torque converter

Abstract

To select a torque converter in which a thermal restriction caused by the use of high torque of an electric motor is appropriately suppressed.SOLUTION: A reference torque capacity coefficient Ks is obtained based on a reference rotation speed Ns and a heat rating torque Th, in which the reference rotation speed Ns is a rotational speed of an intersection S between a maximum output curve Lm and the heat rating torque Th of an electric motor MG. A torus diameter D is defined according to the reference torque capacity coefficient Ks, thus obtaining a torque amplification effect by a torque converter in a region of the reference rotation speed Ns or less including all heat restriction torque region. With this, the use of the heat restriction torque region of the electric motor MG is suppressed even in a high load operation and the risk of heat restriction on the electric motor MG is reduced, thereby suppressing anxiety and discomfort of a driver in a reduction in drive force caused by the heat restriction. Also a torque amplification effect by a torque converter is obtained including a region of maximum output of the electric motor MG, which increases a drive force of a power region.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a torque converter, and more particularly to a torque converter used in an electric vehicle equipped with an electric motor as a power source for running, which amplifies and outputs the torque of the electric motor. [Background technology]

[0002] Patent Document 1 describes a torque converter that is used in an electric vehicle equipped with an electric motor as a power source for driving, and amplifies and outputs the torque of the electric motor. Patent Document 1 proposes a technology for setting the torque capacity coefficient of the torque converter in consideration of the efficiency of the electric motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-24035 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, when electric motors are continuously used at high torque, the coils may overheat, causing damage or shortening of the motor's lifespan. To prevent this, a thermally limited torque range (see FIG. 3) is provided, and the motor's use may be restricted to a torque range below the thermally limited torque range due to thermal limitations. The torque converter described in Patent Document 1 may also be subject to thermal limitations due to the high torque of the motor, depending on the torque capacity coefficient setting. In this case, the driving force reduction increases by the amount of torque amplified by the torque converter, which may cause anxiety or discomfort to the driver.

[0005] The present invention has been made in light of the above circumstances, and its object is to select a torque converter that appropriately suppresses thermal limitations caused by the use of high torque from an electric motor. [Means for solving the problem]

[0006] In order to achieve this object, the first invention is (a) a torque converter used in an electric vehicle equipped with an electric motor as a power source for driving, which amplifies and outputs the torque of the electric motor, and (b) a reference rotational speed of the electric motor at the intersection of a maximum torque characteristic, which is the relationship between the maximum torque and rotational speed of the electric motor under normal conditions, and a thermal rated torque, which is the maximum torque when the electric motor is thermally limited, is used, and a torus diameter is set according to the torque capacity coefficient of the torque converter, which is calculated based on the reference rotational speed and the thermal rated torque. The torus diameter is the outer diameter of the fluid working chamber, a typical dimension of the torque converter, and is equal to the outer diameter of the pump impeller or turbine impeller. In general, the torque capacity coefficient is proportional to the fifth power of the torus diameter.

[0007] A second aspect of the present invention is characterized in that, in the torque converter of the first aspect of the present invention, (a) a torque converter characteristic, which is a relationship between the rotation speed and torque of the pump impeller, is determined so as to pass through the intersection point, and (b) a reference torque capacity coefficient is determined based on the torque converter characteristic, and the torque converter is selected within a range of torque capacity coefficients equal to or less than the reference torque capacity coefficient.

[0008] A third aspect of the present invention is characterized in that, in the torque converter of the second aspect of the present invention, the torque converter having the reference torque capacity coefficient is selected. [Effects of the Invention]

[0009] With this torque converter, the rotational speed at the intersection of the maximum torque characteristic and the thermally rated torque is set as a reference rotational speed, and the torque capacity coefficient and even the torus diameter are set based on this reference rotational speed and the thermally rated torque. This allows the torque converter to achieve torque amplification in a range below the reference rotational speed, including the entire thermally limited torque range. This reduces the use of the thermally limited torque range of the electric motor even under high load, reducing the possibility of the electric motor being thermally limited. This prevents the driver from feeling uneasy or uncomfortable due to a reduction in driving force caused by thermal limiting. Furthermore, because the torque converter achieves torque amplification in the range including the electric motor's maximum output, driving force in the power range increases.

[0010] In the second aspect of the invention, the torque converter characteristic is determined so as to pass through the intersection point, in other words, the torque converter characteristic is determined so that the intersection point is the stall torque / stall rotation speed, and a reference torque capacity coefficient is calculated based on the torque converter characteristic, and a torque converter is selected within a range of torque capacity coefficients equal to or less than the reference torque capacity coefficient. In the third aspect of the invention, a torque converter having a reference torque capacity coefficient is selected. Therefore, in the second and third aspects of the invention, the torque converter can amplify torque in a range equal to or less than the reference rotation speed, including the entire thermally limited torque range, thereby appropriately achieving the effect of the present invention, which is to prevent the driver from feeling uneasy or uncomfortable due to a reduction in driving force caused by thermal limitation of the electric motor. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a drive device for an electric vehicle having a torque converter according to an embodiment of the present invention; [Figure 2] 2 is a flowchart illustrating a procedure for selecting the torque converter of FIG. 1. [Figure 3] 2 is a diagram illustrating the relationship between the maximum output curve Lm of the electric motor of the electric vehicle of FIG. 1 and two types of torque converter characteristics Ltcs and Ltc2. FIG. [Figure 4]FIG. 4 is a diagram showing a comparison of torque capacity coefficients Ks and K2 in the two types of torque converter characteristics Ltcs and Ltc2 shown in FIG. 3. [Figure 5] FIG. 3 is a diagram illustrating the trends of a plurality of torque converters having different torque capacity coefficients K and torus diameters D, and is a diagram for explaining step S4 in FIG. 2 in which a torque converter is selected based on the reference torque capacity coefficient Ks. [Figure 6] FIG. 4 is a diagram illustrating a comparison of the driving force characteristics (solid line) of an electric vehicle of this embodiment equipped with a torque converter having the torque converter characteristic Ltcs of FIG. 3 selected according to the flowchart of FIG. 2 with the driving force characteristics (dash-dotted line and broken line) of a conventional electric vehicle equipped with a torque converter having the torque converter characteristic Ltc2 of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention is preferably applied to torque converters for electric vehicles equipped only with an electric motor as a power source, but may also be applied to torque converters for hybrid electric vehicles equipped with an internal combustion engine (ICE) as a power source in addition to an electric motor. Various embodiments are possible, including: (a) determining torque converter characteristics, which are the relationship between the pump wheel rotation speed and torque, so that the torque converter characteristics intersect with the maximum torque characteristic and the thermally rated torque, i.e., so that the torque converter characteristics intersect with the maximum torque characteristic at a reference rotation speed; (b) determining a reference torque capacity coefficient based on the torque converter characteristics, and selecting a torque converter with a torque capacity coefficient that is equal to or less than the reference torque capacity coefficient; and (c) determining the torque converter characteristics so that the torque converter characteristics intersect with the maximum torque characteristic at the reference rotation speed or a rotation speed higher than the reference rotation speed, and selecting a torque converter based on the torque capacity coefficient determined from the torque converter characteristics. A torque converter with a torque capacity coefficient greater than the reference torque capacity coefficient can also be selected, provided that the torque capacity coefficient is near the reference torque capacity coefficient. [Example]

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating a drive unit 12 of an electric vehicle 10 equipped with a torque converter 14 according to one embodiment of the present invention. The drive unit 12 includes an electric motor MG, a torque converter 14, a reverse gear mechanism 16, and a reduction gear mechanism 18, arranged in that order along an axis O (the left-right direction in FIG. 1 , parallel to the axis O). The electric motor MG, torque converter 14, reverse gear mechanism 16, and reduction gear mechanism 18 are configured substantially symmetrically about the axis O. FIG. 1 shows the upper half of the vehicle above the axis O, with an output shaft 20 provided at its center on the axis O. The electric motor MG is a motor-generator that also functions as a generator, and is used as a power source for traveling by being controlled to function as an electric motor. The electric motor MG rotates in a predetermined, constant positive direction whether the electric vehicle 10 is traveling forward or backward. The electric vehicle 10 is an electric vehicle equipped solely with the electric motor MG as a power source. In FIG. 1, the squares marked with an x ​​are bearings such as roller bearings.

[0014] The rotor of the electric motor MG is connected to a TC input shaft 22, which is an input member of the torque converter 14. The torque converter 14 includes a pump wheel 30 connected to the TC input shaft 22, a turbine wheel 32 connected to a TC output shaft 24, which is an output member of the torque converter 14, and a stator wheel 34 connected to a fixed member 36 via a one-way clutch. The fixed member 36 is fixed to a case 26 of the drive unit 12. The TC input shaft 22 and the TC output shaft 24 of the torque converter 14 are directly connected via a lock-up clutch LU. The lock-up clutch LU is, for example, of a normally closed type that is disengaged when energized, and is disengaged when the vehicle is traveling at a low vehicle speed below a predetermined vehicle speed V1 (see FIG. 6), including when the vehicle starts, i.e., when a high load requiring high torque is likely to be required. In this disengaged state, the torque converter 14 amplifies the torque. The lockup clutch LU is, for example, a hydraulic friction engagement device, and when an exciting current is applied to a solenoid valve that controls the engagement oil pressure, the output of the engagement oil pressure is stopped and the lockup clutch LU is released. When the exciting current is not applied, the engagement oil pressure is output and the lockup clutch LU is maintained in an engaged state, the TC input shaft 22 and the TC output shaft 24 are directly connected, and the torque of the electric motor MG is transmitted as is to the TC output shaft 24. Note that the dimension D in Fig. 1 is the torus diameter.

[0015] The reverse gear mechanism 16 is primarily configured as a single-pinion planetary gear set having a sun gear S1, a carrier CA1, and a ring gear R1. The sun gear S1 is connected to the TC output shaft 24, the carrier CA1 is selectively fixed to the case 26 via a first brake B1, and the ring gear R1 is connected to the output shaft 20. The reduction gear mechanism 18 is primarily configured as a single-pinion planetary gear set having a sun gear S2, a carrier CA2, and a ring gear R2. The sun gear S2 is connected to the TC output shaft 24, the carrier CA2 is connected to the output shaft 20, and the ring gear R2 is selectively fixed to the case 26 via a second brake B2. The ring gear R1 of the reverse gear mechanism 16 is connected to the output shaft 20 via the carrier CA2 of the reduction gear mechanism 18. Therefore, when the first brake B1 is released and the second brake B2 is engaged, the forward rotation output from the electric motor MG and transmitted to the TC output shaft 24 via the torque converter 14 or the lock-up clutch LU is decelerated, i.e., torque is amplified, by the reduction gear mechanism 18, and then output from the output shaft 20 to the drive wheels (not shown), causing the electric vehicle 10 to travel forward. On the other hand, when the second brake B2 is released and the first brake B1 is engaged, the forward rotation output from the electric motor MG and transmitted to the TC output shaft 24 via the torque converter 14 or the lock-up clutch LU is reversed in its direction and decelerated, i.e., torque is amplified, by the reverse gear mechanism 16, and then output from the output shaft 20 to the drive wheels, causing the electric vehicle 10 to travel backward. When both the first brake B1 and the second brake B2 are released, the vehicle enters a neutral state in which power transmission is interrupted. The reverse gear mechanism 16 and the reduction gear mechanism 18 can both be configured using a double-pinion type planetary gear device, or a parallel-axis type gear mechanism can be adopted, and various other configurations are possible.

[0016] FIG. 2 is a flowchart illustrating the procedure for determining the torque converter 14, i.e., a selection method including selection conditions, etc. In step S1 of FIG. 2, the maximum output curve Lm of the electric motor MG used in the electric vehicle 10 and the thermal rated torque Th during thermal limiting are obtained. The maximum output curve Lm is a maximum torque characteristic that is the relationship between the maximum torque and rotation speed of the electric motor MG during normal operation, as shown in FIG. 3. The thermal rated torque Th is a maximum torque that is predetermined to prevent damage to the electric motor MG due to coil heat generation, etc., and the torque region between the thermal rated torque Th and the maximum output curve Lm is a thermally limited torque region in which use is prohibited during thermal limiting. In step S2, the rotation speed of the electric motor MG at the intersection S between the maximum output curve Lm and the thermal rated torque Th is calculated as a reference rotation speed Ns.

[0017] In step S3, the torque converter characteristic Ltcs where the intersection S is the stall torque / stall rotational speed is determined, and the torque capacity coefficient of the torque converter characteristic Ltcs is calculated as a reference torque capacity coefficient Ks. The torque converter characteristic is the relationship between the rotational speed and torque of the pump wheel 30 of the torque converter 14, and the rotational speed of the intersection S, the reference rotational speed Ns, is the stall rotational speed, and the torque of the intersection S, the thermal rated torque Th, is the stall torque. The torque converter characteristic Ltcs passes through the intersection S, i.e., is the torque converter characteristic that intersects with the maximum output curve Lm of the electric motor MG at the reference rotational speed Ns. The torque converter characteristic is calculated by dividing the rotational speed of the pump wheel 30 by Np [rpm], the torque by Tp [Nm], and the torque capacity coefficient by K [10 -6 ×Nm / rpm 2 ], the relationship shown in the following equation (1) holds: Therefore, it is possible to calculate the torque capacity coefficient K from equation (2), and by applying the rotation speed and torque of the intersection S, the reference rotation speed Ns, and the thermal rated torque Th, it is possible to calculate the reference torque capacity coefficient Ks from equation (3). Tp = K × Np 2 ···(1) K=Tp / Np 2 ···(2) Ks = Th / Ns2 ···(3)

[0018] The torque converter characteristic Ltc2 shown by the two-dot chain line in Figure 3 is for a torque converter that has been widely used in the past, and has a steeper torque rise than the torque converter characteristic Ltcs of this embodiment. That is, as is clear from equation (1) above, the rise of the torque converter characteristic corresponds to the torque capacity coefficient K, and the larger the torque capacity coefficient K, the steeper the torque rise. Figure 4 compares the reference torque capacity coefficient Ks, which is the torque capacity coefficient of the torque converter characteristic Ltcs of this embodiment, with the torque capacity coefficient K2 of the conventional torque converter characteristic Ltc2, and the torque capacity coefficient K2 is approximately four times larger than the reference torque capacity coefficient Ks. Since the reference torque capacity coefficient Ks varies depending on the speed ratio e, the reference torque capacity coefficient Ks is calculated for the case where the speed ratio e = 0, i.e., the turbine rotation speed = 0.

[0019] Returning to FIG. 2, in the next step S4, a torque converter 14 is selected from the benchmark market value of the characteristics of the reference torque capacity coefficient Ks. FIG. 5 is a diagram illustrating a number of torque converters used in the benchmark, with the torque capacity coefficient K and torus diameter D as variables, and a torque converter with a torque capacity coefficient K that is approximately the same as the reference torque capacity coefficient Ks is selected. Furthermore, since the torque capacity coefficient K is generally proportional to the fifth power of the torus diameter D, it is also possible to determine the reference torus diameter Ds from the reference torque capacity coefficient Ks and select a torque converter with a torus diameter D that is approximately the same as the reference torus diameter Ds. It is also possible to select a torque converter with a torque capacity coefficient K smaller than the reference torque capacity coefficient Ks, or to select a torque converter with a torus diameter D smaller than the reference torus diameter Ds.

[0020] With the torque converter 14 selected in this manner, the rotational speed at the intersection S between the maximum output curve Lm of the electric motor MG and the thermal rated torque Th is defined as the reference rotational speed Ns. Based on the reference rotational speed Ns and the thermal rated torque Th, the reference torque capacity coefficient Ks is calculated according to equation (3). The torus diameter D is then determined according to the reference torque capacity coefficient Ks. This allows the torque converter 14 to amplify torque in the range below the reference rotational speed Ns, which includes the entire thermally limited torque range. This reduces the use of the thermally limited torque range of the electric motor MG even under high loads, reducing the likelihood of the electric motor MG being thermally limited. This prevents the driver from feeling uneasy or uncomfortable due to a reduction in driving force caused by thermal limitation. Furthermore, because the torque converter 14 amplifies torque in the range including the maximum output range of the electric motor MG, the driving force in the power range increases.

[0021] Furthermore, the torque converter characteristic Ltcs is determined so as to pass through the intersection S, in other words, the torque converter characteristic Ltcs is determined so that the intersection S is the stall torque / stall rotation speed, and a reference torque capacity coefficient Ks is calculated based on the torque converter characteristic Ltcs, and the torque converter 14 is selected within a range of torque capacity coefficient K equal to or less than the reference torque capacity coefficient Ks. As a result, the torque converter 14 can amplify torque in a range equal to or less than the reference rotation speed Ns, which includes the entire thermally limited torque range, thereby appropriately achieving the effect of suppressing the driver's anxiety or discomfort caused by a reduction in driving force due to thermal limitation of the electric motor MG.

[0022] FIG. 6 illustrates the driving force characteristics (solid line) of the electric vehicle 10 when the torque converter 14 is selected within a range of torque capacity coefficients K equal to or less than the reference torque capacity coefficient Ks, compared with the driving force characteristics (dashed and dotted lines) of a conventional electric vehicle equipped with a torque converter having the torque converter characteristic Ltc2 of FIG. 3. The driving force characteristics (dashed and dotted lines) of the electric vehicle under normal MG conditions, shown by the dashed line, provide high driving force, but do not cover the entire thermally limited torque range of the electric motor MG. Therefore, if the electric motor MG is thermally limited due to excessive use of the thermally limited torque range, the driving force characteristics degrade as shown by the dashed line. In this case, the drop in driving force is greater by the torque amplification by the torque converter, which may cause anxiety or discomfort to the driver. In contrast, the driving force characteristics of this embodiment, shown by the solid line, are lower than the driving force under normal MG conditions of the conventional electric vehicle. However, because the torque converter 14 provides torque amplification across a vehicle speed range that includes the entire thermally limited torque range, the use of the thermally limited torque range of the electric motor MG is suppressed even under high loads, reducing the likelihood of the electric motor MG being thermally limited. In addition, the maximum output of the electric motor MG can be used, increasing the driving force in the power range.

[0023] Although the embodiments of the present invention have been described in detail above with reference to the drawings, this is merely one embodiment, and the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0024] 10: Electric vehicle 14: Torque converter MG: Electric motor Lm: Maximum output curve (maximum torque characteristics) Th: Thermal rated torque S: Intersection Ns: Reference rotation speed Ltcs: Torque converter characteristics Ks: Reference torque capacity coefficient D: Torus diameter

Claims

1. A torque converter used in an electric vehicle having an electric motor as a power source for traveling, amplifying and outputting torque of the electric motor, The rotational speed of the electric motor at the intersection of a maximum torque characteristic, which is a relationship between the maximum torque and rotational speed of the electric motor under normal conditions, and a thermal rated torque, which is the maximum torque of the electric motor under thermal limitation, is set as a reference rotational speed, and the torus diameter is set according to the torque capacity coefficient of the torque converter, which is calculated based on the reference rotational speed and the thermal rated torque. A torque converter characterized by:

2. a torque converter characteristic, which is a relationship between the rotation speed of the pump impeller and the torque, is determined so as to pass through the intersection point; A reference torque capacity coefficient is determined based on the torque converter characteristics, and the torque converter is selected within a range of torque capacity coefficients equal to or less than the reference torque capacity coefficient.

2. The torque converter according to claim 1.

3. The torque converter having the reference torque capacity coefficient is selected.

3. The torque converter according to claim 2.

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