Hydraulic System For Utility Vehicles, In Particular Agricultural Tractors

Abstract

A hydraulic system for utility vehicles, in particular agricultural tractors, with a regulated hydraulic pump (1) is disclosed for prioritised pressure medium supply to internal and external pressure medium consumers (6, 11, 12), which are fed via load sensing spool valves (20, 26), the external pressure medium consumers (11, 12) being supplied with pressure medium via a priority valve (17). In the case of known utility vehicles the lowest priority is assigned to the internal pressure medium consumers. Situations are known however, when operating an air seeder for example, in which it is not expedient with the pressure medium supply to give preference to the internal pressure medium consumers over the external because the power capacity of the hydraulic system is not then exploited to an optimum. Short supply to such implements leads to a negative influencing of the work pattern.

Description

Claims

1. A hydraulic system for utility vehicles, in particular agricultural tractors, with a regulated hydraulic pump for the prioritised pressure medium supply to internal and external pressure medium consumers, which are fed via load sensing spool valves, wherein the external pressure medium consumers are supplied with pressure medium via a priority valve and a control means is provided which allows an operator to selectively assign priority to the internal or the external pressure medium consumers and to set the pressure medium demand of the external consumers to be use when the external consumers are prioritised.

2. A hydraulic system according to claim 1, in which priority valve limits the pressure medium supply to the external pressure medium consumer, so long as the pressure medium demand of the internal and external pressure medium consumer exceeds the maximum flow rate of the hydraulic pump and no priority is assigned to the external pressure medium consumers, and in that the control means also comprises: means for setting the pressure medium demand of each of the internal consumers;sensor means for providing a signal indicative of the maximum flow rate being delivered by the pump;a control unit which repeatedly calculates from the sensor signal the maximum flow rate being delivered by the pump and if the external consumers are prioritised reduces the value of demand set for the internal consumers so that the sum of the internal and external demands corresponds to the maximum flow rate being delivered by the pump and, if the internal consumers are prioritised and the sum of the set internal and external demands exceed the maximum flow rate being delivered by the pump, allows the priority valve to limit the flow to the external consumers.

3. A system according to claim 2 in which the pump sensor provides the speed of rotation of the pump and the pump maximum flow rate is calculated from the equation FM max=n×Fmaxwhere n=speed of rotation of the pumpand Fmax=flow rate of pump per rotation.