Hydraulic system for an automatic transmission of a motor vehicle

Patent metadata

Field	Value
Publication number	US-11280404-B2
Application number	US-201716317846-A
Country	US
Kind code	B2
Filing date	Aug 1, 2017
Priority date	Aug 3, 2016
Publication date	Mar 22, 2022
Grant date	Mar 22, 2022

Abstract

A hydraulic system for an automatic transmission of a motor vehicle, with which hydraulic cylinders of at least one clutch and of gear selectors can be actuated, which hydraulic system has a pressure accumulator for providing an accumulator pressure in the hydraulic system, wherein a clutch valve that can be actuated by the control unit is arranged in a clutch path leading from the pressure accumulator to the clutch hydraulic cylinder.

First claim

The invention claimed is:

1. A hydraulic system for an automatic transmission, comprising:
a dual clutch transmission, of a motor vehicle, with which hydraulic cylinders of at least one clutch and of gear selectors can be actuated, which hydraulic system has a pressure accumulator for providing an accumulator pressure in the hydraulic system, wherein a clutch valve that can be actuated by the control unit is arranged in a clutch path leading from the pressure accumulator to the clutch hydraulic cylinder, with which clutch valve a hydraulic pressure applied at the clutch hydraulic cylinder can be adjusted, and a gear selector valve that can be actuated by an electronic control unit is arranged in at least one gear selector path leading from the pressure accumulator to the gear selector hydraulic cylinder, with which gear selector valve the hydraulic pressure applied at the gear selector hydraulic cylinder can be adjusted, to which control unit is assigned a pressure sensor, with which the hydraulic pressure applied at the clutch hydraulic cylinder can be detected, and comprising a charging hydraulic pump, which delivers hydraulic fluid into the hydraulic system in a charging process, in order to increase an actual accumulator pressure, wherein the control unit has a diagnosis module, with which a diagnosis of the gear selector path can be carried out, in which the diagnosis module checks a leakage behavior in the gear selector path using the pressure sensor arranged in the clutch path and identifies a fault condition, which can be stored in memory in a gear selector path fault memory unit,
wherein the gear selector path diagnosis is conducted as a diagnosis following in time after a precharge pressure diagnosis and/or a clutch path diagnosis, and in that the gear selector path diagnosis occurs only under the condition that at least one clutch path with fault-free leakage is identified in the clutch path diagnosis, and in that the fault-free identified clutch path can be used as a reference clutch path for the gear selector diagnosis.

2. The hydraulic system as claimed in claim 1 , wherein, for the gear selector path diagnosis, the diagnosis module opens the clutch valve situated in the clutch path, in order to detect with the pressure sensor an actual accumulator pressure curve, and produces a pressure connection between the gear selector valve situated in the gear selector path and the pressure sensor by opening a pressure regulating valve.

3. The hydraulic system as claimed in claim 2 , wherein, to carry out the gear selector path diagnosis, a diagnosis charging operation takes place, during which the actual accumulator pressure is increased up to an upper threshold value (pmax) at an end time, and in that, after the end of the diagnosis charging operation, the pressure sensor detects a pressure gradient of the accumulator pressure curve, and in that a third evaluating unit compares the pressure gradient of the accumulator pressure curve to a reference pressure gradient and evaluates whether a fault-free or a fault-related pressure drop or gear selector leakage is present in the accumulator pressure curve.

4. The hydraulic system as claimed in claim 1 , wherein the gear selector valve can be adjusted between a blocking valve position and two through-flow valve positions, and in that the gear selector path diagnosis is conducted with the gear selector valve in both its first and in its second through-flow valve position.

5. The hydraulic system as claimed in claim 1 , wherein at least a first and a second gear selector path is provided, and in the gear selector path diagnosis is conducted separately for each gear selector path.

6. The hydraulic system as claimed in claim 5 , wherein, for a gear selector path diagnosis performed on the first gear selector path, the gear selector valve situated in the second and any other gear selector paths is or are in the blocked position.

7. The hydraulic system as claimed in claim 3 , wherein the pressure gradient in the accumulator pressure curve is detected within a measurement time interval whose start time corresponds to the end of the diagnosis charging operation or occurs immediately thereafter, and/or in that both the actual accumulator pressure at the measurement start time and the actual accumulator pressure at the measurement end time is detected.

8. The hydraulic system as claimed in claim 1 , wherein a precharge pressure diagnosis can be performed with the diagnosis module, during which the diagnosis module checks a precharge pressure of the pressure accumulator using the pressure sensor arranged in the clutch path and identifies a fault condition, which can be stored in memory in a precharge pressure fault memory unit.

9. The hydraulic system as claimed in claim 8 , wherein, in order to carry out the precharge pressure diagnosis, the diagnosis module starts a charging process at a start time in order to increase the actual accumulator pressure up to an upper threshold value, wherein the clutch valve situated in the clutch path is fully opened, in order to detect an actual accumulator pressure curve as a function of time, and in that the diagnosis module comprises an evaluating unit that identifies a fault condition upon the presence of a significant deviation between at least one reference value and the actual accumulator pressure curve, which can be stored in memory in a precharge pressure fault memory unit.

10. The hydraulic system as claimed in claim 8 , wherein the pressure accumulator is a piston-cylinder unit, in which an oil chamber connected to the clutch path is acted upon by means of a prestressed pressure piston, and in that, when the oil chamber is fully empty, the pressure piston is pushed with a prestressing force against an end stop of the pressure accumulator and ambient pressure prevails in the hydraulic system, and in that, during a filling or charging process, in order to overcome the prestressing force, a hydraulic pressure needs to be applied to the pressure piston that is greater than the temperature-dependent precharge pressure correlated with the prestressing force.

11. The hydraulic system as claimed in claim 9 , wherein the upper threshold value is larger by a pressure difference than the precharge pressure of the pressure accumulator, and in that, in the diagnosis charging operation, the actual accumulator pressure detected by the pressure sensor at a precharge pressure time reaches the precharge pressure of the pressure accumulator, and in that, in the further diagnosis charging operation, starting from the precharge pressure time, the oil chamber of the pressure accumulator is filled, under adjustment of the pressure piston and with further increasing of the actual accumulator pressure.

12. The hydraulic system as claimed in claim 11 , wherein the evaluating unit of the diagnosis module compares the actual accumulator pressure detected by the pressure sensor at the precharge pressure time to a predefined reference precharge pressure of the pressure accumulator, and in that, when the pressure accumulator has a faultless function, the actual accumulator pressure detected at the precharge pressure time corresponds to the reference precharge pressure, and in that, when a significant precharge pressure deviation is present, the evaluating unit establishes a precharge pressure fault.

13. The hydraulic system as claimed in claim 11 , wherein, in the diagnosis charging operation the actual accumulator pressure curve rises with a steep pressure gradient until it reaches the precharge pressure in the pressure accumulator, and in the further course, the actual accumulator pressure curve rises with a flatter pressure

Assignees

• Audi Ag

Inventors

• Weinhardt Mathias

Classifications

• F15B1/033

  with electrical control means · CPC title

• F16H61/688

  with two inputs, e.g. selection of one of two torque-flow paths by clutches · CPC title

• F16H61/0021

  Generation or control of line pressure · CPC title

• F16H2059/683

  Sensing pressure in control systems or in fluid-controlled devices, e.g. by pressure sensors · CPC title

• F16H2061/0034

  Accumulators for fluid pressure supply; Control thereof · CPC title