Method of operating a combustion engine

Abstract

 The invention relates to a method of operating a combustion engine (10), wherein a clutch torque (M_cl) of said combustion engine (10) is determined, characterized in that a value (M_ω_k) of said clutch torque (M_cl) for a specific, particularly k-th, operating cycle of said combustion engine (10) is determined depending on a value (M_ω_k-1) of said clutch torque (M_cl) for a preceding, particularly (k-1)-th, k=1, 2, 3, .., operating cycle of said combustion engine (10), and on a delta torque value (ΔM) characterizing a change of said clutch torque (M_cl) between said preceding operating cycle and said specific operating cycle.

Description

Prior Art

[0001] The present invention relates to a method of operating a combustion engine, wherein a clutch torque of said combustion engine is determined. The present invention also relates to a control unit for operating a combustion engine, wherein said control unit is configured to determine a clutch torque of said combustion engine.

[0002] German patent publication DE 10 2006 056 708 A1 discloses a determination of a torque of a crankshaft of a combustion engine depending on the crankshaft speed.

[0003] It is an object of the invention to improve the prior art systems.

Disclosure of the Invention

[0004] The invention solves this object by a method according to claim 1. As well, the invention solves this object by a control unit according to claim 9.

[0005] The method according to the invention is characterized in that a value of said clutch torque for a specific, particularly k-th, operating cycle of said combustion engine is determined depending on a value of said clutch torque for a preceding, particularly (k-1)-th, operating cycle of said combustion engine, and on a delta torque value characterizing a change of said clutch torque between said preceding operating cycle and said specific operating cycle. I.e., according to one aspect, the inventive approach proposes to incrementally build the clutch torque taking into consideration a previous value / previous values of the clutch torque and a change / changes of the torque between different operating cycles of the combustion engine. This enables a particularly efficient determination of an instantaneous clutch torque, because a previous clutch torque value of a previous operating cycle is usually already known and the delta torque value can easily be determined according to embodiments of the invention.

[0006] According to a preferred embodiment, said delta torque value is determined depending on at least one of the following parameters: a signal characterizing a rotational speed of a crankshaft, a polar moment of inertia of the combustion engine's components coupled to a crankshaft of the combustion engine. According to a preferred embodiment, it is beneficial to consider a current value of the polar moment of inertia, which may depend on a drive train condition such as e.g. a state of the clutch (engaged or disengaged) and/or a gear currently selected if the clutch state is engaged, and/or a geometry of wheels of a vehicle comprising the combustion engine and/or two-wheel-drive or four-wheel-drive, and the like.

[0007] According to a further embodiment, said signal characterizing said rotational speed of the crankshaft is determined by a crankshaft sensor.

[0008] According to a further preferred embodiment, which enables a particularly precise assessment of the clutch torque, a friction torque corresponding with friction losses in the combustion engine is considered for determining said clutch torque.

[0009] According to a further embodiment, said value of said clutch torque for said specific, particularly k-th, operating cycle of said combustion engine is determined depending on the following equation:


wherein M(ω_k) represents a value of the clutch torque for said specific k-th operating cycle of the combustion engine, wherein M(ω_k-1) represents a value of said clutch torque for a preceding, i.e. (k-1)-th, operating cycle of said combustion engine, wherein M_F represents a friction torque of said combustion engine, wherein J represents a polar moment of inertia corresponding to the parts of the combustion engine coupled with the crankshaft, wherein ω represents an angular crankshaft speed, wherein N represents a number of tooth time values considered for determining said delta torque value between two subsequent operating cycles of the combustion engine, and wherein Δt_i represents the i-th tooth time value associated with the respective crankshaft speed.

[0010] According to a further embodiment, a crankshaft sensor is used that cooperates with a tooth wheel which is coupled to the crankshaft.

[0011] According to a further embodiment, for a plurality of operating cycles k of said combustion engine, preferably for all operating cycles of the combustion engine counted from a start of said combustion engine, a respective delta torque value is determined and at least temporarily stored.

[0012] According to a further embodiment, said clutch torque is used for at least one of the following procedures: A closed-loop control of said combustion engine, e.g. for setting a desired clutch torque, determining torque losses of the combustion engine, verifying an inner torque of the combustion engine.

[0013] A further solution to the object of the present invention is given by a control unit according to claim 9.

[0014] Further advantageous embodiments are given by the dependent claims.

[0015] Further features, possible uses and advantages of the invention will become apparent from the ensuing description of the exemplary embodiments of the invention, which are shown in the drawing figures. All the features described or shown are the subject of the invention on their own or in arbitrary combination, regardless of how they are summarized in the claims or of their dependency and regardless of how they are worded or shown in the specification and the drawings, respectively.

[0016] In the drawings:

figure 1

schematically depicts a block diagram according to a first embodiment of the present invention,

figure 2

schematically depicts a tooth wheel of a crankshaft sensor that can be used for the present invention,

figure 3

schematically depicts crankshaft tooth time distances that may be used according to the invention, and

figure 4

schematically depicts a block diagram of a combustion engine according to the invention.

[0017] Figure 1 schematically depicts a block diagram of an embodiment of a method according to the present invention. According to the present invention, it is proposed to determine a clutch torque of a combustion engine depending on a previous value of the clutch torque of a preceding operating cycle and depending on a delta torque value which characterizes a change of the clutch torque between said preceding operating cycle and a specific operating cycle.

[0018] For example, if a specific value of a clutch torque of a combustion engine at a k-th operating cycle is to be determined, according to the present invention, an already known value for the clutch torque of the preceding operating cycle, i.e. the (k-1)-th operating cycle, is taken into consideration. Further, to account for any changes in the clutch torque between the preceding operating cycle and the considered k-th operating cycle, a delta torque value ΔM is also considered. Based on these two parameters, the actual value of the clutch torque for the considered specific operating cycle k, namely the value M_ω_k is determined. Fig. 1 depicts these function relationships by a function block that receives as input parameters the clutch torque M_ω_k-1 of a preceding operating cycle and said delta torque value ΔM. The function block determines based on these input parameters a clutch torque M_ω_k of a current operating cycle, wherein M_cl denotes a specific clutch torque value so obtained.

[0019] The function block of Fig. 1 may e.g. be implemented in form of software and/or hardware and/or firmware, e.g. of a control unit 20 (Fig. 4) controlling an operation of the combustion engine 10.

[0020] Figure 4 depicts a block diagram of the combustion engine 10 which comprises a crankshaft 12. A crankshaft sensor 14 comprises a tooth wheel 14a that is coupled with the crankshaft 12 and that operates together with the crankshaft sensor 14 in a per se known manner to provide a crankshaft speed signal which characterizes the angular velocity of the crankshaft 12.

[0021] According to an embodiment of the present invention, this angular velocity of the crankshaft 12 is determined, and on this basis, the clutch torque M_cl of the combustion engine 10 is determined for specific operating cycles of the combustion engine 10.

[0022] The method according to the embodiments may e.g. be implemented in form of a software program for a processor (not shown) which is comprised within the control unit 20 that controls operation of the combustion 10 in a per se known manner.

[0023] Fig. 2 schematically depicts a tooth wheel 14a of a crankshaft sensor 14 (Fig. 4) that can be used with the present invention. Presently, the tooth wheel 14a comprises a total number of 58 teeth T, wherein teeth number 0, 1, 40, 48 are denoted with corresponding numbers for illustrative purposes. This type of wheel is also denoted as "60-2 wheel". An angular distance between two neighboring teeth e.g. comprises about six degrees. When the wheel 14a turns together with the engine's crankshaft 12 (Fig. 4), the sensor 14 detects a nearly rectangular or at least substantially sinusoidal, periodic signal (caused by the teeth T and gaps between said teeth passing by), the fundamental frequency of which corresponds with an angular speed of the wheel 14a and enables determination of the wheel speed.

[0024] Fig. 3 schematically depicts crankshaft tooth time distances that may be used according to the invention, which may be obtained by using a tooth wheel 14a as depicted by Fig. 2. As can be seen from Fig. 3, an angular movement of the wheel by a first angle θ₁ corresponds to a "tooth time" of Δt₁, and a second angle θ₂ corresponds to a "tooth time" of Δt₂, and so on.

[0025] According to a particularly preferred embodiment, the clutch torque of a k-th operating cycle of the combustion 10 is determined depending on the following equation:


wherein M(ω_k) represents a value of the clutch torque M_cl (Fig. 1) for said specific k-th operating cycle of the combustion engine 10 (Fig. 4), wherein M(ω_k-1) represents a value of said clutch torque M_cl (Fig. 1) for a preceding, i.e. (k-1)-th, operating cycle of said combustion engine 10, wherein M_F represents a friction torque of said combustion engine 10, wherein J represents a polar moment of inertia corresponding to the parts (not shown) of the combustion engine 10 coupled with the crankshaft, wherein ω represents an angular crankshaft speed, wherein N represents a number of tooth time values considered for determining said delta torque value between two subsequent operating cycles of the combustion engine, and wherein Δt_i represents the i-th tooth time value associated with the respective crankshaft speed.

[0026] Parts of the engine 10 coupled with the crankshaft 12 may e.g. be parts of the drive train when the clutch is engaged, as well as e.g. wheels driven by the drive train, and the like. As such, for evaluating the above equation, it is beneficial if a specific value of the polar moment of inertia J is considered which reflects the actual situation of elements coupled to the crankshaft. For example, when the clutch is engaged, the value of J is expected to be higher than when the clutch is disengaged, and the like. The different values for parameter J may be determined during a test series and e.g. stored in the control unit 20 in form of a look-up table or the like.

[0027] For a stopped combustion engine 10, assuming that this state represents the operating cycle k=0, the above equation can be reduced to:

wherein M_F may also be determined during a test series and stored for future use.

[0028] For the subsequent operating cycle, i.e. k = 1, the above equation yields:


wherein M(ω₀) can be taken from the preceding evaluation of the equation, M_F is also known, e.g. by testing and/or look-up table. Insofar, only the portion

of the equation remains to be evaluated to determine the current clutch torque of the operating cycle k=1. Hence, the portion

is also referred to as delta torque value ΔM (Fig. 1) in the sense of the present invention, because it characterizes the torque change between subsequent operating cycles k=0, 1, ...

[0029] The term

may e.g. be evaluated over one engine revolution (crankshaft revolution), wherein the Δt_i represents the tooth time values as illustrated by Fig. 3, which can be determined in a per se known manner, and wherein "N" determines the overall number of subsequent tooth times the corresponding sum

is evaluated for.

[0030] On this basis, the clutch torque M(ω₁) of operating cycle k = 1 may be determined, and so on.

[0031] According to one embodiment, the series M(ω_k) k=0, 1, 2, .. may be determined from the start of the engine 10, e.g. up to a subsequent deactivation of the engine 10. By temporarily storing already determined values of M(ω_k), the subsequent values M(ω_k+1), M(ω_k+2), .. may be efficiently determined.

[0032] According to a further embodiment, the clutch torque M_cl so determined is used for at least one of the following procedures:

• a closed-loop control of said combustion engine 10, e.g. for setting a desired clutch torque,
• determining torque losses of the combustion engine 10, e.g. by comparing the clutch torque determined according to the invention with an inner torque obtained by some other function well known to the skilled man,
• verifying an inner torque of the combustion engine (10).

[0033] Advantageously, since the inventive principle is based on the crankshaft angular speed, an existing sensor 14 may be used and especially no cylinder pressure sensors or the like are required.

Claims

1. Method of operating a combustion engine (10), wherein a clutch torque (M_cl) of said combustion engine (10) is determined, characterized in that a value (M_ω_k) of said clutch torque (M_cl) for a specific, particularly k-th, operating cycle of said combustion engine (10) is determined depending on a value (M_ω_k-1) of said clutch torque (M_cl) for a preceding, particularly (k-1)-th, k=1, 2, 3, .., operating cycle of said combustion engine (10), and on a delta torque value (ΔM) characterizing a change of said clutch torque (M_cl) between said preceding operating cycle and said specific operating cycle.

2. Method according to claim 1, wherein said delta torque value (ΔM) is determined depending on at least one of the following parameters:

• a signal (s_ω) characterizing a rotational speed of a crankshaft (12),

• a polar moment of inertia of the combustion engine's components coupled to a crankshaft of the combustion engine (10).

3. Method according to one of the preceding claims, wherein said signal (s_ω) characterizing said rotational speed of the crankshaft (12) is determined by a crankshaft sensor (14).

4. Method according to one of the preceding claims, wherein a friction torque corresponding with friction losses in the combustion engine (10) is considered for determining said clutch torque (M_cl).

5. Method according to one of the preceding claims, wherein said value (M_ω_k) of said clutch torque for said specific, particularly k-th, operating cycle of said combustion engine (10) is determined depending on the following equation:

wherein M(ω_k) represents a value of the clutch torque for said specific k-th operating cycle of the combustion engine, wherein M(ω_k-1) represents a value of said clutch torque for a preceding, i.e. (k-1)-th, operating cycle of said combustion engine, wherein M_F represents a friction torque of said combustion engine, wherein J represents a polar moment of inertia corresponding to the parts of the combustion engine coupled with the crankshaft, wherein ω represents an angular crankshaft speed, wherein N represents a number of tooth time values considered for determining said delta torque value between two subsequent operating cycles of the combustion engine, and wherein Δt_i represents the i-th tooth time value associated with the respective crankshaft speed.

6. Method according to one of the preceding claims, wherein a crankshaft sensor (14) is used that cooperates with a toothed wheel (14a) which is coupled to the crankshaft (12).

7. Method according to one of the preceding claims, wherein for a plurality of operating cycles k of said combustion engine (10), preferably for all operating cycles of the combustion engine (10) counted from a start of said combustion engine (10), a respective delta torque value (ΔM_k) is determined and at least temporarily stored.

8. Method according to one of the preceding claims, wherein said clutch torque (M_cl) is used for at least one of the following procedures:

- a closed-loop control of said combustion engine (10),

- determining torque losses of the combustion engine (10),

- verifying an inner torque of the combustion engine (10).

9. Control unit (20) for operating a combustion engine (10), wherein said control unit (20) is configured to determine a clutch torque (M_cl) of said combustion engine (10), characterized in that said control unit (20) is further configured to determine a value (M_ω_k) of said clutch torque (M_cl) for a specific, particularly k-th, operating cycle of said combustion engine (10) depending on a value (M_ω_k-1) of said clutch torque (M_cl) for a preceding, particularly (k-1)-th, k=1, 2, 3, .., operating cycle of said combustion engine (10), and on a delta torque value (ΔM) characterizing a change of said clutch torque (M_cl) between said preceding operating cycle and said specific operating cycle.

10. Control unit (20) according to claim 9, wherein said control unit (20) is configured to perform the method according to one of the claims 1 to 8.

Drawing