Method and engine brake system to control an engine brake of a vehicle

Abstract

A method and system to control an engine brake of a vehicle is provided. The vehicle is provided with a combustion engine having cylinders, an exhaust pressure governor (EPG) regulating the air flow out of the cylinders, an intake air throttle valve (ITV) regulating the air flow into the cylinders, pressure sensing means for sensing a pressure downstream of the cylinders, wherein an engine braking torque can be regulated in two different engine braking modes (a, b), a first engine braking mode (a), in which the air flow through the EPG is regulated by a closed loop control using the pressure downstream of the cylinders and the ITV is regulated in a feed forward control dependent of the engine speed and a demanded brake torque; a second engine braking mode (b), in which the EPG is regulated in a feed forward control dependent of the engine speed and the demanded brake torque, and the ITV regulates the braking torque by a closed loop control using the pressure downstream of the cylinders.

Claims

1. A method to control an engine brake of a vehicle, the vehicle being provided with a combustion engine having cylinders, an exhaust pressure governor (EPG) regulating the air flow out of the cylinders, an intake air throttle valve (ITV) regulating the air flow into the cylinders, and pressure sensing means for sensing a pressure downstream of the cylinders, the method comprising regulating an engine braking torque in a first engine braking mode (a), in which the air flow through the EPG is regulated by a closed loop control using the pressure downstream of the cylinders and the ITV is regulated in a feed forward control dependent of the engine speed and a demanded brake torque; regulating the engine braking torque in a second engine braking mode (b), in which the EPG is regulated in a feed forward control dependent of the engine speed and the demanded brake torque, and the ITV regulates the braking torque by a closed loop control using the pressure downstream of the cylinders; and determining which of the first and the second engine braking mode (a, b) should be used based on a demanded braking torque and an actual engine speed.

2. The method according to claim 1, comprising sensing exhaust manifold pressure from the cylinders via the sensing means for sensing a pressure downstream of the cylinders.

3. The method according to claim 1, wherein a determination to use the second braking mode (b) is at least partially based on whether a demanded braking torque is below a braking torque threshold value, or an actual engine speed is above an engine speed threshold value.

4. The method according to claim 3, wherein a determination to use the first braking mode (a) is at least partially based on whether a demanded engine braking torque is above an engine torque threshold value and an actual engine speed is below an engine speed threshold value.

5. The method according to claim 4, comprising switching from the second braking mode (b) to the first braking mode (a) when the demanded braking torque increases above an engine torque threshold value and the engine speed is below an engine speed threshold value, or when the actual braking torque is above an engine torque threshold value and the engine speed is increasing above the engine speed threshold value.

6. The method according to claim 4, comprising switching from the first braking mode (a) to the second braking mode (b) when the demanded braking torque is decreasing below an engine torque threshold value, or when the actual engine speed is increased above an engine speed threshold value, or when the EPG is completely open and the demanded exhaust manifold pressure is lower than an actual exhaust manifold pressure, or when an EPG actuator failure occurs.

7. The method according to claim 4, wherein the engine torque threshold value comprises a first and a second engine torque threshold value, wherein the first engine torque threshold value is lower than the second engine torque threshold value, and the engine speed threshold value comprises a first and a second engine speed threshold value, wherein the first engine speed threshold value is lower than the second engine speed threshold value, wherein the first engine torque and engine speed threshold values are used when a respective value of the first engine torque and engine speed threshold values decreases and the second engine torque and engine speed threshold value are used when the respective value of the first engine torque and engine speed threshold values increases.

8. The method according to claim 7, wherein the first engine torque threshold value is dependent of the engine speed.

9. The method according to claim 1, wherein the engine is equipped with a charge air cooler bypass valve (CAC), the method comprising controlling the CAC to increase or decrease the exhaust manifold pressure.

10. An engine brake system for a vehicle, comprising a control unit arranged to perform the method steps of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described in detail with reference to the figures, wherein:

(2) FIG. 1 shows a schematic drawing of an engine and its inlet and exhaust gas system;

(3) FIG. 2 shows a schematic diagram of the available engine braking torque; and

(4) FIG. 3 shows a diagram over the inventive regulation modes of the engine torque.

DETAILED DESCRIPTION

(5) In the following only one embodiment of the invention is shown and described, simply by way of illustration of one node of carrying out the invention. The invention is not limited to the specific diagrams presented, but includes all variations within the scope of the present claims.

(6) Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.

(7) FIG. 1 shows a schematic view of an engine (10) and its air intake and exhaust gas flows, in FIG. 1 is only flows relevant for the invention disclosed. The engine (10) comprises six cylinders (11), the number of cylinders is however not important for the invention. The air intake flow is regulated by an intake air throttle valve (ITV) arranged in the air intake channel (21). A charge air cooler (CAC) is arranged upstream in the intake air flow, the CAC is able to cool the intake air flow. A CAC bypass-valve (22) is arranged upstream of the CAC, such that the intake air flow can bypass the CAC through the CAC bypass-valve (22). The CAC bypass-valve (22) leads to a bypass channel (23), which joints with the air intake channel (21) downstream of the ITV. In the FIG. 1 is also a turbo component 24 disclosed. The turbo component 24 obviously influences the specification of the whole engine system, does however not influence the inventive control modes. The invention is applicable to an engine with or without a turbo component 24. Further in FIG. 1 is also auxiliary devices 25 disclosed. The auxiliary devices 25 obviously influences the specification of the whole engine system, does however not influence the inventive control modes. The invention is applicable to an engine with or without a turbo component 25.

(8) FIG. 2 discloses a characteristic diagram showing a relationship between engine braking torque (Nm) and rotational speed (rpm) of the engine (10). The upper curve (TEPG) discloses the braking torque (T) achieved with just the EPG activated. The middle curve (TCB) discloses the minimum braking torque (T) that can be achieved with the EPG and the compression brake activated, i.e. the EPG is regulated to deliver its minimum contribution to the total braking torque. The lowest curve (Tfull) discloses the maximum braking torque deliverable by the engine brake. With a control method according to the prior art, the area (A) between the upper (TEPG) and the middle (TCB) corresponds to none adjustable engine brake area (A). Due to the inventive engine brake modes (a, b) of the ITV for controlling the braking torque of the compression brake, the engine brake is adjustable within a large part of this area.

(9) By throttling the air flow into the cylinders (11) of the combustion engine (10) a smaller amount of air mass is compressed in the cylinders (11) during engine braking, and thereby is less braking torque developed. A decreased braking torque contribution from the compression brake is thereby achieved. An infinite or discrete regulation of the total braking torque (T) is available within the whole available braking torque area.

(10) FIG. 3 discloses a schematic diagram of the control between the first and the second engine brake mode a, b. The only curve Tmax discloses the maximum braking torque at different engine speeds S. The two vertical lines tS1 tS2 represent the engine speed threshold values S at which a switch from braking mode a to braking mode b is actuated and at which a switch from braking mode b to braking mode a is actuated respectively. The two horizontal lines tT1, tT2 represent the engine braking torque threshold values T at which a switch from braking mode b to braking mode a is actuated and at which a switch from braking mode a to braking mode b is actuated respectively, at engine speeds below the engine speed threshold value tS. The actual braking torque threshold values can however vary with the engine speed.

(11) Having different values tS1, tS2, tT1 and tT2 for decreasing and for increasing actual respectively demanded speed (S) and torque (T) values and decreasing, actual respectively demanded speed (S) and torque (T) values, minimises the risk for unnecessary switching between the different engine brake modes.

(12) A not disclosed control unit is arranged to perform the method steps according to the different embodiments.

(13) As will be realised, the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims. Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.