Method and apparatus for testing the brake system of a vehicle

• US 5,767,397 A
• Filed: 11/15/1996
• Issued: 06/16/1998
• Est. Priority Date: 02/03/1996
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Eisele, Uwe
• Primary Examiner(s): Dombroske, George M.
• Application Number:
  US08/751,128
• Time in Patent Office: 578 Days
• Field of Search: 73/121, 73/122, 73/126, 73/129, 73/39, 340/452, 340/453, 340/454, 364/426.01
• US Class Current: 73/121
• CPC Class Codes: B60T 17/221 Procedure or apparatus for checking or keeping in a correct functioning condition of brake systems hydraulic pressure systems in general F15B19/00, F15B21/04; testing structures or apparatus G01M

Abstract

In at least one operating situation, especially while the vehicle is stopped, pressure is built up in a defined manner and then released for test purposes without waiting for a steady state value to be reached. On the basis of the pressure-time or force-time curve in at least one wheel brake, a determination is made on whether or not an unacceptable amount of undissolved gas is present in the brake system.

Claims

1. A method for detecting undissolved gas in a hydraulic brake system of a vehicle having brakes supplied with fluid under hydraulic pressure by electrically actuated valve means, said method comprising

building up pressure in at least one wheel brake by actuating said valve means for a predetermined time which is not sufficient for a steady state pressure to be reached,

releasing said pressure after said predetermined time,

forming a pressure versus time curve during buildup and release of pressure,

forming an integral of said pressure versus time curve,

comparing said integral to a predetermined value, said predetermined value representing a predetermined amount of undissolved gas in the fluid of the brake system, and

informing the driver when said integral is less than said predetermined value by a predetermined amount.

2. Method as in claim 1 wherein said integral is formed over a time when the pressure exceeds a specified limit value.

3. Method for testing the brake system of a vehicle having brakes supplied with hydraulic pressure by electrically actuated valve means said method comprising:

building up pressure in at least one wheel brake by actuating said valve means for a predetermined time which is not sufficient for a steady state pressure to be reached;

releasing said pressure after said predetermined time;

forming a pressure versus time curve during buildup and release of pressure;

forming an integral of said pressure versus time curve;

comparing said integral to a predetermined value; and

informing the driver when said integral is less than said predetermined value by a predetermined amount;

said predetermined value representing a integral representing a predetermined amount of undissolved gas in the brake system.

4. Method as in claim 3 wherein said predetermined amount of undissolved gas is none.

5. A method for detecting undissolved gas in a brake fluid in hydraulic brake system of a vehicle in which pressure is built up and released in at least one wheel brake by electrically actuated valves, said method comprising:

building up and then releasing pressure in at least one of the wheel brakes for testing purposes in at least one operation situation;

detecting the brake pressure;

determining a characteristic curve of the pressure versus time for the at least one wheel brake in which pressure was built up;

detecting presence of undissolved gas in the brake fluid on the basis of the characteristic curve; and

outputting an indication when the presence of undissolved gas is detected.

6. Method according to claim 5, wherein the integral of the pressure-time curve is determined.

7. Method according to claim 6, wherein the integral is determined when the pressure exceeds a specified limit value.

8. Method according to claim 5, wherein said building up of pressure includes sending a pulse of predetermined duration to at least one pressure buildup valve, and at least one pressure release valve is then actuated to release the pressure which was built up.

9. Method according to claim 5, wherein the brake system is an electro-hydraulic brake system, which, under normal operating conditions, builds up or releases the pressure in the wheel brakes as a function of a driver'"'"'s braking command by actuation of the electrically operated valves, and wherein said detecting of the presence of undissolved gas is performed by an electric control, said brake system, upon a failure of the electric control, allows the brakes to be actuated as a function of the operation of the brake pedal by way of an emergency hydraulic brake circuit.

10. Apparatus for detecting undissolved gas in brake fluid in a brake system of a vehicle, said apparatus comprising:

an electronic control unit building up and then releasing pressure in at least one wheel brake for test purposes in at least one operating situation by actuating electrically operated valves;

said electronic control unit detecting pressure in said at least one wheel brake and determining a characteristic curve of the pressure versus time for the wheel brake in which pressure was built up;

said electronic control unit including means for detecting the presence of undissolved gas in the brake fluid on the basis of the characteristic curve, and

said electronic control unit having means for outputting an indication when the presence of undissolved gas is detected.

11. The apparatus according to claim 10, and

said electronic control unit using an integral of the characteristic curve to detect the presence of undissolved gas in the brake fluid.

12. The apparatus according to claim 10, and

an emergency hydraulic brake circuit in said brake system providing actuation of the brake responsive to the brake pedal in the event of a failure of said electronic control unit.