The present invention relates to a brake actuator for a vehicle, in particular a commercial vehicle, the brake actuator comprising: an actuator housing, and a push rod mounted inside said actuator housing, said push rod being adapted to be coupled to a brake mechanism and to move in a reciprocating manner between a retracted position and an extended position, wherein the movement between the retracted position and the extended position defining a stroke.

Spring brake actuators of the aforementioned type are known from the prior art and are frequently implemented in commercial vehicles to generate brake forces that are applied to vehicle wheels.

An actuator is a device used for braking which consists of spring side and service side - only service side in case of brake chambers. Actuators convert pneumatic pressure into mechanical stroke through linear motion. An end user, in particular a driver of the vehicle, has no direct connection to the stroke of the actuator. For this reason, the stroke of the actuator is usually not known to the end-user. The latter can serve as a characteristic value to be aware of the braking force generated.

Therefore, it was an object of the present invention to suggest a brake actuator that overcomes the disadvantages mentioned above as much as possible. In particular, it was an object to provide a brake actuator, whereby a stroke of the brake actuator can be measured and preferably be displayed it in the driver’s cabin. The invention attains the aforementioned object in a first aspect by suggesting a brake actuator according to claim 1 . In particular, the actuator comprises a sensor device for measuring a stroke position of the push rod of the brake actuator. The sensor device determines a position of the push rod between its retracted position and its extended position and outputs an echo output signal, which can be transmitted to a processor unit, preferably a micro controller, to estimate the stroke position of the brake actuator. A stroke position is a position of the push rod between a retracted position and an extended position. The stroke may be measured from an initial position, i.e. in fully retracted position, to an end position, i.e. in fully extended position. The stroke position is a function of an according brake force. The proposed brake actuators with sensors for stroke measurement are able to track the linear motion (stroke) of the push rod and thus determine a position within the motion, or stroke, without affecting the primary function of the actuators.

In one embodiment said brake actuator is a spring brake actuator or double diaphragm spring brake actuator.

In a preferred embodiment, said push rod comprises a piston plate and a piston rod, and the sensor device measures a position of said piston plate within its movement, preferably the sensor device measures a distance to the piston plate relative to the position of the sensor device. The piston plate preferably has a large flat surface. This moving element of the push rod is accordingly well suited for performing distance measurements on it.

In a further preferred embodiment, the sensor device comprises a sensor head, said sensor head comprises a transmitter and a receiver. The transmitter emits sonic wave at the speed of sound when a trig pin of the sensor device is set to high for at least 10 ps. The sonic waves hit the piston plate and are reflected by it and received by the receiver of the sensor. The reflected sonic waves are received by an echo pin. The echo pin then outputs the time that the sonic waves traveled. ln a further preferred embodiment, the sensor head is mounted within said actuator housing, preferably on an actuator housing wall or at least partially inside said actuator housing wall. The actuator housing provides a stable base for the sensor device. The sensor device, preferably the sensor head, may be located on the housing directly or on a bracket at a distance to the housing. Preferably, the sensor device or the sensor head is mounted on an actuator housing wall that is oriented essentially perpendicular to the stroke direction. The actuator housing comprises a hole configured to receive a cable routing of the sensor device or external components configured to be connected to the sensor device.

In a further preferred embodiment, the push rod comprises a reflection surface, and the sensor device is positioned inside the actuator housing such that the transmitter faces the reflection surface, and the receiver receives a wave after being reflected off the reflection surface. Preferably, the transmitter is oriented so that the wave is emitted at a transmission angle in the range 0° - 30°, preferably at an angle in the range 5° - 10°, relative to the center axis of the push rod. The wave is a sonic, light or radio wave. The wave can be pulsed or emitted continuously.

In a further preferred embodiment, the sensor device comprises an ultrasonic sensor. Ultrasonic sensors work by emitting cyclically a short, high-frequency sonic waves by a transmitter, which travels through air at the speed of sound. If the ultrasonic wave hits an object, it is reflected. The sensor device, e.g. the receiver of the sensor head, detects the resulting echo and the distance to the object is calculated from the time interval between the transmission and reception of the sonic wave. The dimension of a proposed ultrasonic sensor is about 40 x 20 x 10 mm.

In a further preferred embodiment, said sensor device is configured to generate a sensor signal, preferably an echo output signal, which is characteristic for a transit time of a sonic wave from said transmitter to said receiver. ln a further preferred embodiment, said sensor device is configured to transmit said sensor signal to a processor unit or said sensor device comprises a processor unit, wherein said processor unit is configured to determine the stroke position of the push rod based on said sensor signal from the sensor device. Preferably, a microprocessor code reads the transit time of a sonic wave from the sensor device. The following formula can be used to calculate a distance from the sensor device to the push rod, preferably the piston plate of the push rod:

The distance can thus be used to determine a stroke position of the push rod.

In a further preferred embodiment, said processor unit is configured to transmit a coded signal to a display to graphically show the stroke position on the display. For a driver of a vehicle, this information can be useful information to get a better understanding of braking forces applied by him.

In a further preferred embodiment, the sensor device comprises a power supply and a data output interface, wherein preferably, the power supply and the data output interface are arranged outside said actuator housing. In one embodiment, the power supply and/ or the data output interface are part of the sensor device. In other embodiments, the power supply and/ or the data output interface are external components independent of the sensor device.

In a further preferred embodiment, the data output interface is configured to be connected with one or more external components, wherein the external components are selected from a group consisting of a processor, a data storage, a display. The external components may be an electronic control unit, a BUS system, a micro controller, an analog circuit. In one embodiment, the external components are part of the sensor. In other embodiments, the external components are independent components. The external components are interconnected via a BUS system. When connected data output interface provides signal communication between the sensor device and the external components.

In a further preferred embodiment, said brake actuator comprises a pressure chamber located in said actuator housing, wherein said pressure chamber comprises a variable volume that is configured to move said push rod from its retracted position towards its extended position. This pneumatic energy is converted into mechanical energy by moving the push rod. Thus, a braking force can be generated. This creates a relationship between a stroke position and an according braking force. A return spring is disposed adjacent said push rod inside said actuator housing, said return spring is configured to push against said push rod in its retracted position.

In a further preferred embodiment, a membrane separates said pressure chamber from an unpressurized chamber, wherein the sensor device and said push rod are arranged in said unpressurized chamber. The piston plate abuts against the membrane.

The invention has herein above been described with reference to a brake actuator in a first aspect of the invention. In a second aspect, however, the invention relates to a brake system of a vehicle, in particular commercial vehicle. The brake system comprising a brake actuator according to one of the previously mentioned preferred embodiments and a brake mechanism operatively coupled to the brake actuator.

In a further preferred embodiment the brake system comprises external components, wherein the external components are selected from a group consisting of a processor, a data storage, a display. The external components may be an electronic control unit, a BUS system, a micro controller, an analog circuit. The electronic control unit is operatively coupled to the brake actuator. The display is in communication with said electronic control unit. ln a third aspect, the invention relates to a method of monitoring a braking force of a brake actuator, preferably a brake actuator according to one of one of the previously mentioned preferred embodiments. The method comprising the steps: generating a brake command by an operator, preferably a brake command with a predetermined braking force, transmitting the brake command to the brake actuator, generating a braking force as a function of a brake command, and monitoring a stroke position of a push rod of the brake actuator with a sensor device, wherein the braking force is a function of a stroke position of the push rod.

In preferred embodiment, the method further comprises the steps: converting said stroke position into a coded signal, transmitting said coded signal to a display, visualizing said coded signal on the display, preferably as braking force.

The advantages and preferred embodiments of the brake actuator of the first aspect are at the same time also advantages and preferred embodiments of the brake system of the second aspect and the method of the third aspect. In order to avoid unnecessary repetition, reference is made to the description herein above.

For a more complete understanding of the invention, the invention will now be described in more detail with reference to the accompanying drawing. The detailed description will illustrate and describe or is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the scope of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and disclaimed hereinafter. Further, the features described in the description, the drawing and the claims disclosing the invention may be essential for the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The word “comprising” does not exclude other elements or steps. The wording “a” or “an” does not exclude a plurality.

In brief, the figures to which reference will be to made show the following:

Fig. 1 shows a brake actuator comprising an integrated sensor device according to a preferred embodiment,

Fig. 2 shows the brake actuator according to fig. 1 ,

Fig. 3 shows a flow chart of monitoring a braking force of a brake actuator.

Figs. 1 and 2 show a brake actuator 100 for a vehicle (not shown). The brake actuator 100 comprises an actuator housing 1 10, a push rod 120 and a sensor device 130.

The brake actuator 100 further comprises membrane 140 and a return spring 150.

The actuator housing 110 comprises an actuator housing wall 1 12, a pressure chamber 1 14 and an unpressurized chamber 116. The pressure chamber 1 14 and the unpressurized chamber 1 16 are located within the actuator housing 110. The actuator housing wall 1 12 surrounds the pressure chamber 1 14 and the unpressurized chamber 1 16.

The push rod 120 is adapted to be coupled to a brake mechanism and to move in a reciprocating manner between a retracted position S1 and an extended position S2 (not shown), wherein the movement between the retracted position S1 and the extended position S2 defining a stroke S. The retracted position S1 is shown in figures 1 and 2. The stroke positions S1 , S2 are exemplarily shown by the arrow Sx in Fig. 2.

The push rod 120 has a piston plate 122 and a piston rod 124. The push rod

120 is mounted inside the actuator housing 1 10. The push rod 120 is arranged inside the unpressurized chamber 116. In this embodiment, the piston plate 122 further comprises a reflection surface 126.

The pressure chamber 114 comprises a variable volume that is configured to move the push rod 120 from its retracted position S1 towards its extended position S2.

The membrane 140 separates the pressure chamber 1 14 from the unpressurized chamber 116. For this purpose, the flexible membrane 140 is in abutment with a moving part of the push rod 120, i.e. the piston plate 122.

The sensor device 130 comprises a sensor head 132. The sensor head 132 has a transmitter 134 and a receiver 136.

The sensor head 132 is mounted within the actuator housing 1 10. In this embodiment, the sensor head 132 is mounted on an actuator housing wall 112 or at least partially inside the actuator housing wall 112, for example within a recess in the actuator housing wall 112. The sensor head 132 is arranged inside the unpressurized chamber 116.

Fig. 2 shows a preferred embodiment of the sensor device 130, wherein the sensor device 130 comprises an ultrasonic sensor 130’.

The sensor device 130 is configured to measure a stroke position Sx of the push rod 120 of the brake actuator 100. For this purpose, sensor device 130 measures a position of the piston plate 122 within its movement. In this embodiment, the sensor device 130 measures a distance to the piston plate 122 relative to the position of the sensor device 130.

Fig. 2 shows an arrow indicating the stroke position Sx, wherein the piston plate 122 of the brake actuator 100 shown in Fig 2 is in the retracted position S1 . When the piston plate 122 moves from the retracted position S1 in the direction of the arrow Sx a braking force is generated by the brake actuator 100. The piston plate 122 is arranged in the extended position S2 when the piston plate 122 is at the level of S2.

The sensor device 130 is configured to generate a sensor signal, preferably an echo output signal, which is characteristic for a transit time of a sonic wave W from the transmitter 134 to the receiver 136.

The sensor device 130 is positioned inside the actuator housing 110 such that the transmitter 134 faces the reflection surface 126, and the receiver 136 receives the wave W after being reflected off the reflection surface 126.

Fig. 3 shows a flow chart of monitoring a braking force of a brake actuator 100.

The ultrasonic sensor 130’ is placed inside the brake actuator 100. The ultrasonic sensor 130’ is transmitting a signal, preferably a sonic wave W, by ultrasonic sensors 130’ transmitter 134 to a target. In this embodiment, the target is the piston plate 122. The piston plate 122 is reflecting the ultrasonic wave W by its reflecting surface 126 and thereby sending the signal to the receiver 136 of the ultrasonic sensor 130’.

The sensor device 130 transmits the signal, preferably the echo output signal, via an analog circuit 160 to a processor unit 170. In this embodiment, the processor unit 170 is a micro controller. The processor unit 170 is configured to determine the stroke position Sx of the push rod 120 based on the sensor signal from the sensor device 130.

The processor unit 170 transmits a coded signal to a display 180 to graphically show the stroke position Sx on the display 180. The display 180 is arranged in the vehicle, such that a driver of the vehicle can watch it (not shown).

The sensor device 130 further comprises a power interface unit 190. The power interface unit 190 is arranged outside the actuator housing 110. The power interface unit 190 is connected to the micro controller.

A brake system of a vehicle comprises the brake actuator 100 and a brake mechanism operatively coupled to the brake actuator 100.

A method of monitoring a braking force of the brake actuator 100 is then performed by the steps:

An operator is generating a brake command, preferably a brake command with a predetermined braking force (not shown). The brake command is then transmitted to the brake actuator 100.

By means of a pressure build-up in the pressure chamber 114, for example, a pneumatic force is generated that moves the membrane 140 and thus the push rod 120 in another stroke positon Sx. This stroke S is transferred to a brake mechanism by coupling the push rod 120 to the same.

Thereby a braking force is generated a as a function of the brake command.

The sensor device 130 monitors the stroke position Sx of a push rod 120 of the brake actuator 100, wherein the braking force is a function of a stroke position Sx of the push rod 120.

The stroke position Sx is converted into a coded signal by the processor unit 170. The processor unit 170 transmits the coded signal to the display 180. The display 180 visualizes the coded signal on the display 180, preferably as braking force. List of references (part of specification)

100 brake actuator

110 actuator housing

112 actuator housing wall

114 pressure chamber

116 unpressurized chamber

120 push rod

122 piston plate

124 piston rod

126 reflection surface

130 sensor device

130’ ultrasonic sensor

132 sensor head

134 transmitter

136 receiver

140 membrane

150 return spring

160 analog circuit.

170 processor unit

180 display

190 power interface unit

S stroke

51 retracted position

52 extended positon

Sx stroke position

W sonic wave