Measuring and testing – Instrument proving or calibrating – Fluid pressure
Reexamination Certificate
2001-12-26
2003-12-16
Williams, Hezron (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Fluid pressure
Reexamination Certificate
active
06662622
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for compensating the offset of a pressure value having the steps: detecting a pressure value, lowpass filtering of the pressure value and storing the lowpass filtered pressure value as an offset value. In addition, the present invention relates to a device for compensating the offset of a pressure value with means to detect a pressure value, means to lowpass filter the pressure value and means to store the lowpass filtered pressure value as an offset value.
BACKGROUND INFORMATION
In numerous systems to control vehicle dynamics, it is necessary to precisely determine the pressure in the braking system. For example, in the electronic stability program (ESP), the driving state of the car is monitored in short time intervals, for example, 25 times a second. Specific brake interventions in each individual wheel and possibly a reduction of the engine speed stabilizes the vehicle and returns it to the lane. In an understeered curve, for example, the vehicle breaks away to the outside. The electronic stability program (ESP) brakes the wheel to the inside of the curve before breakaway and reduces the engine power. As a result, the car is held in the curve.
Since it is highly important to precisely know the pressure in the braking system so that effective interventions in the brakes can be made as a function of the pressure, it is appropriate to determine the offset value of the brake sensor signal as precisely as possible. It is possible in this manner to attain a high control accuracy, and if a pressure value exceeds a maximum magnitude, it is possible to recognize an incorrect pressure value. In determining the offset, it must be ensured that an increased pressure value cannot be caused either internally, e.g., through the action of the supply pump or the return pump or externally by a braking intention of the driver, which is recognized via the brake pedal. Only in these cases may an offset compensation take place, since otherwise an increased pressure sensor signal will be present when, for example, the brake pedal is pressed, the increase not arising due to an increased offset related to a pressure sensor or line.
A particular problem in recognizing the conditions for a permitted offset compensation is the timely recognition of the driver's braking intention. The primary reason for this is that in some motor vehicles, in particular due to elasticities in the pedal system, the brake light switch is not set until a pressure value corresponding to the braking intention is already present when the brake pedal is pressed with fast, highly dynamic force, in particular in panic braking. The setting of the brake light switch, which in many systems is used as an indicator of the braking intention, may, for example, occur with a 20 to 60 ms delay.
The pressure value determined at the time the brake light switch signal occurs does not then correspond to the actual offset value, or it is already above the cutoff threshold for fault detection. In existing logics, lowpass filtering of the pressure signal is carried out permanently if the acceptance conditions
driver is not pressing the brake pedal,
the supply or return pumps are not activated or no longer running on,
no undervoltage in the system,
no residual pressure in the system
were valid for a specific period of time. Due to the aforementioned delayed setting of the brake light switch, the first acceptance condition, according to which the driver is not pressing the brake pedal, is violated. Consequently, a reliable offset compensation can no longer occur.
SUMMARY OF THE INVENTION
The present invention builds on the method according to the definition of the species in that the lowpass filtered pressure value is stored as an offset value if at least the condition is present that a logical signal has or assumes a first value and that a substitute value is stored as an offset value if the logical signal has or assumes a second value. The result of this is that a new lowpass filtered pressure value is stored as an offset value only if a specific condition is present. This condition is preferably present if the driver has not shown a braking intention by suddenly pressing the brake pedal, for example. If, however, such a braking intention is present, meaning that the logical signal has a second value it must be assumed, for reasons of safety, that the pressure in the system and accordingly the lowpass filtered pressure value have already assumed an increased value. Consequently, the lowpass filtered pressure value is not stored as an offset value in the event that the logical signal has a second value. Rather, a substitute value is used. Offset compensation is thus frozen during a time in which a braking intention is present. In times when there is no braking intention, offset compensation then takes place continuously.
It is particularly advantageous that the logical signal has assumed or assumes the first value if a brake light switch is not being set or is not set and that the logical signal has assumed or assumes the second value if a brake light is being set or is set. The brake light switch signal is thus used as a criterion for the presence of a braking intention by the driver. If the brake light switch is set, there is a high probability of an increased pressure in the braking system caused by the braking intention. Consequently, no offset compensation is carried out.
It is a particular advantage that a query of the logical signal takes place in a time-slot pattern, which has sequential time intervals, that the lowpass filtered pressure value of the preceding time interval is stored as an offset value if the logical signal has assumed or assumes the first value in the present time interval, and that the offset value of the penultimate time interval as a substitute value is stored as an offset value if the logical signal has assumed or assumes the second value in the present time interval. The time-slot pattern makes it possible to use offset values stored in the past as substitute values. This ensures that the offset value will not deviate excessively from the actual offset value even if the offset value of the penultimate time interval is stored as a substitute value. Consequently, a precision, which is consistent with a high control accuracy in the ESP system, is made possible.
It is advantageous that the logical signal can assume two different values, that the first value is FALSE and that the second value is TRUE. A binary logical signal can be processed in digital circuits in a simple manner.
It is useful that the lowpass filtered pressure value is stored as an offset value if, in addition to the condition that the logical signal has or assumes a first value, additional conditions are present. These additional conditions are associated with the fact that no influence may be exercised on the braking system that is contrary to a precise offset compensation.
For example, it is advantageous in this connection that the additional conditions are that the supply or return pumps are not activated or are not running on and that there is no undervoltage or there is no residual pressure in the system. All these conditions would prevent the precise determination of an offset value so that it is useful to include the consideration of these conditions in deciding if offset compensation should take place or not.
It is useful if the time intervals of the time-slot pattern have a length of approximately 200 ms. Since a typical delay between a quick pressing of the brake pedal and the setting of the brake light switch can range, for example, between 20 and 60 ms, a time-slot pattern having a length of 200 ms is adequate to supply the suitable values for the offset value storage.
It is useful that the offset value is stored in an EEPROM. An EEPROM is a memory chip that is adequate to store the offset values permanently, it being nonetheless possible to change the contents of the memory by electrical means using the advantageous time cycles.
The present invention builds on the devi
Garber C D
Kenyon & Kenyon
Robert & Bosch GmbH
Williams Hezron
LandOfFree
Method and device for compensating the offset of a pressure... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for compensating the offset of a pressure..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for compensating the offset of a pressure... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3101822