Overspeed prevention control method and device for engine

Abstract

To set a proper gain in feedback control that calculates an overspeed-prevention limit torque Trev and to secure the responsiveness of reacceleration.SOLUTION: A limit torque Trev for preventing overspeed is calculated through feedback control which is based on a deviation between an upper-limit rotational speed Nmax and a current engine rotational speed Ne, and an output torque of an engine is limited with the limit torque Trev. The limit torque Trev is a sum of P-component torque Tp and I-component torque Ti. After lowering of the I-component torque Ti, an I-gain Ig for the calculation of the I-component torque Ti is switched to a relatively smaller second gain IgL. When an engine rotational speed Ne reaches a gain switch rotational speed NeS or lower and a prescribed time has elapsed after a torque limitation, the I-gain Ig is switched to a relatively larger first gain IgH (S13 to 15).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a control method and apparatus for preventing engine overspeed. [Background technology]

[0002] Patent Document 1 discloses a technology in which, when the rotation speed of an engine driving a vehicle approaches an upper limit rotation speed, a limit torque is calculated by feedback control based on the deviation between the upper limit rotation speed and the current engine rotation speed, and the limit torque is used to restrict the output torque of the engine to prevent over-revving.

[0003] The above feedback control is performed in the form of PI control including a P component (proportional component) and an I component (integral component) each calculated based on the deviation, and the limit torque is calculated by adding the P component and the I component. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-245191 A Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned Patent Document 1 does not disclose the gain in the feedback control that calculates the limit torque. In the control that always uses a constant gain, there is a risk that hunting may occur after preventing over-revving, and if the gain is reduced after preventing over-revving, a phenomenon may occur in which the responsiveness during re-acceleration is limited by the limit torque. [Means for solving the problem]

[0006] The present invention provides an engine over-rev prevention control method, which controls an output torque of the engine in accordance with a requested target torque, calculates a limit torque for preventing over-rev by feedback control based on a rotation deviation between an upper limit rotation speed and a current engine rotation speed, and limits the output torque by the limit torque when the limit torque is equal to or less than the target torque, After the output torque is limited by the limit torque, when the limit torque decreases, the feedback gain in the feedback control is reduced, Thereafter, when the engine speed becomes equal to or lower than a predetermined gain switching speed, the feedback gain is increased. Effect of the Invention

[0007] According to this invention, the control behavior is stabilized by reducing the feedback gain after the limit torque is reduced, and then, when the engine speed becomes equal to or lower than a predetermined gain switching speed, the feedback gain is increased, allowing acceleration with good response to a request for re-acceleration at the stage when the engine speed has decreased. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a drive system of a vehicle according to an embodiment. [Diagram 2] 4 is a flowchart showing a basic process flow of over-rotation prevention control. [Diagram 3] 6 is a flowchart showing the flow of a process for switching between large and small I gain Ig. [Figure 4] 4 is a time chart showing an example of the operation of the over-rotation prevention control according to the embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the configuration of a drive system of a vehicle according to the embodiment. The vehicle according to the embodiment is a rear-wheel drive type vehicle, in which a transmission 2 is connected to an engine 1 made of an internal combustion engine, and drive wheels 4 are driven by the output of the transmission 2 via a final reduction gear 3. The transmission 2 may be a manual transmission, but in the embodiment, it is a stepped automatic transmission. Although not shown in detail, the automatic transmission 2 is composed of a torque converter having a lock-up clutch, and a stepped speed change mechanism including a planetary gear mechanism and a plurality of frictional fastening elements (clutches or brakes). The lock-up clutch and the speed change mechanism of the automatic transmission 2 are controlled by an AT controller 5. For example, when a selector 8 for selecting a driving range selects an automatic speed change range (so-called D range), an appropriate speed change stage is selected based on a predetermined speed change map with the accelerator pedal opening and vehicle speed as parameters, and the gear change is performed automatically.

[0010] The automatic transmission 2 also includes an upshift switch 9 and a downshift switch 10, which are paddle switches located on the left and right sides of the steering wheel, for example, so that the driver can change gears. When the selector 8 selects the manual range, the upshift switch 9 and the downshift switch 10 are used to change gears and select a gear stage as desired. In this manual range, the rotation speed of the engine 1 may increase excessively, so that the output torque of the engine 1 may be limited by an overspeed prevention control on the engine 1 side, as described later. In the automatic gear range, the gear stage is automatically changed, so basically, an overspeed prevention control on the engine 1 side is not required.

[0011] The engine 1 is a four-stroke cycle spark ignition internal combustion engine, a so-called gasoline engine. The engine 1 is controlled by an engine controller 6. The AT controller 5 and the engine controller 6 are connected to each other via an in-vehicle network 7 (for example, CAN communication) and transmit and receive necessary signals. The engine controller 6 receives detection signals from sensors such as a crank angle sensor 11 for detecting the engine speed, an air flow meter 12 for detecting the intake air amount corresponding to the load, a water temperature sensor 13 for detecting the cooling water temperature, an accelerator opening sensor 14 for detecting the opening (depression amount) of an accelerator pedal operated by a driver, and an air-fuel ratio sensor 15 for detecting the exhaust air-fuel ratio, directly or via other controllers. Based on these detection signals, the engine controller 6 optimally controls the fuel injection amount and injection timing by the fuel injection valve, the ignition timing by the spark plug, the opening of the throttle valve, and the like.

[0012] Here, the engine controller 6 determines a target torque requested by the driver (also called driver requested torque) based on the accelerator pedal opening and the vehicle speed, and normally controls the output torque of the engine 1 according to this requested target torque. On the other hand, when the engine speed approaches a predetermined upper limit speed, the engine controller 6 calculates a limit torque for preventing over-revving, and limits the output torque of the engine 1 by this limit torque. In other words, the opening of the throttle valve that controls the amount of intake air of the engine 1 is controlled according to the limit torque, thereby preventing the engine 1 from over-revving.

[0013] This over-rev prevention control will now be described.

[0014] 2 is a flowchart showing the flow of basic processing of over-rev prevention control executed by the engine controller 6. First, in step 1, the current gear position of the transmission 2 is read. As described above, it is assumed here that the driver has selected the gear position as the manual range. In the next step 2, the target differential rotation DNt is calculated by multiplying the rotation deviation (Nmax-Ne) between the upper limit rotation speed Nmax and the current engine rotation speed Ne by the rotation speed change rate gain Dg as shown in the following formula.

[0015] DNt = (Nmax-Ne) × Dg The rotation speed change rate gain Dg is set to an optimal value for each gear of the transmission 2. Basically, the lower the gear, the larger the gain Dg is set to. This makes it possible to achieve an output torque limit that is more responsive to the lower gear so as to reliably prevent over-rotation in response to a sudden increase in rotation speed in the lower gear. Note that, in relation to the output characteristics of the engine 1, the gain Dg of a specific gear may be set to a value relatively higher than the value of a gear lower than that.

[0016] Next, in step 3, the target torque requested by the driver, i.e., the driver requested torque Tac, is compared with the limit torque Trev (previous value) at that time. The limit torque Trev is calculated by PI control including a proportional component (P component) and an integral component (I component), as described later.

[0017] If the driver required torque Tac is equal to or less than the limit torque Trev, the process proceeds to step 4, where the I component torque Ti is set to a value equal to the driver required torque Tac. In other words, while the driver required torque Tac is equal to or less than the limit torque Trev, "Ti=Tac." If the driver required torque Tac is equal to or less than the limit torque Trev, no substantial rotation speed restriction (torque restriction) is performed.

[0018] If the driver required torque Tac is greater than the limit torque Trev, the process proceeds from step 3 to step 5, and the I component torque Ti is calculated by integral operation using the target differential rotation speed DNt and I gain Ig as shown in the following equation. As described above, while the driver required torque Tac is equal to or less than the limit torque Trev, "Ti=Tac", so the initial value of the I component torque Ti when the integral operation starts becomes the driver required torque Tac.

[0019] Ti = Ti (previous value) + DNt × Ig When the engine speed Ne exceeds the upper limit speed Nmax and the target differential speed DNt becomes a negative value, the I component torque Ti decreases with each calculation.

[0020] The I gain Ig is set to an optimum value for each gear stage of the transmission 2. Basically, the lower the gear stage, the smaller the I gain Ig is set to.

[0021] Next, in step 6, the P-component torque Tp is calculated by multiplying the target differential speed DNt by the P gain Pg as shown in the following equation.

[0022] Tp = DNt x ​​Pg When the engine speed Ne approaches the upper limit speed Nmax and the target differential speed DNt becomes smaller, the P component torque Tp becomes smaller. When the engine speed Ne exceeds the upper limit speed Nmax and the target differential speed DNt becomes a negative value, the P component torque Tp becomes negative.

[0023] In the next step 7, the P component torque Tp and the I component torque Ti obtained as above are added together to obtain the limit torque Trev, as shown in the following formula.

[0024] Trev=Tp+Ti In the next step 8, the driver required torque Tac and the limit torque Trev are compared in magnitude, and the smaller one is selected as the torque command value. The throttle valve opening of the engine 1 is controlled in accordance with this torque command value.

[0025] Due to the action of such basic over-speed prevention control, when the engine speed Ne approaches the upper limit speed Nmax, the output torque of the engine 1 is limited in accordance with the limit torque Trev calculated by PI control based on the rotation deviation between the two (more specifically, the target differential rotation DNt multiplied by the rotation speed change rate gain Dg), and the engine speed Ne is limited to the vicinity of the upper limit speed Nmax.

[0026] Next, the large / small switching control of the I gain Ig will be described with reference to the flowchart of FIG. 3. As described above, the I gain Ig is set to an appropriate value for each gear stage, and further, a relatively large first gain IgH and a relatively small second gain IgL are provided as the I gain Ig for each gear stage, and either one is selected according to the conditions. In other words, the first gain IgH and the second gain IgL are set to appropriate values ​​for each gear stage. If the I gain Ig is a large value (i.e., the first gain IgH), when the engine rotation speed Ne exceeds the upper limit rotation speed Nmax and the target differential rotation speed DNt continues to be negative, the limit torque Trev is rapidly reduced by the integral action, and the engine rotation speed Ne is rapidly reduced. On the other hand, if the I gain Ig is a small value (i.e., the second gain IgL), the behavior of the control is stable. According to the flowchart of FIG. 3, either the relatively large first gain IgH or the relatively small second gain IgL is selected.

[0027] First, in step 11, it is determined whether the driver required torque Tac exceeds the limit torque Trev. In other words, it is determined whether the output torque is being limited by the limit torque Trev. If the answer is YES, the process proceeds to step 12. If the answer is NO, the output torque limit for preventing over-revving has not started, so the process proceeds to step 15, where a relatively large first gain IgH is selected as the I gain Ig.

[0028] In step 12, it is determined whether the I component torque Ti (previous value) calculated by the integral action is less than a predetermined gain switching torque TiS. If the I component torque Ti is less than the gain switching torque TiS, this means that the I component torque Ti, which occupies a relatively large portion of the limit torque Trev, has been reduced to a sufficiently low level by the action of the over-speed prevention control. If the answer is YES, proceed to step 13. If the answer is NO, proceed to step 15, and a relatively large first gain IgH is selected as the I gain Ig. The gain switching torque TiS is set to an optimal value for each gear.

[0029] In step 13, it is determined whether the engine rotation speed Ne is higher than a predetermined gain switching rotation speed NeS. If the answer is YES, the process proceeds to step 16, where a relatively small second gain IgL is selected as the I gain Ig. If the answer is NO, that is, the engine rotation speed Ne is equal to or lower than the predetermined gain switching rotation speed NeS, the process proceeds to step 14, where it is determined whether the state in which the engine rotation speed Ne is equal to or lower than the predetermined gain switching rotation speed NeS has continued for a predetermined time. If the answer is YES, the process proceeds to step 15, where a relatively large first gain IgH is selected as the I gain Ig. If the answer is NO, that is, the state has not continued for the predetermined time, the process proceeds to step 16, where a relatively small second gain IgL is selected as the I gain Ig.

[0030] Therefore, basically, before the overspeed prevention control is started and immediately after the output torque limit is started as the overspeed prevention control, the I gain Ig is the relatively large first gain IgH, and as a result, the limit torque Trev is quickly reduced to a level required for preventing overspeed. Then, when the I component torque Ti constituting the limit torque Trev is reduced below the gain switching torque TiS, the I gain Ig becomes the relatively small second gain IgL. This stabilizes the control behavior and suppresses hunting. Then, when the engine rotation speed Ne becomes equal to or lower than a predetermined gain switching rotation speed NeS due to a decrease in the driver request torque Tac by the driver, and this state continues for a predetermined time, the I gain Ig becomes the relatively large first gain IgH. This enables re-acceleration according to the driver's request. By setting the condition that the engine rotation speed Ne is equal to or lower than the gain switching rotation speed NeS for a predetermined time, hunting of the I gain Ig switching and therefore undesirable rotation speed fluctuations are suppressed.

[0031] FIG. 4 is a time chart showing an example of the operation of the over-rev prevention control of the embodiment. In FIG. 4, (b) shows the change in the engine speed Ne together with the upper limit speed Nmax. In (a) shows the change in the target differential speed DNt calculated as "(Nmax-Ne) x Dg". In (c) shows the driver required torque Tac, the limit torque Trev, and the I component torque Ti. In (d) shows which of the first gain IgH and the second gain IgL is used as the I gain Ig.

[0032] As can be seen from the change in the driver required torque Tac in Fig. 4, this corresponds to a situation in which, in a certain gear position, the driver required torque Tac becomes large (e.g., maximum), the engine speed Ne reaches the upper limit speed Nmax, over-rev prevention control is started, the driver required torque Tac then decreases, and the driver then accelerates again. Note that Fig. 4 is intended mainly to explain the operation of switching between large and small values ​​of the I gain Ig, and each characteristic line does not necessarily strictly represent the behavior of each part.

[0033] In the illustrated example, the first gain IgH is relatively large in the initial stage. At time t1, the driver depresses the accelerator pedal heavily, resulting in a large driver request torque Tac, and the output torque of the engine 1 increases along with the driver request torque Tac. As a result, the engine speed Ne approaches the upper limit speed Nmax. The limit torque Trev is given as the sum of the P component torque Tp (=DNt×Pg) and the I component torque Ti, but until time t2, the driver request torque Tac is equal to or less than the limit torque Trev, and the I component torque Ti is equal to the driver request torque Tac. Between time t1 and time t2, the limit torque Trev decreases as the target differential rotation speed DNt gradually decreases.

[0034] At time t2, the engine speed Ne reaches the upper limit speed Nmax, and the target differential speed DNt turns from positive to negative. Also, from time t2, the limit torque Trev becomes smaller than the driver required torque Tac, and the output torque of the engine 1 is limited by this limit torque Trev. As the target differential speed DNt becomes a negative value, the P component torque Tp constituting the limit torque Trev becomes negative, and the I component torque Ti by the integral action with the driver required torque Tac as the initial value drops rapidly. Therefore, the increase in the engine speed Ne is quickly suppressed. At this stage, the I gain Ig remains at the relatively large first gain IgH.

[0035] In the illustrated example, when the driver releases the accelerator pedal from a state in which the output torque of the engine 1 is limited as an over-rev prevention control, the driver required torque Tac decreases and becomes smaller than the limit torque Trev. Therefore, the I component torque Ti decreases in a state limited to the driver required torque Tac, and becomes smaller than the predetermined gain switching torque TiS at time t3. Therefore, the I gain Ig is switched to a relatively small second gain IgL. By reducing the I gain Ig in this way, the behavior of the control is stabilized. In addition, even if the accelerator pedal is pressed again immediately after the target differential rotation speed DNt turns positive, the I gain Ig is small, so that the limit torque Trev does not increase rapidly, and the increase in the engine rotation speed Ne from a state close to the upper limit rotation speed Nmax is suppressed.

[0036] After limiting the output torque, at time t4, the engine speed Ne becomes equal to or lower than a predetermined gain switch speed NeS, and when this state continues for a predetermined time, at time t5, the I gain Ig is switched to the first gain IgH.

[0037] In the illustrated example, the driver depresses the accelerator pedal at approximately the same time as time t5, and the driver-requested torque Tac increases rapidly. At this time, the target differential rotation speed DNt is positive, and the I gain Ig is the first gain IgH, so the limit torque Trev becomes even larger than the driver-requested torque Tac. Therefore, the output torque of the engine 1 is not limited to the limit torque Trev, and re-acceleration with good responsiveness is possible. In other words, once the engine speed Ne drops to or below the gain switch speed NeS, re-acceleration according to the driver's request is permitted. Note that, in the illustrated example, this re-acceleration causes the engine speed Ne to exceed the upper limit speed Nmax, and torque restriction is again executed as over-rev prevention control.

[0038] If the I component torque Ti becomes equal to or greater than the gain switching torque TiS before the engine speed Ne becomes equal to or less than the predetermined gain switching speed NeS, the I gain Ig also becomes the first gain IgH.

[0039] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, the transmission 2 may be a manual transmission or a continuously variable transmission that performs a pseudo step shift. In addition, in the above embodiment, the feedback gain is made small when the I-component torque Ti constituting the limit torque Trev becomes less than a predetermined gain switching torque TiS, but the feedback gain may be made small when the entire limit torque Trev becomes less than the predetermined gain switching torque. Furthermore, in the above embodiment, the feedback gain is switched between two values, large and small, but the value of the feedback gain may be changed by multiplying it by a coefficient, for example. [Explanation of symbols]

[0040] 1. Engine 2. Transmission 5...AT controller 6. Engine controller 11...Crank angle sensor 14...Accelerator opening sensor

Claims

1. A control method for preventing over-revving of an engine, comprising: controlling an output torque of the engine in accordance with a requested target torque; calculating a limit torque for preventing over-revving by feedback control based on a rotation deviation between an upper limit rotation speed and a current engine rotation speed; and limiting the output torque by the limit torque when the limit torque is equal to or less than the target torque, After the output torque is limited by the limit torque, when the limit torque decreases, the feedback gain in the feedback control is reduced, Thereafter, when the engine rotation speed becomes equal to or lower than a predetermined gain switching rotation speed, the feedback gain is increased. A control method for preventing engine overspeed.

2. The feedback gain is increased on the basis of a weighted condition that the engine rotation speed continues to be equal to or lower than the gain switching rotation speed for a predetermined period of time.

2. The engine overspeed prevention control method according to claim 1.

3. the limit torque includes a proportional component and an integral component calculated based on the rotation deviation, As the feedback gain, the I gain for calculating the integral is switched between large and small.

2. The engine overspeed prevention control method according to claim 1.

4. After the output torque is limited by the limit torque, when the integral falls below a predetermined gain switching torque, the I gain is made small. Thereafter, when the integral becomes equal to or greater than the gain switching torque, the I gain is increased.

4. The engine overspeed prevention control method according to claim 3.

5. A feedback gain for calculating the proportional portion is set for each gear of the transmission so that the feedback gain is larger for a lower gear.

4. The engine overspeed prevention control method according to claim 3.

6. The rotation deviation is multiplied by the D gain to obtain the target rotation difference. The value obtained by multiplying the target difference rotation by the I gain is successively integrated to obtain the integral, The limit torque is calculated by adding the integral to the proportional part obtained by multiplying the target difference rotation by the P gain.

4. The engine overspeed prevention control method according to claim 3.

7. 1. An engine overspeed prevention control device which controls an output torque of an engine in accordance with a requested target torque, calculates a limit torque for preventing overspeed by feedback control based on a rotation deviation between an upper limit rotation speed and a current engine rotation speed, and limits the output torque by the limit torque when the limit torque is equal to or less than the target torque, When the limit torque starts to be limited by the limit torque and the limit torque decreases, the feedback gain in the feedback control is reduced, and when the engine speed thereafter becomes equal to or lower than a predetermined gain switching speed, the feedback gain is increased. An engine overspeed prevention control device.

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