公司主营: 风电液压扳手 液压扭矩扳手 液压油缸专用泵

新闻资讯 / NEWS

新闻资讯

联系方式

0571-88841109

行业资讯

当前位置: 网站首页 > 新闻资讯 > 行业资讯
  • 液压传动——能量的基础知识
  • 本站编辑:杭州耐准精密机械有限公司发布日期:2019-10-27 17:14 浏览次数:

1、能量

能量在实际生活中是一个看不见,摸不着的东西。 它只是我们用来描述一个物体性质的一个术语,就像颜色亦或是冷暖一样。

我们先举一些例子,看看哪些物质是具备能量的:

一个快速运动的物体具有较大的动能;

一个温度高的物体具有热能;

汽油等燃料具有化学能;

运动的电子具有电能和电磁能。

当我们说一个物体具有能量时,我们主要关注以下两点:

能量会导致这个物体本身会发生什么变化?

能量是如何改变周围的事物的,也就是说能量是如何传递的?

前面我们说过,能量并非实际看得见,摸得着的物体,所以很难画出它的样子。但是请看图1,如果你用鼠标点击这个动图,那么你就正在给它施加一定的动能。

综上,我们知道,能量是可以在不同物体之间传递的。请看图2和图3,都可以很好证明这一点。

当能量在物体之间进行传递时,必然会有一些能量会在这个过程中损失掉,这主要是由于摩擦之类的阻力造成的。

我们之所以称之为损失,是因为他们并没有起到我们希望它们应该起到的作用。也就是没有做有用功,做的都是无用功。

例如:在汽车发动机内,当化学能从汽油中转化为汽车的动能时,一些能量会以向外散发热量以及噪声的形式损失掉了。

最完美的引擎是你用手摸上去是冰凉的,而且是完全静音的。但是,大千世界,芸芸众生,没有任何系统是如此的完美。生活中我们所看到的一切能量转换系统都是有能量损失的。

正因为摩擦损失的存在,我们可以得出结论,有效的输出能量总是会小于输入的能量。图5很好地给我们展示了这个结论。

不过,如果你加上损失掉的能量,那么能量一定是守恒的,也就是输入的能量等于有效的输出能量加上损失掉的能量。如下述公式所示。

能量输入 = 能量输出 + 能量损耗

能量守恒定律说的是能量可以从一种形式变化到另一种形式,但是能量从来没有被创造或毁灭。在一点处产生的能量必然都会在某一处消散。

系统的效率是用来衡量有效输出能量占总的输入能量的比重;效率越高的系统,就说明越多的能量用于做有用功,相反损失的能量也就越少。

好了,现在我们回到我们今天的主角,液压系统;液压系统如果设计合理,且能得到很好的维护,是可以达到很高的效率的。

2、力

我们先举一个例子:

一辆火车,以非常快的速度向西行驶。

突然,火车撞上了一块巨石,我的天呐。

呃呃呃,别担心,没有人员伤亡!

其实,你需要考虑的只是下面两个问题:

1、巨石会何去何从呢?

巨石会开始向西运动,因为火车是向西推它的。

巨石发生了运动,说明它从火车上获得了动能。

2、火车会发什么变化?

火车的运动会减慢,因为它把一部风动能给了石头。

当发生碰撞时,火车对巨石施加了一个力。即火车上的一部分能量传递到了石头上,所以石头发生了移动。

那么,力究竟是指什么呢?它是两物体接触后,发生的一种相互作用,这种作用能使两者发生相对的运动。

我们最熟悉的力莫过于重力了。你的身体受到重力的作用而拖拽你向地心运动。如果你跳到空中,重力会重新把你拽回地面。

力既即可以使物体沿某一条直线运动,也可以使物体绕某一个中心转动。图7为直线力多种力可以同时施加在一个物体之上。在图9所示的铲车上,有多个力施加在上下运动的箱子上。到底有几个力呢?大家可以思考一下。

首先,重力永远是将重物拽向地面的,即便重物在向上运动的过程中也是如此。

其二,摩擦力总是起减慢物体运动的作用,它从物体中获取动能,并转化为热和噪声,作了无用功。

另外,压力也同样是一种力。当液压油或者是压缩气体被压缩时,它们自身就存储了大量的能量。当压力得到释放时,油液或压缩空气中存储的能量,就会跟随介质一起流动,这些能量可以提升重物或者使重物下降。即使物体处于静止状态,但这不代表没有力作用于它,当然,如果一个物体静止不动,或者以匀速运动,那么作用于该物体上的所有力是平衡的。

如果一个物体处在加速运动或者是减速运动,亦或是运动方向发生改变的过程中,那么作用于该物体上的力是不平衡的。

为了求解作用于物体上的力,你需要知道下面两件事。

质量——你需要知道该物体的构成成分。

加速度——由于力的作用,该物体在加速或减速时速度变化的快慢。

举个例子,我们从飞机上扔下一个质量为2500kg的重物,如图11所示。由于受到重力的作用,这个物体会以9.81m/s2的加速度向下加速运动。施加于该物体上的重力到底是多少呢?我们看下面的计算。力 = 质量 x 加速度,数学式为F=ma

F = 2500 kg x 9.81 m/s2

F = 24525 kg·m/s2

F = 24525 N

我们继续往下看,牛顿是衡量力大小的单位。表示这个力能改变某一质量块的运动(加速、减速、运动方向的改变)的快慢程度

如果你想快速改变质量为100kg的物体的速度,那就需要对其施加很大的力。

如果你想快速改变质量10kg的物体的速度,那就需要对其施加中等的力。

如果你想慢慢地、逐渐地改变质量100kg的物体的速度,那就需要对其施加中等的力。

如果你想慢慢地、逐渐地改变质量10kg的物体的速度,那就需要对其施加很小的力。

3、力矩

力矩是用来衡量旋转力的大小的物理量。

有很多方法可以产生旋转力。最常见的就是如图12所示,你用老虎钳去拧螺栓了。

为了计算出图12中的力矩,我们需要计算出施加给扳手的合力的大小,以及力臂的长度。

图12

替换高清大图

力矩 = 力 x 力臂

力矩 = 15 newtons x 0.2 meters

力矩 = 3 newton-meters(Nm)

综上,施加于老虎钳上的力矩是3Nm。记住,力矩的单位是Nm。

4、功

当力施加于某一物体时,物体会改变其原先的运动状态,与此同时,该物体会得到或损失一部分能量。为了衡量这部分能量的大小,我们引入功的概念。

如果力作用于物体之上,并没有改变物体的运动状态,那就说明没有发生能量的传递,也就是该力没有对物体做功。看看图13能给你什么启发?

想要计算出功的大小,你必须知道以下两个量:

力的大小

物体运动的距离

让我们举个例子,如图14所示,向上举升15kg的质量块到4米高的位置。为了是描述简单,我们取重力加速度的值为10m/s2

图14

力F = 质量m x 加速度a

F = 15kg x 10 m/s2

F = 150 newtons

功W = 力F x 距离S

W = 150 newtons x 4 meters

W = 600 joules

功的单位是焦耳J。1J是指1N的力施加于质量块上,使质量块移动1m所做的功。

虽然我们用焦耳来衡量力对物体做的功,但是焦耳也同样可以表示物体所蕴含的能量的大小。就比如,食物、燃料汽油等所含的能量我们都用焦耳表示。其实两者并不矛盾,因为力对物体做功,也是物体中能量的相互传递的过程。

5、功率

功率是指单位时间内力对物体所做的功。它的单位是J/s,也是我们所熟知的瓦特w。

瓦特这个单位是以蒸汽机的发明者James Watt的名字来命名的,下面放一张伟人的头像,供大家膜拜。

1, energy

Energy in real life is an invisible, intangible thing. It's just a term we use to describe the nature of an object, like color or warmth.

Let's start with some examples of what has energy:

A fast moving object has greater kinetic energy;

A hot body has heat energy;

Fuels such as gasoline have chemical energy;

Moving electrons have electrical and electromagnetic energy.

When we say that an object has energy, we mainly focus on the following two points:

What will the energy cause to happen to the object itself?

How does energy change things around, that is, how does energy travel?

As we said before, energy is not something that you can actually see or touch, so it's hard to draw. But if you look at figure 1, if you click on the GIF, you're applying some kinetic energy to it.

In conclusion, we know that energy can be transferred between different objects. See figures 2 and 3 for a good illustration of this.

When energy is transferred between objects, some energy must be lost in the process, mainly due to resistance such as friction.

We call them losses because they're not doing what we want them to do. That is, no useful work, do is useless.

In an automobile engine, for example, when chemical energy is converted from gasoline to kinetic energy, some of it is lost in the form of heat and noise.

The perfect engine is cold to the touch and completely silent. But no system in the world is so perfect. All the energy conversion systems we see in life have energy losses.

Because of the friction loss, we can conclude that the effective output energy is always less than the input energy. Figure 5 gives a good illustration of this conclusion.

But if you add in the energy lost, then the energy must be conserved, which is that the input energy is equal to the effective output energy plus the lost energy. As shown in the following formula.

Energy input = energy output + energy loss

The law of conservation of energy says that energy can change from one form to another, but it is never created or destroyed. Whatever energy is produced at one point must dissipate somewhere.

The efficiency of the system is used to measure the proportion of the effective output energy in the total input energy. The more efficient the system, the more energy it USES for useful work, and the less energy it loses.

All right, now let's go back to our main character of the day, the hydraulic system; Hydraulic system can achieve high efficiency if it is designed properly and maintained well.

2,

Let's start with an example:

A train, travelling at a very fast speed to the west.

Suddenly, the train hit a boulder. Oh, my god.

No casualties!

In fact, you only need to consider the following two questions:

1. Where will the boulder go?

The boulder would start moving west because the train was pushing it west.

The boulder moved, indicating that it had gained kinetic energy from the train.

2. What will happen to the train?

The motion of the train slows down because it gives a kinetic energy of wind to the stone.

When the collision occurred, the train exerted a force on the boulder. That is, some of the energy on the train was transferred to the rock, so the rock moved.

What, then, is a force? It is an interaction between two objects that comes into contact and causes them to move relative to each other.

The most familiar force is gravity. Your body is pulled towards the center of the earth by gravity. If you jump into the air, gravity will pull you back to the ground.

A force causes a body to move either in a straight line or around a center. Figure 7 shows linear forces. Multiple forces can be applied to an object at the same time. In the forklift shown in figure 9, multiple forces are applied to the box as it moves up and down. How many forces are there? Think about it.

First, gravity always pulls a weight toward the ground, even when it's moving upwards.

Second, friction always ACTS to slow down the motion of the body. It takes kinetic energy from the body and converts it into heat and noise.

In addition, pressure is also a force. When hydraulic oils or compressed gases are compressed, they store a lot of energy in themselves. When pressure is released, energy stored in the oil or compressed air flows with the medium, lifting or lowering heavy objects. Even if a body is at rest, it does not mean that there is no force acting on it. Of course, if a body is at rest or moving at a constant speed, the force acting on that body is balanced.

If an object is in accelerated or decelerated motion, or the direction of motion is changed, the force on the object is unbalanced.

To solve for the force on an object, you need to know two things.

Mass -- you need to know what the object is made of.

Acceleration - the rate at which a body's speed changes as it accelerates or decelerates due to a force.

For example, we drop a weight of 2500kg from an aircraft, as shown in figure 11. Due to the force of gravity, the object will accelerate downward at an acceleration of 9.81m/s2. What is the force of gravity on the object? Let's look at the following calculation. Force = mass x acceleration, and the mathematical formula is F=ma

F = 2500 kg x 9.81 m/s2

F = 24525 kg · m/s2

F = 24525 N

Let's move on. Newton is a unit of force. Indicates how quickly this force can change the motion (acceleration, deceleration, change in direction) of a mass

If you want to change the speed of something that has a mass of 100 kilograms very quickly, you have to apply a lot of force to it.

If you want to change the speed of a 10kg mass very quickly, you need to apply a moderate force to it.

If you want to change the speed of a 100kg object slowly and gradually, you need to apply a moderate force to it.

If you want to change the speed of a 10 kilogram mass slowly and gradually, you need to apply a very small force to it.

3, moment

Torque is a physical quantity used to measure the rotational force.

There are many ways to generate rotational forces. The most common is shown in figure 12, where you use a vise to turn the bolt.

To calculate the torque in figure 12, we need to calculate the resultant force applied to the wrench and the length of the moment arm.

Figure 12

Replace the hd image

Torque is equal to force x moment arm

Torque = 15 newtons x 0.2 meters

Torque = 3 newton-meters (Nm)

So the torque applied to the vise is 3Nm. Remember, the units of torque are nanometers.

4, work

When a force is applied to a body, the body will change its original motion state, and at the same time, the body will gain or lose some energy. To measure the magnitude of this energy, we introduce the concept of work.

If a force is applied to an object and does not change its motion, then no energy has been transferred, that is, no work has been done on the object. What does figure 13 tell you?

To calculate the amount of work, you must know two things:

The size of the force

The distance an object travels

Let's take an example, as shown in figure 14, of lifting a mass block of 15 kilograms up to a height of 4 meters. For simplicity, let's take the acceleration of gravity as 10 meters per second

Figure 14

Force F is equal to mass m x acceleration a

F = 15kg x 10 m/s2

F = 150 newtons

Work W = force F x distance S

W = 150 newtons x 4 meters

W = 600 joules

The unit of work is joule J. 1 joule is the work done by a force of 1N applied to the mass, making it move 1 meter.

Although we use joules to measure the work done by a force on an object, joules can also indicate the amount of energy contained in an object. For example, the amount of energy in food, fuel, gasoline, etc., is expressed in joules. The two aren't contradictory, because work done by a force on a body is also the transfer of energy between bodies.

5, power

Power is the work done by a force on an object per unit of time. It's in J/s, which is also known as watt w.

Watt is named after James Watt, the inventor of the steam engine, and here is a head of a great man for you to admire.