Description

Engine control system

Technical field

[0001] The present invention relates to a system for controlling the operation of an engine of a motor vehicle provided with a gearbox associated with the engine, a retarder, a cooling circuit with cooling medium for cooling the engine and the retarder, and a cooling medium pump and/or a cooling fan driven by the engine in dependence on the rotational speed thereof. The invention also relates to method for controlling the operation of an engine of such a motor vehicle. Furthermore, the invention relates to a computer program comprising computer program code for implementing such a method, a computer program product comprising a data storage medium readable by an electronic control unit and having said computer program stored thereon, and an electronic control unit.

Background art

[0002] The present invention is applicable to motor vehicles provided with a supplementary brake in the form of a retarder, especially heavy motor vehicles such as lorries, towing vehicles and buses. The retarder is a hydraulic brake, which e.g. acts on the output shaft of the gearbox. A retarder is normally cooled by means of a retarder cooler connected to the ordinary cooling system of the vehicle. A simple and convenient manner of incorporating the retarder cooler into the cooling system is to connect the retarder cooler to the cooling circuit in series with the engine cooling ducts between the outlet of the engine cooling ducts and the inlet of the radiator. This conventional solution implies that the cooling medium flows through the radiator, from the outlet of the radiator to the inlet of the engine cooling ducts, through the engine cooling ducts, from the outlet of the engine cooling ducts to the inlet of the retarder cooler, through the retarder cooler and then from the outlet of the retarder cooler back to the radiator. A cooling medium pump is arranged in the cooling circuit, normally between the outlet of the radiator and the inlet of the engine cooling ducts, in order to circulate the cooling medium in the cooling circuit. The pump is normally driven mechanically by the engine with the pumping effect depending on

the rotational speed of the engine, which implies that the circulation of the cooling medium increases with increasing rotational speed of the engine. The cooling system also comprises a cooling fan for cooling the cooling medium as it flows through the radiator. The cooling fan is often driven mechanically by the engine with the blowing effect depending on the rotational speed of the engine, which implies that the blowing effect of the fan and thus the cooling effect of the radiator increases with increasing rotational speed of the engine. The cooling effect of the retarder cooler depends on the pumping effect exerted by the cooling medium pump and the blowing effect exerted by the cooling fan. A large amount of heat is generated in the retarder when it is in operation, i.e. when it is exerting a breaking effect, e.g. on the output shaft of the gearbox. This heat is to be removed via the cooling medium flowing through the retarder cooler. If the cooling system is unable to remove a sufficient amount of the generated heat and the heating level of the retarder thereby becomes dangerously high, the breaking effect of the retarder is reduced by the control unit which is controlling the operation of the retarder. Thus, in order to secure an efficient use of the retarder, it is important during retarder breaking to maintain a sufficient cooling effect of the cooling system associated with the retarder. When the cooling system, as indicated above, comprises a cooling medium pump and/or a cooling fan driven by the vehicle engine in dependence on the rotational speed thereof, it is important to have the engine running at a high rotational speed during retarder breaking so as to thereby maintain a high pumping effect of the pump and/or a high blowing effect of the fan and thereby a high cooling effect of the retarder cooler. In order to secure a high cooling effect, the vehicle driver is recommended to shift down to a lower gearing before or during the retarder breaking so as to thereby make the engine run at a high rotational speed when the retarder is in operation. There is always a risk that the shifting operation is failed or that an engaged gearing is unintentionally disengaged due to a human or technical error resulting in neutral gear position in the gearbox. In such a case, the engine would run at the rather low idling speed implying a reduced cooling effect

of the cooling system. If such an error occurs in connection with retarder breaking, there would be a risk of reduced or even lost breaking effect of the retarder.

Disclosure of the invention

[0004] The object of the present invention is to achieve a system for controlling the operation of a vehicle engine, by means of which the above-indicated problem of reduced or lost breaking effect of a retarder could be eliminated or at least mitigated.

[0005] This object is achieved by means of a system having the features defined in claim 1.

[0006] The inventive system comprises engine control means adapted to automatically increase the rotational speed of the engine above the normal idling speed of the engine when the following conditions, optionally in combination with one or several further conditions, are simultaneously fulfilled:

- the engine control means receives information indicating that the retarder is in operation, and

- the engine control means receives information indicating that the output shaft of the engine is disconnected from the output shaft of the gearbox. The magnitude of the automatic rotational speed increase is to be so adapted that the pumping effect of the cooling medium pump and/or the blowing effect of the cooling fan will be so high when the engine is idling that the retarder cooler will be able to efficiently remove heat from the retarder at the increased idling speed of the engine. A reduction of the breaking effect of the retarder will thereby be prevented or at least reduced in connection with idling engine during retarder breaking.

[0007] According to an embodiment of the invention, the engine control means is adapted to refrain from automatically increasing the rotational speed of the engine above the normal idling speed of the engine if it receives information indicating that a heating value representing the prevailing heating level of the retarder does not exceed a given threshold value. Hereby, the automatic rotational speed increase may be limited to those situations where it is established that a certain amount of heat has to be

removed from the retarder, which is favourable in respect of fuel economy and driver convenience.

[0008] According to another embodiment of the invention, the engine control means is adapted to adjust the magnitude of the automatic rotational speed increase in dependence on said heating value. Hereby, it will be possible to adjust the automatic rotational speed increase in dependence on the amount of heat required to be removed from the retarder so as to thereby optimise the automatic rotational speed increase with respect to cooling requirements, driver convenience and fuel economy.

[0009] According to another embodiment of the invention, the engine control means is adapted to adjust the magnitude of the automatic rotational speed increase in dependence on a breaking effect value representing the prevailing breaking effect exerted by the retarder. The amount of heat generated in the retarder depends on the exerted breaking effect and increases with increasing breaking effect. Thus, this embodiment will make it possible to optimise the automatic rotational speed increase with respect to cooling requirements, driver convenience and fuel economy.

[0010] The invention also relates to a method having the features defined in claim 5 for controlling the operation of an engine of a motor vehicle provided with a gearbox associated with the engine, a retarder, a cooling circuit with cooling medium for cooling the engine and the retarder, and a cooling medium pump and/or cooling fan driven by the engine in dependence on the rotational speed thereof.

[0011] The invention also relates to a computer program having the features defined in claim 9, a computer program product having the features defined in claim 13 and an electronic control unit having the features defined in claim 14.

Brief description of the drawings

[0012] The invention will in the following be more closely described by means of embodiment examples, with reference to the appended drawings, where:

[0013] Fig 1 is a schematical outline diagram illustrating a system according to the present invention,

[0014] Fig 2 is a schematical outline diagram of an electronic control unit for implementing a method according to the invention, and

[0015] Fig 3 is a flow diagram illustrating a method according to an embodiment of the invention.

Mode(s) for carrying out the invention

[0016] A part of a drive line 1 of a motor vehicle is schematically illustrated in Fig 1. The drive line 1 comprises a vehicle engine 2, e.g. in the form of a conventional combustion engine, which is connected to driving wheels (not shown) of the vehicle via a clutch 3 and a gearbox 4. The output shaft 5 of the engine 1 is connected to the input shaft 6a of the gearbox via said clutch 3, which is arranged to transfer the torque exerted by the engine to the input shaft 6a of the gearbox. The clutch 3 is controlled by the driver of the vehicle via a clutch lever 7, normally in the form of a clutch pedal.

[0017] The gear position in the gearbox 4 is controlled by the driver via a gear shift lever 8. The gear shift lever 8 may be directly connected to the gearbox 4 mechanically, as illustrated in Fig 1 , so as to mechanically control the gear position in the gearbox. As an alternative, the gear shift lever 8 may be indirectly connected to the gearbox 4 electronically. In the latter case, switches are provided to sense the position of the gear shift lever 8 and the gear position in the gearbox 4 is controlled by a control unit based on signals from these switches. As a further alternative, the gearbox 4 may be an automatic gearbox. Thus, the gearbox 4 may be a manual, a semi-automatic or an automatic gearbox.

[0018] The gearbox 4 is associated with a retarder 10, which acts on the output shaft 6b of the gearbox. Retarder control means 11 , e.g. in the form of an electronic control unit, is provided for controlling the breaking effect of the retarder 10. The breaking effect of the retarder 10 may be controlled by the driver via a retarder lever 12. Sensing means 13, e.g. comprising switches associated with the retarder level, is arranged to sense the position of the retarder lever 12 and the breaking effect of the retarder 10 is controlled by the retarder control means 11 based on signals from this sensing means. The retarder control means 11 may also be adapted to control the retarder 10 based on signals from an engine control unit or

another control unit of the vehicle, e.g. in accordance with control signals from a speed control system. The retarder 10 comprises hydraulic fluid in the form of oil. The temperature of the oil increases rapidly when the retarder is brought into operation, i.e. when the retarder is activated so as to exert a breaking effect on the output shaft 6b of the gearbox. The heat of the retarder oil is removed by heat exchange with a cooling medium in a retarder cooler 14. The retarder cooler 14 is incorporated in a cooling circuit 20, parts of which being illustrated in the outline diagram of Fig 1. The retarder oil circulates from the retarder 10 to an inlet of the retarder cooler 14 via a conduit 15a, through the retarder cooler 14 and then from the outlet of the retarder cooler 14 back to the retarder 10 via a conduit 15b. The cooling medium of the cooling circuit 20 circulates from a radiator 21 to the inlet of engine cooling ducts 22 via a conduit 23a, through the engine cooling ducts 22, from the outlet of the engine cooling ducts 22 to the inlet of the retarder cooler 14 via a conduit 23b, through the retarder cooler 14 and then from the outlet of the retarder cooler 14 back to the radiator 21 via a conduit 23c. Thus, the retarder cooler 14 is in this case connected to the cooling circuit 20 in series with the engine cooling ducts 22. A cooling medium pump 24 is arranged in the cooling circuit between the outlet of the radiator 21 and the inlet of the engine cooling ducts 22, in order to circulate the cooling medium in the cooling circuit. The pump 24 is driven mechanically by the engine 2 with the pumping effect depending on the rotational speed of the engine. The radiator 21 is located at the front of the vehicle and is designed to allow transfer of heat from the cooling medium that flows through the radiator to air that is blowing through the radiator. A cooling fan 25 is arranged to blow air through the radiator 21. In the illustrated example, the fan 25 is driven mechanically by the engine 2 with the blowing effect depending on the rotational speed of the engine. As an alternative, the fan 25 may be driven by a separate motor, such as an electric motor, which is controlled by fan controlling means, e.g. in the form of an electronic control unit. The cooling effect of the cooling circuit depends inter alia on the pumping effect exerted by the pump 24 and the

blowing effect exerted by the fan 25. The cooling circuit 20 may also comprise other parts in addition to those illustrated in Fig 1. [0020] The inventive system 30 comprises engine control means 31 , e.g. in the form of an electronic control unit, for controlling the engine 2, e.g. by controlling the amount of fuel injected into the engine. According to the invention, the engine control means 31 is adapted to automatically increase the rotational speed v _e of the engine 2 above the normal idling speed Vi of the engine when the following conditions, optionally in combination with one or several further conditions, are simultaneously fulfilled:

- the engine control means 31 receives information indicating that the retarder 10 is in operation, i.e. that the retarder is activated so as to exert a breaking effect on the output shaft of the gearbox, and

- the engine control means 31 receives information indicating that the output shaft 5 of the engine 2 is disconnected from the output shaft 6b of the gearbox 4.

Thus, when said conditions are fulfilled, the engine control means 31 secures that the engine 2 is run at a rotational speed v _e that is higher then the normal idling speed Vi of the engine. The automatic rotational speed increase is terminated when the engine control means 31 receives information indicating that the engine output shaft 5 has been reconnected to the gearbox output shaft 6b or information indicating that the breaking operation of the retarder 10 has ceased.

[0021] That the output shaft 5 of the engine 2 is disconnected from the output shaft 6b of the gearbox may be established in a conventional manner based on a comparison between the prevailing rotational speed of the engine output shaft 5 and the prevailing rotational speed of the gearbox output shaft 6b. In the example illustrated in Fig 1 , the rotational speed of the engine output shaft 5 is determined by rotational speed determining means comprising a member 32 arranged to generate a value representing the rotational speed of the engine output shaft 5, whereas the rotational speed of the gearbox output shaft 6b is determined by rotational speed determining means comprising a member 33 arranged to generate

a value representing the rotational speed of the gearbox output shaft 6b. The inventive system 30 comprises means 34, for instance included in the engine control means 31 or in another control unit of the vehicle, for comparing the prevailing rotational speed of the engine output shaft 5 with the prevailing rotational speed of the gearbox output shaft 6b so as to establish whether or not these output shafts 5, 6b are disconnected from each other. Thus, the engine control means 31 is adapted to establish whether or not said output shafts 5, 6b are disconnected from each other or receive information about that from another control unit.

[0022] The engine output shaft 5 is disconnected from the gearbox output shaft 6b if the clutch 3 is completely disengaged or if the gearbox 4 is in the neutral gear position. Information indicating that the clutch 3 is completely disengaged or that the gearbox 4 is in the neutral gear position may therefore be used by the engine control means 31 as a redundant indication of the fact that the engine output shaft 5 is disconnected from the gearbox output shaft 6b, in addition to the indication based on the above-indicated comparison of the rotational speeds of said output shafts 5, 6b. The fact that the clutch 3 is completely disengaged may be established based on information as to the prevailing position of the clutch lever 7, which may be sensed by sensing means 35 associated with the clutch lever 7. The fact that the gearbox 4 is in the neutral gear position may be established in any suitable manner, e.g. based on information as to the prevailing position of the gear shift lever 8 or by evaluation of the gear ratio values. The gear ratio values may for instance be established by forming the ratio between measuring values representing the rotational speed of the gearbox input shaft 6a and measuring values representing the rotational speed of the gearbox output shaft 6b. The prevailing position of the gear shift lever 8 may be sensed by sensing means 36 associated with the gear shift lever 8.

[0023] That the retarder 10 is in operation is suitably established based on the prevailing breaking effect of the retarder. The prevailing breaking effect of the retarder 10 may be determined in a conventional manner based on a value of the prevailing pressure of the retarder oil and a value of the

prevailing rotational speed of the gearbox output shaft 6b. The prevailing pressure of the retarder oil is sensed by means of a pressure sensor 37 and the prevailing rotational speed of the gearbox output shaft 6b may be determined by the previously indicated rotational speed determining means. Information as to the prevailing pressure of the retarder oil and information as to the prevailing rotational speed of the gearbox output shaft is suitably supplied to and evaluated in the retarder control means 11 , from which information as to the prevailing breaking effect of the retarder 10 is supplied to the engine control means 31. A breaking effect value Vbe representing the prevailing breaking effect of the retarder 10 may also be used by the engine control means 31 as a parameter for determining the magnitude of the automatic rotational speed increase, which implies that the engine control means 31 is adapted to automatically increase the rotational speed of the engine 2 in dependence on the breaking effect value Vbe when the above-indicated conditions are simultaneously fulfilled. According to an embodiment of the invention, the engine control means 31 is adapted to refrain from initiating the above-indicated automatic rotational speed increase if it receives information indicating that a heating value Vh representing the prevailing heating level of the retarder 10 does not exceed a given threshold value Vth. An initiated automatic rotational speed increase of the above-indicated type is terminated when the engine control means 31 receives information indicating that the heating value Vh has decreased below the threshold value Vth. According to this embodiment, the inventive system 30 comprises means 39, for instance included in the engine control means 31 or in another control unit of the vehicle, for comparing the heating value Vh with the threshold value V^. Thus, the engine control means 31 is adapted to establish whether or not said heating value Vh exceeds the threshold value Vth or receive information about that from another control unit. The threshold value Vth is to be so chosen that the retarder cooler 14 at the normal idling speed of the engine will be capable of removing sufficient heat from the retarder when the heating level thereof is below this threshold value.

[0025] The above-indicated heating value Vh may also be used by the engine control means 31 as a parameter for determining the magnitude of the automatic rotational speed increase, which implies that the engine control means 31 is adapted to automatically increase the rotational speed of the engine 2 in dependence on the heating value Vh when the above-indicated conditions are simultaneously fulfilled.

[0026] The heating value Vh may be determined based on a value representing the prevailing temperature of the retarder oil or based on a value representing the prevailing temperature of the cooling medium that is leaving the retarder cooler 14. Information as to the heating value Vh may be supplied to the engine control means 31 directly from a temperature sensor arranged to sense, directly or indirectly, the temperature of the retarder oil or the cooling medium, or from a control unit connected to such a sensor. As an alternative, the heating value Vh may be established by means of calculations based on a calculation model. In the example illustrated in Fig 1 , a temperature sensor 38 is arranged to sense the temperature of the cooling medium that is leaving the retarder cooler.

[0027] A suitable magnitude of the automatic rotational speed increase as a function of the breaking effect value Vb _θ and/or the heating value Vh may be established for a certain vehicle by means of empirical tests and/or calculations based on a calculation model.

[0028] According to a simplified embodiment of the invention, the rotational speed of the engine may always be automatically increased to the maximum allowed engine speed when the above-indicated conditions are fulfilled or to another fixed value between the normal idling speed of the engine and the maximum allowed engine speed.

[0029] The above-indicated engine control means 31 could be implemented to constitute or form part of the engine control unit of the vehicle. As an alternative, the engine control means could be implemented to constitute or form part of another control unit of the vehicle, such as the control unit that is arranged to control the operation of the retarder, adapted to send control signals to the engine control unit so as to make the engine control unit run the vehicle engine at the desired speed.

[0030] A flow diagram illustrating a method according to an embodiment of the invention is shown in Fig 3. In a first step S1 , it is determined whether or not the retarder 10 is in operation or information about that is received. In a second step S2, it is determined whether or not the output shaft 5 of the engine is disconnected from the output shaft 6b of the gearbox or information about that is received. In a third step S3, a heating value Vh representing the prevailing heating level of the retarder 10 is determined or received. In a fourth step S4, the heating value Vh is compared with a given threshold value V _t h. If it is established in these steps S1-S4:

- that the retarder 10 is in operation,

- that the output shaft 5 of the engine is disconnected from the output shaft 6b of the gearbox, and

- that the heating value Vh exceeds the threshold value Vth, then the rotational speed v _e of the engine is automatically increased above the normal idling speed Vi of the engine in a fifth step S5. The automatic rotational speed increase is terminated in a sixth step S6 under the previously indicated conditions. The above-indicated steps S1-S3 may be executed essentially simultaneously and in any desired order.

[0031] Computer program code for implementing a method according to the invention is suitably included in a computer program, which is loadable directly into the internal memory of a computer, such as the internal memory of the engine control unit of the vehicle. Such a computer program is suitably provided via a computer program product comprising a data storage medium readable by an electronic control unit, which data storage medium has the computer program stored thereon. Said data storage medium is for instance an optical data storage medium in the form of a CD-ROM disc, a DVD disc etc, a magnetic data storage medium in the form of a hard disc, a diskette, a cassette tape etc, or a memory of the type ROM, PROM, EPROM or EEPROM or a Flash memory.

[0032] The computer program according to an embodiment of the invention comprises computer program code for causing a computer, e.g. in the form of a microprocessor of an electronic control unit such as an engine control unit:

- to determine whether or not the output shaft of an engine of a motor vehicle is disconnected from the output shaft of a gearbox associated with the engine or receive information about that,

- to determine whether or not a retarder of the vehicle is in operation or receive information about that, and

- to automatically increase the rotational speed v _e of the engine above the normal idling speed Vi of the engine when the following conditions, optionally in combination with one or several further conditions, are simultaneously fulfilled:

- it is established that the retarder is in operation, and

- it is established that the output shaft of the engine is disconnected from the output shaft of the gearbox.

[0033] Fig 2 very schematically illustrates an electronic control unit 40 comprising an execution means 41 , such as a central processing unit (CPU), for executing computer software. The execution means 41 communicates with a memory 43, for instance of the type RAM, via a data bus 42. The control unit 40 also comprises data storage medium 44, for instance in the form of a memory of the type ROM, PROM, EPROM or EEPROM or a Flash memory. The execution means 41 communicates with the data storage medium 44 via the data bus 42. A computer program comprising computer program code for implementing a method according to the invention is stored on the data storage medium 44.

[0034] The invention is intended to be used in a motor vehicle, such as for instance a lorry, a towing vehicle or a bus.

[0035] The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.