Vehicle constant speed control device

Abstract

To suppress the occurrence of a busy shift in a transmission when a vehicle is traveling on an uphill road.SOLUTION: A constant speed travel control device 41 comprises: an engine control unit 43 which controls the drive of an internal combustion engine 11; a gear change control unit 44 which causes a transmission 15 to down-shift when a requested driving force exceeds a down determination driving force; and an uphill determination unit 42 which determines whether or not a vehicle 100 is traveling on an uphill road equal to or greater than a prescribed gradient. The gear change control unit 44, when it is determined that the vehicle 100 is traveling on the uphill road equal to or greater than the prescribed gradient, sets the sum of a reference driving force defined from a down-shift line, a gradient equivalent driving force defined from the prescribed gradient, and the difference between a driving force derived from engine torque and the requested driving force as the down determination driving force.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a vehicle constant speed cruise control device that is applied to a vehicle equipped with an internal combustion engine and a stepped transmission. [Background technology]

[0002] Patent Document 1 describes an example of a constant speed cruise control device that controls an internal combustion engine and a transmission so that the vehicle speed becomes a set vehicle speed. In this constant speed cruise control device, a required driving force, which is a required value of the driving force of the vehicle, is set to a magnitude required to maintain the vehicle speed at the set vehicle speed, and engine operation is controlled based on the required driving force. Then, when the required driving force crosses a downshift line, the transmission is downshifted.

[0003] In the constant speed cruise control device described in Patent Document 1, when the vehicle is traveling on an uphill road, the downshift line is shifted to the higher driving force side compared to when the vehicle is not traveling on an uphill road. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 62-155142 Summary of the Invention [Problem to be solved by the invention]

[0005] The output torque of the internal combustion engine is defined as the engine torque, and the engine torque required to realize the required driving force is defined as the required engine torque. When the vehicle starts traveling on an uphill road, the required driving force is increased in order to maintain the vehicle speed at the set vehicle speed. Then, since the required engine torque is increased, the engine operation is controlled to increase the engine torque. However, a response delay of the engine torque may occur. In this case, even if the required driving force increases, the actual driving force does not increase easily, so the required driving force is further increased so that the vehicle speed does not deviate from the set vehicle speed. As described above, even if the downshift line is shifted to the high driving force side because the vehicle is traveling on an uphill road, the required driving force may exceed the downshift line due to a response delay of the engine torque. Then, the transmission is downshifted. After the downshift is performed in this way, when the engine torque starts to increase and the actual driving force increases, the required driving force is reduced in order to maintain the vehicle speed at the set vehicle speed. As a result, the required driving force may fall below the upshift line, and the transmission may be upshifted. That is, when the vehicle is traveling on an uphill road, a busy shift may occur in the transmission. [Means for solving the problem]

[0006] A constant speed cruise control device for a vehicle that solves the above problems is applied to a vehicle equipped with an internal combustion engine and a stepped transmission, and is a device that controls the internal combustion engine and the transmission so that the vehicle speed is maintained at a set vehicle speed. This constant speed cruise control device includes an engine control unit that derives, as a required engine torque, an output torque of the internal combustion engine for realizing a required driving force, which is a driving force necessary to maintain the vehicle speed at the set vehicle speed, and controls operation of the internal combustion engine based on the required engine torque, a gear change control unit that downshifts the transmission when the required driving force exceeds a down-judgment driving force, and a climb judgment unit that judges whether the vehicle is traveling on an uphill road with a predetermined gradient or more. When it is not determined that the vehicle is traveling on an uphill road with a gradient of the specified gradient or greater, the gear shift control unit sets a reference driving force, which is a driving force determined from a downshift line, as the down judgment driving force, and when it is determined that the vehicle is traveling on an uphill road with a gradient of the specified gradient or greater, sets the down judgment driving force to the sum of the reference driving force, a gradient-equivalent driving force, which is a driving force determined from the specified gradient, and the difference between the driving force derived from the output torque of the internal combustion engine and the required driving force.

[0007] According to the above configuration, when the vehicle is traveling on an uphill road with a gradient of a predetermined gradient or more under the condition that the internal combustion engine and the transmission are controlled so that the vehicle speed is maintained at the set vehicle speed, the down-determination driving force is set as follows. That is, the sum of the reference driving force determined from the downshift line, the gradient-equivalent driving force determined from the predetermined gradient, and the difference between the driving force derived from the output torque of the internal combustion engine and the required driving force is set as the down-determination driving force. That is, a value larger than that in the case where it is not determined that the vehicle is traveling on an uphill road with a gradient of a predetermined gradient or more is set as the down-determination driving force, and the larger the difference, the larger the value is set as the down-determination driving force. As a result, even if the required driving force increases because there is a delay in the increase in the output torque of the internal combustion engine relative to the increase in the required engine torque, the required driving force is less likely to exceed the down-determination driving force. As a result, the transmission is less likely to be down-shifted due to a response delay in the output torque of the internal combustion engine.

[0008] Therefore, with the above configuration, it is possible to prevent busy shifts from occurring in the transmission when the vehicle is traveling on an uphill road. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing a vehicle including a control device and a drive train that is an object of control by the control device; [Diagram 2] FIG. [Diagram 3] 3 is a flowchart illustrating the flow of a series of processes executed by a constant speed cruise control device of the control device. [Figure 4] 13A and 13B are timing charts showing a case where the vehicle starts traveling uphill with a predetermined gradient or more while constant speed cruise control is being performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, one embodiment of a vehicle constant speed cruise control device will be described with reference to Figs. <Overall composition> As shown in FIG. 1, a vehicle 100 includes a control device 40 and a drivetrain 10 of the vehicle that is an object to be controlled by the control device 40. The drivetrain 10 includes an internal combustion engine 11 and a transmission 15. Engine torque, which is an output torque of the internal combustion engine 11, is input to drive wheels 20 via the transmission 15. The transmission 15 includes a torque converter 16 and a stepped transmission mechanism 17. For example, the transmission mechanism 17 can change the gear stages from "1st gear" to "6th gear". The engine torque is input to the transmission mechanism 17 via the torque converter 16.

[0011] The control device 40 receives detection signals from various sensors. Examples of the sensors include a throttle opening sensor 51, a crank angle sensor 52, a transmission output shaft sensor 53, a vehicle speed sensor 54, and an acceleration sensor 55. The throttle opening sensor 51 detects a throttle opening SL, which is the opening of a throttle valve provided in an intake passage of the internal combustion engine 11, and outputs the detection result as a detection signal. The crank angle sensor 52 outputs a signal corresponding to an engine speed NE, which is the rotation speed of the crankshaft 11a of the internal combustion engine 11, as a detection signal. The transmission output shaft sensor 53 outputs a signal corresponding to an output speed Nat, which is the rotation speed of an output shaft of the transmission mechanism 17, as a detection signal. The vehicle speed sensor 54 detects a vehicle speed SP, and outputs the detection result as a detection signal. The acceleration sensor 55 detects a longitudinal acceleration GX of the vehicle 100, and outputs the detection result as a detection signal.

[0012] The control device 40 includes a CPU and a ROM. The ROM stores various control programs executed by the CPU. <Constant-speed cruise control device 41> As shown in FIG. 1, the control device 40 has a constant speed cruise control device 41 as a functional unit for implementing constant speed cruise control that controls the internal combustion engine 11 and the transmission 15 so that the vehicle speed SP is maintained at a set vehicle speed SPS.

[0013] The constant speed cruise control device 41 includes a hill-climbing determination unit 42, an engine control unit 43, and a gear shift control unit 44. The uphill determination unit 42 determines whether the vehicle 100 is traveling on an uphill road with a predetermined gradient or more while constant speed traveling control is being performed. For example, the predetermined gradient is set to "10%."

[0014] An example of a method for determining whether the vehicle 100 is traveling on an uphill road with a predetermined gradient or more will be described. There is a correlation between the driving force and the longitudinal acceleration GX of the vehicle 100. Assuming that the vehicle 100 is traveling on an uphill road with a predetermined gradient, and assuming that the longitudinal acceleration GX corresponding to the driving force is set as a reference acceleration, the uphill determination unit 42 determines whether the longitudinal acceleration GX is equal to or less than the reference acceleration. If the longitudinal acceleration GX is equal to or less than the reference acceleration, the uphill determination unit 42 determines that the vehicle 100 is traveling on an uphill road with a predetermined gradient or more. On the other hand, if the longitudinal acceleration GX is greater than the reference acceleration, the uphill determination unit 42 does not determine that the vehicle 100 is traveling on an uphill road with a predetermined gradient or more.

[0015] The engine control unit 43 controls the operation of the internal combustion engine 11 during the implementation of constant speed cruise control. That is, the engine control unit 43 derives an engine torque for realizing a required driving force DPRq, which is a driving force required to maintain the vehicle speed SP at the set vehicle speed SPS, as a required engine torque TQeR. For example, when the vehicle speed SP is less than the set vehicle speed SPS, the engine control unit 43 increases the required driving force DPRq. On the other hand, when the vehicle speed SP exceeds the set vehicle speed SPS, the engine control unit 43 reduces the required driving force DPRq. The engine control unit 43 derives the required engine torque TQeR based on the required driving force DPRq and the current gear stage (gear ratio) of the transmission mechanism 17. For example, when the gear stage of the transmission mechanism 17 is not changed, the engine control unit 43 derives a larger value as the required engine torque TQeR as the required driving force DPRq increases. Then, the engine control unit 43 controls the operation of the internal combustion engine 11 based on the required engine torque TQeR.

[0016] The gear shift control unit 44 controls the gear stage of the transmission mechanism 17 while constant speed cruise control is being performed. Fig. 2 shows an example of a shift map of the transmission 15. In the shift map, upshift lines and downshift lines are set, which are determined by the relationship between the vehicle speed SP and the throttle opening SL. In Fig. 2, the upshift lines are shown by solid lines, and the downshift lines are also shown by solid lines.

[0017] The gear shift control unit 44 derives an upshift reference driving force as a driving force determined from the upshift line. For example, when the third gear is set as the gear stage, the gear shift control unit 44 selects an upshift line for upshifting from the third gear to the fourth gear as a selected upshift line. Next, the gear shift control unit 44 selects a throttle opening SL corresponding to the current vehicle speed SP as a reference throttle opening based on the selected upshift line. In this case, in the graph shown in FIG. 2, the point indicating the current vehicle speed SP and the reference throttle opening is located on the selected upshift line. The gear shift control unit 44 derives an engine torque corresponding to the reference throttle opening as a reference engine torque. Then, the gear shift control unit 44 derives an upshift reference driving force using the reference engine torque and the gear ratio of the gear change mechanism 17.

[0018] The gear shift control unit 44 derives a value corresponding to the upshift reference driving force as the up-judgment driving force. When the required driving force DPRq transitions from a state in which it is equal to or greater than the up-judgment driving force to a state in which it is smaller than the up-judgment driving force, the gear shift control unit 44 upshifts the transmission mechanism 17. That is, the gear shift control unit 44 selects a higher speed gear with a larger gear ratio as the gear.

[0019] On the other hand, the gear shift control unit 44 derives a downshift reference driving force as a driving force determined from the downshift line. For example, when the fourth gear is set as the gear stage, the gear shift control unit 44 selects a downshift line for downshifting from the fourth gear to the third gear as a selected downshift line. Next, the gear shift control unit 44 selects a throttle opening SL corresponding to the current vehicle speed SP as a reference throttle opening based on the selected downshift line. In this case, in the graph shown in FIG. 2, the point indicating the current vehicle speed SP and the reference throttle opening is located on the selected downshift line. The gear shift control unit 44 derives an engine torque corresponding to the reference throttle opening as a reference engine torque. Then, the gear shift control unit 44 derives a downshift reference driving force DPb using the reference engine torque and the gear ratio of the transmission mechanism 17.

[0020] The gear shift control unit 44 derives the downshift determination driving force DPTh based on the downshift reference driving force DPb. When the required driving force DPRq transitions from a state in which it is equal to or less than the downshift determination driving force DPTh to a state in which it is greater than the downshift determination driving force DPTh, the gear shift control unit 44 downshifts the transmission mechanism 17. In other words, the gear shift control unit 44 selects a lower gear ratio with a smaller gear ratio as the gear ratio.

[0021] 3 illustrates the flow of a series of processes executed by the constant speed cruise control device 41 to determine whether or not to downshift the transmission mechanism 17 while the constant speed cruise control is being performed. The constant speed cruise control device 41 repeatedly executes the series of processes while the constant speed cruise control is being performed.

[0022] In the series of processes, first in step S11, the gear shift control unit 44 of the constant speed cruise control device 41 derives a downshift reference driving force DPb based on the selected downshift line. Then, in step S13, the climb determination unit 42 of the constant speed cruise control device 41 determines whether the vehicle 100 is traveling on an uphill road with a predetermined gradient or more. If it is not determined that the vehicle 100 is traveling on an uphill road with a predetermined gradient or more (S13: NO), the constant speed cruise control device 41 shifts the process to step S15. In step S15, the gear shift control unit 44 sets the downshift reference driving force DPb as a downshift determination driving force DPTh. Then, the constant speed cruise control device 41 shifts the process to step S23.

[0023] On the other hand, if it is determined in step S13 that the vehicle 100 is traveling on an uphill road with a gradient equal to or greater than a predetermined gradient (YES), the constant speed cruise control device 41 transitions the process to step S17. In step S17, the gear shift control unit 44 derives an actual driving force DP, which is the actual driving force at the current time. For example, the gear shift control unit 44 can derive the actual driving force DP based on the current engine torque TQe and the gear ratio of the transmission mechanism 17.

[0024] Next, in step S19, the gear shift control unit 44 derives the difference ΔDP between the required driving force DPRq and the actual driving force DP. Then, in step S21, the gear shift control unit 44 derives the sum of the downshift reference driving force DPb, the difference ΔDP, and the gradient equivalent driving force DPup as the downshift determination driving force DPTh. The gradient equivalent driving force DPup is a driving force determined from a predetermined gradient. After deriving the downshift determination driving force DPTh, the gear shift control unit 44 transitions the process to step S23.

[0025] In step S23, the gear shift control unit 44 determines whether the required driving force DPRq is greater than the down-determination driving force DPTh. If the required driving force DPRq is equal to or less than the down-determination driving force DPTh (S23: NO), the gear shift control unit 44 ends the series of processes. In this case, the gear shift control unit 44 does not change the gear position of the transmission mechanism 17.

[0026] On the other hand, if the required driving force DPRq is greater than the down-determination driving force DPTh in step S23 (YES), the gear shift control unit 44 transitions the process to step S25. In step S25, the gear shift control unit 44 downshifts the transmission mechanism 17. That is, the gear shift control unit 44 changes the gear position to a lower gear position by one position. Then, the gear shift control unit 44 ends the series of processes.

[0027] <Actions and Effects of the Present Embodiment> Fig. 4 shows a timing chart when the vehicle 100 starts traveling on an uphill road with a predetermined gradient or more while the constant speed cruise control is being performed. Fig. 4(A) shows the transition of the driving force. Fig. 4(B) shows the transition of the engine torque.

[0028] 4, before timing t1, the gradient of the road surface on which the vehicle 100 is traveling is less than a predetermined gradient. Therefore, the downshift reference driving force DPb is set as the downshift determination driving force DPTh.

[0029] However, at time t1, it is determined that the vehicle 100 is traveling on an uphill road with a gradient equal to or greater than a predetermined gradient. Then, the downshift determination driving force DPTh is increased. That is, the sum of the downshift reference driving force DPb, the gradient equivalent driving force DPup, and the difference ΔDP is derived as the downshift determination driving force DPTh.

[0030] When the gradient of the road surface on which the vehicle 100 is traveling increases, it is necessary to increase the driving force of the vehicle 100 in order to maintain the vehicle speed SP at the set vehicle speed SPS. Therefore, the required driving force DPRq is increased.

[0031] When the required driving force DPRq is increased, the required engine torque TQeR is also increased. Then, the operation of the internal combustion engine 11 is controlled based on the required engine torque TQeR. However, as shown in FIG. 4(B), even if the required engine torque TQeR is increased in response to an increase in the required driving force DPRq, the increase in the actual engine torque TQe is delayed. In this case, the deviation between the vehicle speed SP and the set vehicle speed SPS tends to increase. Therefore, as shown in FIG. 4(A), the required driving force DPRq becomes even larger.

[0032] When the increase in engine torque TQe is delayed and the deviation between requested engine torque TQeR and engine torque TQe becomes large, such as in the period from timing t1 to timing t2, the difference ΔDP between requested driving force DPRq and actual driving force DP becomes large. Therefore, during this period, the down determination driving force DPTh becomes large.

[0033] As a result, even if the required driving force DPRq increases due to a response delay of the engine torque TQe, the required driving force DPRq is unlikely to become larger than the down-determining driving force DPTh. As a result, it is possible to suppress a downshift from occurring during the response delay period of the engine torque TQe. Therefore, in this embodiment, it is possible to suppress a busy shift from occurring in the transmission mechanism 17 when the vehicle 100 starts traveling on an uphill road while the constant speed traveling control is being performed.

[0034] (Example of change) The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0035] The determination as to whether the vehicle 100 is traveling on an uphill road with a gradient of a predetermined gradient or more may be made by a method different from that described in the above embodiment. For example, if the road information obtained from the navigation device includes information on the gradient of the road, the determination can be made based on the road information obtained from the navigation device.

[0036] The transmission mechanism may be different from the transmission mechanism 17 as long as it is configured to be able to select multiple gears. For example, the transmission mechanism may be one that has seven or more selectable gears, or one that has five or fewer selectable gears.

[0037] The transmission does not have to include the torque converter 16 so long as it includes a stepped transmission mechanism. The control device 40 is not limited to a device having a CPU and ROM and executing software processing. That is, the control device 40 may have any one of the following configurations (a) to (c). (a) The control device 40 includes one or more processors that execute various processes according to a computer program. The processor includes a CPU and memory such as RAM and ROM. The memory stores program codes or instructions that are configured to cause the CPU to execute processes. The memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or special-purpose computer. (b) The control device 40 includes one or more dedicated hardware circuits for executing various processes. Examples of the dedicated hardware circuits include application specific integrated circuits, i.e., ASIC and FPGA. ASIC is an abbreviation for "Application Specific Integrated Circuit" and FPGA is an abbreviation for "Field Programmable Gate Array." (c) The control device 40 includes a processor that executes some of the various processes in accordance with a computer program, and a dedicated hardware circuit that executes the remaining processes among the various processes. [Explanation of symbols]

[0038] 11...Internal combustion engine 15…Gearbox 41... Cruise control device 42...Climbing judgement section 43...Engine control unit 44...Gear shift control section 100…Vehicle

Claims

[Claim 1] A vehicle constant speed control device that is applied to a vehicle having an internal combustion engine and a stepped transmission and controls the internal combustion engine and the transmission so that a vehicle speed is maintained at a set vehicle speed, an engine control unit that derives, as a required engine torque, an output torque of the internal combustion engine for realizing a required driving force, which is a driving force necessary to maintain the vehicle speed at the set vehicle speed, and controls an operation of the internal combustion engine based on the required engine torque; a gear shift control unit that downshifts the transmission when the down-shift determination driving force exceeds the required driving force; a slope determination unit that determines whether the vehicle is traveling on an uphill road with a gradient of at least a predetermined gradient, The gear shift control unit is When it is not determined that the vehicle is traveling on an uphill road having a gradient equal to or greater than the predetermined gradient, a reference driving force, which is a driving force determined from a downshift line, is set as the downshift determination driving force, When it is determined that the vehicle is traveling on an uphill road having a gradient equal to or greater than the predetermined gradient, the sum of the reference driving force, a gradient-equivalent driving force which is a driving force determined from the predetermined gradient, and a difference between a driving force derived from an output torque of the internal combustion engine and the required driving force is set as the downhill determination driving force. A vehicle constant speed control device.

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