WO2008118073A1

WO2008118073A1 - Exhaust gas brake control

Info

Publication number: WO2008118073A1
Application number: PCT/SE2008/050305
Authority: WO
Inventors: Klas Telborn
Original assignee: Scania Cv Ab (Publ)
Priority date: 2007-03-27
Filing date: 2008-03-18
Publication date: 2008-10-02
Also published as: SE0700761L; SE530717C2

Abstract

An exhaust brake system for a motor vehicle, comprising an adjustable valve (107) in a recirculation passage (115) connecting an exhaust gas conduit (150) with an air intake (105) to the engine (110), and a control unit (120) that produces a first control signal (Cl) in response to a set value (Treq) designating a desired brake -torque, the control unit being adapted to: check if the set value (Treq) designates a brake-torque below a first threshold level and the engine (110) is controlled to a drive-torque below a second threshold level, and if both these conditions are fulfilled, generate a second control signal (C2) such that the adjustable valve (107) is adjusted to a closed position, generate a third control signal (C3) such that the turbo unit (160) opens up maximally with respect to the exhaust gasses (Eout), test if the exhaust gas pressure level (Pm) exceeds a third threshold level, and if so, produces an alarm triggering signal (A) in respect of a first adjustable valve (135) that obstructs the exhaust gas from the engine.

Description

Exhaust Gas Brake Control

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates generally to brake solutions for motor vehicles that are based on exhaust gas restriction. More particularly the invention relates to an exhaust brake system according to the preamble of claim 1 and a motor vehicle according to claim 8. The invention also relates to a method of controlling an exhaust gas brake according to the preamble of claim 9 and a computer program product according to claim 15.

An exhaust brake system for a combustion-engine vehicle typically includes a valve, which is arranged in the engine's exhaust passage. When the exhaust brake is activated, the valve is controlled to a position wherein it obstructs the exhaust gasses flowing from the engine. Thereby, the pistons in the engine ex- perience an increased resistance during the engine's exhaust stroke, and consequently a brake effect occurs. Additionally, solutions are know for handling various exhaust-gas-brake related problems.

JP 2001 -263134 discloses an auxiliary brake device, which is designed to accurately adjust the exhaust gas pressure of an engine during operation of the exhaust brake. Here, an excessive exhaust gas pressure is avoided by adjusting a valve in an exhaust gas recirculation (EGR) passage that connects an upstream side of the exhaust gas brake valve with an air intake to the engine.

JP 2004-324417 describes an EGR system capable of preventing damages of an EGR cooler due to a pressure wave generated during operation of an exhaust gas brake. The design includes a shut-off valve for the EGR valve, which is activated upon activation of the exhaust gas brake.

JP 2001 -280173 reveals an exhaust braking device for an internal combustion engine. Here, a bypass passage is opened over the exhaust braking device in case of an electric short-circuit in respect of the exhaust braking device. Thereby, unintentional exhaust gas braking can be avoided.

However, there is no solution wherein information regarding the actual positioning of the exhaust brake valve is fed back to the control unit responsible for exhaust-gas-brake function. Thus, even if a control signal has been generated which is intended to control the exhaust brake valve to an open position, the valve may in fact be closed, or at least be positioned differently than what is reflected by the control signal. This, in turn, may result in material damages (e.g. to the engine and/or to its associated valves and turbo units) as well as safety risks due to unexpected braking of the vehicle.

SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a solution, which alleviates the problems above, and thus offers a reliable supervision of the exhaust brake valve functionality.

According to one aspect of the invention, the object is achieved by the initially described exhaust brake system, wherein the control unit is adapted to check if the set value designates a brake-torque below a first threshold level and the engine is controlled to a drive-torque below a second threshold level. If both these conditions are fulfilled, the control unit is adapted to: generate the second control signal such that the second adjustable valve is adjusted to a closed position, generate the third control signal such that the turbo unit opens up maximally with respect to the exhaust gasses, and then test if the exhaust gas pressure level exceeds a third threshold level. If this is found to be the case, the control unit is adapted to produce an alarm triggering signal in respect of the first adjustable valve.

This system is advantageous because it provides an automatic testing of the exhaust brake, which will be executed at repeated occasions during normal operation of the vehicle.

According to one embodiment of this aspect of the invention, the first and second threshold levels represent a motoring state in which the engine does not propel the vehicle. Hence, no disrupting pressures will be built up in the exhaust gas conduit during the test procedure.

According to another embodiment of this aspect of the invention, the control unit is adapted to receive a status signal indicative of a functionality condition of an actuating means adapted to influence an adjustment of the first adjustable valve. For example, the actuating means may include a piston member and a valve means. The piston member is here operative in response to a pressurized fluid (e.g. compressed air or hydraulic oil), and the valve means is operative in response to the first control signal. The valve means is adapted to forward the pressurized fluid to the piston member. The control unit is further adapted to test whether or not the status signal fulfills an alarm criterion, and if so, generate the second control signal such that the second adjustable valve is adjusted to a predetermined position, preferably fully opened. Thereby, in addition to detecting a malfunctioning exhaust brake, the proposed system can also reduce the effects of certain malfunctions.

According to yet another embodiment of this aspect of the invention, the first control signal is an electric-type of signal, and the status signal is based on at least one electric parameter associated with an operation of the actuating means. For example, the first control signal may have a pulse-width-modulation (PWM) format, and the first adjustable valve may be adapted to open a passage for the exhaust gasses from the engine based on a pulse width of the first control signal. Consequently, a short circuit of the first adjustable valve to the supply voltage might be interpreted as an order to fully close exhaust gas brake valve. This highly undesired effect, however, is avoided by the above- described testing of the status signal.

According to another aspect of the invention, the object is achieved by the motor vehicle described initially, wherein the vehicle includes the above-described exhaust brake system that is configured to apply an adjustable brake-torque with respect to at least one drive axis of the vehicle's engine.

According to another aspect of the invention, the object is achieved by the method described initially, wherein it is checked if the set value designates a brake-torque below a first threshold level and if the engine is controlled to a drive-torque below a second threshold level. If both these conditions are fulfilled, the method further involves: generating the second control signal such that the second adjustable valve is adjusted to a closed position and generating the third control signal such that the turbo unit opens up maximally with respect to the exhaust gasses. Thereafter, it is tested if the exhaust gas pressure level exceeds a third threshold level, and if so, the method involves producing an alarm triggering signal in respect of the first adjustable valve. The advantages of this method, as well as the preferred embodiments thereof, are apparent from the discussion hereinabove with reference to the proposed vehicle arrangement.

According to a further aspect of the invention the object is achieved by a computer program product loadable into a memory of a computer. The program product includes software adap- ted to control the above proposed method when the program product is run on a computer.

BRIEF DESCRI PTION OF THE DRAWINGS

The present invention is now to be explained more closely by means of embodiments, which are disclosed as examples, and with reference to the attached drawings.

Figure 1 shows a block diagram over an exhaust brake system according to one embodiment of the invention, and

Figures 2a-b show diagrams illustrating a format of a control signal and its relationship to an opening of the exhaust brake valve according to one embodiment of the invention,

Figure 3 shows a motor vehicle including the proposed exhaust brake system, and Figure 4 shows a flow diagram illustrating the general method according to the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

We refer initially to Figure 1 , which shows a block diagram over an exhaust brake system for a motor vehicle according to one embodiment of the invention.

The system includes a first adjustable valve 135, a second adjustable valve 107, a sensor means 155, a turbo unit 160 and a control unit 120, which is adapted to receive an exhaust gas pressure signal P_m from the sensor means 155 and a set value T_req designating a desired brake-torque to be applied by the exhaust gas brake. Moreover, the control unit 120 is adapted to generate a first, second and third control signal C1 , C2 and C3 respectively, and an alarm triggering signal A in respect of the first adjustable valve 135.

The first adjustable valve 135 is arranged in an exhaust gas conduit 150 from an internal combustion engine 1 10 of the vehicle and is adapted to obstruct the engine's 1 10 exhaust gasses E_out in response to the first control signal C1 , and as a result, cause a brake-torque during the engine's 1 10 exhaust stroke. The second adjustable valve 107 is arranged in a recirculation passage 1 15 connecting the exhaust gas conduit 150 with an air intake 105 to the engine 1 10. The second adjustable valve 107 is operable in response to the second control signal C2.

The sensor means 155 is arranged to register the exhaust gas pressure level P_m in the exhaust gas conduit 150 between the engine 1 10 and the first adjustable valve means 135, and forward the exhaust gas pressure signal P_m to the control unit 120. The turbo unit 160 is arranged in the exhaust gas conduit 150, and is controllable in response to the third control signal C3.

The control unit 120 is adapted to repeatedly check if the set value T_req designates a brake-torque below a first threshold level. Additionally, the control unit 120 is adapted to repeatedly check if the engine 1 10 is controlled to a drive-torque below a second threshold level. Preferably, the first and second threshold levels are set to such low values that they represent a motoring state in which the engine 1 10 does not propel the vehicle (and at the same time brakes the vehicle insignificantly). If the control unit 120 finds that both the above conditions are fulfilled simultaneously (i.e. that the set value T_req designates a brake-torque below a first threshold level and the drive- torque to which the engine is controlled is below the second threshold level), the control unit 120 is adapted to generate the second control signal C2 such that the second adjustable valve 107 is adjusted to a closed position. Consequently, no exhaust gasses E_r will be recirculated from the engine's 1 10 exhaust gas output to its air intake. Figure 1 shows the second adjustable valve 107 being arranged relatively proximate to the air intake. However, the valve 107 may equally well be located at any other position in the recirculation passage 1 15, e.g. at the intersection between the recirculation passage 1 15 and the exhaust gas conduit 150.

Upon simultaneous fulfillment of the above two conditions (i.e. the set value T_req designating a brake-torque below a first threshold level and the drive-torque being below the second threshold level), the control unit 120 is also adapted to generate the third control signal C3 such that the turbo unit 160 opens up maximally with respect to the exhaust gasses E_out. Hence, the exhaust gasses E_out will have minimal influence on an amount of air A_in fed to the engine's 1 10 air intake. More important, however, the turbo unit 160 will restrict the exhaust gasses E_out minimally. Therefore, the influence of the first adjustable valve 135 of the exhaust gas brake can be tested in a straightforward manner. To this aim, the control unit 120 is adapted to test if the exhaust gas pressure level P_m exceeds a third threshold level. If this condition is found to be fulfilled, the control unit 120 is adapted to produce the alarm triggering signal A (i.e. to indicate a malfunction of the first adjustable valve 135). Preferably, the alarm triggering signal A reflects a jammed condition for the exhaust brake valve. Namely, the set value T_req designates a desired brake-torque below the first threshold level, say a zero value, while the exhaust gas pressure level P_m shows an abnormally high value exceeding the third threshold level.

Referring to Figure 1 , it is worth mentioning that, according to the invention, the turbo unit 160 may be arranged at arbitrary position relative to the first adjustable valve means 135. For example, the turbo unit 160 may be located between the engine 1 10 and the first adjustable valve means 135. Additionally, it should be pointed out that the first adjustable valve means 135 is a distinct component separated from the turbo unit 160. Consequently, the valve means 135 cannot for example be represented by the nozzle-area adjusting guide vanes of a variable geometry turbo (VGT).

According to one embodiment of the invention, the control unit 120 is further adapted to receive a status signal m_v indicative of a functionality condition of an actuating means adapted to influence an adjustment of the first adjustable valve 135. The actuating means, in turn, preferably includes a piston member 130 and a valve means 145. The valve means 145 is operative in response to the first control signal C1 . This signal C1 may thus cause the valve means 145 to open up and forward a pressurized fluid Fp (e.g. in the form of compressed air or hydraulic oil) to the piston member 130. The pressurized fluid F_P. is preferably supplied by a pump means 140 in the vehicle. The piston member 130 is operative in response to a pressurized fluid F_P This means that the piston member 130 will cause the first adjustable valve means 135 to adjust its position depending on the status of the valve means 145.

Specifically, the control unit 120 is adapted to test whether or not the status signal m_v originated by the valve means 145 fulfills an alarm criterion. If so, the control unit 120 is further adapted to generate the second control signal C2 such that the second adjustable valve 107 is adjusted to a predetermined posi- tion, preferably fully open.

According to one embodiment of the invention, the valve means 145 is configured to be driven by a supply voltage +U, and the first control signal C1 is an electric-type of signal. In this case, the status signal m_v is based on an electric parameter associated with an operation of the valve means 145. For example, the status signal m_v may here reflect whether or not the valve means 145 has been short-circuited to the supply voltage +U.

Figure 2a shows a diagram illustrating a format of the first control signal C1 according to one embodiment of the invention. The signal C1 has a PWM format. Furthermore, the opening of the first adjustable valve means 135 is inversely proportional to a pulse width of the signal C1 , such that a relatively narrow pulse, say 0,25T, results in a comparatively large valve opening, and vice versa, a relatively wide pulse, say 0,95T, results in a comparatively small valve opening.

Figure 2b shows a diagram specifically illustrating this relation- ship, where the vertical axis reflects the opening angle φ of the first adjustable valve 135 and the horizontal axis designates the pulse width PW_Ci for the PWM signal C1 ranging from zero to a maximum value T (given by the period time of the PWM signal C1 ). Hence, a largest possible opening angle φ corresponds to a fully opened FO valve 135, and a zero opening angle φ corresponds to a fully closed FC valve 135.

Returning now to Figure 2a, we see that the first control signal C1 alternates between a ground-level voltage and the supply voltage +U with a pulse cycle T. A widest possible pulse (i.e. having pulse width PW_Ci = T) is thus equivalent to that the first control signal C1 is constantly equal to +U. Consequently, short- circuiting the valve means 145 to the supply voltage +U has the same effect as deliberately controlling the valve 135 to a fully closed position. However, an unintentional closure of the valve 135 (e.g. due to a short circuit of the valve means 145) may lead to highly undesired results, such as damages to the engine 1 10, the exhaust conduit 150 and/or the turbo unit 160. Naturally, the vehicle will also be braked, which might cause handling problems (e.g. manifested in skidding or over steering), especially if the vehicle is connected to a lightly loaded, or unloaded trailer. Nevertheless, one embodiment of the present invention mitigates this problem by opening the EGR valve (107) as described above. Figure 3 shows a motor vehicle 200 including the proposed exhaust brake system, which is configured to apply an adjustable brake-torque with respect to at least one drive axis of the engine 1 10. Thus, the system has a control unit 120 adapted to test the operative status of the first adjustable valve 135 as has been described above.

In order to sum up, the general method of testing an exhaust brake in a motor vehicle according to the invention will be described below with reference to the flow diagram in figure 4.

A first step 410 investigates whether or not a set value is received which designates an exhaust gas brake-torque below a first threshold level. Step 410 also investigates whether or not the engine is controlled to a drive-torque below a second threshold level. If it is found that both these conditions are fulfilled simul- taneously, a step 420 follows. Otherwise, the procedure loops back and stays in step 410 (i.e. If it is found that the set value designates an exhaust gas brake-torque equal to or above the first threshold level and/or the drive-torque is equal to, or above the second threshold level).

Step 420 generates a signal such that the EGR valve (e.g. represented by the second adjustable valve 107 in Figure 1 ) is adjusted to a closed position. Subsequently, a step 430 generates a control signal such that the turbo unit opens up maximally with respect to the exhaust gasses. Then, a step 440 tests if the ex- haust gas pressure level exceeds a third threshold level, and if so, a step 450 follows. Otherwise, the procedure loops back to step 410. Step 450 produces an alarm triggering signal in respect of the first adjustable valve. Thereafter, the procedure may either end, or loop back to step 410 for continued supervision of the exhaust gas brake system.

All of the process steps, as well as any sub-sequence of steps, described with reference to the figure 4 above may be controlled by means of a programmed computer apparatus. Moreover, although the embodiments of the invention described above with reference to the drawings comprise computer apparatus and processes performed in computer apparatus, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code; object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal which may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

1 . An exhaust brake system for a motor vehicle, comprising: a first adjustable valve (135) adapted to obstruct the exhaust gasses (E_out) from an internal combustion engine (1 10) of the vehicle in response to a first control signal (C1 ) so as to accomplish a brake-torque during the engine's (1 10) exhaust stroke, a second adjustable valve (107) operable in response to a second control signal (C2) and arranged in a recirculation passa- ge (1 15) connecting an exhaust gas conduit (150) from the engine (1 10) with an air intake (105) to the engine (1 10), a sensor means (155) arranged to register an exhaust gas pressure level (P_m) in the exhaust gas conduit (150) between the engine (1 10) and the first adjustable valve means (135), a turbo unit (160) arranged in the exhaust gas conduit (150) and controllable in response to a third control signal (C3), and a control unit (120) adapted to produce the first control signal (C1 ) in response to a set value (T_req) designating a desired brake-torque, characterized i n that the control unit (120) is ad- apted to: check if the set value (T_req) designates a brake-torque below a first threshold level and the engine (1 10) is controlled to a drive-torque below a second threshold level, and if both these conditions are fulfilled generate the second control signal (C2) such that the second adjustable valve (107) is adjusted to a closed position, generate the third control signal (C3) such that the turbo unit (160) opens up maximally with respect to the exhaust gasses ) test if the exhaust gas pressure level (P_m) exceeds a third threshold level, and if so produce an alarm triggering signal (A) in respect of the first adjustable valve (135).

2. The system according to claim 1 , wherein the first and se- cond threshold levels represent a motoring state in which the engine (1 10) does not propel the vehicle.

3. The system according to any one of the claims 1 or 2, wherein the control unit (120) is adapted to: receive a status signal (m_v) indicative of a functionality condition of an actuating means (145, 130) adapted to influence an adjustment of the first adjustable valve (135), test whether or not the status signal (m_v) fulfills an alarm criterion, and if so generate the second control signal (C2) such that the second adjustable valve (107) is adjusted to a predetermined posi- tion.

4. The system according to claim 3, wherein the predetermined position represents an adjustment of the second adjustable valve (107) to a fully opened position.

5. The system according to any one of the claims 3 or 4, whe- rein the actuating means comprises: a piston member (130) operative in response to a pressurized fluid (Fp), and a valve means (145) operative in response to the first control signal (C1 ) and adapted to forward the pressurized fluid (F_P) to the piston member (130).

6. The system according to any one of the claims 3 to 5, wherein the first control signal (C1 ) is an electric-type of signal, and the status signal (m_v) is based on at least one electric parameter associated with an operation of the actuating means (145, 130).

7. The system according to claim 6, wherein the first control signal (C1 ) has a pulse-width-modulation format and the first adjustable valve (135) is adapted to open a passage for the exhaust gasses (E_out) from the engine (1 10) based on a pulse width (PW_C) of the first control signal (C1 ).

8. A motor vehicle (200) comprising an internal combustion engine (1 10), characterized i n that the vehicle (200) comprises the exhaust brake system according to any one of the claims 1 to 7, the system being configured to apply an adjustable brake-tor- que with respect to at least one drive axis of the engine (1 10).

9. A method of controlling an exhaust brake in a motor vehicle, wherein a first adjustable valve (135) is adapted to obstruct the exhaust gasses (E_out) from an internal combustion engine (1 10) of the vehicle in response to a first control signal (C1 ) so as to accomplish a brake-torque during the engine's (1 10) exhaust stroke, a second adjustable valve (107) is operable in response to a second control signal (C2) and arranged in a recirculation passage (1 15) connecting an exhaust gas conduit (150) from the engine (1 10) with an air intake (105) to the engine (1 10), a sensor means (155) is arranged to register an exhaust gas pressure level (P_m) in the exhaust gas conduit (150) between the engine (1 10) and the first adjustable valve means (135), and a turbo unit (160) is arranged in the exhaust gas conduit (150) and controllable in response to a third control signal (C3), the method comprising producing the first control signal (C1 ) in response to a set value (T_req) designating a desired brake-torque, characterized by: checking if the set value (T_req) designates a brake-torque below a first threshold level and the engine is controlled to a drive-torque below a second threshold level, and if both these conditions are fulfilled generating the second control signal (C2) such that the second adjustable valve (107) is adjusted to a closed position, generating the third control signal (C3) such that the turbo unit (160) opens up maximally with respect to the exhaust gas¬

testing if the exhaust gas pressure level (P_m) exceeds a third threshold level, and if so producing an alarm triggering signal (A) in respect of the first adjustable valve (135).

10. The method according to claim 9, wherein the first and second threshold levels represent a motoring state in which the engine (1 10) does not propel the vehicle.

1 1 . The method according to any one of the claims 9 or 10, comprising: receiving a status signal (m_v) indicative of a functionality condition of an actuating means (145, 130) adapted to influence an adjustment of the first adjustable valve (135), testing whether or not the status signal (m_v) fulfills an alarm criterion, and if so generating the second control signal (C2) such that the second adjustable valve (107) is adjusted to a predetermined position.

12. The method according to claim 1 1 , wherein the predetermined position represents an adjustment of the second adjustable valve (107) to a fully opened position.

13. The method according to any one of the claims 1 1 or 12 wherein the first control signal (C1 ) is an electric-type of signal, and the status signal (m_v) is based on at least one electric parameter associated with an operation of the actuating means (145, 130).

14. The method according to claim 13, wherein the first control signal (C1 ) has a pulse-width-modulation format and the first adjustable valve (135) is adapted to open a passage for the exhaust gasses (E_out) from the engine (1 10) based on a pulse width (PW_C) of the first control signal (C1 ).

15. A computer program product loadable into a memory (125) of a computer included in a motor vehicle (200) which is equipped with an exhaust brake system and an exhaust gas recirculation system, the computer program product comprising software adapted to control the steps of any of the claims 9 to 14 when the program product is run on the computer.

16. The computer program product according to claim 15, wherein the program product is recorded onto a carrier.