GB2041848A

GB2041848A - Hydrostatic Steering Arrangements

Info

Publication number: GB2041848A
Application number: GB7901340A
Authority: GB
Original assignee: Massey Ferguson Perkins Ltd
Current assignee: Perkins Engines Group Ltd
Priority date: 1979-01-13
Filing date: 1979-01-13
Publication date: 1980-09-17
Also published as: FR2446214A1; GB2041848B; FR2446214B1

Abstract

A tractor (10) with a resiliently suspended cab (15) enclosing an operator's station, a steering wheel assembly (23) carried by the cab and a hydrostatic steering unit (21) carried by a portion of the tractor (for example the engine block (11)) which does not form part of the cab or in any way define the operator's enclosure. The steering wheel assembly (23) is connected with the steering unit (21) via a linkage which includes a vibration isolating coupling (24) which is also capable of accommodating any relative movement between the steering wheel assembly and steering unit and completes the isolation of the steering unit from the cab. The invention minimises transmission of noise from the steering unit to the operator's cab. <IMAGE>

Description

SPECIFICATION Hydrostatic Steering Arrangements This invention relates to tractors and specifically to hydrostatic steering arrangements for use on tractors fitted with resiliently mounted operators' cabs.

It has been well known for some time to improve operator comfort by providing an agricultural or industrial tractor with an operator's cab resiliently mounted on the tractor chassis which is normally provided by the engine block, transmission housing and back axle housing.

Such resiliently mounted cabs have also, for some time, often employed a hydrostatic steering unit supplied with pressurized fluid from an engine or transmission driven pump. Heretofor, such hydrostatic steering units have been mounted on the cab and have contributed significantly to the noise level within the cab.

Studies carried out by the Applicants have shown that the noise emanating from the steering unit is basically of three types. Firstly, there is the so-called "hiss" which is associated with fluid flow conditions within the steering unit and associated pipes. Secondly there is so-called "sing", which is the noise most complained of by operators, and which is caused by fluid pulsations wit the steering unit these pulsations being at the tooth ripple frequency of the pump when this is of the gear type. Thirdly there is so-called "growl" which is associated with tyre stiction which results in tyre wind-up and, when the wheels are turned to be near full lock position with the tractor stationary, this wind-up is fed back to the steering unit resulting in growl.

The problem of cab noise emanating from the steering unit has been experienced by the tractor manufacturing industry in general for some time.

Until the present invention, no simple solution has been forthcoming which enables the maximum cab noise levels now stipulated in many countries tobe easily and relatively cheaply met consistently on a production line basis.

It is an object of the present invention to provide an arrangement which greatly reduces the noise emanating from the hydrostatic steering unit which is transmitted into the operator's cab and whose noise reduction benefits are easily reproducible on a production line basis.

According to the present invention there is provided a tractor including a resiliently suspended cab enclosing an operator's station, a steering wheel assembly carried by the cab, a hydrostatic steering unit carried by a portion of the tractor not forming part of the cab or in any way defining the operator's enclosure and vibrationally isolated from the cab by the resilient cab suspension, and a linkage operatively connecting the steering unit and the wheel assembly and including a coupling which vibrationally isolates the steering wheel assembly from the steering unit and also accommodates any relative movement therebetween which occurs as a result of movement of the cab on its resilient suspension during use of the tractor.

In a conventional tractor arrangement in which the cab is resiliently suspended from a chassis provided by the engine block, transmission housing and a back axle housing, the hydrostatic steering unit in the arrangement of the present invention can conveniently be mounted directly on the engine block using appropriate bracketry.

It has been found, somewhat surprisingly, that a significant reduction in the noise emanating from the steering unit is achieved using the simple arrangement described in the two preceding paragraphs. This significant reduction in noise level can be readily confirmed subjectively by the tractor operator by the absence of "hiss" and "sing" and a reducing, if not complete elimination, of "growl".

A further advantage of the arrangement of the present invention is that since the hydrostatic steering unit is no longer mounted on the cab it is no longer necessary to employ flexible hydraulic hoses connacting the steering unit with the rest of the steering circuit and rigid metal piping can now be employed for this purpose. This should result in a significant economy in the make-up of the steering circuit and should also render the circuit less liable to fail due to hose rupture.

One example of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a side view, partly cut-away, of an agricultural tractor embodying the present invention; Figure 2 is a scrap view showing the steering unit mounting of Figure 1 on a larger scale; Figure 3 is a perspective view of the bracket used to mount the steering unit shown in Figures 1 and 2;; Figures 4 and 5 are graphical representations of the noise levels through the frequency spectrum heard in the cabs of tractors fitted with steering arrangements A and B (as hereinafter defined) respectively when the steering units are in their neutral conditions (as hereinafter defined), and Figures 6 and 7 are graphical representations of the noise levels through the frequency spectrum heard in the cabs of tractors fitted with steering arrangements A and B respectively when the steering units are in a small selected condition (as hereinafter defined).

Figure 1 shows an agricultural tractor 10 employing a conventional arrangement in which the tractor chassis is provided by the block of engine 1 , the transmission housing 12 and the back axle housing constituted by the rear centre housing 1 3 and transversely extending axle trumpets 1 4. An operator's cab 1 5 is resiliently supported from the tractor chassis by rubber antivibration mounts 16 and 17 positioned at the front and rear of the cab respectively. Each side of the cab is supported at the front by two transversely spaced mounts 1 6 supported from a bracket 18 secured to the transmission housing 12.The rear of each side of the cab is supported by a pair of longitudinaliy spaced element 1 7 carried by a bracket 1 9 secured to the respective rear axle trumpet 14 by bolts 20.

The tractor shown in Figure 1 is provided with a steering arrangement in accordance with the present invention which includes a hydrostatic steering unit 21 secured to the rear of the engine 11 by bracketry 22 and a steering wheel assembly 23 which is connected with the steering unit via a vibration isolating coupling 24.

The front of the cab 1 5 is provided with a recessed portion 25 which partially houses the steering unit 21 and the associated bracketry 22 and also serves as the support means for the steering wheel assembly 23.

The bracketry 22 is shown in greater detail in Figures 2 and 3 and comprises a first bracket 26 which is secured to the engine block by bolts 27 extending through holes 28. A top-hat shaped bracket 29 is secured to the bracket 26 by bolts 30 extending through corresponding holes 31 in brackets 29 and 26. The hydrostatic steering unit 21 is suspended from the bracket 29 via bolts 32 extending through holes 33 in the top portion of the bracket. Since the precise constructional details of the steering units 21 are not germane to the present invention they will not therefore be described. The Danfoss hydrostatic steering unit Orbitrol Type OSPB 80 is an example of a typical proprietary unit suitable for use in the arrangement of the present invention.

The steering unit 21 is supplied in conventional manner with pressurised hydraulic fluid from an engine driven gear pump (not shown) via piping (not shown) which can be flexible or advantageously rigid as described above. Since the details of the hydrostatic steering circuit itself are conventional they will not be further described.

The vibrational isolating coupling 24 is again of proprietary form and, since its precise constructional details form no part of the present invention, it will not be described in detail. As is conventional, the coupling includes vibration and thus noise actuating elastomeric elements 50 through which the turning forces are transmitted from the steering wheel assembly 23 to the steering unit 21. A safety device is included in the coupling to enable the coupling to still transmit turning forces in the event of the failure of the elastomeric elements.Any coupling which will vibrationally isolate the steering unit from the steering wheel assembly, accommodates the relative movement which will occur between the steering wheel assembly and steering unit as the cab moves relative to the steering unit during use of the tractor, and includes a safety device is suitable for use in the arrangement of the present invention.

The particular coupling 24 shown in the drawings has a spigot 33 which passes through the hole 34 in the bracket 29 and engages an input member (not shown) in the steering unit 21.

The other side of the coupling 24 is provided with a sleeve 35 which receives the bottom end of the steering column 36 which is splined at 37 and held in the sleeve 35 by a pinch bolt 38. The column 36 is supported from the recessed portion 25 of the cab 1 5 by a tube 39 whose bottom end is provided with a flange 40 which is secured to part of the recessed portion 25 by bolts 41. The upper end of the tube 29 supports a bearing 42 which in turn supports the upper end of the column 36. Additional support for the tube 39 from the recessed portion 25 of the cab is provided by a stay 43 which is clamped around the tube 39 at 44 and secured to the recessed portion 25 at 45.

As can be seen from the above description the steering unit 21 is rigidly secured to the block of the engine 11 by the bracketry 22 and is thus completely isolated from the cab 1 5 by the cab mounts 1 6 and 17.

As indicated above the Applicants have found, after an appreciable amount of studying of the problem of cab noise, that this apparently simple mounting of the steering unit on the engine block and connection of the steering wheel with the steering unit via a vibrational isolating coupling results in a significant reduction in the noise within the cab emanating from the steering system. In particular, a subjective analysis of cab noise by the tractor operator indicates the absence of "hiss" and "sing" as discussed above and a reduction, if not complete absence, of "growl".This subjective assessment by the tractor operator is confirmed by measurement of the noise levels in the cab of a tractor provided with a steering arrangement in accordance with the present invention (hereinafter referred to as "steering arrangement A") as compared with noise levels in the same type of cab when the steering unit is mounted on the cab in the previously known manner (hereinafter referred to as "steering arrangement B").

To illustrate the above point Figures 4 and 5 graphically illustrate the noise levels through the frequency spectrum heard inside the cabs of tractors fitted with steering arrangements A and B respectively when the engines are running at 1 500 rpm and the steering units of the arrangements are in the neutral condition (i.e. the units are not operating to change the steering setting of the wheels).

As can be seen from Figure 4 there is a complete absence of noise at the gear pump tooth ripple frequency which is 450 Hz at 1 500 rpm. This is subjectively confirmed by the operator in the lack of "sing". Figure 5 shows the noise level at the gear pump tooth ripple frequency of 450 Hz when using the prior art steering arrangement B. This is subjectively confirmed by the presence of "sing". It will also be noted from Figure 4 that the general noise level in the cab of steering arrangement A is significantly lower than that in the cab of steering arrangement B. This is due to the reduction of other noises emanating from the steering unit by the steering arrangement of the present invention.

In a similar fashion Figures 6 and 7 graphically illustrate the noise levels through the frequency spectrum heard inside the cabs of tractors fitted with steering arrangements A and B respectively when the steering units of the arrangements are in a small selected condition (i.e. the units are operating to produce a small change in the steering setting of the wheels). This is the setting when noise emanating from the steering units is most obtrusive when using steering units of the Danfoss Orbitrol OSPB 80 type.

Again Figure 6 shows a complete absence of noise at the gear pump tooth ripple frequency of 450 Hz and a significantly lower general noise level when compared with Figure 7 which shows the presence of "sing" at the 450 Hz frequency.

As a further illustration of the benefits provided by the present invention the Applicants would point out that, in a test conducted by them, when a tractor with steering arrangement A had its engine run at the engine speed which produced a general noise level of 83db in the cab of the same type of tractor fitted with steering arrangement B and selected at random from their current production tractors, the noise level in the cab of the tractor with steering arrangement A was of the order of 5 db lower when tested in the same production line sound booth.

Although the invention has been described above in relation to a tractor having a particular type of resilient cab mounting it will be appreciated that the invention is applicable to a wide range of tractors employing different types of resiliently mounted cab. For example, the invention is applicable to a tractor with a cab resiliently mounted from a roll-over-protection structure as described in U.K. Patent Specification No. 1,534,373.

Also, although the invention has been described above in relation to a hydrostatic steering arrangement whose pressurised fluid is provided by a gear type pump it is thought that the invention will also give benefits when used in steering arrangements whose pressurised fluid is provided by other types of pumps, for example valve or piston type pumps, and whose moving parts tend to produce fluid pulsations giving rise to "sing".

Claims

1. A tractor including a resiliently suspended cab enclosing an operator's station, a steering wheel assembly carried by the cab, a hydrostatic steering unit carried by a portion of the tractor not forming part of the cab or in any way defining the operator's enclosure and vibrationally isolated from the cab by the resilient cab suspension, and a linkage operatively connecting the steering unit and the wheel assembly and including a coupling which vibrationally isolates the steering wheel assembly from the steering unit and also accommodates any relative movement therebetween which occurs as a result of movement of the cab on its resilient suspension during use of the tractor.

2. A tractor including a chassis provided by an engine block, transmission housing, and rear axle housing; a cab enclosing an operator's station and resiliently suspended either directly or indirectly from the chassis by vibrational isolating units; a steering wheel assembly carried by the cab; a hydrostatic steering system including a hydrostatic steering unit, said steering unit being carried by part of the chassis; and a linkage operatively connecting the steering unit and the wheel assembly and including a coupling which vibrationally isolates the steering wheel assembly from the steering unit and also accommodates any relative movement therebetween which occurs as a result of movement of the cab relative to the chassis during use of the tractor.

3. A tractor according to claim 2 in which the steering unit is mounted on the engine block.

4. A tractor according to any one of the preceding claims in which the steering unit is connected with a source of pressurised fluid via rigid piping.

5. A tractor constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.