METHOD FOR TESTING THE LEAK TIGHTNESS OF A HYDRAULIC VEHICLE BRAKING SYSTEM

Abstract

To prevent the loss of any brake fluid from a hydraulic vehicle braking system after a detected leakage, a testing or a re-testing of a leak tightness of the vehicle braking system is carried out only after release, for example, after a repair of the vehicle braking system.

Claims

1-7. (canceled)

8. A method for testing the leak tightness of a hydraulic vehicle braking system, which includes a brake pressure generator for generating a hydraulic brake pressure in the vehicle braking system, the method comprising: detecting a leakage of the vehicle braking system; and after the detecting of the leakage, carrying out a leak tightness test only after a release.

9. The method as recited in claim 8, wherein the leak tightness test is carried out only at a sufficient fill level in a brake fluid reservoir of the vehicle braking system.

10. The method as recited in claim 8, wherein the vehicle braking system encompasses a power brake pressure generator including a piston-cylinder unit, which is hydraulically separated from a remaining portion of the vehicle braking system by closing a valve, the piston of which is displaced in the cylinder within a scope of a pressure build-up, and a pressure increase and/or a piston movement is measured, and the leak tightness test of the vehicle braking system is not carried out when the pressure increase is too slow or the piston shifts in the cylinder.

11. The method as recited in claim 9, wherein, to test the sufficient fill level in the brake fluid reservoir, brake fluid is initially displaced out of the brake pressure generator into the brake fluid reservoir and is then drawn in again from the brake fluid reservoir using the brake pressure generator and, thereafter, a brake pressure build-up using the brake pressure generator is tested.

12. The method as recited in claim 8, wherein the leak tightness test is carried out only after a repair of the vehicle braking system.

13. The method as recited in claim 8, wherein, after a brake pressure build-up in the vehicle braking system using the brake pressure generator, the leak tightness test is carried out only when the brake pressure increases at at least an established speed.

14. The method as recited in claim 8, wherein the vehicle braking system encompasses a power brake pressure generator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention is explained in greater detail in the following with reference to a specific embodiment represented in the FIGURE.

[0011] The sole FIGURE shows a simplified hydraulic diagram of a hydraulic vehicle braking system for carrying out the method according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0012] Hydraulic vehicle braking system 1 represented in the drawing includes a muscle power-actuatable main brake cylinder 2, a brake pressure control valve system 3, and one or multiple hydraulic wheel brake(s) 4, which is/are connected to main brake cylinder 2 via brake pressure control valve system 3. Two wheel brakes 4 are shown. For a passenger car, vehicle braking system 1 typically encompasses two brake circuits and four wheel brakes 4, of which two are assigned to one brake circuit in each case.

[0013] Brake pressure control valve system 3 includes solenoid valves 5 for brake pressure control and a power brake pressure generator 6 encompassing a hydraulic pump 7 and an electric motor 8 for its drive. Further components of brake pressure control valve system 3, such as check valves, hydraulic accumulators, damper chambers, are not shown. Moreover, brake pressure control valve system 3 encompasses one or multiple pressure sensor(s) 9 for controlling a brake pressure. With the aid of brake pressure control valve system 3, the control of the brake pressure in vehicle braking system 1 is possible in the case of a brake application by muscle power and/or a power brake application, “regulation” also encompassing a “control” of the brake pressure. In the case of a brake application by muscle power, main brake cylinder 2 is actuated with the aid of a foot brake pedal 10 or a hand brake lever (not shown) and, as a result, a hydraulic brake pressure is generated in vehicle braking system 1. In the case of a power brake application, hydraulic pump 7 of power brake pressure generator 6 is driven with the aid of electric motor 8 and, as a result, a hydraulic brake pressure is generated in vehicle braking system 1.

[0014] Hydraulic pump 7 is, for example, a piston pump or an (internal) gear pump. In slip controlled vehicle braking systems, such hydraulic pumps 7 are also referred to as recirculating pumps.

[0015] With the aid of brake pressure control valve system 3, a slip control is also possible, such as an anti-lock system, a traction slip control system and/or an electronic stability program or vehicle dynamics system, the latter two often also being referred to colloquially as anti-slip regulation. The abbreviations ABS, ASR, VDR, and ESP are common for these slip controllers. Such slip controllers are conventional and are not explained here. A slip control is possible in the case of a brake application by muscle power as well as in the case of a power brake application. In the case of slip controllers, wheel brake pressures are normally controlled individually wheel-specifically in each wheel brake 4.

[0016] The present invention provides that, after a leakage of vehicle braking system 1 has been detected, a leak tightness test is carried out only after a release, in order not to lose brake fluid from uptight vehicle braking system 1 due to the leak tightness test, which would then no longer be available for brake applications. The release may take place after repair of vehicle braking system 1, in order to test the leak tightness of vehicle braking system 1 and, therefore, the success of the repair.

[0017] In order to test the leak tightness, for example, a hydraulic brake pressure is generated in vehicle braking system 1 with the aid of power brake pressure generator 6 and main brake cylinder 2 is hydraulically separated from vehicle braking system 1 or from brake pressure control valve system 3 by closing a separating valve (not represented individually) in each brake circuit, so that hydraulic pump 7 of power brake pressure generator 6 does not displace brake fluid out of vehicle braking system 1 via main brake cylinder 2 into a pressureless brake fluid reservoir 11, which is mounted onto main brake cylinder 2. If the brake pressure in vehicle braking system 1 drops after power brake pressure generator 6 is switched off, this means vehicle braking system 1 is uptight. The leak tightness of vehicle braking system 1 is then tested again, according to the present invention, only after a release, for example, after the repair of vehicle braking system 1.

[0018] Another criterion for carrying out the leak tightness test is a fill level in brake fluid reservoir 11: If the fill level in brake fluid reservoir 11 is less than an established minimum, a leak tightness test is not carried out, in order not to lose any brake fluid due to the leak tightness test. The minimum of the fill level in brake fluid reservoir 11 is established in such a way that brake fluid sufficient for any possible braking operation, also for repeated application of the brakes, is present in brake fluid reservoir 11 for the application(s) of the brakes. The fill level of brake fluid reservoir 11 is measured with the aid of a fill level sensor 12. The criterion of the at least minimum fill level in brake fluid reservoir 11 may be applied regardless of or after a previously detected leakage of vehicle braking system 1.

[0019] In order to test whether air is present in a piston-cylinder unit as hydraulic pump 7 of power brake pressure generator 6, the piston-cylinder unit is hydraulically separated from the remaining vehicle braking system by closing a valve 5 and the piston is displaced in the cylinder within the scope of a pressure build-up. If the cylinder is filled with brake fluid, the piston and electric motor 8 do not move or move hardly at all due to the incompressibility of brake fluid, the pressure in the cylinder increases abruptly and a current consumption of electric motor 8 is high. If air is present in the cylinder, the piston and electric motor 8 move and are decelerated, the current consumption drops after a start-up of electric motor 8 and then increases again and the pressure in the cylinder increases. In this case, a leak tightness test is not carried out until the vehicle braking system has been repaired or at least brake fluid reservoir 11 has been filled, which may also be construed as a repair of vehicle braking system 1. This test is preferably carried out before the beginning of a trip, i.e., for example, when a vehicle door is unlocked or opened or when an ignition is switched on.

[0020] One possibility for testing whether the fill level in brake fluid reservoir 11 suffices is to initially displace brake fluid out of power brake pressure generator 6 into brake fluid reservoir 11 and, thereafter, to draw in brake fluid out of brake fluid reservoir 11 again with the aid of power brake pressure generator 6. If no brake fluid is contained in brake fluid reservoir 11, power brake pressure generator 6 draws in air out of brake fluid reservoir 11, thereafter, due to which a pressure build-up with the aid of power brake pressure generator 6 is no longer possible, which is measurable with the aid of one of pressure sensors 9. If the fill level in brake fluid reservoir 11 is too low, power brake pressure generator 6 draws in a mixture of brake fluid and air, which impairs a subsequent pressure build-up with the aid of power brake pressure generator 6. This is also measurable with the aid of pressure sensor 9. In both cases, no further leak tightness tests are carried out until brake fluid reservoir 11 has been filled and, if necessary, vehicle braking system 1 has been repaired. This method is intended, in particular, for a power brake pressure generator 6, which includes a piston pump or a piston-cylinder unit as a hydraulic pump 7.

[0021] Another criterion for the release of the leak tightness test is a speed of the brake pressure build-up in vehicle braking system 1 with the aid of power brake pressure generator 6, since power brake pressure generator 6 always generates the brake pressure at the same speed, at least theoretically. If the brake pressure build-up is slower than it normally is or than would be anticipated, this may be an indication of a possible leakage of vehicle braking system 1. In this case, a leak tightness test of vehicle braking system 1 is not carried out again before a release. The criterion of the speed of the brake pressure build-up in vehicle braking system 1 with the aid of power brake pressure generator 6 may also be applied regardless of a previously detected leakage of vehicle braking system 1. In order to detect the speed of the brake pressure build-up, for example, a period of time until a predefined brake pressure has been reached in vehicle braking system 1 or the brake pressure reached in vehicle braking system 1 after a predefined period of time may be measured when the brake pressure is generated with the aid of power brake pressure generator 6.

[0022] The criteria for the release of the leak tightness test may be applied independently of one another or also in basically arbitrary combinations.