A CVT speed ratio optimization control method and system

Abstract

A CVT speed ratio optimization control method and system includes the following steps: Step 1) Using the current speed ratio of the vehicle as a benchmark, calculate the corresponding comprehensive efficiency based on the speed ratio under different search directions, compare the comprehensive efficiency under different search directions, and determine the optimal search direction; Step 2) In the optimal search direction, continue to adjust the current speed ratio according to different search step sizes, and calculate the corresponding comprehensive efficiency value respectively. The speed ratio corresponding to the maximum comprehensive efficiency value is the target optimized speed ratio; Step 3) Determine whether using the target optimized speed ratio affects the vehicle's backup driving force. If it does not affect it, control the current CVT speed ratio to become the target optimized speed ratio; if it does affect it, do not optimize the current speed ratio. This invention can improve the overall efficiency of the vehicle without complex offline calibration, improving energy economy while ensuring the user's driving experience.

Description

Technical Field

[0001] This invention relates to the field of CVT speed ratio control technology, and in particular to a CVT speed ratio optimization control method and system. Background Technology

[0002] CVT (Continuously Variable Transmission) has many advantages over traditional transmissions. Its speed ratio is a series of continuous values, which allows the engine to run on an ideal operating curve, thereby improving the car's power, economy and smoothness.

[0003] The transmission efficiency of a continuously variable transmission (CVT) is not a fixed value, but varies with its own speed ratio and external input torque. CVT efficiency generally ranges from 70% to 95% depending on its operating conditions. Traditional CVT speed ratio control typically focuses on ensuring the engine operates in its high-efficiency range under the current vehicle operating conditions. However, in reality, overall vehicle efficiency is determined by both engine and CVT efficiency. While the engine efficiency may be at its highest, the CVT efficiency may not be at its highest. Therefore, there is room for further optimization in traditional CVT control to maximize the combined efficiency of the engine and CVT.

[0004] The existing paper, "Optimization Algorithm for Dynamic Control Strategy Based on CVT Efficiency" (Mechanical Transmission, No. 6, 2020), proposes using matrix optimization to pre-calibrate all working state matrices, allowing the optimal CVT speed ratio for overall efficiency to be obtained during control. However, this method requires a large number of calibrations, making calibration and calculation complex. Moreover, it is a static optimization that only pursues maximizing current efficiency without considering whether the optimized speed ratio can adapt to the vehicle's external environment. It is possible that while the optimized speed ratio may improve efficiency during steady-state driving, it could negatively impact the vehicle's acceleration performance, causing driver discomfort. Summary of the Invention

[0005] The main objective of this invention is to overcome the shortcomings of existing optimization algorithms, which are static optimizations that only pursue current efficiency maximization without considering whether the optimized speed ratio can adapt to the vehicle's external environment. This invention proposes a CVT speed ratio optimization control method and system that uses dynamic search for a better CVT speed ratio to improve the overall efficiency of the vehicle. While improving energy economy, it also ensures the user's driving experience.

[0006] The present invention adopts the following technical solution:

[0007] A CVT speed ratio optimization control method, characterized by comprising the following steps:

[0008] Step 1) Based on the current speed ratio of the vehicle, calculate the corresponding comprehensive efficiency according to the speed ratio under different search directions, compare the comprehensive efficiency under different search directions, and determine the optimal search direction;

[0009] Step 2) On the optimal search direction, continue to adjust the current speed ratio according to different search step sizes, and calculate the corresponding comprehensive efficiency value. The speed ratio corresponding to the maximum comprehensive efficiency value is the target optimized speed ratio.

[0010] Step 3) Determine whether using the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect the vehicle, control the current speed ratio of the CVT to the target optimized speed ratio. If it will affect the vehicle, do not optimize the current speed ratio.

[0011] In step 1), the search direction includes a first search direction and a second search direction. The speed ratio under the first search direction is the current speed ratio increasing by the search step size, while the speed ratio under the second search direction is the current speed ratio decreasing by the search step size. The search direction with the highest overall efficiency under different search directions is taken as the optimal search direction. The overall efficiency η corresponding to the search direction is the CVT efficiency value η. cvt and engine efficiency η e The product value.

[0012] The speed ratio in the search direction is taken as the target speed ratio. The engine speed corresponding to the target speed ratio is calculated. The engine torque is calculated based on the engine speed. The CVT efficiency value can be obtained by looking up the CVT efficiency table based on the target speed ratio and the engine torque.

[0013] Using the speed ratio in the search direction as the target speed ratio, calculate the engine speed corresponding to this target speed ratio. Based on this engine speed, calculate the engine torque. Then, using the engine speed and torque, query the engine universal characteristic curve data to obtain the fuel consumption rate b. e Further calculations yielded the engine efficiency η. e =3600000 / (b e R), where R is the calorific value constant of the fuel used in the engine.

[0014] In step 3), the backup driving force F2 after optimizing the target speed ratio is calculated and compared with the vehicle's backup driving force F1 in the current state. If F2 ≥ F1, there is no impact; otherwise, there is an impact. The backup driving force F1 of the vehicle in the current state is calculated as follows:

[0015] F1=(T max -T)ii0 / r

[0016] Wherein: T maxLet T be the engine's maximum torque, i be the current engine torque, i be the current gear ratio, i0 be the vehicle's final drive ratio, and r be the vehicle radius. The backup driving force F2 after the target optimized gear ratio is calculated as follows:

[0017] F2=(T max -T f )i f i0 / r+mgsin(θ2-θ1)

[0018] Where i f To optimize the gear ratio, θ1 is the gradient of the road where the vehicle is currently located, θ2 is the gradient at a distance vt from the vehicle's current location on the road, t is the CVT switching time, v is the current vehicle speed, and T... f The engine output torque is optimized at the target speed ratio, where m is the vehicle mass and g is the acceleration due to gravity. This is achieved by using an electronic map or electronic horizon system with slope information and a satellite positioning system to obtain the slope of the vehicle's current road position and the slope at a distance vt ahead of the vehicle on the current road.

[0019] A CVT speed ratio optimization control system, characterized in that it includes:

[0020] The data acquisition module is used to collect vehicle information, including at least the current speed ratio;

[0021] The overall efficiency calculation module calculates the corresponding overall efficiency based on the speed ratio under the search direction.

[0022] The comparison module compares the overall efficiency under different search directions to determine the optimal search direction, and determines the target optimization speed ratio by comparing the overall efficiency values ​​corresponding to different search step sizes under the optimal search direction.

[0023] The control module determines whether using the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect the vehicle, it controls the current speed ratio of the CVT to the target optimized speed ratio. If it will affect the vehicle, it will not optimize the current speed ratio.

[0024] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The method and system of the present invention determine the optimal search direction by the comprehensive efficiency corresponding to the speed ratio under different search directions; and in the optimal search direction, the target optimized speed ratio is searched by adjusting the search step size to maximize the comprehensive efficiency value, and the terrain is considered to determine whether to optimize the speed ratio. This can improve the overall efficiency of the vehicle without the need for complex offline calibration, and at the same time improve energy economy, it can also ensure the user's driving experience.

[0026] 2. The method and system of the present invention have a comprehensive efficiency that is the product of the CVT efficiency value and the engine efficiency. The optimal search direction and target optimized speed ratio are determined by the comprehensive efficiency, ensuring the highest vehicle efficiency while guaranteeing the user's driving experience.

[0027] 3. The method and system of the present invention can obtain relevant slope information of the vehicle through an electronic map or electronic horizon system with slope and a satellite positioning system. Based on the slope, the backup driving force of the vehicle in the current state and the backup driving force after the target optimized speed ratio are calculated and compared. If F2≥F1, it indicates that the backup driving force of the vehicle has not decreased after the speed ratio optimization, that is, it does not affect the power performance that may require acceleration operations to increase driving force. Therefore, the CVT can be controlled to switch to the target optimized speed ratio i. f If not, it means that the vehicle's backup driving force will be affected after optimization, and speed ratio optimization will not be performed. Attached Figure Description

[0028] Figure 1 This is a flowchart of the present invention.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0030] The present invention will be further described below through specific embodiments.

[0031] In this invention, the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be interpreted as indicating or implying relative importance.

[0032] See Figure 1 This invention proposes a CVT speed ratio optimization control method, comprising the following steps:

[0033] Step 1) Based on the current speed ratio of the vehicle, calculate the corresponding comprehensive efficiency according to the speed ratio under different search directions, compare the comprehensive efficiency under different search directions, and determine the optimal search direction.

[0034] In this step, the search direction for a better gear ratio is calculated based on the vehicle's current CVT gear ratio. The search direction can include a first search direction and a second search direction. In the first search direction, the gear ratio increases by a search step size, while in the second search direction, the gear ratio decreases by a search step size. The specific value of this change can be set according to requirements and is not limited here.

[0035] Specifically, the overall efficiency η corresponding to the search direction is the CVT efficiency value η. cvt and engine efficiency η eThe product of these values ​​can be used to determine the optimal search direction based on the overall efficiency achieved across different search directions.

[0036] For the efficiency value η corresponding to one of the search directions cvt and engine efficiency η e The specific calculation method is as follows: First, take the speed ratio in the search direction as the target speed ratio, calculate the engine speed corresponding to the target speed ratio, calculate the engine torque based on the engine speed, and then look up the CVT efficiency table based on the target speed ratio and engine torque to obtain the CVT efficiency value. Finally, obtain the fuel consumption rate b from the engine universal characteristic curve data based on the engine speed and torque. e The engine efficiency was further calculated, as follows:

[0037] Assuming the current CVT speed ratio is i, the search step size can be a small speed ratio change Δi, thus obtaining the speed ratio i in the direction of speed ratio increase, i.e., the first search direction. a =i + Δi, and the speed ratio i in the direction of decreasing speed ratio, i.e., the second search direction. b =i-△i.

[0038] Taking the direction of increasing speed ratio as an example, with current vehicle speed v and torque T, the target speed ratio is calculated as i. a At that time, the engine speed was: Where i0 is the vehicle's final drive ratio and r is the vehicle's radius.

[0039] Because the vehicle's driving state must remain consistent with the state before the speed ratio change, according to the power balance principle, the engine output power P should remain unchanged. Therefore, based on the current engine power P, the target speed ratio of the CVT is calculated as i. a When the engine speed changes to n, the torque T that the engine should output is... a :

[0040]

[0041] According to the torsion spring T a and i a The efficiency value η of the CVT transmission can be obtained by consulting the CVT efficiency table. cvt .

[0042] Furthermore, the fuel consumption rate b is obtained by querying the engine universal characteristic curve data based on the engine speed and torque. e Further calculations yielded the engine efficiency η. e =3600000 / (b e R), where R is the calorific value constant of the fuel used in the engine, for example, the calorific value constant of gasoline is 46000kJ / kg.

[0043] Therefore, the overall efficiency η in the direction of increasing speed ratio is obtained. a =η cvt η e Similarly, the overall efficiency η can also be obtained in the direction of decreasing speed ratio. b Determine η a With η b Choose the direction with the larger value as the optimization search direction.

[0044] Step 2) On the optimal search direction, continue to adjust the current speed ratio according to different search step sizes, and calculate the corresponding comprehensive efficiency value. When the comprehensive efficiency value is the largest, the corresponding speed ratio is the target optimized speed ratio.

[0045] In this step, if the optimal search direction is the first search direction, the gear ratio is increased by the search step size Δi; if the optimal search direction is the second search direction, the gear ratio is decreased by the search step size Δi. The calculation method for the overall efficiency corresponding to the adjusted gear ratio in this step is the same as that in step 1), that is, the product of the CVT efficiency value and the engine efficiency after the gear ratio adjustment is calculated as the overall efficiency value.

[0046] Adjusting the current speed ratio by varying the search step size means repeating this step to continuously change the search step size to adjust the current speed ratio. Different search step sizes can be multiples of the change Δi. Assuming this is repeated k times, the speed ratio i corresponding to the largest product of overall efficiency is selected. f =i+k△i or i f =ik△i is the target optimized speed ratio. Obviously, k is not an infinitely large value. The range of values ​​for k is such that i f Between the physical minimum speed ratio that the gearbox can achieve and the physical maximum speed ratio that the gearbox can achieve, we can also obtain from equation (1) that the engine output torque is T when maintaining the same power demand. f .

[0047] Step 3) Determine whether using the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect the vehicle, control the current speed ratio of the CVT to the target optimized speed ratio. If it will affect the vehicle, do not optimize the current speed ratio.

[0048] In this step, the reserve driving force F2 after the target optimized speed ratio is calculated and compared with the vehicle's reserve driving force F1 in the current state. If F2 ≥ F1, it indicates that the vehicle's reserve driving force has not decreased after the speed ratio optimization, meaning it does not affect the power performance that may require acceleration or other operations that increase driving force. Therefore, the CVT can be controlled to switch to the target optimized speed ratio i. f If not, it means that the vehicle's backup driving force will be affected after optimization, and speed ratio optimization will not be performed.

[0049] Furthermore, the slope of the road where the vehicle is currently located can be obtained through an electronic map or electronic horizon system with slope, and a satellite positioning system, assuming it is θ1, and the CVT switching time is assumed to be t seconds, and the slope θ2 at a distance vt in front of the vehicle on the current road can be obtained, where v is the current vehicle speed.

[0050] Assuming the engine's maximum torque is T max Given that the current torque is T, the current speed ratio is i, the vehicle's final drive ratio is i0, and the vehicle radius is r, the vehicle's backup driving force F1 in the current state is:

[0051] F1=(T max -T)ii0 / r

[0052] Suppose the vehicle's current speed ratio is to be optimized to the target optimized speed ratio i. f Then the optimized backup driving force F2 is:

[0053] F2=(T max -T f )i f i0 / r+mgsin(θ2-θ1)

[0054] Where m is the vehicle mass, g is the acceleration due to gravity, and T is the acceleration due to gravity. f To optimize engine output torque at the target speed ratio.

[0055] Based on this, the present invention also proposes a CVT speed ratio optimization control system, including a data acquisition module, a comprehensive efficiency calculation module, a comparison module, and a control module. The data acquisition module is used to collect vehicle information, including at least the current speed ratio. This data acquisition module can obtain vehicle information through a CAN network, and the acquired vehicle information may also include the current vehicle speed, current torque, final drive ratio, vehicle radius, etc.

[0056] The overall efficiency calculation module calculates the corresponding overall efficiency based on the speed ratio under the search direction, including the overall efficiency calculation when the optimal search direction is determined, and the overall efficiency calculation after the optimal search direction is determined. The comparison module is used to compare the overall efficiency under different search directions to determine the optimal search direction, and to determine the target optimized speed ratio by comparing the overall efficiency values ​​corresponding to different search step sizes under the optimal search direction. The control module is used to determine whether adopting the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect it, it controls the current speed ratio of the CVT to become the target optimized speed ratio; if it will affect it, it will not optimize the current speed ratio.

[0057] In the system of the present invention, when the control module determines whether the target optimized speed ratio affects the vehicle's backup driving force, it needs to use the slope θ1 of the current road position of the vehicle and the slope θ2 at the distance vt in front of the vehicle on the current road. Therefore, the system of the present invention can also be equipped with an electronic map or a baseline horizon system and a satellite positioning system, which can be used to provide the required slope.

[0058] The system of this invention uses the above-mentioned CVT speed ratio optimization control method to optimize the current speed ratio. Its working principle is as follows:

[0059] Step 1) The current speed ratio of the vehicle is collected by the acquisition module. The comprehensive efficiency calculation module uses the current speed ratio of the vehicle as a benchmark and calculates the corresponding comprehensive efficiency according to the speed ratio under different search directions. The comparison module compares the comprehensive efficiency under different search directions to determine the optimal search direction.

[0060] Step 2) The comprehensive efficiency calculation module continues to adjust the current speed ratio according to different search step sizes in the optimal search direction, and calculates the corresponding comprehensive efficiency value. The comparison module takes the speed ratio corresponding to the maximum comprehensive efficiency value as the target optimized speed ratio.

[0061] Step 3) The control module determines whether using the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect the vehicle's backup driving force, the control module will change the current speed ratio of the CVT to the target optimized speed ratio. If it will affect the vehicle's backup driving force, the control module will not optimize the current speed ratio.

[0062] The method and system of this invention do not employ offline calibration. Instead, they use real-time search to determine the optimal gear ratio for the combined efficiency of the engine and CVT. Based on the current terrain and the predicted terrain ahead of the vehicle, they assess whether gear ratio optimization is suitable. This improves overall vehicle efficiency, enhances energy economy, and ensures a superior driving experience for the user.

[0063] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A CVT speed ratio optimization control method, characterized in that, Includes the following steps: Step 1) Based on the current speed ratio of the vehicle, calculate the corresponding comprehensive efficiency according to the speed ratio under different search directions, compare the comprehensive efficiency under different search directions, and determine the optimal search direction; Step 2) On the optimal search direction, continue to adjust the current speed ratio according to different search step sizes, and calculate the corresponding comprehensive efficiency value. The speed ratio corresponding to the maximum comprehensive efficiency value is the target optimized speed ratio. Step 3) Determine whether using the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect the vehicle, control the current speed ratio of the CVT to the target optimized speed ratio. If it will affect the vehicle, do not optimize the current speed ratio. Calculate the backup driving force after optimizing the target speed ratio And compare it with the vehicle's reserve driving force in the current state, if If yes, it will have no effect; otherwise, it will have an effect. The vehicle's backup driving force in the current state The calculation is as follows: ； Wherein: T max T represents the engine's maximum torque, and T represents the engine's current torque. For the current speed ratio, This is the vehicle's final drive ratio. The radius of the vehicle; The backup driving force after the target optimized speed ratio The calculation is as follows: ； in Optimize the speed ratio to achieve the target. The slope of the road where the vehicle is currently located. The slope is vt, where t is the CVT switching time and v is the current vehicle speed. The engine output torque is optimized for the target speed ratio, where m is the vehicle mass and g is the acceleration due to gravity.

2. The CVT speed ratio optimization control method as described in claim 1, characterized in that, In step 1), the search direction includes a first search direction and a second search direction. The speed ratio under the first search direction is the current speed ratio increasing by the search step size, and the speed ratio under the second search direction is the current speed ratio decreasing by the search step size. The search direction with the highest overall efficiency under different search directions is taken as the optimal search direction.

3. The CVT speed ratio optimization control method as described in claim 1, characterized in that, Overall efficiency corresponding to the search direction CVT efficiency value and engine efficiency The product value.

4. The CVT speed ratio optimization control method as described in claim 3, characterized in that, The speed ratio in the search direction is taken as the target speed ratio. The engine speed corresponding to the target speed ratio is calculated. The engine torque is calculated based on the engine speed. The CVT efficiency value can be obtained by looking up the CVT efficiency table based on the target speed ratio and the engine torque.

5. The CVT speed ratio optimization control method as described in claim 3, characterized in that, The speed ratio in the search direction is taken as the target speed ratio. The engine speed corresponding to this target speed ratio is calculated. The engine torque is calculated based on the engine speed. The fuel consumption rate is obtained by querying the engine universal characteristic curve data based on the engine speed and torque. Further calculations yielded the engine efficiency. R is the calorific value constant of the fuel used in the engine.

6. The CVT speed ratio optimization control method as described in claim 1, characterized in that, The gradient of the road where the vehicle is currently located and the gradient at a distance vt ahead of the vehicle on the road can be obtained through an electronic map or electronic horizon system with gradients and a satellite positioning system.

7. A CVT speed ratio optimization control system, characterized in that, A method for executing the CVT speed ratio optimization control method according to claim 1 includes: The data acquisition module is used to collect vehicle information, including at least the current speed ratio; The overall efficiency calculation module calculates the corresponding overall efficiency based on the speed ratio under the search direction. The comparison module compares the overall efficiency under different search directions to determine the optimal search direction, and determines the target optimization speed ratio by comparing the overall efficiency values ​​corresponding to different search step sizes under the optimal search direction. The control module determines whether using the target optimized speed ratio will affect the vehicle's backup driving force. If it will not affect the vehicle, it controls the current speed ratio of the CVT to the target optimized speed ratio. If it will affect the vehicle, it will not optimize the current speed ratio.

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