JPH0415134B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle speed control device that controls vehicle speed by controlling the displacement of at least one of a hydraulic pump and a hydraulic motor in a hydraulic transmission.

This type of hydraulic transmission has a variable displacement hydraulic pump (swash plate pump) driven by the engine on the engine side, and a variable displacement hydraulic motor (swash plate pump) on the drive shaft side that drives the wheels or tracks of the vehicle. The hydraulic oil discharged from the swash plate pump is guided to the swash plate motor via hydraulic piping to transmit the driving force of the engine to the wheels or tracks. By controlling the inclination angle of the swash plate, the discharge amount of the hydraulic pump and the suction amount of the hydraulic motor per engine revolution can be adjusted, and the speed of the vehicle can be adjusted by changing the number of rotations of the drive shaft per engine revolution. It is for controlling.

However, in this conventional vehicle speed control method, the operator operates the vehicle speed setting lever, brake pedal, and slot lever, and this movement mechanically controls the tilt angle of the swash plate to control the vehicle speed. As a result, the configuration of the control system becomes complicated, and there are problems such as it is difficult to control the vehicle speed in consideration of riding comfort, safety, etc.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a vehicle speed control device that provides a comfortable ride and can perform smooth vehicle speed control, and can also perform vehicle speed control with excellent safety.

According to this invention, electric signals corresponding to the operation positions of the vehicle speed setting lever and the brake pedal are formed,
The electrical signals are appropriately calculated and processed to achieve the above object. That is, depending on whether the vehicle speed command generated in response to the vehicle speed setting lever position is an acceleration command or a deceleration command, the vehicle speed command is outputted through different delay compensating means, and the vehicle speed command is insensible before the compensating means. A changeover switch is provided that changes depending on whether the vehicle speed command is in the dead range or not, and the vehicle speed command is formed so that as soon as the vehicle speed command exceeds the dead range, the vehicle speed command becomes a vehicle speed command corresponding to at least a preset minimum speed; Furthermore, the brake signal generated in response to the depression of the brake pedal is subtracted from the vehicle speed command, this subtracted value is used as a new vehicle speed command, and a mechanical brake that operates the mechanical brake when the vehicle speed command is less than or equal to 0 vehicle speed. I am trying to generate a signal.

The present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. In FIG. 1, a hydraulic transmission 10 is provided with a variable displacement hydraulic pump (hereinafter simply referred to as hydraulic pump) 11 and a variable displacement hydraulic motor (hereinafter simply referred to as hydraulic motor) 12, which are connected to hydraulic pipes 13a, 13b. is connected with
A shaft 11a of the hydraulic pump 11 is connected to an output shaft 1a of the engine 1, and is rotationally driven by the engine 1. Shaft 1 of hydraulic motor 12
2a is connected to a drive wheel of a vehicle (not shown) and rotates the drive wheel.

In general, variable displacement hydraulic pumps are suitable for applications with constant output shaft torque, and variable displacement hydraulic motors are suitable for applications with constant output; however, in this embodiment, hydraulic pump 11, hydraulic motor 12 Both use variable capacitance type and combine the features of both. Further, both the hydraulic pump 11 and the hydraulic motor 12 are variable displacement pumps and variable displacement motors whose displacement volume is changed by changing the inclination angles of the swash plates 11b and 12b.

The pump swash plate servo device 14 controls the discharge direction and discharge amount of hydraulic fluid from the hydraulic pump 11, and receives a pump displacement change signal Sp from the control device 20.
The direction and angle of inclination of the swash plate 11b are controlled according to the polarity and size of the swash plate 11b. Hydraulic pump 11 is swash plate 1
Hydraulic oil is discharged in a direction and at a flow rate according to the inclination direction and inclination angle of 1b. Motor swash plate servo device 15
is for controlling the amount of hydraulic oil taken into the hydraulic motor 12, and is designed to control the inclination angle of the swash plate 12b of the hydraulic motor 12 in accordance with the motor capacity change signal Sm from the control device 20. The rotational direction and torque of the hydraulic motor 12 change depending on the direction and amount of inflow (suction amount) of hydraulic oil. Therefore, the discharge amount of the hydraulic pump 11 and the hydraulic motor 12
By controlling the suction amount, the transmission 10 can be controlled to change its speed.

The control circuit 20 includes a potentiometer 21 that generates a signal corresponding to the position of the vehicle speed setting lever 2 for setting the speed of the vehicle, a potentiometer 22 that generates a signal corresponding to the position of the brake pedal 3,
The hydraulic pump 11 responds to various signals from the potentiometer 23, which generates a signal corresponding to the position of the throttle lever 4, and the engine rotation sensor 5, which generates a pulse signal corresponding to the rotation speed of the engine 1.
It generates a pump capacity change signal Sp and a motor capacity change signal Sm that control the capacity of the hydraulic motor 12, and also generates a mechanical brake signal that controls the mechanical brake 6.

The control circuit 20 will now be explained with reference to the block diagram shown in FIG. This control circuit 20 includes a vehicle speed control calculation circuit 30 to which signals are applied from potentiometers 21 and 22, and a potentiometer 23.
and an automatic shift calculation circuit 40 and a servo drive circuit 50 to which signals are applied from the engine rotation sensor.
It is composed of etc.

The details of the vehicle speed control calculation circuit 30 will be described later, but the vehicle speed control calculation circuit 30 includes a dead area setting circuit 31, and a compensation circuit 3.
2. Absolute value circuit 33, comparator 34, judgment circuit 3
5. A brake signal compensation circuit 36 and the like are configured. The dead area setting circuit 31 is a potentiometer 2
A dead area for the signal applied from 1 is set, and a step-up amount is set so that the input signal rises to a predetermined value or rises as soon as the input signal exceeds the set dead area. The compensation circuit 32 adds an appropriate time delay to the signal applied from the dead area setting circuit 31 and outputs a response, and applies this to the absolute value circuit 33 and the discrimination circuit 35. The determination circuit 35 determines whether the input signal is positive or negative, and when the input signal is positive, it becomes "1" and when it is negative, it becomes "-1".
Output K _FR . Further, the absolute value circuit 33 takes the absolute value of the input signal and adds it to the subtraction point 37.

On the other hand, the brake signal compensation circuit 36 outputs an appropriate brake signal according to the signal applied from the potentiometer 22.
A time delay is added to the signal applied from the brake pad and outputted, and when the input signal exceeds a preset level, the signal is instantaneously outputted as a brake signal. This brake signal is subtraction point 37
added to. Subtraction point 3 Nana Absolute value circuit 33
The brake signal is subtracted from the signal input from
It is output to the subtraction point 51.

When the vehicle speed command signal Vs becomes equal to or less than the value indicating vehicle speed 0, the comparator 34 outputs a signal "1" to the reset terminal R of the flip-flop 52 and also to the coil 54a of the brake solenoid valve 54. , and also operates the mechanical brake 6 (see Figure 1). The charge pressure switch 55 detects that the charge pressure of the hydraulic transmission 10 has fallen below a predetermined pressure, and upon this detection outputs a signal "1" to the set terminal S of the flip-flop. Flip-flop 52 is switch 55
When set by the output of , a signal "1" is outputted to the coil 54a of the brake solenoid valve 54 via the OR circuit 53, and also outputted to the switch 56. When the switch 56 receives a signal "1", it opens its contacts and prevents the vehicle speed command from being output to the servo drive circuit 50.

Further, a speed change signal Sf is applied to the other input of the subtraction point 51 from the automatic speed change calculation circuit 40. The automatic speed change calculation circuit 40 calculates the difference between the engine rotation speed set by the slot lever 4 and the current rotation speed, and prevents the engine rotation speed from falling below a preset rotation speed due to load fluctuations. This outputs the speed change signal Sf for the purpose. In other words, a condition is created in which the engine 1 can always operate near its maximum horsepower point.
The automatic speed change calculation circuit 40 includes a subtraction point 41, a frequency-voltage converter 42, and a PID compensation circuit 43. A signal corresponding to the position of the throttle lever 4 is applied from the potentiometer 23 to one input of the subtraction point 41. Further, a pulse signal with a number of pulses corresponding to the number of rotations of the engine 1 is applied from the engine rotation sensor 5 to the frequency-voltage converter 42, and the frequency-voltage converter 42 converts the input pulse signal into the number of pulses. It is converted into a corresponding voltage signal and added to the other input of the subtraction point 41. A subtraction point 41 calculates the difference between the signal output from the potentiometer 23 and the signal output from the frequency-voltage converter 42, and applies this to the PID compensation element 4.
The gear shift signal Sf is outputted via 3. Furthermore, this
The PID compensation element 43 controls engine rotation during automatic gear shifting.
This is provided to prevent the vehicle speed from becoming unstable.

Subtraction point 51 is the speed change signal Sf from the vehicle speed command signal Vs
is subtracted and added to the servo drive circuit 50 via the switch 56. Servo drive circuit 5
0 controls the discharge direction and discharge amount of the hydraulic pump 11 of the transmission 10 and the suction amount of the hydraulic motor 12, and is a pump capacity change signal of a preset ratio according to the signal added from the subtraction point 51.
Outputs Sp and motor capacity change signal Sm. The servo drive circuit 50 also determines the polarity of the pump capacity change signal Sp in accordance with the polarity of the direction signal _KFR . The pump capacity change signal Sp is sent to the coil 57 of the solenoid valve 57 that operates the pump swash plate servo device 14.
a and 57b, motor capacity change signal
Sm is applied to the coil 58a of the solenoid valve 58 that operates the motor swash plate servo device 15.

Therefore, the pump swash plate servo device 14 and the motor swash plate servo device 15 control the inclination angle of the swash plate according to the signals Sp and Sm, and control the discharge amount of the hydraulic pump 11 and the suction amount of the hydraulic motor 12. The transmission 10 is controlled to change speed.

Next, details of the shift control calculation circuit 30 will be explained.

FIG. 3 is a circuit diagram showing one embodiment of the vehicle speed control calculation circuit. The potentiometer 21 outputs a voltage from 0 to _Vcc depending on the position of the vehicle speed setting lever 2. Here, voltage 0 corresponds to the maximum reverse speed setting, voltage V _cc corresponds to the maximum forward speed setting,
Voltage 1/2V _cc corresponds to 0 vehicle speed.

This voltage signal is applied to the negative input of comparator C ₁ and the positive input of comparator C ₂ , respectively, and
It is applied to contact S _1a of switch S ₁ via resistor R ₁ . Dead area setting voltages D _b1 and D _b2 for setting a dead area are applied to the positive input of the comparator C ₁ and the negative input of the comparator C ₂ . Note that the set voltage D _b1 is higher than the voltage 1/2V _cc , and the set voltage D _b2
is a voltage value lower than the voltage 1/2V _cc .

Therefore, when the voltage signal output from potentiometer 21 is within the range of set voltage D _b1 to D _b2 , comparators C ₁ and C ₂ both become high level. This causes the diodes D ₁ , D ₂
No current flows through, and the voltage on line _l1 connects the movable contact _S1c of switch _S1 to contact _S1b . In addition,
A voltage of 1/2V _cc corresponding to zero vehicle speed is applied to contact S _1b .

Also, if the voltage signal output from the potentiometer 21 exceeds the range of the set voltage D _b1 to D _b2 ,
Since one of the comparators C ₁ and C ₂ falls to the low level and the voltage on the line l ₁ also falls to the low level, the movable contact S _1c of the switch S ₁ is connected to the contact S _1a .

Now, set voltage D _d1 from potentiometer 21
When a voltage signal higher than 1 is output, comparator C ₁
The output of switch S1 falls to a low level, and the movable contact _S1c of switch _S1 is connected to contact _S1a . At this time, the contact
The voltage signal is divided by resistors R ₁ and R ₂ and applied to S _1a . Similarly, when a voltage signal lower than the set voltage C _b2 is output from the potentiometer 21, the output of the comparator C ₂ falls to a low level, and the movable contact S _1c of the switch S _1c becomes the contact S _1a. Connected. At this time, the voltage difference between the voltage signal and the high-level output voltage of the comparator _C1 is applied to the contact _S1a after being divided by the resistors _R1 and _R2 . In other words, when the voltage signal output from the potentiometer 21 exceeds the dead area, the switch
The movable contact S _1c of S ₁ is switched to the contact _{S 1a} , and a predetermined step-up voltage divided by the resistance ratio of the resistors R ₁ and R ₂ is applied to the contact S 1a. Note that the step-up amount is determined by the resistance R ₁ ,
This step-up amount can be set appropriately depending on the resistance ratio of _R2 , but it is preferable to set the step-up amount to correspond to the minimum vehicle speed, that is, the minimum speed at which a human can feel the speed.

Thereby, it is possible to easily determine whether the vehicle is in a running state or a stopped state, and a highly safe dead area can be set. In addition, the above comparators C ₁ , C ₂ , resistors R ₁ , R ₂ , diodes D ₁ , D ₂ and switch S ₁
This circuit corresponds to the dead area setting circuit 31 (FIG. 2) of the vehicle speed control calculation circuit 30.

On the other hand, the outputs of comparators C ₁ and C ₂ are respectively connected to NAND circuits N ₁ and NAND circuits constituting a flip-flop.
Added to _N2 . Thereby, when comparator C ₁ falls to low level, NAND circuit N ₂ outputs a high level signal to line l ₂ , and when comparator C ₂ falls to low level, NAND circuit N ₂ outputs a low level signal. Output to line l ₂ . Line L ₂ is Switch S ₂
and S ₃ , and when line l ₂ becomes high level, the movable contacts S _2c and S _3c of switches S ₂ and S ₃ are connected to contacts S _2a and S _3a , respectively;
When line l ₂ becomes low level, switch S ₂ and
Movable contact pieces S _2c and S ₃ of S ₃ are connected to contacts S _2b and S _3b , respectively.

Comparator C ₃ , which has the output of switch S ₁ as its negative input and the signal corresponding to the current speed, that is, the signal appearing on line L ₃ , as its positive input, is a comparator that receives positive feedback through resistor R ₃ . , outputs a deviation signal to diodes D ₃ and D ₄ so that the signal on line l ₃ matches the input voltage with a constant width.

Therefore, when the voltage signal output from the potentiometer 21 is in the forward and acceleration direction, the output of the comparator _C3 is connected to the diode _D4 , the switch _S3 , and the resistor.
The output of comparator C ₃ is connected to the negative input of operational amplifier OP ₁ via R ₄ and, in the case of forward and deceleration directions, is connected via diode D ₃ , switch S ₂ and resistor R ₅ to the negative input of operational amplifier OP ₁ . Participate in input. In addition, when the voltage signal output from potentiometer 21 corresponds to the reverse direction, switch S ₂ and switch S ₃
is switched by a low level signal appearing on line _l2 , and the output of comparator _C3 is connected to diode _D3 , switch _S2 and resistor _R4 when said voltage signal accelerates.
It is applied to the negative input of operational amplifier OP ₁ through diode D ₄ , switch _{S 3} and resistor R ₅ during deceleration.

The operational amplifier OP ₁ is an integrator for delay compensation that has resistors R ₄ and R ₅ and a capacitor BP ₁ , and the charging direction (acceleration direction) and discharging direction (deceleration direction) is determined by the resistance values of resistors R ₄ and R ₅ . Determining the delay time of the signal on line _l3 .

In other words, by appropriately setting the resistance values of resistors R ₄ and R ₅ , the response of the delay element during acceleration can be set faster than the response of the delay element during deceleration, so that an appropriate acceleration feeling can be obtained during acceleration. In addition, during deceleration, the optimum delay time is set so that no deceleration shock occurs.

Note that when the lever position of the speed setting lever 2 is switched from forward to reverse or from reverse to forward, a delay time in the acceleration direction is set in both cases.
Also, in this case, the signal on line _l3 smoothly responds from a signal corresponding to forward movement to a signal corresponding to reverse movement or from a signal corresponding to reverse movement to a signal corresponding to reverse movement. This is due to the fact that the switch _S1 for setting the dead area is provided before the comparator _C3 .
In addition, comparator C ₃ , diodes D ₃ , D ₄ , switch
A circuit consisting of S ₂ , S ₃ , resistors R ₄ , R ₅ , capacitor BP ₁ and operational amplifier OP ₁ is a vehicle speed control circuit 30.
This corresponds to the compensation circuit 32 (FIG. 2).

The output voltage of the operational amplifier OP ₂ is connected to the contact S _4a of the switch S ₄ , the negative input of the operational amplifier OP ₂ and the comparator C ₄
is added to the positive input of The operational amplifier OP ₂ is an inverting amplifier that inverts the input voltage by a voltage of 1/2 V _cc and applies it to the contact S _4b of the switch S ₄ . Comparator _C4 determines whether the input voltage is in the forward range or reverse range, and if it is in the forward range, it outputs a high-level direction signal _KER and also outputs a high-level direction signal KER to switch _S4 via line _l4 . Connect the movable contact piece S _4c to the contact S _4a , and output a low level direction signal K _ER in the reverse range, and connect the movable contact piece S _4c of the switch S ₄ to the contact S _4b via the line l ₄ . Connect to.

The circuit consisting of the switch S ₄ , the operational amplifier OP ₂ and the comparator C ₄ corresponds to the absolute value circuit 33 and the discrimination circuit 35 (FIG. 2) of the vehicle speed control circuit 30, and the direction signal K _ER corresponds to the servo drive circuit. Added to 50.

The output voltage of switch S ₄ is applied to the positive input of operational amplifier OP ₃ . This operational amplifier OP ₃ is a subtracter, and a brake signal related to depression of the brake pedal 3 is added to the negative input.

Here, the brake signal will be explained.
The potentiometer 22 generates a voltage signal corresponding to the amount of depression of the brake pedal 3, and the voltage signal is sent to the comparator.
Add to the positive input of C ₅ , resistor R ₆ and diode D ₅ . Comparator C ₅ operates in the event of a sudden stop, and when a voltage signal greater than the preset voltage V _b is generated from potentiometer 22, it instantly charges capacitor BP ₂ via diode D ₆ and inputs it. Apply voltage to the positive input of operational amplifier OP ₄ . Note that the preset voltage V _b needs to be set to a voltage sufficient to apply a mechanical brake, which will be described later.

On the other hand, if a voltage signal smaller than the preset voltage V _b is generated from the potentiometer 22 when the brake pedal 3 is depressed, this voltage signal is charged in the capacitor BP ₂ via the resistor R ₆ and its charging The voltage is applied to the positive input of operational amplifier _OP4 .

Also, when the brake pedal 3 is released, the charge stored in the capacitor BP ₂ is transferred to the resistor R ₆ and the resistor
It is discharged through two systems: R ₇ and diode D ₅ . That is, the delay time of the voltage signal (brake signal) appearing at the positive input of the operational amplifier OP ₄ is different between when the brake pedal 3 is depressed and when it is released.

In other words, by setting the delay response when the brake is released earlier than when the brake is depressed, it will be possible to reduce the spillage of cargo during deceleration and obtain a quick acceleration feeling. By setting the response to be slow, the vehicle can be stopped quickly during hopper work, etc., and the shock when starting can be reduced.

The operational amplifier OP ₄ is a voltage follower circuit,
The brake signal applied to the positive input is directly applied to the negative input of operational amplifier _OP3 . In addition, the comparator
C ₅ , diodes D ₅ , D ₆ , resistors R ₆ , R ₇ , capacitor BP ₂ and operational amplifier OP ₄ are connected to the brake signal compensation circuit 36 of the vehicle speed control calculation circuit 30
(Fig. 2).

The operational amplifier _OP3 subtracts the brake signal from the voltage signal input from the switch _S4 and outputs it as a vehicle speed command signal _Vs.

A portion of the vehicle speed command signal V _s is led to the negative input of the comparator C ₆ . The comparator _C6 operates the mechanical brake 6, and the vehicle speed command signal _Vs is set to a preset voltage _Vp.
When the voltage becomes smaller than , a high level voltage signal is output and the mechanical brake 6 is operated. In addition,
The preset voltage V _p is the voltage signal (1/2
V _cc ).

As a result, when the brake pedal 3 is not depressed and a voltage signal corresponding to the vehicle speed of 0 is output from the switch _S4 , the vehicle speed command signal _Vs becomes a voltage of 1/2V _cc and is mechanically recorded by the output of the comparator _C6 . Brake 6 is applied. That is, the mechanical brake 6 is automatically applied during parking. Also, by depressing the brake pedal 3, a vehicle speed command signal is generated.
Of course, the mechanical brake 6 is applied even when V _s drops below the voltage 1/2 V _cc . Further, when the brake pedal 3 is depressed and a brake signal equal to or higher than the set voltage V _b is output from the potentiometer 22, the mechanical brake 6 is applied regardless of the voltage signal output from the switch _S4 .

In this embodiment, the positions of the vehicle speed setting lever and brake pedal, etc. are detected by the potentiometer, and the vehicle speed is controlled based on this detection signal. The above signal may be given based on. Further, in this embodiment, the case where one system of transmission is used has been described, but a similar configuration can be applied to the case where two systems are used.

As explained above, according to the present invention, depending on whether the vehicle speed command is an acceleration command or a deceleration command, it is possible to give each vehicle speed command an optimal delay characteristic,
As a result, a feeling of acceleration can be obtained during acceleration, and vehicle speed control can be performed without causing a deceleration shock during deceleration.
Furthermore, by providing a switch in front of the feedback system that changes depending on whether or not the vehicle speed command is in the dead range, vehicle speed control from forward to reverse or from reverse to forward can be smoothly performed. Furthermore, the step-up amount when the vehicle speed command exceeds the dead range can be adjusted as appropriate, thereby making it easier to determine whether the vehicle is at a standstill or running, thereby improving safety. Further, the brake according to the present invention can appropriately use an engine brake and a mechanical brake as appropriate or in combination as the vehicle speed command decreases, thereby achieving desired control.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram showing one embodiment of the control circuit according to the present invention, and FIG. 3 is a circuit diagram showing one embodiment of the vehicle speed control calculation circuit according to the present invention. 1...Engine, 2...Vehicle speed setting lever, 3...
...Brake pedal, 4...Throttle lever, 5
...Engine rotation sensor, 6...Mechanical brake, 10...Hydraulic transmission, 11...
...Variable capacity hydraulic pump, 12...Variable capacity hydraulic motor, 14...Pump swash plate servo device, 15...
Motor swash plate servo device, 20...control circuit, 2
1, 22, 23... Potentiometer, 31...
Dead area setting circuit, 32... Compensation circuit, 33...
Absolute value circuit, 34... Comparator, 35... Discrimination circuit, 36... Brake signal compensation circuit, 40... Automatic speed change calculation circuit, 50... Servo drive circuit.

Claims (1)

[Scope of Claims] 1. A vehicle speed control device that controls the speed of a vehicle by controlling the displacement volume of at least one of a hydraulic pump and a hydraulic motor of a hydraulic transmission via an electric servo device, the device comprising: a lever; A vehicle speed setting lever that instructs forward/reverse movement and vehicle speed depending on the position and generates a voltage signal corresponding to the instruction; Generates a predetermined sudden stop brake signal that reduces the corresponding voltage signal to a voltage signal corresponding to a vehicle speed of 0, and also generates a voltage corresponding to the amount of depression of the brake pedal when the brake pedal is depressed without exceeding the predetermined position. a brake signal generating means for generating a signal; a charge pressure detecting means for detecting that the charge pressure of the hydraulic transmission has fallen below a predetermined pressure; means for subtracting a voltage signal corresponding to the amount of depression or the sudden stop brake signal and applying the subtracted electric signal to the electric servo device; a switch means for cutting off the application to the electric servo device; and a mechanical brake for generating a mechanical brake signal when the subtracted electric signal corresponds to a vehicle speed of 0 or less or when a detection signal is output from the charge pressure detecting means. A vehicle speed control device comprising: a signal generating means; and a mechanical brake for braking a vehicle operated by a mechanical brake signal from the mechanical brake signal generating means.