Patent Publication Number: US-2020290585-A1

Title: By-pass of air supply protection for electronic parking brake system and vehicle comprising such system

Description:
The present invention concerns an electronic parking brake system and a vehicle comprising such system. 
     In the automotive industry, the conventionally mechanical parking brake is progressively replaced by electronic parking brake. The control unit of an electronic parking brake requires however electrical energy to function. Accordingly, the failure of the electric power supply can be a problematic event in such electrically controlled brake systems as electric components, such as electric control systems and electrically actuated solenoid valves, can no longer be actuated. The driver may then be stuck inside the vehicle as he has no possibility to immobilize the vehicle. 
     US 2010/0025141 A1, which is probably the closest prior art, discloses an electronic parking brake system according to the preamble of claim  1 . In this disclosure, the control pressure present at the control input of the relay valve can be placed in communication with the air reservoir tank in the event of an unexpected failure of the electric power supply. By repeated actuation of the service brake in the case of a failed electric power supply, the pressure in the reservoir tank drops and implies the venting of the spring store parts of the spring brake cylinders. Thus, the spring actuators are activated and the parking brake is applied. 
     One drawback of this system is that an additional pressure sensor is needed to confine the control chamber of the relay valve when the pressure during normal operation drops below a critical pressure. This arrangement is complicated and costly. 
     EP 0 394 065 A2 discloses a vehicle braking system wherein a first valve is actuated by depression of the vehicle brake pedal in order to modulate a pressurized air supply with braking demand and wherein a second valve is disposed between the first valve and an auxiliary brake. The second valve is actuated in response to failure of the normal vehicle braking system to connect the output of the first valve to the auxiliary brake 
     EP 2 090 481 A2 discloses a parking brake module wherein a trailer control module is controlled by a single-channel-pressure control module or the brake module during malfunction of an electrical brake circuit. The module is controlled by the trailer control module during malfunction of another electrical brake circuit. 
     The aim of the present invention is to propose an electronic parking brake system that remedies the abovementioned drawbacks. 
     To this end, the invention concerns an electronic parking brake system according to claim  1 . 
     Thanks to the invention, there is no need of a pressure sensor to confine the control chamber of the relay valve when the pressure, during normal operation, drops below a critical pressure. Indeed, the control chamber of the relay valve is confined by the check valve itself because the check valve is bypassed only in the event of an electrical failure and/or when the pressure of the air supply falls below a critical threshold. In other words, the check valve is not bypassed in normal operating conditions of the EPB system. This arrangement is simpler and cheaper. 
     Further advantageous features of the electronic parking brake system are defined in claims  2  to  13 . 
     The invention also concerns a vehicle according to claim  14 . 
    
    
     
       The invention will be better understood from reading the following description, given solely by way of two non-limiting examples and with reference to the appended drawings, which are schematic depictions, in which: 
         FIG. 1  is a flow chart representing a first embodiment of an electronic parking brake system in normal working conditions; 
         FIG. 2  is flow chart analog to that of  FIG. 1 , representing the electronic parking brake system in the event of an electrical failure; 
         FIG. 3  is a flow chart analog to that of  FIGS. 1 and 2 , representing the electronic parking brake system in the event of an electrical failure and of low pressure conditions in the air supply; 
         FIG. 4  is flow chart analog to that of  FIG. 1 , representing a second embodiment of an electronic parking brake system in normal working conditions; 
         FIG. 5  is a flow chart analog to that of  FIG. 3 , representing the electronic parking brake system according to the second embodiment in the event of an electrical failure and of low pressure conditions in the air supply; and 
         FIG. 6  represents a vehicle equipped with an electronic parking brake system according to the invention. 
     
    
    
       FIG. 1  represents an electronic parking brake system  2  (or EPB system) of a vehicle V. In the example, and as shown on  FIG. 6 , the vehicle V is a truck comprising a lorry and a trailer. 
     The EPB system  2  comprises at least one, preferably two park brake actuators  10 . 
     In the example, and as know per se, each park brake actuator  10  includes a spring brake cylinder (not represented). The spring brake cylinder includes a pressurized chamber which is vented when the driver requests the application of the parking brake, and which, in turn, leads to the application of a braking effort arising from spring unloading. The spring brake cylinder chamber is pressurized with compressed air when the driver request parking brake release. 
     Advantageously, the driver may electronically command the application and release of the parking brake through a park brake input device (not represented), such as a hand brake lever or an operating switch. Such device is well known per se, that is why it is not described. 
     The EPB system  2  includes an air supply  4 , in particular an air tank, and a check valve  6  connected to the air supply. 
     In this paper, the terms “upstream” and “downstream” shall be interpreted with regards to the flow of compressed air when each park brake actuator  10  is released, i.e. when compressed air is extracted from the air tank  4  to pressurize the spring brake cylinder chamber of the park brake actuator(s)  10 . Accordingly, the air supply  4  is located fully upstream and the park brake actuators  10  are located fully downstream. 
     The check valve  6  is known per se, for example from US 2010/0025141 A1. The function of the check valve  6  is to protect each spring brake cylinder chamber from a pressure drop in the air supply. The check valve  6  is a one-direction valve that lets compressed air through only from the upstream side to the downstream side. This means that the check valve  6  remains open as long as the pressure at the upstream side of the valve  6  is above the pressure at the downstream side of the valve and that the valve  6  closes when the pressure at the upstream side falls under the pressure at the downstream side. For example, if an air leak occurs in the air tank  4 , leading to a pressure drop in the air tank, then the check valve  6  closes and the pressure in the spring brake cylinder(s) is maintained (i.e. does not decrease due to the connection with the air supply). Accordingly, there is no risk of activating the parking brake in case of an accidental pressure drop in the air supply  4 . 
     The EPB system  2  includes an electro-pneumatic control unit  8  and a relay valve  12 . 
     The relay valve  12  is known per se, for example from US 2010/0025141 A1. It comprises a first port  12   a  connected to the check valve  6 , a second port  12   b  connected to the electro-pneumatic control unit  8 , a third port  12   c  connected to the park brake actuator(s)  10  and a fourth port  12   d  which is in communication with the atmosphere. 
       18  denotes the connecting line between the check valve  6  and the relay valve  12 .  22  denotes the connecting line between the electro-pneumatic control unit  8  and the relay valve  12 .  30  denotes the connecting line between the relay valve  12  and the park brake actuator(s). In the example,  30 . 1  and  30 . 2  denote respectively the connecting lines between the relay valve  12  and the two park brake actuators  10 . 
     The electro-pneumatic control unit  8  includes an Electronic Control Unit (ECU)  80  that is electrically powered by a battery  20 . Typically, the battery  20  may be the vehicle battery. The electro-pneumatic control unit  8  includes control means (not represented) for controlling the pressure in the connecting line  22 . Typically, control means may comprise a proportional valve that is electrically piloted by the ECU  80  through the maneuvering of the park brake input device. 
     The relay valve  12  is configured so that the pressure in line  30 , and therefore in lines  30 . 1  and  30 . 2 , is proportional to the pressure in line  22 . Accordingly, a pressure drop in line  22  implies a pressure drop in line  30 , and therefore in lines  30 . 1  and  30 . 2 , leading to the activation of the parking brake. On the contrary, a pressure rise in line  22  leads to a pressure rise in line  30 , and therefore in lines  30 . 1  and  30 . 2 , leading to the parking brake release. It is to be noted that the pressure in line  30  is never greater than the pressure in line  18 . 
     Typically, when the parking brake is activated, the compressed air contained in the spring brake cylinder of each park brake actuator  10  is vented through the fourth port  12   d  of the relay valve  12 , which is opened to the atmosphere. 
     The EPB system  2  also includes an electrically actuated valve  14 , which is controlled by the electro-pneumatic control unit  8  and which includes a first orifice  14   a  connected to a compressed air line  16  extending between the check valve  6  and the air supply  4 .  28  denotes the connecting line between the first orifice  14   a  of the electrically actuated valve  14  and the compressed air line  16 . The first orifice  14   a  then opens upstream of the check valve  6  on the path of compressed air flowing in line  16 . 
     The electrically actuated valve  14  also includes a second orifice  14   b  connected to the compressed air line  18  extending between the check valve  6  and the first port  12   a  of the relay valve  12  and a third orifice  14   c  connected to the electro-pneumatic control unit  8 .  26  denotes the connecting line between the second orifice  14   b  of the electrically actuated valve  14  and the compressed air line  18  and  24  denotes the connecting line between the third orifice  14   c  of the electrically actuated valve  14  and the electro-pneumatic control unit  8 . 
     The compressed air lines  22  and  24  can be connected to each other. In particular, the proportional valve mentioned above may be arranged at the junction between lines  22  and  24 . When the parking brake is released, the pressure in line  22  is a function of the pressure in line  24 , as there is a connection between lines  22  and  24 . In particular, the pressure in line  22  varies proportionally to the pressure on line  24 . However, when the parking brake is applied, the pressure in line  22 , which is close to 0 bar, does not depend on the pressure in line  24 , which can be of 8,5 bar for instance. This means that, when the parking brake is applied, the lines  22  and  24  are no more connected to each other. 
     On  FIGS. 1 to 5 , four small bargraphs represent the level of pressure in the air tank  4 , in the connecting line  24 , in the connecting line  22  and in the spring brake cylinder chamber of each park brake actuator  10 . 
     Preferably, the electrically actuated valve  14  is a 3/2 way valve. This means that the electrically actuated valve  14  is capable of taking up 2 configurations, i.e.  2  positions, and that the electrically actuated valve  14  includes 3 connecting orifices, which are respectively the orifices  14   a  to  14   c . A connecting orifice is an orifice that can be connected with another orifice of the valve  14 , not to be confused with a pilot orifice, which is used to switch the valve configuration and which cannot be connected with another orifice of the valve. 
     In the example, the orifices  14   a  to  14   c  are all connecting orifices. More precisely, orifices  14   a  and  14   b  are inlet orifices that can be selectively connected with orifice  14   c , which is an outlet orifice. Then, the orifice  14   c  is either connected with the orifice  14   a  or with the orifice  14   b . The inlet orifices  14   a  and  14   b  cannot be connected one with the other. 
     Typically, the electrically actuated valve  14  is an electromagnetically actuated valve, comprising a solenoid  140  and an elastic return means  142 , such as a spring. The solenoid  140  is electrically supplied via the electro pneumatic module  8 . 
     In the example, the electrically actuated valve  14  is capable of taking up a first configuration (represented on  FIG. 1 ), wherein the second orifice  14   b  is connected to the third orifice  14   c  and a second configuration (represented on  FIGS. 2 and 3 ), wherein the first orifice  14   a  is connected to the third orifice  14   c . This means that, in the first configuration, the compressed air lines  24  and  26  are connected to each other and that, in the second configuration, the compressed air lines  24  and  28  are connected to each other. 
     Advantageously, the electrically actuated valve  14  remains in the first configuration as long as it is electrically supplied, i.e. as long as the solenoid  140  is electrically supplied. 
       FIG. 1  represents a normal driving conditions mode, wherein electrical power is available and wherein the electrically actuated valve  14  is electrically supplied. In this mode, the solenoid  140  generates a magnetic field that maintains the electrically actuated valve  14  in the first configuration. On  FIG. 1 , the lightning flashes between the battery  20  and the electro-pneumatic control unit  8  and between the electro-pneumatic control unit  8  and the valve  14  indicate that the electrical connections are established (healthy). 
       FIG. 2  represents a failure mode wherein the EPB system  2  can no more be controlled by the park brake input device. Typically, the failure may be an electrical failure, because of which the solenoid  140  can no more be electrically supplied. The failure may also be an internal failure of the EPB itself, as a result of which the solenoid  140  is voluntarily no more electrically powered by ECU  80 . Accordingly, when such failure occurs, the valve  14  cannot be electrically controlled. On  FIG. 2 , the crosses between the battery  20  and the electro-pneumatic control unit  8  and between the electro-pneumatic control unit  8  and the valve  14  indicate that the electrical connections are shut down. 
     In the event of loss of electrical power, the 3/2 way valve  14  is no more electrically controlled but mechanically (spring) controlled. The electrical power loss provokes the change of configuration of the valve  14 : the valve  14  switches from the first configuration ( FIG. 1 ) to the second configuration ( FIG. 2 ). In the second configuration, the compressed air lines  24  and  28  are connected to each other. The lines  16 ,  28  and  24  are then at the same pressure. A pressure drop in line  28  then leads to a pressure drop in line  24  which, in turn, leads to a pressure drop in line  22 . Accordingly, the driver may apply the parking brake by provoking a pressure drop in line  28 , i.e. in the air supply  4 . Advantageously, the driver may cause a pressure drop in the air supply  4  by successively depressing the service brake pedal (not represented) of the vehicle. Indeed, the service brake of the vehicle is purely pneumatic and remains operable even in the event of an electrical failure. When the driver depresses the brake pedal, compressed air is consumed and the pressure in the air tank  4  drops. 
     As shown on  FIG. 3 , when the driver voluntarily consumes compressed air from the air supply  4 , the pressure drop in the air tank  4  leads to a pressure drop in the connecting lines  22  and  24 , and also to a pressure drop in the connecting line  30 . This results in a pressure drop in the spring brake cylinder chamber of each park brake actuator  10 . 
     Accordingly, the pressure in the spring brake cylinder chamber of each park brake actuator  10  becomes not high enough to counteract the force of the spring and there is a braking effort arising from spring unloading: the parking brake is applied, or at least partially applied. Indeed, to be fully applied, the pressure in the spring brake cylinder chamber of each park brake actuator  10  must be close to 0 bar, meaning that the pressure in the air tank  4  must also be close to 0 bar. This means that the driver has to consume the integrality of the compressed air stored in the air tank  4  to fully apply the parking brake. However, in practice, the driver has to depress the brake pedal a number of times before the air tank  4  is completely empty. 
     Therefore, this system  2  is not convenient for parking a vehicle on a downhill, especially when the vehicle is a fully loaded lorry unit, because maximum braking effort is needed in this case to immobilize the vehicle. 
     This problem no more exists in the embodiment of  FIGS. 4 and 5 , which represent the second embodiment of the invention. In the following, only the differences with respect to the first embodiment are depicted for the purpose of conciseness. 
     In the second embodiment, the electrically actuated valve  15  further includes a vent orifice  15   d . The electrically actuated valve  15  then includes four orifices, among which three of them ( 15   b ,  15   c ,  15   d ) are connecting orifices and one of them ( 15   a ) is a pilot orifice. This means that the orifice  15   a  cannot be put in communication with another orifice of the valve  15  and that the only function of the orifice  15   a  is to command the switching of the valve  15  in the event of an electrical failure. 
     The first orifice  15   a  is connected to a compressed air line  16  extending between the check valve  6  and the air supply  4 . The second orifice  15   b  is connected to another compressed air line  18  extending between the check valve  6  and the first port  12   a  of the relay valve  12 . The third orifice  15   c  is connected to the electro-pneumatic control unit  8 . 
     In the first configuration of the valve  15 , there are no differences with respect to the first embodiment. However, in the second configuration, the third orifice  15   c  is connected to the vent orifice  15   d , meaning that the compressed air lines  22  and  24  are vented to the atmosphere. 
     Unlike the first embodiment, when the valve  15  is not electrically supplied, it is designed for switching into the second configuration only when the pressure in the air supply  4  falls below a critical threshold value. Typically, the valve  15  switches into the second configuration when the pressure of the air entering by the orifice  15   a  is not high enough to counteract the force of the spring of valve  15 . The spring then moves from a loaded position to an unloaded position. 
     In other words, the valve  15  switches into the second configuration only when a pressure drop occurs in the air supply  4 . It is then the job of the driver to provoke such pressure drop. Advantageously, the driver may cause a pressure drop in the air supply  4  by successively depressing the service brake pedal (not represented) of the vehicle. When the driver depresses the brake pedal, compressed air is consumed and the pressure in the air tank  4  drops. 
     As long as the pressure in the air supply  4  is above the critical threshold value, the valve  14  remains in the first configuration and the lines  24  and  26  are connected to each other. The lines  18 ,  24  and  26  are then at the same pressure and the check valve  6  keep ensuring his function of protection. In this configuration, the spring brake cylinder chamber of each park brake actuator  10  remains pressurized and the parking brake system  2  is fully released. 
     However, when the pressure in the air supply  4  falls below the critical threshold value, lines  22  and  24  are vented, i.e. connected to the atmosphere through the vent orifice  15   d . As a reminder, the pressure in the spring brake cylinder chamber of each park brake actuator  10  is proportional to the pressure in the compressed air line  22 . Accordingly, this results in a severe pressure drop in the spring brake cylinder chamber of each park brake actuator  10 , leading to a full parking brake activation. Therefore, as soon as the pressure of the air supply  4  is voluntarily decreased below the threshold critical value, the parking brake is fully applied. 
     Alternatively, in the event of an electrical failure, the driver may consume compressed air from the air supply other than by depressing the brake pedal. For example, the driver may have to depress a specific button provided on the park brake input device. 
     The invention is not limited to the described embodiments. The features of the embodiments and not-represented alternative embodiments may be combined to generate new embodiments of the invention.