Transmission lubrication oil temperature control system

Abstract

This system appropriately addresses the increased fluid stirring losses within the transmission. [Solution] The control unit calculates the transmission loss based on the input torque and input rotational speed of the transmission (ST2), estimates the amount of heat generated other than the transmission loss based on the environment in which the transmission is located (ST3), estimates the amount of heat removed from the lubricating oil based on the environment in which the transmission is located (ST4), calculates the maximum allowable heat amount to reach the upper limit temperature after a set time from the calculated transmission loss, the estimated amount of other heat generated, the estimated amount of heat removed, the detected lubricating oil temperature, a preset upper limit temperature, and a preset lubricating oil heat capacity (ST5), a maximum input torque calculation means (ST6) that finds the maximum input torque corresponding to the calculated maximum allowable heat amount, and controls the input torque of the transmission to be less than or equal to the maximum input torque using the calculated maximum input torque (ST7).

Description

Technical Field

[0001] The present disclosure relates to a lubricating oil temperature control system for controlling the lubricating oil temperature of a transmission.

Background Art

[0002] In a vehicle, a transmission is often provided to efficiently transmit the driving force from a driving source that outputs a driving force such as an engine or a motor to the wheels.

[0003] In this transmission, in order to change the gear ratio according to the vehicle speed, output torque, etc., the gear ratio of the gears that transmit power is changed. Therefore, the energy loss in the transmission is large. Thus, sufficient lubricating performance is required for the lubricating oil.

[0004] Here, since the performance of the lubricating oil deteriorates when its oil temperature rises, there is a requirement to keep it below a predetermined upper limit temperature.

[0005] In Patent Document 1, when it is estimated that the transmission loss has risen rapidly, overheating of the lubricating oil is detected, and when overheating is detected, overheating suppression control is executed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Patent Document 1 calculates the internal stirring judgment value using the formula "Internal stirring judgment value = Change in motor loss per unit time / Change in transmission lubrication oil temperature per unit time," and determines that transmission loss has increased sharply when this internal stirring judgment value falls below a certain value. Here, the change in temperature is used as the denominator of this judgment value. Therefore, early detection of overheating may be difficult due to the measurement delay. For example, even if the temperature actually rises sharply due to transmission loss, if the change in temperature does not change or the change is smaller than it actually is due to the measurement delay or filtering process, or if the denominator of the internal stirring judgment value is zero or too small and the internal stirring judgment value approaches infinity, it is thought that overheating cannot be properly detected. [Means for solving the problem]

[0008] The lubrication oil temperature control system relating to this disclosure is a lubrication oil temperature control system for controlling the lubrication oil temperature of a transmission, and includes a control unit that controls the input torque of the transmission based on the lubrication oil temperature of the transmission, the input rotational speed of the transmission, and the input torque of the transmission, wherein the control unit includes a transmission loss estimation means that calculates the transmission loss based on the detected input torque of the transmission and the input rotational speed of the transmission, and other heat generation estimation means that estimates other heat generation amounts that add heat to the lubrication oil of the transmission other than the transmission loss based on the environment in which the transmission is located, and based on the environment in which the transmission is located, The system includes a heat extraction estimation means for estimating the amount of heat extracted from the lubricating oil, including natural heat dissipation; a maximum allowable heat calculation means for calculating the maximum allowable heat amount to reach the upper limit temperature after a set time, based on the calculated transmission loss, the estimated amount of other heat generated, the estimated heat extraction amount, the detected lubricating oil temperature, a preset upper limit temperature, and a preset lubricating oil heat capacity; and a maximum input torque calculation means for determining the maximum input torque corresponding to the calculated maximum allowable heat amount. The system uses the calculated maximum input torque to control the input torque of the transmission to be less than or equal to the maximum input torque. [Effects of the Invention]

[0009] The transmission lubrication oil temperature control device according to this disclosure can appropriately address the increase in fluid stirring losses inside the transmission. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing an example of the configuration of the transmission lubrication oil temperature control system 100 according to this embodiment. [Figure 2] This is a flowchart illustrating the operation of the control unit in the transmission lubrication oil temperature control system according to this embodiment. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are not limiting to this disclosure, and configurations formed by selectively combining multiple examples are also included in this disclosure.

[0012] "System Configuration" Figure 1 is a block diagram showing an example configuration of the transmission lubrication oil temperature control system 100 according to this embodiment. The transmission lubrication oil temperature control system 100 is mounted on a vehicle and controls the temperature of the transmission lubrication oil while the vehicle is in motion.

[0013] The transmission lubrication oil temperature control system is preferably installed in electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs), but is not limited to these. Figure 1 shows an example of installation in a hybrid vehicle.

[0014] One of the power sources, the engine 10, is an internal combustion engine that burns fuel such as gasoline to produce driving force. The driving force of the engine 10 is output as the rotation of the output shaft.

[0015] The output shaft is connected to the torque converter 12. The torque converter 12 is a fluid clutch that transmits and interrupts the incoming driving force, and also has the function of amplifying engine torque. The transmission 14 is connected to the output shaft of the torque converter 12.

[0016] Further, a motor generator 24 is connected to the battery 20 via an inverter 22. The DC power output from the battery 20 is converted into a predetermined AC current by the inverter 22 and supplied to the motor generator 24. The output of the motor generator 24 can be controlled by controlling the inverter 22. The inverter 22 usually controls a plurality of switching elements by PWM to convert them into a desired three-phase AC current and supply it to the motor generator 24. Therefore, the output of the motor generator 24 can be controlled by controlling the switching of the inverter 22. Also, by the switching control of the inverter 22, the motor generator 24 can be regeneratively braked, and the obtained regenerative power can be charged to the battery 20.

[0017] Thus, the inverter 22 controls the power transfer between the battery 20 and the motor generator 24.

[0018] The output shaft of the torque converter 12 and the output shaft of the motor generator 24 are connected to the transmission 14. A tire 16 is connected to the transmission 14, and the tire 16 rotates according to the rotation of the output shaft of the transmission 14, causing the vehicle to move.

[0019] Here, in this example, the transmission 14 has a planetary gear mechanism in its input stage, and appropriately changes the connection between the output shaft of the torque converter 12, the output shaft of the motor generator 24, and the output shaft of the transmission 14.

[0020] That is, the transmission 14 enables the vehicle to run by the output of the engine 10 or by the output of the motor generator 24. Further, the rotational force of the tire 16 can be input from the transmission 14 to the motor generator 24 to generate electricity by the motor generator 24, and the obtained power can be charged to the battery 20.

[0021] The transmission 14 is provided between the engine 10 and the motor generator 24, which are power sources, and the tire 16, and appropriately shifts gears and transmits power.

[0022] The control unit 30 is a computer, usually called an ECU (Electronic Control Unit). In this example, the detection values from the accelerator opening sensor 40, vehicle speed sensor 42, oil temperature sensor 44, MG temperature sensor 46, and coolant temperature sensor 48 are supplied. Various sensors for detecting the outside air temperature, engine output, brake operation state, road surface state, etc. can be provided, and the detection values can be supplied to the control unit 30.

[0023] Based on the detection values of various sensors, the control unit 30 determines the vehicle state and the driver's intention, controls the actuators mounted on the engine 10, transmission 14, etc. to control their outputs, or controls the current and voltage of the motor generator 24 by the switching of the inverter 22.

[0024] "Lubricating oil temperature control" FIG. 2 is a flowchart for explaining the operation of the control unit 30 in the transmission lubricating oil temperature control system according to the present embodiment. Here, the case where only the motor generator 24 not equipped with the engine 10 is the power source is taken up to explain the operation of the control unit 30.

[0025] (ST1) First, detection values of vehicle states such as accelerator opening, vehicle speed, inverter current, voltage, lubricating oil temperature, MG temperature, and coolant temperature are acquired from various sensors.

[0026] When the step of the detection value in ST1 ends, the three steps of ST2, ST3, and ST4 are performed in parallel.

[0027] (ST2) The transmission loss (heat generation amount) [W = J / sec] is directly estimated from the input rotation speed N and input torque τ to the transmission 14 by an equation such as the following. The implementation of this step in the control unit 30 corresponds to the transmission loss estimation means. Transmission loss = (A + B×τ + C×N)×N×2π / 60

[0028] Here, the rotational speed N is in units of rpm (revolutions per minute), and is converted to angular velocity per second by multiplying by 2π / 60. A, B, and C are constants, where B is a constant that converts to the loss (W) corresponding to the input torque, and B is a constant that converts to the loss (W) corresponding to the input rotational speed.

[0029] Input rotational speed and input torque are more responsive than lubricating oil temperature, making it easier to detect overheating early.

[0030] Here, the rotational speed of the output shaft of the motor generator 24 may be detected by a rotational speed sensor, and the output torque may also be detected by a torque sensor to obtain the input rotational speed N and input torque τ to the transmission 14, but it is not always necessary to detect them with sensors. For example, the target rotational speed and target output torque of the motor generator 24 are determined from the accelerator opening and vehicle speed, and the inverter 22 is controlled accordingly, so the target values ​​at that time can be used as the output rotational speed and output torque of the motor generator 24, and these can be used as the input rotational speed N and input torque τ of the transmission 14. Alternatively, the input rotational speed of the transmission can also be determined from the vehicle speed and the gear ratio of the transmission 14.

[0031] (ST3) The amount of heat generated other than transmission losses is calculated as other heat generation [W]. The execution of this step in the control unit 30 corresponds to the other heat generation estimation means.

[0032] The transmission 14 is mounted in the vehicle, and the temperature of the transmission lubricating oil is affected by other mounted components. For example, if the motor generator 24 is located nearby, the lubricating oil temperature will change due to heat transfer. These heat sources are known, and the amount of heat generated other than transmission losses that affects the temperature of the transmission lubricating oil can also be calculated.

[0033] (ST4) The amount of heat removed [W] to lower the temperature of the lubricating oil, such as through natural heat dissipation, is calculated. The execution of this step in the control unit 30 corresponds to the heat removal amount estimation means.

[0034] The transmission 14 becomes hot and dissipates heat naturally due to the temperature difference with the ambient temperature. The engine 10, battery 20, inverter 22, and motor generator 24 are also heat sources, and normally coolant is circulated around them for cooling. This coolant is also used to cool the transmission 14. Therefore, there is a amount of heat dissipated by the coolant. This amount of heat dissipation can be determined by detecting environmental conditions such as the coolant temperature. Normally, the coolant circulates to the radiator, where it dissipates heat.

[0035] (ST5) Once the calculation of heat quantities in ST2-ST4 is complete, the amount of heat Q [W] required to change the temperature of the transmission lubricating oil is calculated using the following equation 1. Q = Transmission losses + Other heat generation - Heat dissipation ... (Equation 1)

[0036] (ST6) Next, calculate the torque τ at which the lubricating oil temperature T does not reach the upper limit temperature Tmax.

[0037] If Tmax [degC] is the maximum allowable oil temperature for the transmission lubricant and T [degC] is the current lubricant temperature, then the maximum allowable heat Qmax [W] at which the oil temperature reaches Tmax after a set time Δt seconds is determined by the following formula. Qmax=c×(Tmax-T) / Δt...(Formula 2)

[0038] Here, c is the lubricating oil heat capacity [J / K]. The calculation of this maximum allowable heat quantity Qmax in the control unit 30 corresponds to the maximum allowable heat quantity calculation means.

[0039] Substituting the heat quantity Q in Equation 1 as the maximum allowable heat quantity Qmax into Equation 2, Transmission losses + other heat generation - heat dissipation = c × (Tmax - T) / Δt This is the result.

[0040] Therefore, the maximum transmission loss [W] of the transmission 14 that does not reach Tmax after a set time Δt seconds can be expressed as follows: Maximum transmission loss = c × (Tmax - T) / Δt + heat dissipation - other heat generation

[0041] Here, expressing the torque τ explicitly, we get the following. This torque τ in the control unit 30 corresponds to the maximum input torque calculation means. τ = {(c × (Tmax - T) / Δt + heat released - other heat generated) × 60 / (N × 2π) - (A + C × N)} / B

[0042] (ST7) Then, the maximum output torque of the motor generator 24, which is the input to the transmission 14, is defined as τ.

[0043] This prevents the transmission lubricant from overheating.

[0044] Here, the set time Δt should be at least equal to or greater than the control cycle. Furthermore, if time averaging is performed on oil temperature sensor values, the set time Δt must be greater than or equal to that range. Increasing the set time Δt reduces τ, making overheating less likely, but this may result in excessive torque limiting. Therefore, it is advisable to determine the set time Δt considering both torque limiting and overheating prevention.

[0045] When an engine is installed, it is possible to limit not only the MG torque but also the engine torque. Furthermore, if the rotational speed of the engine or transmission shafts can be selected, such as with a continuously variable transmission or automatic transmission, it is possible to limit the rotational speed to the lower end. In other words, by limiting torque, rotational speed, or both, it is possible to keep the transmission below its maximum heat generation limit and effectively prevent overheating of the transmission lubricating oil.

[0046] Furthermore, transmission lubricant is used not only for lubricating the transmission but also for cooling heat-generating parts such as the motor generator. In this case, if the temperature of the lubricant rises too high, it will not be able to cool the heat-generating parts. Also, as mentioned above, if the viscosity of the lubricant decreases, lubrication may not be performed properly. Conventionally, the fluid temperature is measured, and if it reaches an upper limit, temperature rise suppression control is implemented. However, even if temperature rise suppression control is implemented after the upper limit has been reached, the temperature may continue to rise for a while. Therefore, in this embodiment, the transmission loss (heat generation), motor heat generation, and heat dissipation are measured or estimated sequentially, and based on these, control is implemented in advance to prevent the upper limit temperature Tmax from being reached. Thus, overheating of the lubricant can be prevented. [Explanation of symbols]

[0047] 10 Engine, 12 Torque converter, 14 Transmission, 16 Tires, 20 Battery, 22 Inverter, 24 Motor generator, 30 Control unit.

Claims

[Claim 1] A lubrication oil temperature control system for controlling the lubrication oil temperature of a transmission, It has a control unit that controls the input torque of the transmission based on the lubricating oil temperature of the transmission, the input rotational speed of the transmission, and the input torque of the transmission. The control unit is A transmission loss estimation means calculates transmission loss based on the detected transmission input torque and transmission input rotational speed, Based on the environment in which the transmission is located, other heat generation estimation means estimate the amount of heat generated by the transmission's lubricating oil, in addition to transmission losses. A heat extraction amount estimation means that estimates the amount of heat extracted from the lubricating oil, including natural heat dissipation, based on the environment in which the transmission is located, A maximum allowable heat calculation means calculates the maximum allowable heat amount to reach the upper limit temperature after a set time, based on the calculated transmission loss, estimated other heat generation amount, estimated heat dissipation amount, detected lubricating oil temperature, a preset upper limit temperature, and a preset lubricating oil heat capacity. A maximum input torque calculation means for determining the maximum input torque corresponding to the calculated maximum allowable heat quantity, Includes, Using the calculated maximum input torque, the transmission's input torque is controlled to be less than or equal to the maximum input torque. A system for controlling the lubricating oil temperature of a transmission.

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