WO2007129970A1

WO2007129970A1 - Exhaust gas brake control

Info

Publication number: WO2007129970A1
Application number: PCT/SE2007/050264
Authority: WO
Inventors: Klas Telborn
Original assignee: Scania Cv Ab (Publ)
Priority date: 2006-05-09
Filing date: 2007-04-24
Publication date: 2007-11-15
Also published as: EP2016268A4; SE529870C2; EP2016268A1; SE0601033L

Abstract

The invention relates to obstruction of the exhaust gasses from an internal combustion engine of a vehicle, such that during the engine's exhaust stroke a brake torque is accomplished, which counteracts a drive torque produced during the engine's combustion phase. An adjustable valve in an exhaust conduit from the engine is controlled in response to a control signal. A set value designating a desired brake torque is received (410), an exhaust gas pressure in the exhaust conduit is registered (420), an input pressure in an air intake to the engine is also registered (430) as well as an engine parameter reflecting a speed of the engine (440). Then, a reference parameter is generated (450) in response to the input pressure engine parameter, the engine speed and either of the set value or the exhaust gas pressure. Finally, the control signal is produced (460) based on the reference parameter and either of the exhaust gas pressure or the set value.

Description

Exhaust Gas Brake Control

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates generally to brake solutions for motor vehicles being 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, a computer program product according to claim 16 and a computer readable medium according to claim 17.

Exhaust brake systems for combustion-engine vehicles typically include 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 experience an increased resistance during the engine's exhaust stroke, and consequently a brake effect occurs.

US 6,810,850 discloses a solution according to which an exhaust restrictor is located in an exhaust system downstream of the engine's exhaust manifold. Here, a controller determines a set pressure in the exhaust manifold correlated with speed of the engine. The controller then adjusts the restrictor to achieve and maintain the set pressure in the exhaust manifold.

US 6,418,719 describes a variable geometry turbocharger (VGT) being controlled in response to the engine's exhaust back pressure. Here, a control system determines a desired exhaust back pressure based on engine speed and engine load.

However, controlling the exhaust brake's valve, such that a desired brake torque occurs is an intricate task. Namely, various un- certainties and tolerances in each component in the exhaust brake control chain (e.g. including the engine, the control unit, the exhaust system and the restriction valve) lead to that an ac- tual brake torque produced by the exhaust brake cannot be predicted with sufficient accuracy directly from the adjustment of the valve. Consequently, the actual brake torque may deviate more or less from the desired value. If the brake torque is too low, the vehicle may fail to fulfill applicable regulatory and/or certifying requirements. If, on the other hand, the brake torque is too high, the exhaust brake system and its components risk being damaged. Furthermore, any turbo unit operating in the exhaust system may likewise be impaired.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a solution, which alleviates the problems above, and thus offers predictable, reliable and efficient exhaust brake function.

According to one aspect of the invention, the object is achieved by the initially described exhaust brake system, wherein the system includes a second pressure sensor adapted to register an input pressure in an air intake to the engine. Moreover, the brake torque regulator includes a processing means, which is adapted to receive the registered input pressure, receive an engine para- meter reflecting a speed of the engine, model a gas exchange work performed by the engine and generate a reference parameter based on this model. The brake torque regulator also includes a control means that is adapted to receive at least the reference parameter, and based thereon, produce the control sig- nal. I.e., the control signal is produced, directly or indirectly, based on the registered exhaust gas pressure, the reference parameter and a set value, which designates a desired brake torque.

It is advantageous the control signal is generated on the basis of a model describing a gas exchange work being performed by the engine. Thereby, a feedback loop may be used to determine how well a current adjustment of the exhaust brake valve matches the desired brake torque. Thus, the valve can be adjusted very accurately irrespective of, whether or not, one or more components in the control chain deviate reasonably from their nominal characteristics. According to one embodiment of this aspect of the invention, the processing means is adapted to receive the set value, and on the further basis thereof, generate the reference parameter in the form of a first modeled parameter reflecting an estimation of the exhaust gas pressure in the exhaust conduit. Hence, the gas exchange model for the engine implemented by the processing means bases its generated estimation of the exhaust gas pressure on the input pressure registered in the air intake to the engine, the speed of the engine and the set value.

Preferably, the control means is further adapted to receive this estimation of the exhaust gas pressure and receive the exhaust gas pressure registered in the engine's exhaust conduit. In response thereto, the control means is adapted to produce the control signal to the adjustable valve. Consequently, the control means may produce the control signal in order to minimize an error between the registered and the estimated exhaust pressure. According to another embodiment of this aspect of the invention, the control means is specifically adapted to implement a proportional-integrating-derivative algorithm. Namely, this vou- ches for a desirable balance between response time, accuracy and stability.

According to yet another embodiment of this aspect of the invention, the processing means is instead adapted to receive the registered exhaust gas pressure. On the further basis thereof, the processing means is adapted to generate the estimated reference parameter in the form of a second modeled parameter reflecting an estimation of the desired brake torque. Hence, the gas exchange model for the engine implemented by the processing means bases its estimation of the desired brake torque on the input pressure registered in the air intake to the engine, the exhaust gas pressure registered in the exhaust conduit and the speed of the engine. Consequently, the control means may produce the control signal in order to minimize an error between the estimated desired brake torque and the actually desired bra- ke torque (designated by the set value). According to another embodiment of this aspect of the invention, the control means is specifically adapted to implement a proportional-integrating- derivative algorithm, which provides a desirable balance between response time, accuracy and stability.

According to another aspect of the invention, the object is achieved by the motor vehicle described initially, wherein the vehicle includes an internal combustion engine and the above-proposed exhaust brake system. This system, in turn, is configured to apply an adjustable brake torque with respect to at least one drive axis of the engine.

According to another aspect of the invention, the object is achie- ved by the method described initially, wherein an input pressure is registered in an air intake to the engine; an engine parameter is registered that reflects a speed of the engine, and a reference parameter is generated based on a model of a gas exchange work performed by the engine and in response to the registered input pressure and the registered engine parameter. Finally, the control signal is produced on the further basis of the reference parameter.

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 directly loadable into the internal memory of a computer, comprising software for controlling the above proposed method when said program is run on a computer.

According to another aspect of the invention the object is achieved by a computer readable medium, having a program recorded thereon, where the program is to make a computer control the above proposed method.

BRIEF DESCRIPTION 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 a first embodiment of an exhaust brake system according to the invention,

Figure 2 shows a block diagram over an exhaust brake system according to a second embodiment of an exhaust brake system according to the invention,

Figure 3 schematically depicts a motor vehicle equipped with the proposed exhaust brake system, and

Figure 4 shows a flow diagram illustrating the general me- thod 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 according to a first embodiment of an exhaust brake system 100 according to the invention. The pro- posed system 100 operates on an internal combustion engine 1 10 of a vehicle, wherein the engine 1 10 receives input air A_in via an air intake 140 and emits exhaust gasses E_out via an exhaust conduit 150. The system 100 includes an adjustable valve 135, a first pressure sensor 155, a second pressure sensor 145 and a brake torque regulator 160, here in the form of an electronic control unit (ECU). This regulator 160, in turn, includes a control means 130 and a processing means 120. Each of the means 120 and 130 may be implemented in hardware as well as in firmware or software. I.e. one or both of the means 120 and 130 respectively may be represented by a physical unit, or a firmware/software module.

The adjustable valve 135 is arranged in the exhaust conduit 150. The valve is adapted to obstruct the exhaust gasses E_out in the conduit 150 in response to a control signal C. The valve 135 is preferably connected to a lever and piston arrangement (not shown), which for instance is electronically, pneumatically or hydraulically operated. A brake effect is accomplished if the control signal C, which may be a pulse width modulated (PWM) electrical or optical signal, controls at least one obstructive ele- ment of the valve 135 to attain a position in which the exhaust gasses experience a resistance being higher than otherwise. Thus, a brake torque occurs during the engine's 1 10 exhaust stroke. The brake torque either counteracts a drive torque being produced during the engine's 1 10 combustion phase, or genera- tes a torque that reduces the vehicle's kinetic energy (or momentum), e.g. when the vehicle rolls down a slope. As a result, a brake effect occurs with respect to the engine's 1 10 drive axis (i.e. the axis devised to convey propelling energy to the vehicle's drive wheels). Especially for heavy vehicles, such as trucks and busses, this is a desirable complement to the conventional brake system.

The first pressure sensor 155 is adapted to register an exhaust gas pressure P_m in the exhaust conduit 150 between the engine 1 10 and the valve 135. Naturally, for a given amount of exhaust gasses emitted from the engine 1 10, the exhaust gas pressure P_m becomes higher if the adjustable valve 135 is adjusted to a more obstructive position.

The control means 130 is adapted to receive the exhaust gas pressure P_m registered by the first pressure sensor 155, and produce the control signal C at least partially based on this pressure P_m. The control signal C is also produced, directly or indirectly, based on a set value T_req designating a desired brake torque. The set value T_req, in turn, may either be assigned manually by an operator/driver (e.g. via a pedal or a lever), or this parameter may be generated automatically by a control means in the vehicle, for instance being adapted to limit the amount of white smoke emitted, or to accomplish a quick heat- up of the engine 1 10.

In this embodiment of the invention, the processing means 120 is adapted to receive an input pressure P_in registered by the second pressure sensor 145, which is arranged in the air intake 140. Additionally, the processing means 120 is adapted to receive an engine parameter rpm reflecting a speed of the engine 1 10 (e.g. the number of revolutions per unit time performed by the engine's 1 10 crank axle). In response to these parameters rpm, P_in and T_req, the processing means 120 is adapted to gene- rate a reference parameter P m-mod -

According to the invention, the processing means 120 is adapted to model a gas exchange work being performed by the engine 1 10. Here, the processing means 120 produces the refe- rence parameter in the form of a first modeled parameter P_m-_mOd that reflects an estimation of the exhaust gas pressure in the exhaust conduit 150 between the engine 1 10 and the valve 135. The first modeled parameter P_m-_moci is produced based on the engine speed rpm, the exhaust gas pressure P_m and the set value T_req.

The control means 130 is adapted to receive the reference parameter (i.e. here the first modeled parameter P_m-_moci) and produce the control signal C on the basis thereof in addition to the above-mentioned exhaust gas pressure P_m. Preferably, the control means 130 is specifically adapted to implement a proportional- integrating-derivative algorithm, which in turn, is adapted to produce the control signal C in order to minimize an error between the registered exhaust gas pressure P_m and the first modeled parameter P_m-_mOd (representing the processing means' 120 esti- mation of this pressure). Thereby, a stabile and accurate and adjustment of the valve 135 can be performed, such that an actual brake torque applied to the vehicle's drive axis quickly approaches the desired brake torque indicated by the set value

' req - Figure 2 shows a block diagram over an exhaust brake system according to a second embodiment of an exhaust brake system according to the invention. All reference labels occurring in Figure 2, which are identical to those used Figure 1 designate the same entities, parameters and variables as those described above with reference to this figure.

Thus, analogous to the embodiment shown in Figure 1 , in this embodiment of the invention, the control means 130 is adapted to receive a reference parameter T_mOd and produce the control signal C based thereon. In this case, however, the control means 130 also receives the set value T_req directly. Preferably, the control means 130 is specifically adapted to implement a proportional-integrating-derivative algorithm, which in turn, is adapted to produce the control signal C in order to minimize an error between the set value T_req and the second modeled para- meter T_mod.

Moreover, in this embodiment of the invention, the processing means 120 is adapted to receive both the registered input pressure P_in and the registered exhaust gas pressure P_m in addition to the engine parameter rpm that reflects the speed of the en- gine 1 10. Based on these parameters P_in, P_m and rpm, the processing means 120 is adapted to generate the reference parameter T_mod, which here reflects an estimation of the desired brake torque designated by the set value T_req.

Consequently, the processing means 120 is adapted to apply a model of the gas exchange work performed by the engine 1 10, which is essentially reverse to the model applied by the control means shown in Figure 1 . Such a model reversion is rendered relatively uncomplicated if the modeled relationship between the brake torque and the exhaust gas pressure is linear.

The model of the gas exchange work performed by the engine 1 10 may derived by applying a polynomial regression algorithm to least-square fit a set of measurement data from the engine 1 10. Thus, provided that the set value T_req is modeled T_mocι, the resulting polynomial includes a respective term pertaining to the input pressure P_in, the exhaust gas pressure P_m and the engine speed rpm. Preferably, the polynomial further includes an offset term and possibly a number of cross terms and/or relevant temperature parameters. For example, the model may be expressed as: T_mod = C₀ + C₁ - P_1n + C₂ - P_m + C₃ rpm

where C₀, C₁ , C₂ and C₃ are constants, and

Alternatively, if higher accuracy is desired, the expression:

Tmo_d = C₀ + C₁ - P_1n + C₂ - P_m + C₃ - TPm ₊ C₄ - Ti_{n +} C₅ - T_n may be used, where in addition to the above, C₄ and C₅ are constants, T_in designates the temperature in the air intake 140, and

T_m designates the temperature in the exhaust conduit 150 between the engine 1 10 and the valve 135.

If instead the exhaust gas pressure P_m is modeled P_m-_mOd, the following expression may be used:

Pm-mo_d = ~^~ V re_q - C₀ - C₁ - P_in - C₃ ^• rpm - C₄ ^• T_in - C₅ ^• T_m j.

Although neither of the embodiments illustrated in Figures 1 or 2 includes a turbo unit, it is worth noticing that the proposed adjustable valve 135 is to be arranged downstream of any turbo unit in the exhaust conduit 150. Hence, if included, the turbo unit is positioned between the engine 1 10 and the valve 135.

Figure 3 schematically depicts a motor vehicle 200 in the form of a truck, which is equipped with the proposed exhaust brake system 100. The vehicle 200 includes an internal combustion engine 1 10 having an air intake 140 and an exhaust conduit 150 for receiving air A_in and emitting exhaust gasses E_out respectively. The exhaust brake system 100 is configured to apply an ad- justable brake torque with respect to at least one drive axis of the engine 1 10 by adjustment of a valve in the exhaust conduit 150, such that the exhaust gasses E_out from the engine 1 10 experience an increased resistance.

Preferably, the system 100 includes, or is associated with, a computer readable medium 1 70 (e.g. a memory module) storing a program, which is adapted to make at least one control unit in the vehicle 200 execute the above-described steps.

In order to sum up, the general method according to the invention will be described below with reference to the flow diagram in figure 4.

A first step 410 receives a set value designating a desired brake torque to be applied to a vehicle's drive axis; a second step 420, registers an exhaust gas pressure in an exhaust conduit from an internal combustion engine of the vehicle; a third step 430, registers an input pressure in an air intake to the engine; and a fourth step 440 registers an engine parameter reflecting a speed of the engine. The steps 410, 420, 430 and 440 may be completed in any order relative to one another, as well as in parallel.

Nevertheless, after these steps, a step 450 follows, wherein a reference parameter is generated. The reference parameter ei- ther reflects an estimation of the exhaust gas pressure in the exhaust conduit, or an estimation of the desired brake torque. The reference parameter is generated in response to (i) the input pressure, the engine parameter and set value, provided that the reference parameter reflects an estimation of the exhaust gas pressure; and (ii) if the reference parameter reflects an estimation of the desired brake torque, the reference parameter is generated in response to the input pressure, the exhaust gas pressure and the engine parameter.

Subsequently, a step 460 produces a control signal for the ad- justable valve, so as to obstruct the exhaust gasses from the engine, and thus accomplish a brake torque during the engine's exhaust stroke to counteract a drive torque produced during the engine's combustion phase. The control signal is produced based on the reference parameter and either of the exhaust gas pressure and the set value. Specifically, (i) if the reference parameter is based on the input pressure, the engine parameter and set value, the exhaust gas pressure is used; and (ii) if the reference parameter is based on the input pressure, the exhaust gas pressure and the engine parameter, the set value is used.

After that, the procedure loops back to the steps 410, 420, 430 and 440 again.

Although the above procedure has been described as a sequential process, in an actual implementation, the procedure is preferably executed repeatedly, or continuously, such that for examp- Ie while the step 460 operates on data registered at a particular instance t, the steps 410, 420, 430 and 440 operate on data registered at a somewhat later instance t + Δt.

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 pro- grams 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: an adjustable valve (135) adapted to obstruct the exhaust gasses from an internal combustion engine (1 10) of the vehicle in response to a control signal (C) so as to accomplish a brake torque during the engine's (1 10) exhaust stroke, a first pressure sensor (155) adapted to register an exhaust gas pressure (P_m) in an exhaust conduit (150) from the engine (1 10), and a brake torque regulator (160) adapted to produce the control signal (C) based on the registered exhaust gas pressure (P_m) and a set value (T_req) designating a desired brake torque, characterized i n that the system comprises a second pressure sensor (145) adapted to register an input pressure (P_in) in an air intake (140) to the engine (1 10), and the brake torque regulator (160) comprises: a processing means (120) adapted to: receive the registered input pressure (P_in), receive an engine parameter (rpm) reflecting a speed of the engine (1 10), model a gas exchange work performed by the engine (1 10) and, generate a reference parameter (P_m-_mOd; T_mocι) based on this model, and a control means (130) adapted to receive the reference parameter (P_m-_mod; T_mOd) and based thereon produce the control signal (C).

2. The system according to claim 1 , wherein the processing means (120) is adapted to receive the set value (T_req), and on the further basis thereof, generate the reference parameter in the form of a first modeled parameter (P_m-_mOd) reflecting an estimation of the exhaust gas pressure in the exhaust conduit (150).

3. The system according to claim 2, wherein the control means (130) is adapted to: receive the registered exhaust gas pressure (P_m), receive the first modeled parameter (P_m-_mOd), and in response thereto produce the control signal (C).

4. The system according to any one of the claims 2 or 3, wherein the control means (130) is adapted to implement a pro- portional-integrating-derivative algorithm adapted to produce the control signal (C) in order to minimize an error between the registered exhaust gas pressure (P_m) and the first modeled parameter (Pm-mod)-

5. The system according to claim 1 , wherein the processing means (120) is adapted to: receive the registered exhaust gas pressure (P_m), and on the further basis thereof generate the estimated reference parameter in the form of a second modeled parameter (T_mocι) reflecting an estimation of the desired brake torque.

6. The system according to claim 5, wherein the control means (130) is adapted to: receive the second modeled parameter (T_mod), receive the set value (T_req), and in response thereto produce the control signal (C).

7. The system according to any one of the 5 or 6 claims, wherein the control means (130) is adapted to implement a pro- portional-integrating-derivative algorithm adapted to produce the control signal (C) in order to minimize an error between the set value (T_req) and the second modeled parameter (T_mocι)-

8. A motor vehicle comprising an internal combustion engine (1 10), characterized i n that the vehicle (200) comprises the exhaust brake system (100) according to any one of the claims 1 to 8, the system (100) being configured to apply an adjustable brake torque with respect to at least one drive axis of the engine (1 10).

9. A method of controlling an adjustable valve (135) of an exhaust brake system in a motor vehicle having an internal combustion engine (1 10) in such a manner that the exhaust gasses from the engine (1 10) are obstructed to accomplish a brake torque during the engine's (1 10) exhaust stroke, the method comprising: registering an exhaust gas pressure (P_m) in an exhaust conduit (150) from the engine (1 10), and producing a control signal (C) for the adjustable valve

(135) based on the registered exhaust gas pressure (P_m) and a set value (T_req) designating a desired brake torque, the control signal (C) being adapted to control the adjustable valve (135), characterized by: registering an input pressure (P_in) in an air intake (140) to the engine (1 10), registering an engine parameter (rpm) reflecting a speed of the engine (1 10), and generating a reference parameter (P_m-_mOd; T_mocι) based on a model of a gas exchange work performed by the engine (1 10) and in response to the registered input pressure (P_in) and the registered engine parameter (rpm), and producing the control signal (C) on the further basis of the reference parameter (P_m-_mOci; T_mocι)-

10. The method according to claim 9, comprising: receiving the set value (T_req), and generating the reference parameter in the form of a first modeled parameter (P_m-_mOd) reflecting an estimation of the ex- haust gas pressure in the exhaust conduit (150), the first modeled parameter (P_m-_mOd) being generated based on the registered input pressure (P_in), the registered engine parameter (rpm) and the set value (T_req).

1 1 . The method according to claim 10, comprising: receiving the registered exhaust gas pressure (P_m), receiving the first modeled parameter (P_m-_mOd), and producing the control signal (C) in response thereto

12. The method according to any one of the claims 10 or 1 1 , wherein the control signal (C) is produced based on a propor- tional-integrating-derivative algorithm, in order to minimize an error between the registered exhaust gas pressure (P_m) and the first modeled parameter (P_m-_mOd)-

13. The method according to claim 9, comprising: receiving the registered exhaust gas pressure (P_m), and generating the estimated reference parameter in the form of a second modeled parameter (T_mocι) reflecting an estimation of the desired brake torque, the second modeled parameter (T_mod) being generated based on the registered input pressure (P_in), the registered engine parameter (rpm) and the registered exhaust gas pressure (P_m).

14. The method according to claim 13, comprising: receiving the second modeled parameter (T_mocι), receiving the set value (T_req), and producing the control signal (C) in response thereto.

15. The method according to any one of the claims 13 or 14, wherein the control signal (C) is produced based on a propor- tional-integrating-derivative algorithm, in order to minimize an error between the set value (T_req) and the second modeled parameter (T_mod).

16. A computer program product directly loadable into the internal memory of a computer, comprising software for controlling the steps of any of the claims 9 to 15 when said program is run on the computer.

17. A computer readable medium (170), having a program re- corded thereon, where the program is to make a computer control the steps of any of the claims 9 to 15.