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Tips for CLUTCH HYDRAULIC RELEASE MECHANISM, Clutch Release Cylinders (C.R.C.), Clutch Concentric Slave Cylinders (C.S.C.), Clutch Hydraulic Pipes, Clutch Maste

Technical Service Bulletin for CLUTCH HYDRAULIC RELEASE MECHANISM, Clutch Release Cylinders (C.R.C.), Clutch Concentric Slave Cylinders (C.S.C.), Clutch Hydraulic Pipes, Clutch Master Cylinders (C.M.C.), Clutch Hydraulic (Other), 404965 - Valeo Service

HYDRAULIC DAMPERS

<h3>Benefit of Clutches system</h3>

The clutch system is installed between the engine output-Crankshaft and the input of Transmission to give us the ability of changing gears and Vehicle standstill while the engine in idle state. 
The release and engagement is made &nbsp;via cable or hydraulic.

The Hydraulic clutch system consist of Clutch Master Cylinder (CMC) &nbsp;, Clutch Release Cylinder (CRC) ,Concentric &nbsp;Slave Cylinder (CSC) &nbsp;and Hoses, &nbsp;example see Fig. 1, 2, 3 &amp; 4 &nbsp;respectively

<h3>Pressure pulsation in Hydraulic clutches&nbsp;</h3>

Due to the internal combustion which happens in the engine, low frequency vibration generated and crankshaft imbalance are produced, this two phenomenons are transmitted by the clutch cover through clutch bearing &nbsp;and hydraulic column to the pedal as hydraulic pulsations.&nbsp; 
This pulsation are felt by the driver when driver depress the pedal which is uncomfortable feeling.

To eliminate the problem, Three possible solutions hereunder

<ol type="A">
	<li>Damping the pulsation amplitudes&nbsp;</li>
	<li>Isolating the clutch circuit from the master cylinder</li>
	<li>Modulating the pulsation frequency by increasing the vibration frequency from the engine 
	&nbsp;</li>
</ol>

Master Cylinder CMC Fig.1

Clutch release Cylinder CRC Fig.2

Concentric Slave Cylinder CSC Fig.3

Hoses Fig.3

<ol type="A">
	<li>Hydraulic Damping Pulsation</li>
</ol>

The Damping can be performed either by hydraulic circuit design or &nbsp;by Installing Damper (frequency modulator) in the circuit.

<ol>
	<li>Damping by circuit design:- &nbsp;the pulsation is affected and damped by the volume and the elastic material in the circuit</li>
</ol>

Hereunder table shows the methods of hydraulic Circuit design&nbsp;

<table border="1" cellpadding="1" cellspacing="1" class="DJ__responsiveTable__processed table">
	<tbody>
		<tr>
			<td>
			Methods
			</td>
			<td>
			Method 1:Volume
			</td>
			<td>
			Method 2: Shape design
			</td>
			<td>
			Method 3: Material
			</td>
		</tr>
		<tr>
			<td>
			Design
			</td>
			<td>
			<ul>
				<li>Increase the length of the metal pipe</li>
			</ul>
			</td>
			<td>
			<ul>
				<li>S shape</li>
				<li>U Shape</li>
				<li>Spiral shape</li>
			</ul>
			</td>
			<td>
			<ul>
				<li>Rubber with elastic walls</li>
			</ul>
			</td>
		</tr>
		<tr>
			<td>
			Advantages
			</td>
			<td colspan="3">
			<ul>
				<li>Method 1&amp; 2:-&nbsp; Increasing the length of the metal pipe or cross section&nbsp; or having different shapes&nbsp; will increase the flow resistance and damping effect</li>
				<li>Method 3:- Using soft materials like&nbsp; rubber or elastic materials will decrease the pulsation effect in the pedal</li>
			</ul>
			</td>
		</tr>
		<tr>
			<td>
			Disadvantages
			</td>
			<td colspan="3">
			<ul>
				<li>Increasing the volume of hydraulic circuit will results in soft pedal (spongy feeling)&nbsp; and lack of tactile feedback&nbsp; or having longer stroke</li>
				<li>Having longer pipes with higher flow resistance will results in exerting more force on the pedal and reducing the return speed of the pedal especially when the the fluid temperature is low (high viscosity)&nbsp;&nbsp;</li>
				<li>Some systems are working on specific frequency, so it may not reduce the pulsation on the entire frequency range</li>
			</ul>
			</td>
		</tr>
	</tbody>
</table>

<h3>2. Hydraulic Damper; Frequency modulator&nbsp;</h3>

For better driving comfort, cost efficiency and space reduction, A Hydraulic dampers is installed in the hose pipes to separate the slave cylinder from the master cylinder and pedal ( Fig. 4 )

Damper operation:The engine generates low frequency pressure pulsation, this low frequency will vibrate the membrane in the damper ( Fig.5 a) at higher frequency than the disruptive source. This high frequency is transmitted to the master cylinder and pedal, but due to the inertia generated, it prevent the driver to feel any vibration in the pedal, it remain idle no movement.

<h3>Advantages of Hydraulic dampers.</h3>

<ul>
	<li>Temperature doesn't affect the system</li>
	<li>More sensitive to pressure variation and range&nbsp;</li>
	<li>Plastic molding house, therefore, high productivity with low cost</li>
	<li>The housing and the closing cap are rounded threaded profile which ensure high durability, (Fig 5. C)</li>
	<li>Housing construction allows air bleeding&nbsp;</li>
	<li>Possibility of increasing diameter/thickness ratio membrane, this has great effect of hysteresis loss and system elasticity which should be as small as possible</li>
	<li>Housing structure allows using thinner metallic membrane with large diameter without having risk to be damaged by high pressure&nbsp;</li>
	<li>As membrane is pretensioned by coil spring (fig. 5 b) allows to control the volume. as there is no pressure in the system the membrane is still pretensioned leading to have stiffer pedal and shorter stroke compared to other systems not having coil spring</li>
	<li>Hydraulic dampers can be fit for almost all the systems, just using same housing and change the thickness, diameter of membrane and coil spring rigidity &nbsp; &nbsp; &nbsp; 
	&nbsp;</li>
</ul>

<h3>B. Hydraulic Isolators</h3>

How does it work?

The pulsation isolator (Fig. 6) &nbsp;is installed on the hydraulic line between the master cylinder and slave cylinder.

The housing consist of two valves with two coil springs &nbsp;(Fig 6 b, c.) depending on the direction of the fluid flow only one valve can be opened . hereunder a table shows the open/close status of each valve. 
&nbsp;

<table border="1" cellpadding="1" cellspacing="1" class="DJ__responsiveTable__processed table">
	<thead>
		<tr>
			<th colspan="4">Isolators Valve b, c status</th>
		</tr>
	</thead>
	<tbody>
		<tr>
			<td>
			Valve Status
			</td>
			<td>
			Valve b
			</td>
			<td>
			Valve c
			</td>
			<td>
			Flow direction
			</td>
		</tr>
		<tr>
			<td>
			Pedal depressed
			</td>
			<td>
			open
			</td>
			<td>
			closed
			</td>
			<td>
			from Master cylinder to slave cylinder
			</td>
		</tr>
		<tr>
			<td>
			Pedal released
			</td>
			<td>
			closed
			</td>
			<td>
			opened
			</td>
			<td>
			from slave cylinder to master cylinder
			</td>
		</tr>
		<tr>
			<td>
			No Fluid flow
			</td>
			<td>
			closed
			</td>
			<td>
			closed
			</td>
			<td>
			No flow
			</td>
		</tr>
	</tbody>
</table>

&nbsp;

<h3>The advantage of hydraulic isolators.</h3>

<ul>
	<li>No temperature affecting the hydraulic circuit.</li>
	<li>Pedal clutch rigidity, travel and elasticity are always same as there is not volume variation.</li>
	<li>Isolating the master cylinder from the rest of the circuit results no pulsation felt by the driver.</li>
	<li>Very simple and compact design requires small space to be fitted.</li>
	<li>The valve design allows a great quantity of fluid to flow with minimum flow resistance.</li>
	<li>The spring which located in the housing (Fig. 6 a) it role to damp the remaining pulsation.</li>
	<li>The isolation device can be fitted in any direction, having no dependence on the direction of flow&nbsp; 
	&nbsp;</li>
</ul>