Torsion Bush

A wide range of standard versions is available providing characteristics to suit diverse applications. They are commonly used in automotive applications for suspension system linkages or leaf spring mounting, where some degree of movement is desirable. This bush design provides for displacement in a combination of radial, axial, torsional or conical loadings (see diagrams below)

Bushes are placed at the pivot points for any of the following reasons:

· Smooth and predictable movement without the wear associated with solid metal bushes. No surface to surface sliding motion for any required motion.

· Vibration isolation - rubber bushes reduce road noise in automotive applications whilst absorbing impact loads.

· Deflection under load - when engineered into a system, this deflection can allow the linkage freedom of movement. If deflection is not accommodated within the torsion bush, stresses may be transferred to other mechanical components.

· Modern suspension systems are designed so that the bush deflection does not seriously impact alignment, allowing for vibration isolation whilst maintaining the steering geometry.

Torsion Bush Type BB

Torsion Bush Type TB

Torsion Bush Type BP

Torsion Bush Type B

Torsion Bush Type BE

Torsion Bush Type SAB

Loading Methods

Typical application – automotive suspension

Polyurethane bushes

Spares for non-current production vehicles

Torsion Bush Type BB

This bush comprises inner & outer tubes in which the rubber is chemically bonded to both tubes allowing applications requiring loading in all possible directions and combinations

(BB~double bonded).

Standard BB type bushes

Part No	A Inner Tube I/D	B Inner tube length	C Outer tube O/D	D Outer tube length
BB1273	16.13 -16.00	28.70 - 28.44	38.40 - 38.10	25.30 - 25.05
BB1306	20.23 - 20.10	80.85 - 80.55	50.50 - 50.25	75.00 - 74.75
BB1310	14.28 - 14.14	44.61 - 44.35	30.70 - 30.40	38.21 - 37.95
BB1311	16.18 - 16.00	62.08 - 61.78	35.05 – 34.92	57.40 – 56.70
BB1378	16.27 - 16.13	47.78 - 47.48	50.92 - 50.80	38.15 - 37.85
BB1388	11.28 - 11.15	66.24 - 65.99	47.70 – 47.50	50.50 - 50.10
BB1389	11.28 - 11.15	66.24 - 65.99	47.70 – 47.50	50.50 - 50.10

Torsion Bush Type TB

With the addition of an intermediate tube which is again chemically bonded in place during the moulding & vulcanisation process. This type of bush is suitable for the highest loads.

Standard TB type bushes

	A Inner Tube I/D	B Inner tube length	C Outer tube O/D	D Outer tube length
TB1308	15.69 -15.55	48.43 - 48.13	51.45 - 51.30	38.15 - 37.85
TB1309	19.01 - 18.87	54.25 - 53.95	41.89 - 41.75	38.15 - 37.85
TB1317	15.69 - 15.55	54.93 - 54.67	50.93 – 50.80	44.55 - 44.25

Torsion Bush Type B

This type of bush embodies both chemical bond (inner tube only) and interference fit. The interference fit provides for pre-stressing of the rubber making it stiffer for normal radial, conical and torsional loads. It is not intended for use in high axial loading situations.

One advantage of this bush type is that occasional extreme torsional overloads can be accommodated since the bush will slip within the outer tube under these conditions.

Standard B type bushes

Part No

A

Inner Tube I/D

B

Inner tube length

C

Outer tube O/D

D

Outer tube length

B165

14.48 - 14.35

46.15 - 45.90

30.30 - 30.15

35.05 - 34.80

B602/2

9.68 - 9.55

22.35 - 22.10

19.11 - 19.05

19.30 - 19.05

B602/9

9.64 - 9.47

31.08 - 30.83

19.15 - 19.05

29.21 - 28.70

B603A

11.29 - 11.16

22.23 - 22.10

23.88 - 23.80

19.18 - 18.92

B605/9

14.48 - 14.35

62.03 - 61.77

31.83 - 31.75

57.28 - 57.02

B606/8

16.13 - 16.00

50.89 - 50.76

35.00 - 34.93

44.55 - 44.32

B606/10

16.13 - 16.00

71.55 - 71.30

35.00 - 34.93

63.63 - 63.37

B608/10

19.18 - 19.05

41.40 - 41.15

38.23 - 38.10

38.23 - 37.97

B608/26

19.18 -19.05

66.77 - 66.65

38.23 - 38.10

61.34 - 61.09

B629/11

11.29 - 11.16

30.30 - 30.05

22.30 - 22.22

25.65 - 25.40

B630

11.29 - 11.16

54.10 - 53.83

25.50 - 25.35

50.93 - 50.67

B630/7

11.29 - 11.16

50.60 - 50.40

25.50 - 25.35

45.08 - 44.58

B632/9

16.13 - 16.00

28.70 - 28.45

31.83 - 31.75

25.53 - 25.27

B636/2

12.83 - 12.70

35.05 - 34.80

27.10 -26.95

32.13 - 31.88

B636/5

12.83 -12.70

38.1 -37.9

27.10 -26.95

32.13 -31.88

B636/7

12.83 - 12.70

60.45 - 60.20

27.10 - 26.95

50.93 - 50.67

B637/6

14.43 - 14.30

50.93 - 50.67

30.30 - 30.15

44.58 - 44.32

B637/8

14.48 - 14.35

69.98 - 69.72

30.30 - 30.15

63.63 - 63.37

B637/18

14.48 - 14.35

92.20 - 91.95

30.30 - 30.15

85.85 - 85.60

B638

9.68 - 9.55

43.00 - 42.75

20.70 - 20.63

38.23 - 37.97

B638/6

9.68 - 9.55

16.00 - 15.75

20.70 - 20.63

12.83 - 12.57

B1046

14.48 - 14.35

92.20 - 91.95

38.23 - 38.10

85.85 - 85.60

B1059

12.88 - 12.75

63.37 - 63.12

28.70 - 28.60

57.30 - 57.00

Torsion Bush Type BP

Higher radial and conical loads can be accommodated than with the standard B type bush.

The ends of the outer tube are permanently deformed after assembly to provide higher axial loading possibilities compared to the B type bush whilst maintaining similar torsional loading performance.

Standard BP type bushes

	A Inner Tube I/D	B Inner tube length	C Outer tube O/D	D Outer tube length
BP630/7	11.29 - 11.16	50.60 - 50.40	25.50 - 25.35	45.08 - 44.58
BP636/2	12.83 - 12.70	35.05 - 34.80	27.10 - 26.95	32.13 - 31.88
BP636/6	12.83 -12.70	38.1 -37.9	27.10 -26.95	32.13 -31.88
BP700	Solid rod 31.75 - 31.62	152.53 - 152.27	51.13 - 50.98	90.68 - 90.42
BP1023	24.16 - 24.03	79.50 - 79.25	44.53 - 44.42	77.34 - 77.09
BP1027	22.40 - 22.28	78.61 - 78.36	46.79 - 46.66	76.33 - 76.07

Torsion Bush Type BE

Employing both chemical bond (inner tube only) and interference fit as for the B type bush, this version has a chemical bond for the full length of the inner and tube and a specially shaped rubber section designed to prevent metal to metal contact under axial overloads.

Standard BE type bushes

Inner Tube I/D

Inner tube length

Outer tube O/D

Outer tube length

BE1025

11.29 - 11.16

54.10 - 53.85

35.00 - 34.93

44.58 - 44.32

Torsion Bush Type SAB

This bush type is designed for use where a machined housing is available and hence no outer tube is provided. An interference fit provides the required pre-compression as for the B type bush. This construction is intended for only light axial loads.

Standard SAB Bushes

Part No	A Inner Tube I/D	B Inner tube length	C Outer O/D
SAB930	9.68 - 9.55	36.63 - 36.38	21.92 - 21.64
SAB935	12.88 - 12.75	38.23 - 37.97	28.14 - 27.87
SAB1013	11.29 - 11.16	63.63 - 63.37	41.40 - 40.89
SAB1024	19.23 - 19.10	78.61 - 78.36	36.07 - 35.81
SAB1060	12.88 - 12.75	76.33 - 76.07	27.05
SAB1071	11.30 - 11.18	38.99 - 38.74	23.57 - 23.32

Steering Column Bush

These special bushes are designed for use in automotive steering columns to reduce vibration transmission. The Acetal resin liner provides for a close fit with the steering column shaft whilst minimising friction and radial play. The liner locks in place when fitted to eliminate axial displacement.

Part No

Inner tube I/D

Inner tube length

User Shaft dia when liner fitted

User housing diameter

SAB1289

24.28 - 24.21

30.50 - 30.20

22.18/22.07

37.30/37.00

SAB8466

21.11 - 21.03

30.50 - 30.20

19.05/18.97

29.31/29.06

Loading Methods.

The degree of displacement for a 2 tube system and based on a constant elastomer can be designed-in by adjusting the basic parameters of length plus inner and outer tube diameters as follows:

Radial

This relates to displacement such that the inner tube is moved towards the outer tube whilst remaining axially parallel to it such that the thickness of rubber is reduced uniformly on one side. The radial displacement can be decreased by increasing the projected area (diameter of inner tube x length of outer tube). This can be facilitated by increasing the overall length of the bush or by increasing the outside diameter of the inner tube. When only radial loading is anticipated, these bushes will withstand significant shock loads in excess of normal rated load for the size (up to 5 times rated loading) However, if conical loading is anticipated in addition to radial loading, the nominal rated loading must be reduced. Also if cyclic loading is anticipated, the load catered for should be at least halved.

Torsional

When one tube is rotated relative to the other whilst remaining axially parallel, this implies a torsional load. Reducing the thickness of the elastomer will reduce the angular displacement for a given torque (increasing the inner tube’s outer diameter or decreasing the outer tube’s inner diameter) or by increasing the overall length of the bush. Typically the maximum frequency of torsion loading accommodated is 8Hz (480 cycles per minute) and this would be for small angular movements up to /-5 ° For lower frequencies /-40° can be accommodated for some bushes where the rubber thickness allows.

Conical

If an angle is developed between the axes of the two tubes such that they are no longer parallel, this is a conical load. The displacement from such loads can be minimised by reducing the thickness of the elastomer or by increasing the length of the bush as above. Applications should limit the angular movement such that the thickness of elastomer at the end of the outer sleeve is not reduced by more than 30%. Clearly, greater conical movement is provided by a greater thickness of elastomer, which in turn can be determined by changes in tube diameters.

Axial

When the ends of the tubes are displaced relative to their no-load position whilst the axes remain parallel, this is an axial load. The displacement can be reduced by reducing the thickness of the elastomer or by increasing the length of the bush as above. Design loads should be kept to a maximum of 10% of the rated radial load.

The deflection parameters can also be modified by altering the hardness of the elastomer (harder reduces deflection) or by inserting an intermediate tube which reduces deflection in all directions as for example in our TB (triple bonded) bush type.

Installation

The outer tube is either clamped in place or is an interference fit in a machined housing requiring insertion using a mechanical or hydraulic press. The inner tube is typically held in place by a clamping bolt which is tightened to sufficient torque to prevent the inner tube from rotating in use under the forces likely to be experienced.

Press Fit Tolerances on Bores

In most applications bushes are intended to be a press fit in a bore. In this case the following bore tolerances should be applied: The bush diameter should be taken as its nominal size – mid-tolerance.

Note: where the bush is to be inserted into a rolled spring eye, the interference is greater due to the yielding of the spring eye.

Outside diameter of bush (mm)	Bore limits from nominal bush O/D	Rolled Spring eye Bore	SAB Style Bushes
6 to 23	-0.04 / -0.06	-0.25 / -0.50	-0.25/ - 0.35
24 to 40	-0.05 / -0.08	-0.40 / -0.70	-1.00 / -1.10
41 to 50	-0.06 / -0.09	-0.9 / -1.10	-1.50 / -1.60
51 to 70	-0.08 / -0.0.10	-1.00 / -1.40	-1.70 / -1.80

For SAB style bushes without the outer steel tube, the degree of interference is also much greater. This provides for security of installation and also has the effect of stiffening the bush due to the compression of the rubber during assembly.

Typical application – automotive suspension

The torsion bushes on most cars consist of a larger steel sleeve mounted inside the control arm, with a smaller steel sleeve inside for the mounting bolt, held in place with rubber which was bonded and vulcanised in place. The sleeve is fixed into the arm, and the inner tube held tight by the mounting bolt. As the arm moves, the rubber material gives way to the shear forces, allowing smooth movement of the arm without any sliding motion or surface-to-surface friction and hence nothing to wear, squeak or rattle. Most modern rubber torsion bushes are double bonded (i.e. the rubber is chemically bonded to both metal surfaces during the curing (vulcanising) of the rubber. In some cases the outer surface is held in place by creating a significant interference fit during assembly of the bush. Such bushes are not intended to slide within the outer sleeve but allow for occasional extreme torsional overloading of the bush.

Materials

Inner & outer tubes are of steel which is zinc plated or ‘Sherardized’ and clear or yellow passivated. For the chemical bonding process, the bonded surfaces are further treated with special purpose priming and bonding agents. To achieve the required quality and ensure that the surfaces are not contaminated prior to bonding, the latter operations are under in-house control.

Polyurethane bushes

Polyurethane bushes have become popular, as they noticeably stiffen the suspension and are claimed to outlast the OEM rubber equivalents. The same effects could be accommodated by using harder rubber compounds or by changing the tube diameters. However most users do not understand how torsion bushes are intended to work and how these alternatives differ in principle and the problems they create. The recent popularity of polyurethane after-market replacements has drowned out the advantages of the proven designs, resulting in stiction, binding, squeaking, harshness, and need for regular greasing.

Polyurethane is used in place of the rubber portion of the factory bushes. Unlike the rubber bushings, these bushes are not bonded to an inner and outer sleeve and are sometimes used simply because they are easier to fit. However, if easy to fit then there is no interference and hence a loss of stiffness will result. In typical automotive use, movement of the control arm will cause the internal surfaces of the sleeves and bush to slide to accommodate the shearing forces. This raises the issues of stiction and binding, both of which can affect steering predictability under extreme handling conditions.