WO2011002594A1

WO2011002594A1 - Brake reservoir fluid sensing system

Info

Publication number: WO2011002594A1
Application number: PCT/US2010/038269
Authority: WO
Inventors: Robert A. Dougherty
Original assignee: Illinois Tool Works Inc.
Priority date: 2009-07-02
Filing date: 2010-06-11
Publication date: 2011-01-06

Abstract

A brake fluid level sensing system for a brake fluid reservoir of a vehicle includes a capacitance switch on a brake fluid reservoir responsive to changes in the dielectric value of the reservoir from a changing brake fluid level in the reservoir. A microcontroller connected to the capacitance switch discriminates between an actual low brake fluid level condition and a transient condition, and issues an alarm signal to a notification device when an actual low-level condition exists.

Description

BRAKE RESERVOIR FLUID SENSING SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[01] The present application claims the benefits of United States Provisional

Application Serial No. 61/222,575 filed July 2, 2009.

FIELD OF THE INVENTION

[02] The present invention relates generally to brake systems on motor vehicles; and, more particularly, to brake fluid reservoirs and systems associated therewith for sensing the amount of brake fluid in the reservoir.

BACKGROUND OF THE INVENTION

[03] It is required that motor vehicle brake systems include subsystems for monitoring the brake fluid level in the brake fluid reservoir to ensure an adequate amount of fluid is available for safe operation of the vehicle. It is known to divide the brake fluid reservoir into multiple chambers or compartments. For example, on passenger cars it is known to use reservoirs having two chambers, with each chamber supplying brake fluid to two of the four wheels. If one brake fluid line from the reservoir to two wheels is broken, the vehicle can still be capable of stopping. On some vehicles, one chamber of the reservoir supplies brake fluid to the front wheels, and the other chamber in the reservoir supplies brake fluid to the rear wheels. In other vehicles, it is known to cross-split the system, with one chamber supplying one front wheel and the rear wheel diagonally opposite of the front wheel, while the second chamber supplies the other two wheels on the diagonal. Divided in this way, if part of the system fails, more balanced stopping can be provided on the two remaining of the four wheels.

[04] Manufacturers of brake fluid reservoirs install systems that, when attached to the electronics of the vehicle, will notify the vehicle operator if the brake fluid level is below a minimum operating level in either of the two chambers. Several brake fluid sensing systems are known, and have been used effectively for various vehicles.

[05] One known brake fluid level sensing system uses a mechanical switch.

The switch is can be located in the filler cap of the reservoir, and can include a set of contacts in the cap. A flotation device is also attached to the filler cap, and includes a stem centered between the contacts in the filler cap, with a metal ring attached to the end of the stem. So long as the brake fluid in the reservoir is above the minimum required level, the floatation device will maintain a distance between the metal ring and the contacts, keeping the circuit open. If the fluid level drops below the minimum established level, the metal ring touches the contacts and closes the circuit, activating a warning signal. Corrosion on the contacts can result from exposure to the atmosphere.

[06] Another known system uses a pressure differential switch mounted in the master cylinder casting. A drop in pressure due to loss of fluid from one of the chambers causes an imbalance in pressure, closing the switch and activating the warning signal. Installation of this type of system requires an additional machining operation in the master cylinder casting and is expensive. For the most part, use of pressure differential switches for brake fluid level sensing in new motor vehicles has been discontinued.

[07] More recently, reed switches assembled to the exterior of the brake fluid reservoir have been used. The reed switch is mounted between or spanning the two chambers and does not come in contact with the brake fluid. The interior of the reservoir contains a floatation device, centered over and aligned with the reed switch. A ceramic magnet imbedded in the floatation device closes the reed switch if the brake fluid level drops and the flotation device lowers below an established minimum level. Reed switches are a common method for monitoring the brake fluid level in vehicles throughout the world.

[08] While reed switches work effectively to monitor brake fluid levels in brake fluid reservoirs, the use thereof is not without disadvantages. A problem with using reed switches is that the contacts are encapsulated in a glass tube with a relatively thin wall. The glass tube is filled with gas that protects the contacts from corrosion. The glass tube also gives the contacts structure. An important part of this assembly is the distance between the contacts. Any change in the distance between the contacts can allow for a false reading or an inability for the switch to function. If the glass is broken, the switch may not function properly due to change in the distance between the contacts. Further, if the glass is broken the gas normally contained therein will escape, allowing air with moisture to enter the tube, creating the potential for corrosion. Integrity of the reed switch is most at risk before it is assembled. After the switch is welded into the switch assembly, it is better protected. Installing the switch assembly into the reservoir provides more protection. Manufacturers are known to perform 100% testing of the assemblies, to ensure that the reed switch works at the final assembly operation. However, broken reed switches can still be a problem.

[09] The activation range of a reed switch and the ceramic magnet flotation device require a large operating range and with large tolerances. Design requirements mandate volume proportions above and below the normal operating range and the critical level for switch activation. The required volume results in an increase in the physical size of the brake fluid reservoir, thus increasing the cost of manufacture and the amount of brake fluid required to fill the system. Due to the available space under-hood of vehicles, the increase in physical size of the brake fluid reservoir limits the number of different vehicle models that can accept a specific reservoir and increases the number of different size and shape reservoirs that are required. To achieve the required total reservoir volume in the limited space available, it is sometimes necessary to use oddly shaped reservoir configurations fitting an under-hood available space, such that the reservoir will have application to only one or a small number of vehicle models.

[10] Accordingly, a reliable, robust and easy to install switch/sensor mechanism for vehicle brake fluid reservoirs would be advantageous. SUMMARY OF THE INVENTION

[11] A capacitance switch is provided on a brake system reservoir to measure changes in the dielectric value of the reservoir resulting from changes in the level of brake fluid in the reservoir. Multiple switches can be used for a reservoir have separate brake fluid levels in different reservoir chambers.

[12] In one aspect of one form thereof, a brake reservoir fluid sensing system is provided with a brake fluid reservoir having a predetermined minimum brake fluid level therein required for safe operation, and a sensor component including a capacitance switch mounted on the brake fluid reservoir and responding to changes in the dielectric value of the reservoir. A signal line connects the capacitance switch to a microcontroller. A notification device provides a warning signal if an actual brake fluid level in the reservoir is below the predetermined minimum brake fluid level. An alarm signal line connects the microcontroller to the notification device.

[13] In another aspect of a form thereof, a brake reservoir fluid sensing system is provided with a brake fluid reservoir having a pre-determined minimum brake fluid level for operation, brake fluid in the brake fluid reservoir, the brake fluid having an actual brake fluid level in the reservoir, and a fluid sensing system for responding to changes in the actual brake fluid level. The fluid sensing system is provided with a capacitance switch on the brake fluid reservoir, a microcontroller receiving signals from the capacitance switch differing in response to changes in the dielectric value of the brake fluid reservoir, and a notification device receiving an alarm signal from the microcontroller if the actual brake fluid level is below the predetermined minimum brake fluid level.

[14] In a still further aspect, a form of a brake reservoir fluid sensing system is provided with a brake fluid reservoir, a capacitance switch on the reservoir and responsive to an actual brake fluid level in the reservoir; and a notification device issuing a notification signal in response to a low brake fluid level condition present in the reservoir as determined by dielectric value changes in the brake fluid reservoir sensed by the capacitance switch.

[15] An advantage of a form of a brake reservoir fluid sensing system is that the switch/sensor is easy to install and reliable.

[16] Another advantage of a form of a brake reservoir fluid sensing system is that the sensor is precise and a lower tolerance volume for the reservoir may be available.

[17] Still another advantage of a form of a brake reservoir fluid sensing system is that the mechanism is robust, reliable and easy to install.

[18] Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features.

BRIEF DESCRIPTION OF THE DRAWINGS

[19] Fig. 1 is a view of a brake system reservoir, partially broken away and having a fluid sensing system as described herein;

[20] Fig. 2 is a schematic illustrations of the fluid level sensing system;

[21] Fig. 3 is a view of the fluid sensing system on the reservoir with adequate brake fluid in each of the chambers of the reservoir;

[22] Fig. 4 is a view of the fluid sensing system on the reservoir with inadequate brake fluid in both chambers of the reservoir;

[23] Fig. 5 is a view of the fluid sensing system on the reservoir with inadequate brake fluid in only one of the chambers of the reservoir; and

[24] Fig. 6 is a view of the fluid sensing system on the reservoir with inadequate brake fluid in only the other one of the chambers of the reservoir

[25] Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use herein of "including", "comprising" and variations thereof is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items and equivalents thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[26] Referring now more specifically to the drawings and to Figs. 1 and 2 in particular, a brake fluid reservoir 10 is shown, having a fluid sensing system 12 thereon for sensing the brake fluid level in the reservoir and activating a warning signal if the fluid level drops below a prescribed minimum level.

[27] Reservoir 10 includes a side wall 14, a bottom 16 and a top 18 defining an interior volume for containing brake fluid 20. An interior baffle or wall 22 divides reservoir 10 into a first chamber 24 and a second chamber 26. Outlets 28, 30 are provided from chambers 24 and 26, respectively, for connecting to brake fluid lines of a vehicle brake system, as those skilled in the art will understand. It should be understood further that reservoir 10 can be of other shapes and configurations to fit within available space in the engine compartment of a vehicle or other location and may include various internal structures to provide fluid balancing between chambers 24 and 26 and for minimizing sloshing of brake fluid 20 in the reservoir. A filler neck 32 is provided for providing access to reservoir 10 for adding brake fluid 20 to reservoir 10, and may include a screw-on cap (not shown) engaging a screw thread 34 on filler neck 34 to close the reservoir. While flow-through features can be provided for balancing fluid levels in first and second chambers 24, 26, an abrupt condition change can cause brake fluid levels to be different in each of the chambers. Accordingly, actual brake fluid levels 36, 38 are provided in chambers 24, 26 respectively, which may be at the same level in reservoir 10 or at different levels. Mounting features 40, 42 can be provided for attaching reservoir 10 within a vehicle. Reservoir 10 can be made of suitable plastic materials resistant to brake fluids, and may, for example, be made of polypropylene by an injection molding process.

[28] Fluid sensing system 12 includes a sensor component 50 having a sensor body 52 and first and second capacitance switches 54, 56 on sensor body 56. Sensor body 52 is mounted on or in side wall 14, generally straddling interior wall or baffle 22 such that first capacitance switch 54 overlies first chamber 24 and a second capacitance switch 56 overlies second chamber 26. Capacitance switches 54, 56 preferably are of a type suitable for use in areas of high environmental and/or electrical contamination. One such switch is disclosed, for example, in International Publication Number WO 2008/131213. Other capacitance switches also may be suitable.

[29] As those skilled in the art will understand readily, a non-intrusive capacitance switch can detect the presence of liquid or air by measuring the conductive or dielectric value present in all materials, which value will change as a fluid level against the material rises or falls. The capacitance switches can be mounted on the exterior surface of the brake fluid reservoir as shown, or can be mounted or embedded within the reservoir side wall during manufacture such that the switches are encased in the polypropylene or other material forming reservoir 10. In use, the capacitance switches measure the dielectric value of the reservoir, which value will change depending on the presence or absence of brake fluid against areas of the inner surface of the reservoir. The change in dielectric value can be used to generate a signal for activating a warning mechanism to warn that a low brake fluid volume condition may exist.

[30] First and second capacitance switches 54, 56 are connected to signal lines

58, 60, respectively, for transmitting signals from capacitance switches 54, 56 to a microcontroller 62. Each capacitance switch 54, 56 is separately connected to microcontroller 62 so that fluid levels in first and second chambers 24, 26 are separately sensed and evaluated. Signal processing is performed in microcontroller 62 to discriminate between actual low brake fluid level conditions and random false readings that may result from certain transient conditions such as, for example, brake fluid sloshing or level changes due to unlevel conditions along which the vehicle is operated.

[31] Microcontroller 62 is connected by an alarm signal line 64 to a notification device 66. It should be understood that notification device 66 can be a simple visual warning illumination light, can be an illuminated or other activated text message, or can be an audible warning, all as commonly used to notify a vehicle operator of various vehicle conditions. Multiple warning signals can be used including visual signals and auditory signals to warn the operator of a low brake fluid level condition.

[32] Figs. 3-6 illustrate various operating conditions and the resultant warning condition for fluid sensing system 12. In Fig. 3 brake fluid levels 36, 38 in chambers 24, 26 are both above the minimum required level and above capacitance switches 54, 56. Accordingly, first and second capacitance switches 54, 56 each sense a dielectric value of reservoir 10 consistent with brake fluid at an acceptable level in each of first and second chambers 24 and 26 of reservoir 10 and transmit such to microcontroller 62 via signal lines 58, 60. The signals are processed in microcontroller 62 and no alarm signal is sent to notification device 66, which remains in a non-activated condition indicated in Fig. 3 for illustrative purposes as a non-illuminated bulb 66a.

[33] Fig. 4 illustrates a condition in which brake fluid levels 36, 38 in first and second chambers 24, 26 are both below the minimum required level, and capacitance of switches 54, 56 responded to the change in the dielectric value from the lowering fluid levels. A signal indicating such is sent to microcontroller 62 from each first capacitance switch 54 and a second capacitance switch 56 via signal lines 58, 60 respectively. These signals are processed in microcontroller 62, which determines that a non-transient condition is present. An alarm signal is sent along alarm signal line 64 to notification device 66 which is activated. To illustrate the activation of notification device of 66, an illuminated bulb 66b is shown.

[34] Fig. 5 illustrates a condition in which brake fluid level 36 of first chamber

24 is at an inadequate elevation; however, brake fluid level 38 in second chamber 26 is above the minimum required level. Accordingly, second capacitance switch 56 will send a signal along signal line 60 to microcontroller 62 indicative of adequate brake fluid. At the same time, first capacitance switch 54 will respond to the change in dielectric value from the lowering fluid level and will send a signal along signal line 58 to microcontroller 62 indicative of a low brake fluid condition. These signals will be processed in microcontroller 62 to determine whether a transient condition is present. Since a low brake fluid condition exists in first chamber 24, an alarm signal is sent along alarm signal line 64 to notification device 66, which is activated. To illustrate the activation of notification device 66, an illuminated bulb 66b is shown for illustrative purposes.

[35] Fig. 6 illustrates a condition in which brake fluid level 36 of first chamber

24 is at an adequate elevation; however, brake fluid level 38 in second chamber 26 is below the minimum required level. Accordingly, first capacitance switch 54 will send a signal along signal line 58 to microcontroller 62 indicative of adequate brake fluid. At the same time, second capacitance switch 56 will respond to the change in dielectric value from the lowering fluid level and will send a signal along signal line 60 to microcontroller 62 indicative of a low brake fluid condition. These signals will be processed in microcontroller 62 to determine whether a transient condition is present. Since a low brake fluid condition exists in second chamber 26, an alarm signal is sent along alarm signal line 64 to notification device 66, which is activated. To illustrate the activation of notification device 66, an illuminated bulb 66b is shown for illustrative purposes.

[36] The exemplary embodiment shown and described herein includes two chambers 24, 26 and two capacitance switches 54, 56; one capacitance switch operative for each chamber. It should be understood that for a brake fluid reservoir having only a single chamber therein and a single actual brake fluid level, only one capacitance switch is necessary. So also, if a brake fluid reservoir were provided with more than two chambers therein, each having potentially different actual brake fluid levels, one capacitance switch could be provided for each such chamber in the reservoir.

[37] The capacitance switches of the present fluid level sensing system can be placed behind a non-conductive surface. In the illustrated embodiment, the capacitance switches are mounted to the exterior of the reservoir and can sense when fluid drops below the level at which the capacitance switch is mounted. There are no moving features in the capacitance switches, so reliability is superior to reed switches and other switches having moving parts. Monitoring both chambers independently and the very small activation range required for the capacitance switch to operate, result in an ability to reduce the physical size of the brake fluid reservoir compared to reservoirs required when using switches that monitor a common fluid volume and require a large range for activation, such as for a reed switch/float combination. Sensing the actual fluid level in each chamber independently further promotes precision and accuracy, making smaller reservoirs possible. Reducing reservoir size can directly reduce the cost of material required for manufacturing the reservoir. In addition, by reducing the physical size of the reservoir, the reservoir can be more versatile in use and can have application in additional models of vehicles, potentially increasing annual manufacturing volumes of a specific reservoir, reducing tooling costs and eliminating part numbers for manufacturers, suppliers and users.

[38] Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.

[39] Various features of the invention are set forth in the following claims.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A brake fluid sensing system for a motor vehicle brake system, comprising;

a brake fluid reservoir having a predetermined minimum brake fluid level therein required for safe operation;

a sensor component including a capacitance switch mounted on said brake fluid reservoir and responding to changes in dielectric value of the reservoir; a signal line connecting said capacitance switch to a microcontroller; a notification device providing a warning signal if an actual brake fluid level in the reservoir is below said predetermined minimum brake fluid level; and an alarm signal line connecting said microcontroller to said notification device.

2. The brake fluid sensing system of claim 1, said capacitance switch mounted on an exterior surface of said brake fluid reservoir.

3. The brake fluid sensing system of claim 1, said brake fluid reservoir having first and second chambers therein.

4. The brake fluid sensing system of claim 3, said sensor component including a first capacitance switch and a second capacitance switch.

5. The brake fluid sensing system of claim 4, said first capacitance switch and said second capacitance switch mounted on an exterior surface of said brake fluid reservoir.

6. The brake fluid sensing system of claim 1, said brake fluid reservoir defining first and second chambers therein and said sensor component having a first capacitance switch mounted on said first chamber and a second capacitance switch mounted on said second chamber.

7. The brake fluid sensing system of claim 6, said first capacitance switch and said second capacitance switch connected to said microcontroller by separate signal lines.

8. The brake fluid sensing system of claim 1, said notification device being at least one of an auditory notification device and a visual notification device.

9. A brake fluid system for a motor vehicle, comprising:

a brake fluid reservoir having a pre-determined minimum brake fluid level for operation;

brake fluid in said brake fluid reservoir, said brake fluid having an actual brake fluid level in said reservoir;

a fluid sensing system responsive to changes in said actual brake fluid level, said fluid sensing system including:

a capacitance switch on said brake fluid reservoir; a microcontroller receiving signals from said capacitance switch differing in response to changes in the dielectric value of said brake fluid reservoir; and

a notification device receiving an alarm signal from said microcontroller if said actual brake fluid level is below said predetermined minimum brake fluid level.

10. The brake fluid system of claim 9, said brake fluid reservoir having an interior wall dividing said reservoir into a first chamber and a second chamber.

11. The brake fluid system of claim 10, said fluid sensing system having a first capacitance switch on said first chamber and a second capacitance switch on said second chamber.

12. The brake fluid system of claim 11, including a first signal line connecting said first capacitance switch to said microcontroller and a second signal line connecting said second capacitance switch to said microcontroller, and said microcontroller separately processing signals from said first capacitance switch and said second capacitance switch to issue an alarm signal to said notification device if at least one of said first capacitance switch and said second capacitance switch has issued a signal indicative of an actual brake fluid level below said predetermined minimum brake fluid level.

13. The brake fluid system of claim 12, said notification device being at least one of an auditory notification device and a visual notification device.

14. The brake fluid system of claim 9, said notification device being at least one of an auditory notification device and a visual notification device.

15. A brake fluid sensing system for a motor vehicle; comprising: a brake fluid reservoir;

a capacitance switch on said reservoir and responsive to changes in an actual brake fluid level in the reservoir; and a notification device issuing a notification in response to a low brake fluid level condition present in the reservoir as determined by changes in a dielectric value of said brake fluid reservoir.

16. The brake fluid sensing system of claim 15, said reservoir having a first chamber and a second chamber therein.

17. The brake fluid sensing system of claim 16, including a first capacitance switch connected to said first chamber and a second capacitance switch connected to said second chamber; and said notification device issuing a notification in response to a low brake fluid condition present in at least one of said first chamber and said second chamber.

18. The brake fluid sensing system of claim 17, said first capacitance switch and said second capacitance switch each mounted on an exterior surface of said reservoir.

19. The brake fluid sensing system of claim 15, said capacitance switch mounted on an exterior surface of said reservoir.

20. The brake fluid sensing system of claim 15, said notification device issuing at least one of an auditory notification and a visual notification.