Patent Publication Number: US-11649773-B2

Title: Control device and method for controlling a compression release brake arrangement for an engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage Patent Application (filed under 35 § U.S.C. 371) of PCT/SE2020/050597, filed Jun. 10, 2020 of the same title, which, in turn claims priority to Swedish Patent Application No. 1950884-5 filed Jul. 11, 2019 of the same title; the contents of each of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present disclosure relates in general to a method for controlling a compression release brake arrangement for an engine. The present disclosure further relates in general to a control device configured to control a compression release brake arrangement for an engine. The present disclosure further relates in general to a computer program and a computer-readable medium. Moreover, the present disclosure relates in general to a vehicle comprising an engine and a compression release brake arrangement associated with the engine. 
     BACKGROUND OF THE INVENTION 
     A vehicle may comprise one or more auxiliary brakes. One example of an auxiliary brake is a compression release brake, sometimes also referred to as a Jacobs brake or a Jake brake. Compression release braking is based on opening one or more exhaust valves of an engine after the compression stroke so as to release compressed gas from the cylinders. Thereby, the energy stored in the compressed gases during the expansion stroke will not be returned to the crankshaft of the engine on the subsequent expansion stroke. This in turn results in a braking torque of the crankshaft of the engine, and consequently slowing down of the vehicle. 
     A compression release brake arrangement may be formed by a hydraulic system using for example engine oil as the hydraulic fluid. The compression release brake arrangement may typically comprise an exhaust valve actuator assembly configured to perform compression release braking of one or more cylinders of the engine when subjected to a hydraulic pressure above a threshold value. The compression release brake arrangement may further comprise a hydraulic arrangement comprising an actuator valve and a pump. The pump is typically driven by the engine of the vehicle and is thus dependent of the operation of the engine. The pump is typically configured to provide a hydraulic pressure, when the engine is running, which is above the above-mentioned threshold value. The actuator valve is configured to control the activation/deactivation of the exhaust valve actuator assembly. In an open state of the actuator valve, hydraulic fluid may be transferred to the exhaust valve actuator assembly at a pressure above the threshold value. When the actuator valve is closed, the hydraulic pressure will be reduced to a value below the threshold value, thus deactivating the exhaust valve actuator assembly and thereby terminating compression release braking. 
     The time it takes to activate compression release braking comprises a few delays, such delays comprising pure software delays, actuator valve activation delays, as well as time for filling the compression release braking arrangement with hydraulic fluid. The reason for the delay associated with the time for filling is that hydraulic fluid may leak out from various locations in a compression release brake arrangement. This in turn creates a delay in activation of compression release braking when the exhaust valve actuator assembly has been inactive for a longer period of time. Examples of such situations include, but is not limited to, when the vehicle has been at standstill during the night/weekend or during long driving cycles without usage of compression release braking. The above mentioned delays are added up to a total delay time for activation of compression release braking. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to enable a reduction of the time it takes to activate compression release braking upon a request for compression release braking. 
     The object is achieved by means of the subject-matter in accordance with the appended independent claims. 
     In accordance with the present disclosure, a method for controlling a compression release brake arrangement for an engine is provided. The method is performed by a control device. The compression release brake arrangement comprises an exhaust valve actuator assembly configured to, when activated, perform compression release braking of at least a first cylinder of the engine. The compression release brake arrangement further comprises a conduit. The conduit is fluidly connected to the exhaust valve actuator assembly. The conduit comprises a first actuator valve and a second actuator valve. The second actuator valve is arranged in parallel to the first actuator valve. The compression release brake arrangement further comprises at least one pump configured to supply hydraulic fluid via the conduit to the exhaust valve actuator assembly. The method comprises, in advance of activation of the exhaust valve actuator assembly, controlling the first actuator valve and the second actuator valve so as to achieve a first state in which one of the first actuator valve and the second actuator valve is in an open state whereas the other one of the first and the second actuator valve is in a closed state. 
     By means of controlling the first actuator valve and the second actuator valve so as to achieve the first state, hydraulic fluid will be allowed to flow into the arrangement so as to fill the conduit. Thereby, the delay in the activation of the compression release brake action after a request for compression release braking has been issued may be considerably reduced since the delay caused by the need to fill the arrangement with hydraulic fluid before the pressure can be increased has been minimized. At the same time, the hydraulic pressure in the conduit will be below a pressure which may risk activation the exhaust valve actuator assembly. Thereby, the risk of unintentional activation of compression release braking is minimized. This in turn minimizes the risk for disturbances in the operation of the vehicle. Furthermore, it avoids the risk for damages to the constituent components of the vehicle that may result from inappropriate activation of compression release braking. 
     The method may further comprise, after controlling the first actuator valve and the second actuator valve so as to achieve the first state, controlling the first actuator valve and the second actuator valve so as to achieve a second state in which both the first actuator valve and the second actuator valve are in a closed state. Thereby, it can be avoided that hydraulic fluid is continuously pumped into the entire conduit of the compression release brake arrangement. Furthermore, the risk for increasing the pressure above a threshold value which may risk unintentional activation of the exhaust valve actuator assembly may be minimized. Moreover, the power consumption for operation of the actuator valves may be minimized by allowing both the actuator valves to be in a closed state, when possible. 
     The step of controlling the first actuator valve and the second actuator valve so as to achieve the first state may be performed at predetermined intervals. Thereby, it is possible to ensure that the conduit may be sufficiently refilled to compensate for leakage of hydraulic fluid during operation of the engine. This in turn reduces the activation time for compression release braking when a request therefore has been issued. 
     The step of controlling the first actuator valve and the second actuator valve to the first state may be performed in response to information indicating that start-up of the engine has occurred. If the engine has been shut-off for a period of time, for example as a result of the vehicle being as standstill during the night/weekend, hydraulic fluid has likely leaked out from the conduit. This implies that the activation time for the compression release brake is long as a result of having to fill the conduit until the pressure can be increased to the threshold value at which the exhaust valve actuator assembly can be activated. By controlling the first and second actuator valves to the first state upon information that the engine has been started, the conduit is allowed to be pre-filled such that the time to pressurise the hydraulic fluid in the conduit may be reduced. 
     The step of controlling the first actuator valve and the second actuator valve to the first state may be performed in response to information from a look-ahead system indicating an expected future desire to use compression release braking on the engine. Thereby, it can be ensured that the compression release brake arrangement is prefilled with hydraulic fluid when the compression release brake should be activated. Thus, activation time for compression release braking may be reduced without significant increase of parasitic hydraulic fluid flow losses. 
     The present disclosure further relates to a computer program, wherein said computer program comprises program code for causing a control device to perform the method described above. 
     The present disclosure further relates to a computer-readable medium comprising instructions, which when executed by a control device, cause the control device to perform the method as described above. 
     In accordance with the present disclosure, a control device configured to control a compression release brake arrangement for an engine is provided. The compression release brake arrangement comprises an exhaust valve actuator assembly configured to, when activated, perform compression release braking of at least a first cylinder of the engine. The compression release brake arrangement further comprises a conduit. The conduit is fluidly connected to the exhaust valve actuator assembly. The conduit comprises a first actuator valve and a second actuator valve. The second actuator valve is arranged in parallel to the first actuator valve. The compression release brake arrangement further comprises at least one pump configured to supply hydraulic fluid via the conduit to the exhaust valve actuator assembly. The control device is configured to, in advance of an activation of the exhaust valve actuator assembly, control the first actuator valve and the second actuator valve so as to achieve a first state in which one of the first actuator valve and the second actuator valve is in an open state whereas the other one of the first and the second actuator valve is in a closed state. 
     The control device provides the same advantages as disclosed above with regard to the corresponding method for controlling a compression release brake arrangement for an engine. 
     The control device may further be configured to, after controlling the first actuator valve and the second actuator valve so as to achieve the first state, control the first actuator valve and the second actuator valve so as to achieve a second state in which both the first actuator valve and the second actuator valve are in a closed state. 
     The control device may further be configured to control the first actuator valve and the second actuator valve so as to achieve the first state at predetermined intervals when the exhaust valve actuator assembly is not activated. 
     Furthermore, the control device may be configured to control the first actuator valve and the second actuator valve to the first state in response to information indicating that start-up of the engine has occurred. 
     Moreover, the control device may be configured to control the first actuator valve and the second actuator valve to the first state in response to information from a look-ahead system indicating an expected future desire to use compression release braking on the engine. 
     The present disclosure also relates to a vehicle comprising an engine and a compression release brake arrangement associated with the engine. The vehicle comprises a control device configured to control a compression release brake arrangement as described above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    schematically illustrates a side view of a vehicle according to one example; 
         FIG.  2    schematically illustrates a compression release brake arrangement according to one exemplifying embodiment; 
         FIG.  3    represents a flowchart schematically illustrating a method for controlling a compression release brake arrangement according to an exemplifying embodiment; 
         FIG.  4    schematically illustrates a device that may constitute, comprise or be a part of a control device configured to control a compression release brake arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will be described in more detail below with reference to exemplifying embodiments and the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and/or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof. 
     When the terms “upstream” and “downstream” are used herein, they shall be considered in relation to the direction of flow of hydraulic fluid when the compression release brake arrangement is activated. In other words, they are used in reference to the flow direction trough the arrangement during compression release braking. 
     The present disclosure is directed to a method for control of a compression release brake arrangement associated with an engine, more specifically an engine of a vehicle. The method is performed by a control device. The compression release brake arrangement comprises an exhaust valve actuator assembly configured to, when activated, perform compression release braking of one or more cylinders of the engine. The compression release brake arrangement further comprises a conduit. The conduit is fluidly connected to the exhaust valve actuator assembly. The conduit comprises a first actuator valve and a second actuator valve. The first and second actuator valves may be configured to reduce the hydraulic pressure downstream of the respective actuator valves when in a closed state. The second actuator valve is arranged in parallel to the first actuator valve. The compression release brake arrangement further comprises at least one pump configured to supply hydraulic fluid via the conduit to the exhaust valve actuator assembly. 
     The method for controlling a compression release brake arrangement in accordance with the present disclosure comprises, in advance of activation of the exhaust valve actuator assembly, controlling the first actuator valve and the second actuator valve so as to achieve a first state. In said first state, one of the first actuator valve and the second actuator valve is in an open state whereas the other one of the first and the second actuator valve is in a closed state. In the present disclosure, “in advance of activation of the exhaust valve actuator assembly” shall be considered to mean at a point in time where compression release braking of the engine is not performed. It may be just before compression release braking of the engine is initiated or intended, or at any point in time at which there is no pending request for compression release braking. A request for compression release braking of the vehicle may be initiated by a driver of the vehicle, or by any control arrangement of the vehicle (for example a cruise control or the like). 
     The method for controlling a compression release brake arrangement according to the present disclosure may for example be initiated at any point in time at which it may be expected that hydraulic fluid at least partly has been leaked out from the conduit. This could typically be after a certain period of time after an active compression release brake action. For example, if the vehicle has not been operated for a period of time it is likely that hydraulic fluid has been leaked out of the conduit of the compression release braking arrangement. Furthermore, hydraulic fluid could also have leaked out of the conduit when the vehicle has been driven for a longer period of time without compression release braking. 
     The method may be initiated based on information indicating that start-up of the engine has occurred. In other words, the step of controlling the first actuator valve and the second actuator valve to the first state may be performed in response to information indicating that start-up of the engine has occurred. 
     The method may additionally, or alternatively, be initiated based on information relating to an expected future desire for compression release braking, such as information from a look-ahead system indicating an expected future desire to use compression release braking. The look-ahead system may be any previously known look-ahead system, such as a global positioning system in combination with map data, a camera in combination with image analysis, or the like. Information relating to an expected future desired for compression release braking may also be received from other sources, such as a vehicle-to-vehicle (V2V) communication system or any other vehicle-to-everything (V2X) communication system. 
     The method may further comprise, after controlling the first actuator valve and the second actuator valve so as to achieve the first state, controlling the first actuator valve and the second actuator valve so as to achieve a second state. In the second state, both the first actuator valve and the second actuator valve are in a closed state. By means of controlling the first and second actuator valves so as to achieve the second state hydraulic fluid will no longer be transferred to the conduit downstream of the actuator valves. The second state may be advantageous for example when there is no longer a need for further filling of the conduit. By controlling the first and second actuator valves so as to achieve the second state, the power consumption of the actuator valves may be reduced. 
     Furthermore, the risk of unintentionally increasing the pressure in the conduit to a level at which the exhaust valve actuator assembly may be activated may be minimized. 
     The step of controlling the first actuator valve and the second actuator valve so as to achieve the first state may be performed at predetermined intervals as long as there is no pending request for compression release braking. In other words, it may be performed continuously with a predetermined frequency. Each step of controlling the first and second actuator valves so as to achieve the first state may be alternated with steps of controlling the first and second actuator valves so as to achieve the second state. 
     According to one example, the method may comprise controlling the first actuator valve to an open state and the second actuator valve to a closed state, and thereafter controlling the first actuator to a closed state and the first actuator valve to an open state. In other words, which one of the first and second actuator valves are in the open state may be alternated. Thereby, there is less risk for unintentional effects if one of the actuator valves would be malfunctioning. Furthermore, it could thereby be possible to determine if one of the actuator valves are not operating as intended by usage of for example information from one or more sensors configured to determine hydraulic pressure in the conduit. 
     The method for controlling a compression release brake arrangement in accordance with the present disclosure is performed by a control device configured therefore. The control device is configured to, in advance of an activation of the exhaust valve actuator assembly, control the first actuator valve and the second actuator valve so as to achieve a first state in which one of the first actuator valve and the second actuator valve is in an open state whereas the other one of the first and the second actuator valve is in a closed state. The control device may further be configured to perform any one of the steps of the method for controlling a compression release brake arrangement as disclosed herein. The control device may also be configured to control the compression release brake arrangement so that a compression release braking action is performed, if desired. This may be achieved by controlling the first actuator valve and the second actuator valve to a third state in which both the first actuator valve and the second actuator valve are in an open state. 
     The control device may comprise one or more control units. In case of the control device comprising a plurality of control units, each control unit may be configured to control a certain function or a certain function may be divided between more than one control units. 
     The performance of the method for controlling a compression release brake arrangement as disclosed herein may be governed by programmed instructions. These programmed instructions typically take the form of a computer program which, when executed in or by a control device, causes the control device to effect desired forms of control action. Such instructions may typically be stored on a computer-readable medium. 
       FIG.  1    schematically illustrates a side view of an example of a vehicle  1 . The vehicle  1  comprises a powertrain  3  comprising an internal combustion engine  2  and a gearbox  4 . A clutch (not shown) may be arranged between the internal combustion engine  2  and the gearbox  4 . The gearbox  4  is connected to the driving wheels  5  of the vehicle  1  via an output shaft  6  of the gearbox  4 . The vehicle may further comprise a compression release brake arrangement  10  associated with the internal combustion engine  2 . The compression release brake arrangement  10  is configured to allow compression release braking. 
     The vehicle  1  may be, but is not limited to, a heavy vehicle, e.g. a truck or a bus. Furthermore, the vehicle may be a hybrid vehicle comprising an electric machine (not shown) in addition to the internal combustion engine  2 . 
       FIG.  2    schematically illustrates a compression release brake arrangement  10  according to one exemplifying embodiment. The compression release brake arrangement  10  is configured to selectively perform compression release braking of an engine, such as the internal combustion engine  2  of the vehicle  1  illustrated in  FIG.  1   . 
     The compression release brake arrangement  10  comprises an exhaust valve actuator assembly  12  configured to, when activated, perform compression release braking of at least a first cylinder  2   a  of the engine. In  FIG.  2   , the first cylinder  2   a  is schematically illustrated as a dotted box. The exhaust valve actuator assembly  12  may be connected to any one of the cylinders of the engine. The compression release brake arrangement  10  further comprises a conduit  14  fluidly connecting a reservoir  22  for hydraulic fluid with the exhaust valve actuator assembly  12 . The conduit  14  is thus arranged to allow flow of hydraulic fluid from the reservoir  22  to the exhaust valve actuator assembly  12  when compression release braking is to be performed. The conduit  14  is further configured to allow flow in the reverse direction, i.e. from the exhaust valve actuator assembly  12  towards the reservoir  12 , when there is no need for compression release braking. The compression release brake arrangement  10  further comprises a pump  20  configured to supply hydraulic fluid via the conduit  14  to the exhaust valve actuator assembly  12  at a desired hydraulic pressure. 
     In  FIG.  2   , only one exhaust valve actuator assembly  12  is illustrated. It should however be noted that the compression release brake arrangement  10  may comprise a plurality of exhaust valve actuator assemblies  12 , each such exhaust valve actuator assembly being associated with a respective cylinder of the engine. Alternatively, the exhaust valve actuator assembly  12  may be associated with a plurality of the cylinders of the engine. Furthermore, in case of a cylinder of the engine comprising more than one exhaust valve, a first exhaust valve actuator assembly  12  may be associated with a first exhaust valve of the cylinder. In such a case, a second exhaust valve actuator assembly may optionally be associated with a second exhaust valve of the cylinder. 
     The exhaust valve actuator assembly  12  is configured to be activated when subjected to a fluid pressure above a pre-determined threshold value, and deactivated when subjected to a fluid pressure below the predetermined threshold value, as will be described in more detail below. 
     The exhaust valve actuator assembly  12  comprises a compression release brake valve  26  and an exhaust valve actuator  28 . The compression release brake valve  26  is fluidly connected to the conduit  14 . The exhaust valve actuator  28  comprises a portion of a camshaft  30 , which in turn comprises at least one cam lobe  31 . The camshaft  30  is configured to rotate upon rotation of a crankshaft of the engine. The exhaust valve actuator  28  further comprises a hydraulic component  32  comprising a fluid chamber  33 . 
     The compression release brake valve  26  may be configured to assume a first open state when the hydraulic pressure in the conduit  14  is above a predetermined threshold value. The compression release brake valve  26  may further be configured to assume a second closed state when the hydraulic pressure in the conduit  14  is below the predetermined threshold value. When the compression release brake valve  26  is in an open state, it allows transport of hydraulic fluid into the fluid chamber  33 . Thus, the fluid chamber  33  is thereby filled with hydraulic fluid when the compression release brake valve is in the first open state. Furthermore, when the compression release brake valve is in the first open state, the compression release brake valve also hinders transport of hydraulic fluid out of the fluid chamber  33 . As a result thereof, when the cam lobe  31  abuts against the hydraulic component  32 , an exhaust valve  34  of the engine is opened. This because the motion of the cam lobe  31  can be transferred to an opening motion of the exhaust valve  34 . The camshaft  30  and the cam lobe  31  are arranged such that the opening of the exhaust valve  34  occurs towards the end of a compression stroke of the first cylinder  2   a . As a result, gases compressed during the compression stroke are released from the first cylinder  2   a . Thereby, compression release braking is provided. 
     The conduit  14  may be described as comprising a first conduit second  14   a , a second conduit section  14   b , a third conduit section  14   c  and a fourth conduit section  14   d . The first and second conduit sections  14   a ,  14   b  are arranged in parallel to each other, and thus allow parallel flow of hydraulic fluid in a part of the conduit  14 . The first and second conduit sections  14   a  and  14   b  of the conduit  14  are combined into the third conduit section  14   c  upstream of the exhaust valve actuator assembly  12 . The fourth conduit section  14   d  is arranged upstream of the first and second conduit sections  14   a ,  14   b , such that the fourth conduit section  14   d  is divided into the first and second conduit sections  14   a ,  14   b  upstream of the exhaust valve actuator assembly  12 . The first conduit section  14   a  thus connects the fourth conduit section  14   d  with the third conduit section  14   c . Furthermore, also the second conduit section  14   b  thus connects the fourth conduit section  14   d  with the third conduit section  14   c . The fourth conduit section  14   d  may be connected to the reservoir  22 . Furthermore, the pump  20  may be arranged in the fourth conduit section  14   d.    
     The compression release brake arrangement further comprises a first valve actuator  16  and a second valve actuator  18  arranged in the conduit  14 . The first valve actuator  16  and the second valve actuator  18  may be arranged downstream of the pump. Furthermore, the first and second valve actuators  16 ,  18  are arranged upstream of the exhaust valve actuator assembly  12 . Moreover, the second valve actuator  18  is arranged in parallel with the first valve actuator  16 . In other words, the first and second valve actuators  16 ,  18  are arranged in the respective first and second conduit sections  14   a ,  14   b  of the conduit  14 . The first actuator valve  16  and the second actuator valve  18  are configured to control flow of hydraulic fluid in the conduit  14  and thus control the operation of the exhaust valve actuator assembly  12 . The first and second actuator valves  16 ,  18  may each be a 3-2 solenoid valve. 
     The pressure supplied by the pump  20  may be above the above the predetermined threshold value for opening the compression release brake valve  26  when the engine is running. The first and second actuator valves  16 ,  18  are arranged to open/close a respective fluid connection between the fourth conduit section  14   d  and the third conduit section  14   c , i.e. through the first conduit section  14   a  or second conduit section  14   b , respectively. 
     When the first actuator valve  16  and the second actuator valve  18  are both in an open state, the exhaust valve actuator assembly  12  may be activated. This is due to the exhaust valve actuator assembly  12  being subjected to a hydraulic pressure supplied by the pump  20  which pressure is above the predetermined threshold value. However, when at least one of the first actuator valve  16  and the second actuator valve  18  are in a closed state, the exhaust valve actuator assembly  12  is in a deactivated state. Thus, the purpose of arranging the first and second actuator valves  16 ,  18  in parallel is to enable deactivation of the exhaust valve actuator assembly  12  by closing only one of the first and second actuator valves  16 ,  18 . In other words, the purpose of having two actuator valves is to increase the safety of the compression release brake arrangement  10  by allowing termination of compression release braking by closing only one of the actuator valves if the other one of the actuator valves is not functioning properly. Thus, although it is not necessary to have two actuator valves for the purpose of performing compression release braking by means of a compression release brake arrangement, the presence of two actuator valves  16 ,  18  improves the operation and safety of the compression release brake arrangement. 
     More specifically, the first actuator valve  16  and the second actuator valve  18  are each configured so as to enable reducing the hydraulic pressure in the conduit  14  downstream of the respective actuator valve. This may be achieved by a respective pressure reducer  16   a ,  18   a . The pressure reducers  16   a ,  18   a  are configured to open a connection between the conduit upstream of the first and second actuator valves, i.e. third conduit section  14   c , and a portion of the compression release brake arrangement having a lower pressure, such as the reservoir  22  as shown in  FIG.  2   . Thereby, the exhaust valve actuator assembly  12  will cancel compression release braking when one of, or both, the first and second actuator valves  16 ,  18  are closed. 
     The compression release brake arrangement  10  may, if desired, comprise further actuator valves in addition to the first and second actuator valves  16 ,  18 . For example, the first conduit section  14   a  and/or the second conduit section  14   b  may comprise two actuator valves arranged in series. Furthermore, the compression release brake arrangement  10  may comprise one or more further actuator valves arranged in parallel to the first and second actuator valves  16 ,  18 . 
     Although not illustrated in  FIG.  2   , the compression release brake arrangement may further comprise one or more sensors configured to determine the hydraulic pressure in the conduit. By means of such a sensor, it may for example be possible to determine that the conduit  14  has been drained from hydraulic fluid between the actuator valves  16 ,  18  and the exhaust valve actuator assembly  12 . 
     The compression release brake arrangement  10  further comprises a control device  100  configured to control the compression release brake arrangement  10 . The control device is connected to the first actuator valve  16  and to the second actuator valve  18  for the purpose of control thereof. The control device  100  may also be connected to at least one sensor configured to determine hydraulic pressure in the conduit  14 . Thus, the control device may be configured to receive information regarding hydraulic pressure in the conduit  14  and to control the first and second actuator valves  16 ,  18  in dependence of such information. The control device may further be connected to other constituent components of the compression release brake arrangement  10 , as well as the engine  2  or an engine control device. The control device may for example be configured to determine or receive information regarding a duration since the last compression release braking action has been performed. 
     The time it takes to activate compression release braking comprises a few delays, such delays comprising pure software delays, actuator valve activation delays, as well as time for filling the conduit  14  with hydraulic fluid. These delays are added up to a total delay time for activation of compression release braking. As previously mentioned in the background section of the present disclosure, hydraulic fluid may leak out from various locations in a compression release brake arrangement, for example parts of the conduit and/or cavities formed in or between constituent components of the arrangement. This in turn creates a delay when the exhaust valve actuator assembly  12  has not been activated for a longer period of time. Examples of such situations include, but is not limited to, when the vehicle has been at standstill during the night/weekend or during long driving cycles without usage of compression release braking. The delay comes from the need for the hydraulic fluid to flow into the partly or completely empty conduit  14  before a pressure increase can be achieved. The method as disclosed herein reduces the delay in the increase of pressure in the conduit by controlling the first actuator valve and the second actuator valve such that a pre-filling of the conduit section downstream of the first and second actuator valves is achieved prior to compression release braking. It has been found that by means of usage of the present method, the total activation time of compression release braking can be at least about 5-10 times shorter (depending on the specific circumstances relating to the point in time at which compression release braking is requested) than the conventional total activation time of compression release braking. 
       FIG.  3    represents a flowchart schematically illustrating a method for controlling a compression release brake arrangement, such as the one disclosed above with reference to  FIG.  2   , according to one exemplifying embodiment. In the figure, optional steps are illustrated by dashed shapes. The method may comprise one or more of the optional steps in any combination. 
     The method may comprise a first step S 101  of determining a condition indicative of a need to fill the conduit of the compression release brake arrangement before a hydraulic pressure therein can be increased to a value sufficient for activation of the exhaust valve actuator assembly. The step S 101  may for example comprise determining that there conduit is empty or only partially filled with hydraulic fluid, or determining a parameter which indicates an expected need for filling the conduit. The latter may for example comprise determining that a certain period of time has lapsed since a preceding compression release braking action. The step S 101  may comprise determining the condition indicative of a need to fill the conduit by receiving information indicating that start-up of the engine has occurred. The step S 101  may comprise determining the condition indicative of a need to fill the conduit based on information from a look-ahead system indicating an expected future desire to use compression release braking on the engine. 
     The method may further comprise a step S 102  of determining whether there is a pending request for compression release braking. Such a request may be issued by any previously known method therefore. For example, a request for compression release braking may be issued by a cruise control of the vehicle, or by a driver of the vehicle. In case there is a pending request for compression release braking, the method may be proceeded to a step S 103  as will be described below. In case there is no pending request for compression release braking, the method may proceed to step S 104  which will be described below. 
     The method may comprise a step S 103  of controlling the first actuator valve and the second actuator valve so as to achieve a third state. In the third state, both the first actuator valve and the second actuator valve are in an open state. Thereby, the exhaust valve actuator assembly is activated and compression release braking thus performed. The method may be ended after step S 103 . 
     The method comprises a step S 104  of controlling the first actuator valve and the second actuator valve so as to achieve a first state. In the first state, one of the first actuator valve and the second actuator valve is in an open state whereas the other one of the first actuator valve and the second actuator valve is in a closed state. Step  104  is performed in advance of an activation of the exhaust valve actuator assembly. In other words, step S 104  is performed when compression release braking is not performed. 
     Step S 104  may be followed by a step S 105  of controlling the first actuator valve and the second actuator valve so as to achieve a second state. In the second state, both the first actuator valve and the second actuator valve are in a closed state. Thereby, no hydraulic fluid is transferred to the exhaust valve actuator assembly. 
     After step S 104  and the optional step S 105 , the method may be returned to the optional step S 102 . 
     In case the method does not comprise the optional steps, the method may be ended after step S 104  and the optional step S 105 . 
       FIG.  4    schematically illustrates an exemplifying embodiment of a device  500 . The control device  100  described above may for example comprise the device  500 , consist of the device  500 , or be comprised in the device  500 . 
     The device  500  comprises a non-volatile memory  520 , a data processing unit  510  and a read/write memory  550 . The non-volatile memory  520  has a first memory element  530  in which a computer program, e.g. an operating system, is stored for controlling the function of the device  500 . The device  500  further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory  520  has also a second memory element  540 . 
     There is provided a computer program P that comprises instructions for controlling a compression release brake arrangement for an engine. The compression release brake arrangement comprises an exhaust valve actuator assembly configured to, when activated, perform compression release braking of at least a first cylinder of the engine. The compression release brake arrangement further comprises a conduit. The conduit is fluidly connected to the exhaust valve actuator assembly. The conduit comprises a first actuator valve and a second actuator valve. The second actuator valve is arranged in parallel to the first actuator valve. The compression release brake arrangement further comprises at least one pump configured to supply hydraulic fluid via the conduit to the exhaust valve actuator assembly. The computer program P comprises instructions for, in advance of an activation of the exhaust valve actuator assembly, controlling the first actuator valve and the second actuator valve so as to achieve a first state in which one of the first actuator valve and the second actuator valve is in an open state whereas the other one of the first and the second actuator valve is in a closed state. The computer program P may further comprise instructions for, after controlling the first actuator valve and the second actuator valve so as to achieve the first state, controlling the first actuator valve and the second actuator valve so as to achieve a second state in which both the first actuator valve and the second actuator valve are in a closed state. 
     The program P may be stored in an executable form or in a compressed form in a memory  560  and/or in a read/write memory  550 . 
     The data processing unit  510  may perform one or more functions, i.e. the data processing unit  510  may effect a certain part of the program P stored in the memory  560  or a certain part of the program P stored in the read/write memory  550 . 
     The data processing device  510  can communicate with a data port  599  via a data bus  515 . The non-volatile memory  520  is intended for communication with the data processing unit  510  via a data bus  512 . The separate memory  560  is intended to communicate with the data processing unit  510  via a data bus  511 . The read/write memory  550  is adapted to communicate with the data processing unit  510  via a data bus  514 . The communication between the constituent components may be implemented by a communication link. A communication link may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. 
     When data are received on the data port  599 , they may be stored temporarily in the second memory element  540 . When input data received have been temporarily stored, the data processing unit  510  is prepared to effect code execution as described above. 
     Parts of the methods herein described may be effected by the device  500  by means of the data processing unit  510  which runs the program stored in the memory  560  or the read/write memory  550 . When the device  500  runs the program, methods herein described are executed.