JP2744706B2 - Traveling speed control device for hydraulically driven vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling speed control device for a hydraulically driven vehicle such as a wheel type hydraulic excavator.

[0002]

2. Description of the Related Art The applicant has previously disclosed in Japanese Patent Application No. 1-40354 the traveling speed control of a hydraulically driven vehicle in which the displacement of a hydraulic pump is controlled so that the vehicle speed does not exceed a predetermined value. The device is proposed. This control device controls the pump displacement volume as follows. The load pressure P is detected, and the displacement q of the hydraulic pump is calculated from the P-q diagram. The engine speed N is detected, and the engine speed N is multiplied by the displacement q to calculate the flow rate Qd. Limit flow rate Q corresponding to a predetermined maximum vehicle speed, for example, 35 km / h
c is given as the sum of the basic flow rate Q1 and the minute flow rate Q2. The difference between the detected flow rate Qd and the limited flow rate Qc is obtained, and when the difference ΔQ is larger than the minute flow rate Q2,
The pump displacement volume is reduced by the difference flow rate ΔQ.

[0003] The present applicant has previously disclosed in Japanese Patent Application Laid-Open No. 62-156.
No. 440 proposes a hydraulic control device as disclosed. This hydraulic control device limits the vehicle speed to a predetermined value by reducing the displacement volume of the hydraulic pump in accordance with the rotation speed of the prime mover when the rotation speed exceeds a rotation speed suitable for a light load such as traveling on level ground.

[0004]

However, the control device described in Japanese Patent Application No. 1-40354 has the following problems. In this control device, a feedback control system for controlling the displacement volume so that the product of the displacement volume detected from the load pressure and the rotation speed of the prime mover does not exceed a predetermined value is used. However, the pump flow rate may momentarily exceed the predetermined value and the vehicle speed may exceed the predetermined value.

In the hydraulic control apparatus disclosed in Japanese Patent Application Laid-Open No. Sho 62-156440, an optimal prime mover speed is set in advance for a light load. However, even prime movers of the same specification have variations. It is difficult. Furthermore, there is a possibility that a predetermined vehicle speed may not be achieved at a prime mover rotation speed that is optimal for a predetermined light load due to variations in hydraulic pumps.

It is an object of the present invention to provide a traveling speed control device for a hydraulically driven vehicle that can travel at a predetermined vehicle speed without exceeding a predetermined vehicle speed even if there is variation in each device.

[0007]

The present invention will be described with reference to FIGS. 1 and 2 showing one embodiment. The present invention relates to a variable displacement hydraulic pump 1 driven by a prime mover 21 and a hydraulic pump 1 comprising: The displacement hydraulic motor 4 driven by the discharge oil of the hydraulic pump 1, the displacement volume changing means 9 for changing the displacement volume of the hydraulic pump 1, the pressure detection means 27 for detecting the discharge pressure of the hydraulic pump 1, and the power of the prime mover A first displacement volume calculating means 241a for calculating a target displacement volume (q1) based on the detected pump pressure from a correspondence relationship between the pump pressure and the displacement volume set in advance so as not to exceed. ,
The present invention is applied to a traveling speed control device of a hydraulically driven vehicle that controls the displacement volume changing means 9 so as to have the calculated target displacement volume. Then, the motor rotation speed detection means 26 for detecting the rotation speed of the motor 21 and the correspondence relationship between the motor rotation speed and the displacement set in advance so as not to exceed a predetermined speed, Second displacement volume calculation means 241 for calculating the maximum displacement volume (q2) based on the
b and the first and second displacement volume calculating means 241a,
Selecting means 241c for selecting the minimum value (qi) of the displacement volumes (q1) and (q2) calculated in 241b, and the displacement volume so as to become the target displacement volume selected by the selection device 241c. By controlling the changing means 9,
Achieve the above objectives. According to the control device of the second aspect, the second
A plurality of types of correspondence between the rotation speed of the prime mover and the displacement are set in the displacement volume calculating means, and a selection operation means for selecting any one of the correspondence relations is provided.

[0008]

The target displacement volume (q1) is calculated from the pump pressure (P), and the maximum displacement volume (q) is calculated from the motor rotation speed (N).
2) is calculated. Those minimum values are selected as the target displacement volume (qi), and the displacement volume of the hydraulic pump 1 is controlled to be changed through the displacement volume changing means 9. Since the maximum displacement volume (q2) is the maximum value of the displacement volume determined corresponding to each rotation speed so as not to exceed a predetermined speed in the entire prime mover rotation speed region, the control displacement volume is determined by the maximum displacement volume. By limiting, it is possible to reliably operate within the maximum pump flow rate corresponding to the predetermined speed.

In the section of the means for solving the above problem and the operation of the present invention, the drawings of the embodiments are used for easy understanding of the present invention. However, the present invention is not limited to this.

[0010]

【Example】

-First Embodiment- An embodiment in which the present invention is applied to a traveling speed control device of a wheel type hydraulic excavator will be described with reference to FIGS.

In FIGS. 1 and 2, an engine (motor) 2
Discharge oil from the variable displacement hydraulic pump 1 driven by the hydraulic pump 1 is guided to a traveling hydraulic motor 4 via a counterbalance valve 3 via a hydraulic pilot control valve 2. The control valve 2 is switched by a pilot hydraulic circuit including a hydraulic pump 5, a pilot valve 6, a slow return valve 7 and a forward / reverse switching valve 8.

The displacement volume of the variable displacement hydraulic pump 1 is controlled to be changed by a regulator 9. Basically, as in the well-known constant horsepower control, the displacement volume q1 is changed according to the discharge pressure P of the hydraulic pump 1. Is changed. And in this example,
The displacement q2 is calculated corresponding to the engine speed so that the traveling speed does not exceed 35 km / h in the entire engine speed range, and the maximum value of the displacement is limited by the displacement q2. You. The regulator 9 is of an electro-hydraulic type as is well known.

The governor 21a of the engine 21 is connected to a pulse motor 23 via a link mechanism 22, and the rotation of the pulse motor 23 controls the rotation speed of the engine 21. That is, the rotation speed increases with the forward rotation of the pulse motor 23 and decreases with the reverse rotation. The rotation of the pulse motor 23
It is controlled by a control signal from the controller 24. A potentiometer 25 is connected to the governor 21a.
The potentiometer 25 detects a governor lever position corresponding to the number of revolutions of the engine 21, and inputs the governor lever position detection signal to the controller 24. Further, a rotation speed sensor 26 for detecting the actual rotation speed of the engine is provided, and this detection signal is also input to the controller 24.

The controller 24 also includes a hydraulic pump 1
The detection signal from the pressure sensor 27 for detecting the discharge pressure of the pressure is also input. Further, the controller 24 is also connected to a fuel lever, a forward / reverse changeover switch, a brake switch, a pressure gauge for detecting a pilot circuit pressure, and the like, which are provided in an operator's cab. Control is possible. In such engine speed control, the target engine speed is calculated from the operation amounts of the fuel lever and the travel pedal, and the drive of the pulse motor 23 is controlled so that the deviation from the actual speed becomes zero. The forward position F, the reverse position R, and the neutral position N of the forward / reverse switching valve 8 are switched by a forward / reverse switching switch, and at the time of work, both the parking brake and the service brake are operated by the brake switch. .

FIG. 1 shows an example of a regulator control circuit for controlling the displacement volume as described above. The control circuit 241 is provided in the controller 24, and includes two function generators 241a and 241b and a minimum value selection circuit 2
41c. The function generator 241a receives the pump pressure signal P from the pump pressure sensor 27 and outputs a displacement q1 corresponding to the pump pressure P based on a known Pq diagram as shown in the figure. On the other hand, the function generator 241b
Receives the engine speed signal N from the engine speed sensor 26 and outputs a displacement q2 corresponding to the engine speed N based on a diagram as shown in the figure. And
The minimum value selection circuit 241c selects the smaller one of the displacement containers q1 and q2 and outputs the smaller value to the regulator 9 as the target displacement volume qi.

Here, on the diagram of the function generator 241b, the maximum flow rate Qmax calculated by the number of revolutions N1 × the maximum displacement volume qmax corresponds to the speed of 35 km / h. N− so that N × q2 does not exceed Qmax.
The q diagram is substantially defined as a hyperbola. It should be noted that the diagram of the region where the rotation speed is equal to or higher than N1 is set in consideration of various efficiencies.

The operation of the traveling speed control device thus configured will be described. When the traveling pedal 6a is operated with the forward / reverse switching valve 8 switched to the F position (forward position) or the R position (reverse position), the discharge pressure of the hydraulic pump 5 is controlled by the pilot valve 6, and the operation is controlled in accordance with the operation of the pedal 6a. The pressure is controlled by the control valve 2 via the slow return valve 7 and the forward / reverse switching valve 8.
To the pilot port 2a or 2b. At this time, the control valve 2 switches in a predetermined direction by a predetermined amount, and only the amount corresponding to the switching amount of the control valve 2 out of the discharge oil of the hydraulic pump 1 that rotates according to the operation amount of the traveling pedal 6a is the hydraulic motor 4.
It is led to. Thus, the hydraulic motor 4 is driven, and the vehicle moves forward or backward at a speed corresponding to the operation amount of the travel pedal 6a. At this time, the engine speed is also increased or decreased according to the operation amount of the travel pedal 6a.

During such a running operation, the displacement volume of the hydraulic pump 1 is controlled as follows. From the function generator 241a based on the pump pressure P, the first displacement q1
Is calculated based on the engine speed N.
The second displacement volume q2 is calculated from 41b. These displacements q1 and q2 are input to the minimum value selection circuit 241c, and the smaller one is selected and the target displacement q
It is input to the regulator 9 as i.

Now, when three rotation speeds satisfying Na <Nb <Nc are represented on the Nq diagram enlargedly shown in FIG. 3A, the rotation speeds can be obtained from the Pq diagram of the function generator 241a. The engine displacements Na, Nb, and Nc are stored in the first displacement volume q1.
Are calculated as shown in FIG. 3B with respect to the pump pressure P. In this embodiment, since the maximum value of the target displacement is limited by the second displacement q2 calculated so as not to exceed the maximum speed of 35 km / h, the relationship between the pump pressure P and the pump discharge flow rate Q is obtained. 3 (c), and does not exceed the maximum discharge flow rate Qmax at any engine speed. That is, the speed does not exceed 35 km / h regardless of the engine speed. Further, since the feedforward control is performed without performing the feedback control as in the conventional speed limiting method, there is no secondary delay, and the pump flow rate Q does not instantaneously exceed Qmax. further,
As can be seen from FIG. 3 (c), the higher the engine speed, the wider the pressure range where Qmax is constant. Therefore, the higher the engine speed, the smaller the speed fluctuation due to the pump pressure.

Second Embodiment FIG. 4 shows another embodiment of the regulator control circuit shown in FIG. The same parts as those in FIG. 1 are denoted by the same reference numerals, and differences will be mainly described. In this embodiment, the two types of Nq diagrams that determine the maximum displacement are respectively represented by the function generator 241b.
-S and 241b-L, and the selection switch 241d
Switches the switch 241e to select one of the function generators. The function generator 241b-S is selected when the tire diameter is small, and the function generator 241b-L is selected when the tire diameter is large. Since the maximum speed is limited to 35 km / h for any tire diameter, in the diagram with the larger tire diameter, the maximum flow rate Qmax indicates the rotation speed N2 (<N
The broken line portion of the Nq diagram is determined as obtained in 1),
Further, the minimum displacement volume qmin is determined so that the maximum flow rate Qmax is obtained at the maximum rotation speed Nmax. That is,
The rotation speed N2 is represented by N2 = N1 × DS / DL when the large and small tire diameters are represented by DL and DS, respectively, and the minimum displacement is also represented by the same relational expression.

The selection switch 241d is provided in the driver's seat, and when the driver switches according to the tire diameter, the switch 241e is switched, and one of the function generators is selected, and the optimum Nq for the tire diameter is selected. The maximum displacement volume q2 is set from the diagram. Therefore, even when tires having different diameters are mounted, the maximum speed can be limited to 35 km / h.

The present invention is not limited to wheel shovels, but can be applied to other hydraulic traveling vehicles. Further, the maximum displacement volume q2 may not be obtained from the actual rotation speed N but may be obtained from the target rotation speed, and the present invention is not limited to the circuit configuration of the above embodiment.

In the configuration of the above embodiment, the regulator 9 serves as the displacement volume changing means, the pressure sensor 27 serves as the pressure detecting means, and the function generator 2 of the regulator control circuit 241.
41a and 241b constitute first and second displacement volume calculation means, the rotation speed sensor 26 constitutes a motor rotation speed detection means, and the minimum value selection circuit 241c constitutes a selection means.

[0024]

According to the present invention, the displacement volume is determined so that the flow rate of the hydraulic pump becomes the maximum value corresponding to the predetermined speed in the entire range of the rotation speed of the prime mover, and the displacement volume determined by the pump pressure is determined. The feed-forward control that limits the maximum displacement of the pump is not used, so there is no second-order lag unlike the conventional feedback control method, and therefore, the pump flow rate does not instantaneously exceed the maximum value. You can limit the maximum speed. In addition, since the correspondence between the motor rotation speed and the displacement volume can be selected according to the tire diameter, etc.,
The running speed can be reliably limited even if the tire diameter changes.

[Brief description of the drawings]

FIG. 1 is a block diagram showing details of a regulator control circuit.

FIG. 2 is a diagram showing an overall configuration of a traveling speed control device according to the present invention.

3A shows the correspondence between the engine speed and the displacement volume, FIG. 3B shows the correspondence between the pump pressure and the pump flow rate, and FIG. 3C shows the pump pressure and the pump pressure with the maximum flow rate restricted. Diagram showing the correspondence of flow rates

FIG. 4 is a block diagram showing a second embodiment of the regulator control circuit;

[Explanation of symbols]

 Reference Signs List 1 hydraulic pump 2 control valve 4 hydraulic motor 6 traveling pilot valve 6a traveling pedal 7 slow return valve 8 forward / reverse switching valve 21 engine 24 controller 26 engine speed sensor 27 pump pressure sensor 241 regulator control circuit 241a, 241b function generator 241b -S, 241b-L Function generator 241c Minimum value selection circuit 241d Selection switch 241e Switcher

Claims (2)

(57) [Claims] A variable displacement hydraulic pump driven by a prime mover; a traveling hydraulic motor driven by oil discharged from the hydraulic pump; a displacement volume changing means for changing a displacement volume of the hydraulic pump; A pressure detecting means for detecting a discharge pressure of the hydraulic pump, and a target displacement volume based on the detected pump pressure, based on a correspondence relationship between a pump pressure and a displacement volume set in advance so as not to exceed the motor horsepower. A traveling speed control device for a hydraulically driven vehicle, comprising: first displacement volume calculating means for calculating; and controlling the displacement volume changing means to attain the calculated target displacement volume. Based on the detected number of rotations of the motor, based on the relationship between the number of rotations of the motor and the displacement set in advance so as not to exceed a predetermined speed. A second displacement volume calculation means for calculating a large displacement volume, and a selection means for selecting a minimum value of the displacement volume calculated by the first and second displacement volume calculation means, A travel speed control device for a traveling drive vehicle, wherein the displacement volume changing means is controlled so as to have a target displacement volume selected by the means. 2. The speed control device according to claim 1, wherein said second displacement volume calculating means has a plurality of types of correspondences between the rotation speed of the motor and the displacement volume, and selects any one of the relationships. A traveling speed control device for a hydraulically driven vehicle, further comprising a selection operation means for performing the operation.