inadequate maintenance of the brake system

10

, that is, a lack of brake fluid in the supply container

12

or a lack in the intake line

39

, there is the risk that air will enter the brake circuit I during the above-described mode of operation. It has now been found that according to the invention this is prevented by disposing the siphon

40

in the intake line

39

. That is, if the brake fluid level in the intake line

39

reaches the bend of the siphon

40

, then the charge pump

36

aspirates such a large quantity of air that this air abruptly discontinues further pumping by the charge pump

36

. Air can therefore not reach the brake line

27

of brake circuit I.

In the second exemplary embodiment shown in

FIGS. 2 and 3

, the invention is realized inside the charge unit

35

. The charge unit has a housing

44

with a drive motor

45

of the charge pump

36

flanged to it. A motor shaft

46

that engages the housing

44

carries a gear wheel

47

with teeth on the outside that meshes with a gear ring

48

with teeth on the inside. Two crescent-shaped recesses

49

and

50

in the housing

44

are associated with the charge pump

36

; of these, one recess

49

is disposed on the intake side of the pump, and the other recess

50

is disposed on the compression side of the pump. In addition, the housing

44

is provided with a connection stub

51

for the portion of the intake line

39

extending outside the charge unit

35

. Leading away from the connection stub

51

is a blind bore

52

extending with a parallel axis to the motor shaft

46

. Likewise extending parallel to the motor shaft

46

, a bore

53

is provided, which discharges into the intake-side recess

49

of the charge pump

36

. Three bores

54

,

55

and

56

are also provided, which as

FIG. 3

clearly shows extend approximately in a U to one another and mutually connect the first two bores

52

and

53

to one another. Toward the outside, the bores

53

,

54

,

55

and

56

are tightly closed off by closure elements

57

.

In the position for use of the charge unit

35

, the bores

54

,

55

and

56

form the siphon

40

, which is located in the course cf the intake line

39

between the brake fluid supply container

12

and the charge pump

36

.

The pressure line

41

is connected to the compression-side recess

50

. For the sake of simplicity, the further course of the pressure line

41

in the housing

44

of the charge pump

36

is not shown.