JP2874339B2 - Variable speed drive for continuously variable transmission for vehicles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid-type continuously variable transmission suitably applied to a vehicle intended for a vehicle speed range from a low speed to a medium speed, and particularly to its start. The present invention relates to a shift driving device that is effective for improving characteristics.

[Prior Art] Conventionally, the most desirable engine speed corresponding to the throttle opening is generally determined from the viewpoint of fuel consumption and / or exhaust gas. On the other hand, if a continuously variable transmission is used, the engine can be driven at an arbitrary speed regardless of the vehicle speed. For this reason, in the related art, the continuously variable transmission is controlled via a speed change driving device so that the above-described desirable relationship between the throttle opening and the engine speed is satisfied. More specifically, in a conventional general continuously variable transmission, a variable speed static pressure transmission system is configured between a pair of hydraulic pumps / motors having at least an input side of a variable displacement type, and an input side hydraulic pressure transmission system is provided. With the displacement of the pump / motor set to zero, the speed ratio represented by the output speed / input speed can be made substantially zero. On the other hand, variable-speed drive devices generally use an ECU (Electronic Control).
rol unit), detects the throttle opening (that is, the amount of accelerator depression) and the engine speed, and inputs it to the ECU so that the engine speed is maintained at the target value corresponding to the throttle opening. The displacement of the side hydraulic pump / motor is controlled.

To explain the outline of this control, when the driver steps on the accelerator, the throttle is opened by linking to the accelerator, the target engine speed corresponding to the throttle opening is obtained from the throttle opening / target engine speed chart, and the actual engine speed is obtained. The flow is such that the speed ratio of the continuously variable transmission is controlled to the target value (the displacement of the hydraulic pump / motor is controlled).

[Problems to be Solved by the Invention] However, such conventional speed change driving devices have the following three main problems.

First, there is a time lag between when the accelerator is depressed at the time of starting and when the vehicle starts moving, resulting in poor responsiveness. That is,
When the cause is sequentially pursued, when the driver steps on the accelerator (the accelerator and throttle change stepwise), the target engine speed SD greatly increases stepwise. However, since the actual engine speed SE increases by "first order delay + dead time", SE <SD for a while. Then, when SE> SD, the displacement of the input-side hydraulic pump / motor (until then zero) is increased in order to apply a load to the engine in order to reduce SE.
As a result, the hydraulic fluid starts flowing into the output hydraulic pump / motor, and the vehicle starts to move. As described above, even when the accelerator is depressed, the displacement of the input side hydraulic pump / motor does not start until the engine speed is increased, and the vehicle does not start moving.

Second, the overshoot of the engine speed increases. That is, even after SE> SD, the SE continues to increase until the engine load torque exceeds the engine output torque corresponding to the throttle at that time, so that an overshoot of the SE occurs. For example, when the accelerator is depressed as if by a general driver, the throttle greatly opens in a step-like manner, and the engine output torque corresponding to the throttle opening tends to increase. At this point, the input-side hydraulic pump / motor is displaced. Due to the small volume, even when the high pressure side of the static pressure transmission system reaches the relief pressure, the engine load torque is still small, so that the SE rises above SD and the relief valve also works. That is, while the vehicle speed is low, the engine output is excessive, and the engine overshoots while the engine is close to idling while the excess energy is discarded by blowing the relief.
For this reason, there is a disadvantage that fuel-efficient traveling cannot be performed at least during this time.

Third, pressure fluctuation at the time of starting is large, and torque fluctuation is large. After the engine speed overshoots for the above reason, the displacement of the input hydraulic pump / motor is rapidly increased in order to recover the control delay, so that the flow rate of the hydraulic fluid flowing through the hydraulic power transmission system suddenly increases. There is a drawback that the pressure suddenly increases, the torque suddenly increases, and the acceleration at the start of movement tends to be excessive.

The present invention has been made in view of such a problem. First, the present invention solves the first and third problems relating to the starting characteristic which is to be given the highest priority in a vehicle, and provides an economical solution based on this. It is an object of the present invention to solve the above second problem.

[Means for Solving the Problems] The present invention employs the following means to achieve the above object.

That is, the continuously variable transmission drive device for a vehicle according to the present invention includes:
A variable speed static pressure transmission system is formed between a pair of hydraulic pumps / motors having at least an input side of a variable displacement type, and the output speed / input is set in a state where the displacement volume of the input side hydraulic pump / motor is set to zero. In a continuously variable transmission for a vehicle in which a speed ratio represented by a speed can be made substantially zero, an effective differential pressure of the static pressure transmission system is set to a set pressure corresponding to an accelerator pedal depression amount (accelerator angle in a broad sense). The input side hydraulic pump /
The basic configuration is to perform negative feedback control on the displacement volume of the motor.

In addition to such a configuration, the present invention obtains the engine load torque from the effective differential pressure and the displacement of the input-side hydraulic pump / motor in order to enable variable-speed driving in accordance with the optimum operating conditions. It is characterized in that the throttle is feed-forward controlled so as to have an optimum opening with respect to the engine load torque.

[Operation] If the above-described basic configuration of the present invention is applied to a conventional device, it is possible to eliminate the time delay from when the accelerator pedal is depressed to when the accelerator starts moving, improve responsiveness, and at the same time, prevent sudden jumping out. That is, when the driver depresses the accelerator at the time of starting, the throttle changes in a step-like manner in conjunction with each other (assuming that the accelerator and the throttle are directly connected). In this case, the displacement of the input-side hydraulic pump / motor starts changing by the negative feedback control without waiting for the engine speed to increase so that the effective differential pressure is maintained at the set value corresponding to the accelerator depression amount. That is, when the output side hydraulic pump / motor is stopped, the displacement of the input side hydraulic pump / motor is first increased slightly to generate an effective differential pressure. As it begins to rotate, the displacement of the input hydraulic pump / motor increases further to compensate for the reduction in effective differential pressure due to the pump / motor swallowing the hydraulic fluid. Such actions occur in a chain, and the displacement of the input-side hydraulic pump / motor increases as the vehicle speed increases from the moment the accelerator is depressed. When the effective differential pressure is stably maintained in this manner, the effective differential pressure is proportional to the acceleration of the vehicle body. In this control, the differential pressure is constant, that is, the acceleration is constant as long as the accelerator is kept constant. (Of course, the driver can adjust the acceleration to the intended level by changing the depression of the accelerator.) From the moment the accelerator is depressed, a stable and effective traction force is obtained, and the vehicle starts to move. Therefore, it is possible to eliminate the time corresponding to the “first-order delay + dead time” until the engine speed rises in the related art, and to improve the responsiveness. Moreover, according to this control, it is not necessary to rapidly increase the displacement volume of the input-side hydraulic pump / motor in order to recover the control delay after the start-up as in the conventional control. Will not be invited. As a result, the above-described configuration makes it possible to drive the vehicle equipped with the continuously variable transmission stably and smoothly.

By the way, such a configuration improves the shifting performance of the vehicle, but does not include the content of achieving a desired engine speed corresponding to the throttle opening from the viewpoint of fuel consumption and / or exhaust gas as it is. In other words, a desirable relationship between the throttle opening and the engine speed means a desirable relationship between the throttle opening and the engine load torque (because they have a trinity relationship). In the above control, the engine load torque is substantially proportional to the displacement of the input side hydraulic pump / motor × the effective differential pressure, and increases as a linear function of the displacement. For this reason, the engine load torque at the start is small. On the other hand, under the assumption that the accelerator and the throttle are directly connected as described above, when the accelerator is depressed with a normal driving feeling, a high output torque unilaterally appears in the engine from the start. As a result, the engine initially starts to overshoot with no load or near it, and then gradually decreases as the load torque increases, deviating from the optimal operating conditions. Become. Further, such an excessive engine output torque does not necessarily have an adverse effect on the above-described shift drive control.

Therefore, adding a characteristic configuration of the present invention to the above configuration is one effective means. That is, in the above configuration, it is easy to know the effective differential pressure and the displacement volume of the input-side hydraulic pump / motor, and by multiplying them, the engine load torque can be obtained.
Therefore, since the optimum throttle opening corresponding to the engine load torque is known in advance, if the feedforward control is performed to such an optimum value instead of linking the throttle with the accelerator, the above-described shift drive control becomes more appropriate. At the same time, the generation of surplus energy can be prevented and the condition of low fuel consumption and / or low exhaust gas can be met.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The continuously variable transmission A to which the speed change driving device is applied has a first transmission
As shown in the figure, a pair of variable displacement hydraulic pumps / motors 1 and 2 are connected by a hydraulic circuit 3 to form a so-called HST (Hydrostat).
ic Transmission), which constitutes a variable speed static pressure transmission system a. As these hydraulic pumps / motors 1 and 2, for example, a static pressure balance type which realizes a volume change by eccentricity of a pintle as disclosed in Japanese Patent Application No. 56-175190 is preferably used. A gasoline engine 4 is connected to an input-side hydraulic pump / motor (hereinafter, referred to as a hydraulic pump) 1, and a speed reducer 5 is connected to an output-side hydraulic pump / motor (hereinafter, referred to as a hydraulic motor) 2. Through wheels 6
Are linked. In this case, the maximum value DP _{MAX of the} displacement volume DP of the hydraulic pump 1 and the maximum value DM _{MAX of the} displacement volume DM of the hydraulic motor 2 are set to be equal.
The static pressure transmission system a is backed up by a boost pump 7 and protected from pressure damage by a relief valve 8. In such a continuously variable transmission A, the speed of the engine 4 is set to SE, and the speed of the hydraulic motor 2 is set to SM.
(Proportional to the vehicle speed V), the speed ratio e can be represented by SM / SE. Then, the speed ratio e is changed to the displacement DM of the hydraulic motor 2 as shown in FIG.
_The displacement volume DP of the hydraulic pump 1 is changed from 0 <e ≦ 1 by increasing the displacement volume DP of the hydraulic pump 1 from 0 to DP _MAX while maintaining the displacement volume DP at a maximum value. By reducing the displacement volume DM of the hydraulic motor 2 from DM _MAX toward 0 while holding it at DP _MAX , it can be changed in the region of 1 <e.

In such a configuration, the present embodiment connects the pressure compensator 9 to the operating end 1a of the hydraulic pump 1 which changes the volume, and connects the accelerator modulator between the throttle valve 4a and the accelerator 11 in the engine 4.
The pressure compensator 9 and the accelerator modulator 12 are connected via separate wires 12a and 12b
Is controlled through the ECU 10. That is,
The pressure compensator 9 uses the ECU 10
Signal s for achieving the set pressure P ₀ corresponding to the stepping amount ACL of
_{When 1} is output, the displacement volume DP of the hydraulic pump 1 is changed until the effective differential pressure ΔP between the discharge pressure and the suction pressure of the hydraulic pump 1 becomes equal to the set pressure P _{0 according} to the signal s ₁ . In this embodiment, the set pressure P ₀ is provided in substantially direct proportion to the accelerator pedal depression amount ACL as shown by the solid line in FIG. As a specific configuration example of the pressure compensator 9, although not shown, a duty control valve is connected to the hydraulic pump 1, and a set pressure signal s ₁ proportional to the accelerator pedal depression amount ACL is sent from the ECU 10 to the duty control valve. To the set pressure internally
Keep so as to generate the P _0. Then, the set pressure P _{0 is applied} to one end of the internal spool, which is the operation end 1 a of the hydraulic pump 1, while the actual effective differential pressure ΔP is applied to the other end of the spool in an antagonistic state. Accordingly, if the effective differential pressure ΔP is smaller than the set pressure P ₀ , the spool moves to one side to introduce a hydraulic fluid to the pintle drive control piston in the direction of increasing the displacement volume DP, and the effective differential pressure ΔP is set to the set pressure.
It is larger than P ₀ spool advance to be able to introduce the liquid to the control piston in the decreasing direction of the exception volume DP press moves to the other. The accelerator modulator 12 is, for example, disclosed in Japanese Patent Application No. 61-136968 as an acceleration adjusting device, and divides a wire connecting the accelerator 11 and the throttle valve 4a into a front part 12a and a rear part 12b. A differential gear for differentially distributing the accelerator depression amount ACL and outputting it to the throttle valve 4a and the variable fixing mechanism is disposed in the dividing portion (not shown). When the fixing position of the fixing mechanism is moved by an external operation, the displacement of the wire 12b with respect to the wire 12a is reduced, and as a result, the throttle opening THL with respect to the accelerator pedal depression amount ACL can be shifted in the decreasing direction. It has become. An eccentricity sensor 1b is provided on the hydraulic pump 1,
ECU10 whereas determining the engine load torque TE by multiplying the push aside volume DP and the set pressure (effective differential pressure) P ₀ was removed via a detection signal s ₂ (see FIG. 3 and FIG. 5), this The ECU 10 stores in advance a table of the throttle opening THL which is considered to be optimal for the engine load torque TE from the viewpoint of fuel consumption and / or exhaust gas (this THL corresponds to each operation on the optimal operation line shown in FIG. 6). corresponds to a point), such throttle opening THL and outputs a control signal s ₃ on the securing mechanism varying actuator or the like of the accelerator modulator 12 so as to obtain the throttle valve
4a is sequentially feedforward controlled.

According to such a configuration, the start-up characteristics of the continuously variable transmission A can be improved and the fuel efficiency can be improved at the same time by the operation described above. That is, when the driver depresses the accelerator 11 at the time of starting, the throttle valve 4a opens to the optimum opening THL through the behavior of the accelerator modulator 12, and sends a sufficient amount of fuel to the engine 4. On the other hand, in parallel with this, the displacement DP of the hydraulic pump 1 changes by negative feedback control without waiting for the engine speed SE to increase, and the effective differential pressure ΔP (= P ₀₎ proportional to the accelerator pedal depression amount ACL. ) To maintain.
That is, when the hydraulic motor 2 is stopped, the displacement DP of the hydraulic pump 1 first increases slightly, and the effective differential pressure P ₀
When the hydraulic motor 2 starts rotating due to this, the effective differential pressure P ₀ due to the hydraulic motor 2 swallowing the hydraulic fluid is generated.
Displacement of the hydraulic pump 1 to compensate for the pressure drop
DP increases. Such actions occur in a chain, and the displacement volume DP of the hydraulic pump 1 increases as the vehicle speed V increases from the moment the accelerator 11 is depressed. When the effective differential pressure P ₀ is stably maintained in this way, the effective differential pressure P ₀
Is proportional to the acceleration of the vehicle.
As long as 11 is kept constant, the differential pressure P _{0 is} constant, that is, the acceleration is constant (of course, the driver can adjust to the intended acceleration by changing the degree of depression of the accelerator 11), and as shown in FIG. , A constant effective traction force F is obtained, and the vehicle starts to move from the moment the accelerator 11 is depressed. For this reason, conventionally, the time corresponding to “first-order delay + dead time” until the engine speed SE rises can be eliminated, and the responsiveness can be improved.
Moreover, this control starts up like the conventional control,
Displacement volume of hydraulic pump 1 to recover control delay
There is no need to sharply increase the DP, and it does not cause unexpected jumping out. As a result, in this embodiment, the vehicle equipped with the illustrated continuously variable transmission A can be driven to change gears stably and smoothly. Besides, throttle opening
Since the THL is always feed-forward controlled to the optimum value, the engine 4 at the time of starting in the above-described speed change drive control.
To prevent the overshoot from blowing up with no load or close to it, making the above-mentioned shift control itself more appropriate, and at the same time, preventing the generation of excess energy and adapting to the conditions of low fuel consumption and / or low exhaust gas. Can be.

Note that instead of using the accelerator modulator,
An auxiliary throttle valve is provided in series with the throttle valve,
The ECU may control this auxiliary throttle valve to regulate fuel supply. Further, in the above embodiment, as shown in FIG. 3, the set pressure P ₀ is set so as to increase substantially directly in proportion to the accelerator pedal depression amount ACL.
If it is desired to end the process up to ≦ 1 and shift to the conventional control at 1 <e (that is, to control the throttle opening so as to provide a target engine speed corresponding to the accelerator depression amount), the torque should be set at the moment of the shift. also effective that you modify the set pressure P ₀ corresponding to the accelerator operation degree ACL so as not to receive a shock occurring variations as shown in FIG. 3 in phantom lines slightly. Further, in the above embodiment, the effective differential pressure ΔP is the differential pressure between the discharge pressure and the suction pressure of the hydraulic pump, but the differential pressure between the discharge pressure and the atmospheric pressure and the absolute value of the discharge pressure (that is, the difference from the pressure 0). Pressure) can also be used as the effective differential pressure. Furthermore, in place of the throttle control of the above-described embodiment, a mode may be considered in which an overspeed governor mainly used for a diesel engine is provided, and the shape of the pump / motor may be a variable displacement type on both the input side and the output side. The maximum displacement volume on the output side and the output side may be different, and the variable capacity type may be any type such as a swash plate type or an oblique axis type. As the capacity control mechanism, a well-known means such as a hydraulic actuator or a servo mechanism using a stepping motor is used. In addition, various modifications can be made without departing from the spirit of the present invention.

[Effects of the Invention] When the speed change drive device according to the present invention is applied to a continuously variable transmission for a vehicle, it is possible to eliminate a response delay and a feeling of jumping out, and to perform speed change driving at the time of starting stably and smoothly.
Further, under such a configuration, it is easy to prevent the engine from overshooting at the time of starting, and it is possible to improve fuel efficiency. As a result, the present invention is particularly useful when traveling in an urban area where frequent starts are made.

[Brief description of the drawings]

1 shows an embodiment of the present invention, FIG. 1 is a circuit diagram, FIG.
FIG. 3 is a graph showing the relationship between the speed ratio of the continuously variable transmission and the displacement volume, FIG. 3 is a graph showing the relationship between the accelerator depression amount and the set pressure, FIG. 4 is a graph showing the relationship between the speed ratio and the traction force, FIG. 5 is a graph showing the relationship between the speed ratio and the engine load torque, and FIG. 6 is a graph showing the relationship between the engine speed and the engine load torque. 1 ... input side hydraulic pump / motor (hydraulic pump) 2 ... output side hydraulic pump / motor (hydraulic motor) 4a ... throttle valve a ... static pressure transmission system A ... stepless transmission e …… Speed ratio ΔP …… Effective differential pressure DP, DM …… Displacement volume ACL …… Accelerator angle (accelerator depression amount) P ₀ …… Set pressure TE …… Engine load torque THL …… Throttle opening

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F16H 61/38-61/46 B60K 41/00-41/28 F02D 41/00 F02D 9/02

Claims (1)

(57) [Claims] 1. A state in which a variable speed static pressure transmission system is formed between a pair of hydraulic pumps / motors having at least an input side of a variable displacement type, and a displacement volume of the input side hydraulic pump / motor is set to zero. Applied to a continuously variable transmission for a vehicle, wherein the speed ratio represented by the output speed / input speed can be made substantially zero, wherein the effective differential pressure of the static pressure transmission system corresponds to an accelerator angle. The negative displacement control of the displacement of the input side hydraulic pump / motor is performed so as to maintain the set pressure, and the engine load torque is calculated from the effective differential pressure and the displacement of the input side hydraulic pump / motor. A variable speed drive for a continuously variable transmission for a vehicle, wherein the throttle is feed-forward controlled so as to obtain an optimum opening with respect to the engine load torque.