GB2457080A

GB2457080A - Detecting the closure of a port by a piston using a light source and sensor

Info

Publication number: GB2457080A
Application number: GB0801941A
Authority: GB
Inventors: Philip Alexander Barber; Balbir Bhajam; Nick Brett
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2008-02-04
Filing date: 2008-02-04
Publication date: 2009-08-05
Anticipated expiration: 2028-02-04
Also published as: GB2457080B; GB0801941D0

Abstract

A method and system for sensing when a piston 11 of hydraulic master cylinder (10, Fig.3) has closed an inlet port 15 to the master cylinder. The method comprises the steps of: using an artificial light source 30, such as a light emitting diode (LED) arranged such that light from the light source 30 can enter the cylinder through the port 15 when it is not covered by the piston 11; locating a light sensor 35 so as to be able to detect whether light from the light source 30 is entering the cylinder through the port 15; and providing a signal from the sensor 35 indicative of whether light is able to enter the cylinder through the port 15. The port 15 may be an inlet port connected to a reservoir 20 and light may be transferred to the port 15 through the liquid 21 stored in the reservoir 20. The light source 30 may be located in the reservoir 20. The system is applicable to brake and clutch circuits of a motor vehicle.

Description

A Method for sensinQ the Closure of a Port by a Piston The invention relates to the sensing of the position of a piston moveable in a cylinder and in particular to sensing the moment when a port is closed by the piston.

Although the invention is generally applicable to any situation in which the point of closing of a port by a piston is required to be monitored it is particularly advantageously applicable to a brake and clutch circuits of a motor vehicle.

With a conventional motor vehicle sensing the control pedal movement of either a brake system or a hydraulically operated clutch normally involves the setting of microsw,tches mounted on brackets both during vehicle assembly and periodically when the vehicle is serviced.

The setting of these microswitches is critical because plausibility checks, required for safe vehicle operation, use this information. This information must be reliable and robust if false vehicle malfunction alerts are to be avoided. One such check is against the hydraulic brake pressure in the slave cylinders, which only increases once the master cylinder inlet ports are closed by their respective pistons.

If the switch setting is not accurate against this point, then either pedal travel is inferred from the switch, but not confirmed by line pressure or line pressure is detected before the switches change state. In either case, the plausibility test will be failed and a false alert will be given and, with certain systems, the ability to start the car may be disabled as a safety measure.

The installation of the pedal microswitches, which in some cases are multiple switches, has significant component cost and assembly time associated with it. In addition, the various tolerances in the mechanical linkages combined with wear of the linkages means that such switches need to be very accurately set and periodically adjusted or reset if false alerts are not to be generated. it will also be appreciated that the force required to operate these mechanical switches may have a detrimental affect on the sensitivity of the brake pedal, that is to say, the Pedal feel' may be negatively affected.

It is an object of the invention to provide an improved method and system for sensing the closure of a port by a piston that overcomes or minimises the disadvantages associated

with the prior art.

According to a first aspect of the invention there is provided a method for sensing the closure of a port by a piston slideably mounted in a cylinder, the method comprising the steps of: using a light source arranged in such a way that light from the light source can enter the cylinder through the port when it is not covered by the piston, locating a sensor so as to be able to detect whether light from the light source is entering the cylinder through the port, and providing a signal from the sensor indicative of whether light is able to enter the cylinder through the port.

The cylinder may be a hydraulic cylinder and the method may further comprise using liquid located upstream from the port to transmit light to the port from the light source.

The port may be an inlet port connected to a reservoir used to store liquid for the hydraulic cylinder and the method may further comprise transmitting light from a light source located in the reservoir to the inlet port According to a second aspect of the invention there is provided a system for sensing the closure of a port by a piston slideably mounted in a cylinder, wherein the system comprises a light source located in such a way that light from the light source can enter the cylinder through the port when it is not covered by the piston, a light sensor positioned in the cylinder so as to be able to detect whether light is entering the cylinder through the port and an electronic unit connected to the light sensor, the electronic unit being arranged to receive the signal from the sensor and use the signal from the light sensor to determine the closure state of the port.

The light source may comprise a modulated light source to illuminate the port.

The electronic unit may be further operable to control one or more other sub-systems based upon the signal received from the light sensor.

The cylinder may be a hydraulic cylinder having a piston slideably moveable therein and the port may be an inlet port which is connected to a reservoir used to store liquid for the hydraulic cylinder and light may be transferred to the inlet port through the liquid stored in the reservoir.

The light source may be located in the reservoir.

The hydraulic cylinder may be a master cylinder containing liquid to be pressurised by the piston and the master cylinder may have an outlet connecting the master cylinder to a circuit to be pressurised by the master cylinder.

According to a third aspect of the invention there is provided a motor vehicle having at least one system constructed in accordance with said second aspect of the invention.

The invention will now be described by way of example with reference to the accompanying drawings of which: -Fig. 1 is a schematic cross-section through a combined master cylinder and reservoir according to one aspect of the invention showing a piston in the master cylinder in a first position in which an inlet port is in open communication with an operating cylinder of the master cylinder; Fig.2 is a schematic cross-section similar to that shown in Fig.1 but showing the piston in the master cylinder in a second position in which an inlet port has been closed off by the piston; Fig.3 is a schematic diagram of a motor vehicle and sensing system according to the invention; and Fig.4 is a schematic cross-section through a spool valve showing the application of the invention to such a device.

Referring to Fig.3 there is shown a motor vehicle 1 having a hydraulic braking circuit including left and right hand brake calipers 5L and 5R connected to a brake master cylinder 10. The brake master cylinder 10 is connected to a reservoir 20 which in this case is directly mounted on the master cylinder 10 to form what is often called a combined master cylinder and reservoir shown in greater detail in Figs. 1 and 2.

As can be seen in Figs. 1 and 2, a light sensor 35 is attached to the master cylinder 10 for sensing when light is entering the master cylinder 10 through an inlet port 15. A piston 11 is slidingly mounted in the master cylinder 10 and is moveable by an input rod 12 which is connected to a means (not shown) for applying an actuating force to the piston 11 in the direction of the arrow "I". The actuating force may be directly applied by a user of the motor vehicle 1 by operation of a brake pedal (not shown) or via a brake booster (not shown) as is well known in the art. II will also be appreciated by those in the art that the motor vehicle 1 may have a dual circuit braking system and that the invention is equally applicable to such a braking system.

The reservojr 20 contains a supply of liquid 21 for the master cylinder 10 and is connected to the master cylinder by the inlet port 15.

The light sensor 35 is mounted so that it can sense light entering the master cylinder through the inlet port 15 and, in the example shown, the light sensor 35 is positioned close to an outlet port 16 from the master cylinder 10.

The outlet port 16 is used to connect the master cylinder 10 to a circuit to be pressurised which in this case is formed by the calipers 5L and 5R and associated pipes of the hydraulic braking circuit, as shown in Fig.3.

The master cylinder 10 is made from steel and is opaque so that light cannot enter the master cylinder 10 except via the inlet port 15. A vent port 13 is provided to allow air to escape from a rear side of the piston 11 when is moves to the right as shown in Fig 2 so as to reduce the pressure in the circuit connected to the master cylinder 10.

Although it would be possible to use natural light transmitted via the liquid 21 contained in the reservoir 20 as the sensing medium, this is not practical for use in a motor vehicle because no such light is available after sunset. Therefore an artificial light source such as the LED 30 is used to provide a source of light to act as a sensing medium. It will be appreciated that, by using a light source 30 producing light of a particular frequency or a known range of frequencies, it is possible to use a light sensor 35 that is particularly sensitive to these frequencies thereby further reducing the risk of interference.

The use of an artificial light source 30 also allows the light source 30 to be modulated, that is to say, the light source can be switched on and oft. This is useful because it enables dynamic calibration of the light sensor 35 to take place to compensate for changes in signal output of the light sensor 35 due to variations in temperature.

As shown in Fig.3 the output from the light sensor 35 is connected to an electronic unit 36 which may include one or more microprocessors or electronic logic devices. The electronic unit 36 is in this case connected to two brake lights 7R, 7L which form a sub-system that uses the signal from the light sensor 35 as an activation signal. It will be appreciated that the electronic unit 36 could also be used to control other devices or sub-systems such as for example a cruise control sub-system.

Operation of the system is as follows starting from the piston 1 1 in master cylinder 10 position as shown in Fig.1, the application of an actuation force to the input rod 12 will cause the piston 11 to move to the left. Initially during this period light can be transmitted or travel via the liquid 21 in the reservoir 20 from the light source 30 through the inlet port so as to be sensed by the light sensor 35.

Depending upon the type of light sensor used this will result in either a voltage high signal (e.g. 5 volts) being passed to the electronic unit 36 or a signal of variable voltage based upon the intensity of the light received by the light sensor 35.

The electronic unit 36 continuously monitors the output signal from the light sensor 35 and compares the received signal with a calibrated trigger voltage in the following mariner:-Is Vs greater than X volts? (Test 1) If Yes then inlet port is open.

If No then inlet port is closed.

Where:-Vs is the signal voltage from the light sensor; and X is the calibrated trigger voltage.

It will be appreciated that other tests for signal state could be used and that the invention is not limited to the example given.

If the answer to Test 1 is "YES" then the electronic unit 36 functions to control any other sub-systems in a port open' mode.

When a front face 14 of the piston 11 reaches the position "P' the inlet port 15 is suddenly closed off by the piston 11 and no light can reach the light sensor 35 from the lightsource3o.

At this point the signal from the light sensor 35 will indicate to the electronic unit 36 that the position of piston 11 has reached this position that is to say Test 1 will produce a "NO" output and the electronic unit 36 functions to control any other sub-systems in a port closed' mode.

The electronic unit 36 is therefore arranged to receive the signal from the light sensor and use the signal from the light sensor 35 to determine the closure state of the inlet port 15. It will be appreciated that the inlet port 15 has two closure states open' and closed'.

As the piston 11 moves further to the left from this position to the position shown in Fig.2 the inlet port 15 remains closed by the piston 11 and so the liquid in the hydraulic cylinder 10 and the attached brake system is pressurised thereby actuating the brake calipers 5L, 5R.

It will be appreciated that during this period the inlet port 15 remains closed and no light can reach the light sensor 35 from the light source 30, the light sensor 35 therefore continues to send the same signal to the electronic unit 36 and the status of the signal as interpreted by the electronic unit remains port closed'.

In the example shown, when the status of the signal from the light sensor 35 changes from port open' to port closed' the electronic unit 36 is operable to illuminate the brake lights 71, 7R and disengage a cruise control sub-system (not shown) in exactly the same way as these devices would normally be controlled by a microswitch cooperating with a brake pedal. However, in this case the accuracy of the signal produced by the light sensor is not dependent upon the accuracy of setting or adjusting a switch, it is automatically produced by the action of the piston 1 1 closing off the inlet port 15 and provides a direct indication of the status of the inlet port 15.

In addition to the examples given above, the signal produced by the light sensor 35 can also be used as part of a plausibility check to confirm that the braking system is functioning correctly by using the signal from the light sensor 35 in combination with a measurement of hydraulic pressure in the braking system.

The sensing system described above comprising a light source, a light sensor and a piston that selectively closes a port can therefore be said to function in accordance with the following method. Firstly, a light sensor 35 is located so as to be able to detect whether light is entering the cylinder of the master cylinder 10 through the inlet port 15, secondly the inlet port 15 is illuminated such that light can enter the cylinder through the inlet port 15 when it is not covered by the piston 11 and thirdly a signal from the light sensor 35 indicative of when light is no longer able to enter the cylinder through the inlet port 15 is provided to one or more other devices. The signal produced by the light sensor 35 can then be used to perform other tasks as it is a positive and definitive indication of inlet port closure.

Although the invention has been described above with respect to a brake master cylinder it will be appreciated that it could equally be applied to a clutch master cylinder or to a master cylinder for a dual circuit braking system.

In addition, the invention is also applicable to other types of device in which a piston is moveable in a cylinder to open and close a port and the exact moment of port closing needs to be established Fig.4 for example shows the application of the invention to a hydraulic spool valve having a spool 132 slidingly supported in a cylinder 110. The spool 132 has two pistons lilA and 111B, the right hand one of which is selectively moveable so as to cover a port An artificial light source 130 is mounted close to the port 115 and is used to illuminate the port 115 such that light can enter the cylinder 110 through the port 115 when it is not covered by the piston 111 B. A light sensor 135 is mounted so as to be able to sense when light can enter the cylinder 110 through the port 115. As before when the piston 1118 closes the port 115 the signal from the light sensor reflects this change and this signal can therefore be used as an indication of the point of port closure.

It will be appreciated that the source of light need not be directly attached to the port as shown, a remote light source could be coupled to a position upstream from the port by say a fibre optic cable so as to illuminate the port 115.

The mounting of a light source close to a port as shown in Fig.4 allows the invention to be used for devices not using a liquid as the working medium such as, for example, pneumatic devices because the light does not need to use the working medium as a transfer agent that is to say, the light source can be directly aimed through the port at the light sensor The term light sensor as meant herein means a sensor able to detect any form of light or other Electro-Magnetic radiation and includes low cost optic devices such as photodiodes or phototransistors. The term "light" as meant herein therefore includes Natural light and artificially produced light whether visible or invisible and other forms of Electro-Magnetic radiation.

Therefore in summary, the invention relies on the transmission of light or other EM radiation through the hydraulic medium from the inlet port into the master cylinder. When the port closes, the light is cut off. -10-

If a transparent reservoir is used with a visible light source such as a LED in the reservoir, then information could be provided to an operator, such as flashing the LED in the reservoir to bring attention to the location of the reservoir or warning of a low reservoir liquid level.

Since the light sensor in the master cylinder is inherently tied to the closure of the port, no assembly setting is required and the light sensor is of much lower cost and of much higher reliability than pedal switches due to its solid state nature.

The system is inherently fail safe because, once the inlet port is closed, no light can enter the master cylinder to produce a faulty output. -11 -

Claims

1. A method for sensing the closure of a port by a piston slideably mounted in a cylinder, the method comprising the steps of: using a light source arranged in such a way that light from the light source can enter the cylinder through the port when it is not covered by the piston, locating a sensor so as to be able to detect whether light from the light source is entering the cylinder through the port, and providing a signal from the sensor indicative of whether light is able to enter the cylinder through the port.

2. A method as claimed in claim 1 wherein the cylinder is a hydraulic cylinder and the method further comprises using liquid located upstream from the port to transmit light to the port from the light source.

3. A method as claimed in claim 3 wherein the port is an inlet port connected to a reservoir used to store liquid for the hydraulic cylinder and the method further comprises transmitting light from a light source located in the reservoir to the inlet port.

4. A system for sensing the closure of a port by a piston slideably mounted in a cylinder, wherein the system comprises a light source located in such a way that light from the light source can enter the cylinder through the port when it is not covered by the piston, a light sensor positioned in the cylinder so as to be able to detect whether light is entering the cylinder through the port and an electronic unit connected to the light sensor, the electronic unit being arranged to receive the signal from the sensor and use the signal from the light sensor to determine the closure state of the port.

5. A system as claimed in claim 4 wherein the light source comprises a modulated light source to illuminate the port.

6. A system as claimed in claim 4 or in claim 5 wherein the electronic unit is further operable to control one or more other sub-systems based upon the signal received from the light sensor. -12-

7. A system as claimed in any of claims 4 to 6 wherein the cylinder is a hydraulic cylinder having a piston slideably moveable therein and the port is an inlet port which is connected to a reservoir used to store liquid for the hydraulic cylinder and light is transferred to the inlet port through the liquid stored in the reservoir

8. A system as claimed in claim 7 wherein the light source is located in the reservoir.

9. A system as claimed in claim 7 or claim 8 wherein the hydraulic cylinder is a master cylinder containing liquid to be pressurised by the piston and the master cylinder has an outlet connecting the master cylinder to a circuit to be pressurised by the master cylinder.

10. A motor vehicle having at least one system as claimed in any of claims 4 to 9.

11. A method for sensing the closure of a port by a piston slideably mounted in a cylinder substantially as described herein with reference to the accompanying drawing.

12. A system for sensing the closure of a port by a piston slideably mounted in a cylinder substantially as described herein with reference to the accompanying drawing.

13. A motor vehicle substantially as described herein with reference to the accompanying drawing.