JPS642547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydraulic drive system for a vehicle, such as a self-propelled construction machine, in which a traveling device is driven by hydraulic pressure. The present invention relates to a hydraulic drive device for a traveling device using a type of hydraulic pump.

(Prior Art) In self-propelled construction machines such as box hoes, crawlers are often used as traveling devices, and in such cases, the crawlers are generally driven by hydraulic pressure. Conventionally, a hydraulic circuit as shown in FIG. 5 has been used to drive such crawlers.

That is, N-type hydraulic pumps P ₁ and P ₂ are driven by a prime mover E such as an engine, and pressure oil discharged from the hydraulic pumps P ₁ and P ₂ is sent to the left and right through hydraulic lines l ₁ and l ₂ , respectively. Hydraulic motor M ₁ , M ₂
Let yourself be guided. The left and right crawlers are individually driven by these hydraulic motors M ₁ and M ₂ . And forward and backward,
Or for each hydraulic line to perform direction changes etc.
Directional control valves V ₁ and V ₂ are provided at l ₁ and l ₂ .
Further, in order to control the maximum pressure of the circuit and prevent overload, relief valves R ₁ and R ₂ are connected to each hydraulic line l ₁ and l ₂ , respectively.

When the hydraulic pumps P ₁ and P ₂ are driven by the prime mover E, the pressure oil discharged from the hydraulic pumps P ₁ and P ₂ is controlled to the set pressure by the relief valves R ₁ and R ₂ , and the hydraulic oil is Supplied to motors M ₁ and M ₂ . Therefore, when the hydraulic pumps P ₁ and P ₂ are of constant displacement type, the outputs of the hydraulic motors M ₁ and M ₂ are constant.

(Problems to be Solved by the Invention) However, in a vehicle running device, the required output varies depending on the running state. For example, high output is required when starting or climbing a slope. Therefore, when the traveling device is driven by a hydraulic motor, the hydraulic motor must be supplied with high pressure oil. On the other hand, when driving at a constant speed, the output may be small, but high-speed driving is required.
Therefore, in that case, it is necessary to supply a large flow of pressure oil to the hydraulic motor.

For this purpose, in a hydraulic drive system as shown in FIG _.
When using P ₂ , the hydraulic pumps P ₁ and P ₂ must be of high pressure and large capacity, and the prime mover E that drives the hydraulic pumps P ₁ and P ₂ must also be of high output. It was hot.

Therefore, in the past, variable displacement hydraulic pumps were often used to drive the traveling gear, but such variable displacement hydraulic pumps were expensive, so they There was a problem with rising prices.

The present invention has been made in view of these problems, and its purpose is to use a fixed displacement hydraulic pump, but to adjust the output and rotational speed obtained by the hydraulic motor depending on its running condition. The purpose of the present invention is to enable automatic switching, thereby reducing the output required of the prime mover.

(Means for Solving the Problems) In order to achieve this object, the present invention provides two constant displacement hydraulic pumps that supply pressure oil to the respective hydraulic motors for driving the left and right crawlers. Furthermore, separate fixed displacement hydraulic pumps are added, and these hydraulic pumps are driven by the same prime mover, and the pressure oil discharged from the added hydraulic pump is routed through a relief valve and a flow divider. The hydraulic power is supplied to each hydraulic motor. The set pressure of the relief valve is relatively low, and when the main circuit pressure rises above the set pressure, the pressure oil discharged from the additional hydraulic pump is returned to the oil tank, and the hydraulic pump is turned off. I'm trying to get it loaded.

(Function) With this configuration, when the load is large, such as when the vehicle starts or climbs a hill, the pressure in the main circuit increases, so the additional hydraulic pump is unloaded and the original secondary pump is High-pressure oil is supplied to each hydraulic motor by two hydraulic pumps.
Therefore, the output torque of the hydraulic motor becomes large.

In addition, when the load decreases, such as when shifting to constant speed driving, the pressure in the main circuit decreases, so the pressure oil discharged from the additional hydraulic pump
The water is divided and supplied to each hydraulic motor via a flow divider. Therefore, a large flow of pressure oil is supplied to the hydraulic motor, allowing it to rotate at high speed.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a circuit diagram showing an embodiment of an automatic transmission type hydraulic drive system for a vehicle running system according to the present invention.

As is clear from this figure, this hydraulic drive device is provided with triple hydraulic pumps P ₁ , P ₂ , P ₃ driven by a prime mover E, and these hydraulic pumps P ₁ , P ₂ and P ₃ suck up the hydraulic oil in the oil tank T, pressurize it, and discharge it. These hydraulic pumps P ₁ , P ₂ ,
P ₃ are all fixed displacement type, two of them, P ₁ and P ₂ , are of the same high pressure and small capacity, and the other hydraulic pump, P ₃ , is of low pressure and large capacity. There is.

The discharge side ports of hydraulic pumps P ₁ and P ₂ are connected to the left and right hydraulic motors via hydraulic lines L ₁ and L ₂ , respectively.
Connected to M ₁ and M ₂ . These hydraulic lines
l ₁ and l ₂ are provided with directional control valves V ₁ and V _2, respectively, and by switching and controlling the directional control valves V ₁ and V ₂ , the respective hydraulic motors M ₁ and M ₂ are controlled. It is designed to rotate forward, reverse, or stop. Each of the hydraulic motors M ₁ and M ₂ is configured to individually drive left and right traveling devices of the vehicle, such as crawlers, respectively. Therefore, the directional control valve V ₁ ,
By switching _V2 , the vehicle moves forward, backward, stops, or changes direction.

Each hydraulic line _l1 , _l2 has a relief valve.
R ₁ and R ₂ are connected, and when the pressure in the hydraulic lines l ₁ and l ₂ exceeds the set value, the hydraulic lines l ₁ and
l ₂ is opened to the oil tank T, and each hydraulic line l ₁ ,
The pressure of l ₂ is controlled below the set pressure. The set pressures of the relief valves R ₁ and R ₂ are relatively high.

The discharge side port of the other hydraulic pump P ₃ is connected via a hydraulic line l ₃ to a flow divider F, and the pressure oil discharged from the hydraulic pump P ₃ is normally equalized by this flow divider F. The hydraulic pressure is divided into two parts and led to hydraulic lines _l1 and _l2 via check valves _C1 and _C2 , respectively.
The hydraulic line _l3 is provided with a spool-type relief valve _R3 . This relief valve R ₃ is designed to be switched by pilot pressure led from the hydraulic lines l ₁ , l ₂ via the throttle valves Th ₁ , Th ₂ and the shuttle valve _S. If the pressure in l ₂ is lower than the set value, the hydraulic line l ₃ is made conductive and the pressure oil discharged from hydraulic pump P ₃ is guided to the flow divider F. If the pressure exceeds the set value, the pressure oil is diverted to oil. The water is refluxed to tank T. The set pressure of the relief valve _R3 is set to a value lower than the set pressure of the relief valves _R1 and _R2 .

Next, the operation of the hydraulic drive device configured as described above will be explained.

Hydraulic motors M ₁ , M ₂ as in normal constant speed driving
If the required torque of is small, the hydraulic line l ₁ ,
The pressure in l ₂ is maintained at a relatively low pressure. Therefore, the pilot pressure of the relief valve _R3 does not reach the set pressure, and since the relief valve _R3 is in a position to conduct the hydraulic line _l3 , the pressure oil discharged from the hydraulic pump _P3 flows through the flow divider. F divides the flow into equal flow rates on the left and right sides and guides them to the respective hydraulic lines l ₁ and l ₂ .
As a result, in addition to a certain amount of pressure oil discharged from the respective hydraulic pumps P ₁ and P ₂ , each hydraulic motor M ₁ and M ₂ receives half of the pressure oil discharged from this hydraulic pump P ₃ . Since a large amount of pressure oil is supplied, each hydraulic motor M ₁ and M ₂ rotates at high speed. This allows the vehicle to travel at high speeds.

When a large output torque is required from the hydraulic motors M ₁ and M ₂ , such as when climbing a slope, the hydraulic lines l ₁ ,
l ₂ pressure increases. When the pressure becomes higher than the set pressure of the relief valve _R3 , the relief valve _R3 is switched and the pressure oil discharged from the hydraulic pump _P3 is returned to the oil tank T. Therefore, the hydraulic pump _P3 is unloaded, and the output of the prime mover E is used to drive only the hydraulic pumps _P1 and _P2 . As a result, high pressure oil set by the relief valves R ₁ and R ₂ is guided to each hydraulic motor M _{1 and} M ₂ .
The output of M ₂ will be higher. At this time, the hydraulic motors M ₁ and M ₂ are operated only by the pressure oil supplied from the respective hydraulic pumps P ₁ and P ₂ , so they rotate at a low speed.

When the vehicle enters a constant speed running state again and the pressure in the hydraulic lines l ₁ and l ₂ decreases, the relief valve R ₃ is automatically switched and the hydraulic motors M ₁ and M ₂ begin to rotate at high speed. At this time, the hydraulic motor M ₁ ,
The output torque of M ₂ becomes smaller.

Hydraulic line l ₁ or l ₂ as when changing direction
Even when the pressure of only one of the
Since the higher pressure is applied as a pilot pressure to the relief valve _R3 via the shuttle valve S, the relief valve _R3 is switched and the output torque of the hydraulic motor _M1 or _M2 becomes higher. Therefore, direction changes can also be performed smoothly.

In this way, the hydraulic motors M ₁ and M ₂ that drive the left and right traveling devices can be automatically switched to low speed high output or high speed low output depending on the traveling state.

Then, the amount of oil discharged from hydraulic pumps P ₁ , P ₂ , and P ₃ is
p ₁ , p ₂ , p ₃ (l/min), relief valves R ₁ , R ₂ ,
If the set pressure of R ₃ is r ₁ , r ₂ , r ₃ (Kg/cm ² ), then
The total output of the hydraulic motors M ₁ and M ₂ when the hydraulic pump P ₃ is unloaded is (p ₁ × r 1 ) + (p 2 × r 2 )/450 in terms of horsepower, and the total output of the hydraulic pump P ₃ is (p 1 × r ₁ ) + (p ₂ × r ₂ )/450. The total output of the hydraulic motors M ₁ and M ₂ when pressure oil is supplied from the motor is (p ₁ +p ₂ +p ₃ )×r ₃ /450 in terms of horsepower. In other words, two different outputs can be obtained by the prime mover E with constant horsepower.

Also, the amount of oil discharged from these hydraulic pumps P ₁ , P ₂ , P ₃
p ₁ , p ₂ , p ₃ , and therefore the total flow rate supplied to the hydraulic motors M ₁ , M ₂ and the set pressures r ₁ , r ₂ , r ₃ of the relief valves R ₁ , R ₂ , R ₃ , Gattete hydraulic motor M ₁ ,
The relationship with the hydraulic pressure supplied to each of _M2 is as shown by the solid line in Figure 2. On the other hand, if the maximum pressure and maximum flow rate obtained by this hydraulic drive device are to be obtained by a conventional constant displacement hydraulic pump system, the oil pressure and oil amount as shown by the dotted line in the figure are required. That is, the required output of the prime mover E is reduced by the difference compared to the conventional system.

The above embodiment is a two-stage variable speed hydraulic drive system, but by using the same principle, a multi-stage automatic speed range hydraulic drive system can be obtained. FIG. 3 shows an embodiment of a three-speed variable speed hydraulic drive device.

As is clear from this figure, in that case, a fixed displacement hydraulic pump P ₄ and a spool type relief valve R ₄ are further added, and these are connected to the hydraulic line l ₄ .
is connected to the flow divider F by. The set pressure of this relief valve _R4 shall be lower than the set pressure of relief valve _R3 .

By doing this, the hydraulic line l ₁ ,
When the pressure of l ₂ is lower than the set pressure of the relief valve R ₄ , the entire discharge amount of the hydraulic pumps P ₁ , P ₂ , P ₃ , P ₄ is supplied to the hydraulic motors M ₁ , M ₂ , and the hydraulic motors M ₁ ,
_M2 is now driven at high speed and low output. Also,
When the pressure in the hydraulic lines l ₁ , l ₂ is higher than the set pressure of the relief valve R ₄ and lower than the set pressure of the relief valve R ₃ , the hydraulic pump P ₄ is unloaded;
The pressure oil discharged from hydraulic pumps P ₁ , P ₂ , and P ₃ is supplied to the hydraulic motor.
_The hydraulic motors M ₁ and M ₂ are driven at medium speed and medium _output . Furthermore, when the pressure in the hydraulic lines l ₁ and l ₂ becomes higher than the set pressure of the relief valve R ₃ , both the hydraulic pumps P ₃ and P ₄ are unloaded, and the discharge pressure oil of the hydraulic pumps P ₁ and P ₂ is , the hydraulic motors M ₁ , M ₂ are supplied under high pressure set by the relief valves R ₁ , R ₂ . Therefore, the hydraulic motors M ₁ and M ₂ are driven at low speed and high output.

The relationship between the flow rate and pressure of such a three-stage variable speed hydraulic drive system is as shown in FIG. As is clear from this figure, by doing this,
The required output of the prime mover E can be further reduced than in the two-speed hydraulic drive system shown in FIGS. 1 and 2.

In this way, by adding a hydraulic pump and a relief valve, it is possible to create an automatic transmission type hydraulic drive device with a number of gear stages corresponding to the number of hydraulic pumps and relief valves. As the additional hydraulic pump, a fixed displacement hydraulic pump for driving a working machine mounted on a construction machine can also be used.

(Effects of the Invention) As is clear from the above description, according to the present invention, pressure oil is supplied from a dual fixed displacement hydraulic pump to the two hydraulic motors that respectively drive the left and right traveling devices. At the same time, another constant displacement hydraulic pump is added so that when the pressure in the circuit is low, the added hydraulic pump also supplies pressure oil to each hydraulic motor, and when the pressure in the circuit is high, Since the additional hydraulic pump is unloaded, it is possible to automatically switch to low speed high output or high speed low output depending on the driving condition even though a fixed displacement hydraulic pump is used. can. Therefore, the horsepower required for the prime mover can be reduced, or even higher output and higher speed rotation can be obtained with a prime mover of constant horsepower.

Additionally, the discharge pressure oil from the added hydraulic pump is supplied to each hydraulic motor via a flow divider, so the same amount of pressure oil is always supplied to the hydraulic line connected to each hydraulic motor. Therefore, when the vehicle is traveling straight, the rotational speed of the traveling device does not differ between the left and right sides, and traveling stability can be ensured.

Furthermore, the relief valve that controls the direction of the pressure oil discharged by the added hydraulic pump, the pilot pressure circuit that controls the switching, or the flow divider, etc. can be combined into one block, so this can be combined with the conventional fixed volume pump. It can also be easily modified into a hydraulic drive system according to the present invention by assembling it into a hydraulic drive system using a hydraulic pump.

In particular, self-propelled construction machines and the like are equipped with fixed displacement hydraulic pumps for driving working machines that are not used during travel, so the hydraulic pumps can be used as the above-mentioned additional hydraulic pumps.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an automatic transmission type hydraulic drive system for a vehicle running system according to the present invention, FIG. 2 is a graph showing characteristics of the hydraulic drive system, and FIG. A circuit diagram showing another embodiment of the hydraulic drive device according to the present invention, FIG. 4 is a graph showing the characteristics of the hydraulic drive device, and FIG. 5 is an example of a conventional hydraulic drive device for a vehicle running device. FIG. E... Prime mover, F... Flow divider, l ₁ , l ₂ ,
l ₃ , l ₄ ... Hydraulic line, M ₁ , M ₂ ... Hydraulic motor,
P ₁ , P ₂ , P ₃ , P ₄ ... Constant displacement hydraulic pump, R ₁ ,
_R2 , _R3 , _R4 ...Relief valve, S...Shuttle valve, T...Oil tank.

Claims (1)

[Scope of Claims] 1. Fixed-displacement dual hydraulic pumps P ₁ and P ₂ driven by a prime mover E; hydraulic motors M ₁ and M ₂ that drive left and right traveling devices of the vehicle, respectively; Each of these hydraulic pumps P ₁ , P ₂ and each hydraulic motor M ₁ ,
Relief valves R 1 and R 2 connected to respective hydraulic lines l ₁ and l ₂ connecting to M ₂ and regulating the pressures of the respective hydraulic lines _{l 1} and _{l 2 to} below a predetermined value, a vehicle comprising: In a hydraulic drive system for a traveling device of; a constant displacement hydraulic pump P ₃ driven together with the hydraulic pumps P ₁ and P ₂ by _the prime mover E; A flow divider F is provided between the hydraulic pump _P3 and the flow divider F, and the pressure in _the hydraulic lines _l1 and _l2 is connected to _the relief valve R. ₁ , a relief valve _R3 is provided which returns the discharge pressure oil of the hydraulic pump _P3 to the oil tank T and unloads the hydraulic pump _P3 when a predetermined pressure lower than the set pressure of _R2 is exceeded. An automatic transmission hydraulic drive system for a vehicle's running gear.